TOPICSRollingFlat RollingShape RollingRolling MillsProduction Of Seamless Piping & Tubing Munim Shaukat (Lecturer) Mechanical Engineering Department University of Lahore
RollingProcess of reducingthickness orchanging crosssection bycompressive forcesapplied through aset of rolls
A picture of the rolling mill: Adjusting Screw Rolls Rolls Housing/ Stand
RollingRolling is a bulkdeformation process inwhich the thickness ofthework is reduced bycompressive forcesexerted by two opposingrolls. The rolls rotate topull and simultaneouslysqueeze the workbetween them.
Types Of Rolling Flat RollingThe final shape of the product is either classed as sheet or plate .
DraftIn flat rolling, the work is squeezed between tworolls so that itsthickness is reduced by an amount called the draft:
Calculation Of DraftD = to - tf where d: draft to: starting thickness tf : final thicknessAs a fraction of the starting thickness:% reduction = % r = (d/ to) * 100%
Structural Defects In Flat Or Sheet Rolling:Wavy Edges Center cracking Edge cracking Alligatoring
Shapes RollingThe final product may be a round rod or other shaped bar, such as a structural section (beam, channeletc)
CLASSIFICATION OF ROLLINGAS ANY OTHER METAL FORMINGPROCESS, ROLLING CAN BE PERFORMEDHOT (HOT ROLLING) OR COLD (COLDROLLING).MOST ROLLING IS CARRIED OUT BY HOTROLLING, OWING TO THE LARGEAMOUNT OF DEFORMATION REQUIRED.
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
RECRYSTALLIZATIONThe lowest temperature at which thedistorted grain structure of a cold-worked metal is replaced by anew, strain-free grain structure duringprolonged annealing. Time, purity ofmetal, and prior deformation areimportant factors.
After casting we achieve three intermediateshapes called blooms, billets, and slabs:Blooms have square cross section 6” x 6” orlarger. They are rolled into structural shapes.
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” x1.5” or larger. They are rolled into plates,sheets.
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 dont have to pay for the energy to reheat the metal.
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.
Cold RollingIf the temperature of the metal is below its recrystallization temperature, the process is termed as cold 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 doesnt shrink on cooling; also the low temperatures mean the tools such as dies and rollers can last a long time without wearing out.
Disadvantages Of Cold Rolling Higher forces are required to produce a given deformation, which means we need heavily built, strong forming machines .
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.
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.
What is difference b/w a tube &a pipeThe 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.
Production Of Seamless Piping &TubingSeamless 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
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.
Comparison Of Seamless Pipe &TubeSeamless Pipe Seamless Tube Seamless pipe Welded pipe often provides the most has tighter reliable pressure dimensional retaining tolerances. characteristics. cheaper if easily available than manufactured in the welded pipe. same quantities. More Expensive. Size is greater than Size is less than 3 3 inch dia. inch dia.