EP0662031A1

EP0662031A1 - Process for manufacturing hollow plastic moldings made of fiber composite materials

Info

Publication number: EP0662031A1
Application number: EP93919290A
Authority: EP
Inventors: Günter ZILLNER
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-09-11
Filing date: 1993-09-08
Publication date: 1995-07-12
Also published as: WO1994006610A1

Abstract

A process is disclosed for manufacturing hollow plastic parts (6) made of fiber composites by laminating laminated layers on a core (12), by laying the laminated core (12) as a preliminary product into a negative mold (1) and by hardening the preliminary product into a plastic part (6) as a final product in a vacuum and/or an autoclave. The process has the following steps: producing a core (12) made of a gas-permeable dissolvable material, applying a flexible barrier layer (8) which is impervious to a gaseous pressure medium on the core (12), which is smaller than the final product by the thickness of the laminates and barrier layer (8), applying the desired number of laminated layers (10) on the barrier layer (8), and laying the thus obtained preliminary product into a composite negative mold (1), sealing the barrier layer (8) against the negative mold (1) at each opening (14) of the plastic molding (6), applying a relative overpressure on the side of the barrier layer (8) which faces the core (12), thus detaching the barrier layer (8) from the core (12) and pressing it against the laminate (10), detaching the core (12) once the laminate (10) is thoroughly set and removing the barrier layer (8) through at least one opening (14) of the final product.

Description

Process for the production of hollow plastic molded parts from fiber composite materials

The invention relates to a method for producing hollow plastic parts from fiber composite materials according to the preamble of claim 1.

For the production of plastic parts from fiber composite materials, e.g. Hand laminating processes are known from aramid, carbon or glass fibers, in which the laminate is placed in a form which can be in the form of a positive or negative form, the distribution and the impregnation thereof being introduced after the resin has been introduced the tissue is done manually with a spatula, roller or brush.

The manual lamination process can be carried out under vacuum for better ventilation of the laminate and better filling of narrow radii. It is provided that the laminate is provided with a cover film which is sealed off from the mold so that a vacuum can form between the cover film and the mold. _Z for reinforcing the contact pressure of the laminate against the _F orm, the shape may be placed in an autoclave and curing take place under a pressure up to 6 bar and, if necessary, at a temperature of up to 200 ° C.

In the case of hollow plastic parts, it is known to assemble and glue the hollow molds from two or more molded parts. This has the disadvantage that the strength of the hollow body is significantly weakened at the seams in this way, so that such parts with high strength requirements, e.g. Bicycle frames, bicycle forks, wings of wind turbines, etc. are not suitable for reasons of strength.

It is also known to produce hollow plastic molded parts with a foam core remaining in the plastic part. Such hollow plastic parts have the disadvantage of being heavier, the core remaining in the hollow part also being able to impair the strength of the plastic part. Another disadvantage is that the surface cannot be produced in the desired surface quality and consequently has to be reworked in a complex manner.

The invention is based on the object of specifying a method for producing hollow plastic molded parts from fiber composites, in which a higher strength of the plastic molded part is achieved with less weight and with improved surface quality.

The features of claims 1 and 5 serve to achieve this object. According to a first solution to this problem, the following method steps are provided according to the invention:

First of all, a core is formed from an air-permeable, dissolvable material which nevertheless has sufficient strength in the hardened state to enable the production of a core model. A flexible barrier layer is then applied to this porous core, which is suitable for a gaseous pressure medium, e.g. Air is impermeable. The core is made smaller by the size of the laminate layers still to be applied and the thickness of the flexible barrier layer relative to the finished dimensions of the end product.

The desired number of laminate layers is applied to the core coated with the barrier layer and the preliminary product formed in this way is inserted into the multi-part negative mold. The barrier layer must be sealed against the negative mold at the possibly several openings of the plastic molding. Subsequently, either with vacuum and / or with the aid of autoclave technology, a relative positive pressure is applied to the side of the barrier layer facing the core, as a result of which the barrier layer is detached from the core and pressed against the laminate. After the preliminary product has hardened, the core is dissolved and then the barrier layer is removed via the at least one opening of the end product.

The method advantageously enables the hollow plastic molded part to be pressurized from the inside during the curing process, a smooth outer surface being obtained which requires only a small amount of reworking, with no core remaining in the interior of the plastic molded part. Due to the high pressure applied from the inside, excess resin material and air bubbles are pressed out of the laminate, the synthetic resin being able to escape into resin channels which may be provided in the negative form. The elimination of air bubbles and excess synthetic resin in the laminate results not only in an improvement in the surface quality but also in an increase in the strength of the molded plastic part.

