JPS63309325A - Production of u-tube made of stainless steel - Google Patents

Abstract

PURPOSE:To finish the surface roughness in a U-tube into a very small smooth surface by bright-annealing a stainless steel tube, bending it into a U-tube and polishing its inner surface electrolytically. CONSTITUTION:A stainless steel blank tube is cold-drawn, degreased, pickled and cut into stainless steel tube having a prescribed size, then, bright-annealed and made free from residual strain generated in cold drawing stage. The cold drawing and bright annealing are repeated several times, then, the stainless steel tube is bent and formed by heat treatment into U-shaped cross section. This U-shaped stainless steel tube is fixed with its opening upward, an electrode rod is set so that it does not take an eccentric position in the U-tube, then, electrolyte is sent into the U-tube, an electrical voltage is impressed between the U-tube and an electrode rod to polish the inner surface of the U-tube electrolytically and to obtain a smooth finished surface having <=1mum surface roughness. The inner surface of a stainless steel tube having a U-shaped bending radius part can be easily polished to obtain smooth surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing a stainless steel U-shaped tube used in high-purity gas supply equipment in the semiconductor manufacturing industry.

[Conventional technology]

In recent years, with the rapid development and advancement of the semiconductor manufacturing industry, extremely strict purity values have come to be required for the high-purity gases used in this field. For example, one of the specifications for high-purity nitrogen gas in semiconductor manufacturing plants is that the number of dust particles contained in high-purity nitrogen is less than 1 dust particle of 0.1 μm or less per 1 cu-ft. . Therefore, measures are taken to ensure that there is no room for such dust to enter the high purity nitrogen gas manufacturing equipment and supply equipment.

The present invention also relates to a zero-shaped tube whose inner surface is finished by electrolytic polishing and which is used in the above-mentioned apparatus, particularly an evaporator.

1' by vaporizing high-purity liquefied nitrogen! The U'' tube that connects the evaporation tubes of the evaporator for producing i-purity nitrogen gas has conventionally been manufactured using a wire-to-wire manufacturing method, but the inner surface roughness of all of them is from several μm to several U μm. Recently, in order to manufacture a U-shaped tube with a surface roughness that satisfies the specification of 1 am or less, it is necessary to perform mechanical polishing or flow polishing after molding, and then electropolish the inner surface, which requires a complicated process. For example, the conventional JIS
In order to manufacture a 180° elbow (U-shaped pipe with no straight pipe part) with the dimensions specified by the standard and a maximum inner surface roughness of 1 am or less (see Figure 1), the following process is used. Is going. The raw material is hot extruded seamless stainless steel tube, which is degreased by cold widening using the specified jig, coating material, and lubricant.

The maximum surface roughness of the inner surface obtained by pickling and other treatments is 4.5 μm, but this is formed into a U-shape by heat treatment, and then the inner surface is mechanically polished to obtain the maximum apparent surface roughness. The model was polished to a roughness of about 1 Iim, and electropolishing was performed to create a 180° elbow 1 (U-shaped tube) with a maximum surface roughness of about 1 μm.
(shown in the first figure) is obtained.

However, as mentioned above, recently, strict values have been required for the surface roughness after the device is manufactured. For example, the weld 3 between the evaporator tube 2 and the U-shaped tube 1 in FIG. 2 has conventionally been manually welded, resulting in a fairly coarse weld bead, which provides a bed for dust particles to adhere. Therefore, the U-shaped tube 1 and the evaporator tube 2 should be welded using a pipe-specific welding machine so that the surface roughness of the back bead at the welded part is minimized. According to the 4LJIS standard, a return vent) (shown in Figure 3) must be used. Therefore, an attempt was made to minimize the weld back bead on the inner surface of the final product device by manufacturing and using a U-shaped tube with a long straight tube portion and an electrolytically polished inner surface. However, when manufacturing a U-shaped tube with a long straight section, it is difficult to perform mechanical polishing during the manufacturing process. In other words, in mechanical polishing, the inner surface of the U-shaped tube is polished using a polishing machine that uses a grindstone or cloth as an abrasive material, but the inside part of the bent R part cannot be polished (non-shaded areas in Figures 4 and 5). .

