METHOD FOR FORMING FLUOROPLASTIC ARTICLES

Abstract

The present invention relates to a method for forming fluoroplastic article, comprising inner and outer fluoroplastic layers and a metal meshwork, the metal meshwork being arranged between the inner and outer fluoroplastic layers, characterized by the meshwork can be stretched and compressed in the axial direction.

Description

FIELD OF THE INVENTION

The present invention relates to a fluoroplastic article, particularly to a fluoroplastic article with liner made of metal meshwork.

DESCRIPTION OF THE RELATED ART

It has well known that fluoroplastic, particularly polytetrafluoroethylene plastic (briefly to say, F4 or PTFE) is used as liners of steel members such as anticorrosive tubes, towers and vessels. When an article made of F4 is used as liners of a steel member, due to a high difference of thermal coefficient of expansion between the article and the steel member, usually they will be destroyed during using. Thus, it has restricted the wide use of this new material in anticorrosive fields. Therefore, the inventor has proposed a F4 liner with metal web laid in it, such that the excessive expansion of the anticorrosive article made of F4 gets restricted during being heated, so as to increase the life of the F4 liner. But the grids of the metal web in the above solution are invariable square one, that is, the wire of the web is fixedly connected with each other, so the metal web can't be stretched and compressed optionally, as shown in FIG. 1. There are two shortcomings existing in the web with this structure. 1) Since the grids of the metal web can't be stretched and compressed, when the fluoroplastic article is placed into a tube for example and is expanded to be flanged at the two ends, the metal web in the fluoroplastic article can't be flanged together with the fluoroplastic layer. Thus, the quality and performance of the fluoroplastic article are deteriorated. 2) In the winding process during producing the fluoroplastic article, the metal web with above structure can merely be laid outside of the fluoroplastic belt, but can't be made into meshwork and placed in the fluoroplastic layers. Because the diameter of the meshwork with this structure is not stretchable and compressible optionally and the meshwork is difficult to abut against the fluoroplastic inner layer closely, when the fluoroplastic belt is winding outside of the inner layer, the web will distort. When the article is sintered at a high temperature, since the F4 belt, metal web and glass belt can't be pressed against each other closely, the inner pressure due to the expansion is insufficient, and the metal web will disorder and displace. Thus, the finished articles will have a low density and there will be small holes in the structure. At the same time, these articles will have a trend to crack and will have a high ratio of defective and waste products.

SUMMARY OF THE INVENTION

The problem to be solved of the present invention is to provide a fluoroplastic article with a liner made of metal meshwork. It can overcome above shortcomings arising in prior fluoroplastic articles, whose liners are made of metal web with fixed grids.

The fluoroplastic article according to the invention is composed of inner and outer fluoroplastic layers and a metal meshwork. The metal meshwork arranged between the inner and outer fluoroplastic layers can be stretched and compressed in the axial direction.

In order to stretch and compress metal meshwork in the axial direction, the grids of the metal meshwork have variable rhombic shape. They are formed by interweaving metal wires or through welding metal webs with stretchable and compressible rhombic grids.

The advantage of the invention is set forth in the following. 1) Since the metal meshwork is stretchable and compressible, it can be compressed according to the diameter of the inner layer of the wound fluoroplastic article. As the result of being compressed, the diameter of the meshwork extends to be larger than that of the inner layer of the fluoroplastic article. Then, the inner layer of the fluoroplastic article is sheathed by the compressed meshwork. The latter is stretched and the diameter gets small. In this way, the meshwork abuts against the outside of the inner layer. Next, the fluoroplastic outer layer is wound around the meshwork continuously. During winding, the grids of the metal meshwork vary with the state of winding and forces. Thus, the metal meshwork is arranged between the inner and outer layer of the fluoroplastic article submissively, neatly, normally and uniformly without any disorders and displacements. Thereby, both quality and yield of articles are improved. 2) Since the diameter of the meshwork is variable, when the fluoroplastic article with the metal meshwork is lined in a metal member, the metal meshwork can be flanged together with the fluoroplastic layer. Therefore, both quality and performance of the member are improved. 3) As the force applied to different parts of the meshwork is uniform, the article doesn't deform at a high temperature. 4) Since the product of the diameter and the length of the meshwork is a constant, during producing and using, the meshwork will elongate longitudinally and the diameter will expand in the transverse direction with the rise of temperature. Since the tendency to elongate longitudinally and the tendency to expand transversely are restricted with each other, both the length and the diameter of the meshwork can't change. Thus, the performance of expanding with heat and contracting with cold of the article is in an optimum state. 5) Since the metal meshwork of the article is stretchable, during winding or being sintered at high temperature, the meshwork never displaces and will abut against inner and outer fluoroplastic layers closely. Thus, the problem arising by metal web with invariable grids is dissolved absolutely, and the sintered article has a high density and strength, and a good quality and a high success ratio as well. Meanwhile, the finished article whose surface is smooth also has no blowholes or cracks.

