RU2240187C2 - Method of preparing sheet rolling rolls for operation - Google Patents

Abstract

FIELD: rolled stock production, possibly preparation of damaged rolling or backup roll to cold rolling.

SUBSTANCE: method comprises steps of mechanically taking off damaged layer of roll barrel and further shot hatching of; after occurring on rolling roll such flaw as build-up, realizing additional operations for taking off damaged layer by thickness 0.8 -1.2 mm; shot hatching and visually inspecting roll; repeating additional operations until complete removal of dark spot.

EFFECT: elimination of roll barrel crumbling out after occurring build-up type flaw of roll.

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Description

The invention relates to rolling production and can be used in preparation for cold rolling of a damaged working or backup roll of a sheet rolling mill quarto.

A known method of processing rolling rolls, including grinding and notching the barrel with a shot, and the notch is produced in two stages, first with a shot of a larger fraction, and then smaller [1].

A disadvantage of the known method is that it does not completely remove the barrel layer damaged during operation. This leads to premature crumbling of the roll and the need for unscheduled transshipment, which reduces the productivity of the rolling mill.

There is also known a method of notching rolling rolls, including preliminary grinding of the barrel and applying a roughness to it by a stream of shot [2].

This method of preparation of the roll also does not exclude the possibility of the formation of crumb barrels, which affects the quality of the strip and reduces the productivity of the mill.

The closest in technical essence and the achieved results to the proposed invention is a method of preparing for operation the working roll of a cold rolling mill, including mechanical removal of the damaged layer of the barrel by grinding and its subsequent notching by a shot blasting machine [3].

The disadvantages of this method are as follows. If the strip breaks during cold rolling, a fold of a strip of double or triple thickness gets into the gap between the work rolls or between the work roll and the support roll adjacent to it. This leads to local overheating of the roll and welding of the strip to its surface (defect “fat”). The consequence of local overheating of the hardened layer of the barrel is the formation at the site of the defect “fat” of the structure of tempered martensite, which has low hardness and is affected by germinal cracks. The operation of the work and backup roll with a damaged hardened layer leads to the appearance of chips and unscheduled transshipment of rolls, which reduces the productivity of the rolling mill. In addition, all metal rolled on rolls with a crumb is of poor quality and is rejected.

The technical problem solved by the invention is to eliminate the rolls of the roll barrel after the formation of the defect "fat", improving the quality of the strips and the performance of the mill.

The stated technical problem is solved in that in the known method of preparing for operation sheet rolls of a cold rolling mill, including mechanical removal of the damaged layer of the barrel and its subsequent notching by the shot, according to the proposal, after the formation of damage on the roll, the amount of removal is set to 2-4 mm, and a notch with a shot is carried out to a roughness of 2-3 μm R _a , after which a visual inspection of the barrel is carried out, and, in the presence of a dark spot at the site of damage, “fat”, perform additional operations mechanical removal of the damaged layer with a size of 0.8-1.2 mm, notching with a shot and visual inspection, and additional operations are repeated until the dark spot disappears.

The invention consists in the following. To prevent crumbs from the roll with the defect “fat”, the damaged layer of its barrel must be removed. For this, a mechanical removal is performed with a thickness of 2-4 mm from the surface of the barrel by grinding. If during the first machining the damaged layer was completely removed, then upon visual inspection after notching on the roll barrel, there is no dark spot in the place of the “fat” defect. But when the damage to the roll barrel has a large penetration depth and is not removed during the first machining, a dark spot is visually detected after the notch by the shot on the surface of the barrel. This is explained by the fact that since the tempered martensite has less hardness than the hardened layer of the roll barrel, as a result, when the notch is shot, the shot penetrates deeper into it and it acquires an increased surface roughness, which is perceived visually as a dark spot. To remove the damaged layer, the dark spot roll after inspection is again machined to remove the damaged layer with a thickness of 0.8-1.2 mm. Then the roll is again incised and subjected to visual inspection. The procedure is repeated until the dark spot disappears on the surface of the barrel, which indicates the complete removal of damage.

It was experimentally established that in most cases, damage to the roll barrel after a “brew” extends to a depth of 2-4 mm. If the removal rate is less than 2 mm, the damage will certainly not be removed after the first machining. This will lengthen and increase the cost of the roll preparation cycle. With a removal rate of more than 4 mm and a shallow penetration of the defect, the irrational consumption of the active (hardened) layer of the barrel increases. As a result, the consumption of rolls increases.

In cases where the mechanical removal of the damaged layer during additional operations is less than 0.8 mm, the number of treatment cycles increases until the defect is completely removed and the cost of preparing the damaged roll for operation. An increase in removal of more than 1.2 mm leads to an overspending of the active layer of the barrel and lengthening of the machining cycle, which is impractical.

