RU2113297C1 - Method for operation of backing-up roll - Google Patents

Abstract

FIELD: rolling; may be used in quarto mill for hot and cold rolling of sheet steel. SUBSTANCE: method includes alternating of operation of backing-up roll in contact with adjacent working roll and regrinding for removal of cold work layer. Value of removal in regrinding is preset equalling 0.2-0.3 length of contact curve of backing-up roll with adjacent working roll to reduce expandable coefficient of backing-up roller cost of sheet rolled products. EFFECT: higher efficiency. 2 cl, 1 dwg , 1 tbl

Description

 The invention relates to rolling production and can be used on quarto mills for hot and cold rolling of sheet steel.

 There is a method of operating a backup roll, including repeated alternation of low-temperature tempering after cyclic elastic-microplastic deformation of the surface layer of the working part of the roll and determining the maximum degree of strain hardening based on periodic measurements of hardness with the first low-temperature tempering as the number of loading cycles reaches 42.5-55% from the limit [1].

 This method of operation is characterized by a large expenditure coefficient of the backup rolls, requires additional low-temperature holidays, which increases the cost of production of rolled products.

 There is also known a method of operating a back-up roll, including creating a surface riveted layer with the joint rotation of the pressed work and back-up rolls, determining the intensity of strain hardening to increase hardness. Then, the back-up roll is thrown out of the stand and the riveted layer is mechanically removed with a removal value that is directly proportional to the increase in barrel hardness [2].

 A disadvantage of the known method is the need for regrinding of the back-up roll both before filling into the rolling stand (after creating the surface riveted layer), and after the end of the campaign to remove the riveted layer and surface defects. Double the number of resurfacing increases the cost coefficient of the backup rolls and the cost of production of sheet metal.

 Closest to the proposed one is a method of operating a support roll of a sheet rolling mill quarto, including alternating its work in contact with an adjacent work roll during rolling with resurfacing to completely remove the riveted layer before the next filling in the stand. The backup roll is operated until the hardened surface layer is fully developed [3].

 The disadvantages of this method are the high expenditure coefficient of the backup rolls and, as a consequence, the high cost of production of sheet metal. (Under the consumption coefficient of the backup rolls, we understand the ratio of the mass of the consumed backup rolls to the mass of the rolled strips, (kg / t)).

 The purpose of the invention is to reduce the expenditure coefficient of the backup rolls and reduce the cost of production of sheet metal.

 This goal is achieved by the fact that in the known method of operating the backup roll of a sheet rolling mill quarto, including the alternation of its work in contact with an adjacent work roll with resurfacing to remove the riveted layer, according to the proposal, the amount of removal during resurfacing is set to 0.2-0.3 length arcs of contact of the backup roll with an adjacent work roll.

 Known and proposed technical solutions have the following common features. Both of them are ways of operating the back-up roll of a sheet rolling mill quarto. Both include alternating the work of the back-up roll in contact with an adjacent work roll with resurfacing to remove the hardened layer.

 The differences of the proposed method are that the amount of removal during grinding is set equal to 0.2-0.3 of the length of the arc of contact of the backup roll with an adjacent work roll, whereas in the known method, the amount of removal is equal to the thickness of the riveted layer.

 These distinctive signs exhibit in the aggregate new properties that are not inherent in them in the known sets of features and consist in reducing the expenditure coefficient of the backup rolls and the cost of production of sheet metal.

 This indicates that the proposed technical solution meets the criterion of "materiality of differences."

 The drawing shows a contact diagram of the backup roll with an adjacent worker.

The essence of the invention is as follows. During the rolling process, the work roll 1 is rolled along the backup roll 2, forming a riveted layer 3 of thickness H in the backup roll 2. In this case, in the riveted layer 3 from the surface of the backup roll 2, an alternating (reverse) voltage τ _xy acts to a depth Y (layer 4), varying from its maximum positive value + τ _{xy max} to the maximum negative -τ _{xy max} value in a symmetrical cycle. The area of action of the counter-directional shear stresses τ _xy in the backup roll 2 is similar to the advance and lag zones existing during rolling in the deformation zone, where the shear stresses are also opposite, i.e. change sign when passing through a neutral section. Indeed, the contact interaction of the worker 1 and the support 2 rolls can be interpreted as the process of rolling by the work roll 1 a less hard surface of the support roll 2 with the formation of a stress state in the surface layer of the support roll 2, similar to the stress state in the rolled strip.

