2013 UG MM 0412013 UG MM 032 2013 UG MM 043

ROLL MILL

Roller mill

Roller mills are mills that use cylindrical rollers, either in opposing pairs or against flat plates, to crush or grind various materials, such as grain, ore, gravel, plastic, and others.

Roller grain mills are an alternative to traditional millstone arrangements in gristmills..

Working of Roller Mill

In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness and to make the thickness uniform.

The concept is similar to the rolling of dough. Rolling is classified according to the temperature of the metal rolled.

 

1.If the temperature of the metal is above its recrystallization temperature, then the process is known as hot rolling.

 2.If the temperature of the metal is below its

recrystallization temperature, the process is known as cold rolling. In terms of usage, hot rolling processes more tonnage than any other manufacturing process, and cold rolling processes the most tonnage out of all cold working  processes

Hot Rolling

• Hot rolling is a metal working process that occurs above the recrystallization temperature of the material.

• The starting material is usually large pieces of metal, like semi-finished casting products such as slabs, blooms, and billets.

• If these products came from a continuous casting operation the products are usually fed directly into the rolling mills at the proper temperature. In smaller operations the material starts at room temperature and must be heated. This is done in a gas- or oil-fired soaking pit  for larger workpieces and for smaller workieces induction heating  is used.

Cold Rolling

• Cold rolling occurs with the metal below its recrystallization temperature (usually at room temperature), which increases the strength  via strain hardening  up to 20%.

• It also improves the surface finish  and holds tighter tolerances .• Commonly cold-rolled products include sheets, strips, bars, and

rods; these products are usually smaller than the same products that are hot rolled.

• Hot rolled mild steel seems to have a wider tolerance for amount of included carbon than cold rolled, making it a bit more problematic to use as a blacksmith

• Hot rolling is used mainly to produce sheet metal  or simple cross sections, such as rail tracks . Other typical uses for hot rolled metal includes truck frames, automotive wheels, pipe

Classification of Rolling millsClassification based on temperature of

rolling

Under this classification, rolling mills are classified according to the temperature of the metal to be rolled.

Based on this classification rolling mills are basically of two types: (i) hot rolling mill (ii) cold rolling mill.

•Hot rolling mills – In these mills, rolling is done above the recrystallization temperature of the metal. In this type of rolling hot rolled metals have very little directionality in the mechanical properties and deformation induced residual stresses.

Cold rolling mills – In these mills, rolling is done below the recrystallization temperature of the metal. Rolling in these mills which is normally done at the room temperature, increases the strength of the metal through strain hardening.

Classification based on the mill product

This classification is usually done in three ways. The first way of classification is by the type of the product.

•Flat mills – These mills rolls plates, sheets and strips.•Long product mills – These mills rolls rounds, rods and shapes.

The second way of classifying mills on products is based on the nature of the product.

•Finishing mills – These mills produced saleable products.Semi finishing mills – These mills produce semi finished products which need further rolling in the finishing mills

Classification based on rolling processUnder this classification, the rolling mills can be classified as follows:

•Reversing mills – In this type of mills the rolling direction changes after each pass. In these mills the rolls are stopped, reversed, and then brought back up to rolling speed after each pass. _

•Continuous mills – In this type of mills the material to be rolled moves only in one direction and all the mill rolls rotates only in single direction. There are number of stands provided in the mill for giving total reduction to the material being rolled and for giving final shape to the rolled product.

•Semi continuous mills – In this type of mills some roll stands are reversing type while other rolling stands constitutes continuous rolling.

•Tandem mills – A tandem mill is a type of rolling mill where rolling is done in one pass .In tandem mill there are several stands (>/=2 stands) and reductions take place successively. The number of stands ranges from 2 to 18. Tandem mills can be either of hot or cold rolling mill types.

Classification based on stand arrangementsUnder this classification there are two types of rolling mills as given below.

•Cross country mills – In these types of the mills the centre lines of initial rolling stands are parallel to each other and the material being rolled is shifted perpendicular to the rolling directions. Most of the cross country mills are reversing mills.

