Vysoká škola báňská – Technical University of Ostrava

Materials Forming and Casting

Practice

(lecture notes)

doc. Ing. Radim Kocich, Ph.D.

doc. Ing. Petr Lichý, Ph.D.

Ostrava 2015

1. Formed products

Time to study: 1 hour

Aim: After study of this chapter you will know

Basic fabrication processes

Initial intermediate products and the range of final products

Individual forming technologies

Lecture

Forming technologies can be separated into two main groups according to the original

intermediate products, which can either be bulk or flat. Forming starting with bulk

intermediate products are technologies like forming, rolling, drawing and extrusion. Forming

starting with flat intermediate products are e.g. stamping and bending. In the following text,

purely bulk intermediate products forming methods (metallurgical forming methods) will be

dealt with.

All the technologies can be used to produce semi-products from various types of steels, as

well as from non-ferrous metals and their alloys. Cast materials are typically used as initial

intermediate products for production of final formed products. They can be separated into

three main groups. The first group is continuously cast slabs, which are used e.g. to produce

thick sheets and strips. A typical feature of slabs is their shape with a rectangle cross-section,

i.e. ratio of sides higher than 1:1.4 with height of 80-200 mm and width up to 1 600 mm. The

second group consists of blocks used to produce beams, rails etc. They have a characteristic

geometry with the ratio of sides 1:1 to 1:1.4 and dimensions 140x140 mm to 320x320 mm.

The last group is billets used to produce profiles, wires, tubes etc. The geometric shape of

billets is defined with the ratio of sides 1:1 to 1:2 and dimensions 40x40 mm to 130x130 mm.

However, billets can also have circular cross-sections with diameters 90-120 mm. In the past,

intermediate products with thicknesses of 6 to 36 mm and widths mostly 300 mm (sheet

billets) were also used. Nevertheless, they are not common at present. Among continuously

cast intermediate products, ingots are also sometimes used. This is mostly for small-lot

productions or for formed products from specific materials. In special cases, initial materials

prepared using powder metallurgy can also be used.

Forged products

There are two basic types of forging – open die forging and die forging. Die-forged products

are forged using special forms – dies. Die-forged products are e.g. cogwheels, piston rods,

automobile components, stirrups, locks, pegs etc. Open die-forged products are usually large

products, such as crankshafts, ships components, rolls for rolling mills, pistons, flanges etc.

Special forged products are circles, sleeves and rail wheels.

Rolled products

Rolled products can be separated into flat and long products. Flat products are sheets or strips

rolled under hot or cold conditions. Sheets are divided into thin and thick ones separated by

the limit of 3 mm. Long products are rods, wires, tubes, thin-wall profiles, products of

complex shapes (profiles, sheet piles, rails…). Special products are welded tubes welded from

rolled strips or sheets.

Drawn products

Drawn products are usually wires, rods and tubes. Wires are drawn if a diameter smaller than

the limit down to which they can be rolled (5.5 mm) is required, or if a high-quality surface or

specific properties are needed. Drawn products have generally higher dimensional accuracy

than the rolled ones.

Extruded products

Extruded products can be solid or hollow. The mostly fabricated extruded products are

profiles used for fabrication of e.g. windows, doors and window-sills.

-

2. Theory of plastic deformation

Time to study: 10 hours

Aim: After study of this chapter you will know

Possible mechanisms of plastic deformation

Definitions of forming under hot and cold conditions

How to define and influence formability

Differences between individual recovery mechanisms

Mathematic expressions of plastic deformation

Lecture

Conditions for plastic deformation to occur

The aim of forming is to apply plastic deformation to impart required shape and dimensions

to a work-piece. At the same time, material failure/rupture has to be prevented. For plastic

deformation to occur, a certain limit stress within the formed material – deformation

resistance – has to be overcome. Deformation resistance of a material is a reaction to the

effect of external forces during forming. Determination of deformation resistance is difficult,

since it is influenced by several factors, such as thermo-mechanic parameters (temperature,

strain, strain rate), geometry, friction etc. By forming, structure of the final material

(especially grain size) and therefore mechanical properties can be influenced and optimized.

Nevertheless, other factors (chemical composition, heat treatment etc.) are important as well.

Mechanisms of plastic deformation

Slip deformation mechanism, progressing by movement of line defects (dislocations), prevails

during most of the forming processes in metal materials. Deformation then progresses by a

continuous slip of individual crystal layers along slip systems – crystallographic layers and

directions – depending on the type of the particular lattice. The slip distance is a multiple of

the smallest interatomic distance (Burgers vector). The slip direction (layer) is usually

identical to the direction (layer) with the highest atomic density. Each lattice type has a

different number of basic slip systems. It is 48 for cubic body centered (α-Fe, Cr, W…), 12

for cubic face centered (γ-Fe, Cu, Al…) and 3 for hexagonal close packed (Mg, Ti…) lattice.

The more active slip systems within the lattice, the better formability of the individual metal.

Mathematic expressions of deformation

There are several types of mathematic relations expressing shape changes during plastic

deformation. These are summarized in Table 1.

Table 1. Mathematic expressions of deformation

type of deformation symbol unit elongation widening ramming

Absolute Δ [mm] Δl = l1-l0 Δb = b1-b0 Δh = h0-h1

Relative ε [%]

logarithmic e [-]

deformation coefficient λ β γ [-]

Basic laws of plastic deformation

Law of constant volume

When the original dimensions of a body are denoted as 0 and the deformed dimensions are

denoted as 1, the following equation can be written:

h0∙b0∙l0 = V0 = h1∙b1∙l1 = V1 [-] (1)

where: h … height [m]

b … width [m]

l … length [m]

The following can be derived from Equation (1):

[-] (2)

By a logarithmic calculation of Equation (2), the above mentioned law can be expressed using

logarithmic deformations.

→ [-] (3)

This law has exceptions, such as extensibility of metals by the influence of heat or lattice

defects. In these cases, material density changes while weight remains constant. Therefore

small changes in volume can occur.

Law of material movement by the path of least resistance

Material always flows plastically in the direction which has the least resistance. This direction

is perpendicular to the free surface of a work-piece. This law explains the phenomena of

barreling during forging (Figure 1) and widening during rolling.

Figure 1: Barreling during forging

Law of additional stresses and non-uniformity of deformation

Deformation within a material is almost never uniform. This is a result of a non-homogeneous

penetration of force into the volume of a formed work-piece, which causes its non-uniform

deformation (barreling). Due to the non-uniform deformation, additional stresses occur within

a formed material, by the influence of which the stress state becomes non-uniform as well.

This is not favorable, since it can result in a (local) failure of the formed metal.

Stresses and stress states

A unit cube is given in a right-angle coordinate system. Stress effecting perpendicularly on a

plane in a certain point is denoted as normal stress – σ. Stress effecting parallel on a plane in a

certain point is denoted as tangential (shear) stress – τ. A general stress state in a grid system

defined by axes x, y and z consists of three normal and six tangential stress components.

These components are depicted in Figure 2.

Figure 2: General stress state in a unit cube.

In a system of main axes 1, 2 and 3, the tangential components are equal to zero and for the

normal components the following is valid: σ1 ≥ σ2 ≥ σ3. Pressure components are denoted as

negative (-) and tension components are denoted as positive (+). Generally, there can be 9

different stress states: 4 three-dimensional states (+++, ++-, +--, ---), 3 planar states (++,+-,--),

2 uniaxial states (+, -). These states are schematically depicted in Figure 3.

Figure 3: Stress states.

A stress state can be mathematically expressed using the coefficient of stress state, defining

prevalence of either tension or pressure components. Tension stresses increase the probability

of material failure, while pressure stresses increase formability. Therefore formability can

significantly be influenced using a favorably selected forming process. The stress state

coefficient can graphically be expressed using the Kolmogorov diagram.

[-] (4)

Friction

Friction can be described using a friction coefficient, which can have wide range of values

depending on the contacting surfaces, friction forces and possible lubrication and can be

determined using various methods. Friction is usually a negative factor and it should be

minimized. However, friction during forming is also positive. Without friction, capture of a

material into rolls and the entire rolling process would not be realizable.

Friction can be separated into several basic types according to its origin. Generally, it is

higher for cold forming than for hot forming. Therefore, lubrication is used for these

processes. On the other hand, lubrication can also be used during hot forming.

Plastic deformation under hot and cold conditions

Materials are formed under hot conditions if the deformation is performed at temperatures

higher than 40% of the melting temperature – Tm. More precisely, the value should be

between 30 and 80% of Tm, the value depends on the type of material (alloy). Materials can

always be hot formed within a certain interval of forming temperatures. With an increasing

temperature, deformation resistance generally decreases and formability increases, since

dislocation mobility and diffusion speed increase. However, if the temperature is too high and

crosses the upper limit of a forming temperatures interval, overheating or burning of the

material occurs and formability decreases rapidly. Overheating features abnormal coarsening

of grains, the material can still be restored by a proper heat treatment. Burning occurs at very

high temperatures, material can be restored only by remelting since it disintegrates during any

further forming due to a significant grain boundaries weakening.

Cold forming is performed at temperatures lower than 40% of Tm of a material – under

recrystallization temperature. Such forming features strengthening of materials and therefore

high deformation resistances. With progressing deformation, plasticity of a material decreases

and its strength increases. Cold formed materials deform by slip mechanism but also by

twinning, which is a competing process.

During forming, grains significantly flatten and elongate in the direction of main deformation.

Aligning of structural phases (e.g. inclusions) in that direction also occurs and texture,

causing anisotropy of properties, develops continuously. Anisotropy can be planar

(differences between different directions within a material plane), or normal (differences

between two perpendicular planes within a material). Texture can be defined as a regular

geometric and crystallographic structure and substructure alignment within a poly-crystal

metal. Deformation texture can be divided to structural texture (originating from

inhomogeneity of chemical composition and presence of inclusions) and crystalline

(originating from alignment of grains in a certain preferred orientation characteristic for each

lattice type). Recrystallization texture develops after recrystallization.

