Pair of weft carrying and drawing grippers for weaving looms

Abstract: A pair of weft carrying and drawing grippers in a shuttleless loom - of the type controlled by straps caused to perform a to-and-fro motion with the grippers fixed at the ends thereof - comprises: a stiff structural support element (1; 11) formed with oriented carbon fibers poltruded with a thermosetting material; a metal body (2; 12) carrying the weft yarn gripping devices (P); a wearplate (5; 15) to protect the front bottom part of the gripper; and at least an abutting element (7; 17-17') of filled thermoplastic material. The strap (N), the stiff support element (1; 11), the metal body (2; 12) and the wearplate (5; 15) are connected together by screws (4-6-8; 14-16-18), engaged into threaded metal seats inserted into said abutting element (7; 17-17'), or formed into said metal body (2; 12), or into the weft yarn gripping devices (P).

Description: The present invention concerns a pair of weft carrying and drawing grippers for shuttleless looms and, in particular, the general structure of such grippers. A pair of weft carrying and drawing grippers according to the preamble of claim 1 is known from US-A-4 757 844. As known, there is a persistent request on the textile market to constantly improve the weft transport grippers of looms, so that such members may be apt to guarantee a perfect working even on the most modern looms in very critical weaving conditions. In fact, for the production of high-quality precious fabrics, looms are required to provide increasingly higher weaving performances, which particularly involve a high warp yarn tension, the use of very thin or delicate weft yarns or of yarns with other special physical characteristics, and a reduced shed angle; all this, combined with very high loom working speeds. To obtain the aforementioned high weaving performances, it is thus indispensable for a basic component of the loom, such as the pair of weft carrying/drawing grippers, to undergo constant improvements in order to guarantee the required performances of weft yarn insertion, together with a sufficiently long working life of the grippers. In particular - just on account of the very hard working conditions to which the weft transport grippers are subjected in modern looms - there is a great demand on the market for a pair of carrying/drawing grippers having mechanical features such as: high dimensional stability under stress, namely a high rigidity, to guarantee a faultless weft yarn exchange even at high speeds; mass reduction, so as to reduce the inertial loads tied to the continuous alternance of direction in the motion of the grippers; and finally, high wear resistance, to ensure a sufficiently long working life of the grippers, even at the high speeds at which they slide on the respective guides and rub onto the warp yarns on closing of the shed. Up to date, said market demand has not been fully satisfied since, with the construction techniques adopted so far, any increases in the rigidity and wear resistance of the grippers is not compatible with a reduction in the mass thereof. The object of the present invention is to thus supply a pair of weft carrying and drawing grippers - making the most of the materials now available and adopting a different construction technique to produce the same - with improved performances for what concerns all the three aforecited features - i.e. dimensional stability, mass reduction, and wear resistance - so as to be perfectly suited for use in the high-performance looms now existing on the market, said grippers having higher performances and a longer working life than the grippers of known technique. According to the present invention, said object is reached with a pair of weft yarn carrying and drawing grippers in a shuttleless loom - of the type controlled by straps caused to perform a to-and-fro motion with the grippers fixed at the ends thereof - characterized in that, each of the grippers of said pair comprises: a stiff structural support element, formed with oriented carbon fibers poltruded with a thermosetting material; a metal body carrying the weft yarn gripping devices; a wearplate to protect the front bottom part of the gripper; and at least an abutting element of filled thermoplastic material; and in that the strap, the stiff structural element, the metal body and the wearplate are connected together by screws, engaged into threaded metal seats inserted into said abutting element, or formed into said metal body, or into the gripping devices. Further characteristics and advantages of the pair of weft carrying and drawing grippers according to the present invention will anyhow be more evident from the following detailed description of some preferred embodiments thereof, illustrated by way of example on the accompanying drawings, in which: Fig. 1 is an axonometric view of the carrying gripper, forming part of the pair of grippers of the present invention; Fig. 2 is an axonometric exploded view of the gripper shown in fig. 1; Fig. 3 shows in detail, on an enlarged scale and partly sectional, one of the connection points of the different structural elements of the gripper, indicated by the circle III in fig. 1; Fig. 4 is an axonometric view of the drawing gripper, forming part of the pair of grippers of the present invention; and Fig. 5 is an axonometric exploded view of the gripper shown in fig. 4. There follows a detailed description, with reference to figs. 1 and 2, of the structure of the weft carrying gripper - forming part of the pair of grippers according to the invention - which structure is also present in the weft drawing gripper save for the required changes in shape. As it clearly appears from the exploded view of fig. 2, the carrying gripper is formed by a plurality of components, each meant to improve, as better explained hereinafter, a special mechanical feature of the gripper in its whole. Each of said components is then planned to have dimensions such as to reduce its mass to a minimum, compatibly with the functions it has to perform, so as to achieve also the object of an