Method and device for manufacturing curing bladders

Abstract: A method and device for manufacturing curing bladders (2), whereby a curing mold (3) defines, via a first (4) and second (5) half mold and an inner core (6), an inner molding chamber (7) and an outer injection chamber (34) communicating with the inner chamber (7) and consisting of a variable-volume chamber of an injection cylinder (59); the outer chamber (34) being fed with a mass (35) of heated crude rubber which is injected into the inner chamber (7) with the mold (3) closed and, when cured, is extracted from the mold (3) by opening the inner chamber (7) and extracting the inner core (6).

Description: The present invention relates to a method of and a device for manufacturing curing bladders. Curing molds generally comprise an upper and lower half mold connectable in such a manner as to define a toroidal chamber for receiving a green tire for curing, inside which tire a bladder is inflated, usually in two successive stage, so that the outer surface of the tire adheres to the inner surface of the mold, and also for defining a toroidal passage for a high-temperature heat exchange fluid. Due to the mechanical and thermal stress to which they are subjected and the particular function they are called upon to perform, bladders of the aforementioned type demand an extremely high degree of precision. A known method of producing such bladders is by what is known as "compression molding." According to this process, the bladders are produced using a curing mold comprising two half molds and, possibly, an inner core, which, when the mold is closed, define an inner toroidal chamber of exactly the same shape as the bladder being produced. Prior to closing the mold, a mass of crude rubber is fed inside one of the half molds and, when the mold is closed, is subjected to relatively high pressure so as to force it along and fill the inner chamber. The above compression molding process involves a number of drawbacks, foremost of which are the need for relatively high-power presses for closing the molds, and overall inaccuracy of the finished product. The latter is due to variations in the shape and volume of the inner chamber during actual molding, which instability results in friction between the rubber and the walls of the inner chamber, thus preventing the rubber from faithfully reproducing the shape of the inner chamber when the mold is closed. Another known method of producing such bladders is by what is known as "injection molding." According to this process, which is disclosed, for example, in US-A-4,954,074, curing bladders are manufactured using a curing mold comprising a first and second half mold and an inner core which, when the curing mold is closed, define a substantially toroidal inner molding chamber of the same shape as the bladder to be produced. After closing the mold, a mass of crude rubber is injected into the inner chamber via one or more injection ducts and by means of an external injection device such as that disclosed, for example, in US-A-3,892,512. Then the finished bladder is extracted from the mold by opening the inner chamber and extracting the inner core. Injection molding provides for very high precision, but is very expensive, owing to such method involving the use of a separate injection device, and to the energy required. As far as the energy is concerned, it is to be noted that the rubber and both the injection device and the mold are to be heated, and that only the heat in the rubber is transmitted, at least in part, to the mold, whereas the energy for heating the injection device is substantially lost. It is an object of the present invention to provide a method of manufacturing curing bladders, which provides for the same precision as injection molding but at lower cost. According to the present invention there is provided a method of manufacturing curing bladders using a curing mold comprising a first and second half mold and an inner core which, when said curing mold is closed, define a substantially toroidal inner molding chamber of the same shape as the bladder being produced; said method comprising stages of closing said mold; feeding a mass of crude rubber into said inner chamber via at least one injection duct; curing said rubber inside said inner chamber so as to produce a finished bladder; and extracting said finished bladder from said mold by opening said inner chamber and extracting said inner core; and being characterized in that said mass of crude rubber is fed to an outer chamber provided on one of said half molds and communicating with said inner chamber via said injection duct, and is subjected via pressure means inside said outer chamber to sufficient pressure to inject it from said outer chamber into said inner chamber via said injection duct. Owing to the above arrangement, substantially all the energy spent for injecting the rubber is transmitted to the mold thus reducing the energy required for curing to substantially half. According to a preferred embodiment of the method set forth above, said outer chamber is a variable-volume chamber of an injection cylinder provided on said one half mold; said pressure means comprising a mobile piston mounted for movement on said one half mold and along said cylinder and closing said injection duct subsequent to injection. Finally, the above method preferably comprises a further stage consisting in blowing air between said inner core and said finished bladder for detaching the bladder from the inner core. The present invention also relates to a device for manufacturing curing bladders. According to the present invention, there is provided a device