EP2731737A1

EP2731737A1 - Apparatus and method for producing shear deformation

Info

Publication number: EP2731737A1
Application number: EP12810616.8A
Authority: EP
Inventors: Peter Thomson; Silvio MATTIEVICH; James SANDLIN
Original assignee: CECAP Pty Ltd
Current assignee: CECAP Pty Ltd
Priority date: 2011-07-11
Filing date: 2012-07-11
Publication date: 2014-05-21
Also published as: RU2014101249A; WO2013006910A1; AU2012283755A1; BR112014000529A2; US20140137621A1; KR20140066694A; ZA201400494B; EP2731737A4; CN103648672A; JP2014520673A; CA2841333A1

Abstract

An apparatus for producing shear deformation in a work piece, the apparatus comprising: a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other; a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection, wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel.

Description

APPARATUS AND METHOD FOR PRODUCING SHEAR DEFORMATION

FIELD OF THE INVENTION The present invention relates to an apparatus and method of processing a material by performing a shear deformation process. More particularly, but not exclusively, the invention relates to producing shear deformation in a metal.

BACKGROUND OF THE INVENTION

Severe plastic deformation processes can be used to improve the physical properties of a material. Machines for producing shear deformation in a work piece have been previously proposed though reduction to commercial practice has been problematic. In particular, the process has been difficult to maintain for continuous sheet products as the work piece has a tendency to jam in the apparatus, causing the process to halt.

Examples of the invention seek to solve, or at least ameliorate, one or more disadvantages of previous machines for producing shear deformation in a work piece. SUMMARY OF THE INVENTION

According to the present invention, there is provided an apparatus for producing shear deformation in a work piece, the apparatus comprising: a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other; a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection, wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel.

According to the present invention, there is also provided an apparatus for producing shear deformation in a work piece, the apparatus comprising: a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other; a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection, wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece so that the pressure imparted by the drive members on the work piece is maintained at a substantially constant level.

Preferably, each die face includes a plurality of drive members each separated by a guide plate to support the material and thus to prevent buckling. An external surface of the drive members can extend into the first channel section to impart pressure on the work piece. Preferably, each drive member is in the form of a roller, an external surface of which forms part of the die face.

Preferably, the rollers of a respective die face are disposed within a die block, an outer surface of which forms the die face. The separation of the die faces can be varied by moving a single die block relative to the other die block. The single die block can be slidably supported on a plurality of shafts which are disposed perpendicular to the first channel section so as to allow the separation of the die faces to vary. Movement of the die block along the shafts can be restrained by the action of a resilient spring element acting on the die block so that a pressure imparted on the work piece by each die face remains substantially constant. Preferably, at least one of the shafts has a head at one end thereof and the resilient spring element is a plurality of spring washers which are disposed between the at least one head and the die block. The single die block can be movable under the action of a hydraulic system.

In one embodiment, the drive members include a plurality of opposing clamping elements.

Preferably, the clamping elements are disposed around a pair of endless drive members, the clamping elements engaging the work piece as they travel around a straight portion of each endless drive member. Preferably, each endless drive member is a chain.

Preferably, a surface of the clamping elements which is arranged to engage the work piece is grooved, the grooves configured to accept corresponding protrusions on a support member so that as the clamping elements pass around a curved portion of an endless drive member, contact with the work piece passes from the clamping elements to a respective support member.

The support member can be fixed relative to the apparatus and an outer face of the support member can form a part of the first channel section. Preferably, the separation of the clamping elements is variable under the action of a hydraulic system.

Preferably, the apparatus further includes a plurality of drive members disposed in the second channel section to pull the work piece through the processing channel. Preferably, the drive members are configured so that a combined contact area of the drive members acting on the work piece in the first channel section is substantially equal to a combined contact area of the drive members acting on the work piece in the second channel section. The apparatus can further include a roller at the intersection of the first and second channel sections, the roller being disposed across the processing channel from the drive surface. Preferably, the radius of the roller is less than half the thickness of the work piece to obviate a reduction in the shear deformation of the work piece. In practice, the drive surface is at the outer side of the corner formed by the intersection and the roller is at the inner side of the corner.

