What is Rolling Mill? (And how exactly does it work?)

what is rolling mills
Image credits: Indiamart

What is Rolling Mill?
Rolling Mill (or roll stand or steel rolling mill) is a machine in which all the equipment for metal rolling like rolls, bearings, housing, motors, frame, power system, etc are set up to perform a metal rolling operation.

In steel rolling mills, workpiece having greater thickness is fed through the rollers and the final workpiece with reduced thickness and better surface finish is obtained.

Parts/Components of rolling mills

Few important components of steel rolling mills are listed below.

  1. Rolls
  2. Bearings
  3. Housing
  4. Motors
  5. Frame
  6. Gap control mechanism
  7. Power system
  8. Power transmission mechanism

How rolling mills work?

Before knowing the working of rolling mills, first you should know that there are various rolling mills according to the number of rolls, position of rolls, as well as type of rolls.

Various rolling mills used in industries are;

  • Two high reversing mills
  • Two high non reversing mills
  • Three high rolling mills
  • Four high rolling mills
  • Tandem rolling mills
  • Cluster rolling mills
  • Planetary rolling mills

Now let’s see how these rolling mills work.

#1) Two high reversing mills

In two high reversing mills, the rotation of rollers occurs in forward direction as well as reverse direction.

Two high reversing mills

Firstly, the rollers rotate in one direction and then they rotate in opposite directions so that the metal can pass several times in the back and forth direction through the rollers.

Two high reversing mills are used for rough work in flat plate, rails, etc.

#2) Two high non reversing mills

In two high non reversing mills, two rolls rotate only in a single direction.

Two high non reversing mills

As the name suggests, “non reversing” means that the reverse motion of the workpiece is not possible in this type of steel rolling mills.

However, the workpiece is carried back over to the inlet of the roller mill for passing it again through the rollers.

#3) Three high rolling mills

Three high rolling mills consist of three parallel rolls which are arranged one above the other (see below image).

Three high rolling mills

As shown in the above diagram, the above two adjacent rollers rotate in opposite directions which forces the workpiece in the forward direction. Again this workpiece is fed between the middle and lower roller and finally the rolled workpiece is obtained.

In simple words, the workpiece first passes through the top and middle rollers and then it is returned between the middle and bottom roller. 

The thickness of the metal is reduced in each pass of the three high rolling mills.

In three high rolling steel mills, the flat rollers as well as grooved rollers are used as per the applications.

#4) Four high rolling mills

Four high rolling mills consist of four rollers parallely arranged one above the other.

Four high rolling mills

As shown in the diagram, two outermost rollers spin in opposite directions. Also the two inner rollers rotate in opposite directions.

The size of the inner rollers is kept smaller than the size of the outer rollers.

These outer rollers are known as backup rollers which provide rigidity to the inner rollers.

Four high rolling mills are used for hot rolling of steels plates as well as cold rolling of steels plates, sheets and strips.

#5) Tandem rolling mills

In tandem rolling mills, the metal is passed through several stands such that there occurs a gradual reduction of thickness in every passing.

Tandem rolling mills

Tandem rolling mills can also be used with a continuous casting process and this gives more advantages for manufacturing longer workpieces.

#6) Cluster rolling mills

Cluster rolling mills are special types of four high rolling mills in which the working rollers are backed up by two or more larger rollers.

Cluster rolling mills

Cluster rolling mills are generally used for rolling of hard materials.

#7) Planetary rolling mills

Planetary rolling mills are a special type of steel rolling mills in which the smaller diameter working rollers are arranged around the single larger roller (see below image).

Planetary rolling mills

The advantage of planetary rolling mills is that it avoids the sliding friction during the rolling operation.

In planetary rolling mills, generally the feed rollers are sometimes used to feed the metal piece to the planetary rollers.

Each working roller of the planetary mill is used for gradual reduction in thickness of the metal.

Planetary rolling mills have the advantage that they can be used in production plants where there are frequent changes in size of metals.

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