Mechanism for supporting and retaining the beads when building pneumatic tyres

Abstract: Mechanism for supporting and retaining the beads when building at least a portion of a pneumatic tyre on a building drum, said mechanism comprising radially expandable and retractable means for laterally supporting at least a part of each bead, wherein a large number of rocker arms is arranged in a ring shape about the centre line of the building drum, and means serve to shift and swivel all of these rocker arms simultaneously to an expanded position and to retract them again, said swivelling action of each rocker arm being performed in an imaginary plane extending radially through the centre line of the drum and said shifting action including a component directed along the centre line of the building drum.

Description: The invention relates to a tyre building drum for building at least a portion of a pneumatic tyre having beads, said drum comprising radially expandable and retractable means for laterally supporting, i.e. in the direction parallel to the centre line of the building drum, at least part of each bead, said drum comprising a central portion and right-hand and left-hand portions, each of said right-hand and left-hand portions comprising a mechanism for supporting and retaining beads when building at least a portion of a pneumatic tyre on said building drum. Such a tyre building drum is described in US-A-4,149,927. This known tyre buiding drum comprises an expandable central drum segment with hinged drum shoulders which serve to form the bevelled corner on the expandable drum segment. When building a pneumatic tyre the expandable drum segment is expanded and a bead is placed against the bevelled corner formed by the hinged drum shoulders such that only part of the bead is contacted. However, it is desirable that not only the beads are brought and retained in the correct position with respect to the building drum, but that also the apex and flipper pertaining to the bead are laterally supported, i.e. in a direction parallel to the centre line of the buiding drum. Particularly with radial tyres for passenger cars the height of the apex and flipper may amount to at least four times the thickness of the bead wire bundle. Therefore it is necessary that the support means can be expanded to a sufficient height so as to laterally support also the apex and the flipper, said means being retractable again. The hinged drum shoulders as known from US-A-4,149,927, however, are not able to clamp the bead wire bundle from underneath and to support at the same time the apex and the flipper. The present invention therefore aims to provide a tyre building drum with support means that can be expanded far enough to support a high apex and flipper and to give support underneath the bead bundle. The invention particularly aims to provide a mechanism for expanding these support means, which is operated fast and simple and which is reliable. For this purpose the present invention provides a tyre building drum for building pneumatic tyres as defined in the opening paragraph which is characterized in that each of said mechanisms comprising a large number of rocker arms having first ends located on the side thereof opposite said central drum portion and being arranged in a ring shape about the centre line of the building drum, means to shift and swivel all of these rocker arms simultaneously to a radially expanded position of said first ends and to retract them again, said swivelling action of each of said rocker arms being performed in an imaginary plane extending radially through the centre line of the drum and said shifting action including a component directed along the centre line of the drum, pressure segments having radially outer ends and mounted on said drum for radially slidable back and forth movement with respect to the centre line of the building drum, said pressure segments comprising recesses in their radial outer ends, a pressure ring of resilient material disposed in said recesses, and a bellows being secured with one edge in the first ends of all said rocker arms on the side of the rocker arms opposite the centre line of the drum, said bellows being U-shaped in radial section and extending across said pressure ring and serving to fold back any layers protruding beyond the bead in the direction of one end of the building drum, said rocker arms and said bellows forming a drum shoulder on the side of said rocker arms opposite the central drum portion in the radially expanded position of the rocker arms, said drum shoulder serving for laterally supporting each bead and said part of the bellows across the pressure ring and the pressure ring serving for radially supporting each bead. Thus the bead wire bundle, flipper and apex of the bead are not only supported laterally against the rocker arms via the adjacent other elements of the pneumatic tyre and via the adjacent part of the bellows, but said part of the elastic and resilient bellows also abutts airproof onto said other adjacent elements of the pneumatic tyre under construction. Both the radial accuracy with which the bead can therefore be positioned, ensures optimum quality of the tyre under construction and thus a good quality of the finished pneumatic tyre is achieved. In DE-A-1,579,254 a bladder-type drum is described to shape prefabricated green tyre carcasses by means of a soft non-cylindrical bladder with radially expandable and retractable means for externally supporting beads of a joined