Information
-
Patent Grant
-
6223575
-
Patent Number
6,223,575
-
Date Filed
Monday, August 23, 199924 years ago
-
Date Issued
Tuesday, May 1, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 072 51
- 072 52
- 072 178
- 072 181
- 072 182
- 072 2525
- 492 1
- 492 30
-
International Classifications
-
Abstract
A tube forming machine for making a tube from a sheet is disclosed. The forming rolls of this invention include various V-shaped rolls at least some of which are used as part of a three-point bending technique. The three-point bending technique entails the use of a V-shaped bottom roll and a narrow top roll. The sheet is shaped running the sheet through a gap between the narrow top roll and the V-shaped bottom roll. The technique allows a wide variety of tubing to be made from the same set of forming rolls, because the curvature obtained in a sheet can be varied by opening or closing the gap. A V-shaped forming roll disclosed herein is also used at a pinch roll stand with a second complementary V-shaped roll. The pinch roll stand of this invention creates an initial V-shaped sheet which facilitates the threading of the sheet at the start of a forming operation. Brimmed rolls are also disclosed. Brimmed rolls have a relatively sharp included angle, and are used to engage the edges of a sheet and to press the sheet against a single bottom roll in brimmed roll stand.
Description
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to an apparatus for manufacturing tubing from sheet stock using a series of rolls. In particular, the invention relates to an improved tube forming machine and method which utilizes new roll shapes and bending techniques which provide a number of advantages over prior art machines and methods.
Steel tubes have for many years been produced by forming an initially flat sheet or strip into a round shape using cage rolls, cluster rolls and fin-pass rolls, and eventually welding the edges of the sheet together to form a seam. Conventional equipment utilizing such rolls for the formation of steel tubing from strips can be seen in U.S. Pat. Nos. 5,673,579 and 5,784,911.
Because a large component in the cost of producing steel tubing from sheet material is the cost of the sheet material itself, producers of steel tubing are often forced by competition to use the least expensive sheet steel available. However, inexpensive sheet stock often has more variability in the hardness, thickness and other important properties of the sheet as compared to more expensive sheet stock. When inexpensive steel sheet is used with traditional tube forming machines and techniques, a number of problems arise. Those problems include twisting of the sheet as it passes through the various rolling stands, difficulty in controlling the position of the sheet, and difficulty in feeding the sheet at the start of a continuous tube forming operation. Conventional tube forming machines require rolls to be changed frequently in order to form tubing having different sizes and wall thicknesses. It is therefore desirable to provide a tube forming machine which has improved ability to handle inexpensive sheet steel and which has increased capacity to make tubing from different forming rolls.
Important objectives in the design of tube forming equipment include ease of initial threading of the strip into and through the machine, consistent positioning of the sheet both at the forming stands and at the point in the process where the edges of the sheet are welded to form a seam, efficient handling of the strip without damaging either the edges or the surfaces of the sheet, and ability for the machine to handle a wide range of tubing sizes and wall thicknesses without changing the forming rolls.
The present invention utilizes three point bending techniques at various stages in the tube forming operation. One of the three point bending techniques of the present invention involves the use of a V-shaped roll and an opposing narrow roll, with the extent of curvature obtained depending on the relative position, i.e., the proximity, of the two roll. If the narrow roll is brought closer to the V-shaped roll with which it cooperates, a smaller diameter is obtained. Conversely, if the gap between the narrow roll and the V-shaped roll is increased, a larger diameter results. The present invention also utilizes a V-shaped bottom and top roll at an initial or pinch roll stand. The flat surfaces of opposing V-shaped rolls at the first stand in the machine results in improved gripping of the sheet for purposes of driving the sheet through subsequent stands. The resulting V-shaped profile of the sheet after it leaves the initial pinch roll stand is a strong shape for purposes of driving the sheet as it is threaded through the remaining non-driven stands. The initial forming stand is equipped with a duplex regulating system in which hydraulic pressure is used to pinch the sheet between the two V-shaped rolls. Each side of the top roll of the initial station may be independently controlled for purposes of adjusting pressures applied to each side of a sheet being processed to compensate for variability of thickness of the sheet material.
The tube forming machine described below also includes the use of a brimmed roll in which a circumferential slot is formed between two angled surfaces. A pair of brimmed rolls are used to engage the edges of a sheet, and the two brimmed rolls cooperate with a concave bottom roll to form the sheet into a smoothly rounded cross-section.
