Lecture 11 Rolling equipment and Miscellaneous Rolling Processes  Course Hour: 2  Basic requirements: Acquainting with different rolling equipment, their properties and application; Acquainting with the principles of different Miscellaneous Rolling Processes and their applications  Emphasis: Rolling equipment  Difficulties: Principles of Miscellaneous Rolling Processes

Rolling equipment and practice Two-high or three-high rolling mills are used for initial breakdown passes It is desirable to use small-diameter rolls to reduce roll force, but small rolls tend to deflect Cluster mill (Sendzimir) is particularly suitable for cold rolling thin strip of high-strength metal Requirements for roll materials are mainly strength and resistance to wear. Three common roll materials are cast iron, cast steel, and forged steel For hot rolling, rolls surface are generally rough, but for cold rolling, they are finely polished No lubricant is used in ferrous alloys, aqueous solution is used for cooling rolls and removing scale Compounded oils, emulsion, and fatty acids are used as lubricant in hot rolling of nonferrous alloys; low-viscosity lubricants (mineral oil, emulsions, paraffin, fatty oil…) are used in cold rolling

Shape rolling Bars with various cross-sections, channel section, I- beams and railroad tracks can be rolled Airfoil shapes can also be produced by shape-rolling Starting with bloom Normally, the reduction is different at different position, and will lead to warping or crack

Ring rolling Small-diameter thick ring --- large-diameter ring with small cross-section A great variety of cross-sections can be ring rolled with shape rolls Advantages: short production runs, material savings, close tolerances, and favorable grain flow direction Applications: large rings for rockets and turbines, gearwheel rims, ball or roller bearing races, flanges and reinforcing rings for pipes and pressure vessels

Thread and gear rolling Typical products are screw, bolts and similar thread parts Production rates are very high Advantages: without any metal loss, with improved strength due to cold working, with very smooth surface, inducing compressive residual stress on the surface, With improved fatigue property

Thread and gear rolling Comparing with machining, the diameter of the stock is smaller, rolled thread has a better grain flow pattern and improved strength Thread rolling can also be carried out internally with a fluteless forming tap In thread rolling, it is essential that the material have sufficient ductility, lubrication is also important Spur and helical gears can also be produced by cold-rolling similar to thread rolling

Rotary tube piercing A hot-working process for making long, thick-walled seamless tubes Skew rolls is used to facilitate pulling the round bar through the rolls The materials of the mandrel should has high quality due to the severe deformation during the process