overall lightening of the gripper. The carrying gripper thus comprises first of all a stiff structural support element 1, meant to supply the dimensional stability and rigidity to the gripper, and to act as an element onto which are released the active and passive forces present during the to-and-fro movement of the gripper. The support element 1 has the general structure of an angle bar, whose vertical side is suitably tapered along its upper edge 1b, where the warp yarns rub onto the gripper at its outlet from the closing shed. Moreover, the outer surface of the vertical side of said angle bar preferably comprises a shaped depressed zone 1a, for connection of the support element 1 to a metal body 2 carrying the weft yarn gripping devices P. Both the vertical side and the horizontal base of the support element 1 comprise a plurality of through holes for connection to the other components of the gripper, as better described hereinafter. The base of the element 1 has cylindrical holes, while the holes on its side comprise, on their inner part, a countersink for the head of the fixing screw. The structural support element 1 is produced by extrusion of long carbon fibers, thoroughly bound and distributed into a matrix of suitable thermosetting resin, such as for example an epoxy resin. This technique, known in the sector as "poltrusion" technique, is carried out - according to the present invention - by positioning the carbon fibers contained in the matrix of thermosetting resin both in a longitudinal sense, parallel to the extrusion direction, and in a sense perpendicular thereto, according to specific weight percentages in the two directions. Preferably, the fiber/resin weight ratio is in the range between 60/40 and 80/20. This manufacturing technique allows to obtain a component wherein both the horizontal base and the vertical side have a high flatness - of the order of millimeter hundredths - combined with a high thermal, hygroscopic and viscous-elastic stability, both with and without loads applied on the gripper. Furthermore, the mass of the element 1 is reduced by about 50% in respect of a similar element forming part of a conventional gripper. These features of the structural support element 1 allow to obtain a number of advantages, among which the following should be particularly noted: high reduction of the inertial forces during the to-and-fro movement of the grippers; no need to carry out the finishing operations on the planar surfaces of the element 1 coupled with the other gripper components; no warpings produced by machining operations on the element 1 resulting from the poltrusion process - due to unbalance of the inner tensions in correspondence of the machined part - thanks to the fact that the inner tensions of a poltruded product are extremely low and that such machining operations merely involve the forming of connection holes, of the shaped depressed zone 1a, and of the upper tapered edge 1b of the element 1; high stiffness both against flexure in a longitudinal sense and against torsional stress; high resistance to wear, mainly in correspondence of the upper edge 1b of the element 1 - where the warp yarns rub onto the gripper - thanks to the contribution of the carbon fibers positioned in a longitudinal sense; high resistance to delamination, i.e. to cracking in a longitudinal sense, also in correspondence of the fixing holes, thanks to the controlled amount of the carbon fibers positioned in a transversal sense. A second component of the carrying gripper consists of the metal body 2. Said body 2 forms the gripper head and carries the weft yarn gripping devices P, which shall not be described in detail herein since they are of no interest in relation to the present invention. The metal body 2 is preferably produced starting from sheet steel, 1 mm thick, die-formed into the wanted shape and then deep-drawn. Said metal body 2 comprises a rearward extension 2a, to be connected to the support element 1 in correspondence of its depressed zone 1a, so as to efficiently oppose the combined bending and compressive stress to which the gripper is subjected by the weft yarn during its insertion into the loom shed. For this purpose, the body 2 comprises a series of holes (three in fig. 2), mating with corresponding holes provided on the vertical. side of the element 1, to allow a firm and longlasting anchorage of the metal body 2 to the support element 1 by means of the screws 4. As shown in fig. 2, the screws 4 are in fact inserted with their head from the inner side of the element 1 and are then tightened into the metal threading of the holes formed in the metal body 2; on tightening of the screws 4, it is thus the metal body 2 which is subjected to tensile stresses, while the element 1 merely works under compression, thereby ensuring a steady hold of the coupling even with the high stresses and vibrations which characterize the normal working of the gripper, and which could compromise the holding of the screws 4, in the long run, if these were screwed into the element 1 of plastic material and not into the body 2 of metallic material. Alternatively, the screws 4 could be replaced by rivets; in this case, the coupling between the element 1 and the body 2 takes up the configuration shown in detail in fig. 3. As can be seen from figs. 1 and 2, the upper edge 1b of the support element 1 and the top part of the extension 2a of the metal body 2 have an identical profile, with no peaks or sharp bends, so as to provide a uniformly inclined and radiused bearing surface, between the gripper head and the strap N, for the warp yarns bearing onto the gripper surface during its outlet from the loom shed. To allow a high number of weft yarn insertions per unit of time, it is now in fact a custom to anticipate the closing of the shed during the grippers' return stroke, so that the warp yarns may bear onto the gripper surface producing thereon both a compressive load and a considerable friction force. The aforedescribed gripper configuration enables the warp yarns to impart on the gripper a perfectly gradual load - according