The crown and roughness of the work rolls of each stand of the cold tandem rolling mill and the requirements for the use of matching rolls

Since the reduction ratio distribution of each stand of cold tandem rolling is inconsistent, as the work roll is in direct contact with the strip, the hardness of the roll surface and the roll diameter will change after a period of use. At the same time, each rack has different requirements. How to arrange it to best meet the needs of production and at the same time make the best use of the roll materials? Let’s introduce it to you today.

work rolls

Work rolls surface roughness

The roller surface roughness is processed according to the friction conditions of the roller gap and the surface condition of the finished product. Larger roller surface roughness is conducive to improving the bite conditions and increasing the surface roughness of the finished product. Taking the work rolls of five stands of a certain acid rolling combined unit as an example, the surface roughness target value of the outlet strip of the unit is 0.8 μm, so the following work roll surface roughness is selected.​

Rack numberStrip roughness (μm)Roll roughness (μm)Roller replacement mileage
#1std3.0±0.20150km
#2std0.60±0.10200km
#3std0.60±0.10200km
#4std0.60±0.10200km
#5std0.802.5±0.10150km

Crown of support roller and work rolls

Cold-rolled strip steel is rolled using convex rolls. The original crown values of the work rolls and back-up rolls must be ground according to the design requirements. At the same time, the crown values of the work rolls and back-up rolls must match each other. The crown of the upper and lower work rolls is configured according to the width of the rolling strip. Generally speaking, the crown of the work roll and the backup roll of wide strips should be reduced accordingly. The work roll crown and back-up roll crown of a certain acid rolling mill unit are given below for reference.

frameWork roll crown/mm
Width<1600mmWidth>1600mm
10.10/0.100.0/0.0
20.10/0.100.0/0.0
30.10/0.100.0/0.0
40.10/0.100.10/0.10
5CVC Curve No. 4
frameSupport roller grindingRolling tonnage/t
Convexity/mmHypotenuse length/mm
10.15/0.15200about 50,000
20.07/0.07200about 50,000
30.07/0.07200about 50,000
40.07/0.07200about 40,000
50.00/0.0150about 30,000

Requirements for using rollers

(1) Work roll diameter

The upper and lower limits of the work rolls diameter are limited during the equipment design and debugging of the acid rolling mill or continuous rolling mill. That is, the work roll diameter cannot exceed the set upper limit, nor can it be lower than the set lower limit. Generally, the roll diameter of new work rolls is close to the set upper limit. The work roll must be scrapped after the roll diameter falls below the set lower limit. At the same time, the following principles should be followed in actual use:

The working roller with the smallest diameter can be assembled on the second frame, and the largest one can be assembled on the first or fifth frame to facilitate bite-in and increase the speed of exiting the rolling mill.

(2) Work roll diameter difference

The diameter difference between the upper and lower rollers in the same frame cannot exceed a certain range, otherwise even if the roller diameters are within the use range, they cannot be used together. This is the principle of roller diameter difference matching.

According to production experience, generally the maximum allowable diameter difference between the upper and lower work rolls is 3-7mm, and the small diameter roller is the lower roller to press down the strip during rolling.

(3) Hardness matching principle

The hardness matching principle is that the fifth rack has the highest hardness, and the rack numbers are allocated in reverse order to the first rack. In each rack, the roll with high hardness should be used as the lower roller to ensure the quality of the lower surface.

The above is a brief description of the roller matching principles of the work rolls of each stand of the continuous rolling mill. The following table is an example of the roller matching of a certain unit:

Roller formRoller diameter usage range/mmPaired roller diameter difference/mmRoller body hardness configuration usage range HSC
Work rollFive-stand continuous rolling millThe first∮615~∮590≤782~92
The second∮590~∮550≤784~92
The third∮590~∮550≤786~94
The fourth∮590~∮550≤390~94
The fifth∮615~∮590≤388~94
Backup roller∮1550~∮1425 55~60

 

MM GROUP is one of the professional roll manufacturing base in China, which supply all kinds of large-size rolls for iron and steel enterprises with production capacity of 100,000 tons of all kinds of hot strip mill rolls, section mil rolls, rod mil rolls, cold rolling m rolls, casting and forging backup rolls.

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