Softening processes

During forming grains change their shapes while their volumes remain constant. To be able to

refine grains, some of the structure-forming recovery processes have to be activated in the

material. The type of the process depends on the type of forming process – forming under hot

or cold conditions. To start such a process, a certain limit of accumulated energy has to be

exceeded. This energy is imposed into a material by forming processes, due to which defects

and dislocation densities increase.

Softening processes can be separated, from the point of view of time, to dynamic and post-

dynamic. Dynamic processes occur during deformation. Post-dynamic occur after forming is

finished, which can be after finishing of the entire forming cycle, during cooling, or also

between individual passes (e.g. during continuous rolling).

After hot forming, material usually experiences recrystallization during which new grains

nucleate and further grow at energetically favorable locations (grain boundaries). To start

recrystallization, it is necessary to reach a certain critical strain together with meeting other

conditions, such as sufficient temperature etc.

During cold forming, recovery can occur. This is a method of non-perfect softening of a

material, during which dislocation density decreases by their annihilation and rearrangement

and sub-grains generation (polygonization). To evoke recrystallization, i.e. perfect softening

of a structure, additional energy has to be supplied, e.g. by recrystallization heat treatment.

Dynamic recovery of materials is described by the Zener-Hollomon parameter (5). A higher Z

value means shifting of the curve towards higher stresses and strains.

[-] (5)

where: γ … strain rate [s-1

]

Q … activation energy [kJ∙mol-1

]

T … temperature [K]

R … molar gas constant [J∙K-1

∙mol-1

]

3. Fabrication technologies

Time to study: 15 hours

Aim: After study of this chapter you will know

Basic fabrication processes

Concrete application of forming technologies for fabrication of individual

products

Characterization of individual forming processes

Influences of individual forming processes on properties of formed

products

Lecture

Forging

Open die forging

Open die forging is performed on forging machines – hammers and presses – without any

specialized dies. Initial intermediate products are usually forging ingots. The first purpose of

forging is to derange the original cast ingot structure and increase its formability. During the

first forging steps, characteristic fiber structure replaces the dendritic cast structure and

casting defects continuously diminish. High forging temperatures support diffusion, which

also contributes to homogenization of cast structure. The influence of forging on mechanical

properties of a given semi-product is evaluated using a contract unit – forging degree. This

can generally be expressed by Equation (4). For casual ingots, the forging degree should be

PK > 3.

[-] (4)

where: A … ramming equivalent (A = 0,7 – 0,9) [-]

P … degree of ingot ramming ( ) [-]

Sp … surface area of transverse cross-section of rammed ingot [m2]

Si … surface area of the mean ingot transverse cross-section [m2]

Sv … surface area of the largest final forged-piece transverse cross-section [m2]

K … degree of ingot elongation ( ) [-]

n … number of ramming steps [-]

For open die forging includes several basic forging operations.

Elongation

Approximately ¾ of all forging fabrication steps comprise elongation. By elongation, the

transverse cross-section of a semi-product is decreased, while its length is increased. The

entire volume of a formed work-piece is forged continuously by compressions of its parts.

The forged-piece is continuously moved forward and rotated during forging. The strain

imposed during these steps contributes to derangement of the cast dendritic structure, which

results in an increase in plasticity and formability of a material. Elongation can be applied as a

preparation but also finishing forging operation for forged-pieces such as rods, shafts etc.

A correct determination of the relative capture length is essential (Equation (5)). This quantity

influences penetration of the deformation to a specific depth into the forged material and

therefore the stress state and (in)homogeneity of deformation within the entire forged-piece.

The most favorable forming conditions for forming also the axial part of the forged-piece is

achieved when the value of this factor ranges between 0.5 and 0.7. A slight overlap of the

captures (forged areas) in subsequent elongation steps (offset of deformation zones)

contributes to homogenization of deformation.

[-] (5)

where: lz … length of forging area [m]

h0 … thickness of elongated body [m]

The width of the open forging dies should be selected, considering the particular forged semi-

product, according to the following equation (6).

[m] (6)

where: B … width of forging open dies [m]

bk … final width of forged-piece [m]

The basic tools for elongation are flat and shaped open dies. Flat open dies are favorable for

elongation of semi-products with square cross-sections, since they create a favorable

deformation zone reaching to the axis of a forged-piece. Shaped open dies are more favorable

for elongation of semi-products with circular cross-sections, since an unfavorable shape of the

deformation zone develops during elongation of such semi-products by flat open dies and the

deformation influences only peripheral areas of a work-piece. Shaped open dies have a higher

contact surface with circular forged-pieces, reduce widening and favorably influence the

stress state.

During elongation of large ingots, intentional cooling of their surface is sometimes performed.

This results in a generation of large temperature gradients (250 – 350°C) throughout their

cross-sections and additional pressure stresses in their axial parts. This results in a more

intense closing of axial cavities and casting defects during forming.

Elongation of hollow work-pieced is performed using a mandrel. Width of the open dies and

length of the capture are half the sizes comparing to elongation process applied to solid

forged-pieces. Rings are flattened on a mandrel.

Ramming

During ramming, the height of a forged-piece decreases and its cross-section increases. It is

energetically more demanding, since the open dies influence the entire volume of the forged-

piece at once. Deformation is inhomogeneous, since the open dies are in contact with the

upper and lower surfaces of the forged-piece where material cannot flow freely due to the

influence of friction. This results in a generation of additional tension stresses and subsequent

barreling, as mentioned above. This effect is more evident with larger cross-sections and

smaller heights. Deformation inhomogeneity can decrease by using semi-products with lower

slenderness or by forging with larger reductions. Flat open ramming dies are used to forge

smaller semi-products and disks, shaped open ramming dies are used for ingots which are

intended to further be elongated. Forging in simple preparative dies can be used for ramming

of shouldered forge-pieces and flanged disks. Ramming effectively increases the forging

degree.

Narrowing

Such forging steps are in principle elongation of given parts of a forged-piece. More

specifically, this operation is denoted as narrowing if a middle part of a forged-piece is

elongated and shouldering if the end part of a forged-piece is elongated.

Offsetting

Offsetting is a forging step, during which a certain material volume of a forged-piece is

transversely shifted, while the axis of the offset material remains parallel to the axis of the

original forged-piece. Before offsetting, the diameter of the forged-piece has to be increased

to enable offset of a material without fracturing the original forged-piece.

Die forging

Die forging can again be performed using hammers and presses. However, this time a special

form – die – is used to impart a required shape to a material. Die forging is performed under

hot conditions and is characterized by very short working times. Material flow is limited by

die walls. Nevertheless, heat transfer and consequent material cooling occurs during contact

of material with die and it is thus favorable to minimize the contact time periods.

Die forging can be either precise, or the forging dies can be slightly overfilled with material.

For the latter one, the redundant metal is pressed into a flash groove in the dividing plane and

generates a flash, which has to be cut after forging is finished. The flash can contain up to

30% of the entire metal volume and is therefore the largest material loss during the entire

forging process. However, it also has several advantages. Due to its large surface area, the

flash increases the resistance against material outflow from a die and supports the pressure

stress state, which contributes to a perfect filling of the die cavity. It also effects as a shock-

absorber during closing of the dies and helps to balance volume differences between the semi-

product and die cavity. For precise forging, the die is perfectly filled with a metal with no

flash. On the other hand, a precise calculation of the volumes of the die cavity and metal and

their correlation is needed. The die has to also have a suitable construction. Such dies can be

used only for axisymmetric forgings. In precise dies, defects caused by non-perfect fillings of

some parts of the die cavity can occur. Nevertheless, a significant advantage of precise

forging is a favorable flow of material fibers, since they are not disrupted by additional

machining of the forged-piece.

The original intermediate products for die forging are usually rolled bars (for precise forging

they can also be drawn due to their higher dimensional accuracy). The rods are then cut to

required pieces and heated in furnaces. Heating is followed by a preliminary forging in

preparatory dies and eventually forged in final dies. After possible flash cutting, finishing

operations, such as heat treatment, calibration and straightening can be performed.

Rolling

Rolling is a continuous process, during which height reduction is performed on a material via

its forming between rotating work rolls (material thickness decreases). Rolling can be

characterized as longitudinal, transverse and rotary rolling according to the positions of axes

of the rolls towards the axis of a formed material. The most widespread is longitudinal rolling.

Most of the flat and long products, such as sheets, strips, rods and wires are produced by

longitudinal rolling. The work rolls can be either straight or shaped, the latter of which is used

to produce e.g. profiles and rails. Rotary rolling is typically used to roll tubes. Transverse

rolling is a special case applied e.g. to roll grinding balls. The intermediate products for rolled

products are usually slabs, billets and blocks, which can be rolled from ingots or continuously

cast.

Theory of longitudinal rolling

During longitudinal rolling, the metal is captured into the rolling gap using two rotating work

rolls. The rolled semi-product is deformed between the work rolls in the deformation zone,

which is depicted in Figure 4. The length of the deformation zone can be mathematically

derived and described using the following equations (7-10).

; [m] (7,8)

[m] (9)

[m] (10)

where: ld … length of deformation zone [m]

O, A, C … significant points on a roll in Figure 4

R … roll diameter [m]

Δh … height reduction [m]

It is also possible to calculate the width of the deformation zone according to Equation 11.

[m] (11)

where: bd … width of deformation zone [m]

b1 … width of material before entering rolling gap [m]

b0 … width of material after entering rolling gap [m]

The deformation zone consists of several zones according to the way in which the rolls

influence the rolled material.

Figure 4: Deformation zone.

