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A temper mill is a finishing facility that processes steel in the form of sheet and plate in order to give it added strength and uniform flatness to the surface. The metal forming method at a temper mill involves rolling the sheets of steel through what is known as a cold reducing process or temper pass. This increases the density of the steel by reducing its overall thickness between usually 1.5% to 2% without allowing the steel to spread out while under pressure. After steel has passed through a temper mill, it is more useful and reliable in manufacturing facilities that must shape it further or cut it with laser and plasma equipment.
Metal forming using a temper mill is an important stage in the steel manufacturing process. This is because milling work usually follows immediately after sheet or plate steel has been annealed, fired, and cooled. The annealing process tends to relieve micro-crystalline stress to such a degree in the steel that it displays a tendency to bend in non-uniform ways. This propensity for stretching in some areas and not in others along the surface is what the temper mill eliminates by reducing the steel volume by anywhere from 0.5% to 3.5% of its overall thickness.
The steel sheets that are run through a temper mill go through a fairly simple procedure. They arrive in the form of coils of sheet steel that are manufactured in a hot strip mill, or what is commonly known as a pickle line. A machine known as an uncoiler unwraps these rolls of steel and feeds them into the mill. The steel mill also controls the extensions, or ends of the steel, as it is processed and prevents yield point elongation (YPE). Yield point elongation is a deformity that can occur where discontinuous regions succumb to strain from pressure and stretch or flatten out.
After the steel has passed through the mill, its surface layer is more uniform. A pinch roll or shear may also be present at this stage, which is used to cut the steel into smaller finished segments. A machine known as a recoiler then takes the steel as it exits the temper mill and rolls it up once again, ensuring that the sides are straight as well.
Many modern temper mill machines are automated, with each feature in steel plate processing being precisely controlled. These features can include automatic constant rolling force and elongation controls (AFC) and (AEC), as well as automated position and tension controls (APC) and (ATC). The loading and unloading of the steel coil from the machines that feed the temper mill and take off the finished product can also be automated, and this can include a high-pressure water feed that prevents crimping of the steel in the rolling process. Typical speeds for an automated temper mill range from 656 to 2,953 feet (200 to 900 meters) of steel per minute depending on the production schedule of the facility.