METHOD AND DEVICE FOR COATING A FOAM CORE REINFORCED BY A FIBER OVERLAW

Description

[0001] The invention relates to a method for coating a foam core, optionally reinforced by a fiber layer, with a plastic polymerizing from a reaction mixture in a mold composed of a lower part and an upper part, which mold has, on the one hand, a sprue and, on the other hand, an overflow in the region of its abutting surface on opposite sides, wherein the foam core is inserted into the mold while keeping a coating cavity free between the foam core and the shaping surfaces of the mold and the reaction mixture is injected through the sprue into the coating cavity of the closed mold.

[0002] To produce a composite workpiece consisting of a core and a coating enveloping the core, the core can be inserted into a mold while leaving a coating cavity free, and then the plastic can be injected into the coating cavity to form the core coating. If a reaction mixture is introduced into the coating cavity and only polymerizes into the plastic in the coating cavity, difficulties arise with these low-pressure processes regarding the bonding of the plastic to the core, particularly if the core is made of foam with a reinforcing fiber layer, for example in the form of a woven or nonwoven fabric made of glass or carbon fibers, because the plastic formed by polymerization in the coating cavity only partially penetrates the fiber layer and bonds only poorly with the foam core.

[0003] In order to avoid or compensate for defects caused by reactive and thermal shrinkage, as well as air inclusions or gas bubbles that form during the injection of the reaction mixture into the mold cavities during the production of molded parts or coatings from a plastic obtained by polymerizing a reaction mixture in a mold, it is known (EP 1 561 569 A1) to subject the reaction mixture in the mold cavity to an appropriate pressure. For this purpose, after the injection of the reaction mixture, the mold cavity is pressurized with a gaseous pressure medium, which is supplied through an overflow and / or the sprue of the mold.

[0004] Instead of subjecting the reaction mixture reacting in the mold cavity to a pressurized gas, the reaction mixture can also be subjected to appropriate pressure by a plunger (EP 0 294 768 A1). For this purpose, the plunger can form the molding surface of the upper part of the mold, so that the upper part exerts pressure on the reaction mixture across the entire mold surface. Since the evacuated mold cavity, which accommodates a fibrous reinforcing material, has a receiving volume for the reaction mixture injected through a sprue that exceeds the subsequent workpiece volume, part of the reaction mixture is discharged from the mold cavity through an overflow during the compression stroke of the upper part of the mold, which acts as a plunger tool.

[0005] DE 15 04 759 A1 DE 36 44 434 A1 discloses a method for coating a foam core, optionally reinforced by a fiber layer, with a plastic polymerized from a reaction mixture in a mold composed of a lower part and an upper part, which mold has, in the region of its abutting surface on opposite sides, on the one hand a sprue and on the other hand an overflow, wherein the foam core is inserted into the mold while keeping a coating cavity free between the foam core and the shaping surfaces of the mold and the reaction mixture is injected through the sprue into the coating cavity of the closed mold.

[0006] DE 15 04 759 A1 discloses a device for coating a foam core, optionally reinforced by a fiber layer, with a plastic curing from a reaction mixture, with a mold composed of a lower part and an upper part, the lower part of which has, in the region of its abutting surface on opposite sides, on the one hand a sprue and on the other hand an overflow.

[0007] Regardless of whether the pressure on the reaction mixture is exerted by a compressed gas or a stamp during the polymerization of the reaction mixture in the mold cavity, there is a risk, particularly when producing composite workpieces from a foam core having reinforcement in the form of a fiber layer, that during the polymerization of the reaction mixture introduced into the coating cavity between the foam core and the mold surfaces of the mold, the resulting plastic will only be inadequately bonded to the fiber-reinforced foam core.

[0008] The invention is therefore based on the object of designing a method for coating a foam core, optionally reinforced by a fiber layer, with a plastic polymerizing from a reaction mixture in a mold composed of a lower part and an upper part in such a way that an advantageous connection of the plastic shell to the foam core is achieved.

[0009] Starting from a method of the type described at the outset, the invention achieves the stated object in that the reaction mixture is injected into the coating cavity from the sprue in a lower apex region of the coating cavity to the overflow in an upper apex region, and in that after partial curing of the plastic resulting from the reaction mixture, the coating is held pressed against the foam core by a stamp forming the molding surface of the upper part until the plastic has completely cured. The reaction mixture is injected into the coating cavity while the molding tool is pivoted about a pivot axis running transversely to a diameter of the molding tool connecting the sprue with the overflow and parallel to its abutting surface into an end position in which the overflow lies in an upper apex region of the coating cavity.and that after partial curing of the plastic resulting from the reaction mixture, the coating is held against the foam core by a stamp forming the molding surface of the upper part until the plastic has completely cured.

