Extrusion head for producing sheet material reinforced internally with relatively close-packed cords

Abstract: An extrusion head (1) for producing sheet material (2), particularly elastomeric material, reinforced internally with relatively close-packed metal or textile cords (3); on which a die adapter (8) houses a "mandrel" (23) aligned with an output die (16) for the extruded sheet material (2) and having an axial slot (31) for feeding the rein­ forcing cords (3) to the die (16); the aforementioned man­ drel (23) having, on its front end facing the die (16), an insert (32) defining, together with the die adapter (8), an upper channel (34) and a lower channel (35) for supplying plastic material; which insert (32) consists of an upper element (40) and a lower element (41) the front ends of which are arranged contacting so as to de­ fine a cord output guide member (56), and the rear ends of which are gripped together with the interposition of an intermediate element (47), so as to define two super­ imposed cord input guide members (61, 62) converging in­ side the output guide member (56), having a cord density equal to half that of the output guide member (56), and offset by half the cord spacing in relation to each other.

Description: The present invention relates to an extrusion head for producing sheet material reinforced internally with relatively close-packed cords. In particular, the present invention relates to an extrusion head for producing plies of elastomeric material reinforced internally with "high-density" metal or textile cords, i.e. lying in the same plane and packed closely together with an average cord spacing of approximately 0.1 mm. Reinforced plies are normally produced using extruders having an extrusion head comprising a die adapter inside which is housed a mandrel aligned with the output die and having an axial duct for supplying the reinforcing cords to the die. The front end of the mandrel facing the die usually presents an insert through which the cords are fed, and defining, together with the die adapter, an upper and lower channel by which the die is fed with plastic elastomeric material for forming two layers of elastomeric sheet material arranged on either side of an intermediate cord layer, and joined together along the gaps between adjacent cords. The said insert usually consists of an upper and lower element gripped together in contacting manner and defining a cord guide member for maintaining constant cord distribution as the cords are fed through the die and subjected to the lateral thrust of the plastic material supplied to the die along the said supply channels. On known extrusion heads of the aforementioned type, the upper and lower elements of the said insert present respective flat lateral surfaces gripped together in contacting manner and each having a series of grooves mating with corresponding grooves on the other surface so as to define respective cord guide holes. Being located between the said two supply channels, the upper and lower elements of the said insert are therefore subjected to severe pressure, by which the said elements are compressed one against the other. Severe contact pressure is thus exerted on the contact surfaces of the said upper and lower elements, i.e. on the flat strip portions of the said contacting surfaces extending between each pair of adjacent grooves. Obviously, therefore, for cord densities over and above a given value, the width of the said flat strips is so small as to produce specific contact pressures in excess of the yield point of the metal from which the insert is formed, thus collapsing the diaphragms between adjacent grooves on each element, and jamming the cord inside the guide member On account of the above drawback, the extrusion heads of the aforementioned type cannot be employed for cord densities involving strips of less than approximately 0.5 mm in width. In GB-A- 279 383, an improved type of extrusion head is disclosed comprising a die for a sheet material internally reinforced with cords, and a cord guide insert, in which a first and a second element are arranged one on top of the other with the interposition of an intermediate element defining, together with the above first and second elements, two input cord guide members arranged one on top of the other and each offset by half the cord spacing in relation to the other. In the extrusion head of the above improved type, the width of the aforementioned flat strips, owing to the presence of the above two superimposed input cord guide members, may be increased to avoid yielding also when a relatively large number of cords is used. However, the above improved type of extrusion head cannot be employed for production of high-cord-density internally reinforced plies, since the cords coming out from the above two input guide members remain unguided when meshing together to form a single cord layer, and may very easily lead to the production of a non uniform ply. It is an object of the present invention to provide an extrusion head of the above improved type enabling the production of reinforced plies having "high cord density". According to the present invention there is provided an extrusion head for producing sheet material, particularly elastomeric material, reinforced internally with relatively close-packed cords; the extrusion head comprising a die for the internally-reinforced sheet material, a cord guide insert comprising a first and second element arranged contacting and one on top of the other, and an intermediate element arranged between the first and second elements and defining therewith two input