CA2329747A1

CA2329747A1 - Gmt plastic moulding, method and device for producing the same

Info

Publication number: CA2329747A1
Application number: CA002329747A
Authority: CA
Inventors: Alfred Scharrenberg
Original assignee: Individual
Current assignee: Otto Deuschlemodell-Und Formenbau & Co KG GmbH
Priority date: 1999-02-22
Filing date: 2000-01-24
Publication date: 2000-08-31
Also published as: WO2000050211A1; EP1073549A1; DE19907439C2; DE19907439A1

Abstract

A GMT plastic moulding (1) comprises a main body (2) which consists of a known glass fibre mat blank that has been impregnated with thermoplastic material, moulded and cured. A component (3, 4) made of a soft polymer, for example, a sealing lip is attached by direct injection moulding to at least one area of the edge of the main body (2).

Description

GMT plastic mouldina, method and device for producina the same The invention relates to a GMT plastic moulding having a main body which consists of a glass fibre mat blank which is impregnated with a thermoplastic, pressed in a mould and cured, and having at least one component fixed to the main body and consisting of a soft polymer, as well as a method and a device for producing the same.
By GMT plastic mouldings are meant plastic mouldings which are obtained by the so-called "GMT pressing process". In the latter a glass fibre mat impregnated with a thermoplastic is placed in a steel mould which comprises a cavity plate and a core plate movable with respect to the cavity plate with the aid of a conventional press. Cavity plate and core plate bound a cavity whose shape corresponds to the desired shape of the GMT plastic moulding. The cavity is bounded by vertical flash faces of toughened material which are formed on the cavity plate and on the core plate. After a suitable cooling in the mould the GMT moulding may be removed. By virtue of the high proportion of long glass fibres a GMT
moulding of this kind is highly dimensionally stable, robust and in addition recyclable without cumbersome finning. It is suitable for many applications, e.g. for engine cowling and subfloor linings, body parts, seat and back rest supports, instrument supports, sound-proof claddings etc.. In these areas of use, in particular in car construction, it is frequently necessary to apply to the actual GMT plastic moulding sealing lips of soft polymer material which nestle against surrounding components and form a seal with the latter. In the case of known GMT plastic mouldings said seals have to date been extruded separately and fixed subsequently to the "main body" of the GMT plastic moulding, namely to the body obtained from an impregnated glass fibre mat by a GMT moulding process. The two-component parts obtained in this way are however relatively difficult to manufacture; the stability of the joint between the component of soft polymer and the main body leaves something to be desired in many cases.
The object of the present invention is to create a GMT
plastic moulding of the kind mentioned in the preamble which can be manufactured at a reasonable price and exhibits a good connection between "main body" and component of soft polymer.
Said object is achieved according to the invention by the component of soft polymer being gated into the main body.
GMT plastic mouldings according to the invention may be manufactured very cost effectively in a single mould.
Despite the various production methods which are carried out in said single mould, the achievable cycle times are comparable with the cycle times of pure injection moulded parts and may in some cases be further reduced. The production may be carried out fully automatically. Since the two-component materials meet one another in a relatively hot state, they are able to form a good connection. The cooling times may proceed in relatively good harmony with one another.
In an advantageous embodiment of the GMT plastic moulding according to the invention the surface to be bonded between the component of soft polymer and the main body is increased by means of a grading. Particularly in the case of thin wall thicknesses of the GMT plastic moulding such a configuration has proved to be very effective in achieving a good fusion joint. Admittedly in this case a reinforcing bead may be required along the hard-soft joint of the moulding; the latter may however be arranged on the non-visible surface of the GMT plastic moulding and is not troublesome there.

