JPH04294126A - Method for molding of plastic product using elastomer molded body an compression source - Google Patents

Abstract

PURPOSE:To attempt to obtain a large and long molded item or a fiber- reinforced plastic without an increase in cost by utilizing an unrestricted part of an elastomer as a spring part by applying a principle of a spring lid and obtaining a proper pressure by setting a part of an excess thermal expansion pressure of the elastomer. CONSTITUTION:When a prepreg laminated body 3 and an elastomer 4 are placed between a fixed lid 1 and a fixed mold 2 positioned without relative displacement in the up and down direction and with a specified gap between them and they are heated, exposed parts 4' and 4' of the peripheral face in the gaps between the fixed lid 1 and the fixed mold 2 are used without restriction. At this case, if the thermal expansion coefficient of the elastomer 4 is in the range of 150-300X10<-6>/ deg.C, it is pref. as a necessary and enough pressure source can be obtd. By using the unrestricted part of the elastomer as a spring, a large scale fiber-reinforced plastic, e.g. a mast for a large racing yacht is molded under a condition with an initial pressure of 3 kg/cm<2> and a difference an heating temp. of 100 deg.C. If a vacuum bag is used in parallel, reliability can be furthermore improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing autoclave molding using a simple tool, and relates to an improved method for molding plastic products that utilizes the expansion pressure of a conventionally used elastomer.

0002

2. Description of the Related Art There are various molding methods for molding advanced plastic composite materials, especially fiber-reinforced plastics. The most commonly used molding method is to laminate prepreg sheets and press and heat them in an autoclave. The first advantage of autoclave molding is its reliability. Since this molding method applies pressure appropriately, when molding is carried out under appropriate conditions, the resulting molded product has high dimensional accuracy, is free from defects, and has no disordered fiber arrangement. Furthermore, one of the advantages of fiber-reinforced plastics is the economical effect of manufacturing by integrating parts. For this reason, it is now an indispensable method for manufacturing aircraft parts. However, when parts are integrated and molded in one piece, the result is generally a large structure. When molding a long molded product, an autoclave of a size commensurate with the molded product is required, which requires an excessive investment in equipment. For this reason, a molding method that utilizes thermal expansion pressure of elastomer is being considered as a method for molding large parts using simple tools.

0003

However, this molding method using the thermal expansion pressure of an elastomer has the disadvantage that it is difficult to control the pressure. That is, the basis for this argument will be shown by calculation below, but there was a problem in that excessive pressure was generated. The relationship between heating temperature and generated pressure in a block-shaped elastomer as shown in FIG. 2 can be expressed by the following equations 1 to 3.

0004

[Math 1]

[0005]

[Math 2]

[0006]

[Math 3]

[0007] Here, P: pressure, E: Young's modulus, ν: Poisson's ratio, ε: strain, α: coefficient of expansion, and ΔT: temperature difference. Using the above formula, calculate the case where the elastomer is confined in a mold and heated. In this case, εx = εy, εz=0
By putting

[0008]

[Equation 4] We obtain Px = Py = Pz = -1.0 x ΔT. Here, α=250×10-6/℃, ν=0.5,
E=40Kg/mm2 was used.

Now, if we set ΔT=100° C. in equation 4, we get P=100 Kg/cm 2 , but such a high pressure will damage the mold.

The object of the present invention is to solve these problems, and to provide a molding method that utilizes the thermal expansion pressure of an elastomer, which has high practical value and can maintain an appropriate pressure.

[0011]

[Means and effects for solving the problems] In order to achieve the above problems, as a result of intensive study on a method for controlling the above-mentioned excessive pressure, which has been a conventional problem in molding methods that utilize the thermal expansion pressure of elastomers, In a plastic product molding method that uses the thermal expansion of an elastomer as a molding pressure source, the thermal expansion coefficient is 150 to 300.
This led to the development of a method for molding plastic products in which a part of the elastomer in the range of x10-6/°C is molded in an unconstrained state. That is, through studies by the present inventors, we have come up with a mechanism that reduces the pressure generated by releasing the restraining lid as the trapped elastomer thermally expands.

This will be explained using formulas and numerical values based on the principle of the spring lid shown in FIG. The relationship between spring force and strain is given by equation 5.

[0013]

[Equation 5] Pz = Pzo-k (εz - εzo) where Pzo: initial pressure applied before heating, k: spring constant. By substituting Equation 5 into Equations 1 to 3 above, the pressure when the spring lid structure is used can be calculated. As a result of further various studies using this formula, the following conclusion was obtained. That is, if the spring constant is the same as that of the elastomer, the initial pressure is 3Kg/cm2, and ΔT=100℃, then P
An appropriate pressure of =7Kg/cm2 can be obtained.

