WO1994021438A1

WO1994021438A1 - Method and core element for producing a hollow shaped article or hollow section made of fibre-reinforced plastic

Info

Publication number: WO1994021438A1
Application number: PCT/EP1994/000795
Authority: WO
Inventors: Wolfgang Frank
Original assignee: Wolfgang Frank
Priority date: 1993-03-16
Filing date: 1994-03-15
Publication date: 1994-09-29
Also published as: DE4308370A1; DE4308370C2

Abstract

Described is a method of producing a hollow shaped article made of fibre-reinforced reactive plastic, the method using an inherently rigid core element (1) consisting of a fusible core (2) with a thin elastic gastight film (3) round it. A blank for production of the hollow shaped article is made by winding the rigid core element with impregrated fibrous material (4), preferably prepregs. The blank, which is inherently rigid owing to the core element, can be easily handled and placed in a two-part mould without any danger of folds forming. After the mould has been closed, the elastic hose-like film is inflated through an aperture so that the fibrous material is pressed against the inside of the mould and at the same time the hose lifted away from the fusible core. The blank is heated by the heated inside wall of the mould so that the fibre-reinforced plastic is cured under the action of pressure and heat. On completion of the curing process, the core material, which has been melted either by the heat of the mould or by independent heating, is drained off through the aperture in the hose. The complete hose can then be pulled out through the opening.

Description

^V experienced and core body for the production of a hollow shape _¬ or profile body made of fiber-reinforced plastic

DESCRIPTION

The invention relates to a method for producing a hollow molded body according to claim 1, to a core body for use in this method according to claim 16 and to a two-wheel frame which can be produced by the method according to claim 20.

It is known to work with a core in the processing of fiber-reinforced plastic. This core, consisting for example of PU foam, is wrapped with fiber material, impregnated with reactive plastic and cured in a mold under the action of heat. A disadvantage of this method is that the core remaining in the shaped body additionally increases the weight of the shaped body.

Furthermore, a method is known in which an inflatable tube is wrapped with impregnated fiber material. The molded body is cured in a mold with the hose inflated and under the action of heat. A disadvantage of this method is that the wrapping of the hose with fiber material is very difficult, particularly in the case of more complex shaped bodies, because of the flexibility of the hose. Furthermore, when handling such a shaped body blank, for example when inserting it into the mold, imperfections such as kinks, bruises, etc. can occur lead to a reduction in the strength of the composite body.

The application of such methods to HI-TEC products such as off-road bike frames led to unsatisfactory results, since the frame weight was too high compared to light metal frames in the first known method or the required fatigue strength of the frame construction was not achieved when using the latter method.

The invention is therefore based on the object of providing a method for providing a two-wheeled frame and a core body, in which the manufacture and handling of a molded body blank or molded body wrapped with fiber material can be carried out simply and reliably with a minimal weight.

This object is achieved by the features of claims 1, 16 and 20.

By the measure of creating a core body provided with the shape of the inner surface of the shaped body, which consists of a fusible core and an elastic jacket surrounding the core, for example in the form of a tube, due to its strength and inherent rigidity this is well suited for wrapping by either yarn-like or fabric-like fiber material. This makes it possible to wrap the fiber tissue cleanly and evenly around the core body while avoiding kinks and folds.

The fiber orientation can be chosen according to the requirements and the loads. The molded body blank created in this way is inherently rigid due to the core body and can e.g. B. when inserted into a divisible form can be handled well without the

Shaped body blank is damaged.

Compared to conventional solutions, the surface of the jacket offers a particularly good adhesive base for the fiber material winding, so that the production of the shaped body blank is made considerably easier.

Curing takes place with the jacket inflated and by the action of pressure and heat. By inflating the jacket by means of compressed air, the sleeve made of fiber material is detached from the core and pressed against the wall of the press mold. This ensures a clean separation between the jacket with the fiber material casing and the mandrel.

After curing, the core melted by the action of heat is drained off and the jacket is pulled out of the inner region of the shaped body or left therein. The method enables the production of coreless hollow molded articles made of fiber-reinforced plastic, the reject rate during production caused by improper winding of the fiber material or improper handling of the molded article blank being minimized.

Because of the coreless hollow construction and the reduced frequency of errors compared to known methods, the method according to the invention is particularly suitable for use in the manufacture of a bicycle frame which is characterized by low weight and high strength.