The invention has in addition the object of creating a method for manufacturing a GMT plastic moulding which is cheap to carry out and results in highly stable joints between main body and soft component.
Said object is achieved according to the invention by the component of soft polymer being gated directly into the main body. The advantages of the method according to the invention follow accordingly from the advantages of the GMT
plastic moulding according to the invention that are described above. The same applies to the advantageous embodiment of the method according to the invention that is given in claim 4.
Finally, it is the object of the invention to further develop a device for manufacturing a GMT plastic moulding of the kind given in the preamble of claim 5 in such a way that the various fabrication methods with which the main body and the component of soft material are manufactured may be carried out in a single mould.
Said object is achieved according to the invention by the fact that d) the cavity plate comprises at least a second shaped recess which, when the mould is in the closed position, partially bounds a second cavity complementary to the form of a component of soft polymer of the GMT plastic moulding;
e) the core plate comprises at least a second shaped recess which, when the mould is in the closed position, partially bounds the second cavity;

f) along the common edges of the two cavities is arranged at least one closing knife-type valve which is displaceable between a first position, in which it interrupts the communication between the two cavities, and a second position, in which it releases the communication between the two cavities;
g) those areas of the edges of the second cavity that are not formed by the closing knife-type valve are formed of toughened vertical flash faces at core plate and cavity plate, between which there exists a defined gap which is narrower than the gap between the vertical flash faces bounding the first cavity;
h) at least one injection nozzle issuing into the second cavity is provided.
The particular advantage of such a device according to the invention consists in the fact that the mould may be mounted in a standard press. Costs are not incurred for the production of a special machine. For the injection phase, a separate injection unit, including one taken out of service, may simply be docked against the press. All the operating steps of the method according to the invention may then be performed in said one station, which reduces considerably the degree of fabrication involved in the manufacture of the GMT plastic moulding. As a result of the closing knife-type valve or valves provided according to the invention the free spaces for the component of soft polymer may be opened even during the curing phase of the main body, as early as shortly after the closure of the mould, for example some 5 seconds after the closure of the mould, and hence create the pre-conditions for the injection phase of the component of soft polymer.

A particular problem in the manufacture of the GMT plastic moulding is presented by the vertical flash faces on cavity plate and core plate, which bound at least in certain areas in the mould both the cavity for producing the main body and the cavity for producing the component of soft polymer.
Vertical flash faces may not be sealed 100%. Because of the constant sliding out and sliding in of the core plate into the cavity plate an air gap of at least 0.035 to 0.05 mm is required. A smaller air gap would inevitably lead to the jamming of the vertical flash faces. In addition, the toughened vertical flash faces wear during the pressing phases down to a gap size of 0.07 to 0.15 mm. The injection material from which the component of soft polymer is produced is however very runny and already escapes through gaps which are only 0.015 to 0.02 mm wide. Such an escape results in poor fusion joints and strong flash formation.
