Method for producing plastic ball valve

Abstract

The present invention relates to a manufacturing method of plastic ball valve, it is characterized by producing as the following steps: a. producing integrated spool which fixes and connects the valve bar and the valve ball into one unit; b, laying the valve ball of said integrated spool and the valve bar position connected with the valve ball in the die used for producing the plastic ball valve body; c. injecting the plastic material into the die used for producing the plastic ball valve body after the plastic material is heated and melted, cooling the plastic material in the die and modeling into plastic ball valve body, and the valve ball of integrated spool and the valve bar position connected with the valve ball is completely limited in the plastic ball valve body and can not be pulled out after the plastic ball valve body is cooled and shaped; d. connecting a plastic valve cover with through-hole on at least one open position of two side openings of plastic ball valve body, and linking the through-hole of plastic valve cover with the flow way in the plastic ball valve body. The invention is benefit for raising the products quality and extending the use life of products, and is facilitated the production of valve body.

Description

Technical field [0001] The invention relates to a manufacturing method of a plastic ball valve. Background technique [0002] Existing plastic ball valves generally adopt one of the following methods to manufacture: [0003] (A). For example, a buried polyethylene plastic ball valve and its packaging method disclosed in Chinese Invention Application No. 03153661.1. The plastic ball valve adopts a split structure of the valve ball and the stem. In this way, after the parts are formed, the valve stem and The valve balls are put into the valve body respectively for assembly. This technology is one of the commonly used and feasible solutions for the production of existing plastic ball valves. However, the drawbacks of this solution are also obvious. That is, during the long-term use of this kind of ball valve, due to polyvinyl chloride, polypropylene or polyvinyl chloride, polypropylene or polyvinyl chloride. The strength of common plastic materials such as ethylene is inherently low...

AI Technical Summary

Problems solved by technology

However, the defect of this scheme is also a technical problem that has puzzled the plastic ball valve industry for a long time, that is, the problem that the plastic valve body has too much grip on the valve ball (correspondingly, the friction force is too large when the relative movement between the two is caused)

Careful analysis shows that the above-mentioned problem of excessive holding force of the plastic valve body on the valve ball is due to the following two reasons: ①. In this plastic ball valve, there is no separate setting that is compatible with the spherical surface of the valve ball and forms a seal. The auxiliary ball seat, when the ball valve is in the closed state, completely depends on the inner wall of the plastic valve body and the surface compatible with the valve ball of the integrated valve core to form a sealing pair with the outer surface of the valve ball, which requires When injecting molds and injection molding valve bodies, it is necessary to make the inner surface of the molded plastic valve fit closely with the outer surface of the valve ball, and this tight fit is a kind of tight fit between the inner surface of the valve and the outer surface of the valve ball. Large-area tight fit, not the ring fit required by the usual ring-shaped sealing pair (for the ball valve, it only needs to form a ring-shaped sealing pair when it is closed)

Corresponding to the above-mentioned large-area tight fit, the kinetic friction between the valve body and the valve ball increases significantly and unnecessarily, resulting in difficulty in the rotation of the valve core

②. When the plastic valve body is made by hot-melt injection molding, in order to realize the large-area close fit between the inner surface of the valve and the outer surface of the valve ball and form a sealing pair, it is necessary to make the valve body being injection-molded The inner wall of the valve body and the outer surface of the valve ball are in a bonded state. However, after the hot-melt injection molding is completed, the molded plastic valve body will shrink to a certain extent due to gradual cooling, and this shrinkage will increase the force between the valve body and the valve core. Clamping force, and correspondingly further increase the friction between the inner cavity of the plastic valve body and the outer surface of the valve ball, making the opening and closing of the ball valve more inconvenient, and even the integrated valve core is extremely difficult to rotate.

But, on the basis of this assumption, the following defects still occur in this plastic ball valve: 1., because the aperture at the place where its body is connected to the bonnet and the through hole where the valve stem passes through the body are relatively large (as mentioned above, this is for the convenience of Put the connected valve stem and valve core into the body), the large through hole on the body has a large part of the redundant space that needs to be filled, which causes the waste of materials when manufacturing the valve body, and at the same time, it is different from the existing Compared with other ball valves with the same nominal diameter (DN), the above-mentioned oversized through hole will also make the shape of the valve body too large, which will cause inconvenience in installation and narrow application range.

②. In this product, the body and the two bonnets are threaded. Due to the creep property of plastic materials, when the body and the two bonnets are made of plastic materials, the connection between the body and the two bonnets The threaded connection will naturally loosen during long-term use, so that the three-piece split valve body will leak (from this point of view, this product is not suitable for making plastic ball valves)

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