However, the method according to the invention is not only suitable for use on two-wheeled frames, but it is also suitable for the manufacture of all hollow-loaded, highly stressed components, such as two-wheeled handlebars, two-wheeled frames, tennis rackets, swimming boards and similar objects. By using wax as a fusible material for the core with a melting temperature of preferably 80 ° C to 140 ° C, a simple melting of the core is ensured on the one hand and on the other hand the hardened plastic material is only exposed to low thermal stress due to the relatively low temperature.

By providing multiple wrapping layers on areas of the molded body that are subject to greater stress, overall a high strength is achieved with a minimized weight of the molded body.

By filling the pre-assembled jacket inserted in an auxiliary form with molten core material, the manufacture of the core body is particularly easy and exactly reproducible.

Since the sheath can be removed after the core has melted, it can be reused so that the manufacturing process can be carried out more economically.

Further advantageous embodiments of the invention are the subject of the remaining subclaims.

The invention is explained in more detail below on the basis of several preferred exemplary embodiments with reference to the drawings.

Fig. 1 shows a partially cut two-wheel handlebar with molded steering tube, which can be produced by the method according to the invention.

Fig. 2 shows a side view of a one-piece two-wheel frame, which is produced by the inventive method. In Fig. 1 is a two-wheel link blank with molded

Steering tube shown how it is inserted into a mold for curing.

The interior of the two-wheel control arm is filled with a core body 1, which consists of a fusible core 2 and a tube 3 surrounding the fusible core 2. Fiber materials 4, for example so-called prepregs, are wound around the core body 1 and later form the shaped body.

The method steps for producing a hollow molded body are described below using the example of the two-wheel handlebar shown in FIG. 1.

A divisible auxiliary form (not shown), the inner surface of which has the shape of the core 2 of the two-wheel control arm, is made with a fusible core material such as e.g. Poured hard wax. After the core 2 has cooled or solidified, it is removed from this auxiliary form.

In a further process step, the core 2 is covered with a gas-tight tube 3. This is done, for example, by applying a suitable hose material, such as latex or silicone rubber, to the core 2. However, a pre-assembled hose can also be used, which either comes from a previous application of the method according to the invention or which is obtained in a separate manufacturing process, which should not be discussed here.

The core 2 surrounded by the tube 3 forms the actual core body 1. The tube 3 surrounding the core body 1 is extended on the handlebar tube of the two-wheel handlebar and has an opening 5 which can be closed by a valve (not shown). The core body 1 is then wrapped with synthetic resin-impregnated fiber fabric 4, preferably carbon fibers, so-called prepregs.

Due to the inherent rigidity of the core body, the fiber fabric can be closely formed around the core body 1. Areas subject to higher stress can be reinforced by multiple layers of fibers and / or stabilized by other materials etc. Furthermore, inserts such as fastening elements for fastening the handlebar can be molded in. The molded body blank produced in this way is easy to handle due to the rigidity of the core body 1.

The molded body blank is now placed in a divisible mold (not shown), the inner surface of which has the shape of the outer surface of the molded body. Due to the stability of the molded body blank, the risk of wrinkling in the fiber material during insertion into the mold is very low.

After the mold has been closed, the tube 3 is inflated so that the fiber material is pressed against the inner surface of the mold. The hose 3 and the fiber winding detach from the core 2. The inner surfaces of the mold can be heated so that the fiber-reinforced plastic hardens under the action of heat and pressure. After curing, the molded body is removed from the mold. The core can be melted by the action of heat during the pressing process or in a further process step and discharged as a liquid medium through the hose opening 5. The draining of the liquid core material can be assisted by applying negative pressure to the hose opening 5. The negative pressure further promotes the detachment of the hose 3 from the Inner surface of the molded body. The hose 3 is thereby easier to pull out of the molded body.

The detachment of the tube 3 from the molded body can be further facilitated by treating the outer surface of the core body 1 with a release agent before wrapping it with fiber material.

The two-wheel handlebar with the molded steering tube, which is the molded body, is essentially finished after the pressing, the stable core ensuring during the pressing process that the hollow body has defined wall thicknesses with a predetermined inner surface structure, which leads to superior strength values compared to known solutions and postprocessing as far as possible superfluous.

