EP2878391A1

EP2878391A1 - Method for the cold deformation of a continuous metal strip

Info

Publication number: EP2878391A1
Application number: EP12881842.4A
Authority: EP
Inventors: Ivan Timofeevich TOTSKY
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-07-27
Filing date: 2012-07-27
Publication date: 2015-06-03
Also published as: EP2878391A4; US20150135790A1; WO2014017944A1; RU2013147504A; RU2557843C2

Abstract

The invention relates to the pressure treatment of metals, specifically to producing a metal strip using cold deformation. The strip is consecutively drawn with back and front tension through bending devices. Moreover, the degree of deformation of a strip is regulated in each bending device by means of changing the ratio of the speed of the strip exiting a bending device to the speed of that strip entering that device, in such a way as to avoid a break in the metal, the required number of bending devices being selected on the basis of the total stretch factor of the strip and on its maximum allowable stretch factor. The result is increased deformation of the strip and reduced energy consumption.

Description

Technical Field

The invention relates to the non-cutting treatment of metals, specifically to producing a metal strip using cold deformation.

Prior Art

A method for cold deformation of a continuous metal strip in the production of welded tubes is known, comprising the drawing of the strip with a pulling device between three non-driven rollers of a bending device in which the central roller has a diameter smaller than the diameter of the outer rollers and together with the strip enclosing it at an angle of more than 180° is pressed to the outer rollers by tensioning the strip, the gap between them being larger than twice the thickness of the strip (USSR Certificate of Authorship 1500405, published August 15, 1989 ).
The shortcoming of the known method is the lack of regulation of the degree of deformation of the strip.
A method for cold deformation of a continuous metal strip in the production of welded tubes is known comprising its drawing with back and front tension caused by a tensioning and a pulling device respectively between three non-driven rollers of a bending device, wherein the central roller, which has a diameter smaller than the diameter of the outer rollers, is enclosed by the strip at an angle of more than 180° and is pressed together with it to the outer rollers by tensioning the strip, the gap between them being larger than twice the thickness of the strip, and regulating the degree of deformation of the strip by means of changing its tension, wherein the front tension does not exceed the level corresponding to the pulling tension in the stretched strip of 0,85 of the yield point of its metal (Patent RU 2412016, published February 20, 2011 ), which is taken as the most pertinent prior art.
The most pertinent prior art provides the possibility of regulating the degree of deformation of the strip; however, its shortcoming is the small degree of deformation of the strip and the increased specific energy consumption per unit of its deformation.

