JP2727184B2 - Method for producing metal tube having inner surface coated with tin or tin-based alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for supplying tin or a tin-based alloy to the inner surface of a metal tube, particularly a relatively small-diameter tube having a diameter of 20 mm or less, which is used as a supply path for various fluids. As a corrosion-resistant coating efficiently and reliably, without producing metal corrosion or blockage of pipes, and even with double-wound pipes, evenly coated without peeling off joints when processing pipes And a method for manufacturing a metal tube. [Prior Art] Conventionally, thin metal pipes used for brake oil pipes or liquid or gaseous fuel pipes or other fluid supply paths of automobiles are made of strip steel sheets having copper plating only on the inner surface or both inner and outer surfaces. Double-wound or single-wound steel pipes are used. However, these steel pipes have a certain degree of corrosion resistance because the inner surface is plated with copper, but when used as brake oil piping, for example, copper is eluted by the brake oil and connected to the piping. Established
For example, there has been a problem that an electrolytic corrosion action is caused on another connecting member made of aluminum or an aluminum alloy, or gasoline is oxidized and deteriorated in a fuel pipe. Therefore, the inner surface is further coated with tin or a tin-based alloy which can prevent the adverse effect without causing the adverse effect. As one of the means, a low melting point metal wire composed of zinc having a melting point of 450 ° C. or less, tin-zinc, or an alloy containing these as a main component is inserted into a thin metal tube, and gradually inserted into a reducing atmosphere in a reducing atmosphere. A method in which a portion of the zinc component of the low-melting metal wire is vaporized by heating to ~ 1100 ° C, and the molten low-melting metal adheres to the entire inner peripheral surface of the thin metal tube to form a plating layer (Japanese Patent Publication No. No. 18745) has been proposed. [Problems to be Solved by the Invention] However, in this method, particularly in a double-wound steel pipe in which a steel strip is brazed with copper, the distribution of tin in the seam portion is X as shown in FIG. As can be seen from the line image, in the heat treatment, by heating at a temperature much higher than the melting point of the coating material and a long holding time, the molten tin diffuses and penetrates into the copper layer of the seam portion, and the brittle Sn
-Form a Cu alloy layer deep into the mating surface. For this reason, the problem that the inner seam part peeled off at the time of forming and bending pipe ends such as balms, flares, and spools after the coating treatment, and the pressure resistance of the metal pipe was greatly reduced was recognized.
Although the heat treatment furnace uses a reducing atmosphere, oxygen in the atmosphere generally remains in the metal tube, and while the temperature of the metal tube is gradually increased, the heat treatment furnace is firmly attached to the surface of the low-melting metal wire. An oxide film is continuously formed in the tube axis direction. Due to the strong oxide film formed continuously like a shell in the axial direction of the tube, even if heated to a temperature higher than the melting point of the coating material, the molten coating material remains inside the oxide film shell and remains inside the tube. This phenomenon cannot occur on the wall surface, and this phenomenon occurs continuously in the longitudinal direction in combination with the fact that the heating furnace is long in the tube axis direction. However, the oxide film forming the shell further heated to a high temperature is melted, thermally decomposed or instantaneously destroyed by the vapor pressure of the low-melting metal wire that has become high pressure, and
The molten metal before and after flows through the inside of the shell and is locally concentrated and flows out, and is heated to a high temperature, and has high activity and a low viscosity, and the molten metal rich in fluidity is coupled with a high metal vapor pressure and vigorously. Because of the continuous outflow, Sn-Fe and Zn-Fe are formed on the steel pipe wall near the outlet, iron is easily eluted and the base metal is locally concentrated and eroded (Fig. 13). A phenomenon called so-called metal corrosion causes the pipe wall to become thinner, causing intermittent phenomena in the pipe axis direction that significantly degrade mechanical strength such as vibration resistance and pressure resistance performance. Issues that can cause
Further, in particular, when using a long material of a small-diameter pipe having an inner diameter of 4 mmφ or less, there is a problem that a blockage occurs in the pipe due to the localized concentrated outflow of the molten metal, and further, in the vicinity of the localized concentrated outflow, A reservoir (FIG. 11) is formed, and a portion where the coating is hardly formed (FIG. 9) is formed at a distant place, and there is a problem that a film is formed unevenly in a longitudinal direction. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a means for easily and surely forming a tin or tin-based alloy film having a uniform thickness in a short time. [Means for Solving the Problems] The present inventor has repeatedly studied to solve the problems and achieve the object, and inserted tin or a coating material containing tin as a main component into a metal tube, The present invention has been accomplished by finding that the object can be achieved by high-frequency heating and cooling as quickly as possible. That is, the present invention inserts a coating material containing tin or tin as a main component into a metal tube, and raises the temperature of the metal tube to 1000 ° C. or more by high-frequency heating in an inert gas, a non-oxidizing atmosphere gas, or a reducing atmosphere gas. A method for producing a metal tube having an inner surface coated with tin or a tin-based alloy, wherein the inner surface is coated with tin or a tin-based alloy after heating to coat the entire inner wall of the metal tube with tin or a tin-based alloy, and then cooling in the atmospheric gas. It is a feature. The metal pipe used in the present invention is generally a carbon steel pipe. Usually, a steel strip having a thickness of about 3 to 5 μm on one or both sides is formed into a double-wound steel strip, and the overlapping surface thereof is formed. Is a double-wound steel pipe formed by brazing and welding with copper, or an electric resistance welded steel pipe in which a strip steel material similarly plated with copper is formed into an open seam pipe, and a butt portion is electrically welded. Also, from the viewpoint of forming the coating of the low-melting-point metal, the tube is preferably a relatively thin tube having a tube diameter of 20 mm or less, and it is preferable to perform a pretreatment such as cleaning with a normal alkali solution or washing with water. For coating formation, for example, tin, tin-zinc alloy, tin-lead alloy, zinc plating on tin base or tin-zinc clad material, etc., are used as wires, foils, powders and granules. It is selected according to the inner diameter of the metal tube.