to the closing of the shed - and thus free from peaks which, due to the high moving speed of the gripper, would at once produce impacts thereon. According to a preferred embodiment, shown in detail in fig. 3, the surface of the gripper along which slide the warp yarns - instead of being formed by the upper edge 1b of the support element 1 and by the adjacent top part of the extension 2a of the metal body 2 - is formed by a flange 3 of the extension 2a, bent by 90° during the deep-drawing process of the metal body 2 so as to cover the whole upper edge 1b of the support element 1. The advantage of this solution is to improve the rigidity and mechanical resistance of the extension 2a of the metal body 2; however, to make sure that the working life of the carrying gripper corresponds to that of the drawing gripper, it is preferable - in this embodiment - to carry out a surface hardening treatment on the flange 3, so that its wear resistance may be comparable to that of the poltruded material forming the corresponding portion of the drawing gripper. A third gripper component consists of a wearplate 5 fixed, by means of screws 6, in correspondence of suitable threaded seats provided in the support base S for the gripping devices P housed into the metal body 2. The support base S is preferably obtained by molding of plastic material, and in this case said seats consist of innerly threaded metal inserts buried into the base S during the molding process. The wearplate 5 forms, in known manner, the final length of the gripper strap N; it is in fact meant to be replaced more frequently than the other components, being more subject to wear, so as to guarantee an equal working life of the gripper components and of the strap. Said wearplate is preferably made from cotton fabric impregnated with phenolic resin, or from polystyrene fabric impregnated with epoxy resin. The wear resistance of such materials is then further improved with an artificial aging treatment, for example an oven drying followed by dipping into an oil bath. The different gripper components, assembled together by means of the screws 4 and 6 - as specified hereabove - are finally fixed to the gripper strap N by making use of an abutting element 7, which forms the fourth and last gripper component. Said element 7 comprises a plurality of threaded inserts 7a, for example of brass or other metallic material, buried into a matrix of thermoplastic material, as for example a polyamide resin, filled with short glass or carbon fibers. The fiber/resin weight ratio is preferably in the range between 20/80 and 40/60. The abutting element 7 is advantageously produced with an injection molding process, by positioning the threaded metal inserts 7a into suitably spaced cavities provided for the purpose in the mold. The purpose of the abutting element 7 is to evenly distribute over the bearing surface of the support element 1 the fixing load concentrated on the threaded inserts 7a, and to simultaneously allow short assembly times by supplying the threaded inserts in a shape easy to handle and in the preset mounting position and distance. To reach these objects and, at the same time, guarantee the utmost lightness of the abutting element 7, this latter comprises thickenings 7b in correspondence of the inserts 7a and thinner parts between one insert and the next. It is moreover necessary for the abutting element 7 to have a perfectly flat bearing surface, so as to uniformly mate with the horizontal base of the support element 1 onto which it bears. The fixing of the strap N to the gripper body is in fact obtained by means of screws 8 (four in fig. 2) which cross said strap, eventually the end of the wearplate 5, the corresponding through holes formed in the horizontal base of the support element 1, and finally tighten into the threaded metal inserts 7a of the abutting element 7. Thus, also in this type of engagement - as in the previously described engagements between the metal body 2 and the support element 1, and between the wearplate 5 and the metal body 2 - the tensile stress of the fixing means is discharged onto an element of metallic material, while the compressive stress is discharged onto an element of plastic material. The aforedescribed abutting element 7, besides providing - as seen - a fixing system of easy, quick and safe application, has the additional advantage of involving a low cost, so that, in case the fixing means should get damaged (due, for instance, to stripping of the thread), said element can be easily replaced, without having to replace more important and costly elements of the gripper. The structure of the weft drawing gripper - forming part of the pair of grippers according to the invention - is illustrated in figs. 4 and 5, and is fully equivalent to the structure of the weft carrying gripper described in detail heretofore. The same elements have thus been indicated by reference numbers corresponding to those used in describing the carrying gripper, except for adding 1 before each number. On examining fig. 5, it can be seen that the metal body 12 of the drawing gripper, carrying the gripping devices, has a far shorter longitudinal extension than the corresponding metal body 2 of the carrying gripper. As known, this depends on the fact that said body is subjected by the weft yarn to a simple tensile force. Seen the reduced extension of the metal body 12, the support element 11 has a further length in respect of the corresponding support element 1 of the carrying gripper, so as to allow anchoring the wearplate 15 which, in this case, is thus fixed to the support element 11 by means of an additional abutting element 17'. Apart from this, the drawing gripper involves no other significant structural changes in respect of the heretofore described carrying gripper. The invention has been described with reference to some preferred embodiments thereof, but it is evident that its protection scope extends to any possible variants, within reach of a technician skilled in the art, falling within the definitions of the present invention given in the following claims.

