Investigation on the Role of Binder, Clay and Grain size on the Properties of Moulding Sand

• Foundry sand is high-quality uniform silica sand that is used to make molds and Cores for ferrous and nonferrous metal castings.

• The metal casting industry annually uses an estimated 100 million tons of foundry sand for production. Over time, foundry sands physically degrade until they are no longer suitable for molds and discarded.

• These have remarkably consistent composition and are typically considered a higher quality material than typical bank run or natural sands used in construction.

• Currently, an estimated 28% of discarded sand is reused in primarily construction related applications, while the remaining sand is disposed of in landfills.

Introduction

GENERAL FOUNDRY SAND PROPERTIES

• Foundry sands consist of green sand and resin sand.

• Green sands typically comprise of high-quality silica sand, 5-10 percent bentonite clay, 2 to 5 percent water and less than 5 percent sea coal.

• Physical Properties• Mechanical Properties• Mineralogical and Chemical Properties• Environmental Considerations

Sand, Clay and Their Standard Properties

• Sands - Silica Sand - Naturally Bonded Sand - Zircon Sand - Chromite Sand - Olivine Sands• Clays - Bonding Clays - Kaolinites - China Clay - Ball Clay - Fire Clay

Properties required in sands

• Sands1. Chemical analysis2. Grain fineness number3. Mechanical grading4. Grain shape5. Specific surface6. Moisture absorption7. Refractoriness8. Acid demand value9. Compactibility10.Bonding properties for natural sands

Properties required in clay

• Chemical analysis of Bonding Clays

-The greater the ratio of alumina to silica in Kaolinite, the better is the refractoriness. The presence of alkalis K20, Na20 is undesirable; refractory clays provide high temperature bond in sand.

• Moisture content

-Clays should preferably have 6-12% moisture as determined by loss in weight on drying for 4 h. at 105-110"C.

• pH Value

-8.2 indicate good clay. 8 g of clay is taken in 100 ml of distilled water for pH measurement.

Properties required in clay(contd)

• Gelling Index

-The minimum amount of clay in 10 ml of distilled water that will flow out of test tube,

is the gelling index.

• Clay Heating Test

-A test carried out on a sample of clay taken in a refractory bent tube and heated at

1300°C for 15 minutes.

• Bonding Properties

-Shattering index of a sand is an indication of toughness and dry strength gives an

idea of how good the sand/clay mix is to withstand the mechanical stresses and

erosion by molten steel.

Types of Base Sands• Silica sand - made by rushing sandstone or taken from natural occurring

locations, such as beaches and river beds fusion point of pure silica is 1,760 °C (3,200 °F).

• Olivine sand -Olivine is a mixture of orthosilicates of iron and magnesium from

the mineral dunite.• Chromite sand -Chromite sand is a solid solution of spinels. It has a very high

fusion point (1,850 °C (3,360 °F).• Zircon sand -Zircon sand is a compound of approximately two-thirds zircon oxide

(Zr2O) and one-third silica. Fusion point 2,600 °C (4,710 °F).• Chamotte sand -Chamotte is made by calcining fire clay (Al2O3-SiO2) above 1,100

°C (2,010 °F). Its fusion point is 1,750 °C (3,180 °F)

The Role of Other Materials

• Binders• Clay and water• Oil• Resin• Sodium silicate• Additives• Parting compounds

Fast Mould Making Processes

• Mechanized sand moulding

• Automatic high pressure sand moulding lines

• Horizontal sand flask moulding

• Vertical sand flask less moulding

• Match plate sand moulding

EXPERIMENTAL WORK In order to envisage the characteristics of foundry sand,

the following laboratory investigations were carried out.

A basic set of parameters to test are:

• Fineness number (grain size/AFS Number) of the base sand

• Moisture content in the mixture

• Permeability (ability of compacted mould to pass air through it)

• Total clay content (dust content)

• Compressive strength