Disclosure of the Invention

The task underlying the invention is an increase in the degree of deformation of the strip and a decrease of the specific energy consumption per unit of its deformation.
The technical result is achieved thus: The method for cold deformation of a continuous metal strip comprises its drawing with back and front tension between three non-driven rollers of each bending device, wherein the central roller, which has a diameter smaller than the diameter of the outer rollers, is enclosed by the strip at an angle of more than 180° and is pressed together with it to the outer rollers by tensioning the strip, the gap between them being larger than twice the thickness of the strip, and regulation of the degree of deformation of the strip by means of changing its tension, wherein the front tension does not exceed the level corresponding to the pulling tension in the stretched strip of 0,85 of the yield point of its metal. The novelty is that the strip is consecutively drawn through a group of bending devices consisting of at least two bending devices, and through each separate bending device, at least through one separate bending device. The drawing of the strip is carried out with back and front tension in each bending device of the group and in each separate bending device. The drawing is carried out by means of a tensioning device arranged in front of the entry side of the bending device of the group that is the first in the course of the process, auxiliary pulling devices, the first of which is arranged behind the exit side of the last bending device of the group, while each of all others is arranged behind the exit side of each separate bending device except the last one, and a pulling device arranged behind the exit side of the last separate bending device. The degree of deformation of the strip is regulated in the group of bending devices and in each separate bending device within ranges whose upper limit does not exceed the maximum allowable stretch factor of the strip for the group of bending devices and for each separate bending device respectively. The regulation of the deformation is carried out in them by means of changing, respectively, the ratios of the speed at which the strip exits the last bending device of the group to the speed at which it enters the first bending device of the group and the speed at which the strip exits each separate bending device to the speed at which it enters that bending device.
By comparison with the most pertinent prior art, in the method according to the invention the degree of deformation of the strip increases several times over, and the specific energy consumption per deformation unit of the strip decreases several times over. The higher the number of bending devices in the group, up to an optimum limit, and the higher the number of separate bending devices, the higher the degree of deformation of the strip and the greater the decrease of specific energy consumption per unit of its deformation.
Since the increase in the deformation and the decrease in the specific energy consumption decelerate relatively to the increase in the number of bending devices in the group, and the costs for their exploitation rise proportionally to their number, the number of bending devices in the group is chosen with a view to minimizing the total costs.
The decrease in specific energy consumption per unit of deformation of the strip rises as the number of bending devices in the group increases because the total deformation of the strip within that group of devices increases while the front tension remains constant. A substantial part of the front tension of the strip, in the range of 80%, which remains after overcoming the resistance to its deformation in the last bending device of the group, is the front tension which draws the strip through the other bending devices of the group. Due to the decrease in the degree of front tension of the strip which pulls it out of the penultimate bending device of the group, the degree of deformation of the strip therein is substantially lower than in the last bending device of the group; however, it increases the total degree of deformation of the strip in the group of bending devices and therefore decreases the specific energy consumption per unit of its total deformation. An additional increase of the number of bending devices in the group (exceeding the two devices mentioned) increases the total degree of deformation of the strip in them, additionally decreasing the specific energy consumption per unit of its deformation. An increase in the number of bending devices in the group lowers the degree of necessary back tension of the strip which the tensioning device must provide.
Due to the proposed consecutive deformation of the strip in the separate bending devices, a substantial part (approximately 80%) of its front tension, which has not been spent on overcoming the resistance to the deformation of the strip in each separate bending device, is the basic component of the other front tension which pulls the strip out of the previous separate bending device or out of the group of bending devices. The amount of that other front tension is equal to the sum of the indicated component of the front tension and the tractive force of the auxiliary pulling device. The tractive force of the auxiliary pulling device is lower, approximately 4 times, than the indicated component of the front tension. That is, the consecutive deformation of the strip in the separate bending devices using the auxiliary pulling devices necessary for adding front tension up to a required standard makes it possible to provide a high deformation of the strip in each of these separate bending devices. With the indicated consecutive deformation of the strip, the decrease in specific energy consumption per unit of its deformation is the greater, the higher the number of separate bending devices and the corresponding number of auxiliary pulling devices is.
The maximum allowable stretch factor of the strip both in the group of bending devices and in each remaining separate bending device generally depends on the value of the ratio of the strip thickness to the diameter of the central roller. The thicker the strip and the smaller the diameter of the central roller, the higher the maximum allowable stretch factor of the strip.
Furthermore, the maximum allowable stretch factor of the strip in the group of bending devices depends on how many there are of them in the group. The more there are of them in the group, up to an optimum limit, the higher the maximum allowable stretch factor for the strip in the group of bending devices.
The necessary amount of separate bending devices depends on the required total stretch factor of the strip and on the maximum allowable stretch factor of the strip both in the group of bending devices and in each of the remaining separate bending devices.
The drawing schematically shows an embodiment of the proposed method for cold deformation of a metal strip by means of a tensioning device, a group of bending devices consisting of two bending devices, three separate bending devices, three auxiliary pulling devices and a pulling device.