Longitudinal rolling on shaped rolls

Besides straight rolls, shaped rolls can also be used for longitudinal rolling. Along the

perimeter of each roll, there is a groove of a certain shape. Usually, a groove forming only a

half (or a part) of the final shape is made on one roll, while the other half (part) is made on the

opposite roll. When the rolls are positioned in a stand, the whole shape is formed. However,

there is always a gap between the individual rolls (they are not in contact). Only one shape

can be made on one pair of rolls. However, one pair of rolls usually contains more shapes. A

set of individual shapes following each other is called a shaped-rolling line and the order of

shapes is given by the individual technological process.

Transverse rolling

For this type of rolling the axis of the rolled semi-product is parallel to the axes of the rolls.

Both the rolls rotate in the same direction, while the semi-product rotates in the opposite

direction as a result of friction forces. Transverse rolling is used to produce shafts or grinding

balls for cement mills.

Rotary rolling

Rotary rolling is a special case of transverse rolling. The plastic deformation mechanism is

similar, but the axes of work rolls are skewed, which ensures not only rotation of the semi-

product, but also its forward movement. Rotary rolling is used to produce seamless tubes. It is

one of the most widespread processes for production of hollow semi-products.

Drawing

The principle of drawing lies in passing of a wire through a conical opening (drawing die).

The wire elongates in the direction of the main acting stress and its diameter decreases.

Drawing is processed under cold conditions, which results in an intensive strengthening and

decreases in plasticity and formability of the drawn wires. The stress state in the drawing die

is three-dimensional with pressure transversal stress providing sufficient deformation.

Nevertheless, the main longitudinal stress invoked by the drawing force is tensile stress and

thus the tensile stress state prevails. This decreases the maximum amount of strain which can

be imposed during one pass. Formability can furthermore be decreased by a presence of

inclusions, inner defects, impurities, surface cracks and others. A scheme of drawing is

depicted in Figure 5.

The initial intermediate product is a rolled wire. For drawing, special drawing machines are

used. They can include single or multiple drawing stands and can operate at dry or wet

working conditions. Heat treatment or metal coating can be applied as a final, or semi-final,

operation.

Figure 5: Schematics of drawing.

Extrusion

Extrusion can be performed under hot and cold conditions. The 3D stress state is very

advantageous – a complete pressure. This enables application of extrusion also for forming of

brittle and low-plasticity materials. This technology can be applied to produce semi-products

(pipes, rods, profiles etc.) and also final products (tubes, cartridges etc.).

The initial material is inserted into a closed supply container and then extruded through a die

with an opening of a required shape using a punch. Extrusion can be either forward, or

backward. During forward extrusion, the material is extruded through a stationary die and the

direction of its movement is conformable with the direction of movement of the punch.

During backward extrusion, the extruded material moves in a direction opposite to the

direction of the punch. This type is used to produce hollow products with possible fins, when

the thickness of the walls is very small comparing to the diameter, or contrariwise.

The quality and initial state of the material have a significant influence on the extrusion

process and technology. Materials, for an extrusion of which a significantly high pressure has

to be applied (more than 2,500 MPa), or which cannot be deformed with more than 25% one-

step reduction due to their chemical composition (high strengthening), are unfavorable.

Materials with low strength can be extruded in one step (aluminum and its alloys). Steels and

other metals are extruded in multiple steps. Deformation for formable steels is up to 60% (e.g.

with carbon content to 0.1%). Extrusion is followed by a surface treatment and possible heat

treatment.

4. Production facilities

Time to study: 5 hours

Aim: After study of this chapter you will know

Basic production facilities

Differences between individual machines and their specification

Principles of individual devices

Lecture

Description of all the individual production facilities reaches way beyond the range of this

text. Therefore, only the basic equipment for the most wide-spread production facilities

(rolling mills) is described in this section. Details on other forming technologies can be found

is specialized literature referenced at the end of the lecture.

Rolling mills

The basic equipment of rolling mills is rolling stands. These can be characterized according to

several factors, one of which is number of rolls, another one direction of their rotation (single-

direction, reversible). Construction of a rolling stand is selected according to the number of

work and backup rolls. The position of the rolls can be horizontal, vertical, or sideways.

Two-rolls stand – duo

The rolling stands with two horizontally positioned rolls are the most widespread. The engine

drives either both the rolls (upper and lower), or only one roll (usually the lower one, the

upper one rotates as a result of friction with the rolled work-piece). The stands can be one-

directional, or reversible. For one-directional duo stand, both the rolls rotate in the same

direction. The work-piece enters only from one direction and has to return to the original

position before a subsequent pass. For reversible stands, the direction of rotation of the rolls

changes after every pass. This type is widely used to roll intermediate products from ingots,

heavy profiles and thick sheets.

Three-rolls stand – trio

Such rolling stands have three horizontally positioned rolls rotating always in the same

direction. They are widespread for production of long work-pieces, since they can be

equipped with more shapes than duo stands. The work-piece is rolled between the lower and

middle rolls in one pass and in another pass it returns between the middle and upper rolls. The

stationary middle roll is driven, while the lower and upper rolls are usually movable and

driven by a transmission.

Four-rolls stand – quarto

The rolling stand has four rolls positioned horizontally in one vertical plane – two inner work

rolls and two outer backup rolls. The backup rolls enable to use higher rolling forces and

decrease bending of work rolls. Small diameters of work rolls enable greater elongation of the

rolled-piece and also achievement of more favorable thickness accuracy. Work rolls are

driven. Quarto stands are used to roll steel sheets and strips under hot and cold conditions and

can be used as one-directional and reversible.

Multi-rolls stand

Such stands can have six, seven, twelve and twenty horizontally positioned rolls. For all the

types, two rolls are always work rolls (usually driven), others are backup rolls (trailing).They

are used to roll very thin sheets, strips and foils.

Universal and special stands

Such stands have vertically positioned rolls supplementing the horizontal rolls. These are

driven by a transmission of conical cogwheels. Vertical rolls ram the work-piece from sides

and therefore form side walls, precise angles and sharp edges. They are usually located on the

front side of a stand, less commonly on the rear side, but also on both sides. Universal stands

are used to roll slabs and wide steel profiles. For rolling of wide-legged beans, the vertical

rolls are positioned in the same plane as the axes of the horizontal rolls. Only horizontal rolls

are driven.

5. Final processing of formed products

Time to study: 10 hours

Aim: After study of this chapter you will know

Basic possibilities of final processing of formed material

Types of heat treatments

The mostly used surface processing of formed products

Lecture

Final processing of formed products includes surface treatment and heat treatment applied to

modify inner structure.

Heat treatment – structure modification

Heat treatment can be used as a semi-final or final operation for all the basic forming

methods. A material is heated to a desired temperature selected according to the required type

of structural changes. The heating is followed by a time dwell and subsequent cooling (free or

controlled).The mostly applied heat treatment is annealing. This can be either with or without

phase transformation and can be separated into several basic groups. Annealing can be

supplemented with quenching and/or tempering. To correctly understand the entire heat

treatment system, it is advised to be familiar with the Fe-Fe3C diagram and IRA and ARA

diagrams.

Annealing without phase transformation

Recrystallization annealing

The aim is to restore plastic properties (eliminate strengthening) after cold forming by a

generation of new ferrite grains. A material is heated to its recrystallization temperature

(usually 550 – 700°C for steels), followed by a short dwell and cooling. Recrystallization

start is influenced by various factors, especially the deformation degree. Therefore the heating

temperature depends on the deformation degree. However, it must not exceed Ac1

temperature to prevent phase transformation.

Spheroidization annealing

The aims are conversion of lamellar pearlite to globular, spheroidization of carbides, possibly

achievement of homogenization of structure suitable for subsequent annealing. Steels with the

content of carbon above 0.4%, eutectoid and above-eutectoid steels experience decrease in

hardness and therefore improvement of cold machinability. The annealing consists in heating

to a temperature slightly under or at phase transformation temperature (approximately 750°C

for steels, depending on chemical composition), dwell or slight oscillation around the

temperature and controlled cooling, usually in a furnace.

Annealing to decrease internal stress

Residual tension inside a material can generate as a result of non-uniform cooling, welding,

local heating or similar processes. The process consists in a slow heating (100 – 200°C/h.)

followed by a dwell on the temperature to uniformly heat the entire material (usually 1 to 2

hours) and slow cooling (30 – 50°C/h.). The temperatures between 450 and 650°C are

especially sensitive.

Annealing with phase transformation

Homogenizing annealing

The aim is to homogenize chemical composition within a material via diffusion. This type of

annealing is applied especially for ingots, in which a lot of casting defects and

inhomogeneities are present. Zone heterogeneity (liquation) depends on the type of the cast or

formed semi-product and includes especially inhomogeneities and gases. Inter-dendritic

heterogeneity (segregation) depends on the morphology of dendrites influencing distribution

of alloying and admixture elements. Homogenizing annealing consists of heating to a

temperature significantly higher than Ac3 or Acm (1000 - 1200°C for steels), long time dwell

(6 – 15 h.) and slow cooling depending on the shape of the particular casting.

Normalizing annealing

It is usually applied to achieve fine equiaxed structure consisting of a mixture of ferrite and

pearlite. Normalizing annealing includes a rapid heating to a temperature 30 – 50°C above

Ac3 or Acm, a short temperature homogenization throughout the cross-section of the work-

piece and further cooling on air (100 – 200°C/h). It is mostly used for castings, forged-pieces

and cold-pressed products. The final structure of steel after normalizing heat treatment

depends on the particular chemical composition and size of the work-piece.

Quenching

The principle of quenching is in a rapid cooling of a work-piece from a high temperature after

forming or annealing. This procedure imparts hard martensitic or bainitic structures. It is

usually performed using cooling media with higher cooling capacities than air, such as water

of various temperatures, oil or salt melts.

