JPS61266234A - Manufacture of bent square pipe made of fiber reinforced plastic - Google Patents

Abstract

PURPOSE:To prevent deviation of fibers, accompanied by outflow of resin, as well as the thinning of corner sections and facilitate the bending process of the pipe by a method wherein specified prepregs are employed at the corner sections of an inner layer while wet type winding are employed at the other sections of the inner layer. CONSTITUTION:The semi-cured prepreg layer 1 of resin impregnated fibers, orientated with the angle of 0 deg. with respect to the lengthwise direction of the pipe, and the wet layer 2 of non-cured resin impregnated fibers, orientated with the angle of 0 deg. with respect to the same direction, are combined to form the inner layer of the pipe. After forming the layers 1, 2, a high angle helical layer 3 is wound by the wet type winding method. A forming mold 4, assembling a plurality of thin metallic plates or the like in the direction of thickness of the plate, absorbs the difference of bending radii upon bending the composite layer including the forming mold after forming the composite layer 5 by sliding the thin plates relatively. On the other hand, pulling resistance of the forming mold upon releasing the mold can be reduced by pulling one sheet of the thin plate off at first. The composite layer 5 is formed on the forming mold 4, is bent in the direction of the thickness of the plates so as to obtain a predetermined curvature by loading a bending stress thereon, and the impregnated resin is heated and cured by holding the composite layer 5 as it is, thereafter, the forming mold is removed to obtain the pipe having square section.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a rectangular bent pipe made of fiber reinforced plastics (FRP). This method is effective in cases where the method includes a step of heating and curing while giving a curvature using a bending means.

[Conventional technology and its problems]

Pipe structural materials are usually required to have rigidity in the longitudinal direction.

In order to meet this requirement with FRP manufactured materials, it is necessary to orient the reinforcing fibers in two directions: the longitudinal direction and the circumferential direction.
For this reason, in the manufacture of FRP pipes, a fiber orientation of 0° is selected for the inner layer and a fiber orientation at a high angle for the outer layer with respect to the longitudinal direction.

However, when using a wet winding method in which resin-impregnated fibers are wound in an uncured resin state, if a mold with a square cross section is used, tension is applied to the fibers of the outer layer only at the corners of the mold. There is a drawback that the o0-oriented inner layer fibers are pushed away, and the corners of the resulting pipe become thin, with no 0°-oriented fibers, as shown in FIG. In particular, this phenomenon becomes remarkable when the fiber is wound with a mold and a bending means is used to impart curvature to the fiber after winding it around the mold.

On the other hand, dry winding involves wrapping prepreg in a semi-cured state after impregnating it with fiber paste resin.
It has the advantage that the corners of the pipe are less likely to become thin because the resin does not flow easily.

However, even with this method, if a bending means is used to give a curvature after winding is completed, the semi-cured state of the resin prevents the fibers from shifting appropriately, and the resin is sticky. There are drawbacks such as wrinkles and bending of the fibers during the bending process.

It should be noted that these problems cannot be fundamentally solved even if efforts are made such as rounding the corners of the mold.

[Means for solving problems]

The present invention was made with the aim of eliminating the above-mentioned problems, and is a method characterized by the combined use of prepreg and wet winding. That is, in the method including the above steps, the corners of the inner layer, which has fiber orientation of 0° with respect to the longitudinal direction of the pipe, contain at least o0-oriented fibers, and the fibers are impregnated with a resin. By forming with unidirectional prepreg in a late-cured state, fibers are prevented from shifting due to resin flow, and wet winding is used for other parts to prevent thinning of corners and reduce the bending process. The feature of the present invention is that it is made easy.

〔Example〕

An example of the method of the present invention will be described below based on the accompanying drawings.

Reference numeral 1 in FIGS. 1 and 2 indicates a prepreg layer containing O0-oriented fibers with respect to the longitudinal direction of the pipe, and 2 indicates a wet layer in which O0-oriented fibers are impregnated with uncured resin. The combination of layers forms the inner layer of the pipe. 3 is a high-angle helical layer that is the outer layer of the pipe, and layers 1 and 2
After forming, it is wrapped on top using a wet winding method.

4 is a mold formed by assembling a plurality of thin plates such as metal in the thickness direction, and facilitates the bending process and demolding after forming the composite layer 5 consisting of layers 1, 2, and 3. It is. That is,
When bending the composite layer including the mold, adjacent thin plates slide relative to each other to absorb the difference in bending radius, improving bendability, and when demolding, one of the thin plates is pulled out first. This reduces the pull-out resistance of the mold.

The prepreg layer 1 to be placed along the corner of this mold 4 is 0°
In addition to the prepreg containing only oriented fibers, it may also be a so-called cross-reinforced prepreg that combines 0° oriented fibers and fibers orthogonal thereto, and in this case, the effect of preventing the fibers from slipping is further enhanced.

Now, after forming the composite layer 5 on the mold 4 as shown in Fig. 1, set both ends of the mold in a bending machine and apply bending stress in the thickness direction of the thin plate to form the shape shown in Fig. 3. Next, the composite layer 5 is bent to a predetermined curvature along with the mold, and then the impregnated resin is heated and cured while maintaining the curvature, and after curing, the mold is removed to obtain the desired product, that is, a pipe with a square cross section.

Although the illustrated method is for manufacturing a pipe with a square cross section, the present invention can also be applied to manufacturing polygonal pipes other than square by changing the cross-sectional shape of the mold.

〔effect〕

According to the method of the present invention described above, since the prepreg is used at the corners of the inner layer with fiber orientation Oo with respect to the longitudinal direction of the pipe, the tension of the fibers of the outer layer acts strongly on the corners. Also, the resin is difficult to flow, the o0-oriented fibers are prevented from shifting, and therefore, the corners of the pipe do not become thin, and a product that exhibits stable proof strength against stress concentration can be obtained.

In addition, since prepreg and wet winding are used together, the wet winding part is easy to slip against the bending stress during the bending process, making the bending operation easy and preventing the fibers from wrinkling or loosening.

[Brief explanation of drawings]

Figure 1 is a perspective view of the prepreg layer, wet layer, and high-angle helical layer formed on the mold, and Figure 2 is the X-X
FIG. 3 is a perspective view of the pipe under bending stress, and FIG. 4 is an end view of the pipe obtained by the conventional method.

Claims (2)

[Claims] (1) After sequentially forming resin-impregnated fiber layers on a mold with a rectangular cross section, with the inner layer having a fiber orientation of 0° with respect to the longitudinal direction of the pipe and the outer layer having a fiber orientation of a high angle, using a bending method, A method for manufacturing a rectangular curved pipe made of fiber reinforced plastics, which is heated and cured while giving a predetermined curvature, and then demolded, wherein the corners of the inner layer include fibers oriented at least at 0°, and the fibers are impregnated with a resin. 1. A method for manufacturing a rectangular bent pipe made of fiber reinforced plastics, characterized in that it is formed from a unidirectional prepreg that is semi-cured after being cured. (2) Claim No. 1, characterized in that the prepreg contains fibers orthogonal to fibers oriented at 0°.
) A method for producing a rectangular bent pipe made of fiber-reinforced plastics.