JPH03211395A - Manufacture of finned pipe - Google Patents

Abstract

PURPOSE:To restrain disks from cracking, by specifying the temperature of an oil supplied between a pipe to be worked and the disks. CONSTITUTION:A device for manufacturing a finned pipe comprises three cutter arbors 1 each of which is provided with a plurality of disks 2 at the periphery thereof. The arbors 1 are arranged at 120 deg. angular intervals, with the axis of each of the arbors 1 slightly inclined with respect to the axis of a pipe to be worked 3, and are driven to rotate by a motor. The pipe 3 is provided with a spiral fin 4 on the on the outer peripheral surface thereof by feeding the pipe 3 into the device comprising the three arbors 1, and moving the pipe 3 forward while rotating the arbors 1. At the time of fin formation, a lubricating oil maintained at 35 to 80 deg.C is supplied between the disks 2 and the pipe 3 from a lubricating oil supply pipe. By this method, the disks 2 for forming the fin 4 on the pipe to be worked, which is formed of a material difficult to work such as titanium, can be restrained from cracking.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a method for manufacturing a finned tube in which spiral fins are integrally formed on the outer surface of the tube, and more specifically, the invention relates to a method for manufacturing a finned tube in which spiral fins are integrally formed on the outer surface of the tube. The present invention relates to a method for manufacturing a finned tube in which the life of an arbor disk is extended by maintaining lubricating oil supplied at an appropriate temperature when forming fins on the outer surface of a processed tube.

BACKGROUND OF THE INVENTION A method for manufacturing a finned tube having fins integrally formed on the outer surface of the tube is generally manufactured using an apparatus in which arbors having a plurality of disks on the outer periphery are arranged at intervals of 120 degrees. In the case of this device, the axis of each arbor is slightly oblique to the axis of the pipe to be processed, and by rotating each arbor and advancing the pipe to be processed, at least one spiral is formed on the outer surface of the pipe. A shaped fin is formed.

In manufacturing this finned tube, when forming the fins, processing is performed while supplying lubricating oil between the tube to be processed and the disk. This lubricating oil is normally supplied from a large-capacity tank using a pump or the like, and then collected back into the tank for circulation.

The main purpose of this lubricating oil is to prevent seizure due to friction between the pipe to be processed and the disc, so there is no particular temperature control.
Used at room temperature.

On the other hand, the processing disk that bites into the pipe to be processed and forms a spiral fin is manufactured using an expensive material such as high-speed steel when processing a material that is difficult to process, such as titanium.

Problems to be Solved by the Invention In the above method for manufacturing finned tubes, cracks occur at the tip during fin forming, even though an expensive material such as high-speed steel is used for the processing disk. However, there is a problem in that the manufacturing cost of the finned tube is high due to a decrease in the yield of the processed material and the large cost spent on the disk.

In view of these circumstances, the present invention aims to reduce the manufacturing cost of finned tubes by suppressing cracks that occur in the disk used to form fins on tubes made of materials that are difficult to process, such as titanium. It is something.

Means for Solving the Problem Three factors can be considered that influence the cracking of the disc of the arbor: (1) surface pressure applied to the disc, slippage between the zero disc and the pipe to be processed, and (2) lubrication and cooling.

■As a method of reducing the surface pressure applied to the disk, changing the composition of the tube material on the pipe to be processed side is possible, but this cannot be done because the composition is limited due to the specifications. Another method is to heat the tube to be processed in advance to reduce its strength; however, the tube is cooled with room temperature lubricating oil for the purpose of lubrication between the disk and the tube before fin forming begins, and the effect is cannot be expected.

Regarding the slippage between the zero disc and the pipe to be processed, as a result of investigating and examining it through simulation tests, it was found that the effect was small.

Therefore, when we investigated a disc that had cracked due to fin forming on a titanium tube, we found that there was a microstructure that had changed in quality due to the effects of heat.

In other words, the tip of the disc has an altered microstructure due to repeated temperature increases due to processing heat and cooling due to lubricating oil.
It is estimated that there will be a loss.

To suppress this thermal effect, the flow rate, pressure, etc. of the lubricating oil are changed from the viewpoint that it is effective to provide a cooling effect to the lubricating oil for the purpose of lubricating the disk and the pipe to be processed. It turned out that there was no significant effect.

Based on the above knowledge, the inventor investigated from the viewpoint of reducing the surface pressure applied to the disk, and as a result, by controlling the temperature of the lubricating oil supplied between the disk and the pipe to be processed, the inventor decided to prevent the disk from cracking. We have found a temperature range that can satisfy the specifications of the fin part, taking into account that the elongation behavior of the material due to fin forming changes depending on the temperature.

