What is Roll Pass?
In metal rolling operation, roll pass (or rolling passes) is a process of changing and reducing the shape of metal by a series of passes through a set of grooves rollers.
Rods of various cross sections can be manufactured by roll pass sequence.
In metal rolling operation, very limited reduction of thickness or shape is achieved in a single pass.
Thus there are multiple series of passes to be done in metal rolling operation that will result in a final desired cross section.
The schematic diagram shown below indicates the transformation of cast ingot into bloom and then bloom to billet and finally structural beams.
Roll passes are categorized as;
- Roughing or breakdown passes: During this process, the cross section area of the metal piece is reduced to preferred area and length of stroke. Roughing roll passes or break down passes are the first step in the rolling pass sequence.
- Leader passes: In leader pass, there is further reduction in the shape and size of the metal piece. This reduction is closer to the preferred shape of the workpiece.
- Finishing passes: Finishing passes are the final passes which give shr final shape to the workpiece.
There can be multiple passings of the metal piece in each of these above passes. This number of roll passings depends upon the required shape of the metal.
Roll pass sequence
Roll pass sequence is a sequential passing of the metal through the rollers in order to achieve the final desired shape. Even for manufacturing a simple shape, the metal has to pass through the rollers multiple times. And this sequential passing is known as roll pass sequence (or rolling reduction schedule).
Example #1): Reducing the diameter of a rod
As shown in the above image, the diameter of the initial rod is larger in size. This requires many passes with complex intermediate passes which reduce its diameter.
The rod of circular section is first rolled into an elliptical section and then it is again reduced by turning it at 90° to form a new reduced elliptical cross section.
Example #2): Rolling of square rod to a square rod of smaller size
This can be done by reducing the square shape to the diamond shape and then again the process is repeated as shown in above image.
Various shapes like I-beams, L-beams, U-channels, etc are made by roll pass sequence. Normally the metal is required to pass through the rollers for 10 to 15 times to get the desired final shape.