Visual confirmation is an important checkpoint for reliable polishing, but as above, it is impossible to check the inner part of the bent R section, and the longer the straight pipe section, the greater the degree of confirmation. .

There is also a method using fluid polishing instead of mechanical polishing. Fluid polishing is a method of polishing the surface of a workpiece by passing an abrasive material containing abrasive grains into a viscoelastic polymeric medium several times through a U-shaped tube. However, when performing fluidized polishing, it is necessary to increase the surface roughness to some extent by mechanical polishing as a base polishing.

[Problem that the invention seeks to solve]

As mentioned above, when mechanical polishing is performed to increase the surface roughness of the inner surface of a U-shaped tube with a long straight section, it is difficult or impossible to polish the inner surface of the curved section (R section), and furthermore, this part It is difficult to check the surface roughness.

Further, polishing by fluidized polishing is usually performed as a finishing step for polishing by mechanical polishing, and therefore, it is meaningless if polishing by mechanical polishing is uncertain. In order to obtain a desired surface roughness using only fluidized polishing, it is necessary to prepare several types of abrasives with adjusted particle sizes and perform the polishing process by passing these abrasives over and over again. is low, resulting in considerable cost and is difficult to implement in practice.

Therefore, as a method of finishing the maximum surface roughness of the inner surface of a long straight U-shaped pipe made of stainless steel to 1 or less,
Mechanical polishing and fluid polishing methods are both inconvenient in practice, and there has been a need to develop other methods.

The present invention eliminates the complicated mechanical polishing or flow polishing process during the manufacturing process of U-shaped tubes with long straight pipe parts and electrolytic polishing of the inner surface, and produces stainless steel with extremely low inner surface roughness. The purpose is to manufacture steel zero-shaped pipes.

[Means for solving problems]

In the present invention, a stainless steel tube is drawn to a predetermined size, the bright annealing process is repeated several times, and then the tube is bent into a U-shape and the inner surface is electrolytically polished. Maximum surface roughness of pipe inner wall is 0.3
This is a method for manufacturing a stainless steel zero-shaped tube, characterized in that the thickness is about um to 0.7 mrl.

(Function) During the manufacturing process of U-shaped tubes, which have a long straight section and undergo electrolytic polishing on the inner surface, the machine rlyl is complicated and causes high costs.
Eliminate the polishing or flow polishing process, perform bright annealing to eliminate residual stress from the drawing process, and achieve the maximum surface roughness of the inner surface of the tube to about 0.7 μm or less and about 0.3 ham by simply performing electrolytic polishing. I can do it.

〔Example〕

Example 1 A hot extruded seamless stainless steel tube was used as the material,
This is subjected to a cold drawing process using a predetermined jig, a coating material, and a lubricant, followed by degreasing, pickling, etc., and then cutting and chamfering to obtain a master tube of a predetermined size. The dimensions at this time may be determined as appropriate depending on the product specifications, or the length of the straight pipe portion may be approximately 0.5 to 5 times the pipe diameter. The maximum surface roughness of the inner surface of the tube at the end of this process is about 4.5 μm. Next, this original tube is bright annealed to eliminate residual stress generated during the cold drawing process. The conditions for this bright annealing treatment are as follows: Put the above original tube into an annealing furnace, hold it in an annealing gas atmosphere with a predetermined composition and temperature of 11 degrees for 4 minutes at a humidity of 0℃±30℃, and then let it air cool by natural cooling. Cool it down.

This process of cold drawing and bright annealing is repeated multiple times. Next, it is formed into a U-shape by bending and forming using heat treatment. The maximum surface roughness of the inner surface at this time is about 6 mm. By electrolytically polishing the molded U-shaped tube to finish its inner surface, a U-shaped tube having a maximum surface roughness of about 0.7 mm on the inner surface of the tube can be obtained. The electrolytic polishing process is performed in the following steps.