Care therefore has be taken with the device according to the invention that at any rate the vertical flash faces which bound the second cavity, which forms the soft component of the GMT plastic moulding, face each other across only a very small gap which is smaller than the gap between the vertical flash faces in the area of the first cavity forming the main body of the GMT plastic moulding.
Said problem is best overcome with that development of the invention in which the outer of the vertical flash faces bounding the second cavity is attached to a movable outer gate valve which is pressable against a stop by a source of energy in such a way that the desired gap with respect to the corresponding inner vertical flash face is obtained.
Said development of the invention has the advantage that whenever core plate and cavity plate are moved relative to one another and there is the danger of wear or the jamming of the vertical flash face, the energy from the outer gate valve may be used. So long as the source of energy is not activated, the vertical flash faces at the second cavity are not pressed against one another under the effect of energy;
the outer vertical flash face may instead "get out of the way". Despite extremely close tolerance between said vertical flash faces, no mutual contact therefore takes place under load during the inward and outward movement. The source of energy used according to the invention in said development is activated only if the core plate is stationary with the mould in the closed position, the liquid injection material is to be injected and the vertical flash faces therefore have to remain at the required distance from one another. Said distance is always reliably found again by the stop between the outer gate valve and the mould on the activation of the source of energy.
The source of energy may incorporate a wedge-type valve whose direction of movement relative to the direction of movement of the outer gate valve is not parallel and which interacts with the outer gate valve via cam faces. Said development of the source of energy operates particularly precisely and is capable of applying high forces to the outer gate valve and conversely absorbing high restoring forces via the outer gate valve.
At least one vertical flash face bounding the second cavity may be formed at a wearing strip. Should therefore the very small gap between the corresponding vertical flash faces have inadmissibly widened, the corresponding wearing strip may simply be replaced.
Particularly preferred for the production of thin-walled GMT
plastic mouldings is that development of the device according to the invention in which the front face of the closing knife-type valve is graded in such a way that the edge areas of the main body of the GMT plastic mouldings, to which edge areas namely a component of soft polymer is to be gated, are obtained with a corresponding grading. The object of said measure has already been explained above.
An embodiment of the invention will be explained in detail below with reference to the drawing, where Figure 1: shows a perspective view of a GMT plastic moulding with moulded-on sealing lips, Figure 2: a vertical section through the mould for producing the GMT plastic mouldings of Figure 1, Figure 3: a detailed enlargement of the mould of Figure 2 and Figure 4: an overhead view onto the cavity mould half of the mould of Figures 1 and 2;
Figures 5 and 6 show detailed enlargements of the mould of Figures 1 to 4 at various stages of the process for producing the GMT plastic mouldings and Figure 7: shows a section through the edge area of the GMT
plastic moulding of Figure 1.
Figure 1 shows a completed GMT plastic moulding 1 such as is used in the car industry. It comprises a main body 2 which consists of a thermoplastic-impregnated glass fibre mat blank moulded in the manner described in detail below. To two edge areas of the main body 2 are gated in manner likewise described further below two sealing lips 3, 4, which consist of a plastic that is soft and suitable for sealing purposes, in particular of a polymer. The further exact shape of the GMT plastic moulding 1 is of no significance in the present context.