Is used. The heat treatment performed by inserting the coating material into the metal tube is performed by rapidly heating the metal tube in which the coating material is inserted in an inert gas, a non-oxidizing atmosphere gas, or a reducing atmosphere gas to 1000 ° C. or more by a high-frequency furnace. By applying a high frequency of 10 to 400 KHz to the furnace and treating it at a predetermined temperature for a short time, the temperature can be raised in a short time even if the inside of the metal tube is not in a reducing atmosphere or the like. Thus, the coating material can be smoothly and sequentially and continuously melted in the tube axis direction without forming a strong oxide film on the surface of the coating material, and can be uniformly coated in the metal pipe. The metal tube is passed through the furnace at a speed of 5 to 50 m / min for heat treatment. By the heat treatment, the metal tube coated with tin or a tin-based alloy is immediately cooled as soon as possible in the same atmosphere gas as the heat treatment, for example, with a cooling nitrogen gas. According to the method of the present invention, for example, first, a coating layer is formed using a high melting point coating material, and then a plurality of coating layers are formed to form a coating layer using a low melting point coating material. Can be. [Effects of the Invention] In the present invention, tin or a coating material containing tin as a main component is inserted into a metal tube and melted and spread without forming an oxide film on the surface of the coating material in a very short time by high-frequency heat treatment. Since it cools down as quickly as possible, a uniform coating can be formed without local pooling of the coating material on the inner surface of the metal pipe or the remaining of the non-forming area of the coating. If so, it is possible to reduce the penetration of the coating material into the inner seam portion due to diffusion and penetration, thereby preventing peeling of the inner seam portion at the time of forming and bending the pipe end, and at the same time, locally by the molten coating material. Metal corrosion, which is the erosion of concentrated materials, can be prevented, and mechanical strength such as vibration resistance and pressure resistance are not degraded.
Even with a small diameter tube of about mφ, excellent effects such as no blockage are observed. [Example] Next, an example of the present invention will be described. Example 1 A double-walled steel pipe having an outer diameter of 6.35 mm, a wall thickness of 0.7 mm, and a length of 6 m manufactured by double winding a steel strip having a thickness of 3 μm and having a thickness of 6 μm, and a wire diameter of 0.4 mm Insert a tin-zinc alloy wire rod into a 500 mm long quartz tube high-frequency furnace to which a 200 KHz high frequency was applied with a nitrogen gas atmosphere at the inside at a feed rate of 50 m / min.The steel pipe surface temperature was 1150 to 1200 ° C. , And then cooled as quickly as possible with nitrogen gas cooled to -10 ° C to obtain a product. The double-wound steel pipe of the product obtained by this treatment is cut in the diameter direction, and the state of the coating layer and the seam formed on the inner surface of the steel pipe are evaluated by a secondary electron image (SEM) and an X-ray image (SEM) using a scanning electron microscope. Dod map). As a result, an SEM image of about 600 times the inner surface of the steel pipe is as shown in FIG. 1, and the dot maps of tin and copper are as shown in FIG. 2 and FIG. It was recognized that an excellent tin-based alloy was formed. In the seam section of the tube wall cross section, an SEM image of about 40 times is as shown in FIG. 4, and the dod maps showing the distribution of copper and tin are as shown in FIGS. 5 and 6. Because the melting time of tin is very short, the brittle Sn-Cu
The diffusion and penetration of the alloy layer into the mating surface of the seam is negligible, and the copper layer rich in extensibility remains as it is, so that the seam does not peel off during post-processing such as valleys and spools. Admitted. Comparative Example 1 Using a double-wound steel pipe manufactured in the same manner as in Example 1 and a similar tin-zinc alloy coating material, in a nitrogen gas atmosphere furnace having a heating part length of 2.6 m according to a conventional method. The speed 22