As a result of repeated cyclic exposure to shear stress τ _xy , which either compresses or stretches the metal of the backup roll 2, in zone 4, the metal softens to a depth Y, nucleation and development of fatigue cracks occurs. The metal of the backup roll 2, lying at a depth greater than Y, to which the destructive action of the reverse voltage τ _xy does not apply, is in a hardened (due to hardening) state. Therefore, if during grinding, remove only the softened and fatigue cracked layer 4 of the backup roll 2, then a riveted defect-free metal capable of effectively resisting the formation of fatigue cracks will be removed onto its surface, and metal removal from the surface of the backup roll 2 for grinding will be reduced. This ensures a reduction in the cost coefficient of the backup rolls and the cost of production of sheet metal.

где
q - погонное межвалковое давление;
Q_раб и Q_оп - упругие постоянные материала рабочего и опорного валков;
R_раб и R_оп - радиус рабочего и опорного валков.The thickness Y of the layer 3 depends on the mutual pressure of the worker 1 and the supporting 2 rolls, their diameters and the properties of the steel from which the rolls are made. Using the polarization-optical modeling method, it was established experimentally that the Y value is directly proportional to the contact length l _{g of the} working 1 and supporting 2 rolls with a proportionality coefficient k = 0.2-0.3. The length of the contact arc l _g is determined experimentally or analytically from the solution of the well-known Hertz equation:

Where
q is the linear roll pressure;
Q _slave and Q _op - elastic constants of the material of the working and backup rolls;
R _slave and R _op - the radius of the working and backup rolls.

 It was experimentally established that if k is less than 0.2, then the thickness of the metal layer removed from the surface of the back-up roll during resurfacing will be insufficient, i.e., a part of the damaged metal containing fatigue cracks will remain on the back-up roll. This leads to the appearance of chips in the backup roll, an increase in the flow coefficient of the backup rolls. When the value of k is more than 0.3, the riveted defect-free layer is removed and the hardness of the surface of the backup roll decreases. This leads to an increase in the removal of metal, a decrease in the resistance of the backup roll, an increase in the expenditure coefficient of the backup rolls and the cost of production of sheet metal.

Example. New back-up rolls made of 9KhF steel with a barrel diameter of 1,600 mm are dumped into the 5th stand of a five-stand mill 2030 quarto of endless cold rolling. Then, a couple of work rolls made of 9x2B steel with a barrel diameter of 615 mm are heaped into the same stand and cold strips of 08Yu steel are cold rolled to a final size of 0.6 x 1700 mm. Under these conditions, the length of the arc of contact of the backup roll of the 5th stand with an adjacent worker l _g = 5.2 mm

After 12 days of work, surface defects (crumbs) appear on the support rolls of the 5th stand, so the support rolls are thrown out of the stand and sent for regrinding. Using an abrasive wheel from the drums of the backup rolls, remove the damaged surface layer with a thickness of:
Y = 0.25 1 _g = 0.25 • 5.2 mm = 1.3 mm.

 After removal of the damaged surface layer, a defect-free riveted metal having increased resistance to crumbling is output to the surface of the backup roll. The reconstructed backup rolls are then again dumped into the mill stand 2030 and cold rolling of sheet steel is carried out. The cycles are repeated until the working layer of the backup rolls is fully developed.

 Variants of the method and performance indicators are shown in the table.

 As follows from the table, when implementing the proposed method (options 2-4), a reduction in the expenditure coefficient of the backup rolls and the cost of production of sheet metal is achieved. With prohibitive values of the declared parameters (options 1 and 5), the expenditure coefficient of the backup rolls and the cost of production of sheet metal increase. The same holds for the prototype method (option 6).

 The technical and economic advantages of the proposed method consist in the fact that when the amount of removal from the surface of the back-up roll when grinding a metal layer with a thickness of 0.2-0.3 lengths of the arc of contact of the back-up roll with an adjacent worker during the rolling process, only the damaged part of the riveted layer is removed. Due to this, the removal during polishing is minimal, the resistance of the surface of the backup roll increases, and the expenditure coefficient of the backup rolls and the cost of production of sheet metal are reduced.

 The prototype method is taken as the base object. The application of the proposed method will increase the profitability of sheet rolling production by 6-8%.

Claims (1)

 A method of operating a support roll of a sheet rolling mill quarto, including the alternation of its work in contact with an adjacent work roll with regrinding to remove the riveted layer, characterized in that the amount of removal during refinishing is set equal to 0.2 - 0.3 of the arc length of the contact of the support roll with an adjacent work roll.

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