CA1078594A - Method and apparatus for sculpturing pile fabrics - Google Patents

Abstract

METHOD AND APPARATUS FOR
SCULPTURING PILE FABRICS

Abstract of the Disclosure The pile is trimmed from selected regions of pile fabrics by applying stiffening agent to the region from which the pile is to be trimmed, this stiffening agent is then hardened and the fibers are then severed from the region to which stiffen-ing agent was applied by drawing the fabric past a cutter having a blade which allows the fibers in the untreated regions to deflect out of its path but severs the fibers to which stiffening agent has been applied. Residual stiffening agent is then removed by scouring.

Description

This invention relates to sculpturing the pile of pile fabrics. More particularly this inven-tion relates to a method ~or removing the pile from selected regions of a pile fabric to form either a predetermined or a random pattern.
Methods of removing the pile from selected regions of pile ~abrics axe well known; hDwever, _ ~ _ many o~ the prior art methods have serious dis-advantages in that size or adhesive is applied to the regions from which tha pile is not to be re-moved and then the pile is crushed or compressed in those regions. This requires large amounts of .

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size or adhesive and the crushing results in degra-dation of the fibers in those regions where the pile is to remain intact.
U. S. Patent Number 605,710 discloses a mekhod in which size is applied to all of the fibers of a pile fabric. The fibers in the regions from which the fibers are not to be removed are then crushed below the level of the fibers in the regions from which the pile is to be removed. The pile is then sheared from the region which has not been crushed.
The size is then removed from the fabric.
U. S. Patent Number 3,422,512 discloses a similar method wherein adhesive is applied only to the regions from which the pile is not to be re-move~.
It is an object of the invention to provide a method of removing the pile from selected regions of pile fabric without degrading the fibers in other regions.
It has been discovered that it is possible to achieve these objects by applying a stiffening agent to those regions from which it is desired to remove the pile. The stiffening agent is then hardened and the fabric is drawn past a blade which allows the fibers in the untreated regions to de-flect out of the way while severing the fibers in the regions to which the stiffening agent has been applied. The residual stiffening agent is then removed by scouring, washing, or other convenient methods.

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This method does not result in degradation of the fibers in the untreated reyions, does not require mechanical means to compress the pile ofthe fabric and is economical of stifening agent.
Figure 1 is a schematic cross-section of the untreated pile fabric.
Figure 2 illustrates sculpturing of a pile fabric by passing it over a roller adjacent to a blade. Only the pile fibers which are embedded in solid stiffening agent are severed.

Figure 3 illustrates the sculpturing of a pile fabric wherein selected fibers have been stiff-ened by application of stiffening agent.
Figure 4 illustrates the sculpturing of a pile fabric as it passes over a nose bar.

Figure 5 is a schematic flow diagram of a process for automatically sculpturing fabric in accordance with the present invention.
Figure 6 is a front elevation of a cutterfor sculpturing of pile fabrics.
Figure 7 is a sectional view taken along line 7-7 in Figure 6.
Figuxe 8 is a sectional view taken along line 8-8 in Figure 6.

Figure 9 is a sectional view taken along line 9-9 in Figure 6.
Figure 10 is a front elevation of a spreader bar.
Figure 11 is an enlarged cross-sectional view showing the threads on a spreader bar.

