Subject: Manufacturing Process I
Unit 2: Metal Forming Processes
Unit 2 Part 2: Rolling Process
Definition of Rolling
It is a forming process in which the raw material is heated to plastic state & it is compressed between two rolls of equal size and the raw material is deformed under the combined action of compression and shear such that the cross-section area is reduced at the expense of increasing length.
Note
Rolling is generally a Hot Working Process. The raw material used in rolling is called INGOTS which are made by casting process. After rolling the ingots, they become BLOOM. Blooms are bars of square cross section. Blooms are further rolled into BILLETS. Billets are shorter in length.
Types of Rolling
Depending upon the working temperature, Rolling can be of two types, like Hot & Cold Rolling.
Hot Rolling
When the working temperature in a particular rolling process is above the recrystallisation temperature of the work metal, then it is called hot rolling.
Cold Rolling
When the working temperature in a particular rolling process is below the recrystallisation temperature of the work metal, then it is called cold rolling.
Rolling Mill
Rolling mills are a type of metal forming machine that process various metals through sets of rolls to reduce thickness or change the cross-section of the input material.
Types of Rolling Mill
There can be various types of rolling mill:
- Two-High Rolling Mill
- Three-High Rolling Mills
- Four-High Rolling Mill
- Cluster Mill
- Continuous Rolling Mill
Two-High Rolling Mill
A two-high rolling mill has two horizontal rolls revolving at the same speed but in opposite directions. The space between the rolls can be adjusted by raising or lowering the upper roll. Their direction of rotation is fixed and cannot be reversed.
Two-high Reversing Rolling Mill
There is another type of two-high rolling mill, which has a drive mechanism that can reverse the direction of rotation of the rolls.
Three-High Rolling Mill
It consists of three parallel rolls, arranged one above the other. The directions of rotation of the upper and lower rolls are the same but the intermediate roll rotates in a direction opposite to both of these.
Four-High Rolling Mill
It consists of four horizontal rolls; the two middle rolls are smaller in size than the top and bottom rolls. The smaller size rolls are known as working rolls which apply rolling pressure over the work-piece. The larger diameter rolls are called back-up rolls and their main function is to prevent the deflection of the smaller rolls.
Cluster Rolling Mill
It is a special type of four-high rolling mill in which each of the two smaller working rolls are backed up by two or more larger back-up rolls. This type of mill is generally used for cold rolling work.
Continuous Rolling Mill
It consists of a number of non-reversing two-high rolling mills arranged one after the other, so that the material can be passed through all of them in sequence.
Rolling Defects
1. Centre Buckle:
Centre buckle is a type of defect in the rolling process of metal sheets that causes a bending along the centre of the rolled metal sheet.
2. Alligatoring:
Alligatoring is a type of rolling defect characterized by the separation of the rolled material into two distinct layers, similar to the open jaws of an alligator.
3. Wavy Edges:
Wavy edges is a type of defect that appears as irregular, undulating waves along the edges of the rolled material, while the central portion may remain relatively straight.
Applications of Rolling
Aluminum sheets for aircraft and steel plates for shipbuilding.
Structural components such as I-beams, H-beams, railway rails, and various other channels.
Pipes and tubes.
Automotive components, such as chassis parts, body panels are produced using the rolling process.
