CA2076402C - Mandrel mill for seamless steel tubes - Google Patents
Mandrel mill for seamless steel tubesInfo
- Publication number
- CA2076402C CA2076402C CA 2076402 CA2076402A CA2076402C CA 2076402 C CA2076402 C CA 2076402C CA 2076402 CA2076402 CA 2076402 CA 2076402 A CA2076402 A CA 2076402A CA 2076402 C CA2076402 C CA 2076402C
- Authority
- CA
- Canada
- Prior art keywords
- roll
- groove
- stand
- rolls
- groove bottom
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B17/00—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling
- B21B17/02—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling with mandrel, i.e. the mandrel rod contacts the rolled tube over the rod length
- B21B17/04—Tube-rolling by rollers of which the axes are arranged essentially perpendicular to the axis of the work, e.g. "axial" tube-rolling with mandrel, i.e. the mandrel rod contacts the rolled tube over the rod length in a continuous process
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)
- Control Of Metal Rolling (AREA)
Abstract
A mandrel mill for rolling seamless steel tubes includes a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, an axis of the rolls of each roll stand being orthogonal to the axis of the rolls of the adjacent roll stands. The mandrel mill further includes a mandrel bar disposed in the roll grooves configured by the roll stands. The ratio between the radius of curvature of a groove bottom of the groove and a distance between the groove bottom of the roll groove of the first stand ranges from 0.46 to 0.54, and that of the second stand ranges from 0.48 to 0.52.
Description
BACKGROUND OF THE INVENTION
Field of the Invention The present invention relates to a method for preventing defects such as holes from being formed on surfaces of blank tubes manufactured by mandrel mill, wherein the holes are produced during the manufacturing of the seamless steel tubes, and more particularly during the manufacturing seamless steel tubes made of a high alloy steel such as stainless steel.
Description of the Related Art In one method of manufacturing seamless steel tubes using a mandrel mill, a heated billet is pierced by a piercing machine, and a finishing rolling process of the billet is applied by rolling the inside of the tube. As is shown in FIG. 4, the mandrel mill employed in this circumstance normally comprises a plurality of--from five to eight--roll stands 1 configuring a roll groove having a plurality of rolls 2 and 2' in alternate pairs arranged horizontally and vertically.
These plurality of grooved roll stands are disposed orthogonally about a rolling shaft, and a mandrel bar 3 is disposed within a roll groove formed by roll stands 1. The inner surface of the blank tube 4 is rolled by the mandrel bar 3.
In the manufacturing of seamless steel tubes by mandrel mill, holes are often formed on surfaces of the blank tubes 4 during the rolling process causing unfavorable defects in the mandrel mill manufacturing.
(Hereinafter, this defect is referred to as the "hole defect" and reference numeral 6 indicates the portions with the "hole defect.~) Conventionally, it was thought that the "hole defect"
was caused by the following reasons. As is shown in FIG.
5, when a blank tube made of a high alloy steel, such as stainless steel, is rolled by the mandrel mill at a temperature ranging between 950C and 1050C which is the normal rolling temperature range for common blank tubes, the hot-working characteristics of the blank tube deteriorates.
When a blank tube having an inferior hot-working characteristic is rolled by the mandrel mill, a longitudinal tensile force is exerted only on a flange portion 5 shown in FIG. 2 of the blank tube receiving no reduction, which eventually causes a rupture or "hole defect" in the tube. These defects tend to occur with much greater frequency in steel tubes having a thin wall thickness.
Various method for preventing the "hole defect" have been proposed.
One of the common methods for preventing the ~hole defect" is disclosed in Japanese Patent Laid-Open Publication No.58-224155, wherein a method of improving the 2076~02 hot-working deformability of the rolling tube materials is proposed.
There is also proposed, in Japanese Laid-Open Publication No.63-84720, a method of reducing the rolling reduction of one stand where the "hole defect" occurs in the mandrel mill and dispersing the reduction load to the remaining stands, and of reducing the wall thickness of blank tubes at the entrance of the mandrel mill so as to reduce the rolling reduction of each stand of the mill.
The method disclosed in Japanese Patent Laid-Open Publication No.58-22455, however, cannot provide a sufficient hot-working deformability at rolling temperatures in the range of 950C to 1050C in the mandrel mill.
Although the method proposed in Japanese Patent Laid-Open Publication No.63-84720 can prevent the "hole defect", it may not be used on blank tubes with a thin wall thickness for the following reason:
If after reduction loads are dispersed to each stand, and there remains a stand in which the rolling load exceeds the reference value, the wall thickness of the blank tube is reduced at the entrance of the mandrel mill so as to reduce the rolling reduction of each stand of the mill.
