The production and applications of Hot-rolled Coils
Have you ever wondered how a beautiful car or your water heater is made? The answer starts in steel manufacturing mills in which raw steel is transformed to usable products that are used by different industries and present us a lot of useful products.
In this article we address one of the most popular types of steel coils that is used in factories to give you a general idea about hot-rolled coils.
What does Rolling Process mean?
“Rolling” is a very popular term in the metalworking world, it refers to a metal forming process in which a metal stock is passed between two rolls in order to reduce its thickness and get a uniform thickness.
Rolling is the initial process of all steel product manufacturing such as structural steel and coils.
Rolling mills can process steel quickly and convert semi-finished casting products including ingots, blooms, billets or slabs into finished products like beams, bars, or coils… etc.
What is the difference between Hot Rolling and Cold Rolling?
Rolling is classified according to the temperature of the metal being rolled.
Here we should introduce the Recrystallization term which is a process by which deformed grains are replaced by a new set of defect-free grains.
This process requires a particular temperature to occur which is called the recrystallization temperature.
While rolling, if the metal’s temperature was above its recrystallization temperature, then it is called a hot rolling process. and if it is under the recrystallization temperature then it is called a cold rolling process.
That is, hot rolling is a process done with heat, whereas cold rolling is done at or near to room temperature.
Prime steel and secondary steel can be either hot-rolled or cold-rolled including all steel grades and specifications.
It is obvious that some types of steel are more suitable for certain uses.
Using the suitable type of steel can save time and money and avoid the wastage of raw materials.
Hot-rolled steel is a steel that had roll-passed at a very high temperature, approximately more than 2000 degrees Fahrenheit which is above the recrystallization temperature for most steel types.
The heat gives steel a workable starting form and makes it easier to shape.
Hot rolling starts with a large long steel called billet which is heated and sent to a large roll to flatten, then it is passed in a series of rolls keeping it’s high temperature until reaching to the final wanted dimensions.
Then steel sheets are spun into coils and left to cool.
For bars and beams steel is sectioned and cooled.
Hot rolling doesn’t give precise dimensions since steel shrinks while cooling, so the resulting steel is suitable for applications where minutely specific dimensions aren’t crucial, like railroads and constructions.
Hot rolling steel can be defined by these features due to shrinking and remnant of cooling:
a scaled surface, slightly rounded edges and corners, and slight distortions
Advantages of hot rolling steel:
- Cost-efficiency because it requires much less processing than cold rolled steel.
- Free from internal stresses that arise while cooling since it left to cool at room temperature.
- Ideal for applications where accurate dimensions are not important as steel strength.
Hot-rolled coils are one of the flat steel products.
They are sheets of prime or second choice steel that are rolled in a hot steel mill into coils while they are very hot.
These coils are very common types of steel coils that form the base product for other steel coils like coated and galvanized coils and also used directly nearly in various industries and machinery, like construction, shipbuilding, automotive…etc.
Hot-rolled coils manufacturing process:
Hot-rolled coils production process goes into three main stages:
A steel slab or billet is heated in a furnace to a very high temperature approximately 2300 degrees Fahrenheit which affects the properties of steel and dissolves the compound of carbon and nitrates that exist in steel.
Heating process makes the steel more malleable, making it easier to be rolled.
When the steel is taken out of the furnace and transferred to the rolling mill it reacts with oxygen and forms a flaky surface scale of iron oxides which reduce the quality of steel.
To remove this unwanted scale steel is sent through a mill scale cleanse and sprayed with high pressure water.
The cleansed steel is sent to a series of rollers consisting of four or five sets of rollers that reduce the thickness to approximately 1/10 of original thickness.
A vertical pressure is applied to control the width.
After that steel is trimmed and sent to another set of rollers to get the desired thickness and winded into coils while it is hot.
The flat rolled steel is passed under cooling sprays and left to cool at room temperature then it goes to coilers to obtain the final product.
The resulting hot-rolled coils can be delivered to steel manufacturers for further processing or directly to customers.
Hot-rolled coils applications:
As we mentioned before, hot-rolled coils are typically used in applications that don’t require a perfect surface finishing and where accurate dimensions are not critical to the project.
Hot-rolled coils are a good choice when tight tolerances are not so important, and when price is more important than precision.
They are a preference for steel companies and metalworking due to their malleability and cost-efficiency.
Hot-rolled coils have an appearance that distinguishes them over other coil types, they are darker gray and have a silvery blue, almost purple strip along both sides makes the steel’s surface appear as if it is still hot to the touch.
This appearance makes hot-rolled coils the most commonly used type for art sculptures.
Common applications for hot-rolled coils include:
- Truck frames.
- Steel doors,shelves and tanks.
- Gas containers.
- Pipes and tubes.
Hot-rolled coils for your project:
Our company imports prime and secondary steel hot-rolled coils directly from steel mills and delivers you high-quality hot-rolled coils at very good price.
Exanvil Gmbh offers specific requirements and specifications of coils and helps you to choose the best suited coil for end use.
coil’s length and size is available as you need, you will get your hot-rolled coils in size, characteristics and time you want it.
For small or large orders Exanvil Gmbh is ready to meet its customer needs.
Hot-rolled coils are indispensable steel products that we see their applications in everyday life from cars to beverage cans.