More detailed descriptions of the inventions disclosed herein are set forth below and will be better understood upon a reading of the following specification read in conjunction with the accompanying drawings wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an overall side elevational view of a machine arranged in accordance with the present invention;
FIG. 2
is a top plan view of the machine shown in
FIG. 1
;
FIG. 3
is a diagram showing the various stages of the tube forming process for large diameter tubing (right side) and small diameter tubing (left side) which can be produced with the machine of the present invention;
FIG. 4
is an elevational view in partial section of driving stands of the machine of the present invention, the right cross-sectional portion corresponding to the first driving stand and the left cross-sectional portion corresponding to the second driving sheet;
FIG. 5
is a top plan view of the stands shown in
FIG. 4
with the rolls not shown;
FIG. 6
is a side elevational view of the station shown in
FIGS. 4 and 5
;
FIG. 7
is a schematic diagram of the hydraulic circuit used to apply clamping pressure at an initial driving stand of the machine of the present invention;
FIG. 8
is a partial side elevational view of a driving stand of the present invention showing the vertical adjustability of the rolls;
FIG. 9
is an elevational view in partial section of the adjustment mechanism for a bottom roll;
FIG. 10
is an elevational view in partial section of a forming roll stand of the present invention;
FIG. 11
is a top plan view of the stand shown in
FIG. 10
;
FIG. 12
is a side elevational view of the stand shown in
FIGS. 10 and 11
;
FIG. 13
is an enlarged elevational view in partial section of the mechanism used to vertically adjust the rolls shown in
FIG. 10
;
FIG. 14
is an enlarged elevational view in partial section of a three point bending stand of the present invention;
FIG. 15
is an enlarged elevational view in partial section of a second three point bending stand of the present invention;
FIG. 16
is an enlarged elevational view in partial section of a third three point bending stand of the present invention;
FIG. 17
is an enlarged elevational view in partial section of a fourth three-point bending stand of the present invention;
FIG. 18
is an enlarged elevational view in partial section of a top and bottom roll at a three point bending stand of the present invention;
FIGS. 19 and 20
are elevational views of a top and bottom roll showing alternative ways in which the rolls may be adjusted to obtain different curvature in a workpiece;
FIG. 21
is an elevational view in partial section of a forming stand of the present invention in which brimmed rolls are utilized;
FIG. 22
is a side elevational view of one side of the stand shown in
FIG. 21
;
FIG. 23
is a top plan view of the stand shown in
FIG. 21
;
FIG. 24
is a elevational view in partial section of a brimmed roll and its mounting;
FIG. 25
is a top plan view of the roll and mounting shown in
FIG. 24
;
FIG. 26
is a side elevational view of the roll and mounting shown in
FIG. 24
;
FIG. 27
is an elevational view showing two brimmed rolls and a bottom roll at a forming stand of the present invention;
FIG. 28
is a top plan view in partial section of a brimmed roll and its mounting mechanism made in accordance with the present invention;
FIG. 29
is an end elevational view of a cage roll stand for use in a machine of the present invention;
FIG. 30
is a side elevational view of the cage roll stand shown in
FIG. 29
;
FIG. 31
is a diagram of the rolls in a cage roll stand; and
FIGS. 32 and 33
are examples in plan view of conventional tube forming machines.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
is a side elevational view showing the various forming stations used in accordance with the present invention. The tube forming machine of the present invention includes pinch roll stands
11
at the first and fourth stations shown in FIG.
1
. The second, third, fifth and sixth stations are three point bending stands
21
. The seventh through twelfth stations are alternating brim roll stands
31
and cage roll stands
41
. After the alternating brimmed and cage roll stands, a series of three fin-pass stations
51
operate on the sheet which is to be formed into tubing. The final rolling station is a squeeze roll station
61
, after which the sheet is welded along a longitudinal seam. As can be seen in the top plan view of
FIG. 2
, the pinch roll stands and the fin-pass stands
51
are used to drive and pull, respectively, the sheet through the tube forming machine.
