This invention generally relates to a grooved roll for a reducer (reducing mill) and to a reducer which are used for manufacturing pipes. More particularly, the present invention relates to a grooved roll for a reducer and to a reducer which can markedly suppress uneven variations in the circumferential distribution of thickness increases, which are a direct cause of the occurrence of polygonization, and which can thereby essentially eliminate the occurrence of polygonization even when a plurality of types of pipes differing in parameters such as wall thickness, outer diameter, and material are subjected to reducing under different conditions.
Sizers and stretch reducers, which are the most common types of reducers, are normally constituted by a plurality of pipe rolling stands (such as 8-28 stands) installed in tandem, with each stand being equipped with grooved rolls of the two-roll or three-roll type. For example, in the three-roll reducing method using grooved rolls of the three-roll type, the grooved rolls are installed in each stand so that the grooved rolls in adjoining stands have a phase angle (phase difference) of 60 degrees with respect to each other. A pipe undergoes rolling by passing through the groove (pass) formed from the grooved rolls each having an elliptical groove shape with no tool being inserted into the interior of the pipe and in the case of a stretch reducer with tension being applied to the pipe between adjoining stands. The rolling greatly decreases the outer diameter of the pipe, with the wall thickness generally increasing in the case of a sizer and generally decreasing in the case of a stretch reducer. In the two-roll reducing method using grooved rolls of the two-roll type in each stand, there is a phase difference of 90 degrees between the grooved rolls of adjoining stands.
Because the roll grooves each have an elliptical shape, a pipe which is subjected to reducing by grooved rolls is strongly deformed in the central portion in the axial direction of each grooved roll (referred to as the groove bottom zone), and the rolling force decreases towards both end portions of the groove (the end portions of the flange zones on both sides of the groove bottom zone). Since a tool is not present in the interior of the pipe, when the pipe is subjected to several passes through rolling stands, so-called polygonization takes place. Polygonization is a phenomenon in which the transverse cross-sectional shape of the inner surface of a pipe becomes hexagonal (or tetragonal in a two-roll reducing method).
A pipe which has developed polygonization has a polygonal transverse cross-sectional shape on its inner surface, but the outer surface of the pipe which has been finished in the reducer is nearly circular. Therefore, the wall thickness of the pipe exhibits wall thickness variations (thickness deviations) in which the wall thickness periodically increases or decreases in the circumferential direction (three or six times in the case of three-roll reducing). Polygonization is known to occur particularly easily when carrying out rolling with a reducer of a pipe having an intermediate or large wall thickness in which the ratio of the finished wall thickness to the finished outer diameter is 8% or greater.
As described in below-listed Patent Documents 1 and 2, the degree of this polygonization varies with the rectangularity of a roll groove, which is expressed by the ratio (CLE/CLG) of the distance CLE from the edge portion entrance surface to the roll exit surface with respect to the distance CLG from the roll groove bottom entrance surface to the roll exit surface. A known countermeasure against polygonization is the rectangularity design method in which the rectangularity is suitably selected.
Patent Document 3 discloses suppressing polygonization by suitably setting the amount of working in each stand of a plurality of roll stands having grooved rolls. Patent Document 4 discloses minimizing polygonization by setting the rotational speed of grooved rolls in each stand to a suitable value so that the overall elongation of a rolled pipe is made uniform by controlling the rotational speed of drive motors which rotationally drive the grooved rolls in each stand of a stretch reducer.
Patent Document 5 discloses suppressing polygonization by water cooling of portions of a pipe during reducing of the pipe. Patent Documents 6 and 7 disclose suppressing polygonization during sizing rolling by adjusting the roll position in each stand. Patent Documents 8-10 disclose suppressing polygonization by suitably setting the phase angle of the rolls in each stand during reducing of a pipe.
Patent Document 1: JP H07-314013 A1
Patent Document 2: JP H08-19808 A1
Patent Document 3: JP H11-151506 A1
Patent Document 4: JP 2001-71012 A1
Patent Document 5: JP 2001-129603 A1
Patent Document 6: JP 2000-158015 A1
Patent Document 7: JP 2000-334504 A1
Patent Document 8: JP 2005-46874 A1
Patent Document 9: JP 2005-305447 A1
Patent Document 10: JP 2005-169466 A1
However, with the techniques disclosed in Patent Documents 1-3, the amount of polygonization, which varies in accordance with conditions such as the wall thickness and tension of a pipe, cannot always be suppressed to a constant range under all conditions. Similarly, the techniques disclosed in Patent Documents 4, 6, and 7 can only slightly decrease the amount of polygonization which occurs, and they cannot suppress polygonization to a fixed range regardless of variations in conditions.