However, rolling reduction on the blank tube by the piercing machine is limited and therefore the wall thickness of the blank tube cannot be reduced below a lower limit. In the above situation, it is difficult to roll blank tubes with a thin wall thickness.
Accordingly, an object of the present invention is to overcome the above described problems of the mandrel mill and prevent the "hole defect."
SUMMARY OF THE INVENTION
The present invention is directed toward a roll groove design of a row of stands consecutively disposed in the mandrel mill to prevent the "hole defect" produced during the rolling process.
According to the present invention, there is provided a mandrel mill for rolling seamless steel tubes which comprises a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stand, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of a first stand ranges from 0.46 to 0.54.
According to the present invention there is provided a mandrel mill for rolling seamless steel tubes, comprising a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stand, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of a second stand ranges from 0.48 to 0.52.
According to the present invention there is also provided a mandrel mill for rolling seamless steel tubes, comprising a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stands, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of the first stand ranges from 0.46 to 0.54, and that of the second stand ranges from 0.48 to 0.52.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a roll groove defined by a pair of forming rolls according to the present invention.
FIG. 2 illustrates a rolling reduction which becomes smaller at the bottom center of a groove and larger at both sides of the center in the third stand of a mandrel mill.
FIG. 3 illustrates the relation between a ratio of the 207640~
groove bottom radius of curvature and a distance of the groove bottom of a pair of rolls and a ratio of defect occurrence.
FIG. 4 is a schematic drawing of a mandrel mill.
FIG. 5 is a diagram illustrating hot working characteristics.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As a result of the survey for the cause of the "hole defect" in a mandrel mill rolling, the present invention has been brought to discover a new mechanism of hole occurrence which is not disclosed in the prior art except as described above.
In a reduced portion of roll groove bottom, when a rolling reduction of bottom center groove is smaller than that of both sides of the center groove, the lack of material on the bottom center groove causes the necking phenomenon during the process of a rolling. Under this circumstance, the tube wall thickness becomes thin which, in an extreme case, will produce a hole.
FIG. 2 illustrates an embodiment of the present invention in which the rolling reduction of both sides of the bottom center groove portion is greater than that of the center groove. In FIG. 2, reference numerals 2,2' indicate a roll groove defined by a pair of rolls, reference numeral 3 indicates a mandrel bar, and reference numeral 4 indicates a blank tube (a portion filled by slant 2076~0~
bars in the FIG. 2).
Reference numeral 4a indicates the thinnest portion of the blank tube wall thickness, which is also a roll bottom center groove portion in the first stand (the first stand refers to stand No.l in FIG. 2). Reference numeral 4b indicates both sides of the bottom center groove portion 4a. Reference numerals 11, 12, and 13 indicate roll grooves of the first, the second, and the third stands, respectively.
For example, as shown in FIG. 2(a), the shape of the roll groove 11 of the first stand is normally elliptical and the mandrel bar 3 substantially round. The wall thickness of the tube 4 in the circumferential direction at the exit area of the first stand becomes thinnest in the lS roll bottom center groove portion 4a, and becomes thicker as you move away from the bottom center groove. As shown in FIG. 2(b), in the rolling process at the second stand, the wall-thickness distribution of the thinnest tube wall of the bottom center portion 4a and both sides 4b from the center portion rolled by the first stand can be maintained even after the tube passes the second stand because the thinner portion 4a and thicker portions 4b do not suffer reduction from the roll groove 12 of the second stand.
As shown in FIG. 2(c), in the third stand, the roll groove 13 is substantially round so as to provide a uniform distribution of the tube-wall-thickness in the circumferential direction. The distribution of the wall thickness at the exit area of the first stand shows that the bottom center groove 4a is thinner and both sides 4b, from the center groove, are thicker. In the third stand, the roll reductions of both sides 4b are greater than that of the center portion 4a in the third stand. Thus, the present invention has successfully investigated that the lack of the material along the bottom center groove portion 4a causes the necking phenomenon to reduce the tube-wall thickness, which eventually causes the "hole defect". The phenomenon that occurs in the third stand will also occur in the fourth stand. Due to the elliptical shape of the roll groove of the second stand, the wall thickness in the circumferential direction is thinnest in the tube bottom groove area and as the area goes away from the bottom center groove, the thickness increases in the second stand.
