Pile fabrics and methods and apparatus for the production thereof
United States Patent [191 Currell et al.  
 [ Apr. 15, 1975 Colin Bourne, both of Stourport-on-Severn, England [73] Assignee: Bond Worth Limited, Stourport-on-Severn, Worcestershire, England [22] Filed: Jan. 22, 1973 [21] App]. No.: 325,801  
 [30] Foreign Application Priority Data Jan. 5, 1973 United Kingdom 675/73 Jan. 5, 1973 United Kingdom 676/73 [52] US. Cl. 156/72; 156/196; 156/298;  
 [51] Int. Cl. D04h 11/00; B32b 5/08 [58] .Field of Search 156/72, 177, 178, 303.1, 156/320, 435, 436, 196, 298, 322, 443, 499,  
 [56] References Cited UNITED STATES PATENTS 2,461,860 2/1949 Victor 156/72 2,588,130 3/1952 Lemon et al....  
 3,390,035 6/1968 Sands 161/67 3,531,343 9/1970 Couquet 156/72 3,537,946 11/1970 Truax et al. 156/72 3,684,600 8/1972 Smedberg 156/72 3,733,226 5/1973 Stoller 161/66 3,745,054 7/1973 Smedberg 161/67 FOREIGN PATENTS OR APPLICATIONS 446,267 4/1936 United Kingdom 156/435 Primary Examiner-Daniel .1 Fritsch Attorney, Agent, or Firm-Markva &amp; Smith [57] ABSTRACT A method of and apparatus for producing pile fabric, especially carpet, by adhering rows of tuft-forming lengths of pile yarn to a preformed ground member. Groups of such lengths of yarn are engaged by respective grippers, each of which holds all yarn lengths of a group, and are drawn over a vertical slot. A midportion of each yarn length is then pushed downwardly through the slot into an adhesive layer on the ground member. The adhesive is a hot melt adhesive which is heated, prior to reaching the tuft attaching station, to a first temperature at which it is sticky, but not liquid. After leaving the attaching station, the adhesive layer is heated to a second higher temperature at which it becomes liquid and permeates those parts of the yarn lengths which have been pressed into the adhesive layer, thereby anchoring the tufts securely.  
 8 Claims, 14 Drawing Figures T&#39;JENTEEAPR 1 51% 3,878,011  
 sum 2 of 1 PILE FABRICS AND METHODS AND APPARATUS FOR THE PRODUCTION THEREOF BACKGROUND OF THE INVENTION This invention relates to pile fabrics. The invention concerns firstly a method of manufacturing a pile fabric, secondly apparatus for carrying out the method, and thirdly the pile fabric itself.  
  The invention has been developed in relation to the manufacture of pile fabrics in the form of carpets but it is to be understood that it may be applied to pile fabrics generally.  
  Two main classes of carpet and methods of manufacturing same exist and are in general use respectively at the present timev The first class of carpets which may be termed traditional&#34; carpets have a ground member woven from warp and weft threads comtemporaneously with the insertion of raising of the pile yarn. Typical in this class are Axminster and Wilton carpets. In the former tuftforming lengths of pile yarn are inserted at the fell of the warp and weft threads of the ground member in successive weftwise extending rows from respective tube frames carrying spools of pile yarn or from grippers which seize tuft-forming lengths of pile yarn presented to the grippers from a creel and associated jacquard-controlled selector mechanism. In the latter pile yarn is contained in the ground member by way of warp yarns and these are raised from the plane of the warp and weft threads of the ground member at the fell by insertion of weftwise extending wires which are subsequently withdrawn and which, in the case of Wilton carpets, carry knives for cutting the raised loops to form tufts.  
  The second main class of carpet (known generally as needle loom carpet) is formed from a prewoven ground member into which successive rows of tufts forming lengths of pile yarn are inserted by a corresponding row of needles penetrating the prewoven ground member, and are thereafter secured by coating the prewoven ground member on its face opposite to that from which the tufts project with a settable binding substance.  
  Traditional carpets can be produced in patterned form, that is to say the tufts of pile yarn present a pattern (either organised or random). The rate of insertion of the weftwise extending row of pile tufts is, however, limited by the method of production and is typically in the region of to rows per minute.  