The mixture was heated at 1000 ° C. by passing at 0 mm / min, and cooled by passing through a water jacket connected to the outlet of the heating unit. The same observations as in Example 1 were performed on this product. In other words, the dod map of tin in the seam portion is as shown in FIG. 7, and it is recognized that tin is extremely diffused and penetrated into the seam portion and that there is a high risk of peeling even in plastic working with a low working rate. Was done. In addition,
The SEM image is as shown in FIG. 8, and the tin and copper dopmaps are as shown in FIGS. 9 and 10, with little tin coating formed and only the copper diffusion layer formed. Did not. In addition, the SEM image shown in FIG. 11 and the dod map of tin shown in FIG. 12 confirmed that the tin was in a so-called pool state and did not collect uniformly on the bottom of the tube to form a uniform coating. Example 2 A 0.5 mm diameter tin wire was inserted into an electric resistance welded steel pipe having an outer diameter of 0.8 mm, a wall thickness of 0.7 mm, and a length of 7 m, in which a copper film having a thickness of 3 μm was applied to the inner surface. In the same manner, a coating was formed on the inner surface of the ERW steel pipe. With respect to the product obtained by this treatment, the SEM of the cut surface in the diameter direction and the Dot map of tin and copper were observed in the same manner as in Example 1. This result is similar to the result of Example 1,
It was noted that a uniform coating was formed. Example 3 Using the same electric resistance welded steel tube as used in Example 2, a zinc-plated wire of 0.5 mm in diameter was inserted into a tin material.
The coating was formed on the inner surface of the electric resistance welded steel pipe in the same manner as in Example 1. Various observations were made on the product obtained by this treatment in the same manner as in Example 2, and it was confirmed that a uniform coating was similarly formed. Example 4 A tin-zinc clad wire having a diameter of 0.5 mm was inserted into the inside of the same electric resistance welded steel pipe as used in Example 2 and treated in the same manner as in Example 1 to obtain an electric wire. A coating was formed on the inner surface of the sewn steel pipe. Various observations were made on the product obtained by this treatment in the same manner as in Example 2, and it was confirmed that a uniform coating was similarly formed. Comparative Example 2 The same electric resistance welded steel pipe as used in Example 2 was used, and a tin-zinc alloy wire having a diameter of 0.5 mm was inserted into the inside thereof. Various observations were made on the product in the same manner as in Example 2. The results are as shown in SEM image in Fig. 13 and tin dod map in Fig. 14, and it was confirmed that metal corrosion was extremely deep and formed intermittently in the longitudinal direction. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a secondary electron image (S: 600 ×) of the coating formed by the embodiment of the present invention, which was confirmed by a scanning electron microscope.
EM) Metallographic diagrams shown by photographs, FIG. 2 and FIG. 3 are X-ray images (dot maps) showing the distribution states of tin and copper at the same positions as FIG.
FIG. 4 is a metallographic diagram of a seam portion of the product of the present invention at a magnification of 40 times by a SEM photograph, FIG. 5 is a copper dot map at the same position as FIG. 4, and FIG. FIG. 7 is a dot map of tin at the same position as FIG. 4, and FIG. 7 is a sixth view showing the formation state of the coating obtained by the comparative example.
FIG. 8 is a metallographic diagram showing the formation state of the coating obtained by the comparative example by a secondary electron image photograph at 400 × confirmed by a scanning electron microscope, and FIGS. 9 and 10 are FIGS. FIGS. 2 and 3 show the distribution of tin and copper at the same position as in FIG. 8, respectively, and FIG. 11 is a metallographic diagram showing the reservoir of the coating in the comparative example by a 25 times SEM photograph. FIG. 12 is a dot map diagram of tin at the same position as FIG. 11, FIG. 13 is a metallographic diagram showing a state of metal corrosion in a comparative example product by a SEM photograph of 65 times, and FIG.
The figure is a dod map of tin at the same position as FIG.

Claims (1)

(57) [Claims] Insert the coating material containing tin or tin as the main component into the metal tube, and raise the temperature of the metal tube to 1000 by high-frequency heating in an inert gas, non-oxidizing atmosphere gas, or reducing atmosphere gas.
° C. or more, the entire inner wall of the metal tube is coated with tin or a tin-based alloy, and then cooled in the atmospheric gas. Production method.