The groove bottom portion rolled by the second stand does not suffer reduction in the third stand, in which the wall-thickness distribution of these portion can be maintained after the tube passes the third stand. In the fourth stand, the roll groove is substantially round to provide a uniform distribution of the tube-wall-thickness in the circumferential direction. The distribution of wall thickness at the exit area of the second stand shows that the wall thickness of the groove bottom is thinner and that of both sides from the groove bottom is thicker. The 2076~02 rolling reduction of both sides from the groove bottom center portion is greater than that of the groove bottom portion, which causes the "hole defect" due to the same reason as described above. To obtain the uniform wall thickness in the circumferential direction of the finished tube, the roll groove in the finishing stands of the mandrel mill is designed such that the groove bottom portion is substantially round. In normal mandrel mills, the above described finishing stands are disposed between the fourth stand and the sixth or eighth stands. In the first stand and the third stand, when even one roll-groove configuration has an elliptical shape, the rolling reduction of both sides from the groove bottom center portion has to be greater than that of the groove bottom portion to unify the wall thickness distribution in either one of the succeeding stands located after the above described stand having the elliptical-shaped roll groove.
Thus, the following measures have been taken to unify the rolling-reduction distribution in the circumferential direction of the groove bottom portions where the rolling force is applied.
The present invention has proposed a mandrel mill having a roll groove in which, as is shown in the representing illustration of FIG. 1, the groove bottom radius of curvature R1 in the first stand ranges from 0.46 to 0.54 of the groove bottom distance B of the pair of rolls, and the groove bottom radius of curvature R1 in the second stand ranges from 0.48 to 0.52 of the groove bottom distance B of the pair of rolls.
According to the present invention, "hole defect"
which is caused by the non-uniformity of the groove bottom draft, a cause which has been overlooked by the prior art, can be prevented by providing an upper limit and a lower limit of the groove bottom radius of curvature in the front stands in the mandrel mill.
Namely, in the mandrel mill which has a tendency to cause the "hole defect'~ in the groove bottom of the third stand, the rolling reduction in the circumferential direction of the groove bottom in the third stand can be unified by designing the groove bottom radius of curvature of the roll groove in the first stand to range from 0.46 to 0.54 of the distance between the groove bottom of the pair of rolls in the first stand. Thus, "hole defect" can be practically eliminated. Likewise, in the mandrel mill which has a tendency to cause the "hole defect" in the groove bottom of the fourth stand, the rolling reduction in the circumferential direction of the groove bottom in the fourth stand can be unified by designing the groove bottom radius of curvature of the roll groove in the second stand to range from 0.48 to 0.52 of the distance between the groove bottom of the pair of rolls in the second stand.
Thus, the occurrence of a "hole defect" can be practically 2076~02 eliminated.
Meanwhile, in the mandrel mill, it depends on the characteristics of the mill or the reduction distribution of each stand and the like whether a "hole defect'~ occurs in either one or both of the third and fourth stands.
Based on the testing results exhibited in FIG. 3, the ratios of the groove bottom radius of curvature Rl and the distance B between the groove bottom of the pair of rolls are determined as ranging from 0.46 to 0.54 in the first stand and from 0.48 to 0.52 in the second stand.
Embodiment 1 Rolling conditions and results of a mandrel mill using a tube material of a plain carbon steel according to the present invention are exhibited in Tables 1 and 2 respectively. In the rolling conditions of the present invention, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.54 and 0.52 respectively. On the other hand, in the rolling conditions of the prior art, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.6 and 0.55 respectively.
2076~2 Table 1 The Present Invention The Prior Art stand No- G.B.R.C.*l D.G.B.*2 G.B.R.C. D.G.B.
Rl Rl B
1 99.1 183.5110.1 183.5 2 93.1 179.098.5 179.0 3 89.2 176.889.2 176.8 4 87.8 175.687.8 175.6 87.3 174.587.3 174.5 6 87.3 174.587.3 174.5 7 87.3 174.587.3 174.5 8 90.0 180.090.0 180.0 (*l G.B.R.C.: Groove Bottom Radius of Curvature) ( *2 D.G.B.: Distance between the Groove Bottom) Diameter of employed mandrel bar: 166.5 mm Rolling material: Plain carbon steel Dimension at the mill exit: Outer diameter 180 mm, Wall thickness 4 mm, Length 24 m Table 2 Rolling by the Rolling by the Present Invention Prior Art Number of Tubes None out of 200 44 out of 200 Having "Hole tubes tubes Defect"
According to the present invention, it is understood that plain carbon steel with dimension of the outer diameter of 180 mm and wall thickness of 4 mm at the exit of the mandrel mill can be manufactured without "hole defect."