Detailed description of exemplary embodiments will be described in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the square web with fixed grids, which is used in prior fluoroplastic articles.

FIG. 2 is a schematic view of the metal meshwork according to the invention, which has variable rhombic grids.

FIG. 3 is a schematic view of the metal meshwork in FIG. 2, which is in the compressed state.

FIG. 4 is a schematic view of the metal meshwork in FIG. 2, which is in the stretched state.

FIG. 5 is a schematic view of the change of metal meshwork according to the invention in the flanged portion, this portion is formed by the metal meshwork engaged with a tube.

FIG. 6 is an section view taken from arrow A-A in FIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The embodiment shown in FIG. 2, FIG. 5 and FIG. 6 is a fluoroplastic article with a metal meshwork. It is used as liners of metal tubes and composed of inner and outer fluoroplastic layers 1 and a metal meshwork 2. The metal meshwork 2 is arranged between the inner and outer fluoroplastic layers. The grids 3 of the metal meshwork 2 have variable rhombic shape and can be formed by interweaving metal wires. They also can be made through welding metal webs with stretchable and compressible rhombic grids. The metal meshwork with such a configuration can be stretched and compressed in the axial direction.

The above fluoroplastic articles with metal meshwork can be made by following processes: (1) A thin fluoroplastic (e.g. F4) belt is wound around a stainless steel mold back and forth until the desired thickness reaches, so as to make the inner layer of the article; (2) The metal meshwork which is compressible in the axial direction is compressed, so that the diameter of the meshwork is larger than that of the fluoroplastic inner layer. Then, the fluoroplastic inner layer is sheathed by the compressed meshwork. The latter is stretched and the diameter of it gets small. As the result, the meshwork abuts against the fluoroplastic inner layer closely; (3) The thin fluoroplastic belt is wound around the metal meshwork until the desired thickness reaches, so as to make the outer layer of the article; (4) The outer layer is closely strapped by a glass belt; (5) The strapped fluoroplastic prefabricated article is placed into an oven. The article is finished after being sintered in the oven. The temperature of the sintering oven may be set according to the different composition of the fluoroplastic. When F4 plastic is used, The temperature of the oven is about 380° C.

Claims

1. A method for producing a fluoroplastic article, having inner and outer fluoroplastic layers and a metal meshwork, the metal meshwork being between the inner and outer fluoroplastic layers, and wherein said meshwork is stretchable and compressible in the axial direction, comprising: (1) winding a thin fluoroplastic belt around a stainless steel mold back and forth until the desired thickness is reached, so as to make an inner layer of the article;(2) compressing the metal meshwork in axial direction, so that the diameter of it is larger than that of the fluoroplastic inner layer, after the fluoroplastic inner layer is sheathed by the compressed meshwork, the latter is stretched and the diameter is made smaller, such that the meshwork closely abuts against the fluoroplastic inner layer;(3) winding the thin fluoroplastic belt around the metal meshwork until the desired thickness is reached, so as to make the outer layer of the article;(4) closely strapping the outer layer with a glass belt;(5) placing and sintering the strapped fluoroplastic article in an oven where it is to form the finished article.