Quarto (rollers)
Quarto is a term used to describe roll stands with a typical basic structure. These roll stands always consist of two work rolls and two back-up rolls and are used in both hot and cold rolling.
Construction of a four-high mill stand
Four-high roll stands consist of:
- Base plate
- open / closed roll stand
- Building pieces with storage
- two backup rolls
- two work rolls
- Roller balancing
- Adjusting device
- Side guide
- Roller fittings
- Bending and sliding devices
In contrast to the two-high roll stand , the four-high roll stand has two backup rolls. On the one hand, these backup rolls make it possible to reduce the work roll diameter and, on the other hand, they reduce the sagging of the work rolls due to the very high rolling forces.
Use in the roughing train
In modern rolling mills they are often found as a rolling stand in the so-called roughing train in reversing operation. Here, the primary material, such as a slab from the continuous caster or a bloom from the ingot casting, is rolled out in several passes.
Use in heavy plate mills
As already indicated, the predecessor of the four-high roll stand is the two-high roll stand. It was only with the use of the four-high mill stand that it was possible to significantly expand the width of the heavy plate while at the same time ensuring the corresponding surface flatness.
Today, heavy plates up to a width of 5,600 mm can be rolled out without any major problems. For this purpose, slabs from continuous casting with a thickness of 450 mm are usually processed. The slabs used are heated to a temperature of approx. 1,250 ° C. This mostly happens in pusher ovens or walking beam ovens . Now it is not possible to immediately roll a heavy plate of 80 mm from a slab with a thickness of 450 mm. For this reason, heavy plate mills work in reversing mode, i.e. roll with several passes . The required rolling forces increase here to more than 22,000 tons.
During the rolling, the rolling stock is rotated several times on the roller table. This turning has a great influence on the technological properties of the heavy plate. This process creates a more or less strong texture . Knowing about the course of this texture is very important for later processing. The main rolling direction is usually marked on the rolling stock so that a boiler maker, for example, can make targeted use of the technological properties of the material.
Frequent changes in the rolling direction, i.e. frequent turning of the rolling stock, can also reduce the extent of the texture. This is also advantageous depending on the later application.
Use in finishing lines
Here, too, four-high roll stands can be found in the so-called finishing lines or finishing lines. In finishing mills, hot strip or hot wide strip is often rolled out in combination with roughing mills. In the area of cold rolling, the finishing mills are also referred to as tandem mills. Finishing mills or tandem mills consist of several rolling stands arranged one behind the other. Part of the forming work is carried out here in every roll stand. The rolling process itself runs continuously, i.e. not reversing.
In the hot rolling area, the roughing strip that comes from the roughing train is turned into a hot strip or hot wide strip of up to 1.5 mm thick.
Rolling out the hot strip in the tandem mill (cold rolling) produces a strip a few tenths of a millimeter thick.