JPH0985888A - Stainless steel tube compounding fluororesin with surface layer and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily smoothen the unevenness of the rough surface while utilizing the corrosiveness of a passivated film by forming a fluorine resin film on the passivated film of the uneven part of the rough surface generated upon pickling of the surface of a solution treated stainless steel. SOLUTION: A fluororesin is formed on the uneven part of the rough surface of the passivated film on the surface of a solid solution treated stainless steel tube. For example, the fluororesin film of the quantity which can cover the surface area of the tube 1 in the thickness of about 30μm is coated in the tube 1 by air spraying, predried at 90 deg.C for 30min, then baked at 280 deg.C for 30min in an electric furnace, and then water-cooled. This is rolled by a roller 4, the surface layer of the fluorine resin film is compressed, densified to thickness of 15μmRmax 0.2 and pencil hardness of 4H, smoothened, kneaded to the uneven part of the rough surface of the passivated film to be coupled by stronger force.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to pharmaceuticals, foods, semiconductors,
The present invention relates to a stainless steel pipe having a composite surface layer of a fluororesin having excellent corrosion resistance, chemical resistance, and abrasion resistance, which is used for piping of various manufacturing plants such as dyeing, and a manufacturing method thereof.

[0002]

2. Description of the Related Art 18Cr-8Ni (that is, SUS304), which is a typical example of non-rust steel, that is, stainless steel, will be described. The solid solution heat treatment of heating SUS304 to a temperature of 1000 ° C. or higher and then rapidly cooling it It has a magnetically complete austenite structure, and provides excellent corrosion resistance and maximum ductility.

The corrosion resistance of this stainless steel is 0.0
It is based on passivation forming an oxide protective coating with a thickness of 5 to 0.10 μm.

In order to exert the maximum corrosion resistance on the surface of the stainless steel pipe itself, the inner surface of the stainless steel pipe is precisely cold drawn, subjected to solution heat treatment, pickled, electrolytically polished or chemically treated. By polishing, the surface is smoothed and, at the same time, a passivation film is formed on the surface.

The surface roughness of the irregularities covered with this electropolished passivation film is usually the maximum height (Rmax) of the rough surface.
It is 0.3 to 0.7 μm.

In electrolytic polishing or chemical polishing, a method of smoothing and brightening the surface of stainless steel by dissolving and removing a larger amount of fine convex portions of the rough surface of the stainless steel than fine concave portions Therefore, the surface impurities can be dissolved and removed, and at the same time, the surface can be covered with the passivation film.

On the contrary, a large number of deep pinholes and pitting corrosion are generated by dissolving and removing relatively large surface roughness and scratches as well as segregation of impurities and the like which are concentrated on the surface of the stainless steel material. However, there is a big drawback that it cannot be removed and it remains as it is.

Therefore, in order to obtain a smooth surface, it is necessary that the surface of the stainless steel to be electropolished is previously removed by mechanical grinding to remove the deep pinholes or the like and highly polished. However, there was a big drawback that the cost was extremely high.

A further major drawback is that the corrosion holes generated by the dissolution of the segregation of the impurities concentrated in the stainless steel material may generate pinholes as deep as 200 μm, which are completely ground and removed. Not only is it difficult and expensive because it requires a large amount of grinding, but it is extremely difficult to detect whether or not it can be removed over the entire inner surface of the stainless steel pipe.

That is, in order to inspect a stainless steel pipe that has been conventionally electrolytically polished for scratches, a light for inspection is irradiated from one end of the pipe, and the inside of the pipe is visually inspected from the other end. Since it is inspected, scratches and pinholes in the stainless steel pipe forming the bright surface are
It is impossible to check 0%.

Further, the defective product thus selected has a drawback that it cannot be regenerated and therefore the yield is deteriorated and naturally expensive.

[0012] However, since the above-mentioned surface treatment makes the stainless steel pipe itself have the highest corrosion resistance that can be carried out, it is too expensive, so that it can be used at low cost or in a lower quality application. There is something to be done.

That is, a stainless steel pipe generally used in the food industry and the like is used as a stainless steel sanitary pipe, which is 400 specified in JIS G 3447.
No. surface finish (Rmax 2-3 μm) is available.