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Figure 12 is an enlarged front view of the blade in Figure 6, showiny khe curvature of the blade in more detail.
Figure 13 is an enlarged view of the roller support.
Referring now to the drawings, pile fabric 22 is shown in Figure 1. Fabric 22 comprises back-ing 41 and pile 42. In Figure 2, fabric 22 is shown passing over roller 30 adjacent to blade 43. Stiff-ening agent has been applied to selected regions of the pile 42' and hardened to form solid layers in which the fibers of the pile become embedded. As fabric 22 is drawn over roller 30 past blade 43, the fibers in the untreated regions 42" are free to deflect away from blade 30 and are not severed while the embedded fibers in regions 42' are restrained by the stiffening agent and are severed by the blade.
In Figure 3 the amount of stiffening agent that has been applied to the fabric is smaller than theamount that was applied in Figure 2. In this case, the fibers in the treated regions 42' are stiffened and joined together into small clusters of fibers. As these clusters pass o~er roller 30, they are not free to deflect away fro~ blade 43 and are severed.
As before, the fibers in untreated regions 42" are not severed. In Figure 4, roller 30 has been re-placed by nose bar 31.
The method of the present invention may be used on any suitable pile fabrics such as velvets, -velours or even carpets. The me-thod may be used whatever the metho,d of fabric construction, weth-er it be tu~ted, woven, knit or bonded. A material which is particularly well suited to the present invention is a velvet of cut pile and tu~ted con-struction. The pile or face fiber has 13 singles acrylic yarn. There are 25 ends in the weft direc-tion and 40 ends in the warp direction. Pile height is 3/32 inch. The substrate is woven poly-ester of a drill construction having 38 picks per - inch and 68 ends per inch. The tufts are held in with a latex backcoating. Final weight of the fabric is l.l lb/yd2. In order to insure maximum flexibility of the p~le fibers, the fabric may be 15' heated by steaming scouring in hot water or other similar methods before printing.
The fabric may be dyed either before or after sculpturing. If it is to be dyed afterwardst then special care must be taken to remove all residual stiffening agent to avoid imperfections.
For the purposes of the present invention, suitable stiffening agents include any materials which upon hardening tend to have a tendency to sti~fen the fibers in the pile or to bond them to-gether or to harden into a film in which the fibers become imbedded. 5uch stif.~ening agents can include sizing materials, adhesives, admixtures of water and thickening agents, and hot melt adhesive. When an admixture of water and thickening agent i~ used, ~5-~7~35~3~

hardening can be accomplished by freeziny the water.
When a hot melt adhesive is used, hardening is ac-complished by allowiny the adhesive to cool. The preferred stiffening agents are liquid admixtures of water and polyvinyl acetate, polyvinyl alcohol, acrylic monomers, sulfonated polyester type size materials, or methyl cellulose, although many other solvents and adhesives may be used. Typical ad-mixtures will contain from about 9% to 100% solids.
The preferred solids content is around 50% solids.
The preferred stiffening agents have a viscosity with range of 800 to 40,000 cp depending upon the method chosen for application. The most preferred stiffening agents are alkali soluble emulsions of the polymers of acrylic monomers in water having solids contents of approximately 50%. Advanta-geously, the solids of the stiffening agents will be formed from 25-50% ethyl acrylate, 25-50~ methyl acrylate, 20-40% methyl methacrylate and 5-15%
acrylic or methacrylic acid, the total being 100%.
Butyl acrylate, 2-ethyl, hexyl acrylate, and ~ari-ous acrylic esters may also be used. These most pre~erred stiffening agents have sufficient flexi-bility to insure that the film resulting after cur-- ing will pass over the rollers of the eq~ipment without cracking or breaking. If it is desired to apply the stiffening agenks by rotary screen print-ing, it is advantageous to include an anti-drying agent and to adjust the viscosity to around 30,000 cp. Suitable anti-drying agents would include any non-volatile polyglycol having hygroscopic prop-erties such as ethylene glycol, propylene glycol or glycsrine. Many other anti-drying agents will be obvious to those skilled in the art. The viscosity can be adjusted by varying the pH. A liquid ad-mixture of water and thickening agent can also be used as a stiffening agent. In that case, hardening can be accomplished by freezing the water. After sculpturing, residual stiffening agent can then be removed by melting the water. Both natural and synthetic thickening agents can be used. The sodium or ammonium salts of polyacrylic acids are examples o~ suitable synthetic thickeners. Natural thick-eners include but are not limited to gums and alginates. Suitable gums include Gum Arabic, Karaya Gu~, Tragacanth and the gum obtained from locust beans.
Different hot melt adhesives are suitable for 20 ~ different fabrics. Pre~erably the adhesive will be a material which melts below the melting point of the pile fibers but is a solid at ambient tempera-ture.
~he amount of stiffening agent required will depend upon the nature of the fibers in the pile and upon the sizing material. Enough stiffening agent should be applied to cause the fibers in the treat~
ed regions to be unable to deflect out of the path of the blade. The amount of stiffening agent which ~7~

