In the metalworking industry, rolling is a crucial process. The metal stock passes through a pair of heavy rolls in this process. This gives it the desired shape and thickness and imparts desired geometrical dimensions and mechanical properties. The idea is similar to rolling dough with a rolling pin.
What is Hot Rolling?
Hot Rolling is a process in metalworking during which the metal is rolled above the recrystallisation temperature. The minimum temperature at which metal is recrystallised is 1700 degrees Fahrenheit. The hot rolling process makes the metal more malleable and easier to shape into desired geometrical dimensions and material properties while maintaining the same volume.
During this process, as the name suggests, a billet of metal is heated and passed between two rolls to flatten and lengthen it. This process helps the metal obtain uniform thickness and reduces the cross-sectional area.
What are the Advantages of Hot Rolling?
1. Improvement in Mechanical Properties
When metal is heated and rolled above the high temperature of 1700 degrees Fahrenheit, the metal gains a lot of new properties due to the hot rolling process. Some of the changes include toughness, resistance to shock, ductility, elongation percentage, and more.
2. Elimination of Porosity and Refined Grain Structure
A significant advantage of the hot rolling process is the removal of defects which include welding pores, coarse grains, and more. During the recrystallisation process, the coarse grain converts into refined grains, causing changes in the properties of the metal.
The pores are also removed during this time, causing a strong and uniform structure.
3. Uniform Distribution of Impurities
During the hot rolling process, any impurities that might be present gets removed from the metal, such as slag and others. The removal of such impurities makes the metal more durable. Had there been impurities, it would have made certain sections weaker.
4. High Production Rate
When the metal is heated at a high temperature, the raw material’s deformation resistance is lowered, and thermoplasticity increases. This process increases the production rate as the machinery and motor get less worn out due to the malleability of the metal at that given point.
What are the Disadvantages of Hot Rolling?
1. High Cost of Equipment
The process of hot rolling might increase the production rate but does raise the cost of production, from expensive tools to trained professionals who need years of experience to operate the machinery properly.
2. Maintaining Accurate Temperature
The majority of the hot rolling process depends on the correct temperature. Maintaining 1,700 Fahrenheit can be a challenging task. If the right temperature is not maintained, it might cause damage to the metal being produced.
3. Surface Finish And Texture
The high temperature causes the surface to have a poor finish as the high temperature increases the oxidation and scaling process.
What is Cold Rolling?
The alternative to hot rolling is known as the process of cold rolling. Metal passes through the roller below the recrystallisation temperature in the cold rolling process. This process increases the strength and durability of the metal. The metal is less malleable because it remains at room temperature than the recrystallisation temperature, but this labour-intensive process reduces the grain size of the metal.
What are the Advantages of Cold Rolling?
1. Surface Finish
Due to the absence of high temperatures, the metal coating of the metal is not damaged. It also has a flat and smooth surface with fewer deformations.
2. Lower Cost
For cold rolling, there is no requirement for expensive tools and machinery. Since the cold rolling process doesn’t need to maintain a specific temperature, the expertise required is also significantly reduced.
3. High Yield Point
Due to the cold rolling process, metal can produce large plastic deformation, which increases the yield of the metal.
4. Close Tolerance Point
With the cold rolling process, the tolerance point of the metal can go as close as 0.025 mm.
Since the cold rolling process does not require high temperatures, the metal maintains its structural integrity and doesn’t turn weak.
What are the Disadvantages of Cold Rolling?
1. High Cost
The cold rolling process takes longer to produce than the hot-rolling process. The metal is more difficult to manipulate and takes longer to process. That is why the price increases.
2. No Distribution of Impurities
When the metal is heated for the hot rolling process, impurities get the chance to distribute evenly. In the cold rolling process, impurities don’t get the opportunity to redistribute.
3. Grain Size
The reduction size of the grain is necessary to obtain strength and durability. During the hot rolling process, metal receives a refined grain structure, but in the cold rolling process, there is no significant reduction in the size of grain due to the lack of high temperature.
The cold rolling process provides minimal leeway to correct things post-production. Width is one of the primary examples of it. In the case of rolled metal, you can shave down unnecessary portions easily. You need to begin with the correct measurement for cold-rolled metal, as customising it might be problematic later.
Which One is Better: Hot Rolling or Cold Rolling?
The question of which process is better is a question that does not have a definite answer. As we discussed, the hot rolling and the cold rolling process both have their advantages and disadvantages. To obtain the answer of which process is better, you need to know what you intend to manufacture in the first place.
The metal we get during the hot rolling process is necessary for railroads, construction steel bars, beams, and more. Due to its appearance, the hot-rolled metal is used more for structural works.
On the other hand, cold-rolled metal would be too brittle for railroads. Instead, due to the close tolerance point, the sheets are thinner. This process creates metal sheets appropriate for furniture, household appliances, cabinets, beverage cans and more.
Why Choose The Steefo Group?
The name of The Steefo Group has become synonymous with premium quality in rolling mill services. With its foundation going back around four decades, we have built our reputation based on our quality. Recognized by the Government of India as the Star Export House and international clientele, we intend to be your reliable partner for all your steel-forming needs. To enquire more about our products and services, contact email@example.com or give us a call at +919824076873.