GB2169845A

GB2169845A - Injection moulding process for composite materials using a textile reinforcing element

Info

Publication number: GB2169845A
Application number: GB08601137A
Authority: GB
Inventors: Bernd Vogel; Wolfgang Wabst
Original assignee: OBERLAUSITZER STAHL FAHRZEUG
Current assignee: OBERLAUSITZER STAHL FAHRZEUG
Priority date: 1985-01-23
Filing date: 1986-01-17
Publication date: 1986-07-23
Also published as: DK28186A; DK28186D0; GB2169845B; DE3543844A1; DD233972A1; NL8600110A; FR2576250A1; GB8601137D0

Abstract

A vacuum injection process for producing composite parts which uses a reinforcing element which is at least partially deep-drawable during the vacuum process, which will enable sufficiently strong thin laminates to be produced in complicated shapes. The reinforcement element consists of at least one ready-made and at least partly deep-drawable textile product, preferably a knitted or machine woven material, which corresponds to the contours of the component required and consists of at least one piece and is mounted onto at least one core. The invention is particularly applicable to the manufacture of vehicle bodies.

Description

SPECIFICATION Injection moulding process for composite materials using a textile reinforcing element This invention relates to a method of producing by a vacuum injection process composite components which incorporate a reinforcing element and to a product incorporating such an element.

The production of small and medium quantities of glass reinforced polyester (GUP) components by the vacuum injection process is known. The production of thin- and thickwalled laminates and also sandwich-type components is likewise known. The production of sandwich-type components from GUP and polyuethane (PUR) by the vacuum injection process is particularly economical. In these processes, the starting materials are PUR foam, highly fluid polyester resins or other synthetic resins, endless glass silk mats forming the reinforcement. The most widely used form of reinforcement consists of endless fibre mats, which show good permeability to resin as well as a structure which ensures that none of the fibres will "float out".With mats which are too highly compressed, such as glass silk stack-bound mats, an additional resin-permeable insert, e.g. of sacking, has to be introduced, or supplementary resin-conducting channels have to be worked into the foam core.

The articles to which preference is given in the vacuum injection process are of the nonstructured type, such as surf boards.

For sandwich-type constructional parts intended mainly for cladding and insulation rather than for mechanical stressing, the main problem is to obtain the minimum possible uniform wall-thickness, as this affects the weight, stability of shape, utility value, surface quality and cost. The solution of this problem is particularly important in the manufacture of vehicle bodies.

Further progress of the highly mechanizable vacuum injection method in vehicle body manufacture, e.g. for caravans, is hindered by the mutally conflicting requirements of utility, value and producability. The demand for light-weight doubly curved sandwich-type components, with relatively thick foam core inserts, is difficult to fulfil, by reason of the limits set to the producability of sandwich-type components with thin covering layers by the vacuum injection process, as the endless mats only enable relatively thick walls to be produced and can only be inserted into the moulds manually.All reinforcement materials hitherto known prevent the vacuum injection process for industrial production from being utilized to the full, particularly for the manufacture of doubly curved GUP or PUR sandwich-type components, the reasons being as follows: The only known mats which can be deepdrawn in a vacuum injection process are endless fibre mats and knitted and, subject to certain limits, machine-knitted materials.

Owing to the structure of endless fibre mats, the laminate thicknesses obtainable with them are 3 mm and over. In zones subjected to considerable deformation, the endless fibre mats become distorted into a comparatively small number of fibre strands so their reinforcement effect at these points is thus nullified.

Sandwich-type components with endless fibre mats are thus rendered relatively heavy, particularly in conjunction with a gel coating or a "surface fleece", as the thickness of the laminate is thereby further increased.

Endless fibre mats, knitted or machine-knitted materials and also glass silk flat-shaped articles not capable of being deep drawn during the vacuum process such glass silk stack bound mats and Malimo materials therefore have to be adapted to fit to the doubly curved foam bodies by using numerous accurately cut blanks. The resulting overlaps between adjacent blanks produce channels in which the resin advances more rapidly, forming "islands" with unsaturated zones. Finishing operations are then required, detracting from the quality of the product and this increases the cost.

The manual insertion of the reinforcement material into the tool and the operation of encasing the foam core in the said material calls for particular care if gaps or creases are to be avoided. Particular care is required at the edges, where no material must project too far or be missing. This is the phase which determines the eventual quality of the composite material. This decisive stage in the process is very time-consuming and therefore lengthens the tool occupancy time, thus shortening the time available for the vacuum injection process itself.

Reinforcement materials in use hitherto suffer from the further drawback of involving excessive input of material not justified by the technical results.