The technique disclosed in Patent Document 5 is premised on variation in the heating of a pipe being the main cause of polygonization. However, if the temperature of a pipe during rolling is locally decreased by water cooling, cooling water unavoidably splashes or flows to portions other than the desired portion, and it is extremely difficult to control the temperature only of a specific portion of a pipe. Accordingly, it is thought to be difficult to stably suppress polygonization with this technique.
In order to carry out the techniques disclosed in Patent Documents 8-10, it is necessary to adjust the phase angle of the grooved rolls of each stand. For this purpose, it is necessary to change the conditions for reducing, and the rectangularity of a groove, which is a direct cause of polygonization, fluctuates, so this method cannot stably suppress polygonization.
Thus, when reduction of a plurality of types of pipes having different parameters such as wall thickness is carried out in a stretch reducer under different conditions using a conventional method as disclosed in Patent Documents 1-10, it is extremely difficult to stably suppress polygonization to an extent that it is essentially eliminated. The present invention provides a grooved roll for a reducer which solves such problems.
A grooved roll for a reducer according to the present invention has a groove having a groove bottom zone including the center in the roll axial direction and flange zones adjoining both sides of the groove bottom zone, characterized in that the surface of the groove has a friction distribution in the roll axial direction such that the frictional force with respect to a material being rolled in the groove bottom zone is greater than the frictional force with respect to a material being rolled in the flange zones.
In this context, the “groove bottom zone” of the groove of a grooved roll means the region which is deeper than the midpoints of the angles between the deepest point of the groove (normally the center point in the axial direction of the groove) and the shallowest points of the groove (normally both ends of the groove) as viewed from the center of the stand (the midpoints being at the intersection between a line bisecting the angle and the surface of the groove). In this context, the “flange zones” of the groove of a grooved roll mean the two regions on both sides of the groove bottom zone remaining after removing the groove bottom zone from the groove, namely, the two side regions which are shallower than the midpoints of the angles between the deepest point and the shallowest points as viewed from the center of the stand.
The term “roll axial direction” as used herein naturally means the direction of the rotational axis of a grooved roll which is rotationally driven. In the case of grooved rolls of the three roll type, the three grooved rolls have roll axial directions which are at 120 degrees with respect to each other.
When the frictional force between the roll surface and a material being rolled in the groove bottom zone is not constant but varies in the roll axial direction in the groove bottom zone, the average value thereof is considered the frictional force in the groove bottom zone. In this case, the frictional force is preferably highest at the center of the groove bottom zone in the roll axial direction. Similarly, when the frictional force in the flange zones of the groove varies, the average value is used as the frictional force.
In a grooved roll for a reducer according to the present invention, the groove bottom zone of the groove preferably has a greater surface roughness than the flange zones, whereby the above-described friction distribution is formed. The surface roughness of the groove bottom zone and the flange zones is made the average value of each when the surface roughness varies in these regions.
From another standpoint, the present invention is a reducer characterized by having the above-described grooved roll according to the present invention and a is friction distribution producing means for producing the above-described friction distribution in the roll axial direction on the groove surface.
The means for producing a friction distribution in the roll axial direction in a reducer can be (a) a surface working device which can work the peripheral surface regions of at least a portion in the axial direction of the groove surface such that the surface roughness of the groove bottom zone of the groove is different from the surface roughness of the flange zones, or (b) a lubricity modifier applicator which can apply a lubricity modifier to the peripheral surface region of at least a portion in the axial direction of the groove surface so that the applied amount and/or the type of a lubricity modifier differs between the groove bottom zone and the flange zones.
The surface working device is preferably an on-line roll grinding machine which can perform grinding of a grooved roll while it remains mounted on a reducer. A lubricity modifier is intended to encompass both a lubricant (antifriction or friction decreasing agent) and an antislipping (friction increasing) agent.
According to the present invention, buildup of the circumferential distribution of wall thickness increases, which is a direct cause of the occurrence of polygonization, can be radically improved. As a result, the occurrence of polygonization can be essentially eliminated even when a plurality of types of pipes having different parameters such as wall thickness, outer diameter, or material undergo reducing under different conditions.
Below, a grooved roll for a reducer and a reducer according to the present invention will be explained more concretely while referring to the accompanying drawings. A three-roll stand with grooved rolls which is the most common type used in a reducing mill will be taken as an example, but a grooved roll for a reducer according to the present invention can be similarly applied to a grooved roll of a two-roll or four-roll stand with grooved rolls.
