Thread: Hot and cold rolled stock

Hot rolled stock is as the name suggest, manufactured while still hot and malleable. It has a surface covered in scale that is slightly hard and brittle, but easily removed. Its dimensionally sloppy compared to other methods. A good common example is 1045.

Cold rolled stock is bright and also has a slightly hard surface, but its from work hardening as a result of the rolling below the recrystalisation temperature. It can (but not always) have different compositions, either to help in the manufacture of the bar or to change its working properties (ie, tool steels come in cold rolled stock, but the composition is there for its hardenability and wear resistence). Cold rolling is significantly more dimensionally accurate to its advertised specs. For the hobby machinist who isnt buying large amounts of stock, its pretty easy to justify buying this more expensive stock. Its NOT extruded, its rolled between a series of rollers. The stock is pushed through and the rollers roll around the centre axis of the rod, squeezing it into a round state. A common variety of mild steel in this form is 1020.

You can also buy some stock in a surface ground or chrome plated finish. Surface ground is even more accurate and chrome is good for wear resistence and sealing (like in hydraulics). Both are dear. Chrome is as hard as chuck norris.

Ok

It seems that my book is outdated , its from 1966 . I quote a bit of it .

Modern workshop technology by H Wright Baker

"Cold drawing . As in wiredrawing the process consists of descaling hot-rolled bar and , after suitable preparation, reducing the cross section of the bar by pulling through a die of smaller dimensions"

This method was used by Bradbury steel works Stockport UK . I guess other companies used different methods ?

scans from the book

An educated guess (for me) says that they probably dont use that method anymore because drawing requires a very large amount of energy, whereas rolling uses less. Someone might be able to chime in as to why.

You can pick the difference with stock on the shelf pretty easily though, draw stock will have surface marks running along the axis of the stock, rolled round rod will have spiral of dried up oil on it, left behind from the rollers. If its been cleaned, its a bit harder. Ive not seen anything smaller than 6mm cold rolled and we're having a hard time finding anything less than 8mm in hot rolled state, and Griffith is pretty good for buying steel in a regional city. Everything smaller than that is drawn in suppliers around here, and usually its high tensile fencing wire.

"Cold Rolling" and "Cold Drawing" are two quite different processes - as you have now seen described. Your book is not out-dater, Morrisman.
Joe