Rolling
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Transcript of Rolling
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TOPICSRollingFlat RollingShape Rolling Rolling MillsProduction Of Seamless Piping & Tubing
Munim Shaukat (Lecturer)
Mechanical Engineering Department
University of Lahore
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RollingProcess of reducing thickness or changing crosssection by compressive forces applied through aset of rolls
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A picture of the rolling mill:
Rolls Rolls Housing/ Stand
Adjusting Screw
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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.
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Types Of Rolling
Flat RollingThe final shape of
the product is either classed as sheet or plate .
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Draft
In flat rolling, the work is squeezed between two rolls so that its
thickness is reduced by an amount called the draft:
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Calculation Of Draft
D = to - tf
whered: draftto: starting thicknesstf : final thickness
As a fraction of the starting thickness:
% reduction = % r = (d/ to) * 100%
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Structural Defects In Flat Or Sheet Rolling:
Wavy Edges Center cracking Edge cracking Alligatoring
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Shapes Rolling
The final product may be a round rod or other shaped bar, such as a structural section (beam, channeletc)
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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
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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
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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.
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Hot Rolling Process
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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.
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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.
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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.
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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.
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Cold Rolling
If the temperature of the metal is below its recrystallization temperature, the process is termed as cold rolling
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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.
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Disadvantages Of Cold Rolling
Higher forces are required to
produce a given deformation, which means we need heavily built, strong forming machines .
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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.
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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.
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Various Configuration Of Rolling Mills
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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.
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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
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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.
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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.
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