assembly of carcass and beads during inflation of the carcass into a toroidal shape. Consequently DE-A-1,579,254 relates to the method of shaping a finished carcass and not to the step of manufacturing a green tyre according to the present application. Since the expandable and retractable means of DE-A-1,579,254 are situated on the side of the bladder opposite the centre line of the device the bladder type drum of DE-A-1,579,254 cannot even execute the manufacture of a green tyre as described in the present application. According to the invention means for shifting right-hand and left-hand portions of the building drum towards and away from one another are provided, which are operable independently from the means for shifting and swivelling the rocker arms. Thus the end parts of the building drum can be shifted even more towards one another after the tyre has been completely built, in order to release the bellows from the tyre as it is bound to stick somewhat to the tyre, which is made of unvulcanized rubber. The invention will be further elucidated in the following description of an example of the invented bead shoulder mechanism, as represented in the accompanying drawing. In the drawing: figure 1 is schematical representation of a tyre building drum according to the present invention, and in which above the centre line of said drum this drum is indicated in radial section, whereas below said centre line this building drum is indicated in side view; figure 2 shows a radial section of a part of the invented tyre building drum in the retracted position, which part is disposed above the centre line of the building drum; figure 3 shows a radial section as shown in figure 2, in which, however, the invented tyre building drum is in the postion in which a shoulder for a bead for a pneumatic tyre is formed; figure 4 schematically shows the succession of the operation of a tyre-building drum with a randomly selected bead shoulder mechanism. The tyre-building drum as shown in figure 1 has a general centre line 2 and as the building drum is substantially cylindrical, it is referred to as a flat building drum. Figure 1 shows above the centre line 2 a radial section of that particular portion of the building drum, whereas figure 1 shows below the centre line a side view of the building drum. As shown in figure 1, the tyre-building drum comprises a hollow shaft 3 extending over the entire length of the building drum, said shaft being coupled with drive means 4 for rotating said shaft. Within the shaft extends a steering spindle 5 with screw thread 6 and 7, each cooperating with a nut 8 or 9, respectively. On each nut a pin 10 or 11, respectively, is mounted, each pin protruding through a slot 12 or 13, respectively, in the wall of the hollow shaft 3. As shown in figure 1, each pin 10, 11 is coupled to either a right-hand or left-hand drum portion 14 or 15, respectively, each being disposed shiftably on the shaft 3. By rotating the steering spindle 5 in the one direction with respect to the shaft 3, the nuts 8 and 9 are moved towards one another along the screw thread parts 6 or 7, respectively, resulting in that the drum portions 14 and 15, respectively, are shifted towards one another by the pins 10 and 11, respectively, by means of the nuts 8 and 9, respectively. If the steering spindle is rotated in the opposite direction, the drum portions 14 and 15, respectively, will shift away from one another along the shaft 3 in the manner as described above. The central drum portion 16 comprises elements that form a cylinder, allowing the left-hand and right-hand drum portions 15 and 14, respectively, to shift towards one another and vice versa. The left-hand and right-hand drum portions 15 and 14 are mirror symmetric with respect to the plane perpendicular to the centre line 2 and through the central drum portion 16, so that it suffices to describe the right-hand drum 14 according to figure 2 at this point. A radial section of part of the right-hand drum portion 14 is represented in figure 2 separately and at a larger scale than in figure 1. It should be noted that the right-hand drum portion 14 extends substantially in a ring shape about the shaft 3 in figure 1, so that figure 2 merely represents the part above the shaft 3 of the total radial section of the right-hand drum portion 14. Figure 3, in turn, shows a part of figure 2 at a larger scale. The right-hand portion 14 comprises an annular carrier 17, slidable along the shaft 3 and having a hole 18 for pin 10 as shown in figure 1. As shown in figures 2 and 3, around the carrier 17 an annular cylinder holder 19 is arranged, having therein an anular cylinder space 20 for an annular piston 21. A closing ring 25 comprises a number of holes 22, a spring 23 protruding with its one end into each hole 22, and each spring protruding with its other end into a hole 24 in the piston 21. As figure 2 only is a radial section of a part of the right-hand drum portion, only one spring 23 with pertaining holes 22 and 24 has been drawn in figure 2. However, a a sufficient number of springs 23 is disposed about the shaft 3 to push the piston 21 back to the position as shown in figure 2 in a reliable manner after this piston has been shifted to the left by means of over-pressure, to the position as shown in figure 3, and after the over-pressure has subsequently been lifted. The means for e.g. pneumatically or hydraulically shifting the piston 21 are easy to design for an expert and therefore they are not discussed