Since the molded plastic part is made in one piece, there are no external seams that could impair the strength of the molded plastic part.

A liquid silicone is preferably used as the barrier layer. Such a barrier layer made of liquid silicone can be applied in a simple manner to the core with high dimensional accuracy, the barrier layer being pressure-tight.

A gypsum mixture mixed with moist sawdust can be used for the core. As the gypsum grows as it sets, the moist sawdust shrinks, which enables the desired porosity of the gypsum mixture to be produced, so that a gas-permeable core can be produced. The gypsum mixture is water soluble.

The method advantageously enables the production of complicated hollow plastic parts, e.g. one-piece spoke wheels for racing bicycles.

According to a second solution, the following method steps are provided according to the invention: First, a core is made smaller than the end product by the wall thickness of the plastic molded part, on which a thin support form is first produced from at least one laminate layer. After the thin-walled support mold has hardened, it is separated for the purpose of removing the core and an inflatable tube is inserted into the support mold instead of the core. The hose is pumped up to the support form. The desired number of laminate layers is then applied to the support mold and the not yet cured laminate is placed in the multi-part negative mold. The tube in the support mold is now inflated to an increased internal pressure, as a result of which the laminate is pressed against the negative mold at high pressure via the support mold. After the laminate has hardened, the hose is removed via an opening in the molded plastic part after pressure relief.

This method is particularly suitable for tubular molded plastic parts. Due to the pressure on the laminate layer that can be generated from the inside against the negative mold, a smooth outer surface can be achieved which requires only a small amount of finishing. In addition, the other advantages already mentioned in connection with the first method with regard to air bubbles and synthetic resin precipitates are achieved. Since the mold is made in one piece, there are no external seams that impair the strength of the plastic molding. In this method, too, no core remains in the plastic molded part, so that the weight of seamless, hollow plastic parts made of fiber composite materials can be reduced and at the same time their strength can be increased. Exemplary embodiments of the invention are explained in more detail below with reference to the drawings:

Show it

1 is a schematic representation of the molded plastic part in a negative form according to a first method,

2 shows a molded plastic part in a negative mold according to a second method, and

3 shows a side view of the negative mold according to FIG. 2.

Figure 1 shows schematically the negative mold 1 from a lower part 2 and an upper part 3, which are sealed against each other with a sealing ring 4. In the negative mold 1 there is a plastic molded part 6 which bears against the inner walls of the lower part 2 and upper part 3 of the negative mold and cures there, pressure being exerted on the preformed laminate 10 of the plastic molded part 6 via a flexible barrier layer 8.

The flexible barrier layer 8 preferably consists of a silicone layer, which is applied in liquid form to a core 12 and sets there to form a gas-tight, highly elastic, up to 300% stretchable layer.

The outer contours of the core 12 correspond to the molded plastic part, but is reduced in terms of the finished dimensions of the molded plastic part by the layer thickness of the laminate 10 and the thickness of the barrier layer 8. The core 12 consists of a gas-permeable porous material which on the one hand has sufficient strength and modeling ability and on the other hand can be dissolved is. A mixture of gypsum and sawdust has proven itself as the core material, whereby the sawdust should be sufficiently watered so that the wood particles swell. While the gypsum increases in volume when setting, the sawdust particles become smaller during drying, so that there is sufficient porosity which makes the core material gas-permeable.

A proportion of approx. 30 to 40% sawdust has proven itself for the production of cores.

The barrier layer 8 must be sealed against the mold so that a pressure difference can arise between the negative mold 1 and the barrier layer 8. It is expedient to provide hollow-cylindrical lugs 16 of the negative mold at openings 14 of the plastic molded part 6 in order to turn the barrier layer 8 over the hollow cylindrical end of these lugs 16, as a result of which a perfect seal of the barrier layer 8 against the negative mold 1 is possible.

The pressure difference between the barrier layer and the negative mold can be generated, for example, using a vacuum in a manner known per se, for which purpose a vacuum connection 18 is provided in the lower part 2 of the negative mold 1 in the exemplary embodiment in FIG. 1. The negative pressure in the negative mold 1 causes the flexible barrier layer 8 to be strongly pressed against the laminate 10, so that air bubbles and excess synthetic resin are pressed out of the laminate 10 in an advantageous manner. For this purpose, the negative mold 1 can have resin channels (not shown) which can accommodate the excess synthetic resin and, if appropriate, the air pressed out. To increase the pressure exerted on the laminate 10, it is also possible, in a manner known per se, to arrange the negative mold 1 in an autoclave 20 in which a pressure of up to 6 bar can be generated, which may still be can also be reinforced by means of a vacuum. Temperatures of up to 200 ° C. can be generated in the autoclave 20 even when thermosetting synthetic resins are used.

