Cold rolling
Cold rolling is the rolling of metals, the rolling stock , below its recrystallization temperature between two or more rotating tools, the rolls. Cold rolling usually takes place at room temperature, i.e. without prior heating. It belongs to the field of cold forming .
application
Cold rolling is widespread in reducing the thickness of sheet metal, both in industry and in the arts and crafts sector (see picture).
In the industrial scale, the cold to be rolled materials frequently used as coils (engl. For "roll" or " coil ") delivered previously by means of a hot-rolled coil were reduced method.
According to this process, aluminum reaches final thicknesses of 4–0.0065 mm, which may require intermediate annealing to remove the work hardening of the metal. Of steel is cold-rolled strip made mm with a thickness of 3 to 0.25. Tinplate , ultra-fine and electrical sheet are rolled down to 0.1 mm thin.
preparation
Loading the material
The strip (coil) to be rolled is placed in a payoff reel and fed into the rolling mill. A tension reel then picks up the beginning of the tape at the end of the line. Since reverse operation is often used (the tape travels through the system in both directions), there is often a second tension reel on the side of the payoff reel.
Pickling, descaling
The primary material, mostly hot strip as shown above, still has to be freed from scale and rust . This is then done with stretch bending and pickling .
While stretch bending involves pulling the raw material around very tight radii in order to break up the coarse layer of scale, fine impurities are removed from the strip surface with the aid of acid during pickling and the material is then fed to the rolling mill. Pickling takes place in several basins that the belt runs through, after which the acid is washed off the belt in order to avoid further corrosion by the acid.
Roll stands
Simple rolling method
The actual rolling process takes place in roll stands . The type and number of stands can differ from plant to plant, as each rolling mill is designed for specific target values for final thickness, product type and type of processing.
There are four types of scaffolding:
- Stand with two rolls
- The stand has two large work rolls between which the strip is rolled. This type of scaffolding is mostly used for non-ferrous metals .
- Stand with four rolls
- The stand has two middle work rolls which are enclosed vertically by two large back-up rolls. The backup rolls stabilize the work rolls, allow a higher decrease per strip pass (stitch) and thus ensure higher productivity.
- Six-roll stand
- The stand has two small work rolls enclosed by two medium-sized intermediate rolls and two large back-up rolls. As with the four-roll stand, this constellation ensures higher performance and stability. The reduction in the size of the work rolls is accompanied by a reduction in operating costs, since the work rolls wear out more quickly than intermediate or backup rolls and therefore have to be changed frequently. The smaller rollers are easier to handle, cheaper to replace and quicker to rework.
- Multi-roll stand
- This type of stand is special, as many rolls of different sizes (usually 18 or more rolls) are arranged symmetrically in two wedges. The two work rolls represent the tips of the wedges, which are each directed perpendicular to the strip. Such multi-roll stands are able to achieve very high acceptance values and / or maintain very precise strip tolerances. They are mostly used for stainless steels, especially stainless steels. The best-known type of multi-roll stand is the Sendzimir stand with 20 rolls.
Coupled roll stands
In large plants, the heavy plate is often rolled continuously, i.e. not in a reversing manner. Since it is not possible to re-feed it to the roll, but the decrease in thickness cannot take place in one pass, coupled roll stands are used. Roll stands stand one behind the other and the sheet metal becomes thinner from stand to stand. The rolling speeds increase steadily.
History of cold rolling
Cold-rolled fine sheet has been around since the end of the 17th century. Tinplate has been cold-rolled in England since around 1810 . In Germany, cold rolling technology, which provided the raw material for a wide variety of products, was mechanized around 1830. The wire puller JP Hüsecken from Altena produced with the water-driven hammer mills in the Hohenlimburg area and with ground and hardened steel rollers from Alfred Krupp Bandstahl z. B. for hoop skirts . Around 70 percent of German cold rolled products are still produced in the Hohenlimburg area today.
Cold rolling with the system of rolling stands arranged one behind the other with different rolling speeds was widespread in England since the 1860s. Up to this time the water drive was replaced by steam engines and in the 20th century by electric drives, which made it easier to reverse the direction of sheet metal.
Since the 1960s, aluminum cold rolling has been gaining ground, e.g. B. for the aircraft industry increasingly important. In the same decade, the automation of continuous cold rolling also began. Today, digital technology also enables extremely thin rolled profiles to be optimized.
The German Cold Rolling Museum was located in Hohenlimburg Castle from 1988 to 2017 ; it will move to the Hagen Open Air Museum by 2019 .
See also
Web links
- Comprehensive Metal forming and welding glossary with technical terms for metal processing (accessed on May 15, 2010)
Individual evidence
- ↑ Ludwig Beck: The history of iron in technical and cultural-historical relation: The XIX. Century from 1860 to the end. Braunschweig 1903, p. 222.