The hose 3 obtained in the above-described method can be used again to produce the next molded body. The core body 1 is produced by filling the tube 3 with molten core material in an auxiliary form.

2 shows a partially cut two-wheel frame which is constructed from a one-piece hollow profile structure with receiving sections for bottom bracket 6, steering head bearing 7, seat post 8 and rear wheel 9. Regarding the details of the Zeiradrahmen please refer to the registered utility model application

DE referenced, the content of which also belongs to the disclosure of the present application.

The method steps for producing a hollow molded body are described below using the example of the bicycle frame shown in FIG. 2. As can be seen from the dashed boundary lines, the core body 1 necessary for the two-wheel frame is made up of a plurality of partial core bodies la, lb, lc, each of which has a fusible core 2 surrounded by a tube 3 and, when joined together, results in the complete core body 1. The division chosen here is only an example. Of course, other divisions or a one-piece mold core are adjustable. The partial core bodies la, lb, lc lie closely together at their abutment points and / or overlap one another. Butt joints should be avoided as far as possible, so that it is preferred for reasons of stability to overlap the transition areas between two partial core bodies la, lb, lc at an angle, ie that the transition areas can be joined together like two round rod ends cut off at an acute angle to the longitudinal axis.

The core body 1 constructed from partial core bodies 1 a, 1 b, 1 c is, as in the exemplary embodiment described above, also wrapped with prepregs, the materials used and the layer thickness being freely selectable depending on the strength, so that the winding layers can lie one above the other several times at highly stressed locations .

The further processing of the shaped body blank is carried out essentially in the same way as in the exemplary embodiment described above.

The two-wheel frame, which is a relatively complex shaped body, has a core body 1, the partial core bodies la, lb, lc of which do not encompass any closed profile structure of the bicycle frame, so that each tube 3 belonging to a partial core body la, lb, lc after the respective core 2 has melted out via appropriate frame openings such as bottom bracket, Steering head bearing or seat post opening 6, 7, 8 is removable.

In another variant of the method for producing a two-wheeled frame constructed from a hollow body profile, an integrally formed core body 1 is used. As described above, the core 2, which consists of meltable material, is produced in a divisible auxiliary form and then coated with a thin, air-impermeable, elastic layer. The resulting tube 3 has extensions 5 for pumping on the various frame openings such as bottom bracket, seat post and steering head bearing openings 6, 7, 8. Following the process steps described above, d. H. , Wrapping with pre-impregnated fiber material, inserting it into the mold, and curing under pressure and heat, the core material melted by the heat is discharged at the various frame openings.

Due to the one-piece design of the core body 1 with undercuts, the hose 3 must remain in the two-wheeled frame. So that the tube 3 forms a bond with the inner surface of the bicycle frame, the tube 3 can be treated on the outer surface with an adhesive agent. In this example, a composite body consisting of the hardened hollow plastic profile and the hose would result.

A core material made of wax or hard wax or similar fusible material is preferably used in the above-described methods, the melting point of which is at a temperature of 40 ° C. to 200 ° C., preferably 80 ° C. to 140 ° C.

For better removal from the interior of the molded body after the plastic has hardened, the surface of the hose 3 can be treated with a release agent. In the production of the hollow shaped body, further shaping insert parts can be inserted into the divisible mold in which the shaped body blank is hardened. Furthermore, reinforcing elements made of other materials, such as metal, can either be inserted into the divisible mold so that they form a bond with the reactive plastic, or specially shaped receiving sections are formed on the molded body, on which the corresponding bearing bushes, receptacles, etc be attached.

The new process described thus enables simple, precise production of even complicated hollow body geometries, which are characterized by low weight and excellent strength.

Disclosed is a method for producing a hollow molded body from fiber-reinforced reactive plastic, in which an inherently rigid core body is used, which consists of a fusible core and a thin elastic gas-tight layer arranged around the fusible core. A shaped body blank is created by wrapping impregnated fiber material around the solid core body, preferably with prepregs. The molded body blank, which is inherently rigid due to the core body, is easy to handle without the risk of wrinkling and can be inserted into a separable mold. After the mold has been closed, the elastic layer in the form of a tube is inflated through an opening so that the fiber material is pressed against the inner wall of the mold and at the same time the tube is lifted off the fusible core. The molded body blank is heated via the heated inner wall of the press mold so that the fiber-reinforced plastic hardens under pressure and heat. After the hardening process, the core material is melted either by the heat of the mold or by separate heating drained through the hose opening. Then the complete hose can be pulled out of the opening.