FIG. 2 shows a negative mold with a plastic molded part 6, which is produced by the second method. The negative mold 1 is in two parts and consists of a lower part 2 and an upper part 3. The upper part 3 is shown partially broken away in FIG. 2, so that the plastic molded part 6 lying in the lower part 2 of the negative mold 1 can be seen, which in turn is shown broken is to show a support mold 22 forming the inner contour of the molded plastic part and an air hose 24 which can be inflated against the support mold. The air hose can be inflated from the outside via an air valve 26, through an opening 14 of the negative mold 1 leading to the outside is.

The support mold 22 is preferably produced as a single-layer laminate on a core (not shown), the dimensions of which are reduced by the laminate thickness of the plastic molding 6 compared to the finished size of the plastic molding. The thin-walled support mold 22 produced in this way is cut open after the laminate 10 has hardened in order to remove the core and to insert the air hose 24 in its place. Then the air hose is inflated until it lies lightly against the inner contour of the support form. Then a plurality of laminate layers corresponding to the desired layer thickness of the laminate 10 or the desired wall Thickness of the molded plastic part 6 applied, preferably stocking-like fabrics made of carbon, aramid or glass material being used.

The plastic molded part is then placed in the mold and the air hose is inflated to an internal pressure of approximately 1.5 to 3 bar, preferably approximately 2 bar, whereby the laminate 10 is pressed against the negative mold 1. When the laminate hardens, the support mold 22 connects to the other layers of the laminate and forms a uniform wall of the plastic molded part.

After the plastic molding has hardened, the air hose 24 can be removed via the passage opening 14 in the plastic molding for the air valve, so that no core remains inside the plastic molding.

In this exemplary embodiment too, curing can take place under vacuum and / or in an autoclave.

Claims

0

- by laminating laminate layers to a core,

by inserting the laminated core as a preliminary product in a negative mold and

- by curing the preliminary product to the plastic molded part as the end product under vacuum and / or in an autoclave, g e k e n n e e i c h n e t d u r c h

Producing a core from a gas-permeable, dissolvable material,

Applying a flexible barrier layer impermeable to a gaseous pressure medium to the core, the core being reduced by the laminate thickness and thickness of the barrier layer to be applied compared to the end product,

Applying the desired number of laminate layers to the barrier layer and inserting the preliminary product thus formed into the multi-part negative mold,

Sealing the barrier layer against the negative mold at each opening of the molded plastic part,

Applying a relative overpressure on the side of the barrier layer facing the core, as a result of which the barrier layer is detached from the core and pressed against the laminate,

- Dissolving the core after the laminate has hardened, and - Removal of the barrier layer via the at least one opening of the end product.

2. The method according to claim 1, characterized in that a liquid silicone is used as the barrier layer.

3. The method according to any one of claims 1 or 2, characterized in that a gypsum mixture mixed with moist sawdust is used for the core.

4. The method according to claim 3, characterized in that a wasεerlöεliche gypsum mixture is used.

5. Process for the production of hollow plastic molded parts from fiber composite materials

- by laying laminate layers on a core,

- By inserting the laminated core as a pre-product in a negative mold and

Production of a core that is reduced by the laminate thickness compared to the end product,

Laminating a thin support form from at least one laminate layer onto the core,

- Unraveling the support form after hardening to remove the core,

Inserting an inflatable tube into the support mold instead of the core, - inflating the hose to the support form,

Applying the desired number of laminate layers to the support mold to form the intermediate product,

- inserting the preliminary product into the multi-part negative mold,

- Inflating the hose in the support form to an increased internal pressure,

- Removing the hose after relieving pressure and after curing the laminate through an opening of the plastic molded part.

6. The method according to claim 5, characterized in that the support form is formed in several parts with parting line.

7. The method according to claim 5 or 6, characterized gekenn¬ characterized in that the inner pressure of the hose is about 1.5 to 3.0 bar, preferably about 2 bar.

8. The method according to any one of claims 1 to 7, da¬ characterized in that the plastic molded part are seamlessly laminated.