is generally e~ective is from abou~ 254 to 200~ o the weight o~ the pile in the area which is to be treated. In determining the amount of stiffening a~ent to be used, the weight of the pile in those areas which are not to be trimmed is immaterial. It has been found that the higher percentages in this range are preferred and that in the most preferred mode enough stiffening agent is applied to form a continuous layer in which the tops of the fibers of the pile become ;mmersed. If the stiffening agent is applied to form a continuous layer, it is often advantageous to include a blowing agent to gi~e the fibers in the pile an upright posture upon harden-ing. Suitable blowing agents include any substances lS which can be caused to expand greatly or evolve gas when the stiffening agent is hardened.
The stiffening agent may be applied by any method which confines the application to those re-gions in which the pile is to be tr;mmed. Ad~anta-geously, the fibers in the pile may be given an up-right posture before the sizing material is appliedO
Suitable methods include rotary screen printing, s~lk screen ~rinting, roller printing, gravure print-ing, jet printing, and many others, as wlll be apparent to those skilled in the art. Advantage-ously, the fibers of the pile will be maintained in an upright posture while the fabric is being cured.
After application of the stiffening agent, it is hardened. ~ardening includes any step which causes the sizing material to solidify, or causes the fibers to bond together or to become stif~
relatively small amounts o stiffening agent have been applied, the effect of hardening is primarily to stiffen each individual fiber by solidifying the coating of sizing material on each individual fiber.
Hardening will also serve to bind the fibers to-gether into small clusters. If larger amounts of stiffening agent have been used, the effect of hard-ening is to imbed the fibers into a film of solid stiffening agent. In either case, the ability of the treated fibers to deflect out of the path of a blade is decreased while those fibers in the un-treated regions remain free to deflect out of the path o~ the blade. For solvent carried stiffening agent, curing can include any step which results in the removal of the solvent or carrier. I~ an appropriate solvent which evaporates very quickly is used, it could even include self-hardening by exposure to ambient conditions. As stated previous-ly, if an admixture of water and thickening agent is used as a stiffening agent, hardening can be accomplished by freeæing the water and if hot melt adhesives are used~ then hardening is accomplished b~ allowing the adhesives to cool.

For the preferred stiffening agents of this invention, hardening is principally effected by the removal o~ the solvent, usually water, from the stiffening agent. Placin~ the fabric in an oven - 107B5~

at about 300F for 5 minutes lg usually sufficient.
An air impingement heater can also be used. It has been found that if the heater discharges 370F air at a velocity of 8,000 feet per minute, then harden-ing can be accomplished in approximately 2 minutes.
It has also been found that heat from infrared lamps may be used to effect curing. If infrared lamps are used alone for the hardening of the adhesive, and if the speed of the fabric is 3 yards per minute, then 6 to 8 banks of quartz ace heaters 10 inches by 80 inches disposed transverse to the fabric and 9 inches from the face of the fabric are usually suficient, if the faces of the heaters are maintained at 800F. For each combination of stiffening agent and fabric, individual hardening conditions will need to ~e determined to avoid scorching of the fabric. Those skilled in the art are familiar with methods to effect maximum drying while not scorching the fabric.
Such adjustments are not difficult since they can be made as the heater operates based on the appear-ance o the fabric as it leaves the heater. It has been found to be especially advantageous to expose the fabric sequentially to infrared heat and then to an air impingément heater. If the fabric speed is 3 yards per minute, this is best accomplished by passing the fabric first under 4 banks of infrared heaters at 800F as above. The fabric is then ex-posed to the output of an air impingement dryer ~q~)785~