  The rate of insertion of rows of pile tufts in forming needle loom carpet is higher but in this case organised patterns cannot be produced (other than very simple patterns such as strips extending longitudinally of the ground member, i.e. at right angles to each inserted row of pile tufts).  
  Various proposals have been made for the manufacture of pile fabric by coating a preformed ground memher with a layer of an adhesive and pressing tuftforming lengths of pile yarn into the adhesive to adhere tuft-forming lengths to the ground member. However, these prior proposals have proved unsatisfactory for various reasons and, so far as we are aware, none of these proposals have been sufficiently successful to be &#39;used on a commercial scale.  
  The main object of the present invention is to provide a new or improved method of manufacture of pile fabrics which will enable fabrics having patterns comparable with those at present produced in traditional carpets to be manufactured at a higher rate, or more economically, or possibly with an improvement in each of these factors.  
 SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a method of manufacturing a pile fabric comprising the steps of feeding a preformed ground member carrying an adhesive coating on one of its faces along a feed path through a tuft attaching station which extends transversely of the feed path, the adhesive having a composition such that its viscosity decreases on heating and being at the attaching station in a sufficiently sticky condition to adhere to yarn pressed into the adhesive, bringing a row of tuft-forming lengths of pile yarn to said station, source presenting yarn ends in a row, pressing a first part of each tuft-forming length into the adhesive to attach said first part to the ground member, leaving a further part of each tuft-forming length to project from the adhesive coated ground member as a tuft, feeding the ground member with said row of tuft-forming lengths adhered thereto away from the attaching station, and then temporarily raising the temperature of said adhesive securing the tuft-forming lengths to the ground member temporarily to reduce the viscosity of the adhesive.  
  The step of raising the temperature of the adhesive after leaving the attaching station enables the viscosity of the adhesive to be reduced sufficiently to obtain a good bond between the tuft-forming lengths and the ground member whilst avoiding the problems which arise if the adhesive has a low viscosity at the attaching station. These problems include migration of adhesive from the ground member onto the apparatus which handles the tuft-forming lengths of yarn and onto those parts of the tuft-forming lengths which form the upstanding tufts. Furthermore, the viscosity of the adhesive can be conveniently maintained at a relatively low value for a period sufficient to permit the adhesive to permeate that part of each tuft-forming length which is pressed into the adhesive, whilst avoiding disturbance of the positional relation of the tuft-forming lengths and the ground member which may occur if the adhesive in a zone occupied by one row of tufts is maintained in a low viscosity condition when that row of tufts is fed from the attaching station and a further row of tuft-forming lengths is pressed into a closely adjacent zone of the adhesive layer.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 to 6 are diagrammatic illustrations of successive stages of the manufacture of pile fabric by the method of the invention,  
  FIG. 7 is a view in side elevation of apparatus in accordance with the invention, side plates and certain other parts of the apparatus being omitted for clarity,  
  FIG. 8 is a fragmentary view in side elevation on an enlarged scale,  
  FIG. 9 is a fragmentary view in side elevation and on a further enlarged scale showing in detail elements of the apparatus corresponding to those shown in FIGS. 1 to 6,  
  FIG. 10 is a circuit diagram of the pneumatic actuating means of the apparatus,  
  FIG. 11 is a diagrammatic cross-sectional view of an adhesive coated ground member to which tuft-forming lengths of pile yarn, are to be applied,  
  FIG. 12 illustrates the adhesive coated ground member of FIG. 11 and tuft-forming lengths of pile yarn immediately after application of same,  
  FIG. 13 is a diagrammatic illustration of the finished pile fabric, and  
  FIG. 14 is a fragmentary plan view of the apparatus shown in FIG. 8, certain parts being broken away for clarity of illustration.  
  The method illustrated in FIGS. 1 to 6 involves feeding a preformed ground member 10 to a pile attaching station 11 and concurrently feeding an adhesive to this station to enable tuft-forming lengths of pile yarn, such as that length indicated by 12, to be adhered to the ground member in a row extending across the width of the ground member transverse to the direction of feed indicated by the arrow 13 in FIG. 1.  
  Preferably, the adhesive is conveyed to the attaching station by the ground member itself, in this case the adhesive being carried as a preformed coating 14 on the side of the ground member. Conveniently, such coating is initially in a non-tacky condition so that the ground member can be stored in bulk as a roll.  