In Figure 2 is shown a vertical section through the mould 5, which serves for the production of the GMT plastic moulding 1 shown in Figure 1. The mould 5 incorporates in manner known per se an upper mould half 6, referred to as "core plate" below, together with a lower mould half 7 interacting with the latter and referred to as "cavity plate" below.
Core plate 6 and cavity plate 7 bound in the closed state a first cavity 8, which is complementary to the shape of the main part 2 of the GMT plastic moulding 1, as well as additional cavities 9 (cf. in this connection also in particular Figures 5 and 6), whose shape is complementary to the sealing lips 3 and 4 of the GMT plastic moulding 1.
Those areas of the cavity 8 which do not correspond to edge areas of the GMT plastic moulding 1 which are provided with sealing lips 3, 4 are bounded at cavity plate 7 or core plate 6 by interacting vertical flash faces 11, 13 which consist in known manner of toughened material and on the closure of cavity plate 7 and core plate 6 exhibit a gap between one another such that jamming is prevented and an escape of air out of the cavity 8 is possible. The gap comes typically to some 0.035 to 0.05 mm. A wear of up to some 0.07 to 0.15 mm may take place during use.
In those areas of its edge which correspond to edges of the GMT plastic moulding which are provided with sealing lips 3, 4 the cavity 8 is bounded or boundable by closing knife-type valves 14, of which one is shown in the drawing. The closing knife-type valve 14 is arranged within a corresponding recess of the core place 6 and is movable vertically between an extended and a retracted position by means of a hydraulic cylinder 15. In the extended position, which is shown enlarged in Figure 5, its front face rests against the opposite surface of the cavity plate 7, while in the retracted position shown in Figure 6 the front face of the closing knife-type valve 14 is moved back flush with the adjacent components and releases the connection between the cavities 8 and 9.
The cavities 9 are at those edges which correspond to free edges of the sealing lips 3 and 4 of the GMT plastic moulding of Figure 1 bounded by vertical flash faces 17, 19, of which the one (17) is arranged at a wearing strip 16 provided within the core plate 6 and the other at an outer gate valve 18 assigned to the cavity plate 7.
The outer gate valve 18 is, as may be seen in particular from Figures 3 and 4, movable in horizontal direction. It is in this guided by guide beads 28, with which it positively engages. The movement of the outer gate valve 18 takes place here via a closing wedge-type valve 20 which is displaceable with the aid of a hydraulic cylinder 21 (cf. Figure 4) in a direction which is perpendicular to the desired displacement direction of the outer gate valve 18. Said construction has, compared with an actuation via a directly acting hydraulic cylinder, the advantage that a greater precision is possible during the movement of the outer gate valve 18 and that in addition greater forces may be transmitted and absorbed.
There issue into the cavities 9 injection nozzles 22, which extend through the cavity plate 7 and are supplied by a heating channel 23 with the plastic used for the production of the sealing lips 3, 4.
There is moulded integral with the front face of the outer gate valve 18 which faces towards the cavity 8 a groove 40 (cf. Figure 3) whose side walls converge in the direction of the base of the groove 40. There engages with said groove 40 of the outer gate valve 18 a fin 41 of the cavity plate 7, which fin 41 possesses inclined stop faces complementary to the side walls of the groove 40. When the outer gate valve 18 is in the normal position shown in Figure 3, the side walls of the groove 40 of the outer gate valve 18 rest against the stop faces of the fin 41 of the cavity plate 7.
In said stop position there exists between the vertical flash faces 17, 19 at the outer gate valve 18 or the wearing strip 16 a desired, minimum distance with which an escape of the air out of the cavity 9 is possible. Said gap is however kept sufficiently small that even the runny material injected into the cavity 9 cannot escape via the gap between the vertical flash faces 17 and 19 and form undesirable flashes and burrs.
The cavity plate 7 is supported via bumper blocks 33 by a large platen 34 which is fixed in turn via an insulating plate 35 and protective steel plate 36 to the stationary part of a conventional press (not shown). Cooling bores 38 furthermore pass through the cavity plate 7 in known manner.
An ejector 30 connected to an ejector plate 31 also extends through bores of the cavity plate 7 and serves for the ejection of the completed GMT plastic moulding 1.
The core plate 6 is fixed to a mounting plate 42 which in turn is mounted on the movable part of the already mentioned press. Through the mounting plate 42 pass hydraulic channels 37 which serve for the feeding of the hydraulic cylinders 15 with which the closing knife-type valves 14 may be moved.
In the drawing are shown in addition small bumper blocks 32 (Figure 2) and 25 (Figure 4), which are attached to the mounting plate 42 or to the edge area of the cavity plate 7 and with which the distance between core plate 6 and cavity plate 7 when the press is in the closed position is exactly defined. Guide beads 29 at core plate 6 and cavity plate 7, which run parallel to the corresponding vertical flash faces 11 and 13, serve for the pre-centring of core plate 7 and cavity plate 6 during the closing phase. The two mould halves are in addition provided with guides 24 (cf. Figure 4), by means of which a defined relative movement is possible.