Explaining the surface finish of the stainless steel sanitary pipe specified in JIS G 3447, it is specified that "the surface finish pipe is, in principle, finished by polishing the inner and outer surfaces of No. 400". The pipe used as the material of this stainless steel sanitary pipe is heat-treated and pickled, and rough surface irregularities of Rmax 8 to 30 μm are usually formed on the surface.

The inner surface of the stainless steel pipe was roughly ground using sandpaper to which alumina abrasive grains were fixed, and then 4
The process until the puffing of No. 00 is usually 3-4 steps from the rough polishing with No. 80 sandpaper which roughens the surface of the stainless steel pipe to the finishing of No. 150 → 240 → 400 No. Is needed.

The cost of polishing the inner surface of this stainless steel pipe is such that the environment is called a 3K workplace, dust pollution occurs, and the surface quality is not uniform due to uneven wear of the abrasive paper. It is difficult to remove the pinholes, and it is extremely difficult to remove the pinholes.

As another means for surface-treating the inner surface of a stainless steel tube which is completely different from the conventional one, there is coating or lining with a fluororesin film. In order to maximize the performance of this fluororesin, it is extremely important that the fluororesin film has no pinholes. For this reason, when lining the fluororesin, a pinhole-free fluororesin tube or sheet should be inserted or attached in advance, or a fluororesin primer,
The surface treatment of a fluororesin film without pinholes is performed by applying multiple layers of liquid or enamel to a predetermined thickness.

That is, when the surface condition of the inner surface of the conventional stainless steel pipe is displayed by the maximum height of surface roughness (Rmax),
The surface of the stainless steel pipe is subjected to the following treatment.

1. Fluororesin tube film Rmax 0.1 μm 2. Fluorine resin coated baking film Rmax 5 to 20 μm 3. Smoothed by machining and electrolytically polished Rmax 0.3 to 0.7 μm 4. No. 400 finished by mechanical polishing Rmax 2 to 3 μm 5. No. 180 finished by mechanical polishing Rmax 5-8 μm 6. Passivated film as it is Rmax 8 to 20 μm 7. Passivation film with segregation holes Rmax20-200 μm

Polishing work with sandpaper in mechanical polishing is said to be typical of 3K, that is, dirty, tight, and dangerous. Abrasive grains of sandpaper, powder of puff, etc. become a large amount of dust, dust, etc. Not only does it disperse in the room and adhere to the whole body of the worker and invade the respiratory organs to impair health, but when the abrasive grains of the sandpaper are not completely wiped off from the product, this is in the middle of polishing or after polishing stainless steel. There is a big drawback that it adheres to the inner surface of the steel pipe and scratches the finished surface of the soft stainless steel pipe, ruining the product.

Further, the greatest drawback of this mechanical polishing is that the passivation film formed on the surface of the bent-angle stainless steel pipe is removed by removing the rough surface.

Further, the electrolytic polishing has a major drawback that the cost is several times higher than that of the mechanical polishing.

Furthermore, the coating film of fluororesin, which is a completely different surface treatment for the inner surface of stainless steel pipe, has a limitation on the fluororesin disversion and baking thickness of the enamel, and a completely pinhole-free structure can be obtained. Therefore, there was a big drawback that repeated coating was required 2 to 4 times.

Therefore, the conventional fluororesin film treatment of a stainless steel pipe is extremely expensive and has been carried out only for particularly strict application purposes such as chemical resistance. Therefore, there has been no stainless steel pipe having excellent smoothness and corrosion resistance at low cost.

[0025]

The problem to be solved by the present invention is to remove the passivation film having an effect on the corrosion resistance by mechanical polishing. It is to use for. The main purpose is to smooth the rough surface irregularities satisfactorily while taking advantage of the corrosion resistance of the passivation film.

[0026]

Means for Solving the Problems The present invention basically comprises:
This is achieved by compounding a fluororesin with the rough surface irregularities of the passivation film on the surface of the stainless steel pipe. Further, by rolling the convex and concave portions on the surface of the stainless steel pipe compounded with the fluororesin with a roller, the fluororesin film on the surface is compressed to make a dense structure and smooth, and at the same time, the passivation film and the fluororesin are formed. This is achieved by strongly binding and.