guide members arranged one on top of the other and each offset by half the cord spacing in relation to the other, characterised in that the intermediate element further defines, with said first and second elements, an output guide member facing the die and having a number of holes arranged in a row; each input guide member having a cord density equal to half that of the output guide member. The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig. 1 shows an axial section of a preferred embodiment of the extrusion head according to the present invention; Fig.2 shows a front view of a detail in Fig.1; Fig.3 shows a section along line III-III in Fig.2; Fig.4 shows a plan view of the Fig.2 detail with parts removed for simplicity; Fig.5 shows a front view of a detail in Fig.2; Fig.6 shows a lateral end view of the Fig.5 detail; Fig.7 shows a section along line VII-VII in Fig.5; Fig.8 shows a section along line VIII-VIII in Fig.5; Fig.9 shows a cross section of a reinforced ply formed using the extrusion head in Fig.1. Number 1 in Fig.1 indicates an extrusion head for producing an elastomeric ply 2 (Fig.9) reinforced internally with "high-density" metal or textile cords 3, i.e. arranged side by side in the same plane and approximately 0.1 of a millimetre apart. Head 1 comprises an outer casing 4 having longitudinal side walls 5 and a front end wall 6 with a substantially rectangular axial through hole 7. Head 1 also comprises a die adapter 8 housed inside a cavity 9 defined by walls 5, and the front of which is arranged contacting the inner surface of wall 6. Die adapter 8 presents an inner axial channel 10 divided into two parts by an inner transverse partition 11. A first of the said parts, located at the rear, consists of a substantially rectangular-section hole 12 tapering towards the said partition 11, whereas the second of the said parts consists of a substantially rectangular-section hole 13 coaxial with hole 7 and the rear end of which communicates with the front end of hole 12 via a substantially rectangular-section hole 14 formed through partition 11 and tapering towards hole 13 commencing from the tapered front end of hole 12. Hole 13 houses a parallelepiped body 15 of a die 16 locked axially between partition 11 and wall 6, and comprising a front, substantially rectangular-section appendix 17 extending outwards of casing 4 through hole 7. Die 16 is defined by a top die 18 and bottom die 19 connected by through pins 20 and defining a transverse slot 21 coaxial with hole 7 and through which ply 2 is extruded. Hole 12 houses the rear body 22 of a cord guide member 23, hereinafter referred to as a "mandrel", said body 22 presenting a substantially rectangular section tapering towards partition 11, and the rear portion of which presents a top and bottom transverse groove, 24 and 25, constituting a manifold for plastic elastomeric material fed into casing 4 and die adapter 8 through a lateral input hole 26. The front portion of body 22 presents a top and bottom axial supply channel, 27 and 28, the respective rear ends of which communicate respectively with grooves 24 and 25. Body 22 consists of a top and bottom plate, 29 and 30, defining a slot 31 through which cords 3 are supplied to die 16. In addition to rear body 22, mandrel 23 also comprises a transverse, substantially triangular-section insert 32 engaging tapered hole 14 and the pointed front end portion of which extends inside a transverse groove 33 formed on the rear surface of body 15 of die 16. On the top and bottom surfaces of hole 14, there are formed two grooves defining, together with the top and bottom surfaces of in sert 32, two tapered, converging channels, 34 and 35, communicating respectively with channels 27 and 28, and designed to supply plastic elastomeric material to slot 21 of die 16. Insert 32 is defined rearwards by a flat surface 36 contacting a flat front surface 37 of body 22 and having an appendix 38 engaging a transverse groove 39 formed on surface 37. As shown particularly in Fig.s 2 and 3, insert 32 consists of a wedge-shaped top and bottom element, 40 and 41, each of which presents, on its opposite lateral ends, two blocks 42 in the form of a rectangular parallelepipedon, and each connected to block 42 on the other element of insert 32 by means of a through bolt 43. Elements 40 and 41 are defined by respective inclined surfaces 44 and 45, the front ends of which are arranged contacting along a line lying in the axial plane of head 1 along which extend slots 21 and 31. Commencing from the front ends, the said two surfaces 44 and 45 diverge to define a dihedral 46, the rear portion of which is occupied by a wedge-shaped intermediate element 47 having, on its opposite ends, two plates 48 fitted through with bolts 43 and gripped between two respective blocks 42. As shown, particularly in Fig.s 5 to 8, intermediate element 47 is defined at the top and bottom by two inclined, converging surfaces, 49 and 50, contacting surfaces 44 and 45 respectively. Contact between surfaces 44 and 49 and surfaces 45 and 50 is limited to the rear portion of surfaces 44 and 45, the front portions 51 and 52 of the same being exposed and facing each other directly. As shown in Fig. 4, front portions 51 and 52 (of which only portion 52 is shown) present grooves 53 coplanar with slots 21 and 31. The said grooves 53, the depth of which obviously decreases commencing from the front end, are separated by ridges 54 having a minimum width of approximately 0.1 mm at the front end and increasing gradually towards the front end of intermediate element 47. Each groove 53 on portion 51 mates