What is rolling , its types with Terminology

 

 Table of contents (toc)

Rolling, Hot Rolling, Cold Rolling, Two high Rolling Mill [Irreversible], Two High Rolling [Reversible], Three High Rolling, Four High Rolling, Cluster Rolling, Planetary Rolling, Terminology for Rolled Products

 

Rolling Principle:

           Flat strip rolling - compressing between two opposite rotating rolls to reduce metal thickness. A high compressive force is applied to the workpiece by the squeezing action of the rolls. The metal is taken into the roll by friction. It is widely used due to its high productivity at low cost.  hot working process unless specifically mentioned as cold rolling, but it is done both hot and cold.
rolling operation

What is hot rolling :

Definition of hot rolling

          The hot plastic state metal is passed between the rolls. Rolling was carried out above recrystallization temperature. As the crystals elongate in the rolling direction, they begin to reform after leaving the stress zone. Best suited for large amounts of deformation. Hot rolled metal is generally free from residual stress and has isotropic properties.
Grain Composition in Hot Rolling Process

What is cold rolling ?

            The rolling process is employed to finish bars, rods, sheets and bars at room temperature. It offers good surface finish, superior dimensional accuracy and superior physical properties. Crystals that are tall will largely retain the shape given to them by the rolling action.
cold rolling

Types of Rolling Mills:

1. Two High Rolling Mill [Irreversible]

2. Two High Rolling [reversible]

3.Three High Rolling

4. Four High Rolling

5.cluster rolling

6. Planetary rotation.

What is Two High Rolling Mill:

        It consists of two rolls which rotate in the same direction about the horizontal axes.
 

 

 High Rolling Mill (Irreversible)

        The stock is returned at the entrance of the rolls for continuous deduction. Stock returned by hand or off the platform. This method of reduction slows down the process. The typical two high rolling mill consists of a roller conveyor, a stand and rolls with a power drive. The upper roller can be moved up or down to change the distance between the rolls. An alternative method is used to speed up the process where the direction of the roll is reversed after each pass - two high rollings [reversible].
 

two high rolling mill (reversible)

        The rolls are brought together for each pass. The diameter of the rolls in these mills varies from 0.6 to 1.5 m. Higher power consumption than inductive two high rolling mill. It is often used for the first rolling operation. hot and cold rolling are both applicable for two high rolling mill

Three High Rolling Mill:

        There are three rolls in a vertical column used for two continuous process.
 

three high rolling mill :

        The direction of rotation of each roll can not be unchanged. The stock is passed through both sides of the rolls. It is raised and lowered after each pass using a lifting mechanism. the top and bottom rolls are drive rolls in this mill . The intermediate roll rotates by friction. These mills are employed as bloom mills, billet rolling and finish rolling. More complicated because of the lifting mechanism.

Four High Rolling Mill:

       As same to two high rolling, but additional two rollers are added.
four high rolling mill
        These additional two rollers are smaller in diameter. Thus the larger roller will act as the backup rollers behind the smaller rollers. The arc of contact is reduced by using smaller rollers. Backup rolls are provided to avoid bending of the rolls due to low strength and rigidity.

Terminology for rolled products:

        Various rolled products are named according to dimensions, but the terminology is quite loose and sharp boundaries cannot be made regarding dimensions.
 

Blossoming of Flowers:

          A blossom is the product of the earlier breakdown of the nodule. It has a square or slightly rectangular section, ranging in size from 150 mm X 150 mm to 250 mm x 300 mm. A bloom is used to form structural shapes, i.e. beams, channels etc., by hot rolling.
 

Billet:

         Billet occurs as a result of reduction in bloom by bottom rolling. 50X50 to 125 x 125 mm this size billet ranges. It is twisted to form rounds, strings and bars.
 

Slab:

      A slab is a product obtained by bottom rolling, either from ingot or from bloom. Slab has a rectangular cross-section, it's thickness between 50mm to 150 mm and width is 0.6 m to 1.5 m. The slab is further rolled to obtain plates, sheets, strips, coils etc.
 

Plate:

       The plate can be finished or semi-finished product with a minimum thickness of 6.35 mm. Its width shall be equal to the width of the roll and shall be equal to the maximum length that can be handled or shipped.
 

Sheet:

A sheet is a thin partner of a plate with a maximum thickness of 6.35 mm.  

Bandage:         

A strip is a narrow sheet and has a maximum width of 600 mm and a maximum thickness of 6.35 mm. Since it is normally handled in coil form, its length can be considerable and is restricted to manufacturing and handling facilities only.  

Foil:       

Foil is available thin strip or coil form also it's max.width is 300 mm and maximum thickness of 1.5mm.  

Rods:       

Rod is uniform cross section of symmetrical peice or straight and lt is long also It can be  round, square or any other configuration. A circular rod is called a rod.  

Wire:           

A wire is a thinner variety of bar, available in coil form and not normally identified to exceed 9.5 mm of cross-section.