here. As shown in figures 2 and 3, between the cylinder holder 19 and the closing ring 25 pressure segments 26 have been disposed, which are radially slidable back and forth with respect to the shaft 3. E.g. twenty-four of these pressure segments are present about the shaft 3. The radial inner ends of all pressure segments 26 are formed by surfaces 27, sloping with respect to the centre line of the shaft and cooperating with equally sloping surfaces 28 of the annular piston 21. On account of these sloping surfaces 27 and 28, the sliding of the piston 21 from the retracted position as shown in figure 2 to the extended position according to figure 3 is converted into a radial, outward pushing of the pressure segments 26 from the retracted position as shown in figure 2 to the expanded position as shown in figure 3. As shown in figures 2 and 3, a pressure ring 29 of resilient material, such as natural rubber, is disposed in recesses in the radial outer ends of the pressure segments 26. This pressure ring extends coaxially about the shaft 3 and has sufficient strength to push the pressure segments 26 continously against the piston 21. The pressure ring 29 particularly pushes the pressure segments 26 radially inwards when the piston 21 is shifted from the extended position as shown in figure 3 to the retracted position according to figure 2. As shown in figure 2, the one end of an inflatable bellows 30, U-shaped in radial section, extends across the pressure ring 29, said bellows being connected airproof at the cylinder holder 19 with its other end 31. This bellows is drawn in figures 2 and 3 in its deflated condition and extends in a ring shape about the shaft 3 (figure 1). The presently described tyre-building drum is operated as indicated schematically in figure 4. In its passive position, i.e. at the start of the construction of a pneumatic tyre or part thereof, the building drum is substantially cylindrical as shown in figures 1 and 2. Subsequently a system 33 of layers is placed about the building drum 1, said system of layers being substantially cylindrical as shown in figure 4A. Then the two bead rings 32 are placed on the outside of the system 33 of layers that is destined to form a part of a pneumatic tyre. For clarity's sake, figure 2 merely shows the bead ring 32 without the pertaining apex and flipper, and the system of layers has been omitted from the drawing as well. Adjacent to the bead ring this system of layers e.g. comprises one or more carcass layers, a chafer strip and a bead strip. Subsequently the piston 21 is shifted from the passive position 2 to the left into the operating position as shown in figure 3 by means of over-pressure. On account of this shifting, the piston 21 via its sloping surface 28 pushes the pressure segments 26 outwards via their sloping surfaces, thus moving the pressure segments from their retracted positions as shown in figure 2 to their expanded positions as shown in figures 3 and 4B. As the bead ring 32 is disposed quite precisely with respect to the pressure ring 29, the pressure ring 29 and the adjacent part of the bellows 30 is pushed airproof against the above-indicated system 33 of layers at the bead ring 32 as shown in figure 3 when the pressure segments 26 are in their expanded positions. As shown in figure 4C the next step involves the formation of a shoulder 34 on the building drum 1 at the lateral inner side of each bead 32. In order to form these two shoulders, the building drum 1 comprises a mechanism that will be discussed further on in this description as the invention relates to this particular mechanism. At this point first a few subsequent steps in the operation of the building drum will be discussed, and such in so far as they are required for a proper understanding of the invented bead shoulder mechanism. Following the formation of the two shoulders 34, the two bellows 30 are inflated, and subsequently these two bellows are folded until they point at one another, as shown in figure 4D. The right-hand bead 32 abuts against the right-hand shoulder 34 and the right-hand bellows 30 pushes against said right-hand bead. Also the parts of the layer system 33 disposed on the right-hand side of the bead 32 as shown in figure 4C are pushed by the inflated and folded bellows 30 until they extend over parts of the rest of the said layer system as shown in figure 4D. Subsequently the layer system 33 is inflated into a toroid as shown in figure 4E, the left-hand and right-hand drum portion 14 or 15, respectively, being moved towards one another to the extent desired for the formation of said toroid. This displacement is effected by rotation of the steering spindle 5 with respect to the shaft 3, on account of which the screw thread parts 6 and 7 on the steering spindle effect the displacement of the nuts 8 and 9, respectively. By means of these nuts 8 and 9, the drum portion 14 or 15, respectively, is displaced as in figure 1 via the pin 10 or 11, respectively. Some known, further steps of processing will subsequently be carried out, but a description of these known, further steps is not required for a proper understanding of the invention. After an example of a tyre-building drum and the steps of its operation have been described above, the actual invention will be elucidated in the following. On the one hand a flat building drum 1 as shown in figures 1 and 4A, i.e. being substantially cylindrical in its starting position, is desired, as it allows the highly mechanized building of radial tyres for passenger cars. The bead rings, having a greater diameter than the building drum 1 in its starting position, can easily be transported coaxially along the building drum to their correct positions. However, such a flat building drum should comprise means that are able to support the bead with high apex and flipper against deformation, said beads with high apex and flipper being a desired feature in radial tyres designed for fast cars. The quality of a tyre is to a great extent determined by the position and the shape of the bead, which position and shape can be positively influenced by means that retain and support the bead in its accurate position and shape during the construction of the tyre. As a bead wire bundle can e.g. be approx. 