FR2750640A1 - Production of fibre reinforced plastic parts - Google Patents

Abstract

Method of making a fibre reinforced plastic part has: a stage of installing at least one shell (2,3), in a mould (4,5), which is made from a resin having low adhesion to the plastic material used to mould the part; a moulding stage of putting the resin in the shell and closing the mould; a demoulding stage during which the shell is removed from the mould; an extraction stage when the moulded part is removed from the shell.

Description

Process for manufacturing a product made of plastic material reinforced with fibers
The present invention relates to a process for molding and manufacturing a fiber-reinforced plastic. More specifically, it relates to a process for molding and manufacturing a fiber-reinforced plastic product in a more efficient manner.

 Different processes are used to mold and manufacture fiber-reinforced plastics (hereinafter referred to as the FRP abbreviation). These methods include, for example, a manual layering method using only a mold or matrix, a simultaneous projection method and a filament winding (FW) method in which a reinforcing fiber impregnated with a resin is wound around a mandrel. Other processes are also known, such as the resin injection molding process on reinforcement (RTM) comprising the use of a mold and a matrix, or a matrix alone, a resin being injected into a reinforcement preform placed in the die, and a press molding process (cold or hot) using both a mold and a die. In the cold or hot press molding process and in the RTM process, heavy and thick molds, such as resin molds, concrete molds, FRP molds, electroforming molds and molds metal are used to form fiber-reinforced plastics.

 Polyesters, vinyl esters and epoxy resins, among others, are generally used as base material resins for FRP. Since the adhesive force between the fiber reinforcement and the resin forming the base material must be high, it is often the case that the adhesion between the resin and the mold surface is also extremely high.

 It is therefore necessary to apply a mold release treatment to the mold in order to avoid this adhesion, the release agent being typically a wax or a similar substance.

 The frequency with which the release agent should be applied to the mold largely depends on the type of FRP base resin, the type of mold and the type of molding process used. Even when a mold is well controlled by the RTM process, a mold release treatment must be carried out after 50 to 70 uses. This mold release treatment is usually done manually and requires a lot of time and labor, which is one of the main factors hindering efficient FRP manufacturing.

When the mold release treatment is not satisfactory, it is often difficult to extract the FRP molded product from the mold, which not only takes time but also frequently causes deterioration of the mold.

In particular, a mold having a thin edge or a thin rib is often deteriorated during the extraction of the molded product, due to an unsatisfactory release treatment.

 Naturally, when a large FRP molded part is desired, the mold must also be designed larger. However, when a large FRP molded part is to be produced, it takes more time to place a reinforcing preform in the mold. An expensive mold is therefore occupied for a long time for something other than direct molding work. This is also the case when a layer of gel has to be applied to the surface of the mold.

 In the cold or hot press molding process, or in the RTM process, a molded fiber-reinforced plastic must be fully cured in the mold until its shape is stabilized. The mold is therefore occupied longer than when the reinforcing preform is used, and therefore cannot be prepared for the next molding operation until the previous molded part has been demolded. With the RTM process, the mold can be placed in a high temperature tank to stimulate the curing of the resin in the mold. However, after the FRP mold is removed from the mold, no further molding operation can be carried out until the temperature of the mold has been lowered. This prevents rational use of the mold and good production efficiency of fiber-reinforced plastics.

 The object of the present invention is precisely to propose a process which makes it possible to reduce the number of manufacturing steps required for the molding of a fiber-reinforced plastic product by the cold or hot press molding process, or the RTM process.

 The invention also aims to extend the life of the molds used to implement these methods.

 Another object of the invention is to propose a high-yield manufacturing method for producing a FRP molded part.

 The method of manufacturing a fiber-reinforced plastic product of the present invention comprises a shell installation step which comprises the installation in a mold of at least one shell produced from a resin which is weakly adherent to a base material resin used to form a fiber reinforced plastic; a molding step comprising placing the base material resin in the shell and closing the mold; a demolding step during which the shell is removed from the mold; and a molded part extraction step during which a molded part is extracted from the shell.

 According to a particular feature of the present invention, a reinforcing preform can be placed in the shell prior to the installation step thereof.

