JPS60103187A - Production of pipe for heat exchanger - Google Patents

Abstract

PURPOSE:To obtain a pipe for a heat exchanger which does not require secondary processing such as painting, plating by heating the steel pipe to the m.p. of a Cu-Su-Bi alloy or above in a prescribed reducing gaseous atmosphere then forming the Cu-Sn-Bi alloy film thereon in the reducing gaseous atmosphere and reheating further the pipe in the reducing gaseous atmosphere. CONSTITUTION:Electric copper, tin and bismuth of the prescribed base are melted and are alloyed and thereafter atomized copper alloy powder 7 having a regulated grain size is manufactured. A stell pipe 2 reduced to a target outside diameter is inserted into a coating device 1 while the pipe is fed longitudinally. The air in the pipe 2 is substd. with reducing gaseous H2 in an atmosphere gas substituting chamber 2 in which said gaseous atmosphere is maintained. Such steel pipe 2 is subjected to high frequency heating 5 in a high frequency heating chamber 4 in which the gaseous reducing H2 atmosphere is maintained to increase the temp. of the pipe 2 to the m.p. 990 deg.C of said alloy powder 7 or above. The pipe 2 is in succession thereto inserted into a coating chamber 6 where the powder 7 is atomized by the spraying and agitation of the gaseous H2 to melt and stick the powder 7 on the surface of the pipe 2. The pipe 2 is subjected to high frequency heating in a reheating chamber 8 in which the reducing gaseous H2 atmosphere is maintained thereby forming a metallic film 9 having a uniform film thickness on the surface of the pipe 2.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing heat exchanger tubes used in radiators forming cooling units of refrigerators, freezers, etc., and in particular to a method for coating the surface of steel tubes with anti-rust coating. Related to technology.

Conventional Structure and Problems The conventional method for manufacturing heat exchanger tubes involves bending the steel strip in the width direction while feeding it in the longitudinal direction, and then butting both ends together. With,
After heating by passing a rectangular wave current, the pipe is annealed in a propane modified gas atmosphere at 850 to 890°C to make the crystal structure uniform.

The copper plating on the butt-welded outer surface of steel pipes produced using the conventional method described above is exposed, as the copper plating is removed before welding. Therefore, when using a steel pipe as a heat exchanger, anti-corrosion treatment such as painting or plating is required as a post-treatment.

In addition, in the case of a copper phase, it may become brittle due to the intrusion of phosphorus, so it is necessary to use silver solder that does not contain phosphorus when brazing steel pipes with exposed iron base like conventional steel pipes. However, since bonding with silver solder requires flux containing chloride, it is necessary to remove the flux by washing with hot water, making it difficult to use conventional steel pipes for heat exchangers.

As a manufacturing method for steel pipes that eliminates the above-mentioned problems, the applicant first applied ultra-thin pure copper foil B to the surface of a steel pipe that has been reduced to a target outer diameter in advance, as shown in Figure 2a.
The present invention provides a manufacturing method in which the pure copper foil B is closely coated and then heated to a temperature higher than the melting point of the pure copper foil B in a reducing atmosphere to form a copper film on the surface of the steel pipe.

However, in the case of this manufacturing method, the temperature at which pure copper begins to flow at 78 digits (solidus temperature) and the temperature at which it begins to flow (liquidus temperature) are the same, so melting occurs instantaneously at the 11.5 point where the initial temperature is reached. The pure steel foil B is melted, and as shown in FIG. 2, the pure copper foil B located at the upper part of the steel pipe A flows to the lower part under its own weight after melting. Therefore, as shown in FIG. 2C, there is a drawback that a uniform coating cannot be formed all around the surface of the steel pipe A.

Purpose of the Invention The present invention provides that when steel pipes are used as a heat exchanger, the steel pipes have high rust prevention properties, and the use of phosphorous copper solder, which can embrittle the steel pipes during joining, and silver solder, which requires flux cleaning, is to be avoided. The purpose of the present invention is to obtain a coating method for steel pipes that eliminates the need for steel pipes, uses the film formed on the surface of the steel pipes as a bonding material, forms a film with a uniform thickness, and prevents decarburization on the surface of the steel pipes.

Structure of the Invention To achieve this objective; the present invention creates a copper alloy containing bismuth and tin that melts at relatively low temperatures and in a short time and has interfacial activity with copper and iron; The steel pipe, which has been reduced to the target outer diameter in advance, is heated to a temperature higher than the melting point of the copper alloy in a 751 constant reducing gas atmosphere, and then the steel alloy is deposited in an atomized state on the surface of the steel pipe in a predetermined reducing gas atmosphere. .

After melting and forming a 1itJ copper alloy film, the original gas atmosphere 1! The steel pipe is heated in a JJ atmosphere to form a copper-tin-bis-7 alloy film of arbitrary thickness on the surface of the steel pipe.

In this way, by atomizing and depositing a copper alloy consisting of copper-tin-bismuth on the surface of a steel pipe in a reducing gas atmosphere and then reheating it, a uniform copper alloy film can be obtained on the surface of the steel pipe, preventing ★I. (J strength is improved, and the copper alloy film itself becomes waxy N.
In order to achieve the objectives of (i) and (I), there is no need to use phosphorous copper solder that may embrittle the steel pipes or silver solder that requires flux cleaning during joining.