Embodiment 2 Rolling conditions and results of a mandrel mill using a tube material of 13 % Cr-steel according to the present invention are exhibited in Tables 3 and 4, respectively.
In the rolling conditions of the present invention, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.54 and 0.52, respectively. On the other hand, in the rolling conditions of the prior art, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.6 and 0.55, respectively.
2076~02 Table 3 The Present Invention The Prior Art stand No- G.B.R.C-*1 D.G.B.*2 G.B.R.C. D.G.B.
1 99.1 183.5110.1 183.5 2 93.1 179.098.5 179.0 3 89.2 176.889.2 176.8 4 87.8 175.687.8 175.6 87.3 174.587.3 174.5 6 87.3 174.587.3 174.5 7 87.3 174.587.3 174.5 8 90.0 180.090.0 180.0 (*l G.B.R.C.: Groove Bottom Radius of Curvature) ( *2 D.G.B.: Distance between the Groove Bottom) Diameter of employed mandrel bar: 164.5 mm Rolling material: 13% Cr-steel Dimension at the mill exit: Outer diameter 180 mm, Wall thickness 4 mm, Length 24 m Table 4 Rolling by the Rolling by the Present Invention Prior Art Number of Tubes None out of 200 30 out of 200 Having "Hole tubes tubes Defect"
2~76~02 According to the present invention, it is understood that a 13 % Cr-steel with dimension of the outer diameter of 180 mm and wall thickness of 4 mm at the exit of the mandrel mill can be manufactured without a "hole defect."
Therefore, to carry out the present invention, it is not necessary to provide a new device for an existing mandrel mill.
According to the present invention, a "hole defect", which conventionally has occurred at the groove bottom center portion in a roll groove, can be successfully prevented by designing the groove bottom radius of curvature of the roll groove at the first and second stands in the mandrel mill. Thus, a remarkable effect is obtained for preventing a "hole defect~ in mandrel mill rolling especially for tubes with thin wall-thickness and for a high alloy steel having an inferior deformability.
Field of the Invention The present invention relates to a method for preventing defects such as holes from being formed on surfaces of blank tubes manufactured by mandrel mill, wherein the holes are produced during the manufacturing of the seamless steel tubes, and more particularly during the manufacturing seamless steel tubes made of a high alloy steel such as stainless steel.
Description of the Related Art In one method of manufacturing seamless steel tubes using a mandrel mill, a heated billet is pierced by a piercing machine, and a finishing rolling process of the billet is applied by rolling the inside of the tube. As is shown in FIG. 4, the mandrel mill employed in this circumstance normally comprises a plurality of--from five to eight--roll stands 1 configuring a roll groove having a plurality of rolls 2 and 2' in alternate pairs arranged horizontally and vertically.
These plurality of grooved roll stands are disposed orthogonally about a rolling shaft, and a mandrel bar 3 is disposed within a roll groove formed by roll stands 1. The inner surface of the blank tube 4 is rolled by the mandrel bar 3.
In the manufacturing of seamless steel tubes by mandrel mill, holes are often formed on surfaces of the blank tubes 4 during the rolling process causing unfavorable defects in the mandrel mill manufacturing.
(Hereinafter, this defect is referred to as the "hole defect" and reference numeral 6 indicates the portions with the "hole defect.~) Conventionally, it was thought that the "hole defect"
was caused by the following reasons. As is shown in FIG.
5, when a blank tube made of a high alloy steel, such as stainless steel, is rolled by the mandrel mill at a temperature ranging between 950C and 1050C which is the normal rolling temperature range for common blank tubes, the hot-working characteristics of the blank tube deteriorates.
When a blank tube having an inferior hot-working characteristic is rolled by the mandrel mill, a longitudinal tensile force is exerted only on a flange portion 5 shown in FIG. 2 of the blank tube receiving no reduction, which eventually causes a rupture or "hole defect" in the tube. These defects tend to occur with much greater frequency in steel tubes having a thin wall thickness.
Various method for preventing the "hole defect" have been proposed.
One of the common methods for preventing the ~hole defect" is disclosed in Japanese Patent Laid-Open Publication No.58-224155, wherein a method of improving the 2076~02 hot-working deformability of the rolling tube materials is proposed.