Preferably, the apparatus further includes a lubrication system configured to apply lubricant to the work piece before the work piece passes through the intersection.

Preferably, the drive surface is an external surface of a roller.

According to the present invention, there is also provided a method for processing metals, including driving a work piece to be treated through a processing channel, the processing channel having first and second channel sections which intersect and are disposed at an angle to each other, the work piece undergoing shear deformation at the region of intersection between said first and second channels, wherein the work piece is driven through the first channel section by engagement of the work piece with a plurality of drive members, the method including varying a separation of the drive members in response to thickness variations of the work piece to maintain drive of the work piece.

Preferably, the work piece is driven through an angle of approximately 90 degrees when passing through the intersection. Preferably, the drive members engage the work piece in . both the first and second channel sections and the contact area of engagement in the first channel section is substantially equal to the contact area of engagement in the second channel section. . ^"

The method can further include the steps of twisting a leading edge of the work piece after it exits the second channel, fixing it to a trailing edge of the work piece to form a continuous mobius strip and feeding it back into the first channel. Preferably, the mobius strip is passed through the processing channel four times.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described, by way of non-limiting example only, with reference to the accompanying drawings in which:

Figure 1 is a schematic sectional diagram of an apparatus for producing shear deformation in a work piece of one embodiment of the invention;

Figure 2 is close sectional view of the apparatus of Figure 1 ;

Figure 3 is another close sectional view of the apparatus of Figure 1 , the section taken along a different plane;

Figure 4 is a close schematic diagram of another apparatus for producing shear deformation in a work piece;

Figure 5 is a perspective view of another apparatus for producing shear deformation in a work piece;

Figure 6 is a close side view of the apparatus of Figure 5;

Figure 7 is a closer view of the apparatus of Figure 5;

Figure 8 is a close perspective of the apparatus of Figure 5; and

Figure 9 is another close perspective of the apparatus of Figure 5 with one of the support members removed for clarity.

DETAILED DESCRIPTION With reference to Figure 1, there is shown an apparatus 10 for producing shear deformation in a work piece. The apparatus 10 comprises a processing channel 12 through which the work piece passes. The processing channel 12 includes first and second channel sections 14, 16 respectively which are of substantially equal cross section and intersect at an angle to each other. The first and second channel sections 14, 16 are shown as being at an angle of 90 degrees to each other, though it will be appreciated that the first and second channel sections 14, 16 could be arranged at other angles which would preferably be in the range of 90 to 135 degrees.

A plurality of drive members 18, in the form of opposing drive rollers, are provided and are configured to engage sides of the work piece to drive it through the processing channel 12 so that the work piece passes from the first channel section 14 to the second channel section 16 to produce shear deformation in the work piece.

The apparatus 10 also comprises a drive surface 20, in the form of an external surface of a drive roller, which is disposed at an intersection of the first and second channel sections 14, 16 at the outer side of the corner formed by the insection. The drive surface 20 is configured to engage the work piece and advance it through the intersection. A replaceable wear tip 31 may be disposed across from the drive roller 20 at the inner side of the corner formed by the intersection. The wear tip may be formed of tungsten carbide. As illustrated in Figure 2, opposing sides of the first channel section 14 are defined by a pair of die faces 22a, 22b, relative to which the drive rollers 18 are rotatably fixed. The separation of the die faces 22a, 22b is variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel. Variation of the separation of the die faces 22a, 22b allows the pressure imparted by the drive rollers 18 on the work piece to be maintained at a substantially constant level.

It was not previously considered that variations in the gauge of the material used for a work piece had any substantial affect on the process. Having regard to the magnitude of the thickness variations in comparison to the forces required to produce shear deformation, such an issue has previously been considered counterintuitive because the variation in material thickness is generally small, in the order of tenths of a millimetre, and materials typically used in the shear deformation process have elastic properties which allow them to withstand increased contact pressures. Surprisingly, it has been found that variations in the thickness of a work piece, even variations within manufacturer's tolerances, can lead to interruptions in drive of the work piece and bring the process to a halt. The applicant has found that by providing an apparatus which can take into consideration slight variations in material thickness and provide a constant driving pressure on the work piece, drive may be maintained on the work piece and unintentional interruption of the process can be reduced, thereby allowing for a more continuous process to be achieved.