Claims: Pair of weft carrying and drawing grippers in a shuttleless loom of the type controlled by straps caused to perform a to-and-fro motion with the grippers fixed at the ends thereof each of the grippers of said pair comprises: a stiff structural support element (1; 11), formed with oriented carbon fibers poltruded with a thermosetting material; a metal body (2; 12) carrying the weft yarn gripping devices (P); a wearplate (5; 15) to protect the front bottom part of the gripper; characterized in that each of the grippers of said pair further comprises at least an abutting element (7; 17-17') of filled thermoplastic material; and in that the strap (N), the stiff structural element (1; 11), the metal body (2; 12) and the wearplate (5; 15) are connected together by screws (4-6-8; 14-16-18) engaged into threaded metal seats inserted into said abutting element (7; 17-17'), or formed into said metal body (2; 12), or into the weft yarn gripping devices (P). Pair of weft carrying and drawing grippers as in claim 1), wherein said stiff structural element (1; 11) is shaped as an angle bar. Pair of weft carrying and drawing grippers as in claim 1), wherein said stiff structural element (1; 11) consists of a main warping of long carbon fibers in a longitudinal sense and of a secondary warping of long carbon fibers in a transversal sense. Pair of weft carrying and drawing grippers as in claim 1), wherein said stiff structural element (1; 11) is produced with a poltrusion process, and then drilled and eventually tapered by machining operations. Pair of weft carrying and drawing grippers as in claim 1), wherein said thermosetting material consists of an epoxy resin. Pair of weft carrying and drawing grippers as in claim 5), wherein the weight ratio between carbon fibers and epoxy resin is in the range between 60/40 and 80/20. Pair of weft carrying and drawing grippers as in claim 1), wherein said metal body (2; 12) is produced from sheet steel, with die-forming and deep-drawing processes. Pair of weft carrying and drawing grippers as in claim 7), wherein the sheet steel forming said metal body (2; 12) is about 1 mm thick . Pair of weft carrying and drawing grippers as in claim 7), wherein said sheet steel forms a stiffening flange (3), apt to cover the whole upper edge (1b) of the structural support element (1). Pair of weft carrying and drawing grippers as in claim 9), wherein said sheet steel is subjected to a surface hardening treatment at least in correspondence of said flange (3). Pair of weft carrying and drawing grippers as in claim 1), wherein said abutting element (7; 17-17') is formed by injection molding, starting from a thermoplastic material eventually filled with short glass or carbon fibers. Pair of weft carrying and drawing grippers as in claim 11), wherein said abutting element (7; 17-17') comprises threaded metal inserts (7a; 17a-17'a), preferably of brass, inserted into said element during the molding process thereof. Pair of weft carrying and drawing grippers as in claim 11), wherein said thermoplastic material is a polyamide resin. Pair of weft carrying and drawing grippers as in claim 13), wherein the weight ratio between said glass or carbon fibers and said polyamide resin is in the range between 20/80 and 40/60.

Inventors: FRANZ ERMANNO, FRANZ, ERMANNO
Applicants: PROMATECH SPA, PROMATECH S.P.A.
Application year: 1999
Main classification: D03D47
IPC codes: D03D47, D03J5