7 mm in cross-section and the difference between the internal diameter of a bead wire bundle and the external diameter of a flat building drum in its passive position amounts approx. to 25 mm, it is desired to have a shoulder to support the bead, the height of this shoulder e.g. amounting to four times the cross-section of the bead wire bundle so as not only to support the bead wire bundle, but also the pertaining apex and flipper. For this purpose, the invention as shown in figures 2 and 3 comprises a number of rocker arms 35 disposed annularly about the shaft 3 (figure 1), which number may e.g. amount to forty-eight. These rocker arms are pivotally supported, e.g. by means of a ball joint 48, by a sleeve 36 which extends in a ring shape about and is slidable over the carrier 17. A part 37 of the sleeve 36 co-operates as a piston together with a ring 38 secured on the carrier 17. Means which are easy to develop for an expert and which will therefore not be discussed here, are employed to supply compressed air to the space 43 between the sleeve part 37 and the ring 38, causing the sleeve 36 to shift from the position as shown in figure 2 to the position as shown in figure 3. On the closing ring 25, as shown in figures 2 and 3, a holder 39 extending annularly about the shaft 3 is mounted. This holder comprises a number of holes 40 of which the radial sections as shown in figures 2 and 3 only show one example. Into each hole 40 one end of a spring 41 protrudes, and the other end of said spring protrudes into a hole 42 in the sleeve 36. These springs 41 serve to push the sleeve 36 back from the position as shown in figure 3 to the position as shown in figure 2, after the pressure created by the compressed air in the space 43 between the sleeve 36 and the ring 38 has been lifted. As shown in figures 2 and 3, one end of the folding bellows 30, essentially U-shaped in radial section, is connected to the rocker arms 35, whereas the other end of the said bellows is connected to the cylinder holder 19. On account of the step of shifting the sleeve 36 from the position as shown in figure 2 to the position as shown in figure 3 by over-pressure as described in the foregoing, the rocker arms 35 are pushed to the right and they swivel upwards in this process as they run up against the conical top 44 of the holder 39. When the over-pressure in the space 43 is lifted, the springs 41 push the sleeve 36 and the rocker arms coupled thereto to the left from the position as shown in figure 3 to the position as shown in figure 2, the resilience of the bellows 30 forcing the rocker arms 35 to swing back to their retracted positions as shown in figure 2. As appears from figure 3, the invented rocker arms 35 in their upward positions push the bellows 30 upwards to a considerable height with respect to the bead wire bundle 32. In this way the aim of the invention is achieved, i.e. that the bead ring 32 with apex 46 and flipper 47 is supported, even when this apex and flipper are high with respect to the bead wire bundle 32. Furthermore it appears from figure 2 that the rocker arms 35 in their retracted positions do not protrude beyond the rest of the building drum 1. Thus the desired starting point of the invention is achieved, being that the bead rings and other materials of which the tyre will be composed, can be disposed coaxially to the building drum 1 easily and fast, and preferably automatically. The resilient deformability of the bellows 30 made of natural or silicon rubber allows the bead 32 with apex 46 and flipper 47 to be supported firmly and airproof by means of the layer system 33 of the tyre under construction and the part of the bellows 30 carried by the rocker arms 35 as shown in figure 3. This results in that the still unvulcanized tyre is of higher quality than a tyre of this type in which the bead is merely supported laterally near the bead wire bundle 32, i.e. in a direction parallel to the centre line of the building drum. Preferably the steering spindle 5 can be operated independently of the piston 21 and the sleeve 36. On account of this, the steering spindle allows the two drum portions 14 and 15 to be shifted further towards one another after the building of the tyre under construction is finished. This results in that the bellows 30 is pulled away from the tyre, as it will stick to some extent to the tyre of unvulcanized rubber. Furthermore the pressure ring 29 as shown in figure 2 is preferably provided with an appendix 45 extending annularly about the shaft 3 (figure 1) and being retained with its radial inner end between the closing ring 25 and the holder 39. This appendix serves to increase the force with which the pressure ring 29 as shown in figure 3 biasses the segments 26 radially inwards.