Straight line mills – In these mills all the roll stands have a common centre line and material being rolled moves only in forward or forward/backward direction.

Classification based on roll configuration

Rolling mills are also classified based on the roll configurations. The types of mills based on roll configurations are given below.

•Two high mills – In this type of mills the rolling stands have two rolls (top and bottom)•.•Three high mills – In these types of mills the rolling stands have three rolls which rotate in one direction. The metal is fed in one direction through two of the rolls and then reversed through other pair. The middle roll is common in each feeding. The upper and the lower rolls are driven while the middle roll rotates by friction.

•Four high mills – In these types of the mills two smaller diameter rolls (lesser strength and rigidity) are supported by two back up rolls with larger diameters.

•Cluster mills – In this type of mills each set of the work rolls is supported by two back up rolls. These back up rolls have a further set of backing rolls in the third tier. Sendzimir mill is having this type of mill.

Planetary mill – This mill consists of a pair of heavy back up rolls surrounded by a large number of planetary rolls. Each planetary roll gives an almost constant reduction to the feed material as it sweeps out of a circular path between the backup roll and the feed material. As each pair of planetary rolls ceases to have contact with the work piece, another pair of rolls makes contact and repeat the reduction

Specialized rolling millsThese rolling mills produce specialized products by combining rolling process with other processes. Under this classification the following are the major types of mills.

•Pipe mills – Under this category, mills for producing different type of pipes (such as ERW, SAW, Seamless etc.) comes.

•Ring mills – These mills are used for rolling rings

•Thread rolling mills – These mills are used for threading of rods or pipes.

Transverse rolling mills – These mills are used for rolling in transverse direction

•The third way classifying mills the product they produce after rolling

Rail mills Beam millsBillet mills etc

Different Rolling Proceses

• Roll Bending• Roll forming• Flat rolling• Foil rolling• Ring rolling• Controlled rolling

Roll Bending

• Roll bending produces a cylindrical shaped product from plate or steel metals .

•

Roll Forming

• Roll forming, roll bending or plate rolling is a continuous bending operation in which a long strip of metal (typically coiled steel) is passed through consecutive sets of rolls, or stands, each performing only an incremental part of the bend, until the desired cross-section profile is obtained.

• Roll forming is ideal for producing parts with long lengths or in large quantities. 

Flat rolling

• Flat rolling is the most basic form of rolling with the starting and ending material having a rectangular cross-section. 

•  The material is fed in between two rollers, called working rolls, that rotate in opposite directions.

Foil rolling

• Foil rolling is a specialized type of flat rolling, specifically used to produce foil, which is sheet metal with a thickness less than 200 µm.

• The rolling is done in a cluster mill because the small thickness requires a small diameter rolls.

Ring rolling

• Ring rolling is a specialized type of hot rolling that increases the diameter of a ring.

•  This workpiece is placed between two rolls an idler roll, while another roll, called the driven roll, presses the ring from the outside. As the rolling occurs the wall thickness decreases as the diameter increases.

Controlled rolling

• Controlled rolling is a type of thermomechanical processing  which integrates controlled deformation and heat treating .

• The heat which brings the workpiece above the recrystallization temperature is also used to perform the heat treatments so that any subsequent heat treating is unnecessary. 

Rolling Mill Applications

Rolling Mills Industry Rolling mill forms an integral part of various factories in metalworking industry. It is basically used for shaping metal by passing it between a pair of work rolls. Rolling mills are often incorporated into integrated steelworks, but also exist as separate plant. This type of mills can be used for other metals, and different materials.

Cement Mill Industry

We offer high quality spare parts that are very useful for cement industry. These spare parts find applications in cement plants as a part of conveyors, cranes, elevators, separators, and kilns. They are widely used for speed reduction or increase, torque multiplication, resolution, and accuracy enhancement for positioning systems. Helical and herringbone gears utilize curved teeth for efficient, high-capacity power transmission.

REFERENCES1. Ispatguru.com

2. Geology.com