As shown in this figure, the fact that the axial strain φ1 of a pipe 1 is nearly uniform around the entire periphery in the circumferential direction can be seen from the upper half of the graph of
The present inventors discovered that the non-uniform pattern of the distribution of strains in the thickness direction, namely, the distribution of increases in wall thickness can be changed by varying the coefficient of friction on the flange zones of a grooved roll and the coefficient of friction of the groove bottom zone, and they discovered that by utilizing this phenomenon, the circumferential distribution of wall thickness increases, which is a direct cause of the occurrence of polygonization, can be suppressed.
Using
Based on this knowledge, when carrying out reducing of a pipe using a grooved roll according to the present invention, by making the frictional force between the roll surface and a material being rolled in the groove bottom zone of a groove larger than the frictional force between the roll surface and a material being rolled in the flange zones of a groove by a convenient means, namely, by imparting a coefficient of friction distribution to the surface of the groove such that the coefficient of friction in the flange zones is smaller than the coefficient of friction in the groove bottom zone, the range of variation of the distribution of wall thickness increase in the circumferential direction of a pipe, which is a direct cause of polygonization, can be minimized even if reducing is carried out on pipes having different wall thicknesses under different conditions. As a result, polygonization can be reduced and essentially eliminated.
Next, some preferred embodiments of a grooved roll for a reducer according to the present invention and a reducer equipped with such rolls will be explained.
First Embodiment
A grooved roll for a reducer of this embodiment has a groove in which the groove surface has a coefficient of friction varying in the roll axial direction. Namely, the groove surface has a friction distribution in the roll axial direction such that the coefficient of friction in the groove bottom zone including the center in the roll axial direction is larger than the coefficient of friction in the flange zones on both sides of the groove bottom zone.
In the illustrated example, the surface of the groove of the grooved roll has a friction distribution in the roll axial direction such that the coefficient of friction which produces a frictional force in at least a portion of the groove bottom including the center in the roll axial direction is 0.3 and the coefficient of friction which produces a frictional force in the flange zones on both adjoining sides of the groove bottom zone is 0.1. The portions of the groove bottom zone close to the flange zones have a coefficient of friction of 0.1, but on average, the coefficient of friction of the groove bottom zone is larger than the coefficient of friction of the flange zones, which is 0.1.
The friction distribution in the roll axial direction of the groove surface of a grooved roll is not limited to one which varies in a step-wise manner as shown in the graph of
The graphs in
In this embodiment, it is not necessary to limit the values of the coefficient of friction to specific ranges as long as the distribution of the coefficient of friction of the surface of the groove can be adjusted so that the frictional force of the roll surface in the groove bottom zone including the center in the roll axial direction is larger than the frictional force of the roll surface in the flange zones adjoining the groove bottom zone.
As stated above, when the coefficient of friction of the surface of the groove of a grooved roll varies, for example, as shown in
In a grooved roll for a reducer according to this embodiment, a grooved roll having the above-described friction distribution can be obtained by making the surface roughness of the groove bottom zone of the groove including the center in the roll axial direction larger than the surface roughness of the flange zones on both sides of the groove bottom zone.
For example, as shown by the cross section in
However, the present invention is not limited to such a mode in which the distribution of the coefficient of friction has three equally divided regions, and it can have 3 regions, one of which comprises all or a portion of the groove bottom zone including the center in the roll axial direction, the other two regions including the flange zones which adjoin the groove bottom zone (and which may include the remainder of the groove bottom zone). In this case, a step-wise friction distribution like that shown in
Surface roughening of the groove surface in region B can be carried out by initial masking of regions other than the central region B, i.e., the two regions A and C positioned at both ends of region B, and then carrying out shot blasting. It is also possible to carry out a method in which lattice-shaped surface scratches with each unit of the lattice having a length of 3 mm, for example, on a side are imparted with a grinder, or a method in which the below-described machining is carried out to form surface irregularities.
A grooved roll for a reducer according to this embodiment can be manufactured by performing working of the groove surface such that the surface roughness varies in the roll axial direction in a manner as described above. Examples of a means for such roll surface working are shot blasting and grinding. The surface roughness may also be previously afforded to the roll surface by a mechanically working means such as dimple formation or grid formation.