discharging air at about 165F at a velocity of about 8,000 feet per minute for about 1 minute.
A~ter the sti~fening agent has been hardened, the fibers in the treated regions may be trimmed by passing the fabric by a blade which allowsthe fibers in the untreated regions to deflect but severs the fibers in the treated regions. Alternatively, the blade may be drawn past the fabric. Advantageously, the fabric may be drawn over a roller or nose bar which is adjacent to a cutter~ In the most preferred mode, the fabric is drawn over a roller. In Figure 8, fabric 22 is being drawn over roller 30 adjacent to blade 43, the motion of which blade is parallel to the surface of support roller 30. As the fibers in the untreated regions pass over roller 30, they are free to deflect away from blade 43 and are not severed. The ~ibers in the treated regions are severed by blade 43 as they pass over the roller 30.
It has been found that if the included angle of the blade is about 60 and if the speed of the fabric is from about 3 to 20 feet per minute and if the speed of the blade is less than about 300 feet per minute, then the fibers in the untreated regions will not be severed, but the fibers in the treated regions will be severed. For~each fabric speed, there appears to be an optimum blade speed. If the fabric speed is 5 feet per minute, it has been found that the best results are obtained when the speed of the blade is approximately S0-100 ~eet per mlnute. The optimum location of the edge of the blade with respect to the nose bar or roller varies with the type o~
fabric being treated. The optimum location is deter-mined by adjusting the cutter while it is running.
It is then possible to determine visually when satis-factory sculpturiny is taking place.
After sculpturing, the fabric may be scoured to remove residual stiffening agent, if any. If the stiffening agent contains acrylic monomers, it is advantageous for the scouring solution to be slightly alkaline.
The present invention can be carried out in a continuous operation on the apparatus shown in Figure 5. Figure 5 shows a storage roller 20, rotary screen printer 24, hardening chamber 27, spreader bars 29, 29', support roller 30, scouring bath 34, squeeæe rollers 36, 36l, drying oven 38, storage roll 40 and a motor for driving the fabric. In oper-ation fabric 22 which is either dyed or undyed is stored on roller 20. Fabric 22 is brought into con-tact with the screen-of a rotary screen printer 24.
The screen is closed in those regions corresponding to the regions of the fabric where it is desired to maintain the length of the fibers in the pile. The stiffening agent passes through the open portions of the screen and onto the fabric in the regions from which it is desired to remove the pile. After the fabric passes through hardening chamber 27, where it is heated by infrared lamps 26 and by air impinge-8~
ment hea~er 2~, it pa~s~,s over spreader bars 29, Z9', ~hen o~er roller 30 past blade 43 where the ~ih~rs in the treated regions are removed. The fabric then passes through scouring bath 34, a pair of squeeze rollers 36, 36', drying oven 38, and is taken up on storage roll 40.
The shearing step of the present invention may be carried out on any cutter which allows the untreat-ed fibers to remain unsevered but severs the treated fibers. It is necessary only that the cutter operate in the same manner as a knife or razor as opposed to cut~ing like a pair of scissors. Such a cutter is shown in Fugures 6, 7, 8 and 9. When the fabric passes over the roller adjacent to the knife balde, it desirably will be uniformly tensioned and free from wrinkles. Conventionally, uniform tension is maintained by underfeeding the fabric and driving the take-up through a slip clutch. It has been found that more satis~actory results are obtained if the fabric is underfed by such an amount that the desired tension is produced by elongation of the fabric. In Figures 7 and 8, motor 68 drives chain 66 which in turn drives sprocket 59 fastened to gear 58 and gears 60 and 60'. Gear 58 drives gears 57, 56, 54 and 52.
Gear 52 drives supply roller 45 and gear 54 drives supply roller 45'. Gears 60 and 60' drive take-up rollers ~6 and 46'. By suitably choosing gears 56, 57 and 58, one can cause take-up rollers 46 and 46' to take up the fabric faster than it is supplied '785~
over supply rollers 45 and 45'. Y~hile it is not al-ways possible to obtain the exact amount of undPr-feed desired using this arrangement, it is generally possible to obtain a rate of underfeed which is with-in a fracti~n of a percent of the desired amount of underfeed. Gears 56 and 57 are fixed to each other and are mounted on shaft 61 which is adjustably positionable in slot 62 on arm 70. Arm 70 pivots on shaft 63 upon which gear 54 is also mounted.
When gears 56, 57 and 58 are changed, the location of shaft 61 can be changed so that gears 57 and 54 engage each other. Arm 70 is then rotated about shaft 63 to bring gears 56 and 58 into engagement.
In this manner a wide variety of gears can be accommodated to yield the desired underfeed.
Just prior to sculpturing, fabric 22 passes over a pair of spreader bars 29, 29' which insure that the fabric will be unwrinkled when it passes over the support roller 30. The spreader bar 29 is shown in more detail in Figures 10 and 11. The bar 29 is generally cylindrical member having a plurality of threaded portions 92, 94, 96, 98...~.
The helix angle of each of the threaded portions is such that the fabric is stretched from the center as iabric 22 passes over spreader bar 29. The helix angle of each threaded portion 92, 94, 96, 98 awa~ from the center of the spreader bar is greater than the helix angle of any threaded portion 92, 94, 96, 98.... which is nearer to the center of the spreader bar. AS shown in Figure lZ each thread is formed with a vertical wall 100 on the gid~ farthest from the cente~ o~ the bar and an inclined wall 101 on the side closest to the center of the bar. After the fabric passes over spreader bars ~9, 29', it passes over support roller 30 adjacent to blade 43.
Advantageously, the position of support roller 30 is adjustable with respect to the blade. Figure 13 shows support roller 30 mounted on extension arm 84 which is fixed to rotating lever arm 86. sy pivoting rotating lever arm 86 about pivot pin 88, support roller 30 can be moved into close proximity with blade 43 and can be withdrawn. Advantageously, ex-tension arm 84 is slidably affixed to rotating lever arm 46 and can be adjusted radially to position support roller 30 at the proper location. If desired the position of blade 43 can also be adjusted with respect to support roller 30.
Blade 43 can be any suitable member which severs the fibers in the treated regions but allows the fibers in the untreated regions to deflect away from the blade. Preferably, blade 43 is the blade of a rotating band saw. In that case, blade 43 would be moving parallel to the surface of support roller ; 25 30. By this means, it is possible to include self-sharpening means (not shown) at a location where the blade is not in contact with the fiber. However, most commercial band saws have blades which are slightly bowed as shown in Figure 13. Preferably 1~7~3~c~