Tempering

Tempering is a heat treatment following quenching and is used primarily for steels. The aim is

to achieve a state close to the equilibrium state. It consists of a heating to a temperature lower

than A1, dwell on the temperature and subsequent controlled cooling. Since inner stresses can

cause development of cracks and fracture after quenching, tempering should follow

immediately after quenching. It can be divided to high-temperature and low-temperature

tempering. An increase in tempering temperature usually leads to decreases in strength and

hardness and increases in plasticity and ductility.

Temper embrittlement

Tempering at temperatures between 250 and 400°C leads to low-temperature embrittlement.

This is caused by processes occurring on the boundaries of the original austenite grains

(precipitation of cementite, possibly nitrides) leading to their embrittlement. This

embrittlement type is irreversible.

For alloyed steels (typically with Cr, Ni, Mn), high-temperature embrittlement occurs during

tempering around 550°C. This is caused by diffusion of atoms of impurities and trace

elements (P, S, Sn, Sb, Bi) to boundaries of the original austenite grains. This embrittlement

type develops isothermally or anisothermally during a slow cooling from high tempering

temperatures (~ 650°C). It can be eliminated by a reheating to a temperature above 650°C and

a rapid cooling into water or oil. A tendency of steel to embrittle is reduced by additions of

molybdenum or tungsten. Contrary to the low-temperature embrittlement, this embrittlement

is reversible.

Surface treatment

Surface treatment procedures are performed to increase surface quality of a work-piece, but

also as a protection against corrosion of the basic material. The surface of a work-piece can be

coated with a protective organic or inorganic layer or with a metal. Metal coating can be

performed via hot-dip galvanization or electrolytically using zinc, aluminum, tin or copper.

The mostly used industrial process is hot-dip zinc galvanization. Zinc-coating by dipping is

the most effective and economic way of protection of steels and cast irons against corrosion.

It is usually performed between 450 and 470°C (low-temperature zinc-coating) or at

temperatures around 520°C (high-temperature zinc-coating). Between 470 and 520°C

dissolubility of iron increases. Therefore, there is a danger of rapid wear of steel galvanizing

tanks used to store the melted metal. At temperatures above 520°C, iron dissolubility

decreases again. Zinc-coating can also be performed electrolytically.

Copper-coating is applied primarily to wires – as an intermediate step during drawing, since

copper coating decreases friction between the wire and drawing die. The final layer is usually

thicker. It is used typically for mattress springs and welding wires. Coper-coating is

performed electrolytically.

Aluminum-coating is performed by hot-dip galvanization. Aluminum coating is more

corrosion resistant than zinc coating in aggressive atmospheres (2-3x). In practice, alloys of

aluminum and zinc are mostly used for coatings.

Tin has very good protective properties since it passivates by an oxide layer. It is not toxic

and therefore is used especially in food-processing industry and due to its good solderability

also in electotechnics. Tin-coating can be performed either by hot-dip galvanization at

temperatures to 310°C, or electrolytically.

Chromium coating is a favorite decorative final treatment. The coatings are highly resistant to

corrosion and to mechanical wear at elevated temperatures.

Literature for further study

[1] HUMPHREYS, F.J., HARTLEY, M. Recrystallization and related annealing

phenomena. 2nd ed. Oxford: Pergamon; 1996, 617 p. ISBN 978-0080441641.

[2] VERLINDEN, B., DRIVER, J., SAMAJDAR, I., DOHERTY, D.R. Thermo-Mechanical

Processing of Metallic Materials, Pergamon Materials Series- series ed. R.W. Cahn,

Elsevier, Amsterdam, 2007, 332 p. ISBN 978-0-08-044497-0.

[3] LENARD, J.G. Primer on Flat Rolling, 1st ed. Linacre House, Jordan Hill, Elsevier,

London 2007, 342 p. ISBN: 978-0-08-045319-4.

[4] ŽÍDEK, M., KUŘE, F. Válcování, VŠB Ostrava, 1986, 379 s.

[5] PŘEPIORA, Z. Tváření neželezných kovů, VŠB Ostrava, 1991, 200 s.

[6] SOMMER, B. Technolgie kování, VŠB Ostrava, 1978, 200 s.

6. Production of castings into single-use and permanent molds

Time to study: 2 hours

Aim: After study of this chapter you will know

Basic casting terms

Technological steps for castings production

Basic types of used molds

Lecture

Foundry is an industrial field enabling to fabricate a product from an original material in the

shortest way – by casting. Casting enables production of work-pieces of such shapes, which

could not be manufactured by any other process. During casting, a melted metal (or another

material) is poured into a mold, the cavity in which has the shape and size of the desired final

product. The product manufactured by solidification of a melted metal inside a mold is called

a casting.

The molds can be:

A. Permanent (metal molds) – made from metals (cast iron, steel, copper, graphite or

another highly thermally conductive material), into which an entire series of castings can be

cast (30 to 250 pcs.) until its disposal due to change in shape, fracture etc. A general example

can be a cast iron permanent mold and a cast ingot product. Some parts of the molds

(thermally and mechanically loaded) can be fabricated from other materials and can be

changeable to increase lifetime of a mold.

B. Semi-permanent – can be used to cast more than 1 casting, but have shorter lifetime

than permanent molds. Manufactured from granular ceramic refractory mixtures. After each

casting they require service and drying (annealing).

C. Single-use – produced from sand mixtures and used for a single casting each. After

casting a mold is crushed and the mixture can be used to form a new mold (core).

Some modern methods use various combinations, e.g. the front part of a mold is equipped

with a thin sand mixture lining, e.g. to optimize cooling effect of a mold while maintaining its

high dimensional accuracy.

This text deals only with single-use molds providing the widest range of application for

various castings regardless their shapes, dimensions and weights. They are manufactured

from sand mixtures by ramming (pouring). Czech Republic is among the countries with

advanced foundry and engineering industries. It is among the 10 best foundry manufacturers

within Europe.

Characterization of molds according to type of cast material

The following text provides information about the average application of individual

technologies of molds and cores production for individual types of castings.

Grey and nodular cast iron

47% green-sand casting into bentonite mixtures

10% dry casting with application of natural or synthetic mixtures

10% self-solidifying mixtures based on water glass

23% mixtures with organic binders

10% special technologies including permanent molds

Malleable iron (white iron)

Cast exclusively into green-sand bentonite molds

Steel castings

42% green-sand casting into bentonite mixtures

7% dried and skin-dried natural sands and synthetic mixtures

8% mixtures based on water glass

43% technologies with organic binders

Non-ferrous metals alloys

78% pressure casting into metal molds

16% green-sand casting

6% mixtures for drying

The above mentioned proves the necessity to especially deal with single-use sand molds

(bentonite mixtures), into which majority of castings is cast in the entire world.

Categorization of molding mixtures

Pattern – prepared from new resources, rammed around a pattern model, in contact with a

molten metal.

Filling (regenerative) – filling the remaining volume of a mold flask (caisson when forming in

soil) or inner part of a core, prepared from a regenerative (already used) sand mixture.

Core – forming the entire volume or a front part (work surface) of a core. Prepared typically

from new resources. The requirements on quality are higher than for pattern sand mixtures

(higher resistance against penetration of metal, good disintegration ability after casting, longer

cores storage ability etc.).

Unified – is used for unified bentonite mixtures technologies, machine-production of molds

when the entire volume of a mold flask consists of one mixture (no double-layer form).

Already once (or multiple times) used mixtures prepared by processing after each casting

(cooling, moistening, revitalization).

Sand mixture – consists of two basic components:

Sand – granular material creating the main volumes of mixtures and molds and cores

scaffolds.

Binder – substance or a mixture of substances creating a binding system, providing to a green-

sand mixture the binding and plastic abilities necessary for forming, high-temperature

strength after hardening (drying) and good disintegration ability after casting.

A forming mixture can furthermore contain:

Water – for clayey and inorganic binders (cement, water glass).

Additives – substances improving properties of mixtures of the basic components. For

example, additives to improve disintegration ability after casting (bauxite, beech saw-dust),

surface quality (ground coal, activated flours, oils) etc.

Literature for further study

[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov

2008, 326 s. ISBN 978-80-89244-38-6.

[2] JELÍNEK, P. Pojivové soustavy slévárenských formovacích směsí (Chemie

slévárenských pojiv). Ostrava, OFTIS, 2004. 184 s. ISBN 80-239-2188-6.

7. MOLDING AND CORE MIXTURES

Time to study: 4 hours

Aim: After study of this chapter you will know

Basic components of forming mixtures

Basic types of forming mixtures

Basic regeneration procedures and their principles

Lecture

The basic component creating up to 98% of a mixture volume is sand.

The mostly used sand is a high-quality silica sand (SiO2), supplied washed and sieved.

Chromite has also found its important application in Czech foundry factories – for casting of

heavy castings. It features higher cooling ability and refractoriness, although its price is

approximately ten times higher comparing to silica sand. Other sands, such as zircon, olivine,

shale, chrommagnesite etc. are used in minority.

Binder, the component providing strength to a mold, is added in the amount of 1 – 10 %

depending on the type of the binding system.

A mixture can further contain water and other additives to improve its properties.

Mixtures with clayey binders

The most widely used clayey binder is bentonite (clay containing montmorillonite -

NaAl3MgSi8O20(OH)4), the water binding ability of which enables green-sand forming.

Bentonite mixture is the most widely used mixture for fabrication of forms in series – 60 to

70% of castings from cast irons and steels to 400 kg are cast into this type of forms.

Bentonite mixtures are regenerative – after removing of the casting, crushing of clusters,

removing of metal particles, mixing and necessary revitalization (addition of water, bentonite,

new sand, possible addition of carbon additives to improve surface quality of cast irons), the

mixture can be reused.