There is also proposed, in Japanese Laid-Open Publication No.63-84720, a method of reducing the rolling reduction of one stand where the "hole defect" occurs in the mandrel mill and dispersing the reduction load to the remaining stands, and of reducing the wall thickness of blank tubes at the entrance of the mandrel mill so as to reduce the rolling reduction of each stand of the mill.
The method disclosed in Japanese Patent Laid-Open Publication No.58-22455, however, cannot provide a sufficient hot-working deformability at rolling temperatures in the range of 950C to 1050C in the mandrel mill.
Although the method proposed in Japanese Patent Laid-Open Publication No.63-84720 can prevent the "hole defect", it may not be used on blank tubes with a thin wall thickness for the following reason:
If after reduction loads are dispersed to each stand, and there remains a stand in which the rolling load exceeds the reference value, the wall thickness of the blank tube is reduced at the entrance of the mandrel mill so as to reduce the rolling reduction of each stand of the mill.
However, rolling reduction on the blank tube by the piercing machine is limited and therefore the wall thickness of the blank tube cannot be reduced below a lower limit. In the above situation, it is difficult to roll blank tubes with a thin wall thickness.
Accordingly, an object of the present invention is to overcome the above described problems of the mandrel mill and prevent the "hole defect."
SUMMARY OF THE INVENTION
The present invention is directed toward a roll groove design of a row of stands consecutively disposed in the mandrel mill to prevent the "hole defect" produced during the rolling process.
According to the present invention, there is provided a mandrel mill for rolling seamless steel tubes which comprises a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stand, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of a first stand ranges from 0.46 to 0.54.
According to the present invention there is provided a mandrel mill for rolling seamless steel tubes, comprising a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stand, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of a second stand ranges from 0.48 to 0.52.
According to the present invention there is also provided a mandrel mill for rolling seamless steel tubes, comprising a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, the rolls being arranged such that the axis of the rolls of each roll stand is orthogonal to the axis of the rolls of the adjacent roll stands, and a mandrel bar disposed in the roll groove configured by the roll stands wherein the ratio between the radius of curvature of groove bottom and a distance between the groove bottom of the roll groove of the first stand ranges from 0.46 to 0.54, and that of the second stand ranges from 0.48 to 0.52.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross sectional view of a roll groove defined by a pair of forming rolls according to the present invention.
FIG. 2 illustrates a rolling reduction which becomes smaller at the bottom center of a groove and larger at both sides of the center in the third stand of a mandrel mill.
FIG. 3 illustrates the relation between a ratio of the 207640~
groove bottom radius of curvature and a distance of the groove bottom of a pair of rolls and a ratio of defect occurrence.
FIG. 4 is a schematic drawing of a mandrel mill.
FIG. 5 is a diagram illustrating hot working characteristics.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As a result of the survey for the cause of the "hole defect" in a mandrel mill rolling, the present invention has been brought to discover a new mechanism of hole occurrence which is not disclosed in the prior art except as described above.
In a reduced portion of roll groove bottom, when a rolling reduction of bottom center groove is smaller than that of both sides of the center groove, the lack of material on the bottom center groove causes the necking phenomenon during the process of a rolling. Under this circumstance, the tube wall thickness becomes thin which, in an extreme case, will produce a hole.
FIG. 2 illustrates an embodiment of the present invention in which the rolling reduction of both sides of the bottom center groove portion is greater than that of the center groove. In FIG. 2, reference numerals 2,2' indicate a roll groove defined by a pair of rolls, reference numeral 3 indicates a mandrel bar, and reference numeral 4 indicates a blank tube (a portion filled by slant 2076~0~
bars in the FIG. 2).
Reference numeral 4a indicates the thinnest portion of the blank tube wall thickness, which is also a roll bottom center groove portion in the first stand (the first stand refers to stand No.l in FIG. 2). Reference numeral 4b indicates both sides of the bottom center groove portion 4a. Reference numerals 11, 12, and 13 indicate roll grooves of the first, the second, and the third stands, respectively.
For example, as shown in FIG. 2(a), the shape of the roll groove 11 of the first stand is normally elliptical and the mandrel bar 3 substantially round. The wall thickness of the tube 4 in the circumferential direction at the exit area of the first stand becomes thinnest in the lS roll bottom center groove portion 4a, and becomes thicker as you move away from the bottom center groove. As shown in FIG. 2(b), in the rolling process at the second stand, the wall-thickness distribution of the thinnest tube wall of the bottom center portion 4a and both sides 4b from the center portion rolled by the first stand can be maintained even after the tube passes the second stand because the thinner portion 4a and thicker portions 4b do not suffer reduction from the roll groove 12 of the second stand.