 According to an additional characteristic of the invention, the shell can be removed from the mold before the resin forming the base material is completely cooked and prior to the step of extracting the molded part.

These aims, characteristics and advantages of the present invention will emerge more clearly from the following detailed description of examples of embodiments, given by way of non-limiting illustration with reference to the appended drawings in which
Figure 1 is a diagram showing the step of installing a reinforcing preform of the manufacturing process of the invention described in Example 1 t
FIG. 2 is a diagram representing the step of closing the upper and lower shells and the step of molding the manufacturing process described in Example 1
FIG. 3 is a diagram representing the post-baking and demolding step of the process described in Example 1
Figure 4 is a diagram showing the step of installing upper and lower shells and setting up a preform of the manufacturing process of the invention described in Example 2
Figure 5 is a diagram showing the molding step of the manufacturing process described in Example 2; and
FIG. 6 is a diagram representing the post-baking and demolding step of the process described in Example 2.

EXAMPLE 1
Figures 1, 2 and 3 illustrate a method of molding a fiber reinforced plastic product (FRP) by a resin injection molding process on reinforcement (RTM) according to a first aspect of the present invention.

 The FRP container intended to be formed (visible in FIGS. 3 and 5) has a diameter of 25 cm and a depth of 10 cm, its walls having a thickness of 3 mm. The rim part of the container has a width of 2 cm and a thickness of 1 mm.

 As shown in FIG. 1, a reinforcement preform 1 has been placed between an upper shell 2 and a lower shell 3. The reinforcement preform 1 is produced from a plain woven glass fabric, 12 sheets of this fabric glass being joined by coating with a binder to form the reinforcing preform.

 The upper shell 2 and the lower shell 3 are preferably made from a resin which is very weakly adherent to the resin forming the base material used to manufacture the plastic material reinforced with fibers, or from a metallic material of which a surface is coated with this weakly adherent resin.

In this example, the upper shell 2 and the lower shell 3 are both 2 mm thick, the invention however not being limited to this value, provided that the two shells are sufficiently robust to withstand the molding pressure. to which they are subject. The upper shell 2 and the lower shell 3 can be manufactured, for example, by injection molding, by vacuum molding or by compression molding.

 When the upper shell 2 and the lower shell 3 have a large thickness and a high degree of rigidity, they can retain their shape outside the mold, which makes it possible to start by installing a preform in the shells before placing them here in the mold. A groove or a reservoir of resin is formed in the lower shell 3 and defines a soft pinch area. On the other hand, the upper shell 2 comprises a degassing / pressure reduction duct 6 and a resin injection duct 7.

 As can be seen in FIG. 2, the upper shell 2 and the lower shell 3 in which the reinforcing preform is installed are then placed in an upper mold 4 and a lower mold 5.

The upper mold 4 and the lower mold 5 are produced from a concrete based on epoxy resin but can be made from any material capable of holding the upper shell 2 and the lower shell 3 precisely while being able to withstand the molding pressure. It should also be specified that the surfaces of the upper mold 4 and of the lower mold 5 do not require any special treatment.

 The upper mold 4 and the lower mold 5 are then applied against each other and closed by means of a clamping device or the like, after which a resin mixed with a cooking agent is injected through the resin injection pipe 7 of the upper shell 2. As can be seen in FIG. 2, the upper mold 4 has holes intended to accommodate the degassing / pressure reduction pipe 6 and the resin injection pipe 7. The resin used here is preferably a polyester resin, but can also be a vinyl ester resin or an epoxy resin. The degassing / pressure reduction duct 6 is connected to a vacuum pump (not shown) intended to reduce the pressure inside the shells. When the resin starts to come out through the pressure reduction pipe 6, the supply of resin in the resin injection pipe 7 is stopped. After 20 minutes, it is found that the resin is solidified, after which the shells 2 and 3 are extracted from the upper mold 4 and from the lower mold 5 and placed in a high-temperature tank 8 at 80 ° C. for one hour. tank is then gradually cooled to reach room temperature, then the FRP molded part is extracted from shells 2 and 3. Compressed air is then blown through the resin injection duct 7, which allows d '' easily extract the FRP molded part from the shells.