In prior apparatus, the height of the first channel 16 or the gap between the die faces 22a, 22b or the drive means 18, which typically includes rollers or a belt, was equal to the nominal thickness of the gauge of the incoming material. In practice, the thickness of the work piece would vary a small amount and, as a result, when the work piece is fed through the fixed-gap rollers, the rollers will apply less or more pressure on the work piece as the thickness decreases and increases respectively. When a thicker section of work piece passes through the rollers, the material may be plastically deformed, which in turn work- hardens the material before it goes through the shear process. Not only will this affect the outcome of the process, but it can also extrude the material and cause damage to the equipment. When thinner material passes into the rollers, the rollers can lose traction which affects their ability to drive the work piece through the machine, causing the process to stall.

In one example, each die face 22a, 22b includes a plurality of drive rollers 18 each separated by a guide surface 24 which supports the material and prevents buckling. The surface 24 may be in the form of a plate. An external surface of the drive rollers 1 8 extends into the first channel section 14 to form part of the die face and to impart pressure on the work piece to engage it and drive it through the processing channel 12. As the drive roller extends into the first channel section, compressive forces will be imparted onto the work piece. The level of compressive stresses in the work piece will be below a level at which plastic deformation occurs so that the work piece is not extruded as it passes through the processing channel 12.

The drive rollers 18 of a respective die face 22a, 22b are disposed within a respective die block 26a, 26b. An outer surface of each die block 26a, 26b incorporates the buckling surface 24 so that the outer surface forms the die face 22a, 22b. By incorporating the drive rollers 18 and the guide surface 24 into a die block, the separation of the die faces 22a, 22b can be varied by moving either or both of the die blocks. For simplicity, in apparatus 10, only a single die block, the inner die block 26b. moves relative to the other die block 26a, thereby allowing the pressure imparted by the drive rollers 18 on the work piece can be maintained substantially constant to maintain drive of the work piece through the processing channel.

The inner die block 26b is slidably supported on a plurality of shafts (not shown) which are received through bore holes 28. Although only the lower bore holes 28 are shown in Figure 1 , both upper and lower bore holes 28 are provided. Figure 3 illustrates the configuration of an upper bore hole 28. Both the upper and lower bore holes may be staggered relative to each other or otherwise aligned. The shafts are disposed perpendicular to the first channel section 14 so as to allow the separation of the die faces 22a, 22b to vary relative to each other whilst maintaining a generally parallel relationship. The shafts extend between the die blocks 26a, 26b and through the first channel section 14 at a height which will be above and/or below the work piece in use.

It will be appreciated that the shafts may be otherwise fixed relative to the apparatus so that the shafts don't impinge on the first channel section 14. In this regard, the inner die block 26b may be suspended within the apparatus 10 relative to the fixed die block 26a external to the first channel section 14.

Movement of the inner die block 26b along the shaft is restrained by the action of a resilient spring element (not shown) acting on the die block 26b so that a pressure imparted on the work piece by each die face remains substantially constant. In this regard, the shaft has a head at one end thereof. The head of the shaft is configured to be received in a correspondingly shaped aperture in bore hole 28. The resilient spring element is a plurality of spring washers which are disposed between the head and the die block.

Movement of the inner die block 26b has been described in relation to a spring loaded system. It will be appreciated that movement of the single die block 26b may similarly be performed by other means, such as under the action of a hydraulic system.

The apparatus 10 further includes a plurality of drive members 18 which are disposed in the second channel section 16 to pull the work piece through the processing channel 12. In the embodiment shown, these are also in the form of rollers. The drive members 18 are configured so that a combined contact area of the drive members 18 acting on the work piece in the first channel section 14 is substantially equal to a combined contact area of the drive members 18 acting on the work piece in the second channel section 16. The drive members 18 acting in the second channel section to pull the work piece apply a controlled pressure to the work piece whereby in conjunction with the controlled pressure applied by the drive members acting in the first channel section control the ratio of forces at the entry and exit sides of the apparatus and thereby a controlled tension is applied to the work piece.