Embodiment of the Invention

By means of a tensioning device 1, auxiliary pulling devices 2, 3, 4 and a pulling device 5 a continuous metal strip 6 is consecutively drawn with back and front tension between three non-driven rollers of each bending device 7 and 8 of a group and each separate bending device 9, 10 and 11.
Part of the traction force of the pulling device 5 is spent on overcoming the resistance to deformation of the strip 6 in the bending device 11. The remaining part of this traction force helps the auxiliary pulling devices 4, 3 and 2 to overcome the resistance to deformation of the strip 6 in the bending devices 10, 9, 8 and 7 and the resistance of the tensioning device 1. This remaining part of the traction force of the pulling device 5 is simultaneously the back tension of the strip 6 entering the bending device 11.
For the deformation of the strip in the other bending devices the situation is similar.
For instance, part of the total traction force, including the traction force of the auxiliary pulling device 3 and the part of the traction force of the auxiliary pulling device 4 and the pulling device 5 that has not been spent on the deformation of the strip 6 in the bending devices 10 and 11, is spent on overcoming the resistance to deformation of the strip 6 in the bending device 9. The remaining part of this total traction force helps the auxiliary pulling device 2 to overcome the resistance to deformation of the strip 6 in the group of bending devices 8 and 7 and the resistance of the tensioning device 1. This remaining part of the total traction force is simultaneously the back tension of the strip 6 entering the bending device 9.
The degree of deformation of the strip 6 in the group of bending devices 7 and 8 is regulated by means of changing the ratio of the speed of its exit from this group, facilitated by the auxiliary pulling device 2, to the speed of its entry into this group of bending devices, facilitated by the tensioning device 1. This change is executed within a range whose upper limit does not exceed the maximum allowable stretch factor of the strip in this group of bending devices. The maximum allowable stretch factor is the maximal stretch factor of the strip which enables its continuous deformation process without disruptions.
The degree of deformation of the strip 6 in each separate bending device 9, 10 and 11 is regulated by means of changing the ratio of the speed of its exit from the corresponding bending device to the speed of its entry into this device. The regulation is executed within a range whose upper limit does not exceed the maximum allowable stretch factor of the strip for each of these bending devices. The exit speed of the strip from each bending device 9, 10 and 11 is regulated by means of the auxiliary pulling devices 3 and 4 and the pulling device 5, respectively. The entry speed of the strip into each bending device 9, 10 and 11 is regulated by means of the auxiliary pulling devices 2, 3 and 4, respectively.
The total degree of deformation of the continuous original strip is regulated in such a way that after deformation it obtains its predetermined thickness irrespectively of the lengthwise differences in thickness of the original strip.
Most preferred is the following embodiment of the regulation of the total deformation of the strip.
By means of the auxiliary pulling device 2 a constant exit speed of the strip 6 from the bending device 8 of the group is provided, while by means of the tensioning device 1 the entry speed of the strip 6 into the bending device 7 of the group is regulated depending on the thickness of the original strip at the entry into this bending device. This regulation is executed in such a way that the thickness of the strip at the exit from the bending device 8 of the group is constant, irrespectively of the original lengthwise differences in thickness of the strip. During the regulation, the ratio of the exit speed of the strip 6 from the bending device 8 to its entry speed into the bending device 7 is provided within a range whose upper limit does not exceed the maximum allowable stretch factor of the strip 6 in the group of bending devices 7 and 8.
By means of the auxiliary pulling devices 3, 4 and the pulling device 5 the constant level of the exit speed of the strip 6 from each of the other separate bending devices 9, 10 and 11 respectively, is provided, wherein its stretch factor in each of them does not exceed its maximum allowable value. These speed levels of the strip are chosen in such a way that a total stretch factor of the strip in all bending devices 7, 8, 9, 10 and 11 is provided which is sufficient to obtain the required thickness of the finished strip.
An experiment showed that during a deformation of the strip by the proposed method and its drawing through the group of bending devices consisting of two devices and through each of three separate bending devices, the deformation of the strip, measured as the size of its elongation, increased 4.4-fold compared to the most pertinent prior art while the total energy consumption increased 1.6-fold, and the specific energy consumption per unit of deformation of the strip fell 2.8-fold.
Thus the proposed method of cold deformation of a continuous metal strip facilitates a multiple increase of the degree of deformation of the strip and a multiple decrease of the specific energy consumption for its deformation by comparison to the most pertinent prior art. Due to this, the method can be used to replace cold rolling of a metal strip.
The usage of the proposed method to replace cold rolling of a metal strip facilitates a decrease in expenditure of assets on obtaining equipment and constructing a plant for strip deformation, a substantial decrease in the wear of the deforming instrument, a decrease in the roughness of the strip surface, a more accurate manufacturing of the strip with respect to thickness and a decrease in energy consumption for its deformation.
The foundation for each of the above-listed advantages which the proposed method for cold deformation of a continuous metal strip has by comparison to its cold rolling is given below.
With equal deformation parameters of the same metal strip, the amount of pressure of the metal on the rollers during its cold rolling is approximately 5-8 times higher than the amount of pressure of the metal on the outer rollers of the bending device during its cold deformation according to the proposed method. Therefore the mass of the equipment of the plant for cold deformation of a continuous metal strip according to the proposed method is several times smaller than the mass of the equipment of a continuous rolling mill for its cold rolling. Correspondingly, the costs for the equipment and the costs for the construction of such a plant will be several times lower compared to the costs for the equipment and the costs for the construction of a continuous rolling mill.
In the cold rolling of a metal strip its speed in the creep zone of the deformation area is smaller, and in the forward slip zone of the deformation area it is greater than the circumferential speed of the rollers. The slipping in these zones of the deformation areas of the strip with respect to the rollers and the high specific metal pressure on the rollers results in their intensive wear.
During the deformation of the strip according to the proposed method, the rollers of each bending device create two deformation areas situated in the zones where the bending of the strip changes direction. In these areas the strip is subjected to a shear deformation practically without slipping with respect to the rollers. The absence of slipping of the strip with respect to the rollers and the reduced specific metal pressure on the rollers makes it possible to reduce their wear tenfold compared to the wear of the rollers in the cold rolling of a strip. This also facilitates a low roughness of the strip surface. This specifically concerns the surface contacting the central rollers of the bending devices, since the central rollers have a small diameter and therefore facilitate a good processing of the strip surface.
The techniques used in the technology provide a high accuracy of the regulation of the speed of the drives. Therefore the regulation of the deformation of the strip by means of regulating the speed of the drives of the tensioning device, the auxiliary pulling devices and the pulling device provide a high accuracy of the deformation of the strip in the bending devices and thus provide a high accuracy of the manufacturing of the strip with regard to thickness.
It is known that with equal parameters of deformation of the same strip by different techniques the energy consumption is minimal when the technique of shear deformation is used, which is also employed in the proposed method. Furthermore, in the proposed method for deformation of a strip there is no slipping of the deformed metal with respect to the rollers, thus no energy needs to be spent on overcoming frictional forces developing when there is such a slipping, which happens when a strip is rolled.
By comparison to cold rolling of a continuous metal strip the proposed method of cold deformation of a continuous metal strip allows a decrease by approximately 15-35% of energy consumption for its deformation. The smaller the diameter of the central rollers of the bending devices and the greater, up to an optimum limit, the number of bending devices in their group, which is situated in a section between the tensioning device and the auxiliary pulling device that is the first in the course of the process, the greater is the amount of energy saved.