The production of closed hollow bodies from fibre-glass-reinforced synthetic materials is also known. Tanks, for example, are assembled from mouldings or "wound" by various different methods. In this connection, pressureless storage' or transport containers have to be distinguished from pressure vessels. Pressure vessels are produced by the "thread winding" process.

Closed hollow bodies made from fibre-glassreinforced plastics are gaining in importance as light-weight supporting components. According to the mechnical stresses to which they are subjected, they are in some cases strengthened wth ribs and/or struts or constructed as sandwich-type bodies in other zones. Among known hollow bodies of this type are containers assembled from two halves.

The disadvantage of these closed hollow bodies is that they can only be produced by the assembly of several shaped parts, the weak points being formed, as already mentioned, by the joins.

It is an object of the present invention to provide a reinforcement element which involves comparatively moderate input of material and which enables the vacuum injection process to be rendered more efficiently and the input of material involved in this process to be reduced.

It is a further object of the invention to provide a reinforcement element for composite materials which is at least partially deep drawable during a vacuum injection process which will allow sufficiently strong thin laminates to be produced in complicated shapes.

According to the invention, there is provided a vacuum injection moulding composite component incorporating a textile reinforcing element at least a part of which is deep-drawable during the moulding process so that it readily conforms to the contours of the moulded component.

Further according to the invention, there is provided a process for the moulding of a composite component by the vacuum injection process characterised by the step of using at least one ready-made, at least partially deepdrawable textile product, which readily corresponds to the contours of the moulded component required, the reinforcing element being in at least one piece and mounted onto at least one core, to tightly encase the latter on all sides.

Preferably, the ready-made, deep drawable textile element is a knitted or machine-knitted material.

Preferred materials for said element are chemical fibres such as polyamide silk, polyester silk and/or glass silk.

In one layer, the reinforcement element consists of at least one ready-made, at least partly deep-drawable textile product.

Due to its limited thickness, a number of layers of the reinforcement element can be used to give the finished product added strength.

The reinforcement element may consist of a number of layers of identical or different materials.

The reinforcement element may likewise consist of layers of material processed in the same way or differently.

The core on which the reinforcement element is formed will usually consist of a foam body. However, it has also been found that composite materials can be produced with a hollow body as a core, e.g. an inflated polyethylene bag.

The invention assists in the production of composite materials which are very light in weight and of sufficient strength. It also proves extremely economical where the consumption of material is concerned and enables the vacuum injection process to be rendered more efficient, inasmuch as the reinforcement element is ready-made in advance at a special work station away from the actual apparatus.

This preparatory operation can take account of the most complex shapes, whether by gusseting, partial welding, sticking or tacking. This greatly reduces "tool occupancy times".

The considerable degree of "deep-drawability" during the vacuum process particularly of the made-up knitted product, enables a wide variety of shapes to be selected for the moulded composite material components. This method, for example, enables sudden depressions in a surace of extremely small radii to be achieved which would be normally not be possible with a vacuum injection process.

The form taken by the reinforcement element also enables various different yarns, stitches and weights per unit area to be selected.

As the reinforcement elements of the invention can expand in three dimensions in the micro geometrical as well as in the macro geometrical range, excellent permeability to resin is obtained.

The use of the reinforcement element of the invention for the production of hollow bodies enables a completely new technology to be adopted for these products.

Other features and advantages of the invention will become apparent from the following description of two examples, given by way of example only.

Example 1~Production of a caravan door.

Wolpryla is used as the starting material for the deep-drawable reinforcement element. This material is a polyacrylonitrile fibre material (PAN or PVY) The acrylic (vinyl cyanide) content is preferably at least 85%. This material is very similar to Dralon.

It is processed on a motor-operated flatknitting machine. The machine is set up to produce a "right-right" or V-type stitch formation.

The strength of the stitches corresponds to that known from the top garment industry.

The weight of the knitted product obtained amounts to 2809 per m2.

The material produced by the metre is cut into layers according to the required pattern.

As regards the size, the cutting is performed as a developed surface of the finished unit, possible recesses and any appreciable deformations having to be taken into account for example by openings or gussets.

The layers to form the reinforcement element are sewn on a three-thread overcasting machine. During cutting and sewing, care is taken to ensure that the opening required for the eventual introduction of the foam core is provided in a place that enables the reinforce ment element to be closed up in due course without difficulty.

The operation of closing up the reinforcement element after the foam core has been accommodated therein is carried out by means of a few manual tackings.

For larger openings within the final component, (e.g. a window or hatch) the foam core is produced with a recess, and the reinforcement element, after sewing is secured by means of a textile adhesive at the point in question, and at the same time, is punched out.