Figure 4 illustrates a roller 30 which is provided to assist in movement of the work piece through the intersection of the first and second channel sections 14, 16. The roller 30 is disposed across the second channel section 16 from the drive roller 20 and thereby at the inner side of the corner formed by the intersection. The radius of the roller 30 is less than half the gauge or thickness of the work piece. It will be appreciated that if the radius of the roller 30 is too large, the amount of shear deformation performed by the work piece will be reduced. If the radius of the roller is too small, it we be difficult to manufacture and vulnerable to breakage. A void 32 may be provided behind the roller 30 for the introduction of lubrication to the work piece. In such an arrangement, the roller 30 would drag the lubricant around its surface and onto the work piece.

In the embodiments shown in Figures 1 to 4, the drive members are shown as drive rollers 18. It will be appreciated that the drive rollers 18 may be substituted with other drive means such as a belt.

Figure 5 illustrates another embodiment of the invention. In this embodiment, the apparatus 1 10 includes a plurality of clamping elements 1 18 which have a generally planar surface for contacting the work piece and are disposed around a pair of endless drive members 130a, 130b, each of which is in the form of a chain. Each chain 130a. 130b passes around a pair of opposing sprockets 132. Each sprocket 132 is arranged so that clamping elements 1 18 which are coupled to a respective chain are in opposing relationship with the clamping elements which are coupled to the other chain so that a first channel section 1 14 is defined between the clamping elements 1 1 8. The clamping elements 1 18 engage a work piece 1 1 1 as they travel around a straight portion of each chain 130a, 130b so as to drive the work piece 1 1 1 through the apparatus 1 10.

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The first and second channel sections 1 14, 1 16 are of substantially equal cross section and intersect at an angle of 90 degrees to each other, though it will be appreciated that the first and second channel sections 14, 16 could be arranged at other angles which would preferably be in the range of 90 to 135 degrees. The second channel section 1 16 extends between an external surface of a drive roller 120 and a die member 134. As a work piece passes 1 1 1 through the apparatus 1 10 from the first channel section 1 14 to the second channel section 1 16, it will contact the drive roller 120 which engages the work piece 1 1 1 and advances it through the intersection. Although the second channel section 1 16 is shown as having a curved profile, it will be appreciated that the first and second channel sections intersect at an angle of 90 degrees and the work piece will be subject to shear deformation through an angle of 90 degrees.

Disposed adjacent the drive roller 120 are a plurality of idler pulleys 136 which are rotatably fixed relative to the drive roller 120. The spacing between the drive roller 120 and the idler pulleys is such that as the work piece 1 1 1 passes through the second channel section 1 16, it is compressed between the idler pulleys and the drive roller 120 so that it is pulled through the second channel section 1 16. As discussed in connection with the first embodiment a controlled tension is applied to the workpiece as it is pulled through the apparatus.

As illustrated in Figure 8, a surface of the clamping elements 1 18 which is arranged to engage the work piece 1 1 1 is grooved. The grooves 140 are configured to accept corresponding protrusions 142 on a support member 144 so that as the clamping elements 1 18 pass around a curved portion of the chain 130a, 130b, contact with the work piece 1 1 1 passes from the clamping elements 1 18 to a respective die face in the first channel section 1 14.

Figure 9 illustrates the apparatus 1 10 with an upper support block 140 removed. It can be seen that the protrusions 142 are configured for close fitting engagement with the grooves 140. Each of the support members 144 is fixed within the apparatus 1 10 and an outer face of the support member 144 forms a part of the first channel section 1 14.