Claims: Tyre building drum (1) for building at least a portion of a pneumatic tyre having beads (32, 46, 47), said drum (1) comprising radially expandable and retractable means (35) for laterally supporting, i.e. in the direction parallel to the centre line (2) of the building drum (1), at least part of each bead (32, 46, 47), said drum (1) comprising a central portion (16) and right-hand (14) and left-hand (15) portions, each of said right-hand (14) and left-hand(15) portions comprising a mechanism for supporting and retaining beads (32, 46, 47) when building at least a portion of a pneumatic tyre on said building drum (1), characterized in that each of said mechanisms comprising a large number of rocker arms (35) having first ends located on the side thereof opposite said central drum portion (16) and being arranged in a ring shape about the centre line (2) of the building drum (1), means (36-44) to shift and swivel all of these rocker arms (35) simultaneously to a radially expanded position of said first ends and to retract them again, said swivelling action of each of said rocker arms (35) being performed in an imaginary plane extending radially through the centre line (2) of the drum (1) and said shifting action including a component directed along the centre line (2) of the drum (1), pressure segments (26) having radially outer ends and mounted on said drum (1) for radially slidable back and forth movement with respect to the centre line (2) of the building drum (1), said pressure segments (26) comprising recesses in their radial outer ends, a pressure ring (29) of resilient material disposed in said recesses, and a bellows (30) being secured with one edge in the first ends of all said rocker arms (35) on the side of the rocker arms (35) opposite the centre line (2) of the drum (1), said bellows (30) being U-shaped in radial section and extending across said pressure ring (29) and serving to fold back any layers (33) protruding beyond the bead (32, 46, 47) in the direction of one end of the building drum (1), said rocker arms (35) and said bellows (30) forming a drum shoulder (34) on the side of said rocker arms (35) opposite the central drum portion (16) in the radially expanded position of the rocker arms (35), said drum shoulder (34) serving for laterally supporting each bead (32, 46, 47) and said part of the bellows (30) across the pressure ring (29) and the pressure ring (29) serving for radially supporting each bead (32, 46, 47). Tyre building drum (1) according to claim 1, characterized in that the drum (1) comprises a hollow shaft (3) extending over the entire length of the drum (1), in that each of the right-hand (14) and left-hand (15) portions comprises an annular carrier (17) slidably mounted on the shaft (3) and in that the means (36-44) to shift and swivel the rocker arms (35) comprise a holder (39) having a conical expanding surface (44) extending around the shaft (3). Tyre building drum (1) according to claim 2, characterized in that the means (36-44) to shift and swivel the rocker arms (35) comprise a sleeve (36) extending in a ring shape about and being slidable over the carrier (17) and a ring (38) secured on the carrier (17), said sleeve (36) comprising a part (37) cooperating with the ring (38) to form a piston displaceable parallel to the centre line (2) of the drum (1), said piston having a space (43), said sleeve (36) being coupled to all rocker arms (35) in order to shift the rocker arms (35) into their expanded positions by means of over-pressure on the piston, holes (42, 40) provided in the sleeve (36) and the holder (39), and springs (41) protruding in the holes (42, 40). Tyre building drum (1) according to claim 3, characterized in that each rocker arm (35) is coupled to the sleeve (36) by means of a ball joint (48). Tyre building drum (1) according to claim 1, characterized in that means for shifting the right-hand (14) and left-hand (15) portions of the building drum (1) towards and away from one another are provided, which are independently operable from the means (36-44) to shift and swivel the rocker arms (35).

Inventors: BIERENS FRANCISCUS CORNELIS, BIERENS, FRANCISCUS CORNELIS
Applicants: VMI EPE HOLLAND, VMI EPE HOLLAND BV
Application year: 1991
Main classification: B29D30
IPC codes: B29D30