1. Field of the Invention
This invention relates to a molding apparatus for a wet friction material that is manufactured by sequential steps including as a rate-determining step, i.e. a molding step or a heat press step of friction material segments on a core plate.
2. Description of the Related Art
One of commonly used wet friction materials for an automatic transmission has a ring-shaped friction material substrate, which is cut out of a friction material substrate, joined on one or both of opposite surfaces of a core metal of a flat ring shape with an adhesive. Another has a plurality of segment pieces or friction material segments joined on one or both surfaces of the core metal with an adhesive. For example, there is provided a segment-type wet friction material as shown in FIG. 6a. FIG. 6a is a plan view showing an overall structure of a segment-type wet friction material. FIG. 6b is a cross-sectional view showing a step of a manufacturing process of a wet-type friction material in which segment pieces are joined by adhesion to a core metal. FIG. 6c is a cross-sectional view showing a next step in which the adhering segment pieces are pressed for thickness setting.
As shown in FIG. 6a, a segment-type wet friction material 50 has twenty segment pieces 52 joined by adhesion respectively on opposite surfaces of a core plate 51 of a flat ring shape. The segment pieces 52 are made by cutting out of a friction material substrate. The adhering segment pieces 52 on both surfaces of the core metal 51 are pressed for thickness setting and heated for thermosetting. In a conventional manufacturing process of such a segment-type friction material 50, the friction material segments or the segment pieces are punched out from the friction material substrate one by one. Then, the punched-out segment pieces are stuck one by one on the surfaces of the core plate or the core metal on which a thermosetting adhesive is coated along an entire circumference thereof. That is, a punching-out step and a next sticking step are repeated twenty times. Accordingly, it takes much time to stick all the segment pieces. Consequently, there has taken place troubles or problems caused by the fact that property of the adhesive changes with time from the sticking of the first segment piece to the sticking of the last segment piece.
In view of the above problems, Japanese Patent Publication No. 3643018 discloses an invention of a manufacturing method of a wet friction material. The manufacturing method does not carry out the alternate steps of the punching-out of the friction material segment (segment piece) from a strip of the friction material substrate and the sticking of the punched segment piece on the core plate (core metal). Instead, the manufacturing method includes a storing step for storing a plurality of segment pieces in a circumferential manner on one surface of a holder and a sticking step for moving the one surface of the holder to a sticking surface of the core metal with an adhesive coated thereon so as to urge and stick the segment pieces held on the holder to the sticking surface of the core metal.
In case of the manufacturing process composed of the alternate steps of punching out of the segment piece and the sticking of the segment piece on the core metal, there arises a problem such as deterioration of positioning accuracy of the segment pieces due to the property change of the adhesive that is caused by taking much time for the sticking work. However, the manufacturing method described in Japanese Patent Publication No. 3643018 solves such problem. Moreover, it completes the sticking work of the segment pieces in a very short amount of time. As a result, the rate-determining step in the manufacturing process of the segment-type friction material becomes a heat press step (molding step) after sticking the plurality of the segment pieces on the entire circumference of the core metal.
An outline of the molding step is described referring to FIG. 6b. As described above, a group of twenty segment pieces 52 are stuck by the holder at fixed intervals as shown in FIG. 6a on one surface (front surface) of the flat ring-shaped core metal 51 on which a thermosetting adhesive is coated. Then, the core metal 51 is reversed and, in the same way, another group of twenty segment pieces 52 are stuck by the holder at fixed intervals as shown in FIG. 6a on a rear surface of the core metal 51 on which the thermosetting adhesive is coated. Thereafter, the core metal with the segment pieces 52 stuck on the opposite surfaces is set inside a shim 42 between an upper die 40A and a lower die 40B.
Then, the upper die 40A is lowered by a not-shown hydraulic cylinder. Alternatively, the lower die 40B may be lifted by a not-shown hydraulic cylinder. As shown in FIG. 6c, the two groups of the twenty segment pieces 52 are pressed respectively so that a total thickness of the core metal 51 and the two groups of the segment pieces 52 becomes equal to a thickness of the shim 42. In this state, the upper die 40A and the lower die 40B are heated at a temperature of 170° C. to 270° C. so as to set or harden the thermosetting adhesive coated on the both surfaces of the core metal 51. Thus, the segment-type wet friction material 50 shown in FIG. 6a is manufactured by sticking, hardening and fixing each group of the twenty segment pieces 52 on the opposite surfaces of the core metal 51.
