FR2643012A1 - DEVICE FOR SEALING THE INJECTION MOLD INTAKE CHANNEL, PARTICULARLY IN THE CASE OF POLYURETHANE ELASTOMER - Google Patents

Abstract

In an injection molding machine intended for molding very sticky material articles such as uncured urethane elastomers, the injected material is prevented from flowing back out of the mold 15, 16 by means of a sealing device 30 which comprises a sealing face of nylon or similar material resiliently urged against the mold face 19A, 19B and which is slidable above the latter to cover or uncover the mold inlet 18.

Description

l 2643012 This invention relates to an improved manufacturing process

  of a molded article and an apparatus for the same purpose, and in particular, but not exclusively, for the manufacture of an article

  made of polymer material by injection molding.

  A known injection molding technique suitable for the manufacture of articles molded in microcellular urethane uses: a carousel arrangement comprising, for example, 16 press units of the binding type each comprising a pair of heated plates. The two plates of a pair support respective halves of a two-part mold of the type in which, when the two mold halves are brought together, the facing surfaces of the mold halves define between them a mold chamber of a shape complementary to that of the article to be produced and a supply channel for the injection of a material to

mold into the mold chamber.

  Conventionally, the supply channel is arranged to extend in a direction either vertical, horizontal, or inclined to communicate with a lower part of the mold chamber. A small vent channel, also defined by the facing surfaces of the mold halves, allows air to be forced out of the region of the upper area of the mold chamber during injection of a molding material such as

  mixture of resin, prepolymer and blowing agent.

  The apparatus of the type described above, when used with care, may be capable of reliably manufacturing high quality articles, each of the press units being positioned in sequence, by movement of the carousel, so as to be aligned with a feed head & from which a molding material is injected through the feed channel to the feed chamber

press unit mold.

  When each press unit sequentially leaves the position facing the feed head, there is often a tendency for reverse flow of injected, uncured material outward through the feed channel. This results in an undesirable loss of material and, more importantly, reduces the material available in the mold to form the finished article. The extent to which uncured material tends to flow from the feed channel depends at least in part on the viscosity of

  the material to be injected and the speed at which it is hardened.

  Since this can vary significantly for small variations of certain factors like mold temperature, mixture of injected material and environmental factors like humidity, it is understood, and this has been understood in the art for a long time , that this results in an undesirable random variation of the

  weights and other peculiarities of the finished products.

  Attempts have been made to remedy this problem by sealing the feed channel after injection so as to allow the injected material to be cured to such an extent that it can no longer tend to flow to outside through the supply channel. Despite the advantages, which have been recognized for a long time, which can be expected from sealing the supply channel, no technique has been proposed before the present invention for working reliably during the molding of a

  urethane elastomer or similar material.

  According to one aspect of the present invention, there is provided a mold device comprising a mold having an inlet orifice for the flow of material to be molded towards a mold cavity situated inside the mold and an actuatable sealing device. to cover said inlet orifice and come into contact with a mold sealing surface surrounding said orifice to prevent the flow of material to be molded from said cavity, said sealing device comprising a support body movable relative to the mold, a sealing member for sliding movement over a sealing surface of the mold and elastic support means arranged to support the sealing member resiliently relative to the body support, said elastic support means being arranged normally to urge the sealing member away from the body of the support towards the mold in a say ction substantially perpendicular to said direction of sliding movement of

  the sealing member above the mold sealing surface.

  The molding device can be of a type suitable for use

  in an injection molding machine for manufacturing -

  articles made of urethane elastomer or a similar material, and the present invention provides the combination of said device

  mold and an injection molding machine.

  The present invention further provides a method for manufacturing a molded article comprising the steps of making a mold device comprising a mold having an inlet for the flow of material & mold to a mold cavity, placing on said mold device a sealing surface surrounding said inlet orifice, and placing a sealing device comprising a support body movable relative to the sealing surface of the mold and a sealing member which is stressed elastically to move away from the support body and bear against the sealing surface, said method further comprising filling said mold with a material to be molded by means of a nozzle injection positioned in the vicinity of said inlet orifice, removal of said nozzle, and then displacement of the support body of the sealing device to bring the sealing member slide to slide over said mold sealing surface to close said inlet. Preferably, the elastic support means act between the sealing member and the support body normally to

  stress the sealing member away from the support body.