with a corresponding groove 53 on portion 52 to define a hole 55 (Fig.2) on a cord output guide member 56 defined between front portions 51 and 52. The rear portions of surfaces 44 and 45 are flat, whereas surfaces 49 and 50 respectively contacting the same present, as shown in Fig.s 4 and 5, respective sets of grooves 57 and 58, each of which grooves is aligned with and presents substantially the same section as a respective hole 55. Grooves 57 and 58 are equally spaced with twice the spacing of holes 55, and are offset by half a space in relation to one another, so as to be aligned with respective alternate holes 55. Each groove 57 and 58 is separated from the adjacent groove 57, 58 by a ridge 59 defined by a flat strip 60 forming part of respective surface 49, 50 and at least equal in width to the diameter of grooves 57 and 58. Together with opposite surfaces 44 and 45, grooves 57 and 58 define two superimposed input guide members, 61 and 62, both converging inside output guide member 56, and each having a guide hole density equal to half that of output guide member 56, and communicating rearwards with slot 31. In actual use, cords 3 are first threaded through slot 31 so that, of each pair of cords 3, one engages a groove 57 on input guide member 61, and the other a groove 58 on input guide member 62. Each cord 3 is then threaded through a respective hole 55 on output guide member 56, at which point, extrusion of ply 2 may be commenced in known manner. Intermediate element 47 thus provides for considerably extending the contact surfaces inside insert 32, and so reducing specific contact pressure to acceptable limits, even when extruding "high-cord-density" plies 2. In the case of such plies, the said contact surfaces are formed, not by approximately 0.1 mm wide strips as on the inserts of known extrusion heads, but by strips, such as strips 60 and 61, at least equal in width to the diameter of cords 3.

Claims: An extrusion head (1) for producing sheet material (2), particularly elastomeric material, reinforced internally with relatively close-packed cords (3); the extrusion head (1) comprising a die (16) for the internally-reinforced sheet material (2), a cord guide insert (32) comprising a first and second element (40, 41) arranged contacting and one on top of the other, and an intermediate element (47) arranged between the first and second elements (40, 41) and defining therewith two input guide members (61, 62) arranged one on top of the other and each offset by half the cord spacing in relation to the other, characterised in that the intermediate element (47) further defines, with said first and second elements (40, 41), an output guide member (56) facing the die (16) and having a number of holes (55) arranged in a row; each input guide member (61, 62) having a cord density equal to half that of the output guide member (56). An extrusion head as claimed in Claim 1, characterised in that the first and second elements (40, 41) have respective front portions facing the die (16), and in direct contact with each other so as to define the output guide member (56); and respective rear portions gripped together with the interposition of the intermediate element (47) so as to define the two input guide members (61, 62). An extrusion head as claimed in Claim 2, characterised in that the intermediate element (47) is defined at the top and bottom by two inclined, converging flat surfaces (49, 50) respectively contacting the rear portion of respective inner surfaces (44, 45) of the said first and second elements (40, 41); the said inner surfaces (44, 45) comprising respective front portions (51, 52) directly facing and contacting each other. An extrusion head as claimed in Claim 3, characterised by the fact that each said front portion (51, 52) of each said inner surface presents a number of grooves (53) each mating with a corresponding groove (53) on the other front portion (51, 52) so as to define a respective said hole (55) on the said output guide member (56); the said grooves (53) on the said first and second elements (40, 41) decreasing in depth from the front end, and being separated by ridges (54) of minimum width at the front and increasing gradually in width towards the front end of the said intermediate element (47). An extrusion head as claimed in Claim 3 or 4, characterised by the fact that the rear portions of the inner surfaces (44, 45) of the said first and second elements (40, 41) are flat, whereas the surfaces (49, 50) of the said intermediate element (47) respectively contacting the same present respective sets of grooves (57, 58) defining the said two input guide members (61, 62); each said groove (57, 58) on the said intermediate element (47) having substantially the same section as a respective said hole (55) on the said output guide member (56). An extrusion head as claimed in Claim 5, characterised by the fact that the grooves (57, 58) on the said intermediate element (47) are equally spaced with twice the spacing of the holes (55) on the said output guide member (56), and are offset by half a space in relation to one another, so as to be aligned with respective alternate holes (55) on the said output guide member (56). An extrusion head as claimed in Claim 6, characterised by the fact that adjacent grooves (57, 58) on the said intermediate element (47) are separated by a ridge (59) at least equal in width to the diameter of the said grooves (57, 58).

Inventors: MINAUDO DIEGO, MINAUDO, DIEGO
Applicants: BRIDGESTONE FIRESTONE INC, BRIDGESTONE/FIRESTONE, INC.
Application year: 1989
Main classification: B29C47
IPC codes: B29C47