Chemically bound mixtures

Mixtures hardened by a chemical reaction of binder with hardening agent are not easily

recyclable. Before their reuse, it is necessary to remove from sand grains residuals of binder

and hardening products inhibiting chemical reactions during new application of a binder.

Moreover, high binder concentration causes undesirable increase in volume of gasses (casting

gaseous defects).

Mixtures with inorganic binders – the binder is water glass – alkalic silicate

(Na2O.mSiO2.nH2O). Hardening is imparted by a chemical reaction of the binder with an

externally supplied hardening agent (CO2 process). For self-solidifying mixtures, the agents

are usually various esters. Considering that the alkalic silicates hardening products (silicic

acid gel) feature high adhesion ability to the silica sand grains, their removal is more difficult

comparing to the below mentioned mixtures with artificial resins.

Mixtures with organic binders (artificial resins) – at present the most widely used binding

systems for fabrication of cores. Especially furan and phenol-formaldehyde resins are used to

fabricate whole molds. Their advantage is especially economic production – rapid preparation

and high quality of cores/molds (resulting in high-quality products) directly influence the

production cost. However, such economic advantages are accompanied by non-favorable

impacts on the hygiene in foundry working environments and on environment in general.

Usually 30 to 40% of side-products from organic resins applications are toxic gases or solid

thermal destruction side-products. A significant portion of the destruction products remains in

the reused “waste” mixture. The up-to-date development has been focused on decreasing in

the content of free monomers (phenol, formaldehyde, furfuryl-alcohol).

Regeneration of forming mixtures

The aim of regeneration is to remove residuals of binders (in various degrees of degradation

depending on heat transferred from the cast metal) and other impurities so that the sand can be

reused in another mold forming process.

REGENERATION OF MOLDING MIXTURES IS A TECHNOLOGICAL PROCESS

COMPRISING REGAINING OF A SIGNIFICANT PORTION OF SAND FROM AN

ALREADY USED MIXTURE FOR ITS REUSAGE IN NEW MOLDS AND CORES.

The intensity of regeneration necessary to remove residuals of binder and deteriorating

substances from sand grains depends on the type of used binder and its adhesion ability to the

sand grains surfaces. Therefore, various devices and technological steps have to be applied in

order to achieve the cleanest grains surfaces possible.

An already used mixture represents a highly chemically inhomogeneous dispersed system.

Sand grains are covered with a film of binder, which is, depending on the state of thermal

exposition, either in the original state (poly-condensed resin, silicic acid gel with other

hardening products, dehydrated clay) or in a state of complete thermal degradation (coke rests

of organic binders, silica glass, oolitic clay layer).

Degree of thermal degradation depends on:

Distance from a casting

Robustness of a casting

Thermal volume of a cast metal (alloy type, casting temperature)

Sand to metal ratio

Binder content

Regeneration processes

For selection of a suitable regeneration process, an entire set of factors has to be considered –

economic and ecological factors (expenses on regeneration, amount of wastes produced

during regeneration and their subsequent processing, cleaning of waste waters, etc.). It is

especially necessary to consider:

- The used binding system from the point of view of regenerating ability and sensitivity to

impurities in a regenerated mixture.

- Composition of the used “waste” mixture (one-component binding system or a

combination of various technologies – binding systems).

Three basic regeneration processes can generally be separated (BAT):

Literature for further study

[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov

2008, 326 s. ISBN 978-80-89244-38-6.

[2] JELÍNEK, P. Pojivové soustavy slévárenských formovacích směsí (Chemie

slévárenských pojiv). Ostrava, OFTIS, 2004. 184 s. ISBN 80-239-2188-6.

8. PROPERTIES OF MOLTEN METALS AND ALLOYS

Time to study: 6 hours

Aim: After study of this chapter you will know

Main processes occurring in a foundry mold

Basic calculations to design a gating system

Basic melting processes and their principles

Lecture

MECHANICAL REGENERATION

THERMAL REGENERATION

WET REGENERATION

To be able to properly design a production process for a casting it is necessary to be familiar

with the processes occurring in a mold and a casting.

Main processes influencing quality of castings.

crystallization and solidification mechanisms,

fluidity and mold filling,

shrinking during solidification,

solid state shrinking,

gasses in the metal and mold.

Crystallization mechanism

Pouring of a molten alloy into a mold results in cooling of the metal due to heat removal

through the mold walls. When the temperature drops to a certain value, the metal starts to

crystallize. The temperature at which the metal starts to crystallize is denoted as liquidus

temperature, while the temperature at which the crystallization is finished is denoted as

solidus temperature. These temperatures vary with varying content of additives (with

content of carbon for iron alloys). A line connecting the two temperatures is the liquidus-

solidus curve. The difference between the temperatures is the solidification interval. Pure

metals and eutectic alloys solidify at a single temperature (zero solidification interval). Most

alloys have a more or less wide solidification interval (Figure 6).

Metal crystals grow preferentially in the heat removal direction. According to the width of

solidification interval, the solidification can be progressive, dual-phase or volumetric. The

solidification intervals are schematically depicted in Figure 7.

Figure 6: Dependence of solidification start

and finish temperatures on chemical

composition of alloys.

Figure 7: Schematics of crystallization at

various solidification intervals. From left

a) progressive solidification, b) dual-phase

solidification c) volumetric solidification.

A set of locations, in which the alloy solidifies last, is called a thermal axis. Its location

depends on the shape of casting and heat removal mechanism. The thermal axis does not have

to necessarily be conformant to the geometric axis and is usually deviated from the geometric

axis in the directions of slower and quicker heat removals (Figure 8).

Monitoring of castings solidification can be performed using simple relations, according to

which the time for complete solidification of a casting (in the thermal axis) and solidification

from the walls of a casting can be calculated. The Chvorinov’s rule applies for solidification

time:

τ = k (R)2

where, τ-time of complete solidification of a casting [s], R-relative thickness (module) of a

casting [m], k-solidification constant,

where, V-metal volume in a casting [m3 ], S-cooled casting surface [m

2].

The size and shape of crystals are significantly influenced by the heat removal mechanism.

The higher the heat removal, the finer the crystals and better mechanical properties of the

alloy. Therefore, casting to metal molds (chill casting, pressure casting) is preferred to casting

to sand molds. Nevertheless, castings cast into sand molds also exhibit thin surface layers of

fine crystals – die chill regions – featuring better mechanical properties comparing to the

central region.

Figure 8: Deviation of thermal axis at various

solidification conditions.

Figure 9: Fluidity testing

a) spiral - horizontal; b) tube – vertical.

Cooling rate decreases with increasing thickness of casting walls. Therefore, mechanical

properties of thick walls are worse comparing to thin walls. Crystallization of alloys can be

influenced externally by inoculation – addition of crystallization nuclei.

Fluidity and mold filling

Fluidity is not a physical property of a metal, such as e.g. viscosity and surface tension. It is a

technological property. It defines the ability of an alloy to fill the mold and is usually

expressed as a length of a cast channel with a certain cross-section under selected casting

conditions. To define fluidity, various casting tests are used. Examples of fluidity test castings

are shown in Figure 9.

Fluidity is not unambiguously given by a type of an alloy, but depends also on mold material

and casting method. The complete length of the filled cast metal can be calculated, but has to

still be proven by testing for specific casting conditions.

In order to fill the mold cavity with molten metal, a gating system is composed. This consists

of:

pouring basin,

down-sprue,

sprue well,

blind riser (slag collector)

gates to castings.

Figure 10 shows an axonometric projection of a gating system for castings from gray cast iron

(LLG). The gating system for steel castings in Figure 11 has different shape of pouring basin

and has a runner instead of blind riser.

Figure 10: Gating system

for gray iron castings.

Figure 11: Gating system for

steel castings.

Figure 12: Attachment of

gates to the molds: a) top;

b) bottom; c) step.

Besides the basic gating system shape, the casting gates positions can be top, bottom and step

according to their attachments to the molds (Figure 12).

A molten metal is poured from a casting ladle to the pouring basin.

The down-sprue is usually of a circular cross-section and gets narrower towards its lower

section to conform to the naturally narrowing shape of a poured metal.

The blind riser (slag collector) leads a molten metal to the gating runner and the individual

gates. It also serves as collector of impurities.

Gates connect the blind riser with the mold cavity.

Shrinking during solidification

Colling of alloys is accompanied by a reduction of their volumes – shrinking. This is a result

of a change of alloy density ρ, which increases with decreasing temperature. The types of

shrinking are shrinking of a molten alloy εVl

, shrinking during solidification ε

Vk and solid state

shrinking ε VS.

Figure 13 shows the process of shrinking for steels and cast irons. The main difference

between these two is in the crystallization mechanism. For cast irons, graphite particles

precipitate from the molten alloy and cause pre-shrinkage dilatation. This results in a smaller

total linear shrinkage of cast iron castings (1%), comparing to steel castings (2 %). For

foundry technology, shrinkage during solidification and solid state shrinking are the most

important since they cause shrinkage cavities and residual stresses, deformations and

fractures, respectively.

Shrinking during solidification depends on the cast material, solidification mechanism, mold

and casting designs. The difference between the volumes of the molten metal before

solidification and the solidified metal is called a shrinkage cavity (Figure 14). A large portion

of its surface consists of free dendritic structure. The main factor influencing shape and

location of a shrinkage cavity is the heat removal mechanism. Shrinkage cavities form in the

thermal center of a casting. Beside shrinkage cavities, shrinkage porosity can occur. This is a

less densely filled location – small cavities apparent on a cut or a fracture of a casting.

In order to compensate volume shrinking during solidification, the volume of the poured

molten metal has to be larger than the volume of the final casting. A reservoir from which a

molten metal is supplied is called riser. It is necessary to locate the shrinkage cavity to this

reservoir.