  Preferably, the sealing member comprises at least one polyamide-facing face part of nylon 66 for sliding movement over a mold part to close an injection channel. 'an injection process. In a particularly preferred manner, it comprises a material of Nylon GS which is nylon impregnated with particles of polytetrafluoroethylene (or

PTFE).

  Another suitable product is PTFE, the material of the face portion being chosen from those for which the urethane elastomer exhibits relatively weak adhesion when the device is used with a mold for injection with

this subject.

  It is further preferred that the sealing member includes a releasably attached face portion & a body portion

  of sealing member and supported by it.

  The elastic support of the sealing member can be constituted by support means such as a mechanical spring, for example a compression spring & rod, or by an element of elastic material such as a micro-cellular urethane elastomer ( for example Microvon) which suitably is not affected by the working temperatures encountered when applied to a heated mold part. The sealing device may include pivot means for support relative to the mold, by virtue of which the sealing member can be tilted on an arcuate path above the mold to cover or uncover a channel. injection supply. Alternatively, guide channels can be arranged to guide the sealing device so that it performs for example a linear movement over the

mold surface.

  The present invention also provides a process for the manufacture of an article of polymeric material, and in particular an urethane elastomer such as Microvon, in which a

  mold device of the present invention.

  An embodiment of the present invention will now be described, by way of example only, with reference to the appended schematic drawings in which FIG. 1 is a plan view of part of a press of the mold carousel type. multiple and a sealing device according to the present invention; Figure 2 is a side view of one of the molds of Figure 1 in a closed position; Figures 3A and 3B respectively show a side view and an end view partially in section of the sealing device of Figure 1;

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  Figures 4A and 4B respectively show side and end views of the support body of the sealing device of Figures 3A and 3B; Figures 5A and 5B respectively show side and end views of the body portion of the sealing member of the sealing device of Figures 3A and 3B, and Figures 6A and 6B respectively show side views and of the rear parts of the sealing device of the

Figures 3A and 3B.

  An injection molding machine 10 to sixteen stations includes

  a carousel It comprising sixteen press units 12 of the type to be connected.

  Each press unit comprises a fixed plate 13 and a hinged plate 14 movable relative to the fixed plate using a hydraulic (or pneumatic) actuator (not shown). On each of the plates 13, 14 of a pair is fixed part of a

  steel mold 17 in two parts 15, 16.

  The facing surfaces of the mold define between them a mold cavity, not shown, and a supply channel 18 which extends from an outer face 19 of the mold 17 towards the mold cavity for injecting in this cavity a material to be molded. The plates 13, 14 incorporate elements

  electric heaters (not shown) of known type.

  The molding machine also comprises a single-head injection device 20 comprising a nozzle 21 which can be advanced until it comes into contact with a supply channel 18 for injection of material to be molded and then retracted to allow the rotation of the carousel in order to bring it into alignment with the nozzle

  injection 21 the supply channel of the next mold.

  When the machine is running, the mold halves are made to move apart, thanks to the hinges of the plate 14, at a station immediately preceding that of the mold which is aligned with the injection device: this allows an operator to remove the article molded out of the mold cavity and the supply channel, to clean this cavity and this channel and to apply

  a release officer as required.

  On the external surface 19A (see FIG. 2) of each part of slack 15 is fixed a sealing device 30 which can be brought across the feed channel in order to close it after the injection of material to mold and prevent this material from flowing out of the mold cavity and the feed channel. The sealing device 30 comprises a support body 31 of machined steel (see Figures 3t, 3B, 4A and 4B) of a generally triangular shape. In a corner region of the body 31 is formed an orifice for receiving a socket 32 through which passes a bolt 33 to be fixed to the mold face 19A4 in the assembled condition, a shoulder 34 of the bolt abuts on the face -19A . The body 31 with its associated socket 32 can pivot around the bolt under the action of a reduced force sufficient to overcome the resistance

  friction between the bolt and the socket.

  In another corner region of the support body 31 is disposed a support pin 33 which extends from the body to rest on a side of the latter opposite to that of the threaded end portion of the bolt 33. The pin 35 supports a ball bearing 36 whose outer radial surface 37 constitutes a counter-cae by means of which the sealing device is caused to move. The third corner portion of the support body 31 supports a sealing member 38 of the supply channel comprising a housing

  39 generally cylindrical in one piece with the body 31.