Claims

1. Process for the production of a hollow molded body from fiber-reinforced plastic with the process steps:

- Forming a core body (1) provided with the shape of the inner surface of the shaped body, which consists of a fusible core (2) surrounded by an elastic, gas-tight jacket (3);

- Creating a shaped body blank by wrapping the core body with a fiber material (4), which is soaked either before or after wrapping with reactive plastic;

- inserting the molded body blank into a divisible mold;

- Inflating the jacket (3) to press the impregnated fiber material (4) of the molded body blank against the inner wall of the mold;

- hardening of the molded body blank by the action of pressure and heat;

- Melting the core (2);

- Drain the molten core (2) and remove the molded body from the mold.

2. The method according to claim 1, characterized in that the core (2) consists of wax or similar fusible material, the melting point of which is at a temperature of 40 to 200 ° C, preferably 80 to 140 ° C.

3. The method according to claim 1, characterized in that more heavily used areas of the molded body are wrapped with impregnated fiber material (4).

4. The method according to claim 1, characterized in that further shaping inserts are inserted into the separable Fo.

5. The method according to claim 1, characterized in that reinforcing elements are either inserted into the divisible mold m, so that they enter into a composite with the reactive plastic, or are attached after curing at the intended locations.

6. The method according to one or more of the preceding claims, characterized in that glass, aramid, polyester or carbon fibers are used as reinforcing fibers in woven form or as individual fibers.

7. The method according to one or more of the preceding claims, characterized in that reaction resins, preferably epoxy, polyurethane, polyesters, phenol or vinyl esters are used as plastics.

8. The method according to one or more of the preceding claims, characterized in that the core body (by filling the inserted in an auxiliary form pre-coated jacket (3) with molten core material is generated.

9. The method according to one or more of claims to 7, characterized in that the prefabricated jacket (3) is drawn over a fusible core (2) made in an auxiliary mold.

10. The method according to one or more of claims to 7, characterized in that jacket material, vo latex or silicone rubber is preferably applied or sprayed onto a fusible core (2) produced in an auxiliary mold, and thus a core body (1) provided with a jacket (3) is produced.

11. The method according to one or more of the preceding claims, characterized in that the jacket is removed after melting the core (2).

12. The method according to claim 11, characterized in that the jacket (3) is treated for better removal on the outer surface with a release agent.

13. The method according to one or both claims 11 and 12, characterized in that the jacket (3) is used again in a subsequent shaping process.

14. The method according to one or more of claims 1 to 10, characterized in that the jacket (3) remains after melting the core (2) in the cavity of the molded body.

15. The method according to claim 14, characterized in that the jacket (3) is pretreated with remaining in the cavity of the molded body with an agent or consists of a material that enters into a bond with the inner surface of the molded body.

16. core body for use in the method according to any one of claims 1 to 15, characterized in that the Kern¬ body (1) consists of several partial core bodies (la, lb, lc), each one for itself with a jacket (3rd ) surrounding the fusible core (2) and by assembling the complete core body (1).

17. Core body according to claim 16, characterized in that the partial core body (la, lb, lc) of the core body (1) lie closely together at their abutment points and interlock overlap.

18. Core body according to claim 16, characterized in that each partial core body (la, lb, lc) does not encompass a closed profile structure of the molded body, so that each jacket (3) belonging to a partial core body (la, lb, lc) Melting of the respective core (2) can be removed via corresponding shaped body openings (6, 7, 8).

19. core body for use in the method according to any one of claims 1 to 15, characterized in that the Kern¬ body (1) is integrally formed, the integral body jacket (3) belonging to the core body remains in the molded body.

20. Two-wheel frame made of plastic, manufactured by the method according to one or more of the preceding claims, characterized in that it consists of an integrally formed hollow profile structure with receiving sections for bottom bracket (6), steering head bearing (7), seat post (8) and rear wheel ( 9) is constructed.

21. Two-wheel frame according to claim 21, characterized gekenn¬ characterized in that the jacket (3) with the inside of the two-wheel frame enters into a bond.