[0014] In a plastic product molding method that utilizes the thermal expansion of an elastomer as a molding pressure source, the following method is available as a method for concretely implementing the above calculation results. That is, as shown in FIG. 1, a prepreg laminate 3 and an elastomer 4 are placed between a fixed lid 1 and a fixed mold 2, which are installed with no relative vertical displacement and with a predetermined gap between them.
A feature is that when the elastomer 4 is placed and heated, a part of the elastomer 4 (in FIG. 1, exposed circumferential parts 4', 4' in the gap between the upper and lower sides of the fixed lid 1 and the fixed mold 2) is used without being restrained. This is a molding method using an elastomer molded body. At this time, the thermal expansion coefficient of the elastomer 4 is 150 to 300 x 10-6/℃
It is preferable that the pressure is within this range because it provides a necessary and sufficient pressure source.

That is, according to the present invention, an appropriate molding pressure can be obtained by using the unconstrained portion of the elastomer as a spring.

[0016]

[Embodiment] Hereinafter, an embodiment in which the present invention is applied to the molding of a mast for a large racing yacht will be described in detail. The mast of a large competition yacht has a total length of approximately 34 meters. This product had to be molded in one piece because the compressive load was high and it was not possible to have a structure that connects it in the longitudinal direction. However, the current situation was that it was too long to be molded in an autoclave. At the same time, since weight reduction is important, high quality with a high fiber content of about 60 vol% and no internal defects is desired. Therefore, in vacuum bag molding, the molding pressure is 1Kg/cm2.
Therefore, the above-described molding method using the elastomer molded article of the present invention was applied.

[0017] The molding material is Pyrofil (Mitsubishi Rayon,
(registered trademark) MR40/#340 carbon fiber prepreg was used. As an elastomer, DAPCO (DAIRCR
AFT (registered trademark) silicone rubber was used. FIG. 4 is a cross-sectional view showing the schematic structure of the apparatus during mast molding for carrying out the present invention, in which 5 is a fixed lid, 6 is a fixed mold, 7 is the above-mentioned silicone rubber as an elastomer, 8 is a heater mat, and 9 is a prepreg laminate, 10 is a vacuum bag, 1
1 is a vacuum outlet, 12 is a reinforcing metal part, 13 is an overlay, and 14 is a fixture for the overlay 12. Under this configuration, heating was performed according to the following curing schedule to obtain a molded mast for a large racing yacht. 80° C. x 1 hr + 130° C. x 2 hr Here, since the silicone rubber 7 is large and external heating alone would impede heat conduction, a heater mat 8 was placed inside the rubber to serve as an auxiliary heat source. Furthermore, since reliability is further increased when the vacuum bag 10 is used in combination, a combined molding method was used.

As shown in FIG. 4, the molded mast is manufactured by dividing it into left and right parts, and after attaching various reinforcing metal parts 12 to the ends thereof, the divided ends are joined with an overlay 13 of carbon fiber reinforced plastic and molded into one piece. did. The resulting molded product had a thickness of about 18 mm at its thickest portion, but both the finished molded thickness and internal structure were good.

[0019] Although the above embodiment deals with the molding of a mast made of reinforced fiber plastic used for a large racing yacht, the present invention can be applied to molding not only reinforced fiber plastic but also other plastic materials. and
Furthermore, the molding can be applied to a wide range of products, including consumer goods, industrial products, aircraft-related parts, and other large structures.

[0020]

[Effects of the Invention] As is clear from the above explanation, the present invention is a molding method that utilizes the thermal expansion pressure of an elastomer, which was previously prohibited to use due to the generation of excessive pressure. This is a practically extremely useful molding method that can produce long fiber-reinforced plastic molded products using pressure without increasing costs.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of an apparatus configuration during molding, showing the molding principle of the present invention.

FIG. 2 is a model diagram showing pressure increase due to heating expansion of an elastomer block.

FIG. 3 is an explanatory diagram showing the principle of a spring lid.

FIG. 4 is a schematic cross-sectional view showing the configuration of a device used to form a mast for a large racing yacht, which is an embodiment of the present invention.

[Explanation of symbols]

1 Fixed lid 2 Fixed mold 3 Prepreg laminate 4 Elastomer 4' Side exposed portion 5 Fixed lid 6 Fixed mold 7 Silicone rubber molded body (elastomer) 8
Heater mat 9 Prepreg laminate 10 Vacuum bag 11 Vacuum opening 12 Reinforcing metal parts 13 Vacuum bag fixture 14 Overlay

Claims (5)

[Claims] Claim 1: A method for molding a plastic product that uses thermal expansion of an elastomer as a molding pressure source, wherein a part of the elastomer is molded in an unrestrained state, and the plastic product uses an elastomer molded body as a pressure source. molding method. Claim 2: The coefficient of thermal expansion of the elastomer is 150 to 3.
The molding method according to claim 1, characterized in that the temperature is in the range of 00x10-6/°C. [Claim 3] The initial pressure due to the elastomer is 3 kg.
2. The molding method according to claim 1, wherein the heating temperature difference is 100°C. 4. The molding method according to claim 1, wherein the plastic product is a mast of a large racing yacht made of fiber-reinforced plastic. 5. The molding method according to claim 1, wherein a vacuum bag method is used in combination.