The ready-made foam core thus obtained is further processed by the vacuum injection method to form the finished part.

Example 2~Production of a larger comparatively narrow-necked container.

The starting material for the reinforcement element consists of twisted glass silk (ES 9 68 tex Z X ZS 100-T 10-B 1). which is processed using a multi-thread method on a motor-driven flat-knitting machine.

ES 9 is an electrically non-conductive glass silk, the elementary filament thickness of which is 0.009 mm.

68 TEX is the filamentary strength which is 689 per 1000 m.

Z X 2 means that the filament is twisted twice in the Z direction.

S 100 means that 100 twists of the Z-twisted filament are present per metre.

T 10 indicates the filament preparation B 1 is the nature of the winding up on a biconical head.

The machine is set up to produce a rightright or V-shaped stitch formation with particular attention being paid to the thread guiding elements, in order to obtain a loose and highly deforamble knitted product.

The weight of the knitted product obtained is 450 g/m2. and it is cut into layers according to the required pattern.

The layers are placed on one another in staggered positions and secured by means of a backstitching machine. The layers thus tacked are sewn to form a shaped bag.

The staggered position in which the layers are placed on one another ensures that the seam determining their shape consists of two layers only and that no rigid seams are formed.

An inflatable rubber ballon with a flexible tube attached to it is introduced into this twolayer reinforcement element. The rubber balloon is lightly inflated and the reinforcement element drawn over it without folds. The entire structure is then placed in the vacuum injection tool.

Particular care must be devoted to the edge zones, so that no pinching takes place between the two halves of the tool.

The rubber balloon is now blown up by means of the flexible tube to which the tool seals off the ingress of air from the outside.

This causes the reinforcement element to come to rest accurately against the internal wall of the tool. (The reinforcement element is thereby pressed against all parts of the internal surface of the tool).

The over-pressure in the rubber balloon has to be adapted to the low pressure prevailing in the vacuum injection process. (Pressure in foil bag: 1000 Torr. Under-pressure in vacuum injection tool: 300 Torr).

The well-known vacuum injection process is then carried out.

The rubber balloon is later removed from the finished component and used again if necessary; it can also, however, be left in place in the finished article.

It will be seen from the foregoing description that the present invention relates to the production of composite components which can be produced by the vacuum injection process.

The purpose of the invention is to provide a reinforcement element for composite components which is at least partially deep drawable during the vacuum injection process and which will enable sufficiently strong thin laminates to be produced in complicated shapes. The vacuum injection process is rendered more efficient by the use of the reinforcement element and the input of material is thereby reduced.

This is achieved by using a reinforcement element which consists of at least one readymade and at least partly deep-drawable textile product which corresponds to the contours of the component required and consists of at least one piece and is mounted onto at least one core.

The invention is particularly applicable to the manufacture of vehicle bodies.

Claims

1. A vacuum injection moulded composite component incorporation a textile reinforcing element at least a part of which is deepdrawable during the moulding process so that it readily conforms to the contours of the moulded component.

2. A moulded component as claimed in claim 1 wherein the reinforcing element is in at least one piece.

3. A moulded component as claimed in claim 1 or claim 2 wherein the textile element is a knitted or machine woven material.

4. A moulded component as claimed in claim 3 wherein the textile material is made of chemical fibre materials.

5. A moulded component as claimed in claim 4 wherein the material is polyamide silk, polyester silk and/or glass silk.

6. A moulded component as claimed in any preceding claim wherein the reinforcing element consists of a layer of at least one piece of said textile material.

7. A moulded component as claimed in any of claims 1 to 5 wherein the reinforcing element consists of a number of layers of said textile material.

8. A moulded component as claimed in any preceding claim wherein the reinforcing element consists of layers of identical or different material and/or material processed in the same way or differently.

9. A moulded component substantially as herein described.

10. A process for the moulding of a composite material component by the vacuum injection process characterised by the step of using at least one ready-made, at least partially deep-drawable textile product which readily corresponds to the contours of the moulded component required, the reinforcing element being in at least one piece and mounted onto at least one core to tightly encase the latter on all sides.

11. The process of claim 10 wherein the core consists of a foam body and/or hollow body.

12. The process of claim 11 wherein the hollow body is inflatable.

13. The process of claim 12 wherein the inflatable hollow body consists of a rubber balloon.

14. A process for moulding a composite material component substantially as herein described.

15. A reinforcement element for use in producing vacuum injection moulded composite components characterised by at least one ready-made, at least partially deep-drawable textile product which can correspond to the contours of the component required, said element being in at least one piece and mountable onto at least one moulding core, so as to tightly encase the latter on all sides.