 It can be seen that the surface of the FRP molded part thus produced is as smooth as the surfaces of the shells. It is also found that no resin forming the base material adheres to the molds, the molds being able to be reused quickly for the next molding step once the shells have been extracted therefrom. Because the shells are extremely light, the preform can be installed very easily. It is also observed that the shells can be used at least 20 times before having to be replaced. Since the following preform can be prepared during the post-curing treatment, no demolding treatment is necessary and the FRP molded part can be easily demolded. As the molds are not used during the post-curing treatment, the productivity for a single mold is consequently multiplied by three compared to the prior art. In addition, since the molding operation is divisible, the yield can be multiplied by at least two compared to the prior art. In addition, since the molds no longer need to be repaired and special surface treatment is no longer necessary, the cost of the molds is equal to or less than 1/3 that of a conventional mold .

Example 2
FIGS. 4 to 6 represent a cold press molding process for producing a cylindrical FRP container with a thin wall, implementing the present invention. The molded product has the same dimensions as that of Example 1. The same shells as in Example 1 are used, and the same types of resins as those listed in Example 1 can be used to make these products. Unlike the RTM molding process, however, the resin injection pipe and the pressure reduction pipe are not provided since the resin is not injected. The same molds as in Example 1 are used, and can be produced from the same materials as those listed in Example 1. However, the upper mold 4 of Example 2 does not have holes intended to accommodate the degassing / pressure reduction pipe 6 and the resin injection pipe 7 of the upper shell 2 used in Example 1.

 As can be seen in FIG. 4, the upper shell 2 is firstly fixed to the upper mold 4 by means of a clamping device. The reinforcing preform 1 is installed in the lower shell 3 which is then placed in the lower mold 5. Since the lower mold 5 constitutes a female part, the lower shell 3 is simply engaged in the lower mold 5. Then, as this can be seen in FIG. 5, a polyester resin mixed with a cooking agent is spread over the reinforcing preform 1.

Once the desired amount of resin has been spread over the reinforcement preform 1, the upper mold 4 is pressed against the lower mold 5 using a 50-ton hydraulic press. A surplus of resin is collected in the resin tank formed in the lower shell 3. After 20 minutes, it is found that the resin has solidified in the shells, after which the upper shell 2 and the lower shell 3 are extracted. upper mold 4 and lower mold 5, fixed by a clamping device and left in the high temperature tank 8 to 80 "C for 1 hour. The tank is then gradually cooled to reach room temperature, and the room molded in FRP is extracted from shells 2 and 3. The molded FRP piece thus obtained has the same characteristics as those obtained in Example 1. The yield-promoting effect of the present invention is the same as in Example 1 .

 As indicated above, no mold release treatment is necessary in the molds used to manufacture FRP using the cold or hot press molding process, or the RTM process, which makes it possible to extend the lifetime of the molds.

On the other hand, the occupation time of the molds during the firing of a FRP molded part can be reduced as well as the occupation time of the molds necessary for the application of a layer of gel and for setting in place of a reinforcement preform. A good manufacturing yield of FRP molded parts is therefore possible.

 Although the preceding description has focused on preferred forms of implementation of the method of the invention, it is of course not limited to the particular examples described and illustrated here and the person skilled in the art will readily understand that 'It is possible to make numerous variants and modifications without departing from the scope of the invention.

Claims (3)

 1. A method of manufacturing a fiber-reinforced plastic product, characterized in that it comprises a shell installation step which includes the placement of at least one shell (2, 3) in a mold (4, 5), said shell (2, 3) being produced from a resin weakly adherent to a resin used to form a fiber-reinforced plastic material; a molding step comprising placing the resin in the shell (2, 3) and closing the mold (4, 5); a demolding step during which the shell (2, 3) is removed from the mold (4, 5); and a molded part extraction step during which a molded part is extracted from the shell (2, 3).  2. Method according to claim 1, characterized in that it further comprises a step of placing a reinforcing preform (1) in the shell (2, 3) prior to the installation step of the shell.  3. Method according to claim 2, characterized in that it further comprises a step which consists in removing the shell (2, 3) from the mold (4, 5) before the resin is fully cured and prior to the step of extracting the molded part.