The purpose of giving mechanical treatment to the steel is to give desired shape to the ingots so as to make steel available in market forms. The mechanical treatment of steel may be hot working or cold working. The hot working is very common.
Following are the operations involved in the mechanical treatment of steel.
Each of the above operation will now be briefly described.
(1) Drawing: This operation is carried out to reduce the cross-section and to increase the length proportionately. In this operation, the metal is drawn through dies or specially shaped tools. The drawing is continued till wire of required diameter or cross-section is obtained. This process is used to prepare wires and rods.
(2) Forging: This operation is carried out by repeated blows under a power hammer or a press. The metal is heated above the critical temperature range. It is then placed on anvil and subjected to blows of a hammer. This process increases the density and improves grain size of metal. The riveting belongs to forging operations. The process is used for the manufacture of bolts, cramps, etc. The steel may be either forged free or die-forged. In the former case, the steel is free to spread in all directions as it is hammered. In the latter case, the steel flows under the blows of a hammer to fill the inside of a die and the excess material is forced out through a special groove and then it is cut off. The die-forged parts have very accurate dimensions.
(3) Pressing: This is a slow process and it is carried out in an equipment known as the press. The main advantage of this process is that it does not involve any shock. A press consists mainly of a die and a punch. The die and punch are suitably shaped to get article of desired shape. The metal is placed on the die and punch is then lowered under a very heavy pressure. The metal is thus pressed between die and punch and article of desired shape is obtained. For preparing articles with wide changes of shape, the pressing is to be carried out in different stages. This process is useful when a large number of similar engineering articles are to be produced.
(4) Rolling: This operation is carried out in specially prepared rolling mills. The ingots, while still red hot, are passed in succession through different rollers until articles of desired shape are obtained. The various shapes such as angles channels, flats, joists, rails, etc. are obtained by the process of rolling. It is possible to prepare joistless pipe with the help of this process. The solid rod is bored by rollers in stages until the pipe of required diameter and thickness is obtained.
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