[0010] Due to the rising pouring, the air is gradually displaced upwards by the reaction mixture injected into the coating cavity against the overflow from the coating cavity, which is an essential prerequisite for avoiding air inclusions remaining in dead spaces of the coating cavity.

[0011] Because the temperature conditions cause the polymerized plastic from the reaction mixture to harden from the outside inward, i.e., from the mold surfaces of the mold to the foam core, the overflow and sprue are sealed off by a sufficiently hardened plastic outer shell after partial curing of the plastic, allowing the upper part's plunger to exert appropriate pressure on the workpiece without running the risk of displacing uncured plastic from the coating cavity through the overflow or sprue. The interaction of the venting enabled by the rising pour with the subsequent pressurization of the partially cured polymerized plastic ensures not only a defect-free surface of the plastic shell that corresponds to the mold surfaces of the mold, but also an intimate bond between the plastic and the foam core.The plastic penetrates through any fiber layer to the foam core and clings to the fiber layer and the porous surface of the foam core.

[0012] Complete venting of the coating cavity during injection of the reaction mixture into the coating cavity requires a runner in a lower apex region and an overflow in an upper apex region of the coating cavity. This can be easily ensured using the overflow diametrically opposite the runner, for example, by positioning the mold with a correspondingly inclined diameter between the runner and the overflow. To improve venting of the coating cavity, the reaction mixture can be injected into the coating cavity while the mold is pivoted about a pivot axis running transversely to a diameter of the lower tool connecting the runner to the overflow and parallel to its abutment surface, from an initial position to an end position in which the overflow is located in the upper apex region of the coating cavity.By pivoting the mold about a pivot axis running parallel to the abutment surface and transverse to a diameter of the mold connecting the sprue to the overflow, usually a horizontal axis, the air within the coating cavity is additionally moved, thereby assisting venting. The air thus escapes from the coating cavity through the overflow, which moves upwards as the mold pivots, until the coating cavity is completely filled. When the mold pivots into its final position, the overflow comes to rest in an upper apex area of ​​the coating cavity and is therefore only sealed off from airflow by the injected reaction mixture once the injection process is complete.

[0013] To assist the venting of the mold during injection of the reaction mixture, the coating cavity can be subjected to a negative pressure through the overflow during filling with the reaction mixture.

[0014] To carry out a manufacturing method according to the invention, a device can be used with a mold composed of a lower part and an upper part, which has, in the region of its abutting surface on opposite sides, a sprue on the one hand and an overflow on the other, and with a frame receiving the mold, which forms an adjustment guide and an adjustment drive for the upper part, which is displaceable relative to the lower part, which is fixed to the frame. In such a device, only the frame needs to be pivotably mounted in a support frame about an axis that runs transversely to a plane that is determined, on the one hand, by the adjustment direction of the upper part and, on the other hand, by a diameter of the mold connecting the sprue to the overflow.In addition, the upper part must comprise a stamp forming its molding surface, which can be moved in the direction of adjustment, in order to be able to exert a corresponding compaction pressure on the curing plastic after the reaction mixture has been injected into the coating cavity between the foam core and the molding surfaces of the mold, accompanied by a pivoting of the mold, and after the plastic polymerized from the reaction mixture, which completely fills the coating cavity, has partially cured.

[0015] The upper part of the mold can form the plunger in the form of a plunger, which plunges into the lower part with a positive fit when the mold is closed. With this type of mold design, advantageous design conditions arise if the plunger is mounted in the upper part so that it can be displaced in the adjustment direction, preferably against a restoring force, and is driven by an actuator. After the mold is closed using the adjustment drive, the actuator can thus additionally apply a corresponding compressive force to the plunger to compact the curing plastic in the coating cavity.

[0016] To assist in venting the mold during its pivoting and filling with the reaction mixture, the overflow can be connected to a vacuum pump.

[0017] To control the injection process, the overflow can have a signaling device connected to a control system for the reaction mixture feed system into the runner. This signaling device detects the reaction mixture entering the overflow if a corresponding fill level is not specified. Since filling of the coating cavity is complete when the signaling device in the overflow is triggered, the reaction mixture feed system and any vacuum pump connected to the overflow can be shut off to initiate pressurization of the workpiece by the plunger after a specified reaction time.