Description of examples An embodiment of the present invention will be described below.

First, copper alloys are produced by melting the champions of electrolytic steel, tin, and bismuth.
It becomes atomized powder. Zunawara, electrolytic copper at a predetermined ratio,
After melting and alloying tin and bismuth, the particles were atomized to a particle size of 200 mS.Meanwhile, the steel pipe 2 was made by butt welding ordinary steel strips as explained in the conventional example above, and after that the target was exceeded. The diameter has been resinized and degreased and cleaned with an organic solvent.

Next, the process of forming a coating on this steel pipe 2 will be explained with reference to the drawings. First, as shown in FIG. 1, the steel pipe 2 is guided in the longitudinal direction and inserted into the coach and running device 1, and the inside of the steel pipe 2 is Replace with air. This copper tube 2 is exposed to a hydrogen reducing gas atmosphere, and a high frequency coil 5 is heated inside the high frequency heating chamber 4.
A predetermined high voltage is applied to heat the steel pipe 2 to a temperature higher than the melting point of the copper alloy powder 7, which is 990°C. Next, the copper gold powder 7 is inserted into the coating chamber 6 which has been atomized by spraying and stirring hydrogen gas, and the copper gold powder 7 is coated on the surface of the steel pipe 2.
to melt [・j゛measure].

Steel refining material 2 with 14 ul <+1 river) 7 melted and adhered to the surface is heated by high frequency in a reheating chamber 8 kept in a hydrogen-reducing chamber atmosphere, and the pressure of the gas discharged from the bottom of the tank is By heating, the metal coating 9 having a uniform thickness is formed on the surface of the steel pipe 2.

A more uniform film is formed on the surface of the steel pipe 2 manufactured in this manner than a film formed using an alloy foil such as pure copper foil. In other words, electrolytic copper, tin, and bismuth? &I
Since the copper-gold powder 7 is atomized and powdered, the melting of this copper-gold powder T is between the initial temperature (in-phase temperature) and the initial temperature (liquidus temperature) of about 160
There is a difference in temperature. Therefore, within the range between the solidus temperature and the liquidus temperature, it gradually melts with a high viscosity. The reheating chamber 8 is maintained at this melting temperature so that a molten film 9 of the metal powder of 3 microns or more is uniformly formed on the surface ih1 of the steel pipe 2.
It is preferable to determine ht of the gas discharged from the lower surface of the tank.

In the steel pipe 2 manufactured by the above method, the iron base at the butt welded portion is not exposed, but is covered with a molten coating 9 of copper, tin, and bismuth, and therefore the rust prevention ability is improved. Moreover, in the case of the above method, since the thickness of the molten film 9 can be changed depending on the heating temperature in the reheating chamber 8, secondary processing such as painting or plating is not required, and the process can be largely subdivided.

In addition, since the iron base of the butt weld is also covered with a molten film of 3 microns or more, it can sufficiently prevent phosphorus intrusion (intrusion is 100 ohmstrong). Since there is no need to use wax and phosphorous copper wax can be used, flux cleaning such as hot water cleaning is not required.

Furthermore, since the alloy 7 is a copper, tin, and bismuth alloy containing bismuth, which has a flux-like activation effect, the molten coating 9 itself serves the purpose of a brazing material, so there is a risk of embrittling the steel pipe 2 at the joint 11.5. It is no longer necessary to use phosphorous copper solder that has phosphorus and silver solder that requires flux cleaning, making it easier to apply to alternating current equipment.

Effects of the Invention As is clear from the above explanation, the present invention provides a method for heating a steel pipe to a temperature higher than the melting point of a copper-tin-bismuth alloy in a predetermined reducing gas atmosphere, and then maintaining the reducing gas atmosphere and heating the alloy. A method for manufacturing a heat exchanger tube, which is inserted into a floating tank to form a film of copper-tin-bismuth alloy on the surface of the steel pipe, and further heated in a reducing gas atmosphere to obtain a desired film thickness. Therefore, secondary processing such as painting and plating is not required, and the process can be largely divided into parts. Furthermore, for joining this steel pipe,
This eliminates the need to use brazing metal at all, allowing for a significant reduction in man-hours and automation.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a coating device used in the method for manufacturing heat exchanger tubes according to an embodiment of the present invention, FIG. 2a is a cross-sectional view of a steel tube before heating in a conventional manufacturing method, and FIG. 02...Steel pipe, 3...
・Atmosphere gas replacement chamber, 4...High frequency heating chamber, 8
...Reheating chamber, 9 times, metal coating. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 ((L) (b) (C)

Claims (1)

[Claims] After heating the steel pipe, which has been reduced to the target outer diameter in advance, in a predetermined reducing gas atmosphere above the melting point of the copper-tin-bismuth alloy, it is inserted into a tank in which the reducing gas atmosphere is maintained and the alloy is floating. the copper on the surface of the steel pipe.
A method of manufacturing a heat exchanger tube, which forms a tin-bismuth alloy film and further heats the film in a reducing gas atmosphere to obtain a desired film thickness.