As shown in FIG. 2(c), in the third stand, the roll groove 13 is substantially round so as to provide a uniform distribution of the tube-wall-thickness in the circumferential direction. The distribution of the wall thickness at the exit area of the first stand shows that the bottom center groove 4a is thinner and both sides 4b, from the center groove, are thicker. In the third stand, the roll reductions of both sides 4b are greater than that of the center portion 4a in the third stand. Thus, the present invention has successfully investigated that the lack of the material along the bottom center groove portion 4a causes the necking phenomenon to reduce the tube-wall thickness, which eventually causes the "hole defect". The phenomenon that occurs in the third stand will also occur in the fourth stand. Due to the elliptical shape of the roll groove of the second stand, the wall thickness in the circumferential direction is thinnest in the tube bottom groove area and as the area goes away from the bottom center groove, the thickness increases in the second stand.
The groove bottom portion rolled by the second stand does not suffer reduction in the third stand, in which the wall-thickness distribution of these portion can be maintained after the tube passes the third stand. In the fourth stand, the roll groove is substantially round to provide a uniform distribution of the tube-wall-thickness in the circumferential direction. The distribution of wall thickness at the exit area of the second stand shows that the wall thickness of the groove bottom is thinner and that of both sides from the groove bottom is thicker. The 2076~02 rolling reduction of both sides from the groove bottom center portion is greater than that of the groove bottom portion, which causes the "hole defect" due to the same reason as described above. To obtain the uniform wall thickness in the circumferential direction of the finished tube, the roll groove in the finishing stands of the mandrel mill is designed such that the groove bottom portion is substantially round. In normal mandrel mills, the above described finishing stands are disposed between the fourth stand and the sixth or eighth stands. In the first stand and the third stand, when even one roll-groove configuration has an elliptical shape, the rolling reduction of both sides from the groove bottom center portion has to be greater than that of the groove bottom portion to unify the wall thickness distribution in either one of the succeeding stands located after the above described stand having the elliptical-shaped roll groove.
Thus, the following measures have been taken to unify the rolling-reduction distribution in the circumferential direction of the groove bottom portions where the rolling force is applied.
The present invention has proposed a mandrel mill having a roll groove in which, as is shown in the representing illustration of FIG. 1, the groove bottom radius of curvature R1 in the first stand ranges from 0.46 to 0.54 of the groove bottom distance B of the pair of rolls, and the groove bottom radius of curvature R1 in the second stand ranges from 0.48 to 0.52 of the groove bottom distance B of the pair of rolls.
According to the present invention, "hole defect"
which is caused by the non-uniformity of the groove bottom draft, a cause which has been overlooked by the prior art, can be prevented by providing an upper limit and a lower limit of the groove bottom radius of curvature in the front stands in the mandrel mill.
Namely, in the mandrel mill which has a tendency to cause the "hole defect'~ in the groove bottom of the third stand, the rolling reduction in the circumferential direction of the groove bottom in the third stand can be unified by designing the groove bottom radius of curvature of the roll groove in the first stand to range from 0.46 to 0.54 of the distance between the groove bottom of the pair of rolls in the first stand. Thus, "hole defect" can be practically eliminated. Likewise, in the mandrel mill which has a tendency to cause the "hole defect" in the groove bottom of the fourth stand, the rolling reduction in the circumferential direction of the groove bottom in the fourth stand can be unified by designing the groove bottom radius of curvature of the roll groove in the second stand to range from 0.48 to 0.52 of the distance between the groove bottom of the pair of rolls in the second stand.
Thus, the occurrence of a "hole defect" can be practically 2076~02 eliminated.
Meanwhile, in the mandrel mill, it depends on the characteristics of the mill or the reduction distribution of each stand and the like whether a "hole defect'~ occurs in either one or both of the third and fourth stands.
Based on the testing results exhibited in FIG. 3, the ratios of the groove bottom radius of curvature Rl and the distance B between the groove bottom of the pair of rolls are determined as ranging from 0.46 to 0.54 in the first stand and from 0.48 to 0.52 in the second stand.
Embodiment 1 Rolling conditions and results of a mandrel mill using a tube material of a plain carbon steel according to the present invention are exhibited in Tables 1 and 2 respectively. In the rolling conditions of the present invention, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.54 and 0.52 respectively. On the other hand, in the rolling conditions of the prior art, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.6 and 0.55 respectively.
2076~2 Table 1 The Present Invention The Prior Art stand No- G.B.R.C.*l D.G.B.*2 G.B.R.C. D.G.B.
