JPH0637935B2 - Method for forming bellows with fluorine film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a bellows with a fluorine film used in expansion joints and flexible joints.

(Prior Art) Expansion pipe joints and flexible joints play a role of absorbing thermal expansion and bending load of pipes and the like, and bellows-shaped bellows are often used.

This bellows is made of metal material such as stainless steel. In order to prevent chemical action and adhesion of fluid by internal fluid, fluorine or bellows pipes for acid, alkali, chemicals, pure water, food etc. The one with the fluorine coating on the inside is used. In addition to the above, fluorine has excellent weather resistance and electrical characteristics, and has various advantages.

(Problems to be Solved by the Invention) However, in order to provide sufficient pressure resistance, the bellows must be thick. However, the unit cost of the fluororesin is high, and if the whole thick bellows is made of fluorine, it is extremely expensive.

On the other hand, when fluorine is coated on the inner surface of the bellows by a spraying method, it is advantageous in terms of cost, but pinholes are easily generated, and the fluorine film peels due to expansion and contraction or bending of the bellows, or a complicated shape. It is difficult to form and apply a uniform film thickness on the part.

(Object of the Invention) The present invention has been made in view of the above circumstances, and an object thereof is to form a fluorine film having a constant film thickness even in a portion having a complicated shape and without causing peeling or pinholes. It is to provide a method for forming a bellows with a fluorine film.

(Means for Achieving the Object) In order to achieve the above object, in the present invention, a biaxially stretchable fluorine film is adhered to the inner surface of a shell for bellows, and then this shell is formed into a bellows shape. There is.

(Operation) By adopting the above-mentioned adhesion means, the fluorine film is surely adhered to the inner surface of the bellows, and the film thickness of the fluorine film becomes uniform even after the bellows molding due to the biaxial stretching property, and no pinhole is generated. Also, since the film is bonded at the stage of the raw tube, there is no problem of conforming to a complicated shape.

(Embodiment) FIG. 1 shows a bellows type pipe joint 10 to which the forming method of the present invention is applied. The pipe joint 10 includes a bellows 11, a flange 12, an end pipe 13, and a blade 14.

The bellows 11 is a bellows-shaped stainless pipe, and absorbs expansion and contraction force and bending from the pipe. Both ends of the bellows have a straight pipe shape, and the ends 15 of the bellows are overlapped with each other to form the flange 1.
It is pressed against the outer surface of 2. A cylindrical end pipe is fixed to the flange 12 by welding, and a pipe connecting hole 1 is provided on the outside.
2a is provided. Further, the flange 12 is sandwiched between the end portion 15 and the peak portion 16 of the bellows 11, and the end pipe 13 includes a straight pipe portion of the bellows and two blade tightening rings 17a,
A bushing 18 made of fluororesin is heat-pressed to the end surface of the flange 12 and the inner surface of the bellows held by 17b.
Also serves as a gasket for the flange.

The outer surface of the bellows 11 is covered with a blade 14 for protection, and the blade 14 is formed by knitting an elongated stainless strip. The blade 14 is fixed to the outer circumference of the end tube 13 by tightening rings 17a and 17b. When the pipe joint 10 is used, the outer surface of the blade 14 may be wrapped with an anticorrosion tape or a heat insulating material.

A fluorine film 20 is attached to the inner surface of the bellows 11 with an adhesive 19. This fluorine film 2
0 has a property of being chemically inert and plays a role of protecting the bellows 11 made of stainless steel from an internal fluid. Further, there are various advantages such as preventing the internal fluid from adhering to the inner surface of the bellows and preventing the fluid from being contaminated. Further, the pressure resistance of the pipe joint 10 is secured by the stainless bellows 11 and the blade 13.

As shown in FIG. 2, this fluorine film 20 is attached to the inner surface of the base pipe 11a with an adhesive 19 at the stage of the base pipe 11a before forming the bellows. Therefore, as compared with the case where the bellows-shaped bellows 11 is attached, the fluorine film 20
Can be easily formed.

Next, this blank tube 11a is formed into a bellows shape as shown in FIG. In this figure, one end of the blank tube 11a is closed by a plug 21, and the outer surface of the plug 21 is the ram 2
It is pressed and supported by 2. Further, a cylindrical cored bar 23 is inserted inside the raw tube 11a, and a hole 24 penetrating in the axial direction is formed in the center of the cored bar 23.

On the other hand, a pair of metal molds 25, 26 abut on the outer surface of the raw pipe 11a, and the metal molds 25, 26 face each other with a notch 27,
28 is provided.

Therefore, when the high pressure fluid is passed through the hole 24 of the cored bar 23 in the state of FIG. 3 to pressurize the inside of the raw pipe 11a, the outer surface of the raw pipe rises as shown by an imaginary line. Next, when the die 26 is moved to the left side in the figure, one ridge is formed on the outer surface of the raw pipe 11a. After that, set the positions of the molds 25, 26 and the core metal 23 to 1
When the pitch is shifted and the above operation is repeated, the bellows-shaped U
The bellows 11 is completed.

In addition, in order to make the peaks into the Ω shape, a step of compressing the raw tube 11a by a predetermined length in the axial direction may be added.

At this time, since the fluorine film 20 is firmly attached to the inner surface of the bellows 11 with the adhesive 19, there is no possibility of peeling during the molding process. The fluorine film 20 is biaxially stretchable, that is, stretchable in the length and width directions, so that the film 20 is uniformly stretched during the bellows molding. With this configuration, the fluorine film 16 can be distributed along the inner peripheral surface of the film even if the bellows-shaped processing is performed after the molding, and pinholes, cracks and the like are not generated.

The bellows molding method shown in FIG. 3 is an example, and other molding means can be adopted.

(Effects of the Invention) As described in detail above, in the present invention, after the biaxially stretchable fluorine film is adhered to the inner surface of the shell for bellows, the shell is formed into a bellows shape, and thus peeled. A uniform fluorine film without pinholes and cracks can be formed on the inner surface of the bellows. .

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of a bellows type pipe joint having a fluorine film formed on the inner surface, FIG. 2 is a vertical sectional view of a fluorine film bonding step, and FIG. 3 is a vertical sectional view of a bellows molding step. . 10 ... Bellows type pipe fitting, 11 ... Bellows, 11a
…… Element tube, 19 …… Adhesive, 20 …… Fluorine film.

Claims (1)

[Claims] 1. A method for forming a bellows with a fluorine film, which comprises bonding a biaxially stretchable fluorine film to an inner surface of a bellows tube, and then forming the tube into a bellows shape.