JPH10183656A - Manufacture of manhole cover - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a cover made of plastic having a little weld, a high fracture strength and being light by a method wherein thin sheets made of plastic resin having continuous glass long fibers serving as a reinforcing material are laminated in a multilayer in forms for a cover and heated and pressurized for integral molding. SOLUTION: A number of sheets 1 made of plastic sealed in a swirl-form state with glass long fibers with a length of approximate 1000mm having a given glass percentage content and physical content, such as a tensile strength and physical properties, are arranged in a lamination state on the whole surface of a lower mold 2a of forms, and by pressurizing an upper mold 2b for integral molding to manufacture a manhole cover 3. The manhole cover made of long glass fibers as a fracture strength approximate two times as large as that of a manhole covet made of short glass fibers and by remarkably reducing the occurrence of a weld to the vicinity of a handle and the whole of a cover, the thickness of a manhole cover is reduced to a very low value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a manhole cover used in a place where a large load acts, such as a sewer, a septic tank, an underground storage tank, a water distribution box, and the like.
The present invention relates to a technique for manufacturing a lightweight, high-strength and inexpensive lid made of plastic.

[0002]

2. Description of the Related Art Conventionally, manhole covers are often manufactured by casting, but in recent years, lightweight plastic manhole covers using glass fiber as a reinforcing material have been used. With conventional plastic manhole covers, short glass fiber SMC
(Conventional SMC) or resin concrete has been used. However, in the conventional manhole cover made of SMC, a weld is generated, the strength of this portion is weak, and the breaking load as the cover is low.
It was difficult to use as a manhole cover in a place where a large load was applied.

[0003]

The problem to be solved by the present invention is to solve these problems of the prior art and to produce a lightweight plastic lid capable of reducing the occurrence of welds and increasing the breaking strength about twice. It is to provide a method.

[0004]

Means for Solving the Problems The constitution of the present invention which has solved the above problems is as follows: 1) A plastic resin thin sheet using continuous glass long fiber as a reinforcing material is laminated in a multilayered form in a lid frame, and this is heated. The method for manufacturing a manhole cover according to the above 2), wherein the continuous glass long fiber is in a swirl shape.

[0005]

According to the present invention, the use of continuous glass long fibers eliminates non-uniformity in strength and achieves uniform and high strength. As a result, it was possible to almost completely eliminate the occurrence of welds that greatly reduce the mechanical strength. by this,
The strength of the conventional short SMC lid could be improved to nearly twice. Particularly, a continuous glass long fiber curved in a swirl shape was effective.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION
A length of 0 mm or more and about 1000 mm is preferable. 25
Short glass fiber cut pieces of millimeters or less may be used in combination as a reinforcing material.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. A manhole cover 3 having a nominal diameter of 600 mm is provided with a glass content of 40%, a tensile strength of 13.2 kgf / mm ^{2 and a} bending strength of 24.0 k.
g / mm ² Long glass fiber L-SM about 1000 mm long
A large number of plastic thin sheets 3 each having a thickness of about 3 mm in which C was swirled were placed on the entire surface of the lower die 2a of the mold in a stacked state, and the upper die 2b was pressed to be integrally molded to manufacture. As a result, almost no weld was generated. The weld strength of this embodiment was nearly twice as high as that of the short fiber SMC using short glass fiber of 25 mm or less as a reinforcing material. FIGS. 2 (a) and 2 (b) show the results of a comparison of the production strength of this example with a manhole cover made of short glass fiber SMC. FIG. 2A is a strength test diagram of a manhole cover manufactured from the long glass fiber of the present embodiment, and FIG. 2B is a strength test diagram of a manhole cover manufactured using a known short glass fiber SMC. is there. As can be seen from this test diagram, the manhole cover manufactured from the long glass fiber L-SMC has a breaking strength almost twice that of the manhole cover manufactured from the short glass fiber SMC.

[0008]

As described above, according to the present invention, the manhole cover using continuous glass long fibers as the reinforcing material can significantly reduce the occurrence of welds near the handle and in the entire cover. Compared to the manhole cover manufactured in
The breaking load was nearly doubled. In addition, the bending strength was nearly five times and the flexural modulus was almost twice. Therefore, the thickness of the manhole cover can be made considerably thin.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a manufacturing process of the present embodiment.

FIG. 2 is a strength test diagram of a test piece of a product using continuous glass long fibers of an example and a test piece using conventional short glass fibers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thin sheet 2a Lower mold 2b Upper mold 3 Manhole cover

Claims (2)

[Claims] 1. A manhole cover manufactured by laminating a plurality of thin sheets of plastic resin using continuous glass long fibers as a reinforcing material in a mold of the cover, and heating and pressurizing the sheets to integrally mold them. Manufacturing method. 2. The method for producing a manhole cover according to claim 2, wherein the continuous glass long fibers are in a swirl shape.