The separation of the clamping elements 1 18, and thus the height of the first channel section 1 14, is variable under the action of a hydraulic system which includes two hydraulic rams 150. Each ram acts on a coupling member 150 to urge an upper pair of sprockets 132, and in turn the chain 130a and the clamping elements 1 18 coupled thereto, toward a lower pair of sprockets, thereby controlling a contact pressure applied by the clamping elements on the work piece 1 1 1. The hydraulic rams 150 are configured to apply a relatively constant pressure on the sprockets so that a relatively constant pressure may be applied to the work piece - I l l despite variations in thickness. If the height of the first channel section 1 14 could not be varied, as the thickness of the work piece varied pressure upon it would change and the clamping elements 1 18 may lose engagement, causing the process to stall.

After the work piece 1 1 1 passes through the second channel section 1 16, the work piece exits the apparatus 1 10 along conveyors 138 where it may be coiled or processed through another process.

The apparatus 1 10 may also include a roller (not shown) at the inside of the corner formed by the intersection of the first and second channel sections 1 14, 1 16. The roller would be disposed across the second channel section 1 16 from the drive roller 120. Again, the radius of the roller is less than half the gauge or thickness of the work piece. It will be appreciated that if the radius of the roller is too large, the amount of shear deformation performed by the work piece will be reduced. A void may be provided behind the roller for the introduction of lubrication to the work piece. In such an arrangement, the roller would drag the lubricant around its surface and onto the work piece.

Embodiments of the invention may include means for reducing friction within the apparatus. In this regard, either of apparatuses 10, 1 10 may include a lubrication system configured to apply lubricant to the work piece before the work piece passes through the intersection of the first and second channel sections.

Embodiments of the invention also relate to a method for processing metals. The method includes driving a work piece to be treated through a processing channel which has first and second channel sections which intersect and are disposed at an angle to each other. The work piece undergoes shear deformation at the region of intersection between said first and second channels. The work piece is driven through the first channel section by engagement of the work piece with a plurality of drive members. The method includes varying a separation of the drive members in response to thickness variations of the work piece to maintain drive of the work piece. Advantageously, thickness variations of the work piece may be accommodated without compromising drive consistency of the work piece and continuity of the process.

The work piece is driven through an angle of approximately 90 degrees when passing through the intersection. The drive members engage the work piece in both the first and second channel sections and are configured so that the contact area of engagement in the first channel section is substantially equal to the contact area of engagement in the second channel section.

Because the work piece undergoes shear deformation in one direction, the described method does not provide uniform material properties in the work piece. Accordingly, it is desirable to repeat the process on the material by performing shear deformation in an opposite direction to provide more uniform material properties in the work piece. This may be achieved by arranging two apparatuses in series with each other, however, it will be appreciated that the cost of such an arrangement may be prohibitive.

In one embodiment, the method includes the step of twisting a leading edge of the work piece after it exits the second channel and feeding it back into the first channel to form a continuous mobius strip. The leading edge of the work piece may be welded to a trailing edge of the work piece after twisting so that it is drawn into the apparatus to be processed again. It has been found that if a work piece is processed a plurality of times, its material properties continue to increase, though with diminishing magnitudes. Processing a work piece four times, i.e. twice in each direction, has been found to be a good compromise in terms of increased properties and processing time. Accordingly, the method may include the step of passing the mobius strip through the processing channel four times.

The embodiments have been described by way of example only and modifications are possible within the scope of the invention disclosed.

Claims

1. An apparatus for producing shear deformation in a work piece, the apparatus comprising:

a processing channel through which the work piece passes, the processing channel including first and second channel sections which intersect at an angle to each other;

a plurality of drive members configured to engage sides of the work piece to drive it through the processing channel so that the work piece passes from the first channel section to the second channel section to produce shear deformation in the work piece; and a drive surface disposed at an intersection of the first and second channel sections, the drive surface being configured to engage the work piece and advance it through the intersection,

wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece to maintain drive of the work piece through the processing channel.

2. An apparatus for producing shear deformation in a work piece, the apparatus comprising:

a processing channel through which the work piece, passes, the processing channel including first and second channel sections which intersect at an angle to each other;

wherein opposing sides of the first channel section are defined by a pair of die faces relative to which the drive members are rotatably fixed, the separation of the die faces being variable in response to thickness variations of the work piece so that the pressure imparted by the drive members on the work piece is maintained at a substantially constant level.