Locations in which the molten metal accumulates (comparing to surrounding walls) solidify

later. These are usually locations of walls attachments and connections. They are called

thermal nodes and are usual locations for formation of shrinkage cavities (Figure 15).

An approximate instrument for finding of thermal nodes is the method of inscribed spheres.

Spheres are inscribed into the cross-sections of casting walls on a drawing (i.e. double the

dimension of a circle diameter). The location with the largest circle is a thermal node, which

is then compensated with a technological addition (wedge). Alloys with wide solidification

intervals can exhibit formation of micro-cavities when individual growing dendrites enclose

islands of still molten metal. Small inner cavities then generate during solidification of the

molten islands.

To produce a well-done casting (Figure 17), solidification has to continue from the most

distant areas through the thermal axis to the riser, which has to solidify as the last part.

Figure 17: 1 - closed riser,

2 - open riser, 3 -

atmospheric core.

Figure 18: Shapes of

shrinkage cavities for

risers: a) unprotected; b)

covered with ash; c)

covered with exothermic

additive; d) with insulation

lining; e) with exothermic

lining.

Figure 19: a) without

chills; b) external shaped;

c) external flat; d) external

flat and shaped; e) internal

(horsenails); f) internal

(hooks).

Risers and chills

The riser – reservoir of a molten metal – has to solidify as the last part. Its positioning has to

ensure optimal filling of the molten metal into a certain area of the casting (feeding area).

According to their construction the risers can be open – opened into the upper plane of a

flask, and closed – hidden inside a mold (Figure 17).

Insulation and exothermal powders and linings are used to increase the riser solidification

time without increasing its dimensions (Figure 18). Shrinkage cavity volume remains the

same, while its shape changes.

Due to their distant locations, some thermal nodes inside a casting can only hardly be

connected to open risers and their connection to local closed risers is very costly. Such

thermal nodes are eliminated by increased chilling of the molten metal via application of

chills. According to their location, chills can be external (located on a casting surface) and

internal (located inside a casting).

Solid state shrinking

The cause for residual stresses, possible cracks, fractures or deformation is solid state

shrinking. Linear shrinkage results in change – decrease – in casting dimensions. The overall

linear shrinkage of a casting is usually around 1% for gray cast irons and tin bronzes, 1.5%

for brasses and aluminum alloys and 2% for white cast irons and steels. During design of a

pattern (mold), the shrinkage has to be considered and the patter has to be correspondingly

oversized. Addition for machining has to also be involved.

Shrinkage stress generates in the casting as a result of resistance of mold, cores etc. against

shrinking (by external forces). This stress typically results in generation of high-temperature

cracks. At higher temperatures, when the material is plastic instead of elastic, internal stress

releases via permanent deformation of dimensions.

During cooling of robust castings (cylinders, stocks etc.)

or castings with various walls thicknesses in the

temperature region of elastic-plastic deformations and

then in the region of completely elastic deformations,

internal thermal stress is generated as results of thermal

gradients. This stress then increase during further

cooling to room temperature. If the stress is higher than

tensile strength, cracks occur (with clean metallic

surface). Generation of internal stress in a casting is

schematically depicted in Figure 20.

Besides internal stress caused by non-uniform cooling of

a casting in solid state, transformation stress is generated

due to γ -> α Fe phase transformation in solid state

during which volume increases. A typical example is residual stress in Fe alloys.

Residual stress is very dangerous for castings, since it leads to deformations (especially

during machining), decreases loading ability (residual stress is added to external stress) and is

the cause of early fracture nucleation.

Thermal stress in a casting can be calculated:

±σ = E.α.(T1-T2)

where σ – stress [MPa], α – coefficient of thermal linear shrinkage [K-1

], E – elasticity module

of metal [MPa] and ∆T – temperature difference in two locations within a casting [K].

Generation of residual stress can be prevented by suitable casting construction (possibility of

a harmless stress release, uniform walls thicknesses, smooth changes etc.), suitable foundry

Figure 20: Generation of

deformations during shrinking.

technology (supple molds, early removal of a casting from the mold, reinforcement of high-

exposure locations by fins) and slow uniform casting cooling.

If inner residual stress after all generates in a casting, it can be released via either natural

release – aging (i.e. long-time storage, favorably at weather conditions) or annealing to

decrease internal stress.

Gasses in metal and mold

Gasses in mold and metal during casting are involved in several phenomena occurring at the

same time:

Dissolution of gases in a molten metal.

Generation of gases in a mold.

Flow of gasses towards a casting surface.

Removal of gases from a mold cavity.

Entry of gases into a molten metal.

Movement of gases inside a molten metal.

Separation of gases from a molten metal.

At a certain temperature, molten metals and alloys can dissolute certain amounts of gas.

Generally, the amount of gas which can be dissolved in a melt increases with increasing

temperature. Dissolubility of gases decreases with decreasing melt temperature and is

decreased significantly at the point of solidification.

Gases separated from a melt have atomic character and synthesize into molecules. They are

especially CO, N2 and H2.

Gases dissolve in pure iron exactly according to the Sieverts law. If a metal is completely

liquid and has low viscosity, gasses are released easily. Mechanical processes such as stirring

can be used to facilitate gasses releasing. An often used method is decreasing of partial gas

pressure above the melt level (vacuum extraction or blowing of inert gas into the melt).

Gases dissolved in a metal can cause generation of bubbles resulting in smooth-surface

cavities on the surface or inside a casting. Besides gases dissolved in a metal (endogenous

bubbles), gases penetrating into the metal from the mold during its filling with the metal

influence generation of bubbles as well (exogenous bubbles). Humidity of molding mixtures

can be very dangerous especially for green-sand molds generating a significant amount of

vapor. Organic binders and additives present in a molding mixture also disintegrate and

generate carbon oxides and carbohydrates.

Permeability of a molding mixture itself is not sufficient for removal of gases, vapor and air

from a sand mold. Therefore, channels for gases removal – gas vents and vent holes – are

usually formed in a mold.

Vent holes – the main gas removal channels – are always positioned in the top parts of

castings. Contrary to this, vents are usually cast through with a metal and can also serve to

control filling of the mold or sometimes as risers. The vent holes remove gases only from a

certain part of a mold. To achieve good gases removal, the mold has to have other degassing

channels – vents.

Vents are among molds formed also in cores and they together create the extract system of a

mold cavity. They are created by perforating a mold (core) above the pattern with a steel spike

of a diameter 3 to 12 mm, the perforations are to the depth of 5 – 20 mm above the pattern.

Vents are made from an external side when the pattern is still in the mold and are not cast

through with the metal. For metal molds, the gas channels are milled and drilled.

Melting and casting of metals

Foundry technologies work only with liquid metals, which have to be produced by melting

and subsequent heating to temperatures higher than Tm. A melt of a required composition is

prepared by melting of a batch, in which the metal part usually consists of recyclable material

(risers, parts of gates, vents), slag-forming resources, external waste, possibly alloying

elements. The non-metal part of the batch consists of slag-forming additions (limestone etc.)

and also fuel for shaft furnaces. Some melting technologies do not enable to influence the

composition of a molten metal. It is therefore necessary to carefully sort individual resources

according to the chemical composition of the batch, optimize the lumpiness and surface

cleanliness.

Melting furnaces can be heated using solid fuels (coke, anthracite), gaseous fuels (natural

gas), liquid fuels (black oil) or electrically. According to the construction and batch heating

method the furnaces can be:

cupola furnaces,

electric induction furnaces,

electric arc furnaces,

converters,

rotating gas furnaces,

resistance and fuel crucible furnaces,

flame furnaces,

gas shaft furnaces.

Literature for further study

[1] MICHNA, Š.; NOVÁ, I. Technologie a zpracování kovových materiálů. Adin, Prešov

2008, 326 s. ISBN 978-80-89244-38-6.

[2] ELBEL,T. a kol. : Vady odlitků ze slitin železa. Matecs, Brno 1992,339s.

9. TECHNOLOGICAL PROCESS OF CASTINGS PRODUCTION

Time to study: 6 hours

Aim: After study of this chapter you will know

Main steps of design of technological process of castings production

Basic principles of production process design

Basic melting processes and their principles

Lecture

Demand process

The design of casting production technology and processing of technical documentation have

to be performed based on “order acceptance decision-making” or “demand process”. The aim

of this process is to make the following issues clear before concluding an “Economic

contract” (or a different form of confirmation of a casting delivery):

- technological possibilities of production of a casting of the required parameters

- acceptability and justification of customer’s requirements

- economical acceptability

- possibility of time filling of the contract

The task of a technologist in this phase is to review suitability of the casting for production

conditions in the foundry, involving especially:

- conformity of the dimensions of the casting with parameters of the existing equipment

(flasks, maximum loads and lifting heights of cranes, openings of blasting machines and

annealing furnaces doors, melting aggregates capacities etc.)

- review of optimum construction of the casting from the technological point of view and

proposition of possible adjustments

- review of the ability to keep quality requirements

- review of optimum serial production from the point of view of time usage of equipment

- review of production risk

Casting production process

A production process consists of two consequential parts: casting production process and

pattern equipment production process.

In the foundry technological department, the basic casting production background papers are

prepared:

a/ foundry work flow drawing

b/ work flow card (usually having the official title "Casting production process”).

These background papers are then forwarded to the pattern technology department, where

drawings of the pattern and its production process are developed. Based on the work flow

drawing and card, the department of foundry production technological preparation (TVP)

prepares documentation for production of all the necessary instruments – drawings of metal

pattern plates, metal cores, reinforcements, templates, pads etc. Furthermore, according to the

custom practice in the foundry, the steps to produce molds, cores and other instruments (e.g.

reinforcements) can be prepared in detail.