Rl Rl B
1 99.1 183.5110.1 183.5 2 93.1 179.098.5 179.0 3 89.2 176.889.2 176.8 4 87.8 175.687.8 175.6 87.3 174.587.3 174.5 6 87.3 174.587.3 174.5 7 87.3 174.587.3 174.5 8 90.0 180.090.0 180.0 (*l G.B.R.C.: Groove Bottom Radius of Curvature) ( *2 D.G.B.: Distance between the Groove Bottom) Diameter of employed mandrel bar: 166.5 mm Rolling material: Plain carbon steel Dimension at the mill exit: Outer diameter 180 mm, Wall thickness 4 mm, Length 24 m Table 2 Rolling by the Rolling by the Present Invention Prior Art Number of Tubes None out of 200 44 out of 200 Having "Hole tubes tubes Defect"
According to the present invention, it is understood that plain carbon steel with dimension of the outer diameter of 180 mm and wall thickness of 4 mm at the exit of the mandrel mill can be manufactured without "hole defect."
Embodiment 2 Rolling conditions and results of a mandrel mill using a tube material of 13 % Cr-steel according to the present invention are exhibited in Tables 3 and 4, respectively.
In the rolling conditions of the present invention, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.54 and 0.52, respectively. On the other hand, in the rolling conditions of the prior art, the ratios between the groove bottom radius of curvature of the roll groove and the distance between the groove bottom formed by the pair of rolls in the first and second stands are set as 0.6 and 0.55, respectively.
2076~02 Table 3 The Present Invention The Prior Art stand No- G.B.R.C-*1 D.G.B.*2 G.B.R.C. D.G.B.
1 99.1 183.5110.1 183.5 2 93.1 179.098.5 179.0 3 89.2 176.889.2 176.8 4 87.8 175.687.8 175.6 87.3 174.587.3 174.5 6 87.3 174.587.3 174.5 7 87.3 174.587.3 174.5 8 90.0 180.090.0 180.0 (*l G.B.R.C.: Groove Bottom Radius of Curvature) ( *2 D.G.B.: Distance between the Groove Bottom) Diameter of employed mandrel bar: 164.5 mm Rolling material: 13% Cr-steel Dimension at the mill exit: Outer diameter 180 mm, Wall thickness 4 mm, Length 24 m Table 4 Rolling by the Rolling by the Present Invention Prior Art Number of Tubes None out of 200 30 out of 200 Having "Hole tubes tubes Defect"
2~76~02 According to the present invention, it is understood that a 13 % Cr-steel with dimension of the outer diameter of 180 mm and wall thickness of 4 mm at the exit of the mandrel mill can be manufactured without a "hole defect."
Therefore, to carry out the present invention, it is not necessary to provide a new device for an existing mandrel mill.
According to the present invention, a "hole defect", which conventionally has occurred at the groove bottom center portion in a roll groove, can be successfully prevented by designing the groove bottom radius of curvature of the roll groove at the first and second stands in the mandrel mill. Thus, a remarkable effect is obtained for preventing a "hole defect~ in mandrel mill rolling especially for tubes with thin wall-thickness and for a high alloy steel having an inferior deformability.
Claims (3)
1. A mandrel mill for rolling seamless steel tubes, comprising:
a plurality of adjacent roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stand; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of a first stand ranges from 0.46 to 0.54.
a plurality of adjacent roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stand; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of a first stand ranges from 0.46 to 0.54.
2. A mandrel mill for rolling seamless steel tubes, comprising:
a plurality of adjacent roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stands; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of a second stand ranges from 0.48 to 0.52.
a plurality of adjacent roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stands; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of a second stand ranges from 0.48 to 0.52.
3. A mandrel mill for rolling seamless steel tubes, comprising:
a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stands; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of the first stand ranges from 0.46 to 0.54, and that of the second stand ranges from 0.48 to 0.52.