  The preferred adhesive 14 is a hot melt adhesive which includes as the main, or one of the main, constituents a thermo-plastic resin. Such hot melt adhesive has a solid, non-tacky character at ambient temperature, becomes tacky on moderate heating and becomes fluid on heating to higher temperature. When at ambient temperatures, the adhesive has sufficient flexibility to avoid undue stiffness of the completed pile fabric and to avoid cracking of the adhesive layer on flexing of the ground member.  
  A suitable hot melt adhesive is that sold by Evode Limited of Stafford, England, under the designation Thermoflow 7504.&#34;  
  The adhesive preferably includes from 20% to 50% by weight of an ethylene/vinyl acetate co-polymer, from 15% to 40% by weight of a tackyfying resin and 25% to 60% by weight of a filler. The adhesive may further include waxes, a stabiliser and plasticisers. The melt index of the preferred adhesive is within the range l-200 as determined by ASTN 1239 65 E. The copolymer preferably has a vinyl acetate content within the range to 35% by weight. An adhesive wherein the proportion of co-polymer is within the range 30% to 40% is especially satisfactory. The tackyfying resin may be wood resin, a hydrocarbon resin, a terpene resin, a modified wood resin, or any combination of these. The filler may be a mineral filler, for example china clay or tale.  
  The adhesive is converted to a tacky condition prior to arrival at the attaching station 11 by heating means in the form of a hot plate 15 over which the ground member 10 passes towards the attaching station. The hot plate engages with that face of the ground member opposite to the face on which the layer of adhesive 14 is formed. Typically, the hot plate 15 is maintained at a temperature within the range 75 to 1 10C and the dimension of the hot plate and the rate of feed of the ground member are such that equilibrium temperature conditions are achieved before the adhesive and ground member pass from the hot plate. Typically, the length of this plate, as measured lengthwise of the feed path of the ground member, is 16 inches.  
  At the attaching station 11, the adhesive coated ground member 10 is supported by a roll 16 which is rotated in accordance with the required feed of the ground member as shown by the arrow 13.  
  Above the feed path of the ground member 10 at the attaching station 11 a slot 17 is defined by constraining means. The slot extends transversely of the feed path across the full width of the adhesive coating 14 on the ground member and has a width (measured lengthwise of the direction of feed of the ground member) which is less than the length of each tuft-forming length 12. The constraining means comprises an end wall of a housing 18 and an end face of a breast plate 19 which define opposite boundaries of the slot. The housing 18 and breast plate 19 have respective horizontal upper faces which are co-planar and across which the tuftforming lengths 12 are drawn as will now be described.  
  A row of pile yarn ends is presented at a seizing station 20 by any of a number of different sources of pile yarn.  
  As illustrated in FIGS. 1 to 6, the source of pile yarn comprises a plurality of spools such as 21 each carrying a plurality of side-by-side windings of pile-forming yarn in the required sequence of colours. Yarn ends project between the dents of a comb 22 provided on a frame on which the spool is supported so that the pile ends are presented generally horizontally as indicated at 23.  
  The spools may be supported in a known manner by chains or like flexible members passing over supporting sprockets, or by a polygonal holder which is mounted for rotation adjacent to the seizing station to present successive spools thereat. Alternatively, the yarn source may comprise a creel incorporating a number of bobbins sufficient to present a group of yarn ends of different colours at each position along the row, and respective carriers for receiving each group of differently coloured yarns ends, Jacquard or other selector means being provided for selectively positioning the carriers to bring the required coloured yarn end into the seizing station at each position along the row for ber 10 is fed to the attaching station. In FIG. 1, the ap-.  
 paratus is illustrated at the begining of a cycle of operation, the grippers 24 being positioned adjacent to the slot 17 at the side thereof remote from the seizing station 20. The grippers are then advanced to the seizing station, being opened simultaneously by engagement of respective rollers 25 with cam plates 26 mounted on the upper arms of the grippers. During advance of the grippers to the seizing station, the position of the rollers 25 is unchanged, although the rollers are permitted to rotate about their axes.  
