MECH2636: Design and Manufacture 2 - Rolling PDF

MECH2636: Design and School of Mechanical Manufacture 2 Engineering FACULTY OF ENGINEERING MECH2636: Design and Manufacture 2 Solid Deformation Processes 2. Rolling MECH2636: Design and Manufacture 2 R...

MECH2636: Design and School of Mechanical Manufacture 2 Engineering FACULTY OF ENGINEERING MECH2636: Design and Manufacture 2 Solid Deformation Processes 2. Rolling MECH2636: Design and Manufacture 2 Rolling (1) Steel is still the most common material used in engineering structures and components The most common ways of producing steel is either casting an ingot or continuous casting Rolling is normally the next step in steel processing. The material is forced through pairs of rolls to generates plates, bars, rods, pipes, and various other shapes Normally rolling will take place on a number of rolls sequentially to get the shape required without excessive force/deformation at each stage  MECH2636: Design and Manufacture 2 Rolling (2) ω Most rolling processes are carried out with metal “hot” or “warm”, with finish rolling v2 normally carried out “cold” v1 h1 In a rolling operation, the h2 speed of the slab at exit must be greater than the speed at entrance to roll ω The output speed can be estimated assuming constant volume (& constant width) of workpiece: v1.h1 = v2.h2 Hence v2 = v1.h1/h2  MECH2636: Design and Manufacture 2 Rolling (3) F Contact between roll and R workpiece falls into two zones: A-B where the roll is travelling faster than the workpiece and B-C where A B C the workpiece travels faster than the roll In both zones, there is slip at the interface between the roll and the workpiece F Inbetween these 2 zones is the no-slip point where contact pressure is max. The roll separating force F acts through centre (B) of contact zone which is of length L MECH2636: Design and Manufacture 2 Rolling (4) The length of contact is approximated by: L  R (h 1 − h 2) where R is the roll radius and h1, h2 are the workpiece thicknesses before and after rolling The force generated on the rolls increases with the flow stress of the material y , the length of contact L, the width and average thickness of the work w & hav and friction :  L  F   y ( Lw ) 1 +   2 hav   MECH2636: Design and Manufacture 2 Rolling (5) If the force generated is high enough to distort the rolls, the workpiece will also be distorted Also a high force implies a high torque & power required to rotate the rolls and deform the workpiece Assuming the force is applied normal to the plane of the workpiece at a moment arm of L/2 to the axis of the rolls, the torque required per roll is given by: T  F L / 2 Power required = Torque x Rotational speed (in radians) MECH2636: Design and Manufacture 2 Worked example: power required in rolling (Ref: S & K – example 13.1) A 225 mm wide 6061 aluminium alloy strip is rolled from a thickness of 25 mm to 20 mm between 2 rolls each of radius 300 mm. Estimate the roll separating force and the total power required for this operation if the roll speed is 100 rpm. Assume the material flow stress is 147 MPa and the friction coefficient between workpiece and roll is 0.2. MECH2636: Design and Manufacture 2 First, calculate contact length: Then calculate force: MECH2636: Design and Manufacture 2 Next, calculate torque & power required: Power per roll Total power required = 608 kW (because there are 2 rolls!) MECH2636: Design and Manufacture 2 Rolling Mills (1) Rolling mills can take a number of forms, depending on the number of rolls and their arrangement, most common are: – Two high - simplest – Three high - more productivity per roll – Four high - small inner roll to do the work reduces force and power requirements, backing roll reduces distortion – Sendzimir - lots of rolls, very rigid and accurate, normally cold rolling MECH2636: Design and Manufacture 2 Rolling Mills (2) MECH2636: Design and Manufacture 2 Rolling mills (3) Lubrication is normally used to minimise friction between rolls and workpiece Shape rolling is used to produce a wide range of structural shapes through multiple passes MECH2636: Design and Manufacture 2 Copyright Notice This presentation is protected by UK and international copyright law. Reproduction and distribution of this presentation without written permission from the originator is prohibited. Copyright © 2024 University of Leeds UK. All rights reserved.