In the manufacturing process of the above-mentioned segment-type wet friction material 50, it is necessary to decrease a manufacturing time per one friction material as short as possible for reducing costs. For such purpose, it is very important to raise a manufacturing efficiency in the molding step that requires a fixed time period (30 seconds to 90 seconds) in order to heat and set or harden the thermosetting adhesive. Therefore, a multi-stage molding die with vertically built-up molding dies is proposed in order to carry out a thickness setting by pressing and a hardening by heating of many segment-type friction materials at one time. That is, the thermosetting adhesive is coated on each of the core metals 51 and each of corresponding groups of the segment pieces 52 is stuck to each surface of the core metal 51 so as to prepare half-finished products. Then, the half-finished products are pressed and heated at on time by the multistage molding die.
Specific examples of multistage molding dies are illustrated, as a related art, that have a structure as shown in FIGS. 7a to 7c and a structure as shown in FIGS. 8a and 8b. FIGS. 7a to 7c are explanatory drawings showing a structure of a multistage molding die according to a first specific example as a related art or a comparative example of the present invention. FIGS. 8a and 8b are explanatory drawings showing a structure of a multistage molding die according to a second specific example as a related art or a comparative example of the present invention. The first specific example of a multistage molding die is shown in FIGS. 7a to 7c. As shown in FIG. 7a, a multistage molding die 55 is composed of a plurality of molding dies 56. Lifting bolts 58 are fixed on opposite side surfaces of each of the molding dies 56. Links 59 are engaged with these lifting bolts 58 respectively at each of the side surfaces of the molding die 56.
As shown in FIG. 7b, in case of opening each of the molding dies 56, upper ends of the links 59 are pulled up in series or in sequence by a not-shown pull-up mechanism. As shown in FIG. 7c, in case of closing each of the molding dies 56 for pressing/thickness setting and heating/hardening of the segment-type friction material 50, the not-shown pull-up mechanism is released. Then, each of the molding dies 56 is pressed and closely contacted or clamped with each other by a not-shown pressing mechanism. In the first specific example of the multistage molding die described above, a weigh of each of the molding dies 56 is supported only by the lifting bolts 58. Accordingly, there is a problem that the lifting bolts 58 are susceptive to breakage.
The second specific example of a multistage molding die is shown in FIGS. 8a and 8b. As shown in FIG. 8a, a multistage molding die 60 is composed of a plurality of molding dies 61. Links 63 that are rotatably opened and closed are fixed on opposite side surfaces of each of the molding dies 61. Each of the molding dies 61 is slidable up and down along a guide post 62. In case of opening each of opening each of the molding dies 61, upper ends of the links 63 are pulled up in series or in sequence by a not-shown pull-up mechanism. As shown in FIG. 8b, in case of closing each of the molding dies 61 for pressing/thickness setting and heating/hardening of the segment-type friction material 50, the not-shown pull-up mechanism is released. Then, each of the molding dies 61 is pressed and closely contacted or clamped with each other by a not-shown pressing mechanism.
As mentioned above, a plurality of segment-type wet friction materials 50 are processed at one time such that all the thermosetting adhesives are set or hardened so as to fixedly stick all the segment pieces on all the core metals. Thus, the multistage molding die improves the manufacturing efficiency of the molding step that requires a fixed time period (30 seconds to 90 seconds) in order to heat and set the thermosetting adhesive.
However, a weight per unit or a weight of each of the molding dies 56, 61 is about 40 kg to 70 kg. A hydraulic cylinder as the pull-up mechanism and the pressing mechanism is usually operated at a speed of 50 mm/s to 100 mm/s. An operation at a higher speed causes a noise (80 dB or more) due to an impact at the time of mold clamping. It also causes a displacement of the segment-type wet friction material 50 due to vibration at the time of mold clamping. Therefore, such speeding up is impossible. Moreover, an increase of a number of the molding dies 56, 61 or stages of the multistage molding die 55, 60 also has a limitation inherently in view of its maintainability and workability. As a result, there is still a problem that the molding step remains a rate-determining step.