the distance between support roller 30 and blade ~3 is uniform along the entire length oE the roller.
In the preferred embodiment, support roller 30 is supported by a plurality of pairs of adjustable bear-ing rollers 80 and 80'~
The following examples will further illustrate this invention. It is to be understood that these are examples only and are not to be construed as limitations on the invention.

EXAMPLE I
Stiffening agent was prepared by adding ethy-lene glycol, anhydrous ammonia and fugitive tint to an aqueous emulsion formed from acrylic monomers.
The particular aqueous emulsion used was GLO-REZ 816 HV which is available from Glo-Tex Chemicals in Roe- -buck, South Carolina. This emulsion has an approxi-mate solids content of 50~. The solids are polymers formed from between 25% and 50~ ethyl acrylate, be-tween 25 and 50~ methyl acrylate, between 20% and 40%
methyl methacrylate, and between 5% and 15% acrylic acid, the total being 100%. To this, 10~ by weight of ethylene glycol was added. 1.5 grams of 28% anhydrous ammonia and 6 grams of a fugitive tint were added to each pound of the emulsion. The result was an emul-sion having a viscosity of 18,000 cp. This emulsion was printed in a pattern onto a velvet fabric using a rotary screen printing machine. The screen mesh number was 30, and the printing speed was 3 yd/min.

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The velvet fabric was of cut pile and tufted construction. The pile ox face fiber was 13 singles acrylic yarn. There ~ere 25 ends in the weft direc-tion and 40 ends in the warp direction. Pile height was 3/32 inch. The substrate was woven polyester of a drill construction having 38 picks per inch and 68 ends per inch. The tufts were held in with a latex backcoating. Final weight of the fabric was l.l lb/yd2. In order to insure maximum flexibility of the pile fibers, the fabric was scoured in hot water before printing.
The particular pattern used in printing had lines about 1/16 inch wide with a total open area of approximately 5%. The weight,of stiffening agent applied to the fabric was approximately equal to fifty percent of the weight of the fabric affected.
The stiffening agent was pre-hardened by ex-posing the fabric to a bank of infrared heaters set at a temperature of 900F and located about 9 inches from the fabric. Final hardening was accompllshed by exposing the fabric to air at 75C in an impinge-ment dryer for about 1 1/2 minutes.
After hardening, the fabric was processed through a bandkni~e where the fibers in the printed areas were se~ered and the fibers in the non-printed areas remained unaffected. The bandknife is basi-cally the same as the more familiar band saw except that the blade does not have teeth. The pile fibers were brought into contact with the knife blade by ~ ~8~ 3~
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drawing the Eabric over a nose bar suitably located relative to the cutting edge. The nose bar had a radius of approximately 1/8 inch. ~he blade moved parallel to the nose bar in the vertical plane with the cutting edge at the top. The fabric move~ down against the cutting edge, entering the cutting zone at an angle of 60 relative to vertical and leaving at an angle of 30 relative to vertical. The posi-tion of the cutting edge was adjusted with the machine running to achieve optimum cutting and no exact measure of the geometry was made. However, the cutting edge was located in a zone represented by an 1/8 inch radius circle centered at the tip end of the nose bar. The blade speed was approxi-mately lOOft/min while the fabric speed was lOft/min.
The included angle of the cutting edge was 60 and was symmetric with respect to a vertical line through the center of the blade.
A sculptured effect was achieved as the fiber in the printed areas was removed and the fiber in the non~printed areas left unaffected.