The device described above operates as follows for the production of the GMT plastic moulding 1 shown in Figure 1:
First of all the two halves of the mould 5 are opened by the movable, upper part of the press (not shown) being moved upwards relative to the stationary, lower part. In this way the inside of the cavity plate 7 becomes accessible. The closing knife-type valves 14 are extended by means of the hydraulic cylinder 15 so that they project above the corresponding surface of the core plate 6.
A glass fibre mat blank is now placed from above in that area of the shaped recess of the cavity place 7 which bounds the cavity 8 on one side when the mould 5 is closed. The glass fibre mat blank is impregnated with hot, liquid thermoplastic. The mould 5 is now closed with the aid of the press (not shown), in the course of which the hydraulic cylinder 21 remains without power. The core plate 6 moves along the vertical flash faces 11, 13, 17, 19 into the cavity plate 7. As soon as the front face of the closing knife-type valves 14 meets the opposite surface of the core plate 7, the cavity 8 is closed. During the further movement of the core plate 6 into the cavity plate 7 the thermoplastic-impregnated glass fibre mat blank is now pressed into its definitive shape. During said further movement of the core plate 6 the closing knife-type valves 14 are pressed back slightly into the core plate 6.
As soon now as the main body 2, now formed in its definitive shape, of the GMT plastic moulding 1 has cooled to such an extent that a certain dimensional stability has been reached, the closing knife-type valves 14 are brought into the retracted position shown in Figure 6 by means of the hydraulic cylinders 15. The hydraulic cylinder 21 is actuated, moves the outer gate valve 18 to stop against the cavity plate 7 and holds the outer gate valve 18 under load in said position, in which the required small gap between the vertical flash faces 17 and 19 is obtained.
Runny polymer material is now injected into the cavities 9 via the injection nozzles 22 at relatively high pressure.
The air thereby displaced exits via the very small, defined gap between the vertical flash faces 17 and 19 at the external gate valve 18 or the wearing strip 16. The polymer material of the sealing lips 3, 4 thereby comes to rest against the still hot material of the main body 2 of the GMT
plastic moulding, said main body 2 having been formed beforehand in the cavity 8, and enters into an intimate connection with said hot material.
After an adequate cooling of the sealing lips 3, 4 formed in this way the press is again opened and the thus completed GMT plastic moulding 1 is ejected with the aid of the ejector 30.
The situation regarding the outer gate valve 18 is as follows:
As already mentioned in the preamble, "normal" vertical flash faces are unsuitable for delimiting a cavity in which an injection phase is to take place because of the clearance required or arising for them. If the gap between said vertical flash faces is of a largeness such as is required for the trouble-free insertion of the core plate 6 into the cavity plate 7, or such as arises after a certain time by virtue of wear, the runny injected material exits through said gap and produces unsightly flashes and burrs on the moulding, which require a re-working. If conversely the gap is of a smallness such that an escape of injection material is not be feared, there is a danger of jamming of the vertical flash faces during the insertion of the core plate into the cavity plate. Said problem is allowed for by the outer gate valve 18 in the following manner:
During the introduction of the core cavity 6 into the cavity plate 7 the hydraulic cylinders 21 which act upon the outer gate valves 18 via the wedge-type valves 20 are pressureless. This means that the outer gate valves 18 may move to the right without any problem in Figures 2 and 3 and the vertical flash faces 17 and 19 may slide past one another virtually load-free at outer gate valve 18 and wearing strip 16. In this way a wear of the vertical flash faces 17, 19 as well as a jamming are reliably prevented.
Only after the retraction of the closing knife-type valves 14 into the position shown in Figure 6 and shortly before the start of the injection phase via the injection nozzles 22 are the hydraulic cylinders 21 activated. The outer gate valves 18 now move into the position shown in Figure 3 in which the side walls of the groove 40 of the outer gate valves 18 come to rest against the corresponding stop faces of the fin 41 of the cavity plate 7 and the correct, small gap between the vertical flash faces 17 and 19 is produced.
The runny polymer material may now be injected into the cavities 9 without there being a danger of said material exiting through the gap between the vertical flash faces 17 and 19. A wear or a jamming of the vertical flash faces 17, 19 is also not to be feared, since no relative movement takes place during the period of the pressurising of the hydraulic cylinders 21.
It is therefore possible with the aid of the outer gate valves 18 to obtain, over the long term and without wear or danger for the operational effectiveness of the mould, a highly dimensionally stable delimitation of the cavities 9 which meets the requirements made of an injection moulding.