FIG. 3
shows the profile of the sheet as it progresses from the initial pinch roll stand through the fin-pass stands. The profile designated
211
a
corresponds to the initial pinch roll stand at the left end of
FIGS. 1 and 2
. The profiles marked
221
a
through
221
d
correspond to the profile at the four three point bending stands
21
. The profiles designated
231
a
through
241
c
correspond to the shape of the sheet at the series of six alternating brimmed rolls and cage roll stands shown in the center portion of
FIGS. 1 and 2
. Finally, the profile designated
251
a
corresponds to the shape of the sheet at the fin-pass stands
51
.
The angle “α” (alpha) shown in the lower portion of
FIG. 3
is the angle with respect to the horizontal of each side of the initial V-shape of the sheet as it is formed by the top and bottom roll of the pinch roll stands shown in
FIGS. 1 and 2
. The V-shaped transverse cross-section of a sheet formed by the combination of the first and second pinch roll stands
11
will have good resistance to buckling as it is passed through non-driven roll stands. This resistance to buckling is particularly important with respect to initial threading of a strip at the time when the machine is first started into operation.
FIGS. 4
,
5
and
6
are elevational views of a pinch roll stand
11
with its top and bottom rolls driven by drive equipment
12
. The drive equipment
12
includes a gear box
12
b
driven by an electric motor
12
a.
The upper drive spindle
14
a
and lower drive spindle
14
b
are connected to the gear box
12
b
and are also connected to the top roll shaft
16
a
and bottom roll shaft
17
a,
respectively. It should be noted that the right hand portion of the top roll corresponds to the first pinch roll stand in
FIGS. 1 and 2
, while the left portion of the top roll shown in
FIG. 4
corresponds to the second pinch roll stand in
FIGS. 1 and 2
, which is the fourth in the series of stations shown therein. Because the top and bottom rolls shown in
FIG. 4
provide the driving force for the sheet as it is threaded through the tube forming machine of the present invention, it is important that good gripping contact exists between the sheet and the top and bottom rolls. To achieve this, hydraulic cylinder/piston assemblies
15
apply downward force to the shaft
16
a
which supports the top rolls
16
. A keyway
16
b
formed in the shaft
16
a
receives a corresponding projection which allows the transfer of driving force to the shaft
16
a
and to the top roll
16
.
A roll stand frame
13
b
supports the roll shafts
16
a
and
17
a.
An electric motor
13
e
operates the height adjustment
13
d
for the lower roll
17
. As in the case of the upper roll
16
, the lower roll
17
has a key which fits into a keyway
17
b
to allow driving forces to be transferred from the lower drive spindle
14
b
to the lower roll
17
. The ends of the shafts
16
a
and
17
a
are each supported in a bearing box such as
13
f.
The bearing boxes
13
f
are supported by a frame
13
b.
FIG. 7
is a diagram of the hydraulic circuit used to operate the assemblies
15
which apply clamping pressure to the sheet as it passes through the pinch roll stands
11
. A hydraulic pump
110
supplies hydraulic fluid from oil reservoirs
120
. A solenoid operated directional valve
111
is used to control the flow of hydraulic fluid from the pump to the driving side of the piston within the assemblies
15
. The pilot operated check valve
112
prevents backflow of hydraulic fluid in the direction of the solenoid operated directional valve
111
. A speed control valve
113
is used as a main control of large flows of hydraulic fluid to the pressing cylinder/piston assemblies
15
, whereby hydraulic fluid is used to apply and release clamping pressure to the top roll of a pinch roll stand
11
. More precise (i.e., fine) control of clamping pressure is achieved by an operator who may send a signal to the electrical signal converter
115
to apply more or less clamping pressure to one or both cylinders
15
. The circuit uses the pressure regulators
114
and
116
to increase or decrease the pressure applied by the pistons within the cylinder/piston assemblies
115
. Indeed, the operator in some instances may want to apply more pressure upon one side of a roll than upon another the opposite side of the same roll to compensate for uneveness in the thickness, hardness, friction or other property of a strip being processed.
Pressure relief valves
119
are in the circuit to protect against machine breakage in the event that the rolls encounter an obstacle. The main hydraulic pressure sensors
117
provide a reading of the pressure within the pressing assemblies
15
at the main control panel of the machine. Auxiliary pressure gauges
118
allow visual inspection of the pressure being applied to the clamping rolls at the pinch roll stands
11
.
As can be seen in
FIG. 8
, the pressing assemblies
15
are used to raise and lower the top roll of the pinch roll stands
11
. The driving equipment
12
is linked by the drive shafts
14
a
and
14
b
through universal joints at each end to the shafts upon which are carried the top and bottom rolls of the pinch roll stands
11
.
