Language selection
Russian (CIS)English (United Kingdom)

REGRINDING OF STRIP MILLS WORK ROLLS IN THEIR CHOCKS

1. Reasons for development and peculiarities of design

It is common knowledge that regrinding of work rolls for continuous strip mills usually requires the removal of chocks and it entails a great amount of work connected with the preparation of sets of rolls and causes leakage of lubrication and impact of the bearings while removing and putting back the chocks.

At the same time, the existing technologies of roll regrinding without removing them from chocks require the usage of special of roll regrinding without removing them from chocks require the usage of special roll grinding machines, cutting dummy necks on the rolls or perfectly fitted rolls and chocks. Such technologies turn out to be very expensive when put into practice, and as a rule they don´t guarantee precise grinding.

The main peculiarities of our devices, which allow the regrinding of rolls without removing them from the chocks, are as follows:
- high precision grinding (0,01 mm at the worst), which meets the requirements set for the rolls of finishing stands for strip mills;
- it is possible to build the device into the existing roll grinding machines without making any major amendments in their construction, and the costs amount to only 5% of the price of a new machine.

2. Functional characteristics

As we can see from the structure of the device, shown in figure 1, its main components are:
- special precision revolving centers 5 (built into the headstock and tailstock of the roll grinding machine 1), on which the сentre holes of rolls 2 are aligned;
- spring-loaded equalizing units 4, built into the roll grinding machine 1 instead of conventional rests, which lower the pressure on precision centers 5 as low as 5% of the weight of the roll and chock assembly.

The spring-loaded equalizing units 4 can be installed directly under the chocks 3, as is shown in the Figure 1, or they can operate through some intermediary elements, depending on the relation of the dimensions of chocks and workspace of a concrete roll grinding machine.

Fig.1. The device for regrinding of rolls in their chocks

The device for regrinding is as a rule supplied with the transitional elements (not shown in the figure), which makes it possible to grind rolls without chocks.

The device can include a special load bar 6, with the help of which it is easy to install the rolls on the roll grinding machine or on the assembly bench and to manipulate the chocks. As our practice shows, the installation and manipulation of chocks and rolls, for example, for finishing stands of a number of strip mills can be done using conventional suspension hangers as well, but the use of special load bars proves to be appropriate as it eases and accelerates the task.

As a rule, one device for regrinding weighs from 1,5 to 3 tons (along with the special load bar), caused, mainly, by work rolls dimensions and weights.

We also developed devices for regrinding of heavy rolls in chocks with basing in special lunettes 4 (Figure 2) on false-necks 3 of work rolls for those mills where work rolls were already executed with falls-necks at edges of a roll barrel (for example for hot strip mill 2000 at Magnitogorsk Metallurgical Works (Figure 2). In this case equalizing units 5 with springs 6, acting at chocks 2 provided radical decrease in load of lunettes contact surfaces of grinding machine 1 and on false-necks 5, preventing their wear unacceptable for ensuring accuracy of grinding.

Fig.2. The device for regrinding of work rolls for finishing stands of hot strip mill 2000 in Magnitogorsk

There were in our practice devices which allow regrinding heavy rolls in their chocks (for instance, for plate mills), aligned with reference to the chocks (this kind of device has been manufactured and delivered to the plant («Amurstal»).

3. Effectiveness

The use of the device guarantees:
- reduction of lab our input in preparation of sets of rolls;
- increase in service life of roll bearings at least by 30%;
- substantial decrease in chock lubricant consumption ;
- extension of roll service life owing to thermo cycling fatigue stress reduction caused by the rolls being warm when ground.

4. Realization

The use of the device proves to be especially effective if the chocks are provided with sealing units, which guarantee both long-term containment of packed grease and effective use of modern «oil-air» type sealing systems.

Devices for regrinding, developed and delivered by our company, have been successfully tested and are mounted in the strip mills of Russian metallurgical plants («МЕCHЕL» in Chelyabinsk, «Severstal» in Cherepovets), plants of Kazakhstan («Mittall Steel Temirtau») and Ukrainian plants («Ilyich Metallurgical Works» in Mariupol).

5. Order completion schedules

- engineering documentation is prepared within 1 month after the contract is signed;
- the device is manufactured and supplied within 4 - 5 months after the engineering documentation is agreed upon;
- briefing the personnel, putting the device into operation, as well as its adjustment with due account of corrections to be introduced into the customer's procedure of roll preparation are carried out within a month after delivery of the device.