  The housing 39 slidingly supports a steel plunger 81 and contains a compression coil spring 40 which biases the head portion 41 of the plunger outward from a rear end face 42 of the housing 39. The longitudinal axis of the cylindrical housing 39 is parallel to the longitudinal axis of the bolt 33 and the spring urges the plunger head to move in the direction of the threaded end of the bolt. To avoid expulsion of the plunger under the action of the spring, a part of the rod 43 of the plunger passes through an orifice in the end face 42 and is held captive by a locking assembly constituted

  a cotter pin 44 and a washer 45.

  On the head part 41 of the plunger is fixed a cap 46 (see FIG. 6A and 6B) made of Nylon GS. On the rear face of the cap 46 is a recess 47 which allows it to be fixed by mounting

  to the press on the plunger head.

  When mounting the sealing device on the mold part, the sealing device can pivot around the bolt 33 and the nylon cap 46 slides over the faces 19A, 19B of the

mold parts.

  A displacement of the sealing device between a position in which it covers the supply channel 18 and a position in which it releases this channel is effected by the action of a pair of pneumatically actuated slide heads 48, the one is shown & Figure 2. The slide head can be actuated to descend and come into contact with the outer surface 37 of the ball bearing 36 and cause movement & pivoting of the body 31, whereupon the support cap 46 resiliently supported slides above the mold face. A second slide, not shown, can operate to mount for a pivoting of the body 31 in return. In this embodiment, the upper slide, to cause the cap to close the sealing channel, is located in the vicinity of the injection head device 20 and it is arranged to operate automatically when the nozzle 21 is retracted following an injection operation. The other slide is located in a spaced position around the carousel to move the cap to a retracted position when the injection material has been sufficiently cured

  - to no longer tend to flow back out of the supply channel.

  It is estimated that a sealing device of a type in accordance with the present invention functions with surprising efficiency to resist undesirable wear and to resist an undesirable accumulation of injected material which conventionally posed

operating problems.

  In the case of wear of the cap 46, it can be directly and economically replaced by mounting to the press or by another

  method of attaching a replacement part.

26 4 3012

Claims (10)

  1. A mold device comprising a mold (17) having an inlet orifice (18) for the flow of material to be molded towards a mold cavity situated inside the mold and a sealing device (30) operable to cover said inlet port (18) and come into contact with a mold sealing surface (19A, 19B) surrounding said port to prevent flow of molding material from said cavity, characterized in that said sealing device (30) comprises a support body (31) movable relative to the mold (17), a sealing member (38) for sliding movement over a surface of sealing (19A, 19B) of the mold and elastic support means (40) arranged to support the sealing member (38) resiliently with respect to the support body, said elastic support means (40) being arranged normally to urge the sealing member (38) away from it t of the body of the support (31) in the direction of the mold (I7) in a direction substantially perpendicular to said direction of sliding movement of   the sealing member above the mold sealing surface.   2. A mold device according to claim 1 characterized in that the sealing member (38) comprises a face part (46) polyamide.   3. A mold device according to claim 2 characterized in that the face part (46) is a nylon-based material such as   nylon impregnated with polytetrafluoroethylene.   4. A mold device according to any one of   previous claims characterized in that the organ   seal (38) includes a face portion (46) which is releasably attached to a body portion (81) of the member   seal (38) and which is supported by it.   5. A mold device according to any one of the preceding   Claims characterized in that the sealing member (38) is   resiliently supported by the support body (31) by a mechanical spring, for example a compression coil spring (40). 26430 12   6. A mold device according to any one of the preceding   claims characterized in that the sealing member (23) is   pivotally attached to the mold (17).   7. A mold device according to any one of the preceding   Claims characterized in that a cam follower (37) is attached on the support body (31).   8. A mold device according to claim 7 characterized in that said cam follower (37) can rotate relative to the support body. 9. A mold device according to claim 8 when it depends on claim 6 characterized in that the axis of rotation of the cam follower (37), direction of the elastic support of the sealing member and 1 axis around which the support body is   pivotally mounted are parallel to each other.   10. A mold device according to any one of the preceding   claims characterized in that the mold (17) comprises two   mold halves (15, 16) and that the sealing member (38) can slide between a first position in which, when the mold halves are in contact to define a mold cavity and an orifice inlet, the sealing member presses against the two mold halves to seal the inlet opening (18), and a second position in which the sealing member   rests only on one of the mold halves.