30

Rolling

Embed Size (px)

Citation preview

Page 1: Rolling
Page 2: Rolling

TOPICSRollingFlat RollingShape Rolling Rolling MillsProduction Of Seamless Piping & Tubing

Munim Shaukat (Lecturer)

Mechanical Engineering Department

University of Lahore

Page 3: Rolling

RollingProcess of reducing thickness or changing crosssection by compressive forces applied through aset of rolls

Page 4: Rolling

A picture of the rolling mill:

Rolls Rolls Housing/ Stand

Adjusting Screw

Page 5: Rolling

RollingRolling is a bulk deformation process in which the thickness of the work is reduced by compressive forces exerted by two opposing rolls. The rolls rotate to pull and simultaneously squeeze the work between them.

Page 6: Rolling

Types Of Rolling

Flat RollingThe final shape of

the product is either classed as sheet or plate .

Page 7: Rolling

Draft

In flat rolling, the work is squeezed between two rolls so that its

thickness is reduced by an amount called the draft:

Page 8: Rolling

Calculation Of Draft

D = to - tf

whered: draftto: starting thicknesstf : final thickness

As a fraction of the starting thickness:

% reduction = % r = (d/ to) * 100%

Page 9: Rolling

Structural Defects In Flat Or Sheet Rolling:

Wavy Edges Center cracking Edge cracking Alligatoring

Page 10: Rolling

Shapes Rolling

The final product may be a round rod or other shaped bar, such as a structural section (beam, channeletc)

Page 11: Rolling

AS ANY OTHER METAL FORMING PROCESS, ROLLING CAN BE PERFORMED HOT (HOT ROLLING) OR COLD (COLD ROLLING).

MOST ROLLING IS CARRIED OUT BY HOT ROLLING, OWING TO THE LARGE AMOUNT OF DEFORMATION REQUIRED.

CLASSIFICATION OF ROLLING

Page 12: Rolling

Hot RollingRolling is classified

according to the temperature of the metal rolled. If the temperature of the metal is above its recrystallization temperature, then the process is termed as hot rolling

Page 13: Rolling

RECRYSTALLIZATIONThe lowest temperature at which the distorted grain structure of a cold-worked metal is replaced by a new, strain-free grain structure during prolonged annealing. Time, purity of metal, and prior deformation are important factors.

Page 14: Rolling

Hot Rolling Process

Page 15: Rolling

After casting we achieve three intermediate shapes called blooms, billets, and slabs:

Blooms have square cross section 6” x 6” or larger. They are rolled into structural shapes.

Page 16: Rolling

Billets have square cross section 1.5” x 1.5” or larger. they are rolled into bars and rods.

Slabs have rectangular cross section 10” x 1.5” or larger. They are rolled into plates, sheets.

Page 17: Rolling

Advantages Of Hot Rolling

The possibility of producing a very dramatic shape change in a single working step, without causing large amounts of internal stress, cracks or cold working;

Sometimes hot working can be combined with a casting process so that metal is cast and then immediately hot worked. This saves money because we don't have to pay for the energy to reheat the metal.

Page 18: Rolling

Disadvantages Of Hot Rolling If the recrystallisation temperature of

the worked metal is high e.g. if we are talking about steel, specialised methods are needed to protect the machines that work the metal. The working processes are also dangerous to human operators and very unpleasant to work near.

Page 19: Rolling

Cold Rolling

If the temperature of the metal is below its recrystallization temperature, the process is termed as cold rolling

Page 20: Rolling

Advantages Of Cold Rolling

A better surface finish may be achieved

Dimensional accuracy can be excellent because the work is not hot so it doesn't shrink on cooling; also the low temperatures mean the tools such as dies and rollers can last a long time without wearing out.

Page 21: Rolling

Disadvantages Of Cold Rolling

Higher forces are required to

produce a given deformation, which means we need heavily built, strong forming machines .

Page 22: Rolling

Rolling Mills

Two-high rolling mill: consists of two opposing rolls. These rolls may rotate only in one direction (non reversing) or in two directions (reversing).

Three-high rolling mill: allows a series of reductions without the need to change the rotational direction of the rolls.

Page 23: Rolling

Rolling Mills

Four-high rolling mill: Using small rolls reduces power consumption but increases the roll deflection. In this configuration, two small rolls, called working rolls, are used to reduce the power and another two, called backing rolls, are used to provide support to the working rolls.

Cluster rolling mill: another configuration that allows smaller working rolls to be used.

Page 24: Rolling

Various Configuration Of Rolling Mills

Page 25: Rolling

What is difference b/w a tube & a pipe

The difference between a pipe and a tube is how they are measured, and ultimately what they are used for.  

      A pipe is a vessel - a tube is

structural.      A pipe is measured ID - a tube is

measured OD.

Page 26: Rolling

Production Of Seamless Piping & Tubing

Seamless Pipes:-. Seamless (SMLS) Steel Pipe is made from a

solid round steel ‘billet’ which is heated and pushed or pulled over a form until the steel is shaped into a hollow tube. The seamless pipe is then finished to dimensional and wall thickness specifications in sizes from 1/8 inch to 26 inch O

Page 27: Rolling
Page 28: Rolling

Seamless Tubes:-

The process involves the progressive bending of metal strip as it passes through a series of rollers at speed up to 80m/sec. Only bending take place, all bends are parallel. Seam welding process carried out to form a proper tube.and wed flashes are removed by scarfing blades.

Page 29: Rolling

Comparison Of Seamless Pipe & Tube

Seamless Pipe Seamless pipe

provides the most reliable pressure retaining characteristics.

easily available than welded pipe.

More Expensive. Size is less than 3

inch dia.

Seamless Tube Welded pipe often

has tighter dimensional tolerances.

cheaper if manufactured in the same quantities.

Size is greater than 3 inch dia.

Page 30: Rolling