For notching the roll to a roughness of less than 2 μm R _a , a low fractional energy is required, the difference in the depth of the notching of the hardened and tempered sections is small, therefore, spots with reduced hardness do not appear during visual inspection of the barrel. Notching by a shot with a roughness of more than 3 μm R _a worsens the light reflectivity of the barrel and makes spots of reduced hardness invisible.

An example implementation of the method

When the strip breaks in a continuous four-stand cold rolling mill 1700, the fold of the strip of triple thickness falls into the gap between the work rolls of the 4th stand. Compression of the fold by rolls made of 9KhF steel with a hardened working layer leads to a sharp increase in temperature and welding of the strip to the surface of the working roll (damage to “fat”). The heat-affected zone from the “bread” extends deep into the roll, and as a result of local overheating, the tempered layer of the barrel is released with a loss of hardness. It is impossible to predict the depth of propagation of the released layer during an emergency rush and “fat”. Further use of the work roll, the barrel section of which has a tempering structure after the “batch”, is not permissible, this will lead to the formation of chips.

A damaged work roll, after aging, for relaxation of internal stresses, is checked for cracks and, if they are absent, mounted on a roll grinding machine, where the first mechanical removal of the damaged layer is carried out using an abrasive wheel. The thickness of the removable layer H _n is 3 mm Then the work roll is rolled on a trolley into the chamber of the shot blasting machine and the barrel is incised by chipping with a cast-iron fraction of a fraction of 1.5 mm to a surface roughness of 2.5 μm R _a . The speed of rotation of the shot blasting wheel with a notch is 1500 rpm.

After cutting the entire barrel, a visual inspection of the surface is performed. If during the first mechanical removal the tempered layer was removed to the full depth, then there will be no dark spots on the roll barrel, and the roll can again be dumped into the rolling stand.

If, during the first removal, the tempered layer was not completely removed, then after notching, dark spots will be present in places of the barrel with lower hardness. A work roll with dark spots is again installed on a roll grinding machine and a second mechanical removal of the damaged layer with a thickness of N _p = 1.0 mm is performed.

The regrind roll is again subjected to notching by a shot blasting machine to a roughness of 2.5 μm R _a and is subjected to visual inspection. Resurfacing with a removal of Н _п = 1.0 mm and subsequent notches on a shot blast machine to a roughness of 2.5 μm R _{a are} repeated until the entire layer damaged in the “fat” is removed from the roll barrel, as evidenced by the absence of dark spots having lower hardness and higher roughness. The work roll, on the barrel of which dark spots do not appear after cutting, are put into operation and dumped into the crate.

Implementation options for the method of preparing for operation sheet rolling roll and indicators of their effectiveness are shown in the table.

From the table it follows that when implementing the proposed method (options 2-4), the elimination of the crumb of the barrel roll sheet after the formation of the defect "fat", improving the quality of the strips and the performance of the mill. With prohibitive values of the declared parameters (options 1 and 5), the specific consumption of rolls increases, downtime increases due to unplanned transshipment of rolls with a crumb, and the yield of defective products increases. Also, a high specific consumption of rolls with increased downtime and marriage occurs in the case of using the prototype method (option 6).

The technical and economic advantages of the proposed method consist in the fact that it allows you to accurately determine the presence on the polished sheet-rolling roll of areas with reduced hardness after the formation of the “fat” defect, and to completely remove it with a minimum consumption of the active layer of the barrel. Due to this, the crumbling of the working and back-up rolls in the stand is eliminated, downtime for unplanned transshipment is reduced, and the yield of defective products is reduced.

As a basic object in determining the effectiveness of the proposed method adopted the prototype method. Industrial application of the proposed method will increase the profitability of the production of cold-rolled sheets by 5-7%.

Sources of invention

1. A.S. USSR No. 1424890, IPC В 21 В 28/02, 1988

2. A.S. USSR No. 1667966, IPC В 21 В 28/00, 1991

3. L.I. Borovik, A.I. Dobronravov. Technology for the preparation and operation of rolls of sheet mills. M .: Metallurgy, 1984, p. 44, 54-55 - prototype.

Claims (1)

The method of preparation for operation of sheet rolls of a cold rolling mill, including mechanical removal of the damaged layer of the barrel and its subsequent notching by a shot, characterized in that after the formation of “weld” damage on the roll, the amount of removal is set to 2-4 mm, and the notching by the shot is carried out to a roughness of 2 -3 m R _a, and then conduct a visual inspection of the barrel, and the presence of dark spots on the spot "fat" damage, additional operations produce mechanical removal of the damaged layer of the magnitude 0.8-1.2 mm, NACE fraction and visual inspection ki, wherein additional operations are repeated until the disappearance of the dark spot.