JPH0218195B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a heat transfer tube in which heat transfer fins are provided inside the tube. Heat transfer tubes with inner fins are used as heat transfer tubes in heat exchangers, etc., in which heat transfer fins (inner fins) are provided inside the tube to increase the internal surface area in order to improve heat flow from the fluid inside the tube to the fluid outside the tube. There is. In this case, copper, which has good thermal conductivity, is used as the tube material, and aluminum or aluminum alloy, which is easy to extrude and has good thermal conductivity, is usually used for the inner fin. Therefore, fixing the inner fin inside the pipe is
After inserting a radially formed inner fin made of aluminum or its alloy into a copper pipe, the outer periphery of the pipe is caulked, or the pipe diameter is compressed and reduced by cold drawing, and the inner fin is attached to the inner wall of the pipe. Usually, the inner fin is held in the pipe by being brought into close contact with the inner fin, or the inner fin is fixed in the pipe by mechanical holding, such as by screwing the inner fin into the pipe. However, as mentioned above, in a heat transfer tube in which the inner fin is fixed inside the tube by a physical method, if the tube is heated by welding or a high-temperature fluid is flowed when assembling it into a device such as a heat exchanger, Since the inner fin is made of aluminum or its alloy, which has a large coefficient of thermal expansion, because it is housed in a tube made of copper, which has a smaller coefficient of thermal expansion, plastic deformation may occur, and when it returns to room temperature, it will shrink even more. If this is extreme, a gap will form between the inner fin of the copper tube and the inner fin made of aluminum or its alloy, which will reduce heat transfer as a heat transfer tube, and furthermore, the inner fin should be fixed within the tube. The inner fin will move. Furthermore, low-temperature fluids, especially liquid nitrogen (boiling point approximately -196℃)
When a fluid such as aluminum or an alloy thereof is flowed, the inner fin, which is made of aluminum or its alloy, which has a higher coefficient of thermal expansion, shrinks greatly, creating a gap between the inner wall of the pipe and the inner fin as described above, and reducing the degree of adhesion. This will reduce heat transfer. For this reason, the above-mentioned disadvantages can be solved by joining and fixing the inner fin to the inner wall of the pipe, but since the materials of the pipe material and the inner fin are different, it is difficult to weld them together. Further, when joining, problems arise such as tight contact between the inner fin and the inner wall of the pipe, complicated fixing work, and occurrence of plastic deformation due to external force applied by crimping work. The present invention was made in view of the above-mentioned current situation, and its purpose is to join different materials of the inner fin and pipe to be joined by diffusion bonding, and to insert the inner fin into the pipe and then The inner fin is fixedly and closely attached to the inner wall of the pipe by skillfully utilizing the coefficient of thermal expansion of the respective materials of the inner fin and the tube, making it possible to carry out the insertion operation and fixing and tightly fitting with only a slight external force. This improves workability and reduces plastic deformation due to loading, making it possible to reliably join each other. The feature is that an inner fin made of aluminum or aluminum alloy material is inserted into a copper tube, and the lower limit temperature is 250℃ and the upper limit temperature is 540℃, preferably 350℃ in a vacuum, inert gas atmosphere, or reducing gas atmosphere. ~500℃
An inner fin made of aluminum or its alloy is diffusion bonded into a copper tube by heating in a temperature range of
This is a method of manufacturing a heat exchanger tube with inner fins that is metallurgically bonded and fixed. The method of the present invention will be explained below with reference to the drawings. FIG. 1 is a perspective view showing the state in which the inner fin is inserted into the pipe, and FIG. 2 is a front view showing the state in which the inner fin is fixed in the pipe. First, the outer diameter 2a of the inner fin 2, which is made of aluminum or its alloy and is to be fixed in the copper tube 1 and has a star-shaped cross section, is adjusted to the inner diameter 1a of the copper tube and is extruded to such a size that it can be slid into the inner fin 2. After obtaining it, insert it into the copper tube 1. Next, the tube 1 is pressed from the outside to such an extent that the peripheral end 2b of the inner fin 2 contacts the inner wall 1b of the copper tube 1 so that the inner fin 2 is not moved by the tube 1. Note that when the inner fin 2 is inserted into the tube 1, if the peripheral end 2b of the inner fin 2 is in sufficient contact with the inner wall 1b of the tube 1 to the extent that it does not move, there is no need to press the tube 1 from the outside. Next, the copper tube 1, in which the inner fin 2 is inserted without moving into the copper tube 1, is heated in a heating furnace. This heat treatment is preferably carried out under vacuum heating in which the inside of the furnace is evacuated, under an inert gas atmosphere containing an inert gas such as argon gas, or under an atmosphere of a reducing gas such as hydrogen. An experiment was conducted to determine whether diffusion bonding was possible when an aluminum cross-shaped fin was inserted into a copper tube and heat treated, and the results shown in the table below were obtained.

[Table] Although the above heating furnace was maintained under vacuum (10 ^-4 Torr.), it is of course possible to obtain similar results in an inert gas atmosphere or a reducing gas atmosphere. . Heating temperature 200℃ as specified in the table above
In this case, even after 24 hours of heat treatment, the aluminum material of the inner fin 2 cannot achieve sufficient thermal expansion and diffusion to press and contact the inner wall of the copper tube 1 to form diffusion bonding, resulting in failure of diffusion bonding. It was possible. and
At a heating temperature of 250°C to 540°C, the thermal expansion of the aluminum inner fin 2 presses and contacts the inner wall of the copper tube 1, and the diffusion between aluminum and copper is extremely good, allowing diffusion bonding without load. . However, at a temperature of 545°C, both the aluminum inner fin and the copper tube became soft and joining became difficult, and at temperatures higher than that, a good heat exchanger tube with inner fins could not be obtained. Note that aluminum alloys (e.g. JIS A3003
Almost similar results were obtained for the material. The heat exchanger tube 10 with inner fins of the present invention obtained as described above has a peripheral end portion 2 of the inner fin 2.
b was extremely well diffusion-bonded to the inner wall 1b of the tube 1, and the inner fin 2 and the tube 1, which were made of different materials, could be metallurgically bonded. When the heat transfer tubes manufactured by the method of the present invention were used in various heat exchangers, the heat transfer efficiency was improved by 20% compared to the conventional heat exchangers using unbonded heat transfer tubes. Even when the temperature is changed, there is no gap between the heat exchanger tube inner fin obtained by the present invention and the tube 1, and the tube 1 can maintain a sufficiently good condition for long-term use.
It is also effective in terms of energy conservation. Furthermore, while in conventional diffusion bonding, a compressive load is applied to bond the members to be bonded, the present invention uses thermal expansion of the metals to be bonded without applying any load. Since the joint surfaces are brought into close contact, there is no plastic change due to the application of a compressive load, residual stress is reduced, and a good heat exchanger tube can be obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a state in which an inner fin is inserted into a pipe according to the method of the present invention, and FIG. 2 is a front view showing a state in which the inner fin is fixed inside a pipe. 1 is a copper tube, and 2 is an inner fin made of aluminum or aluminum alloy material.

Claims (1)

[Claims] 1. A copper tube made of aluminum or an aluminum alloy material and inserted into a state where heat transfer fins formed in a cross shape are in contact with an inner wall is heated without any load.
By heat treatment at a temperature of 250-540℃,
A method of manufacturing a heat exchanger tube with inner fins, characterized in that the heat exchanger fins are diffusion bonded to the inner wall of the copper tube. 2. The method of manufacturing a heat exchanger tube with inner fins according to claim 1, wherein the heat treatment is performed in a vacuum, an inert gas atmosphere, or a reducing gas atmosphere.