[0018] The method according to the invention is explained in more detail with reference to the drawing.

[0019] It shows Fig. 1 an embodiment of a device according to the invention for coating a foam core, optionally reinforced by a fiber layer, in a starting position with an open mold in a schematic side view, Fig. 2 the device according to Fig. 1 with the forming tool swivelled into its final position and Fig. 3 a schematic section through the mold in the pivoted end position on a larger scale.

[0020] According to the Fig. 1 and 2A device according to the invention has a molding tool 2 arranged in a frame 1, comprising a lower part 3 and an upper part 4. While the lower part 3 is fixed to the frame, the upper part 4 is displaceably mounted on guide columns provided laterally next to the lower part 3, forming an adjustment guide 5, which run in the closing direction of the molding tool 2 and thus transversely to the abutment surface 6 of the lower part 3. Between the guide columns, an adjustment drive 7 engages the upper part 4 of the molding tool 2, which according to the exemplary embodiment comprises two hydraulic cylinders supported on a yoke 8 of the frame 1, although this is by no means mandatory.

[0021] The lower part 3 of the mold 2 has, in the area of ​​its abutment surface 6 on one side, a runner 9, which is connected in a conventional manner to a mixing head for a reaction mixture for polymerizing a plastic; however, this is not shown for reasons of clarity. Diametrically opposite the runner 9 is an overflow 10, which is connected to a vacuum pump. However, an arrangement of the runner 9 and / or the overflow 10 in the upper part is by no means excluded.

[0022] The frame 1 is mounted in a support frame 11 so as to be rotatable about a pivot axis 12 and can be moved by means of a pivot drive 13 from a position in the Fig. 1 shown starting position into a final position after the Fig. 2 be pivoted. The pivot axis 12 runs on the one hand parallel to the abutting surface 6 of the lower part 3 and thus usually horizontally, and on the other hand transversely to a diameter of the mold 2 running between the sprue 9 and the overflow 10 and accordingly also transversely to a plane determined by the closing direction of the upper part 4 on the one hand and the diameter between the sprue 9 and the overflow 10 on the other hand. This arrangement ensures that when the mold 2 is pivoted in the sense of an upward displacement of the overflow 10, the mold 2 can be vented through the overflow 10 during the pivoting, avoiding air inclusions, while a reaction mixture is injected through the sprue 9 into the mold 2.With a diametrical arrangement of runner 9 and overflow 10, which depends on the workpiece shape, it is thus possible to ensure that runner 9 is located in the lowest region of the mold cavity when mold 2 is pivoted, and overflow 10 is located in its upper apex region, so that the reaction mixture is introduced into the coating cavity from bottom to top when mold 2 is pivoted. The pivot angle required for mold 2 for the apex position of overflow 10 depends on the mold part geometry and must therefore be adjusted accordingly.This swivel angle for the mold 2 is also decisive if the reaction mixture is not injected into the coating cavity during swiveling but with the mold 2 stationary, because in this swivel position of the mold 2 the sprue 9 is located in the lower and the overflow in the upper apex area of ​​the coating cavity.

[0023] For coating a foam core 14, preferably reinforced by a fiber layer, this foam core 14 is introduced into the mold 2 while keeping a coating cavity between the foam core 14 and the mold surfaces 15 of the lower part 3 and the upper part 4 free. For this purpose, the upper part 4 is Fig. 3 provided with mandrels 16, which hold the foam core 14 in the desired position within the closed mold 2. Of course, the support of the foam core 14 can also be assigned to the lower part 3.

[0024] The upper part 4 forms a punch 17 having its forming surface 15, which plunges into the lower part 3 in the closed position of the mold 2, so that with the help of the punch 17, a subsequent compaction of the plastic shell 18 of the foam core 14 to be produced is possible. As can be seen in particular from the Fig. 3 As can be seen, the punch 17 in the upper part 4 can be guided displaceably in the adjustment direction on columns 19 and can preferably be additionally acted upon against a restoring force, in particular against the force of compression springs 20, by an actuating drive 21, for example by spindle drives or hydraulic cylinders, in order to penetrate deeper into the lower part 3 against the restoring force when the mold 2 is closed. This design feature can also be used to pierce the mandrels 16 into the foam core 14 inserted into the lower part 3 to an extent that ensures the required coating cavity between the foam core 14 and the mold surfaces 15 when the punch 17 is returned to the closed position.