for manufacturing curing bladders, said device comprising a bladder curing mold in turn comprising a mutually-mobile first and second half mold and an extractable inner core, which, when said curing mold is closed, define a substantially toroidal inner molding chamber of the same shape as said bladder; characterised by the fact that it also comprises an outer chamber provided in one of said half molds and designed to receive a mass of crude rubber; at least one injection duct enabling communication between said inner and outer chambers; and pressure means traveling in relation to said mold and along said outer chamber for injecting said mass of crude rubber from said outer chamber to said inner chamber. The invention will now be described by way of example with reference to the accompanying drawings, in which: Fig.1 shows an axial half section of a preferred embodiment of a device in accordance with the present invention in a first operating position; Fig.s 2 to 7 show axial half sections of the Fig.1 device in further operating positions. Number 1 in Fig.1 indicates a device for manufacturing curing bladders 2 (Fig.s 4 to 7). Device 1 comprises a substantially cylindrical bladder curing mold 3 having a longitudinal axis A and in turn comprising a mutually-mobile first and second half mold 4 and 5 and an extractable inner core 6. Said half molds 4 and 5 and said inner core 6 are all coaxial with axis A and, when mold 3 is closed, define an inner molding chamber 7 coaxial with axis A and substantially the same toroidal shape as bladder 2. As shown in Fig.1, half mold 4 comprises a substantially cylindrical annular body 8 having a central hole 9 coaxial with axis A and, at one end, an outer flange 10 by which it is secured to a supporting plate (not shown). On the opposite end to flange 10, body 8 presents a flat annular surface 11 and an axial annular appendix 12 coaxial with axis A and extending from the outer periphery of surface 11 towards half mold 5. The end of appendix 12 facing half mold 5 is defined by a flat annular surface 13, the outer periphery of which presents an annular groove 14 engaged by the inner flange 15 of a cylindrical annular body 16 coaxial with axis A and extending from appendix 12 to half mold 5 so as to define, with surface 13, a toroidal chamber 17. The outer surface of appendix 12 presents an annular groove closed externally by a wall 18 and defining a duct 19 for circulating a heat exchange fluid. Appendix 12 is defined internally by a shaped surface 20 blending at one end with surface 11 so as to define a first outer surface portion of inner chamber 7. On end surface 21 opposite surface 13, body 8 presents a front annular groove surrounding hole 9 and closed outwards by a cover 22, so as to define a duct 23 for circulating a heat exchange fluid. As shown in Fig.1, half mold 5 comprises a substantially cylindrical annular body 24 having a central hole 25 coaxial with axis A and, at one end, an outer annular flange 26. On the opposite end to flange 26, body 24 presents a flat surface 27 and an axial annular appendix 28 coaxial with axis A and extending from the outer periphery of surface 27 towards half mold 4. Appendix 28 engages toroidal chamber 17 of half mold 4, and presents, on its free end facing half mold 5, a flat annular end surface 29 which, when mold 3 is closed, contacts surface 13 of half mold 4. Annular end surface 30 of body 24, opposite surface 29, presents a front annular groove 31 housing an annular body 32. Body 32 presents a substantially L-shaped section, and divides the inside of groove 31 into two parts, a first defining a duct 33 for circulating a heat exchange fluid, and a second defining an outer annular chamber 34 coaxial with axis A and designed to receive a toroidal body 35 consisting of a mass of crude rubber. Appendix 25 is defined internally by a shaped surface 36 blending at one end with surface 24 so as to define a second outer surface portion of inner chamber 7. As shown in Fig.1, inner core 6 comprises a central portion 37 and two end portions 38 and 39 aligned along and coaxial with axis A. In particular, central portion 37 consists of three bodies 40, 41 and 42 packed together by means of screws 43 and the first of which is an annular plate located between the other two. Body 41 is an annular body defined externally by a shaped lateral surface 44 facing surface 36 and defining an inner surface portion of chamber 7, and by a flat annular end surface 45 contacting annular surface 27 of body 24. Surface 44 blends with the outer periphery of surface 45 via an annular groove which, together with surface 36, defines an annular channel 46 for forming a respective annular end expansion 47 of bladder 2 (Fig.2 onwards). On the end facing half mold 5, annular body 41 is fitted integral with end portion 39, which consists of a conical base engaged inside a conical inner portion of hole 25. Body 42 is defined externally by a shaped lateral surface 48 facing surface 20, and by a flat annular end surface 49 contacting an end surface of end portion 38. End portion 38 is also defined externally by a shaped lateral surface 50 facing surface 20 and blending with surface 48 so as to define with the same an inner surface portion of chamber 7. End portion 38 also presents an intermediate annular shoulder 51 contacting annular surface 11 of body 8. Surface 50 blends with the outer periphery of shoulder 51 via an annular groove defining, together with surface 20, an annular channel 52 for forming a respective annular end expansion 53 of bladder 2 (Fig.2 onwards). On the end facing half mold 4, end portion 38 presents a conical base 54 extending from