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Roller matching technology of hot strip finishing mill
Release time:
2018-12-06 11:39
Roller matching usually includes the following contents: matching between upper and lower working rollers, including matching of diameters and materials; The working roller is matched with the supporting roller, mainly in hardness. Elevation configuration and stability of a certain rack; Relative elevation configuration of adjacent racks; The roll type and surface of the upper mill roll are matched with the specifications and varieties of the rolled material.
1. Roller matching
Roller matching usually includes the following contents: matching between upper and lower working rollers, including matching of diameters and materials; The working roller is matched with the supporting roller, mainly in hardness. Elevation configuration and stability of a certain rack; Relative elevation configuration of adjacent racks; The roll type and surface of the upper mill roll are matched with the specifications and varieties of the rolled material. The matching of upper and lower working rolls is of great significance for the effective use of working rolls, the control of the buckle head of the strip steel, and the guarantee of the plate shape and surface quality of the strip steel. The matching of the working roller and the supporting roller mainly means that the hardness of the working roller is higher than that of the supporting roller, so as to avoid excessive wear of the working roller.
2. Rolling stability
According to the position of the strip in the steel finishing mill, the rolling stability includes the stability of the strip before the construction of the tension, the stability of the steady-state rolling and the stability of the steel throwing. Penetrating instability is usually manifested as the head of the strip hitting the upper guide plate at the entrance, which is easy to cause scrap steel or rolling breakage. Steady-state rolling instability is usually manifested as strip deviation, medium waves, unilateral waves and bilateral waves, and is also easy to cause scrap steel or rolling breakage. After the steel is thrown from the front frame, the tail of the strip loses tension, and the unstable operation of the tail of the strip is usually manifested as tail flicking or tail rolling breakage.
The scrap steel, rolling break and strip tail flick caused by unstable rolling will cause different degrees of damage or damage to the roll surface. From the perspective of failure mechanism, scrap steel is in static contact with the roller surface, or the scrap steel sheet is adhered to the roller surface after rolling, and the thermal impact of high-temperature strip steel on the roller surface will cause thermal cracks. When the strip steel flicks its tail, the tail slaps on the roller surface, causing the local mechanical stress on the roller surface to exceed the tensile strength of the roller surface material, which will cause mechanical stress cracks. Field experience shows that mechanical stress often causes damage to the surface of the roll, which is the reason why "one accident must be carried out after three subsequent service. No matter what kind of crack, for high speed steel and high nickel chromium material rolls, must be eliminated, otherwise it may lead to deeper cracks or spalling.
3. Analysis of the influence of the rationality of the roller on the rolling stability
The relationship between the elements of the roll and the rolling stability of each rolling stage is as follows:
(1) Matching of upper and lower work rolls and stability of threading
The upper and lower work rolls are made of the same material, or the hardness of the roll body is similar when the material is the same (the hardness difference is generally controlled within 3HsD), so as to ensure that the upper and lower rolls contact the strip steel with the same friction coefficient and at the same time ensure that the elastic flattening amount is similar; The diameters of the upper and lower work rolls are similar to ensure that the contact arc length with the strip steel is consistent. Generally F1-F3 the difference of the upper and, the diameter difference between the upper and lower work rolls of the F4-F7 stand shall not exceed 0.2mm. The coefficient of friction, the elastic flattening of the roll and the length of the contact arc are the elements of smooth belt threading.
(2) The matching of upper and lower work rolls and the stability of steady-state rolling
In strip rolling, if the upper and lower working rolls cannot match, it will 1) lead to inconsistent elongation of the upper and lower surfaces; 2) inconsistent roll wear, resulting in increased difficulty in controlling the plate type and increasing the possibility of rolling and scrap steel; 3) inconsistent roll surface roughness, resulting in differences in the quality of the upper and lower surfaces of the strip. The upper and lower rollers do not match themselves, which also affects the use economy of the rollers.
(3) The matching of upper and lower working rolls and the stability of steel throwing
The internal stress of the strip caused by the inconsistent elongation of the upper and lower surfaces of the strip caused by the mismatch of the work roll may not be obvious in the stable rolling process. However, when the steel is thrown at the front frame, the internal stress will lead to the bending of the tail of the strip, thus causing the tail flick.
(4) Work roll and backup roll matching and steady-state rolling stability
The work roller is subjected to excessive wear of the support roller, which is often uneven, which will lead to an increase in the difficulty of controlling the plate type and increase the possibility of crushing and scrap steel.
(5) Elevation configuration and threading stability of single rack
When the support roller assembly and work roller assembly are all installed in the rack, the elevation H of the actual rolling line of the rack is the sum of the rack constant C, the thickness H1 of the support roller plate, the radius R of the support roller and the diameter d of the lower work roller. Namely: H = C H1 R d
During the roll change cycle of a backup roll, H depends on the diameter of the upper work roll. When the diameter of the working roll on the machine is too large or too small, the actual rolling line elevation will deviate greatly from the theoretical rolling line elevation, and it will be difficult for the roll to bite the steel. In the extreme case, the strip head hits the inlet side flower frame and scrap steel occurs.
(6) Elevation configuration and steady-state rolling stability of a single stand
In the front section of the finishing mill, due to the large thickness of the entrance, if the elevation configuration is not appropriate, it is easy to slip between the strip and the work roll.
(7) Relative elevation configuration and threading stability of adjacent racks
The relative elevation drop of adjacent racks must be controlled. When there is a large drop, due to the inertia of the strip, the wear of the rear frame is prone to difficulties, which is more prominent when the rear frame is rolled at high speed. In the extreme case, the strip head hits the inlet side flower frame and scrap occurs. Therefore, it is necessary to control the diameter of the upper work roll of the adjacent frame.
(8) The relative elevation configuration of adjacent racks and the stability of steel throwing
After the front frame is thrown, the tension of the strip steel tail is lost. When there is a large drop in the relative elevation of adjacent racks, due to the inertia of the strip steel, the tail of the strip steel will slap the surface of the rear rack work roll, which will cause a tail-flick accident. This difficulty is more prominent in the high-speed rolling of thin strip steel at the rear stand. When the current frame elevation is lower than the rear frame, slap the lower work roll. When the current frame elevation is higher than the rear frame, slap the upper work roll. Tail-flicking accidents are often hereditary. When the F5 frame has a tail-flick accident, the F6 and F7 work rolls are not immune. For this reason, it is necessary to control the diameter of the upper work roll of the adjacent stand, especially the finishing post-rolling stand.
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