[0025] For example, in order to coat a foam core reinforced with a fiber fabric made of glass or carbon with a polyamide 6, after closing the mold 2, in which the foam core 14 is held by means of the mandrels 16 while keeping a coating cavity between the foam core 14 and the mold surfaces 15 of the mold 2, the reaction mixture with the caprolactam to be polymerized is placed in the starting position of the frame 1 after the Fig. 1 through the runner 9 into the coating cavity and the frame 1 is gradually moved into the Fig. 2 The overflow 10 is pivoted into the end position shown in FIG. 1, in which the overflow 10 comes to rest in an upper apex region of the coating cavity. This means that the air displaced by the injected reaction mixture and preferably simultaneously extracted by a vacuum pump connected to the overflow 10 can escape upwards through the overflow without the risk of air inclusions in dead spaces until the coating cavity is in the pivoted end position of the mold 2 according to the Fig. 2 is completely filled with the reacting reaction mixture and the caprolactam polymerizes to a polyamide 6, which cures starting from the mold surfaces 15 and progressing towards the foam core 14. The end of the injection process can be indicated by a signal transmitter that detects the penetration of the reaction mixture into the overflow 10 if the injection process is not controlled by specifying a corresponding fill quantity.

[0026] After partial curing of the caprolactam polymerized to polyamide 6, the plastic sheath 18 surrounding the foam core 14 is subjected to a compressive force by the punch 17, which causes complete penetration of the fiber fabric up to the foam core 14 and results not only in a defect-free surface of the plastic sheath 18, but also in an intimate connection of the plastic sheath 18 with the foam core 14.

Claims

1. Method for coating a foam core (14), which may be reinforced by a fibre layer, with a plastic material polymerized from a reaction mixture in a forming tool (2) comprising a lower part (3) and an upper part (4), which comprises, in the region of its contact surface (6) on opposite sides, a sprue channel (9) on the one hand and an overflow (10) on the other, wherein the foam core (14) is inserted into the forming tool (2) while keeping a coating cavity between the foam core (14) and the forming surfaces (15) of the forming tool (2) and the reaction mixture is injected through the sprue channel (9) into the coating cavity of the closed forming tool (2), characterized in that the reaction mixture is injected from the sprue channel (9) in a lower apex region of the coating cavity to the overflow (10) in an upper apex region rising into the coating cavity, and that after partial curing of the plastic resulting from the reaction mixture, the coating is held pressed against the foam core (14) by a stamp (17) forming the forming surface (15) of the upper part (4) until the plastic has completely cured.

2. Method according to claim 1, characterized in that the reaction mixture is injected into the coating cavity while the forming tool (2) is pivoted about a pivot axis (12) extending transversely to a diameter of the lower tool (3) connecting the sprue channel (9) with the overflow (10) and parallel to its contact surface (6) from an initial position into an end position in which the overflow (10) is located in the upper apex region of the coating cavity.

3. Method according to claim 1 or 2, characterized in that the coating cavity is capable of being subjected to negative pressure through the overflow (10) during filling with the reaction mixture.

4. Device for coating a foam core (14), which may be reinforced by a fibre layer, with a plastic material which cures from a reaction mixture, comprising a forming tool (2) composed of a lower part (3) and an upper part (4), the lower part (3) of which has, in the region of its contact surface (6) on opposite sides, a sprue channel (9) on the one hand and an overflow (10) on the other, and with a frame (1) receiving the forming tool (2), which forms a positioning guide (5) and a positioning drive (7) for the upper part (4) which can be displaced relative to the frame-fixed lower part (3), wherein the frame (1) is mounted pivotably in a support frame (11) about a pivot axis (12) which extends transversely to a plane defined on the one hand by the direction of positioning of the upper part (4) and on the other hand by a diameter of the lower part (3) connecting the sprue channel (9) with the overflow (10), and that the upper part (4) comprises a stamp (17) which can be displaced in the positioning direction and forms the forming surface (15) of the upper part (4).

5. Device according to claim 4, characterized in that the stamp (17) is mounted displaceably in the upper part (4) in the positioning direction and can be driven by an actuating drive (21).

6. Device according to claim 5, characterized in that the stamp (17) is mounted displaceably in the upper part (4) against a restoring force.

7. Device according to one of the claims 4 to 6, characterized in that the overflow (10) can be connected to a vacuum pump.

8. Device according to one of the claims 4 to 7, characterized in that the overflow (10) comprises a signal generator connected to a control device for the conveying device for the reaction mixture into the sprue channel (9) for the penetration of the reaction mixture into the overflow (10).