Rolling in metalworking is a metal forming process that helps to reduce the thickness of metal and make the thickness uniform. The metal stock is passed through one or more pairs of rolls to reduce the material. Rolling is classified according to the temperature of the metal rolled, it is a hot rolling if the temperature of the metal is above its recrystallization temperature. whilst it is known as cold rolling if the temperature of the metal is below the recrystallization temperature.
Today we’ll be looking at the definition, processes, working principle, types, application, hot and cold rolling, lubricant purpose, defects as well as advantages and disadvantages of rolling.
Rolling can be defined as a metal forming process in which metal pieces pass through some pairs of rollers in order to obtain a uniform thickness or reduce the thickness of the material. This is achieved in two ways; hot and cold rolling. in an application, the hot rolling processes are more tonnage than any other manufacturing process, and cold rolling processes are the most tonnage of all cold working processes.
The pairs of rolls are held on roll stands, which are grouped together into roll mills that easily process metal. Generally, steel can be rolled into various products such as structural steel (I-beams, angle stock, channel stock), bar stock, and rails. Well, some steel mills have rolling mill divisions that convert semi-finished casting products into finished products.
Working principle of the rolling process:
In the rolling process, a stock of material is passed between one or more pairs of rollers in order to reduce and maintain the uniform thickness. This process mainly focused on the cross-section of the ingot or metal to be pressed which aids in the reduction of the workpiece thickness. Rolling processes increase the length and decrease the thickness without changing the width of the material.
In this video content below, the working of rolling has been explained:
Hot and Cold rolling:
As earlier mentioned, in the metalworking process hot rolling occurs above the recrystallization temperature of the material. Though, the recrystallization prevents the metal from working hardening.
Unlike hot rolling, cold rolling occurs below the recrystallization temperature of the material usually at room temperature. this increases the strength to about 20% high through strain hardening and enhances the surface finish and also holds tighter tolerances.
The applications of hot rolling are mainly the production of sheet metal or simple cross-sections, such as rail tracks. The general applications of hot-rolled metal include:
- Truck frames
- Pipes and tubes
- Automotive clutch plates, wheels, and wheel rims
- Water heaters
- Agricultural equipment
- Metal Building
- Railroad hopper cars and railcar components
- Guard rails streets and highways
- Doors and shelving
The applications of cold-rolled steel include metal furniture, filing cabinets, tables, desks, chairs, motorcycle exhaust pipes, computer cabinets and hardware, home appliances and components, steel drums, tubing, hinges, lighting fixtures, shelving, water heaters, metal containers, fan blades, frying pans, electronic cabinetry, lawnmowers, construction-related products.
With the list of these rolled-metal applications, you can see almost all applications around us undergoes either cold rolling or hot rolling.
The following represent the different rolling processes:
- Roll bending
- Roll forming
- Flat rolling
- Ring rolling
- Structural shape rolling
- Controlled rolling and
- Forge rolling
Types of rolling mills:
The following represent the five types of rolling mills used for rolling metals:
- Two-high rolling mills
- Three-high rolling mills
- Four-high rolling mills
- Tandem rolling mills
- Cluster rolling mills
As friction occurs between the rolls and metal during the rolling process, lubrication plays a very important role. The friction is also useful as it is responsible for shifting the work forward between the rolls. That is why it is sometimes eliminated or reduced below an appropriate level, which makes it important to choose a suitable lubricant for a rolling process.
While performing cold-rolling on steel, it is necessary to use fluid lubricants that contain low viscosity, like paraffin. Paraffin is suitable for nonferrous metals like aluminum copper and its alloys, which helps to avoid staining during the subsequent heat-treatment process.
For hot rolling, lubrication might not be needed but the flood of water is used to generate steam and break up the scales formed. However, graphite grease is used as a lubricant.
Defects in Rolling:
Defects occur on rolled material due to the high force of rolls pressed. The following stated below are the different types of defects in the rolling process:
- Edge cracking
- Scale formation
That’s it for this article, “rolling process”. I hope you enjoyed the reading, if so, kindly comment and share with other students. Thanks!