3. An apparatus according to claim 1 or claim 2, wherein each die face includes a plurality of drive members each separated by a guide plate.

4. An apparatus according to any one of the preceding claims, wherein an external surface of the drive members extend into the first channel section to impart pressure on the work piece.

5. An apparatus according to any one of the preceding claims, wherein each drive member is in the form of a roller, an external surface of which forms part of the die face.

6. An apparatus according to claim 5, wherein the rollers of a respective die face are disposed within a die block, an outer surface of which forms the die face.

7. An apparatus according to claim 6, wherein the separation of the die faces is varied by moving a single die block relative to the other die block.

8. An apparatus according to claim 7, wherein the single die block is slidably supported on a plurality of shafts which are disposed perpendicular to the first channel section so as to allow the separation of the die faces to vary.

9. An apparatus according to claim 8, wherein movement of the die block along the shafts is restrained by the action of a resilient spring element acting on the die block so that a pressure imparted on the work piece by each die face remains substantially constant.

10. An apparatus according to claim 9, wherein at least one of the shafts has a head at one end thereof and the resilient spring element is a plurality of spring washers which are disposed between the at least one head and the die block.

1 1 . An apparatus according to claim 7, wherein the single die block is movable under the action of a hydraulic system.

12. An apparatus according to claim 1 or claim 2, wherein the drive members include a plurality of opposing clamping elements.

13. An apparatus according to claim 12, wherein the clamping elements are disposed around a pair of endless drive members, the clamping elements engaging the work piece as they travel around a straight portion of each endless drive member.

14. An apparatus according to claim 13, wherein each endless drive member is a chain.

1 5. An apparatus according to any one of claims 12 to 14, wherein a surface of the clamping elements which is arranged to engage the work piece is grooved, the grooves configured to accept corresponding protrusions on a support member so that as the clamping elements pass around a curved portion of an endless drive member, contact with the work piece passes from the clamping elements to a respective support member.

16. An apparatus according to claim 15, wherein the support member is fixed relative to the apparatus and an outer face of the support member forms a part of the first channel section.

1 7. An apparatus according to any one of claims 1 1 to 16, wherein the separation of the clamping elements is variable under the action of a hydraulic system.

18. An apparatus according to any one of the preceding claims, further including a plurality of drive members disposed in the second channel section to pull the work piece through the processing channel.

19. An apparatus according to claim 18, wherein the drive members are configured so that a combined contact area of the drive members acting on the work piece in the first channel section is substantially equal to a combined contact area of the drive members acting on the work piece in the second channel section.

20. An apparatus according to any one of the preceding claims, wherein the apparatus further includes a roller at an inner corner of the intersection of the first and second channel sections, the roller being disposed across the processing channel from the drive surface.

21. An apparatus according to claim 20, wherein the radius of the roller is less than half the thickness of the work piece.

22. An apparatus according to any one of the preceding claims, wherein the apparatus further includes a lubrication system configured to apply lubricant to the work piece before the work piece passes through the intersection.

23. An apparatus according to any one of the preceding claims, wherein the drive surface is an external surface of a roller.

24. A method for processing metals, including driving a work piece to be treated through a processing channel, the processing channel having first and second channel sections which intersect and are disposed at an angle to each other, the work piece undergoing shear deformation at the region of intersection between said first and second channels, wherein the work piece is driven through the first channel section by engagement of the work piece with a plurality of drive members, the method including varying a separation of the drive members in response to thickness variations of the work piece to maintain drive of the work piece.

25. A method according to claim 24, wherein the work piece is driven through an angle of approximately 90 degrees when passing through the intersection.

26. A method according to claim 24 or claim 25, wherein the drive members engage the work piece in both the first and second channel sections, the contact area of engagement in the first channel section being substantially equal to the contact area of engagement in the second channel section.

27. A method according to any one of claims 24 to 26, further including the steps of twisting a leading edge of the work piece after it exits the second channel, fixing it to a trailing edge of the work piece to form a continuous mobius strip and feeding it back into the first channel.

28. A method according to claim 27, wherein the mobius strip is passed through the processing channel four times.