Cold rolling
Cold rolling is the conversion of a wide flat product below its recrystallization temperature, typically is used, the rolling at room temperature.
Cold rolling is widely used in the reduction of thickness of sheets, both in industry as well as in the craft area (see picture).
In the industrial scale, the cold to be rolled materials are often called " coils " (English for " role " or " coil " ) delivered, as is usually done before a first reduction to a hot strip.
Aluminum obtained according to this process a final thickness from 4 to 0.0065 mm, this must be intermediately possibly, to eliminate the work hardening of the metal. Steel cold-rolled strip is produced with a thickness of 3 mm to 0.25 mm. Tinplate, very fine and electrical sheet are rolled as thin as 0.1 mm.
- 2.1 Coupled rolling mills
Preparation
The material to be rolled coil is placed in a wind-off reel ( Payoff Reel ) and introduced into the mill. The beginning of the tape to the back section then takes a tension reel on ( Tension -Reel ). As is frequently used in reverse ( the belt moves in both directions through the plant ) is on the side of the Payoff Reels often a second Tension -Reel available.
Pickling, descaling
During the stretch bending, the raw material is passed under a large train to very tight radii, to break the coarse scale layer, fine impurities of the strip surface during pickling are cleaned with the aid of acid and then fed to the rolling mill. The pickling takes place in a plurality of pools, which passes through the strip, instead, then the acid was washed from the belt in order to prevent further corrosion by the acid.
Rolling mills
The actual rolling process takes place in the rolling stands. Type and number of stands may differ from plant to plant, as each rolling mill is designed for special " setpoints" for final thickness, product type and processing type.
There are four types of scaffolding:
Stand with two rolls: the framework has two large work rolls between which the strip is rolled. This type of scaffold is mostly used for non-ferrous metals.
Stand with four rolls: the framework has two central working rolls, which are enclosed by two large upright support rollers. The support rolls stabilize the work rolls, allow a higher loss per band pass ( stitch) and thus ensure higher productivity.
Backbone with six rollers: The framework has two small work rolls, which are enclosed by two medium-sized intermediate rolls and two backing rolls large. As in the four-roll stand, this constellation to improve performance and stability.
With the reduction of the work roll sizes to reduce the cost of ownership goes hand in hand because the work roll wear out faster than intermediate or back-up rolls and therefore must be changed frequently. The smaller rollers are easier to handle, cheaper to replace and rework faster.
Multi-roll structure: This type of scaffold is a special feature, since many rolls of different sizes (usually 18 or more rolls ) are arranged symmetrically in two wedges. Thereby make the pair of work rolls is the tip of the wedges, which are each perpendicular to the strip. Such multi- rolling mills are able to achieve very high acceptance levels and / or while respecting very precise tolerances band. They are mostly for stainless steels, especially stainless steels used. The most common design of a multi-roll stand is the Sendzimir mill with 20 rolls.
Coupled rolling mills
Often, in large systems the heavy plate is continuous, ie not rolled reversing. As a re- perform the roll is not possible, the thickness decrease, however, can not be done in one pass, coupled rolling mills are used. This mill stands are arranged one behind the other and the sheet becomes thinner from stand to stand. The rolling speeds take it steadily.