  When the grippers 24 reach the seizing station 20, as shown in FIG. 2, the yarn ends 23 are received between the gripper jaws. the rollers 25 are then raised to permit the grippers to close under the action of gripper springs 27 and grip the yarn ends securely. As shown in FlG. 3, the grippers are then withdrawn from the seizing station and when the required tuft-forming length of yarn has been withdrawn from the spool 21, a knife 28 descends to engage with the yarn adjacent to the comb 22 and is reciprocated transversely of the yarns to sever same. The knife is then raised. As shown in FIG. 4, after severing by the knife 28, yarn ends remain projecting through the comb 22.  
  The grippers 24 are withdrawn until they return to the position shown in FIG. 1, thereby drawing the tuftforming lengths 12 to positions in which they overlie the slot 17. The rollers 25 are then caused to descend and open the gripper jaws.  
  As the gripper jaws open, the tuft-forming lengths 12 are engaged by a presser member 29 which is mounted for vertical reciprocation through the slot 17. The presser member engages with a mid-portion of each tuft-forming length 12 and pushes such mid-portion through the slot 17 into the layer of adhesive 14 on the ground member at the attaching station. Since the adhesive has been heated by the hot plate 15 to a temperature at which the adhesive is soft and tacky, the mid portion of each tuft-forming length can readily be pressed into the adhesive and possibly into contact with the ground member.  
  The end portions of each tuft-forming length 12 follow the mid-portion thereof into the slot 17. It will be seen from FIG. 5 that the boundaries of the slot are spaced from the layer of adhesive 14 but approach sufficiently closely thereto to ensurre that end portions of each tuft-forming length 12 remain within the slot 17 when a mid-portion of such tuft-forming length is pressed into the adhesive layer. Thus, these end portions are constrained to adopt an upstanding relation with respect to the ground member 10. The roll 16 may be vertically adjustible relative to the housing 18 and breast plate 19 so that whatever the length of pile provided. up to one halfthe length of that part of each tuftforming length 12 which projects from the adhesive layer remains within the slot 17 when the mid-portion of such length is pressed into the adhesive.  
  When the mid-portion of each tuft-forming length 12 has been pressed into the adhesive layer 14, the presser member 29 is Withdrawn upwardly from the slot 17 to the position shown in FIG. 6 in which it is clear of the grippers 24 when the latter are next advanced to the seizing station 20. After withdrawal of the presser member 29, the cycle of operation is complete.  
  It will be noted that the breast plate 19 is formed adjacent to the slot 17 with a downwardly projecting flange which constitutes a boundary element and separates a tuft-forming length 12 which is pressed through the slot 17 from an adjacent previously applied tuftforming length. Operation of a pusher member 30 displaces the tuft-forming lengths 12 from positions in which they engage with one face of the flange 32 to a position in which they engage with an opposite face thereof. As the tuft-forming lengths pass beneath the flange they are necessarily bent somewhat, but can subsequently straighten out since there is sufficient clearance beneath the main part of the breast plate 19 to accommodate the full height of the tufts without bending or crushing of same. As the tufts are displaced by the pusher member 30 from the slot 17 to positions beneath the breast plate 19, the ground member 10 is advanced by a step corresponding to the spacing between adjacent rows of tufts.  
  It will be understood that during the steps illustrated in FIGS. 5 and 6, the source of pile yarn is operated to bring a further row of yarn ends 23 to the seizing station.  
  The ground member and tufts attached thereto are fed from the tuft attaching station over the surface of a second hot plate 39 by means of which the adhesive is heated to a temperature substantially higher than the temperature of the adhesive at the attaching station, this second temperature being sufficiently high to convert the adhesive to a liquid state. The temperature of the plate of the second heater means is preferably in the region of 200C. This plate may be somewhat longer than the plate of the first heater means.  
  Referring now to FIGS. 7, 8, 9 and 13 wherein is shown one form of apparatus in accordance with the invention, parts therein which have been referred with reference to FIGS. 1 to 6 are indicated by the same reference numerals.  
  The apparatus includes a support 33 for a roll 34 of adhesive coated ground member, the support being so arranged that the roll can rotate freely to permit the ground member 10 to be withdrawn therefrom. The apparatus further includes a draw-off roll 35 which can be driven at a predetermined speed to draw the ground member from the roll 34 at a uniform rate. From the draw-off roll the ground member passes around the rolls of an accumulator 36 which operates to maintain a substantially uniform tension in the ground member downstream of the draw-off roll and accommodates a variable accumulation of the ground member so that minor variations in the rate at which the ground member is drawn from the roll 34 relative to the rate at which the ground member passes through the remainder of the apparatus can be accommodated.  