A plurality of U-shaped tubes to be treated are set with the openings facing upward, and electrode rods are set in the U-shaped tubes so that eccentricity of the seed rod does not occur. Connect a liquid feed pipe to the opening and circulate the liquid from the electrolyte tank using a liquid feed pump. Electrolytic polishing is performed by setting the voltage and current to predetermined values and energizing for a certain period of time.During this treatment process, the temperature of the polishing liquid and the presence or absence of gas generation are carefully checked. After performing electrolytic polishing treatment for a certain period of time, the electrolytic solution is extracted and cleaning is performed by passing cleaning water through it. The maximum inner surface roughness of the U-shaped tube after this process is 0.
7J1111 or less, but the maximum surface roughness is checked by visual inspection of all the products and by a surface roughness meter in a sampling inspection, and only those with the specified surface roughness are considered as products.

Example 2 A hot or cold extruded seamless stainless steel pipe is used as a raw material, which is subjected to cold drawing, degreased, pickled, etc., and then cut to a predetermined size to obtain a master pipe. This was annealed in the atmosphere according to a conventional method, and the maximum surface roughness of the inner surface of the tube was 6μ.
m is obtained. Next, cold drawing is performed again and bright annealing is performed. This cold drawing and bright annealing process is repeated multiple times. The greater the number of repetitions, the better the maximum surface roughness value of the inner surface of the tube obtained. That is, by increasing this number of times, the maximum surface roughness after bright annealing can be improved to about 3 μm. Next, it is bent into a U-shape, and the maximum surface roughness at this time is about 4.5 μm. This molded U-shaped tube is electrolytically polished to obtain a U-shaped tube with an inner surface having a maximum surface roughness of about 0.3 am. The reason why air annealing is performed in the first step is that compared to bright annealing, air annealing does not require an atmosphere gas with a specially adjusted composition, making the process easier in terms of materials and labor, and reducing processing costs. This is because it results in a reduction in In this embodiment, the cold drawing and air annealing are performed once, but it goes without saying that these steps may be repeated. In that case, the number of repetitions of the cold drawing and bright annealing steps may be small.

〔Effect of the invention〕

As described above, the stainless steel tube is drawn to a predetermined size, brightly annealed, then bent into a U-shape, and the inner surface is electrolytically polished to form the largest surface of the inner wall of the tube. This is the IUnh method for stainless steel zero-shaped tubes, which is characterized by a roughness of 0.7 gm or less, which eliminates the complicated mechanical polishing that was necessary to reduce the surface roughness of the inner surface of the tube to an extremely small value. Alternatively, by eliminating the flow polishing process and performing a simple bright annealing process instead, the residual stress required after the center processing process can be eliminated, and at the same time, the rough surface of the inner surface of the tube can be pretreated for electrolytic polishing. It is now possible to easily obtain a maximum surface roughness of 0.7 mark or less with electrolytically polished culms. Therefore, the manufacturing cost is sufficiently reduced compared to the conventional stainless steel O-shaped tube which has undergone internal electrolytic polishing, and the cost of equipment for mechanical polishing or fluid polishing is no longer necessary when newly installed.

[Brief explanation of the drawing]

Figure 1 is a front view of a U-shaped tube without a straight tube section, Figure 2 is a front view of the U-shaped tube shown in Figure 1 connected to an evaporation tube, and Figure 3 is a front view of a U-shaped tube with a straight tube section. A front view of the tube, FIG. 4 is a diagram for explaining the state of mechanical polishing inside the U-shaped tube shown in FIG. 1, and FIG. 5 is a diagram showing the mechanical polishing inside the U-shaped tube shown in FIG. 3. It is a figure for explaining a state.

Claims (1)

[Claims] 1. After repeating the process of drawing a stainless steel raw tube to a predetermined size and bright annealing multiple times, the tube is bent into a U-shape, and the inner surface of the tube is finished by electrolytic polishing. Method for manufacturing stainless steel U-shaped tubes.