FIG. 9
shows the basic elements of the mechanism used to raise and lower the bottom roll of a pinch roll stand
11
. The bottom roll shaft
17
a,
upon which is mounted the bottom roll
17
, extends into a bearing box
124
. The bearing box
124
is mounted to a lifting screw
123
which is raised and lowered by rotation of the worm wheel
121
. Rotation of the worm wheel
121
is achieved by rotation of the worm
120
.
FIGS. 10
,
11
,
12
and
13
are end elevational, top plan and side elevational views, respectively, of a three point bending roll stand
21
. A three point bending roll stand
21
of the present invention includes a pair of opposing rolls, a top roll
91
and a bottom roll
94
. Each pair is mounted to a main vertical frame
21
b
which carries a forming roll mechanism
21
a,
described in more detail below. The forming roll mechanism
21
a
is carried by a vertical slide frame
77
which slides along a vertical slide rail
78
. Rotation of the screw rod
75
a
causes the raising and lowering of the slide frame
77
and the forming roll mechanism
21
a.
The screw rod
75
a
is rotated by operation of the forming roll height adjust drive motor
72
through drive worm shaft
72
a
and worm wheel
75
.
Horizontal adjustment of the main vertical frames
21
b
is achieved by operation of the forming roll with adjust drive motor
71
. Operation of the motor
71
causes rotation of the driving worm shaft
71
a
which causes horizontal movement of the main vertical frames
21
b,
toward and away from each other depending on the direction of the rotation of the shaft
71
a.
FIGS. 14 through 18
are more detailed depictions of the forming roll mechanisms of a three point bending stand
21
. Each forming roll mechanism includes a roll gap adjusting motor
82
which drives a pinion
82
a.
The pinion
82
a
engages a gear fixed to the end of a screw rod
83
. The screw rod
83
is axially fixed but rotatable within an internally threaded member
84
such that rotation of the screw rod
83
results in movement of the threaded member
84
along the screw rod
83
. The top roll holder
85
is connected to the threaded member
84
and slides along a top roll slide roll
86
when the screw rod
83
is rotated within the threaded member
84
. Motion of the top roll holder
85
along the slide rail
86
causes movement of the top roll
91
towards or away from the bottom roll
94
. As can be seen in
FIGS. 14 through 18
, the main adjustment of the position of the top roll
91
is at an angle of about 45° relative to horizontal. A fine adjustment mechanism
89
may be used to further adjust the position of the top roll
91
with respect to its associated bottom roll
94
. The bottom roll
94
is mounted to a bottom roll support shaft
93
which is in turn carried by a bottom roll holder
95
. The bottom roll holder
95
is attached to and carried by a vertical base plate
81
. Depending upon the gap between the top roll
91
and the bottom roll
94
, the curvature of the sheet passing through the rolls
91
and
94
can be increased or decreased by the use of the three point bending technique which will be described in more detail below.
Each of the bottom rolls
94
shown in
FIGS. 14 through 18
has a V-shaped configuration which supplies two of the three points in a three point bending technique. The top roll
91
is a generally narrow roll which provides the third and middle point of a three point bending operation. As can be seen in
FIGS. 19 and 20
, bringing the top roll
91
close to the bottom roll
94
results in a relatively sharp, or small radius, curvature in the sheet between the rolls for use in making smaller diameter tubing. In contrast, the provision of a larger gap between the top roll
91
and the bottom roll
94
results in a less curved sheet as shown in
FIG. 19
, which results in larger diameter tubing. The same top and bottom rolls are used in each case, thus reducing costs associated with the manufacture (or acquisition) or rolls and the labor and down-time associated with changing rolls.