shoulder 51 coaxially with axis A and engaging a conical inner portion of hole 9. As shown in Fig.1, the end surface of outer chamber 34 presents a number of injection ducts 55 (only one of which is shown) enabling communication between outer chamber 34 and inner chamber 7 in the vicinity of channel 46. As shown in Fig.2 onwards, body 8 presents a number of substantially radial through holes 56 (only one of which is shown) each coming out on surface 11 of body 8 and blending with a respective further hole 57 formed substantially axially through end portion 38 and having its outlet on the end surface of end portion 38 extending in contact with surface 49 of body 42. Said pairs of holes 56 and 57 (only one of which is shown) define the end portion of a respective compressed air injection-suction device indicated as a whole by 58. According to a variation not shown, body 8 presents a first and second number of hole pairs 56-57, one defining the end portion of a compressed air injection device and the other a suction device. As shown in Fig.1 and particularly in Fig.2, outer chamber 34 is a variable-volume chamber of an injection cylinder indicated as a whole by 59 and the piston of which is defined by an annular appendix 60 coaxial with axis A and chamber 34, and projecting towards half mold 5 from an annular plate 61 of a mobile annular member 62. Said member 62 presents an outer flange 63 facing flange 26, and is normally connected to a mobile element (not shown) on a press (not shown), the fixed plate of which (mentioned previously and not shown) is fitted with half mold 4. Flanges 63 and 26 present a number of pairs of coaxial holes 64 and 65 (only one pair of which is shown in Fig.1) which are engaged by the opposite ends of a respective pin 66 for guiding mobile member 62 in relation to half mold 5. In particular, each pin 66 presents an end spigot 67 locked axially inside respective hole 64 and, at the other end, a flange 68 which acts as a limit stop and also as a connecting element for flanges 63 and 26 when mobile member 62 is moved away from half mold 5 beyond the point at which flanges 68 of pins 66 contact flange 26. Operation of device 1 will be described commencing with the operating position shown in Fig.1, wherein mold 3 is closed, chamber 7 is empty, mobile member 62 is in the backed-up position with flanges 68 contacting flange 26, and body 35 of crude rubber has been preheated to a given temperature in an oven and fed into chamber 34. At this point, the press (not shown), between whose mobile and fixed elements (not shown) device 1 is mounted, is closed so as to engage appendix 60 of mobile member 62 gradually and at relatively high speed inside chamber 34, and inject the crude rubber of body 35 from outer chamber 34 into inner chamber 7 through injection ducts 55. By the time mobile member 62 reaches the foremost limit position shown in Fig.2, all the rubber of body 35 has been injected inside mold 3 so as to fill chamber 7 and form bladder 2, and ducts 55 are closed by appendix 60 contacting the end surface of outer chamber 34. Bladder 2 is cured by the heat transmitted to it by a heat exchange fluid circulated continuously along ducts 23, 33 and 19 and inside inner core 6. Curing is effected relatively rapidly by virtue of the relatively high initial temperature of the crude rubber injected into chamber 7, which temperature is due to both preheating of body 35 in an oven prior to injection, and the heat transmitted mechanically to the rubber as it is injected through ducts 55, the minimum section of which is relatively small. Moreover, as the shape and volume of chamber 7 remain unchanged during injection, the injected rubber occupies the full volume of chamber 7, thus producing a bladder 2 with an excellent surface finish and accurately reproducing the shape of chamber 7. Total filling of chamber 7 is further assisted by creating a vacuum inside chamber 7 via pneumatic device 58. Once bladder 2 has been cured, the press (not shown) is opened as shown in Fig.3, so as to move mobile member 62 firstly into the extracted position, wherein flanges 68 of pins 66 contact flange 26 (Fig.1), then beyond this position so as to hook up half mold 5 and extract appendix 28 of body 32 from toroidal chamber 17 of half mold 4 and so open mold 3. As shown in Fig.4, upon mold 3 being opened, integral portions 37 and 39 of core 6 are moved away from portion 38 via the action of a rod 69 through mobile member 62 and connected integral with portion 39. Alongside operation of rod 69, air is blown by injection device 58 between surfaces 44 and 48 of inner core 6 and bladder 2, so as to detach bladder 2 from the outer surface of portions 37 and 39, and dilate and expel annular expansion 47 from respective annular channel 46. As shown in Fig.5, expansion of bladder 2 by the air blown in by pneumatic device 58 provides for fully extracting portions 37 and 39 of core 6 from bladder 2. Once freed from bladder 2, which is maintained contacting half mold 4 by portion 38, portions 37 and 39 are moved by rod 69 (Fig.6) into contact with the inner surface of half mold 5, which is maintained by the press (not shown) in the open position shown in Fig.3. Finally, as shown in Fig.7, a further rod 70, coaxial with rod 69 and integral with portion 38 of core 6, extracts portion 38 from half mold 4 and into contact with the inner end of annular expansion 47. Further displacement of rod 70 detaches and at least partially extracts bladder 2 from half mold 4. At this point, bladder 2, by now freed from half mold 4, may be freed from portion 38 of inner core 6 by slightly deforming annular expansion 53 manually.

