Different types of rolling mills and defects in rolled metal

Rolling as one of the important processes in the engineering world, it is available in different types of a suitable specific operation. Like other manufacturing process defects also occurs in rolled products which are we have to discuss to them in order to prevent them.

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Today we’ll be looking at the various types of rolling mills as well as defects that can be found on rolled products.


Types of rolling mills:

The following stated below represent the five common types of rolling mills used in the metalworking field:

Two-high rolling mills:

The two-high rolling mill is of two types; reversing mills and non-reversing mills, in the reversing mill the rollers are both adjustable and their rotations are made in two different directions. The work is done by passing the metal between the two rollers that rotate at the same speed but in the opposite direction. It is often used in slabbing, plumbing, rail, plate roughing work etc. In the non-reversing mills, the rollers revolve in the same direction and their direction cannot be reversed.

Read: Everything you need to know about rolling process

Three-high rolling mills:

There are three roles in this type of rolling mill which stand parallel to each other. These rolls are rotating in opposite directions which allows the material to pass between the first and second rolls. The bottom roll rotates in the opposite direction of the second roll. The machine is designed to roll both in forward and reverse, which is ideal for metal reduction and uniformity of the material.

Four high rolling mills:

In this special type of rolling mill, four parallel rolls lay one after the other. in this design, the rotation of first and fourth rolls occurs in opposite directions of the second and third rolls. These second and third rolls are smaller in shape and size but they provide rigidity where necessary. They are also known as back up rolls. It is used in the cold rolling process of sheets, plates, stripes and hot rolling process of armour.

Tandem rolling mills:

In the tandem rolling mills, there are two or more set of rolls in the parallel alignment which aid the continuous movement of the materials. This also helps to decrease the thickness and makes it uniform.

Cluster rolling mills:

in a cluster rolling mill, there are two basic rolls that receive pressure from backed up rolls which may be two or more rolls. This backed up rolls are bigger than the two-basic roll, making them pass enough pressure to the small rolls.

Read: Hot and Cold Rolling Process

Defects on rolled metals:

The following stated below represent the common types of defects of rolling:

Wavy edges crack:

These types of rolling defects can occur in different cases, which may be caused by the deflection of the compressive load or obtaining thicker result when the middle portion of the rolling part is bent. When there is an imperfection in the roll gaps, variation occurs on the rolling sheets. if the thickness varies along that the volume and width are constant, this may result in the shortened centre than the edges. The edges portion might then be in compression and the centre portion is the tension.

Zipper crack in the centre of the strip:

This rolling defect is a type of wavy crack which occurs when there is uneven stress distribution on the strip. It appears at the centerline of the strip in form of a zip, hence it is named zipper cracks.

Edge crack:

The edge cracks occur on the hot rolling process when cooled which is due to the excessive quenching effects on the strip. When excessive water is used to cool the edges, it may result in unflattens in the strips. As the friction force prevents the corners and increases the length of the centre portion, the edges of the material got rounded off.

Alligator crack:

This is one of the defects that need to be prevented, it appears as a crack on the metal. This crack separates the layers and increases the slabs openings. The defect looks like the mouth of an alligator; thus, it is named alligator crack.

That’s it for this article “types of rolling mills and defects that occur on rolled metals”. I hope you enjoyed the reading, if so, kindly comment, share and check another interesting post below. Thanks!

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