  From the accumulator 36 the ground member 10 passes over guide rolls 37 and then over the surface of the hot plate 15 to the roll 16 at the attaching station. From the attaching station the ground member is guided by further guide rolls 38 over the surface of a second hot plate 39 to a reel 40 on which the tufted ground member 18 wound for storage. The reel 40 is supported on a pair ofrolls 41, at least one of which is driven to rotate the reel and wind the ground member thereonto.  
  As will be described hereinafter, the knife 28, presser number 29 and gripper opening rollers 25 are operated pneumatically. For advancing and retracting the grippers 24, for operating the pusher member 30 and for advancing the ground member 10 through the attaching station there is provided drive means which includes an electric motor 42. The output shaft of the motor 42 is coupled with a variable speed drive unit 43 which is connected by a toothed belt drive with a reduction gearbox 44. The rotary output element of the reduction gearbox is connected by a further belt drive with a pulley secured on a drive shaft 45.  
  A number of grippers 24 are provided, these being arranged in a row extending along the attaching station and the number of grippers depending upon the width of the area of the ground member to which tufts are to be applied. One end of a respective operating rod 46 is secured to the lower member of each gripper, the rod projecting therefrom in a direction away from the attaching station. The other end of each gripper operating rod is connected by a pivoted link with the upper end of an arm 47 secured to a shaft 48 which extends along the full length of the row of grippers. An end portion of the shaft 48 projects through a side plate 49 of the apparatus and an arm 50 is secured to the projecting end portion of the shaft 48 so as to project radially therefrom.  
  An end portion of the arm 50 remote from the shaft 48 is connected by a link 51 with a gripper operating lever 52. Thelever 52 is arranged to be rocked about a pivot 53 by a cam 54 carried on the drive shaft 45, the cam engaging with a cam follower 55 carried on the lever 52. The cam follower is biased into engagement with the cam by means of a spring 56 connected between the lever 52 and a part of the frame structure of the apparatus.  
  The link 51 is pivotally connected with a boss which is adjustable lengthwise of the lever 52 so that the effective length of the lever can be varied. The link 51 incorporates a turn buckle device whereby the effective length of the link can also be adjusted. When the lever 52 is rocked about its pivot 53, the shaft 48 is oscillated and the grippers 24 are reciprocated towards and away from the sizing station 20. The stroke of the motion of the grippers and the rest position of the grippers can be varied by adjustment of the effective length of the lever 52 and the effective length of the link 51.  
  As previously mentioned, each of the pusher members 30 is provided with an operating tail 31 which projects from the housing 18. This operating tail is arranged to be engaged by an abutment 57 carried on the gripper operating rod 46 at the end thereof adjacent to the arm 47. As the grippers 24 are advanced towards the seizing station, the abutment 57 engages with the operating tail 31 and advances the pusher member 30 across the bottom of the slot 17 to displace a newly formed tuft therefrom. The abutment 57 may be adjustable relative to the gripper operating rod 46 in a direction towards and away from the operating tail 31. The pusher member is urged rearwardly by a return spring 63 (see FIG. 14).  
  One of the further guide rollers 38a is arranged to be driven intermittently from a further cam secured on the drive shaft 45. This cam is arranged to oscillate the input element of a sprag clutch once every revolution of the drive shaft and the output element of the sprag clutch is connected with the roll 38a and turns same uni-directionally one step for every revolution of the drive shaft. The range of oscillatory movement of the input element of the sprag clutch may be adjustable so that the length of the feed step by which the ground member is advanced through the attaching station during each cycle of operation of the yarn handling means can be adjusted. v  
  One gripper opening roller 25 is provided for each pair of grippers. The rollers 25 are each mounted pivotally on a gripper opening bar 58 which extends along the full length of the row of grippers. The gripper opening bar is mounted on the lower ends of piston rods of vertical piston and cylinder units 59. The number of piston and cylinder units 59 provided will depend upon the length of the row of grippers, and typically three such piston and cylinder units would be provided.  
