The present invention relates to a method of producing a fiber reinforced bent resin pipe by an automatic molding method of filament winding.
Conventionally, a fiber reinforced bent resin pipe is manufactured by abutting half-split pipes of fiber reinforced resin and adhering them together, or by cutting a straight fiber reinforced resin pipe along a plane crossing the axis thereof into portions each having a trapezoidal shape when viewed as the top view thereof and abutting and adhering them together. In either method, hand lay-up forming is employed for adhering the pipes.
The workability of these conventional methods is therefore very poor. Further, the resultant reinforced resin pipe is inadequate in strength, and has a poor appearance.
In order to improve these problems, it has been proposed to initially manufacture a fiber reinforced straight resin pipe and then to bend it to a predetermined curvature as described in Japanese Examined Patent Publication No. 21769/1984. However, this method has disadvantages in that the resin employed is limited, in that strict control of the bending conditions is necessary, in that the bend radius is limited and pipes to have a curve of very small radius cannot be formed by bending, in that the pipe is apt to be flattened during the bending, and in that the resultant pipe is apt to retain residual stress and to be deformed during use.
It is also known to directly manufacture a bent pipe by the filament winding molding method. That is, a resin-impregnated reinforcing filament is wound on the circumference of a mandrel having a curved configuration, and, after the resin has cured, the mandrel is removed. In this method, since the mandrel is removed from a molded product formed on the circumference thereof, it must have such a structure that it can be disassembled into small parts. This makes the mandrel construction complicated and expensive. Moreover, the inner surface of the molded product is apt to have fins at a position corresponding to the seam of the mandrel parts. This method also necessitates a filament winding machine having a complicated structure for winding the continuous fiber on the curved mandrel at uniform winding angle.