The shape and orientation of the top rolls
91
and bottom rolls
94
in a three-point bending stand
21
are important. The bottom rolls
94
have an overall V-shaped configuration, with each bottom roll
94
having two frustoconical (i.e. partially conical) sections which meet at a circumferential crease. The crease defines a plate in which the bottom rolls
94
are disposed. The planes defined by the two bottom rolls of a three-point bending stand are generally parallel to the longitudinal axis (or Z-axis ) of the machine, i.e. they are generally parallel to the direction of the flow of workpiece material through the machine. The three points (or workpiece engagement locations) referred to as part of a three-point bending technique are the two points of contact on the V-shaped bottom rolls
94
, and the single point of contact provided by the narrow top roll
91
. The degree of curvature obtained by this combination of rolls can be varied greatly simply by adjusting the gap between the rolls. Depending upon the thickness of the sheet material and the distance between the top and bottom rolls, a small or large diameter bend will be imparted to the sheet. One distinct advantage of using a three-point bending technique of the present invention is the reduced amount of friction as compared with tube forming methods in which there is broad lengths of contact between a forming roll and a workpiece. The broad lengths of contact not only create added friction which is not the case with the present invention, but more contact can, in some instances, result in a greater chance for marring of the surface of tube, which can result in tubing products which are not acceptable to customers. It should be noted that planes as they are referred to herein, and in the tube forming field generally, are defined with reference to axes, i.e. the X-axis being the transverse horizontal axis (with respect to work flow), the Y-axis being a vertical transverse axis, and the Z-axis being the longitudinal axis or the direction of work flow. A plane is sometimes identified by reference to the axes which lie in or are parallel to the plane.
FIGS. 21
,
22
and
23
are end elevational, side elevational and top plan views, respectively, of a brimmed roll stand
31
of the present invention. The brimmed roll
133
a
are carried by brimmed roll holders
133
, each of which includes an adjusting mechanism. The brimmed roll holders
133
are mounted to main vertical frames
132
. The lateral positions of which are controlled in a manner similar to the lateral position adjustment mechanism of previously described three-point roll stands
21
shown in
FIG. 10
, i.e., the lateral position is adjusted by operation of the width adjust drive motor
137
, and the vertical position of the brimmed roll holders
133
is adjusted by operation of the height adjust drive motor
136
.
The brimmed roll stand
31
includes a pair of brimmed rolls
133
a,
each of which engages an edge of a sheet. The shape of a brimmed roll, as shown in
FIGS. 24 and 25
, includes a cicumferential slot with frustoconica sections forming an angle of somewhat less than about 90 degrees. A third or bottom roll
139
in a brimmed roll stand
31
engages the underside of the sheet to support and provide upward bending force to the sheet which is resisted by the two brimmed rolls
133
a.
The vertical position of the bottom roll
139
is adjusted by operation of the bottom roll height adjust drive motor
136
. The motor
135
drives the drive shaft
135
b
which is connected to a worm and worm wheel gearbox
135
a.
Adjustment of the brimmed roll body
144
, as shown in
FIGS. 24
,
25
,
26
and
28
, is in the X-Y plane. Vertical adjustment in the X-Y plane of the position of the brimmed roll body
144
is achieved by use of adjustment mechanism
142
. Rotation of the shaft
142
a
results in rotattion of the worm
142
c
carried thereby. The worm
142
c
engages the teeth
145
a
in the top roll holder
145
, and rotational movement of the worm
142
c
results in rotation upward and downward of the brimmed roll holder
145
and brimmed roll body
144
. Dotted lines in
FIG. 28
show various positions of the brimmed roll assembly by
133
a
which achievable by rotation of the worm
142
c.
It should be noted that the worm and associated teeth are shown schematically without reference numerals in
FIGS. 21 and 24
.
FIG. 29
shows a cage roll stand
41
of the kind used in combination with other roll stands, as shown in
FIGS. 1 and 2
, to achieve a tube in accordance with the present invention. Opposing forming roll assemblies
153
include cage rolls
161
acting upon a sheet in combination with a single bottom roll
159
. Each cage roll
161
is held by a cage roll holder
163
, and each cage roll
161
pivots on a cage roll shaft
162
. The cage roll holders are mounted to main vertical frames
152
, which include vertical slide rails
153
b.
The cage roll holders
163
are raised and lowered by rotation of the screw rod
153
c
within a threaded bore in the cage roll holders
163
. The lateral position of the cage rolls
161
is adjusted by operation of the cage roll width adjusting motor
157
which moves the vertical frames
152
on slide rails
152
b.
The cage roll height adjusting motor
156
is used to raise and lower the cage roll holders
163
(and the cage rolls
161
). The drive motor
155
drives the shaft
155
b,
which connects to the gear box
155
a,
to raise and lower the bottom roll
159
.
FIG. 31
shows the rolls
161
and
159
which are typical of the cage roll stands
41
used as part of the present invention.