The present invention does not have the conventional surface treatment of a stainless steel pipe for a fluororesin film alone or a stainless steel alone for pursuing an excellent one. Instead, by combining both the passivation film and the fluororesin film on the surface layer of the stainless steel pipe, it has an excellent smooth surface and excellent corrosion resistance, taking advantage of the advantages of both The stainless steel pipes that have been produced are provided at a low price.

More specifically, the passivation film has a rough surface and pinholes as described above, but these are left as they are, while the fluororesin coating itself is formed. As already mentioned, there are pinholes, but by applying a fluororesin coating that may lead to this pinhole, it is attempted to significantly reduce both pinholes. This is the basic technical idea of the invention. That is, even with a film having pinholes, one of the purposes is to double up the films so that one of the pinholes is closed and the number of pinholes is significantly reduced.

The fluororesin used in the present invention is not limited to the examples, and fluororesins and fluororesins having melt fluidity, powders, pastes, disversions, and enamel are all applicable. Further, fluorocarbon resin, glass fiber, carbon fiber, C, Al ₂ O ₃ , SiC, TiC, MoS, pigment,
Others can be blended as needed.

[0030]

The present invention will be described in more detail with reference to the following examples, but it goes without saying that the present invention is not limited to these examples. Further, in this embodiment, the same components are designated by the same reference numerals and the description thereof will be omitted.

The stainless steel pipes of the examples were 18Ni-8Cr or SUS304 manufactured by electric resistance welding.
A stainless steel pipe with dimensions of outer diameter x wall thickness x length (38.1 x 1.2 x 4.000) produced by cold drawing at 10 ° C or higher is rapidly cooled and solidified. Heat treatment was performed, and the black skin (oxide film) generated by this heat treatment was removed by pickling.

[0032]

EXAMPLE 1 As shown in FIG. 1, a stainless steel pipe 1 has a passivation film 2 on the surface which forms a rough surface with Rmax of 15 μm. "Polyflon TFE Toughcoat Enamel TC-7400" (hereinafter TC-740) manufactured by Daikin Industries, Ltd. was placed in a tube cleaned by pickling, neutralizing and washing with water.
(Abbreviated as 0), and after fully immersing the inner surface of the tube 1, T
Squeeze the surplus of C-7400a with the rubber ball 3. Thereafter, this was pre-dried at 90 ° C. for about 30 minutes, then baked at 180 ° C. for 30 minutes in an electric furnace, and subsequently water-cooled. At this time, as shown in FIG. 2B, the TC-7400B has its volume reduced to 1/3.
Has been reduced to. The surface roughness at this time is Rmax10.
μm, pencil hardness (Mitsubishi Uni) 3H.

When the inner surface of the stainless steel pipe 1 shown in FIG. 2 (b) is rolled by a metal roller 4 so that its inner diameter is expanded by 0.2 to 0.5 mm as shown in FIG. 2 (c), the unevenness of the surface 5
The part of is crushed and collapsed, and it is buried like TC-7400B, and at the same time, TC-7400B is compressed to form a dense structure and the surface is smoothed and its surface roughness is reduced. Has a Rmax of 0.5 μm and a pencil hardness (Mitsubishi Uni) 4H. The metal roller 4 has an axial direction of 0.3-
A spiral wave was formed with a pitch of 1.4 mm.

At this time, the surface layer on the inner surface of the stainless steel pipe has a composite structure in which the convex portions 5 of the passivation film and the fluororesin film B are mixed under the fluororesin film as shown in FIG.

[0035]

Second Embodiment In a second embodiment, an ultrasonic vibration horn (not shown) or a shaft 6 connected to the rubber ball 3 of the first embodiment is connected.
Move the rubber ball 3 while vertically vibrating at 20 kc / s,
This is to rub the TC-7400B securely into the rough surface. The processing subsequent to FIG. 2A is the same as that of the first embodiment.