That is, this invention maintains the temperature of the lubricating oil supplied between the pipe to be processed and the disk at 35 to 80°C,
The purpose is to suppress cracking of the disc.

The reason why the temperature of the lubricating oil was limited to 35 to 80°C is as follows.

The service life of the disc increases as the temperature of the lubricating oil increases.

This is because as the temperature of the lubricating oil increases, the cooling effect on the disk decreases, the temperature rise due to machining heat, the temperature range of cooling by the lubricating oil becomes smaller, and deterioration becomes less likely to occur. It is presumed that the strength of the pipe to be processed is reduced and it becomes easier to process, making it less likely to break.

Therefore, in order to obtain the effect of preventing breakage of the disk, that is, to more than double the disk life in the conventional case (lubricating oil temperature of about 20℃), the temperature of the lubricating oil must be at least 35℃ or higher. There is a need.

On the other hand, the upper limit temperature of the lubricating oil is preferably 80° C. or lower from the viewpoint of the life of the disk in actual production.

This is because the coefficient of friction increases when the temperature is extremely high due to the lubricating oil used, but at about 80°C there is almost no problem. Therefore, the upper limit temperature of lubricating oil is 8.
It is desirable to control the temperature to 71, which is 0° C. or lower and closer to that temperature.

As the method for raising the temperature of the lubricating oil, for example, a method can be used in which a steam pipe is provided in the lubricating oil tank and the lubricating oil is heated by steam.

Embodiment FIG. 1 is a schematic diagram showing an embodiment of the present invention, in which (1) is an arbor, (2) is a disk, and (3) is a pipe to be processed. 3 arbors (1) with (2)
are arranged at 120 degree intervals, and the axis of each arbor is slightly oblique with respect to the tube axis of the tube to be processed (3). These three arbors (1) are rotated by a motor (not shown).

To form the fins (4) on the pipe to be processed (3), the pipe to be processed (3) is fed into a device consisting of three arbors (1), and while rotating the three arbors, the pipe to be processed (3) is formed. By advancing the tube, spiral fins (4) are formed on the outer peripheral surface of the tube. During this fin forming, lubricating oil maintained at a predetermined temperature is supplied between the disk (2) and the pipe to be processed (3) from a lubricating oil supply pipe (not shown).

Next, with the configuration shown in Fig. 1, a finned tube manufacturing device consisting of three arbors equipped with a disk having a material of JIS-SKH9 and a hardness of HRC = 59 was used to manufacture a finned tube made of material ASTM B538.
Gr2, for a welded titanium tube with an outer diameter of 19.05 mm and a wall thickness of 1.24 mm, the average fin height is 0.8 mm or more,
Fins were formed with an average wall thickness of 3.66 mm or more at the base of the fins and a fin density of 30 to 32 fins per inch, which was the standard specification. As the lubricating oil, water-soluble working oil that does not contain substances such as chlorine and sulfur was used.

Figure 2 shows the length of the fin-formed pipe until cracks occur in the disc depending on the temperature of the lubricating oil at that time, the fin density at that time, and the material temperature at the start of fin formation.

As is clear from the results in Figure 2, controlling the temperature of the lubricating oil extends the life of the disk, and the fin density also changes as the lubricating oil temperature changes, which is the normal specification for titanium finned tubes. 30-3 per inch
The temperature of lubricating oil to satisfy 2 fins is 35~
Preferably 80℃.

I understand.

It is assumed that the reason why the number of fins decreases as the temperature of the lubricating oil increases is because the material stretches in the tube axis direction due to the increase in material temperature.

As described in detail, according to the method of this invention, the life of the disk during fin forming can be extended simply by controlling the temperature of the lubricating oil, so it is possible to extend the life of the disk during fin forming, so that it is possible to extend the life of the disk during fin forming. Even if it is, it has the significant effect of reducing the manufacturing cost of the finned tube.

[Brief explanation of drawings]

FIG. 1 is a schematic view showing one embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between lubricating oil temperature, fin forming tube length, fin density, and material temperature in the same embodiment.

Claims (1)

[Claims] A method of forming at least one spiral fin on the outer surface of the tube by advancing the tube to be processed while rotating a plurality of arbors each having a plurality of disks, wherein there is no space between the tube to be processed and the disks. A method for manufacturing a finned tube, characterized by maintaining the temperature of supplied lubricating oil at 35 to 80°C.