  The presser member 29 is in the form ofa blade-like member which extends continuously along the entire length of the slot 17. The presser member is carried on the piston rods of vertical presser piston and cylinder units 60 of which there are typically two.  
  The knife 28 is also in the form of a blade which extends continuously along the full length of the row of tuft ends presented at the seizing station 20. The knife is slidably mounted for lengthwise reciprocation on a carriage which is secured to the lower ends of respective piston rods of-vertical piston and cylinder units 61 of which there are typically two. For reciprocating the knife 28 relative to the carriage there is provided a single horizontal piston and cylinder unit 62 which is mounted at one side of the apparatus and is connected with the knife 28 by link means which accommodates vertical movement of the knife relative to the piston and cylinder unit 62.  
 The pneumatic circuit which includes the piston and cylinder units 59 to 62 is shown diagrammatically in FIG. 10. The circuit includes a mains supply connection 63 which leads through a filter 64 to a pressure regulating valve 65. The pressure regulating valve is connected via a lubricator 66 and a control valve 67 with the inlets indicated at 68. I Operation of the piston and cylinder units 59 to 62 is controlled by nine cam operated valves 69 to 77, the control cams of which are mounted on the drive shaft 45. These cams are arranged to provide the following sequence of operations.  
 Units 59 contracted to close grippers.  
 Units 61 extended to lower knife.  
 Units 62 extended to move knife lengthwise.  
 Units 61 contracted to raise knife.  
 Units 62 contracted.  
 Units 59 extended to open grippers.  
 Units extended to lower presser member.  
 Units 60 contracted to raise presser member.  
  It will be understood that the steps of this sequence may overlap to some extent, one step being commenced before the preceding step is completed. It is envisaged that the sequence will be repeated approximately 80 times per minute. Thus, the apparatus is intended to apply tufts to the ground member at a rate of approximately 80 rows per minute.  
  Each of the grippers 24 includes an upper plate 64 and a lower plate 65 pivotally connected by a spindle 66 which is parallel to the support roll 16. A midportion of each spindle is secured in a bore formed in an upwardly projecting boss portion 67 of the associated lower plate 65. The ends of the boss portion 67 are inset somewhat from the lateral margins of the lower plate, the length of the boss portion being approximately half the width of the lower plate. Each of the upper plates 21 is formed with two downwardly projecting boss portions 68 situated adjacent to respective lateral margins of the upper plate. The boss portions 68 are formed with bores fitted with liners in which respective end portions of the associated spindle 66 are rotatably supported.  
  At their forward ends, the upper and lower plates 64, 65 are formed with respective jaw portions 69, 70 which are serrated or otherwise adapted to grip between them the yarn ends 17. The jaw portions are biased towards a closed position by coiled compression springs 27 of which two or more may be provided for each of the grippers 24, the member depending upon the width of the grippers and upon the gripping pressure which is required to be applied by the jaw portions 69, 70 to the yarn ends. One end of each spring 27 is located on a projection provided on the lower plate 65 at a position near to the rearward end thereof. An opposite end portion of the spring projects through an opening in the upper plate 64 and is received in a cap 71 secured to the upper plate. With this arrangement,  
 when the jaw portions are open the rearward end portion of each upper plate can be brought into contact with the rearward end portion of each lower plate.  
  The respective widths of the upper and lower plates 64, 65 are equal and are within the range 1 inch to 12 inches. Preferably, the width of each gripper is within the range 4V2 inches to 9 inches. With this construction each gripper can hold a group of yarn ends 23 arranged side-by-side in a row. However, the width of the grippers is such that each one of such a group of yarn ends gripped between the jaw portions 69, 70 is subjected to substantially the same pressure so that the risk of one yarn end slipping relative to the jaw portions whilst the other yarn ends are properly held thereby is avoided.  
  The lower plate 65 of each gripper is slidably mounted on the upper face of the housing 18 for reciprocating movement along a rectilinear path towards and away from the seizing station. The grippers 24 are so arranged that adjacent grippers are in contact with one another at their lateral boundaries, or are positioned sufficiently closely to avoid the existence of any significant gap between adjacent grippers at all positions of the reciprocating movement towards and away from the seizing station. E a significant gap&#34; is meant a gap such that there is a possibility of the jaw portions of the grippers failing to grip properly a yarn end which registers with such gap.  