[0036]

Third Embodiment A third embodiment is shown in FIG. TC in FIG. 4 (a)
-7100A is the surface area of the stainless steel pipe 1 (approximately 0.
45m ² ) with a film thickness of about 30 μm (about 2
20 g) was applied to the stainless steel pipe 1 by air spray (not shown), pre-dried at 90 ° C. for 30 minutes, then baked in an electric furnace at 280 ° C. for 30 minutes, and subsequently water-cooled. As a result, the volume of TC-7100B was reduced to 1/5 as shown in FIG. 4B, and the surface of the stainless steel pipe 1 was coated with a film thickness of about 25 μm.

[0037]

[Example 4] In Example 4, the fluororesin film having a thickness of 25 µm on the inner surface of the stainless steel pipe obtained in Example 3, that is, TC-7100B having a surface roughness Rmax10 and a pencil hardness of 3H was used as in Example 1. Rolled with roller 4. TC-710
4B, the surface layer of the fluororesin film is compressed to have a thickness of 15 μmRmax 0.2 and a pencil hardness of 4H to be densified and smoothed, and the rough surface of the passivation film 2 It was kneaded in and became a stronger bond.

[0038]

Example 5 In Example 5, "Polyflon TFE Tough Coat Enamel TCW-8100" (hereinafter abbreviated as TCW-8100) manufactured by Daikin Industries, Ltd. was applied to a stainless steel pipe by air spray to a thickness of about 50 μm. , 90
After preliminary drying at 20 ° C. for 20 minutes, it was baked at 330 ° C. for 20 minutes in a vacuum electric furnace, and subsequently cooled with water.

TCW-8100B has a volume of about 5 to 15 .mu.m, R on the inner surface of a stainless steel pipe with the volume reduced to 1/4.
It was coated with a pencil hardness of 3H at a maximum of 8 μm.

When this is rolled by generating ultrasonic vibration of longitudinal vibration at 18 kc / s and pulling the cored bar 4 which expands the inside of the tube by 0.2 to 0.5 mm, it is rolled as shown in FIG. In addition, the fluororesin film (2) serves as a surface layer occupying a larger surface area than the convex portion (5) of the passivation film and has a surface roughness R
A maximum of 0.4 μm and a pencil hardness of 4H were obtained.

The cored bar 4 can be provided with an arbitrary shape and number of threads as shown in FIG. 6 as required.

When the stainless steel pipe composited with the fluororesin film is rolled by a roller or the like in the above, it is preferably fired again. Moreover, what is combined with the passivation film is not limited to the fluororesin film, and a silicone resin film and other resins can be applied.

Ultrasonic vibration effective for kneading, rubbing, and rolling of fluororesin is not limited to longitudinal vibration in the axial direction,
Vibration such as torsional vibration may be used. Also, the displacement amplitude of vibration is not limited to that in the embodiment. Further, the rubber ball is not limited, and metal, ceramic, plastic or the like can be used. Furthermore, the movement of the rubber ball is not limited to the shaft, and wires, air pressure, etc. can be used. Further, the vibration source of ultrasonic vibration may be inside the rubber ball.

[0044]

As described in detail above, according to the present invention,
Various effects can be obtained as listed below.

(1) It is not necessary to remove the rough surface irregularities of the passivation film on the surface of the stainless steel, which are inevitably generated by heat treatment and pickling in the conventional stainless steel pipes and stainless products.

(2) Conventionally, the rough surface is deep and rough,
In proportion to this, the cost for removing the irregularities on the rough surface has been incurred, but in the present invention, conversely, the rougher surface improves the anchoring effect by the combination of the fluororesin and a strong bond can be obtained.

(3) Therefore, even if there are deep pinholes, scratches and the like caused by dissolution of impurities and segregation on the surface of the stainless steel pipe, these can be easily and completely covered.

(4) When the fluororesin is impregnated or rubbed and kneaded to such an extent that at least a part of the passivation film on the surface of the stainless steel pipe projects, the amount of the expensive fluororesin used may be insignificant and therefore high. A high-performance surface treatment can be provided at a low price.