Foundry work flow drawing

According to ČSN 01 3061 this is a drawing of components supplemented with data

necessary to produce the pattern and mold.

Among the most important data mentioned in the drawing are:

- shrinkage of the proposed alloy

- positioning of the casting within the mold, parting lines, additions, chamfers, pre-cast and

non-pre-cast openings

- positioning of gating system (including shapes and dimensions)

- data about pattern

According to the type and shape of a casting and relevant requirements, more data can be

mentioned in the foundry work flow drawing (e.g. free parts of a pattern, chills, risers,

forming pads etc.).

Shrinkage of cast alloys

Since shrinkage occurs during cooling of foundry alloys (e.g. metals), it is necessary to design

the pattern oversized by the shrinkage of the particular alloy. The size of linear shrinkage

depends on the type, chemical composition and structure of a casting, as well as on the

resistance against shrinking from the mold or construction of the casting itself. Since the size

of shrinking is influenced by many factors, its proper design is very difficult (it is often

necessary to consider empiric experience).

Values of free linear shrinkages for the most widely used foundry alloys are summarized in

Table 2.

Table 2: Linear shrinkage of selected alloys.

Alloy Shrinkage

/%/ Alloy

Shrinkage

/%/

Gray iron 9 – 10 Tin bronze 12 – 15

Inoculated cast iron 10 – 13 Aluminum bronze 15 – 20

Ductile iron 12 – 15 Brass 13 – 18

Malleable iron 15 – 18 Aluminum alloys 12 – 14

Steel from electric furnace 15 – 20 Magnesium alloys 12 – 13

Steel from SM furnace 13 – 18 Zinc alloys 12 – 15

Austenite steel 24 – 30 Pattern metal 3 – 4

On the work flow drawing, the shrinking data is marked in red and located (if possible) above

the corner stamp.

Note:

If a metal pattern, which has been formed using a “maternal pattern” is used, the maternal

pattern has to be designed for double shrinkage – first shrinkage for casting of the pattern and

the second for casting of the casting.

Position of casting within the mold

A suitable positioning of the casting within a mold is important for production of a casting of

a required quality by the easiest possible production process. Determination of the position

has to be based on a set of important principles:

A/ Among the principles based on technological aspects and thus respecting casting quality

are:

- functional (important) planes of cast iron castings with larger walls thicknesses have to be

located at the bottom part of the mold (purest metal); if there are more functional planes

within a casting or if the functional plane cannot be positioned as the bottom plane from

various reasons, it can possibly be designed as a side plane

- for castings from alloys with high tendencies to form shrinkages (e.g. steels), the positioning

of the casting has to enable correct positioning of risers and support directional solidification

B/ From the point of view of easy production, the following principles have to be met:

- the possibility of easy positioning and fixing of cores, fixing of cores into the top part of a

mold is not used (if possible), since this is very difficult to perform

- the possibility of uniform and the easiest possible ramming

- mold cavity, especially highly exposed locations, has to be accessible and enable possible

reparations

C/ From the economic point of view it is necessary to design the position of a casting so that

the area within the mold flask is used in the best way and usage of mold material is the

smallest possible.

On the work flow drawing, the position of the casting is marked in green by the letter U (up)

or T (top) and by an arrow in the direction of the part of the pattern formed into the top of the

mold (see table Č. XVI).

Parting line

Positioning of the parting line has the most significant influence on the design of pattern,

fabrication process of molds and cores, number of cores within a mold and also achievable

dimensional accuracy of the casting. It basically comprises a suitable partitioning of a mold

(usually also pattern) to enable:

- removal of parts of the pattern after ramming

- fixation of cores

- forming of a gating system

Design of the parting line has to be performed in accordance with the following principles:

a/ A mold should have only one parting line (if possible). Application of more parting lines

significantly complicates productions, especially for machine production.

b/ The parting line should be "in plane" (if possible), especially for manual forming. An

irregular parting line should be designed only in exceptional cases – for complicated shapes.

c/ The parting line should be designed to minimize the number of pattern parts – loose parts in

particular – and cores.

d/ During design of partitioning of a free pattern, sufficient strength and stiffness of individual

pattern parts have to be maintained.

e/ The parting line should be designed to enable usage of forming flasks available in the

foundry.

f/ Parts of the casting requiring dimensional accuracy have to be formed in a single mold part

to exclude the possibility of offset.

g/ The parting line should be designed to enable positioning of all the cores in the bottom part

and their possible check before assembling of the mold.

h/ The parting line should also enable easy removal of possible seams and leakings.

The parting line is marked in green on the work flow drawing and is highlighted by end

crosses.

Additions for machining of casting planes - ČSN 014980

An addition for machining is basically a layer of material on the external or internal plane of

the casting enabling achievement of dimensional accuracy and surface quality given on the

drawing of the component by machining.

The size of a particular addition for machining is given by:

a/ The degree of accuracy of the casting according to ČSN 01 4470 and therefore the

technology used to achieve the required degree of accuracy

b/ Basic dimensions of the casting

c/ Nominal dimensions of the casting

d/ Positioning of the machined plane within the mold

e/ Material of the casting

f/ Special requirements

Gating system

The gating system generally consists of riser, down-sprue, blind riser (runner) and gates. Its purpose is

to regulate a stream of melt from a ladle to the mold and to provide perfect filling of the mold cavity in

the shortest possible time (with minimal temperature drop) in the easiest way. The gating system has

to also collect slag and impurities, which could get into the casting with the metal, and regulate

thermal processes during casting solidification. Shapes of gating systems can significantly deviate

from the common shape depending on specific conditions (i.e. character of the casting).

Calculation of gating system

Optimal casting time– τ0 – can be calculated according to the following relation:

0 = s*(m0)1/2

/s/

where: m0 – raw casting mass /kg/ (mass of components including additions for machining,

gating system, vents, possibly risers), s – coefficient depending on casting wall thickness

cast iron: s = 1.53 for thickness 3 - 4 mm

s = 1.85 for thickness 4 - 8 mm

s = 2.20 for thickness 8 - 15 mm

s = 2.50 for thickness 15 - 30 mm

steel: s =1.1 thin-walled castings

s = 2 – 2.4 simple thick-walled castings

Mean ferrostatic pressure height – Hp – can be calculated according to the following

relation.

H =H – P2/2C /m

where: Hp - mean ferrostatic pressure height, H – height of down-sprue above the gate /m/, C

– height of casting /m/, P - height of casting above the gate /m/

According to the location of attachment to the gates, specific cases can occur (Figure 12):

a/ bottom attachment – P = C and Hp = H – C/2

b/ top attachment – P = O and Hp = H

c/ step attachment, for a case when P = C/2 is Hp = H – C/8

Casting speed (metal flow rate) can be calculated according to the following relation:

v = (2g Hp)1/2

/m.s-1

/

where: v – casting speed, Hp – mean ferrostatic metal pressure height /m/, g – gravity

acceleration /m.s-2

/, μ – coefficient of resistance

μ is selected: 0.27 – 0.55 for cast iron

0.30 – 0.41 for steel

0.60 – 0.70 for non-ferrous metals

Calculation of the gating smallest cross-section

For a pressurized gating system, the smallest cross-section is the cross-section of gates, calculated

according to the following relation:

O

O

Zv

ms

Τ

(m2)

where: Sz – total gates cross-section, mo – raw casting mass (kg), – density of the molten

metal (kg.m-3

), v – casting speed (m.s-1

), o – optimum casting time (s)

If relation 8 is substituted for casting speed and relation 6 is substituted for optimum casting

time into the relation for sz and all the constants are consolidated as coefficient x, the

following equation is generated:

Hp

mxs

O

Z (m2)

where: x – coefficient depending on casting wall thickness.

Determination of the coefficient x:

a) for simple castings:

wall thickness 3 - 4 mm x = 3.8

4 - 8 mm x = 3.2

8 - 15 mm x = 2.8

over 15 mm x = 2.4

b) for more complicated castings:

wall thickness 3 - 4 mm x = 5.8

4 - 8 mm x = 4.9

8 - 15 mm x = 4.3

Note:

If the designed gating system has more gates, then a cross-section of one of the gates is

determined by dividing of the total cross-section area sz by the number of gates.

Shape and dimensions of gates can be determined (if the cross-section is known) according to

Figure 21.

Figure 21: Basic types of gates for gating systems.

Determination of other gating system cross-sections:

The sz gates cross-section is the basic parameter for calculation of other parts of the gating

system.

For pressurized systems, the following condition applies: cross-section of the down-sprue in

its narrowest location sk > cross-section of the runner ss > cross-section of gates sz.

The mutual ratio of these cross-sections varies for various foundry alloys. The following

rations are usually selected for gray cast iron castings:

Sk : Ss : Sz

2 : 1.5 : 1 for larger and medium castings

1.4 : 1.2 : 1 for simple and fine castings

1.11 : 1.06 : 1 for fine-walled castings

According to the casting and cast alloy types, it is possible to determine the sz and sk cross-

sections using the mutual ratio of the cross-sections.

Shape and dimension of the blind riser can be determined using Figure 22.

Figure 22: Shape and dimension of blind riser.

The down-sprue is of a circular cross-section. For pressurized systems, the sk cross-section

(i.e. cross-section of down-sprue in the location of attachment to the blind-runner) increases

towards the pouring basin. The chamfer, by which the widening is ensured, is usually 1° - 2°.

Pouring basin – absorbs the first impact of a metal during casting from a ladle and regulates

its flow into other parts of the gating system. It also ensures a constant casting speed during

filling of the mold and collects slag carried from the ladle by the stream of a molten metal.

The basic shape of a pouring basin is depicted in Figure 23a. However, various pouring basins

shape modifications can occur in practice – see Figure 23b-e.