  The ground member 10 and the layer of adhesive 14 which is present thereon prior to reaching the attaching station are illustrated in FIG. 11. In FIG. 12 there are illustrated the ground member and adhesive layer at the attaching station, together with a U-shaped tuft 72, a mid-portion of which has been pressed into the adhesive layer. It will be noted that displacement of adhesive by the tuft 72 has produced a ridge 73 of adhesive between the tuft 72 and an adjacent previously applied tuft 720. There has also been produced a somewhat smaller ridge 74 of adhesive at the side of the tuft 72 opposite to the ridge 73.  
  Since the adhesive is cooling while it is at the attaching station and while it is being advanced therefrom, the adhesive is in a fairly stiff condition as the tuft 72 is fed on from the attaching station, and the ridges 73, 74 help to prevent the upstanding limbs of the tuft from deflecting away from each other out of proper upstanding relation with the ground member 10.  
  As the tuft 72 leaves the attaching station, it is held mainly by adhesion of the adhesive to fibres present at the generally downwardly presented surface of the midportion of the tuft. As shown at 75, some adhesive may rise alongside the mid-portion of the tuft, but owing to its relatively high viscosity, the adhesive will not generally flow over the mid-portion of the tuft to completely embrace same.  
  It will be appreciated that the tuft 72 is not, as such tuft leaves the attaching station, held sufficiently securely to the ground member 10 to produce a hardwearing pile fabric. Accordingly, the layer of adhesive 14 is subsequently heated by the second heater means 39 to a temperature higher than said first temperature in order to reduce the viscosity of the adhesive to a relatively low value temporarily. As shown in FIG. 13, when the viscosity of the adhesive is thus reduced, the adhesive premeates the mid-portion of each tuft 72 and by capilliary action permeates to some extent up the projecting limbs of each U-shaped tuft. Furthermore, the adhesive flows over the mid-portion of each tuft so that each mid-portion is completely embraced by the adhesive. The adhesive is then permitted to cool to ambient temperature at which temperature the adhesive is not sticky and is relatively stiff so that the tufts are securely attached to the ground member.  
  It will be noted that both the first heater means 15 and the second heater means 39 are arranged to engage with that face of the ground member 10 opposite to the face at which the tufts 72 are attached, and accordingly heat is transmitted to the layer of adhesive 14 through the ground member. This establishes a temperature gradient in the layer of adhesive such that the adhesive closest to the ground member is somewhat hotter and therefore, especially when approaching the attaching station, less viscous than adhesive adjacent to the exposed surface of the adhesive layer. This reduces the risk of adhesive migrating from the layer on the ground member to parts of the apparatus, and/or to the upstanding limbs of the tufts 72.  
  The heater means 15 and 39 are preferably heated by electrical heating elements (not shown) in the respective supply circuits of which there are provided control means for controlling the rate of supply of energy to the heater means so that the temperature thereof can be controlled. As shown in FIG. 7, there may be associated with the second heater means a pair of rolls 76 disposed one adjacent either end of the heater means and movable towards and away from the ground member 10 so that in the event of feed of the ground member being interrupted, the rolls 76 can be brought into engagement with the ground member to lift same out of engagement with the heater means and thereby prevent overheating of the ground member. If required, a similar movable roll may be associated with the first heater means 15.  
  It will be appreciated that the spacing of successive U-shaped tufts 72 is exaggerated in FIGS. 12 and 13 for clarity of illustration. Normally, the tufts would be positioned sufficiently close to each other to afford neutral support which prevents the upstanding limbs of each U-shaped tuft departing significantly from a proper upstanding relation with respect to the ground member 10 when the adhesive 14 has a relatively low viscosity.  
  In an alternative method within the scope of the invention, the adhesive may be applied to the ground member whilst the latter is being fed to the attaching station. Thus the adhesive may be applied in a tacky condition at a position just upstream of the attaching station so that the adhesive may be fed by the ground member through the attaching station. In this case, the first heater means may be of a form adapted to heat the adhesive as the latter is fed from a bulk supply but prior to application of the adhesive onto the ground member. If required, the adhesive may incorporate a vollatile solvent or diluent to reduce the viscosity of the adhesive when the latter is applied to the ground member. Such vollatile solvent or diluent would evaporate from the layer of adhesive formed on the ground member so that after the heating step which follows feeding of the ground member from the attaching station, the adhesive layer would cool to form a non-tacky solid layer.  
