Hot and cold rolling 2

Hot rolling

Hot rolling is a metalworking process that occurs the material's recrystallization temperature.After the grains are deformed during processing,they recrystallize to maintain an equiaxed microstructure and prevent metal work hardening.The starting material is usually bulk metal,semi-finished cast products such as ingots,slabs,blooms and billets.If these products come from a continuous casting operation the product is usually fed directly into the rolling mill at the appropriate temperature.In smaller operations,the material starts at room temperature and must be heated.For larger workpieces,this is done in a gas or oil soaking pit; for smaller workpieces, induction heating is used.When processing the material,the temperature must be monitored to ensure it remains the recrystallization temperature.To maintain a safety factor, the final temperature is defined as being above the recrystallization temperature; this is typically 50 to 100 °C (90 to 180 °F) above the recrystallization temperature.If the temperature does fall below this temperature, the material must be reheated before additional hot rolling.Residual stresses induced by mechanical properties or deformation in hot-rolled metals usually have little directionality.However, in some cases, non-metallic inclusions impart some directionality, which is usually present in workpieces less than 20 mm (0.79 in) thick.Uneven cooling can cause a lot of residual stress,which usually occurs in shapes with uneven cross-sections, such as I-beams.While the finished product is of good quality, the surface is covered with scale, an oxide that forms at high temperatures.It is usually removed by pickling or a Smooth Clean Surface (SCS) process,revealing a smooth surface.Dimensional tolerances are typically 2% to 5% of the overall dimension.Hot-rolled mild steels appear to be more tolerant of carbon content than cold-rolled steels, and are therefore more difficult for blacksmiths to work with. Also for similar metals, hot rolled products seem to cost less than cold rolled products.Hot rolling is mainly used to produce sheet metal or simple cross-sections, such as rails. Other typical uses of hot rolled metals: 

• Truck frames

• Automotive clutch plates,wheels and rims

• Pipes and plumbing

• Water heater

• Agricultural equipment

• Strapping

• Stamping

• Compressor housing

• Metal construction

• Railway hopper cars and rail car components

• Doors and shelves

• CD

• Street and highway guardrails

Shape scroll design

Rolling mills are often divided into rough rolling,intermediate rolling and finishing rolling cages.During profiling, an initial billet (round or square) with an edge diameter typically between 100 and 140 mm is continuously deformed to produce a specific finished product with smaller cross-sectional dimensions and geometries.Starting from a given blank,different sequences can be used to produce a specific end product.However,since each rolling mill is very expensive (up to 2 million Euros),a typical requirement is to reduce the number of rolling passes.Different approaches have been implemented, including empirical knowledge,the use of numerical models,and artificial intelligence techniques,validated a finite element model (FE) for predicting the final shape of rolled bars in circular flat passes.One of the main concerns when designing a rolling mill is to reduce the number of passes.One possible solution to such requirements is slot passes, also known as split passes,which divide the incoming rebar into two or more subsections, thereby actually increasing the Cross-sectional reduction ratio.Another solution to reduce the number of rolling mill passes is to use an automated system for rolling pass design, as proposed by Lambiase and Langella.Subsequently, Lambiase further developed an automated system based on artificial intelligence, especially an integrated system including an inference engine based on genetic algorithms, a knowledge database based on artificial neural networks trained by parametric finite element models, and optimized and automatic design mills.