a plurality of roll stands each having a pair of rolls defining a roll groove therebetween, an axis of said rolls of each said roll stand being orthogonal to the axis of the rolls of the adjacent roll stands; and a mandrel bar disposed in said roll grooves configured by said roll stands;
wherein a ratio between a radius of curvature of a groove bottom of said groove and a distance between said groove bottom of said pair of rolls defining said roll groove of the first stand ranges from 0.46 to 0.54, and that of the second stand ranges from 0.48 to 0.52.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP233835/91 | 1991-08-22 | ||
| JP3233835A JPH07102369B2 (en) | 1991-08-22 | 1991-08-22 | Mandrel mill |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2076402A1 CA2076402A1 (en) | 1993-02-23 |
| CA2076402C true CA2076402C (en) | 1996-03-05 |
Family
ID=16961316
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2076402 Expired - Fee Related CA2076402C (en) | 1991-08-22 | 1992-08-19 | Mandrel mill for seamless steel tubes |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0529943A3 (en) |
| JP (1) | JPH07102369B2 (en) |
| CA (1) | CA2076402C (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2008119706A (en) | 2006-11-09 | 2008-05-29 | Sumitomo Metal Ind Ltd | Mandrel mill and operation method thereof, and method for manufacturing seamless pipe |
| JP5062522B2 (en) * | 2007-05-31 | 2012-10-31 | 住友金属工業株式会社 | Mandrel mill and seamless pipe manufacturing method |
| CN114309076B (en) * | 2020-09-30 | 2023-05-16 | 宝武特种冶金有限公司 | Precision trimming method for ring hole type of seamless steel tube cold rolling mill |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58224155A (en) * | 1982-06-19 | 1983-12-26 | Kawasaki Steel Corp | Seamless two-phase stainless steel pipe and its manufacture |
| JPS60106603A (en) * | 1983-11-15 | 1985-06-12 | Kawasaki Steel Corp | Manufacture of seamless steel pipe |
| JPS6384720A (en) * | 1986-09-30 | 1988-04-15 | Kawasaki Steel Corp | Manufacture of seamless pipe by mandrel mill |
| JPH01186205A (en) * | 1988-01-22 | 1989-07-25 | Nippon Steel Corp | Mandrel mill for manufacturing seamless steel tube |
| JPH01284411A (en) * | 1988-05-09 | 1989-11-15 | Nkk Corp | Caliber roll for mandrel mill |
-
1991
- 1991-08-22 JP JP3233835A patent/JPH07102369B2/en not_active Expired - Fee Related
-
1992
- 1992-08-19 CA CA 2076402 patent/CA2076402C/en not_active Expired - Fee Related
- 1992-08-20 EP EP19920307612 patent/EP0529943A3/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| CA2076402A1 (en) | 1993-02-23 |
| EP0529943A3 (en) | 1993-06-30 |
| JPH0550115A (en) | 1993-03-02 |
| JPH07102369B2 (en) | 1995-11-08 |
| EP0529943A2 (en) | 1993-03-03 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US5657659A (en) | Mandrel mill and method of tube rolling by using the same | |
| EP2085158A1 (en) | Mandrel mill, its operating method, and seamless pipe manufacturing method | |
| US4827750A (en) | Method of piercing and manufacturing seamless tubes | |
| US5513511A (en) | Method of producing seamless steel tube by using mandrel mill | |
| CA2076402C (en) | Mandrel mill for seamless steel tubes | |
| US8316680B2 (en) | Method of making a seamless hollow body from steel | |
| EP1889669B1 (en) | Drawing rolling method by mandrel mill | |
| US8122749B2 (en) | Mandrel mill and process for manufacturing a seamless pipe | |
| EP1679136A1 (en) | Method of manufacturing seamless tube by three-roll mandrel mill | |
| JP3633071B2 (en) | Pipe rolling mill and roll position setting method | |
| JP3364814B2 (en) | Method for producing martensitic stainless steel wire rod | |
| JP2973851B2 (en) | Tube continuous rolling method and three-roll mandrel mill | |
| JP3452039B2 (en) | Rolling method of seamless steel pipe | |
| JP3076700B2 (en) | Row of cold drawing mills for circular pipes | |
| JP2812213B2 (en) | Tube rolling method | |
| JP3470686B2 (en) | Rolling method of seamless steel pipe | |
| JP3339434B2 (en) | Rolling method of metal tube | |
| JPS61144204A (en) | Skew rolling method of seamless pipe | |
| JP2001113306A (en) | Manufacturing method for high alloy seamless steel tube and rolling pass used therefor | |
| JP3030597B2 (en) | Welded pipe manufacturing method | |
| JP4035960B2 (en) | Method of rolling a tube with a mandrel mill | |
| JP3606825B2 (en) | Precision rolling method for steel bars and wire rods | |
| JP3064822B2 (en) | Tube rolling method by mandrel mill | |
| JP4314972B2 (en) | Method for constant diameter rolling of metal tubes | |
| JPH0716615A (en) | Method for cold rolling steel tube |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKLA | Lapsed |