These methods of surface working can be suitably combined to make the surface roughness of at least a portion of the groove bottom zone including the center in the roll axial direction larger than the surface roughness of the flange zones on both sides adjoining this groove bottom zone. The groove surface of the roll may initially be worked by machining with a lathe to obtain a mirror surface, and then the above-described various types of surface working are employed in combination to form minute irregularities on the surface of the groove such that the shape of the irregularities varies along the roll axial direction. As viewed microscopically, these irregularities increase frictional force by catching on a pipe, resulting in the formation of a friction distribution in such a manner that the frictional force with respect to a pipe varies in the roll axial direction. A grooved roll having a friction distribution in the roll axial direction which gradually varies on the surface of the groove as shown in
A grooved roll for a reducer according to this embodiment has a friction distribution such that the frictional force with respect to a pipe is not constant in the roll axial direction. Instead, the frictional force with respect to a pipe in the groove bottom zone including the center in the roll axial direction is larger than the frictional force with respect to the pipe in the flange zones adjoining the groove bottom zone. As a result, metal flow particularly in the direction towards the flanges can be suppressed, whereby a suitable distribution in the circumferential direction of the wall thickness increase is attained and the occurrence of polygonization is suppressed.
It is of course desirable to suppress metal flow in the circumferential direction over the entire circumference of a pipe. However, if the frictional force is excessively decreased, a material to be rolled can no longer be gripped by a roll. Therefore, the groove bottom zone preferably exerts a suitable frictional force. From this standpoint, the coefficient of friction with respect to a material being rolled of the roll surface at the center of the groove bottom zone preferably has an average value of at least 0.2.
A reducer according to this embodiment comprises the above-described grooved roll and a friction distribution producing means for producing the above-described friction distribution.
The friction distribution producing means can be a surface working device which can perform working such that the groove bottom zone including the center in the roll axial direction of a groove and the flange zones adjoining both sides of the groove bottom zone have different levels of surface roughness.
This surface working device is preferably an on-line roll grinding machine or surface working device which can perform grinding of a grooved roll while the roll remains mounted on a reducer. The surface condition of the groove of a grooved roll of a reducer varies as the grooved roll is used. As surface bumps wear with time, irregularities in the surface (the surface roughness) gradually decrease. Therefore, in this embodiment, the time at which the height or the depth of irregularities in the roll surface of a groove decreases to a predetermined value or less or the time at which the effect of suppressing thickness variations markedly decreases is empirically determined based on the relationship between the number of roll passes and the change in the roll surface condition. Based on this empirical value, the timing of grinding is determined, and based on this timing, surface working is carried out on the groove of a grooved roll in an on-line state using the on-line grinding machine or surface working device such that the surface roughness and accordingly the frictional force exerted by the groove bottom zone becomes greater than that exerted by the flange zones. It is usually sufficient to carry out this surface working only on the groove bottom zone, but if necessary, it can also be carried out on the flange zones.
The on-line roll grinding machine 10 shown in
As shown in this example, in a preferable system, the actuator 14 and the computer 15 are connected by a network, and the movement, the operational timing, and the like of the actuator 14 are controlled by the computer 15.
The on-line grinding machine 11 shown in
In either of these cases, the actuator is preferably connected to a computer by a network, and the movement and operational timing of the actuator are controlled by the computer. In either of these cases, the grinding machine which is used is one which can grind at least a portion of the groove bottom zone of a grooved roll and which can impart a desired surface roughness with the whetstone mounted on the grinding machine. Such an on-line grinding machine is preferably provided on all of the stands, but it is also possible for one on-line grinding machine to be shared by all the stands or by a plurality of stands. It is also possible to use two or more types of whetstones so as to impart different surfaces to the groove bottom zone and the flange zones such that the surface roughness of the groove bottom zone is greater.
In this embodiment, when it is still not possible to prevent polygonization by a method of imparting a friction distribution to the roll surface according to this invention, the effect of suppressing polygonization is preferably supplemented by suitably varying the operational parameters such as the stretch of the overall rolling mill, the rotational speed of the rolls, or the like in accordance with conventional operational design techniques. When applying a lubricant to the grooved rolls of any of the stands, the lubricant may be uniformly applied to the surface of grooved rolls. Alternatively, as explained below for a second embodiment, it is possible to vary the applied amount or the type of a lubricant.
Second Embodiment
A grooved roll for a reducer according to this embodiment is different from the above-described first embodiment in that the surface roughness of the groove of a grooved roll may be the same in the groove bottom zone including the center in the roll axial direction and in the flange zones adjoining both sides of the groove bottom zone. Namely, the surface of the groove may have a uniform overall surface roughness. Instead, the amount of lubricant applied to the roll surface in a portion of the groove bottom zone including at least the center of the groove in the roll axial direction is made smaller than the amount applied to the roll surface in the flange zones. As a result, the groove surface has a friction distribution in the roll axial direction such that the frictional force in the groove bottom zone is larger than the frictional force in the flange zones.