Figure 23a: Basic pouring basin shape. b) H0 – level of cast opening entrance c)

Plugs, partitions and possibly strainers (see Figure 23b-d) reduce the danger of intrusion of

slag into other parts of the gating system and therefore to the mold cavity.

Plugs – reduce the danger of slag intrusion at the beginning of casting – i.e. in the most

important time period from the slag separation point of view. Plugs are controlled either

manually (for large castings) or automatically.

Funnels (Figure 23e) – do not separate slag and can therefore be applied for bottom-

attachment type of casting.

Pouring basins are formed in the mold either manually, pressed-in or “external” (i.e. formed

in an additional flask outside the main mold).

d) e)

Figure 23d-e: Various types of pouring basins.

On the work flow drawing, the gating system (shape and dimensions) is drawn in red,

possibly blue, color.

CORE

Vents and their calculation

Vents together with natural gas permeability of molding mixtures and exhaust vent holes

perforated into the molds serve to exhaust air and gas generated during casting and

solidification of the molten metal. They are positioned at the highest locations in the molds

and their number is determined according to their size (possibly shape).

The shape of a vent is depicted in Figure 24. Their cross-section is usually circular and

increases towards its outlet from the mold. The chamfer, by which the widening is ensured, is

usually 4° - 8°.

Figure 24: Positioning and shape of vents.

The following simple relation is applied to calculate the smallest vent cross-section sy (i.e.

cross-section in the location of attachment to the casting):

Sv = 1,5 . Sk (m2)………………...11

where: Sv – total vents cross-section, Sk – cross-section of down-sprue – see chapter 2.2.2.1

(m2).

Note:

If more vents are designed for a casting, then the cross-section of a single vent is determined

by dividing of the total vents cross-section area sy by the total number of vents.

On the work flow drawing, the vents (including dimensions) are drawn in red or blue.

Risers

For alloys which tend to form shrinkage cavities (e.g. steels), it is necessary to involve risers.

The riser is basically a container of metal providing metal filling for the solidifying casting.

The molten metal in the riser solidifies as last. Therefore the shrinkage cavity does not form

in the casting but in the riser, which is removed during subsequent machining.

Note:

Calculation of risers and technological principles for their design are described more in detail

in the recommended literature.

On the work flow drawing, the risers (shape, dimensions, number) are drawn in red or blue.

Work flow card

It is in principle a text part of a foundry process. It completes marks drawn in the foundry

work flow drawing and contains more information necessary for production, costs calculation

and control of technological flow in a foundry. The information and method of their

denotation in a work flow card vary substantially in individual foundries and depend

especially on the organization of production in the foundry and method of utilization of the

background papers.

The following details are in particular mentioned in work flow cards: material and weight of

the casting, shrinkage size, complete pattern, used forming machines, flasks sizes, casting

temperature and time. Furthermore, type and consumption of molding mixtures, molds,

conditions for cooling of the casting, cleaning method, heat treatment and delivery conditions.

VŠB-TU Ostrava

Department of

metallurgy and foundry

Ostrava Poruba

CASTING PRODUCTION

PROCESS

Model no.:

Drawing no.:

Casting title Mold

Number of produced

castings Molding mixture

Material of the casting Composition:

sand

Delivery conditions

binder

Casting weight: [kg]

additives

Usage of molten metal [%] Cores

Shrinkage of pattern

equipment [%] Molding mixture

Pattern Composition:

sand

Cores binder

Free risers additives

Number of castings

within a flask

Drying of molds and

cores

Dimensions of molding

flask: upper x / [mm]

Dimensions of molding

flask: lower x / [mm] Chills external

Mold stiffness Chills internal

Surface treatment Casting temperature [°C]

Schematics of the casting:

Production process elaborated

by:

Date: Study group:

Literature for further study

[1] HAVLÍČEK, F. Konstrukce odlitků, učební pomůcka, VŠB-TU Ostrava, 1995

[2] BEDNÁŘ, B. Technologičnost konstrukce odlitků, Univerzita J.E. Purkyně, ÚTŘV, Ústí nad

Labem, 2004

[3] HERMAN, A., SVÁROVSKÝ, M., KOVAŘÍK, J., ROUČKA, J. Počítačové simulace ve

slévárenství, učební texty ČVUT Praha, 2000

[4] GOODRICH, G.M. Iron Castings Enginering Handbook. American Foundry Society.

Schaumburg, Illinois, USA, ISBN 0-87433-260-5, 2006, 418s.

10. CLEANING AND FINISHING OPERATIONS, FINAL CHECK,

DEFECTS OF CASTINGS

Time to study: 4 hours

Aim: After study of this chapter you will know

Individual processes for cleaning of castings

Basic principles of quality check

Basic defects of castings

Lecture

Cleaning of castings

After casting, the casting has to cool down to temperature enabling further manipulation. The

necessary cooling time depends on material, weight and shape of the casting and material of

the mold. After cooling, the casting (usually called raw casting) can be removed from the

mold. This is easy for permanent molds. For non-permanent molds, a special step called

releasing from the mold has to be performed.

Releasing of a casting from the mold

Cooled castings can be released from molds either by impacts (shaking-out) or by tension or

press (pulling or pressing out). Manual shaking-out consists in impacting the flask or casting

with a hammer. Mechanical shaking-out can be performed using vibrators or shaking grids.

Pulling or pressing out is used especially for casting to permanent molds and can be

mechanized and robotized.

Raw cleaning of castings

Shaking-out enables removal of a significant portion of mold material. Nevertheless, burnt-on

sand particles on the surface of the casting and rests of cores usually remains un-removed.

Raw cleaning of castings is performed manually by pneumatic hammers or in cleaning drums

and chambers. These devices enable removal of burnt-on and core sand by milling or jetting

of steel or cast-iron pellets – blasting.

Removal of down-sprues and risers

Down-sprues, risers and vents have to be removed from raw cleaned castings. The removal

process depends on the material of the casting. For fine castings from non-ferrous metals, the

down-sprues and risers are usually cut-off using circular saws. For brittle gray iron castings,

the down-sprues and risers can be broken-off. For steel castings, cutting is performed using

torches with oxygen-acetylene or oxygen in combination with natural gas.

Final cleaning and treatment of castings

Final cleaning comprises modifications of final appearance and dimensions of the casting to

conform to the dimensional and shape requirements. These steps are often performed

manually by chopping and grinding. Eventually, final blasting with a fine blasting agent can

be performed. Castings from iron alloys are protected with basic anticorrosion coatings.

Heat treatment of castings

Foundry castings are often finally heat treated. Since heat treatment is an individual

technological field, it is not mentioned in detail in this text.

Final inspection of castings

After cleaning, the castings are inspected. At first, they are inspected visually on their

surfaces. After this step, the castings are measured. In some cases, the customer also demands

inspection of internal quality by non-destructive testing. For separately cast or additively-cast

samples from each melt (or also each piece), chemical composition and mechanical, possibly

physical, properties are inspected.

Deviations (non-conformations) of the following are denoted as defects:

appearance,

shape,

dimensions,

weight,

structure,

uniformity (homogeneity) and

agreed conditions and standards.

Acceptable defects do not influence the applicability of the casting and have to be either

permitted or at least must not be interdicted.

Non-acceptable defects are usually namely stated and their occurrence signifies a non-

conformant product – spoilage.

Removable defects are defects, which can be removed by suitable technologies – additional

steps have to be performed by the foundry at its own expenses.

Defects (non-conformities) in castings

Various systems have been elaborated to classify casting defects. A relatively simple

classification, based on the international atlas of defects, is included within the still valid ČSN

42 1240 standard, which classifies defects of iron alloys castings into seven individual

categories.

Defects of iron alloys castings, the categorization of which into seven defect classes and

groups together with their classification, explanation of main causes and proposals for their

elimination in foundry industry, have also been summarized by Elbel. His basic classification

of classes, groups and types of casting defects is depicted in Table 3.

Table 3: Separation of foundry defects into classes, groups and types.

Class

of

defects

Title of class of defects Group of defects Title of group of defects Number

of types

100 Shape, dimensional 110 Missing part of the casting without fracture 8

and weight defects 120 Missing part of the casting with fracture 3

130 Deviation of dimensions, inaccurate shape 4

140 Deviation of weight -

200 Surface defects 210 Burning-on 3

220 Expansion scabs 3

230 Erosion scabs 4

240 Veining -

250 Eutectic Sweat -

260 Flash 3

270 Irregularities of casting surface 7

280 Painting Defects -

300 Defects of material continuity 310 Hot Cracks 3

320 Cold Cracks -

330 Failure by mechanical damage 2

340 Failure from unconnected metal 2

400 Voids 410 Gas Holes 5

420 Pinholes -

430 Blowholes 3

440 Shrinkages 6

500 Macroscopic inclusions 510 Slag inclusions 2

and macrostructural defects 520 Non-metal inclusions 6

530 Macro-segregations and segregations 4

540 Cold Shots -

550 Metallic inclusions -

560 Defective fracture -

600 Microstructural defects 610 Microcavities 3

620 Inclusions -

630 Incorrect grain size -

640 Defect o mikrostructure -

650 Hard spots -

660 Inverse chill -

670 Surface Decarburization -

680 Other defects of mikrostructure -

700 Defects of chemical 710 Incorrect chemical composition -

composition and properties 720 Deviations from mechanical properties -

of castings 730 Deviations from physical properties -

740 Wrong homogeneity -

Literature for further study

[1] Havlíček, F. Konstrukce odlitků, učební pomůcka, VŠB-TU Ostrava, 1995

[4] Goodrich, G.M. Iron Castings Enginering Handbook. American Foundry Society.

Schaumburg, Illinois, USA, ISBN 0-87433-260-5, 2006, 418s.

[2] ELBEL,T. a kol. : Vady odlitků ze slitin železa. Matecs, Brno 1992,339s.