EXAMPLE II
The procedure followed was the same as Ex-ample I except that the stiffening agent was formed as follows: 18 parts by weight of solid poly (vinyl alcohol) were mixed with 82 parts boiling water in a high shear mixer. 1 part o~ a fugitive tint was add-ed. This resulted in an emulsion having a viscosity o~ appro~imately 6,000 cp.

Claims (21)

WE CLAIM:

1. A method for trimming the fibers in the pile from selected regions of pile fabrics compris-ing the steps of:
applying stiffening agent only to the regions of the fabric in which the pile is to be trimmed;
hardening the stiffening agent; and passing the fabric by a blade which severs only the fibers in the regions to which stiffening agent has been applied but allows the fibers in those regions to which stiffening agent has not been applied to deflect away from the blade.

2. The method of Claim 1 wherein the upright posture of the fibers in the pile is maintained while the stiffening agent is hardened.

3. The method of Claim 1 wherein the fibers of the pile are given an upright posture before the stiffening agent is applied.

4. The method of Claim 1 wherein the fabric is scoured before the hardening agent is applied to the pile.

5. The method of Claim 1 in which the stiffen-ing agent is a liquid admixture of water and an ad-hesive chosen from the group consisting of polyvinyl alcohol, acrylic monomers, polyvinyl acetate, sul-fonated polyester size material and methyl cellulose.

6. The method of Claim 1 wherein the stiffen-ing agent is applied in a pattern by printing.

7. The method of Claim 1 wherein the stiffen-ing agent is applied to the region of the fabric from which the fibers are to be trimmed so as to form a continuous layer in which the fibers become embedded.

8. The method of Claim 7 wherein the stiffen-ing agent is applied by printing and wherein the stiffening agent is a liquid admixture of water and an adhesive chosen from the group consisting of poly-vinyl alcohol, the polymers of acrylic monomers, polyvinyl acetate and methyl cellulose.

9. The method of Claim 8 wherein the fabric is maintained in an evenly tensioned and unwrinkled state as it is passed by the blade.

10. The method of Claim 1 wherein the fibers of the pile are sheared from the regions to which stiffen-ing agent has been applied by drawing a blade past the fabric which blade severs the fibers in the regions to which stiffening agent has been applied but allows those fibers in the regions to which stiffening agent has not been applied to deflect out of the path of the blade.

11. The method of Claim 9 wherein the stiffen-ing agent is applied to the region of the fabric from which the fibers are to be trimmed so as to form a continuous layer in which the fibers become imbedded.

12. A device for trimming the fibers in the regions of the pile of a pile fabric to which stiffen-ing agent has been applied and hardened, comprising:
a frame;
means mounted on said frame for advanc-ing said pile fabric;
a support member over which said fabric may be passed;
means for mounting said support member on said frame;
a blade mounted on said frame closely adjacent to said support member and adjustable to trim the fibers in the regions to which a stiffening agent has been applied while allowing the unstiffened fibers to deflect away from the blade.

13. The device of Claim 12 further comprising means for maintaining the fabric in an unwrinkled state.

14. The device of Claim 13 wherein the means for maintaining the fabric in an unwrinkled state comprises:
a spreader bar having a plurality of sets of threads, each set of threads from the center of the bar towards the ends of the bar having a helix angle greater than the helix angle of the sets of threads closer to the center of the bar.

15. The device of Claim 12 further comprising means for tensioning the fabric as it passes over the support.

16. The device of Claim 15 wherein said means for tensioning the fabric includes means for under-feeding said fabric.

17. The device of Claim 16 wherein said means fox underfeeding said fabric includes:
a supply roller, mounted on said frame;
a take-up roller, mounted on said frame;
driving means for driving said take-up roller; and supply roller at different speeds, said driving means including change gears.

18. The device of Claim 17 further comprising:
a spreader bar having a plurality of sets of threads, each set of threads from the center of the bar towards the ends of the bar having a helix angle greater than the helix angle of the sets of threads closer to the center of the bar.

19. The device of Claim 18 wherein said support member is a roller.

20. The device of Claim 19 wherein said blade is a translating endless flexible band and wherein said means for mounting said support roller includes means for adjusting the curvature of said support roller to match the curvature of said translating endless flexible band.

21. The device of Claim 20 wherein said means for adjusting the curvature of said support roller includes a plurality of adjustable bearing rollers.