Claims

Method for cold deformation of a continuous metal strip, comprising its drawing with back and front tension between three non-driven rollers of a bending device, wherein the central roller, which has a diameter smaller than the diameter of the outer rollers, is enclosed by the strip at an angle of more than 180° and is pressed together with it to the outer rollers by tensioning the strip, the gap between them being larger than twice the thickness of the strip, and regulation of the degree of deformation of the strip by means of changing its tension, wherein the front tension does not exceed the level corresponding to the pulling tension in the strip of 0,85 of the yield point of its metal, characterised in that the strip is consecutively drawn with back and front tension in each bending device first through a group of bending devices consisting of at least two bending devices, and then through each separate bending device, at least through one separate bending device, by means of a tensioning device arranged in front of the entry side of the bending device of the group that is the first in the course of the process, auxiliary pulling devices, the first of which is arranged behind the exit side of the last bending device of the group, while all others are arranged behind the exit side of each separate bending device except the last one, and except a pulling device arranged behind the exit side of the last separate bending device, while the degree of deformation of the strip is regulated in the group of bending devices and in each separate bending device within ranges whose upper limit does not exceed the maximum allowable stretch factor of the strip for the group of bending devices and for each separate bending device respectively, by means of changing, respectively, the ratios of the speed at which the strip exits the last bending device of the group to the speed at which it enters the first bending device of the group and the speed at which the strip exits each separate bending device to the speed at which it enters that bending device.