  It is also envisaged that the heating step which follows the feeding of the ground member away from the attaching station may be performed on apparatus separate from that in which the tufts are applied to the ground member. Thus, the ground member bearing tufts adhered thereto may be fed from the attaching station onto a reel on which the fabric is stored before being subjected to the further heating step. Such further heating step may be carried out after the tufts of the fabric have been sheared to present a level pile surface.  
 What is claimed is:  
  l. A method of producing a pile fabric comprising the steps of:  
 a. feeding a preformed ground member carrying an adhesive coating on one of its faces along a feed path through a tuft attaching station, the adhesive having a composition such that its viscosity decreases on heating and being fed to the attaching station at a first temperature such that it is in a sufficiently sticky condition to adhere to yarn pressed into the adhesive,  
 b. feeding a row of tuft-forming lengths of pile yarn to said station from a source presenting yarn ends in a row,  
 c. pressing a first part of each tuft-forming length into the adhesive to attach said first part to the ground member, leaving a further part of each tuft-forming length to project from the adhesive coated ground member as a tuft,  
 d. feeding the ground member with said row of tuftforming lengths adhered thereto along said path away from the attaching station,  
 e. causing the viscosity of the adhesive securing the tuft-forming lengths to the ground member to increase as the ground member with said row of tuftforming lengths adhered thereto is fed away from the attaching station along said path to further secure the tuft-forming lengths, and  
 f. then temporarily raising the temperature of said adhesive securing the tuft-forming lengths to the ground member to a second temperature substantially higher than said first temperature to temporarily reduce the viscosity of the adhesive to enable the adhesive to penetrate the tufts and anchor them more securely.  
  2. A method according to claim 1 wherein the adhesive is hot melt adhesive and the composition of the adhesive as it is fed to the attaching station is substantially the same as the composition of the adhesive in the finished pile fabric.  
  3. A method according to claim 2 wherein the temperature of the adhesive at the attaching station is within the range of 75C to 110C, and after passing through the attaching station the adhesive is heated to a temperature above 170C.  
 4. A method according to claim 1 wherein the adhe sive is heated to said first temperature by causing heat to pass through the ground member into the adhesive coating.  
  5. A method according to claim 1 wherein a plurality of tuft-forming lengths of pile yarn are simultaneously fed from said source to said attaching station by a plurality of said lengths in each of a plurality of grippers which hold all of the lengths simultaneously and draw said lengths from the source of pile yarn to the attaching station.  
  6. Apparatus for the production of pile fabric comprising the combination of:  
 a. means for feeding a preformed ground member with an adhesive, having a composition such that its viscosity decreases on heating, along a feed path through a pile attaching station,  
 b. first heater means adapted to heat the adhesive approaching said attaching station to a first temperature above the ambient temperature such that the adhesive is in a sufficiently sticky condition to adhere to yarn pressed into the adhesive,  
 c. means for feeding a row of tuft-forming lengths of pile yarn from a source thereof to the attaching station and for pressing a part of each tuft-forming length into the adhesive at the attaching station,  
 and  
 d. second heater means spaced downstream along said path a sufficient distance from the attaching station to permit the viscosity of the adhesive to increase to further secure the tuft-forming lengths and adapted to heat the adhesive to a second temperature substantially higher than said first temperature to enable the adhesive to penetrate the tufts and anchor them more securely.  
  7. Apparatus according to claim 6 wherein said first and second heater means are each arranged for transmitting heat to the ground member exclusively from the side thereof opposite to that side to which the tuftforming lengths of yarn are attached.  
  8. Apparatus according to claim 6 wherein said means for feeding a row of tuft-forming lengths comprises a plurality of grippers arranged side-by-side, each gripper having a pair of jaws adapted to receive between them and grip simultaneously a plurality of tuft-forming lengths arranged side-by-side at said source, simultaneously transfer said plurality of tuftforming lengths to said attaching station and simultaneously press a part of each tuft-forming length into said adhesive.