Such a friction distribution can be achieved not only by varying the applied amount of a lubricant but by varying the type of lubricant, namely, by applying a lubricant having a higher lubricity (having a greater friction reducing effect) to the flange zones and applying a lubricant having a lower lubricity or applying a friction increasing agent (anti-slipping agent) to the groove bottom zone. Namely, application can be carried out using at least one type of lubricity modifier selected from lubricants and friction increasing agents. It is also possible to vary both the type and applied amount of a lubricity modifier.
In a reducer according to this embodiment, a lubricity modifier applicator which can perform application of a lubricity modifier such that the applied amount and/or type of a lubricity modifier in a portion in the roll axial direction of the groove bottom zone including at least the center of the groove is different from the applied amount and/or the type of a lubricity modifier in the flange zones is provided as a means of producing a friction distribution. This lubricity modifier applicator can be any type which can apply a lubricity modifier to the surface of a groove, such as one which performs application by spraying, while imparting variations in accordance with the position in the roll axial direction of a grooved roll.
For example, the lubricity modifier applicator may be equipped with a lubricity modifier spraying unit which sprays a lubricity modifier and a cooling water removing unit which blows away roll cooling water which is present on the roll surface in order to ensure that the lubricity modifier adheres to the roll surface. A lubricity modifier spraying unit can spray a lubricity modifier in an amount which varies in accordance with the position in the roll axial direction of a groove or which sprays a lubricity modifier only at a portion of a groove (namely, at least a portion of the groove bottom zone including the center in the roll axial direction).
The degree of opening of the regulating valves for controlling the applied amount of a lubricity modifier can be controlled manually, but the valves are preferably connected to and controlled by a computer. When there are a plurality of sets of lubricating nozzles, the type of lubricity modifier is preferably varied for each set, and application of the lubricity modifier is preferably carried out such that the lubricity modifier having the larger effect of decreasing the coefficient of friction is applied to the flanges.
The lubricity modifier which is applied may be a lubricant for rolling which is generally used in reducing of a pipe or an anti-slipping agent (i.e., friction increasing agent). The amount of a lubricity modifier which is applied to the groove surface may be varied in the roll axial direction. For example, a lubricity modifier may not be applied to the central portion in the roll axial direction (corresponding to at least a portion of the groove bottom zone), or the applied amount for that portion may be made smaller than for the flange zones (such as ⅓ thereof).
The lubricity modifier is preferably a combination of an anti-slipping agent which increases the coefficient of friction and a lubricating oil normally used for roll lubrication, but it is possible to use a lubricating oil alone.
The anti-slipping agent which can be used may be, for example, a silicone powder or a grease-based one. The lubricating oil may be a synthetic ester type. The mixing ratio and type of these conventional anti-slipping agent and lubricating oils can be suitably varied between the groove bottom zone and the flange zones.
When performing reducing of a plurality of types of pipe having different wall thicknesses or the like under different conditions in either of the above-explained first and second embodiments, the variation in the increase in wall thickness like that shown in
Three types of pipe having a diameter of 60 mm, a length of 400 mm, and a wall thickness of 12 mm, 8 mm, or 3 mm were subjected to reducing by cold rolling (drawing) using a model mill for reducing having four stands.
Case 1 was a comparative example using a grooved roll which was uniformly subjected to shot blasting over the entirety of the groove surface. Case 2 was an example of the present invention using a grooved roll which, as shown in
As shown in
As shown in the graphs of
Number | Date | Country | Kind |
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2007-029480 | Feb 2007 | JP | national |
This application is a continuation of International Patent Application No. PCT/JP2008/052172 filed Feb. 8, 2008. This PCT application was not in English as published under PCT Article 21(2).
Number | Name | Date | Kind |
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20020100307 | Narita et al. | Aug 2002 | A1 |
Number | Date | Country |
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63-260606 | Oct 1988 | JP |
7-314013 | Dec 1995 | JP |
8-19808 | Jan 1996 | JP |
11-151506 | Jun 1999 | JP |
2000-158015 | Jun 2000 | JP |
2000-334504 | Dec 2000 | JP |
2001-71012 | Mar 2001 | JP |
2001-129603 | May 2001 | JP |
2003-19503 | Jan 2003 | JP |
2005-46874 | Feb 2005 | JP |
2005-169466 | Jun 2005 | JP |
2005-305447 | Nov 2005 | JP |
Number | Date | Country | |
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20100031725 A1 | Feb 2010 | US |
Number | Date | Country | |
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Parent | PCT/JP2008/052172 | Feb 2008 | US |
Child | 12461323 | US |