What is Rolling mills or Rolling Operation: Rolls (or) Rolling mills is a cylindrical shape of roll used in rolling process. The housing and set of rollers mounted on the machine is known as stand.
The rolling operation having different types. The most of rolling operation two- high none reversing used. Which means because of the roll is rotated in only one direction not reversing. The two high reverse rolling having the rolls rotated in both direction. But that disadvantage of rolls are heed to stopped, reversed and become back up to rolling speed between each pass.
The different types of rolling operation are
- Two high rolling mill
- Three- high rolling mills or triple roll
- Four- high rolling mills or 4 high rolling mill
- Tandem mills
- Cluster mills.
Two high rolling mill process:
It consists of two heavy horizontal rolls and which is mounted one over the other. Both the rolls are supported with bearing housed in sturdy upright side frame called stands.
The gap between the rolls are adjusted by the upper roll move lowering when the lower roll is stationary fixed, both the rolls are rotated in opposite direction to each other. The roll rotate direction is fixed which cannot be reverse direction. The work metal rolled by feeding for only one direction.
The two high reverse roll which have incorporate a drive mechanism and work is continuously through back- and –forth passed between the rolls. That are usually employed for initial rolling of an ingot.
Three high rolling mills or triple roll:
The three high rolling having three rolls rotate in only one direction, the work metal is fed between two rolls and then return through the another pair. The must problem is the work metal lifted and lowered by use of elevator. Those are primary rolling and roll diameter range of 60 to 140c.m
The rolls consist of three horizontal rolls directly positioned one direction of upper and lower are same and intermediate roll rotate in opposite direction to both rolls.
The three rolls are continuously revolving same of fixed direction and not reverse direction. The upper and middle rolls are the work piece with one direction and reverse direction between the middle roll and lower roll. That produce high rate of production more than rate of production more than two high roll methods. This three high rolling mill used to billet rolling, blooming or finish rolling.
4 high rolling mill:
That rolling mill having four horizontal rolls, which two rolls are small diameter and another two rolls are larger diameter. It will be arranged with one over other as shown in figure.
The larger diameters of rolls are called back- up rolls and prevents the deflection of smaller rolls. Which give thickening of roll plates or sheet at center due to deflection of rods.
The smaller diameter rolls called working roll. Which is concentrate the total amount of rolling pressure over metal if the rolls are usually subsequent rolling of slabs. The common product of these mills are hot or cold rolled sheets and plates.
tandem rolling mill or continuous rolling mill:
It is a modern rolling mills and the rolling is done by one pass. The rolling is done in several passes for traditional several stands and reduction that take place successive roll. The number of stands like as 2 to 18. Those are either hot or cold rolling mill types.
The tandem mills consist of number of non- reverse roll mill arranged in one after other as shown in figure. The work metals are passed through the roll. Successfully the stands are rotated very fast than that of preceding rolls in order to accommodate. The length of metal would be increased during rolled. That is rapid production because of the metal pass one stand to another stand for continuously until it reaches the final passes. But it is suitable for mass production only because of that require quick changes of setup and consume lot of time and labor.
Cluster mill (or) sendzimir mill:
The cluster mills consist of two working rolls with small diameter and four or more backup roll with larger diameter. The number of back- up rolls high as 20 or more depends upon the support heeded for the working roll. It cluster mill is used for cold rolling process.
Application of rolling process:
Hot rolled product such as concrete reinforcing bars, plates, wire rods, sheet and strip, rails, structural. When the plates, sheet and strip products are used to manufacture of piping and tubes, body panels and construction materials. Cold rolled product such as wire sheet and strip. The wire is often used in manufacturing of cold form such as bolts and screws. The cold rolled sheet and strip used in automotive industries for external application such as electrical motors, doors and more.