Should a greater clearance than desired nevertheless have arisen between the corresponding vertical flash faces 17 and 19 after a very long service life of the mould, it suffices to exchange the wearing strip 16 in order to produce again the correct clearance between the vertical flash faces 17 and 19.
As can be seen from Figures 5 and 6, the front face of the closing knife-type valves 14 is constructed not flat, but graded. Said front face rests against the corresponding surface of the cavity plate 7 only via a relatively narrow "knife edge" 43, which is adjacent to the cavity 9. The following is achieved in this way:
During the production of the main body 2 of the GMT plastic moulding 1 the edge area adjacent to the closing knife-type valves 14 is formed step-wise in a shape which is complementary to the stepped shape of the front face of the closing knife-type valves 14. During the subsequent purging of the cavity 9 in the second step the so formed stepped edge contour 44 of the main part 2 is overfed, so that a large surface to be bonded is obtained between the gated sealing lips 3, 4 and the main part 2 (cf. Figure 7). The strength of the joint between the main part 2 and the sealing lips 3, 4 of the GMT plastic moulding 1 is improved in this way.

Claims

1. GMT plastic moulding having a main body which consists of a glass fibre mat blank which is impregnated with a thermoplastic, pressed in a mould and cured, and having at least one component of a soft polymer which is fixed to the main body, characterised in that the component (3, 4) of a soft polymer is gated to the main body (2).

2. GMT plastic moulding according to claim 1, characterised in that the surface to be bonded between the component (3, 4) of soft polymer and the main body (2) is increased by gradation.

3. Method for producing a GMT plastic moulding, in which first of all a glass fibre mat blank is impregnated with a hot, liquid thermoplastic, pressed in a mould and cured and in which there is applied to the main body so produced at least one component of a soft polymer, characterised in that the component (3, 4) of soft polymer is gated directly to the main body (2).

4. Method according to claim 3, characterised in that the edges of the main body (2), to which edges a component (3, 4) of soft polymer is to be applied, is provided during the pressing of the main body (2) with a gradation which is overfed during the gating of the component (3, 4) of soft polymer in such a way that the surface to be bonded between main body (2) and component (3, 4) of soft polymer is increased.

5. Device for producing a GMT plastic moulding with a mould mountable on a press, which mould comprises:
a) a cavity plate with a first shaped recess which, when the mould is in the closed position, partially bounds a first cavity complementary to the shape of the main body of the GMT plastic moulding;
b) a core plate movable relative to the cavity plate by means of the press and having a first shaped recess, which, when the mould is in the closed position, bounds the first cavity jointly with the first shaped recess of the cavity plate;
wherein c) the edges of the first cavity are formed at least in certain parts of toughened vertical flash faces at core plate and cavity plate, between which a defined gap is present;
characterised in that d) the cavity plate (7) comprises at least a second shaped recess which, when the mould is in the closed position, bounds partially a second cavity (9) complementary to the shape of a component (3, 4) of soft polymer of the GMT plastic moulding (1);
e) the core plate (6) comprises at least a second shaped recess which, when the mould (5) is in the closed position, partially bounds the second cavity (9);
f) along the common edges of the two cavities (8, 9) is arranged at least one closing knife-type valve (14) which is displaceable between a first position, in which it interrupts the communication between the two cavities (8, 9), and a second position, in which it releases the communication between the two cavities (8, 9) ;

g) those areas of the edges of the second cavity (9) that are not formed by the closing knife-type valve (14) are formed of toughened vertical flash faces (17, 19) on core plate (6) and cavity plate (7), between which there exists a defined gap which is narrower than the gap between the vertical flash faces (11, 13) bounding the first cavity (8);

h) at least one injection nozzle (22) issuing into the second cavity (9) is provided.

6. Device according to claim 5, characterised in that the outer (19) of the vertical flash faces (17, 19) bounding the second cavity (9) is attached to a movable outer gate valve (18) which is pressable against a stop by a source of energy (20, 21) in such a way that the desired gap with respect to the corresponding inner vertical flash face (17) is obtained.

7. Device according to claim 6, characterised in that the source of energy (20, 21) incorporates a wedge-type valve (20) whose direction of movement relative to the direction of movement of the outer gate valve (18) is not parallel and which interacts with the outer gate valve (18) via cam faces.

8. Device according to one of claims 5 to 7, characterised in that at least one vertical flash face (17) bounding the second cavity (9) is formed on a wearing strip (16).

9. Device according to one of claims 5 to 8, characterised in that the front face of the closing knife-type valve (14) is graded in such a way that the edge areas of the main body (2) of the GMT plastic moulding (1), to which edge areas a component (3, 4) of soft polymer is to be gated, are obtained with a corresponding grading.