Claims: A method of manufacturing curing bladders (2) using a curing mold (3) comprising a first (4) and second (5) half mold and an inner core (6) which, when said curing mold (3) is closed, define a substantially toroidal inner molding chamber (7) of the same shape as the bladder (2) being produced; said method comprising stages of closing said mold (3); feeding a mass (35) of crude rubber into said inner chamber (7) via at least one injection duct (55); curing said rubber inside said inner chamber (7) so as to produce a finished bladder(2); and extracting said finished bladder (2) from said mold (3) by opening said inner chamber (7) and extracting said inner core (6); and being characterized in that said mass (35) of crude rubber is fed to an outer chamber (34) provided on one (5) of said half molds (4, 5) and communicating with said inner chamber (7) via said injection duct (55), and is subjected via pressure means (60) inside said outer chamber (34) to sufficient pressure to inject it from said outer chamber (34) into said inner chamber (7) via said injection duct (55). A method as claimed in Claim 1, characterised by the fact that said mass (35) of crude rubber is heated to a given temperature prior to being injected into said inner chamber (7). A method as claimed in Claim 1 or 2, characterised by the fact that said outer chamber (34) is a variable-volume chamber of an injection cylinder (59) provided on said one half mold (5); said pressure means (60) comprising a mobile piston mounted for movement on said one half mold (5) and along said cylinder (59) and closing said injection duct (55) subsequent to injection. A method as claimed in any one of the foregoing Claims, characterised by the fact that it comprises a further stage consisting in blowing air between said inner core (6) and said finished bladder (2) so as to detach said finished bladder (2) from said inner core (6). A method as claimed in Claim 4, characterised by the fact that said inner core (6) comprises a first (39, 40, 41, 42) and second (38) separable axial portion; said further stage providing for detaching said finished bladder (2) from said first portion (39, 40, 41, 42), and said second portion (38) acting as an extractor for said finished bladder (2). A device for manufacturing curing bladders (2), said device comprising a bladder curing mold (3) in turn comprising a mutually-mobile first (4) and second (5) half mold and an extractable inner core (6), which, when said curing mold (3) is closed, define a substantially toroidal inner molding chamber (7) of the same shape as said bladder (2); characterised by the fact that it also comprises an outer chamber (34) provided in one (5) of said half molds (4, 5) and designed to receive a mass (35) of crude rubber; at least one injection duct (55) enabling communication between said inner (7) and outer (34) chambers; and pressure means (60) traveling in relation to said mold (3) and along said outer chamber (34) for injecting said mass (35) of crude rubber from said outer chamber (34) to said inner chamber (7). A device as claimed in Claim 6, characterised by the fact that said outer chamber (34) is a variable-volume chamber of an injection cylinder (59) provided on said one half mold (5); said pressure means (60) comprising a mobile piston mounted for movement on said one half mold (5) and along said cylinder (59). A device as claimed in Claim 7, characterised by the fact that guide means (66) are provided between said piston (60) and said one half mold (5) for guiding said piston (60) as it moves axially and reciprocatingly in relation to said mold (3) between a fully extracted position and a position wherein it fully engages said outer chamber (34). A device as claimed in Claim 8, characterised by the fact that said guide means (66) comprise limit stop means (68) for axially displacing an associated half mold (5) together with said piston (60) when said piston (60) is moved beyond said fully extracted position. A device as claimed in any one of the foregoing Claims from 6 to 9, characterised by the fact that it also comprises injection means (58) for blowing air inside said inner chamber (7); said injection means (58) coming out on the outer surface of said inner core (6). A device as claimed in Claim 10, characterised by the fact that said inner core (6) comprises a first (39, 40, 41, 42) and second (38) separable axial portion; said injection means (58) presenting an outlet formed on the outer surface of said second portion (38) which is mobile in relation to said half molds (4, 5) so as to act as an extractor for a finished bladder (2).

Inventors: FRANZINI MARCO, GIOVANNUCCI FABRIZIO, POMENTI ATTILIO, TOMLINSON GORDON MALCOLM, FRANZINI, MARCO, GIOVANNUCCI, FABRIZIO, POMENTI, ATTILIO, TOMLINSON, GORDON MALCOLM
Applicants: BRIDGESTONE FIRESTONE INC, BRIDGESTONE/FIRESTONE, INC.
Application year: 1991
Main classification: B29C45
IPC codes: B29C45, B29D30, B29K21, B29L31, B29C35