While specific embodiments of the inventions disclosed herein have been shown and described in detail, those embodiments are only examples, and it will be apparent to those skilled in the art that numerous other alternatives, modifications, and variations of the inventions may be made without departing from the spirit and scope of the appended claims.
Claims
- 1. A station in a tube forming machine comprising at least one set of forming rolls, said set including a first V-shaped bottom roll and a first top roll opposing said first V-shaped roll, said first V-shaped bottom roll and said first top roll defining a first group of three workpiece engagement locations, said first group of three locations defining a first three-point bending arrangement between said at least one set of forming rolls,said top roll being adjustable toward and away from said bottom roll with said top roll being movable to a plurality of positions defining a line of adjustability, and said bottom roll being mounted rotatable to a bottom roll holder by a bottom roll support shaft, said bottom roll support shaft being generally perpendicular to said line of adjustability, whereby said top roll and said bottom roll are useable together to form tubes with different diameters.
- 2. A station in a tube forming machine in accordance with claim 1 including a second set of forming rolls, said second set including a second V-shaped bottom roll and a second top roll opposing said second V-shaped bottom roll, said second set of forming rolls defining a second set of three workpiece engagement locations, said second set of three workpiece engagement locations defining a second three-point bending arrangement between said second pair of rolls, said second top roll being adjustable toward and away from said second bottom roll, with said second top roll being movable to a plurality of positions defining a second line of adjustability, and said second bottom roll being mounted rotatable to a bottom roll holder by a second bottom roll support shaft, said second bottom roll support shaft being generally perpendicular to said second line of adjustability.
- 3. A station in accordance with claim 1 wherein:said first and second sets of forming rolls are laterally adjacent to one another and opposite sides of a strip of workpiece material are partially formed into a tubular shape by said first and second set of rolls at a single three point bending stand.
- 4. A station in accordance with claim 1 wherein:said first V-shaped bottom roll has a central circumferential crease with frustoconical portions adjacent to each side of said crease, said crease defining a plane, said plane being generally parallel to a direction of flow of said workpiece material though said station, said top roll being moveable generally along said plane to form a gap between said top roll and said bottom roll, said gap being usable to determine the curvature imparted to said workpiece material as it passes between said set of rolls.
- 5. In a tube forming station, a brimmed tube forming roll having a slot for receiving an edge of a sheet, said slot being formed by a first annular portion with a first surface and a second annular portion with a second surface, said first annular portion having a diameter greater than the diameter of said second annular portion, said brimmed tube forming roll being mounted to a roll support and being movable to various positions in an X-Y plane of said station.
- 6. A tube forming roll in accordance with claim 5 wherein:said first and second surfaces form said slot with an included angle of less than about 90°.
- 7. A tube forming roll in accordance with claim 5 wherein said support includes a rotatable worm and a worm wheel segment to which said roll is mounted, whereby said roll may be adjusted to said various positions in said X-Y plane.
- 8. A tube forming machine with a plurality of forming stations comprising a first station including a first top roll and first bottom roll, said first top roll and said first bottom roll being aligned for gripping and driving a sheet to be formed into a tube, at least a portion of said first bottom roll defining a V-shaped profile, a second station including at least one second bottom roll and at least one second top roll, at least a portion of said second bottom roll having a V-shaped profile, a third station with at least one pair of third top rolls, each of said third top rolls having a circumferential slot into which an edge of said sheet fits,said first top roll being mounted on a support shaft, at least one end of said support shaft being forced by action of separately controllable hydraulic pressing cylinder to urge said first top roll into gripping engagement with said sheet against said first bottom roll.
- 9. A tube forming machine in accordance with claim 8 wherein:said second station includes a single second top roll and a single second bottom roll, said single top roll having a width substantially less than the width of said single second bottom roll, whereby engagement of said sheet by said second top roll and said second bottom roll results in three-point bending of said sheet.
- 10. A tube forming machine in accordance with claim 8 wherein:said second station includes two sets of second-station rolls, each set comprising a second-station bottom roll having a V-shaped profile and a second-station top roll with a width substantially narrower than said second-station bottom roll, whereby two portions of said sheet are subjected to three-point bending at said second station.
- 11. A tube forming machine in accordance with claim 8 wherein:said third top rolls press said sheet against a single third-station bottom roll.
Priority Claims (1)
Number |
Date |
Country |
Kind |
10-237561 |
Aug 1998 |
JP |
|
US Referenced Citations (4)