(5) The surface layer of the composite stainless steel pipe is rolled by a roller or the like, so that the fluororesin film constituting the surface has a large rough surface unevenness compressed to form a dense structure and hardness. The surface is high and the number of pinholes is drastically reduced to improve the corrosion resistance, and at the same time it becomes an excellent smooth surface.

(6) By rolling, unevenness on the rough surface buckles and is smoothed, and the fluororesin film and the passivation film can be more strongly bonded.

(7) By rolling with this roller or the like, the roughening of the surface of the stainless steel pipe causes hardening, so that the surface layer is further hardened and wear resistance is enhanced.

(8) Since this composite surface layer has no scratches caused by machining and is finished with smoothness superior to electropolishing, it is non-adhesive equivalent to or close to a fluororesin film. The result is good drainage and good drainage, and the number of cleanings inside the tube can be greatly reduced.

(9) Wavy smooth and dense irregularities of arbitrary pitch provided on the rolled surface layer cause a difference in wear between the convex portion and the concave portion, so that the fluororesin film is formed in at least the concave portion of the surface layer of the pipe. Since it remains evenly, the effect characteristics of the fluororesin film are maintained for a long time.

(10) The intergranular corrosion of the austenite crystal grains of the stainless steel pipe caused by the solution heat treatment becomes difficult to occur, and the application is expanded.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the present invention, which is an enlarged view of a cross section of a surface layer of a stainless steel pipe.

FIG. 2 schematically shows the process of Example 1, and is as follows respectively. (A) It is explanatory drawing which shows a mode that the surplus fluororesin enamel is squeezed off with a rubber ball. (B) It is explanatory drawing which baked the fluororesin film | membrane (b). (C) It is explanatory drawing which shows before and after rolling with a roller following the process of Example 1.

FIG. 3 is a surface view of Example 1.

FIG. 4 is an illustration of Example 3, each of which is as follows. (A) is a state in which fluororesin a is applied. (B) is a state in which the fluororesin B is baked. (C) is a longitudinal cross-sectional view showing a rolled state of fluororesin (b).

FIG. 5 is a surface view of Example 5.

FIG. 6 is a sectional view of a cored bar 4 according to a fifth embodiment.

[Explanation of symbols]

 1. Surface layer of stainless steel pipe 1. Rough surface irregularities of passivation film 3. Rubber ball 4. Metal roller or core 5. Convex portion of rough surface of passivation film 6. Shaft a. Fluorine resin enamel Fluorinated resin enamel

Claims (8)

[Claims] 1. A stainless steel pipe having a fluororesin composite on the surface, characterized in that a fluororesin film is formed on a roughened passivation film produced by pickling the solution heat treated stainless steel surface. . 2. A surface layer comprising at least a part of the passivation film having a defect such as a pinhole and a fluororesin film having at least a part of the film a pinhole. A stainless steel pipe in which the surface layer according to 1 is compounded with a fluororesin. 3. A stainless steel pipe in which a fluororesin is compounded to the surface layer according to claim 1 or 2, wherein the composite fluororesin film is smoothed by a roller or the like. 4. The method according to claim 3, wherein a roll wave in which the fluororesin film rolled by the roller forms spiral irregularities according to the rolling pitch of the roller is formed on the smoothed fluororesin film. A stainless steel pipe in which the surface layer described is compounded with a fluororesin. 5. The fluororesin on the surface layer according to claim 1, wherein the composite fluororesin film is rolled by a cored bar to be smoothed, and an appropriate wave is provided in the axial direction. A composite stainless steel pipe. 6. A stainless steel pipe in which a fluororesin is combined with a surface layer according to claim 1, wherein the composite fluororesin-composited stainless steel pipe is fired in a vacuum furnace at 170 to 400 ° C. Manufacturing method. 7. The method for producing a stainless steel pipe having a composite fluororesin on the surface according to claim 1, wherein the composite fluororesin film is compressed and smoothed by a roller or the like and then fired again. 8. The fluororesin according to claim 1, wherein the fluororesin is compounded on the surface layer, and the fluororesin film is rolled on the surface with a tool which vibrates ultrasonically. Manufacturing method of stainless steel pipe.