JPH01299707A - Manufacture of small and thin wall thickness heat transfer tube - Google Patents

Abstract

PURPOSE:To perform mass production with good workability by forming grooves on the inside surface of a tube whose outside diameter exceeds a specific value and sinking a tube with a backward tension of a specific condition for heat transfer tubes having specific outer diameter, spiral grooves of a specific depth, width, and of a specific number. CONSTITUTION:A heat transfer tube having an outside diameter D0 of 3-7mm and spiral grooves or continued grooves in the tube axial direction whose groove depth (h) of 0.1-0.3mm, groove width W1 of 0.05-0.45mm, and the number of grooves in 25-70 is manufactured. On the inside surface of a tube whose outside diameter D0 exceeds 7mm, grooves of a depth (h), width W1 in the above ranges, and a specific number of grooves are formed. Sinking by draft ratio of 16% per sinking with a backward tension being 30-60% of the breaking force of a tube is performed to reduce the D0 to 3-6mm. By synergetic effect of the backward tension and draft ratio, reduction of a diameter to 3-6mm with a very little variation range of wall thickness and groove depth is performable for even a small tube having a diameter of <=7mm. Hence, mass production of small diameter heat transfer tubes with good workability is performable without complicated working design.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a heat exchanger tube used in a small-sized heat exchanger, and more particularly to a method for manufacturing a small-diameter, thin-walled heat exchanger tube.

[Conventional ° technology]

Heat exchanger tubes in which a large number of continuous spiral grooves are formed on the inner surface of the tube are used in small heat exchangers that use refrigerants such as Freon in order to save energy.

Recently, there has been a demand for thinner heat exchanger tubes as a factor in reducing the cost of heat exchangers. However, thinner tubes are accompanied by a decrease in pressure resistance, so it is necessary to maintain pressure resistance by reducing the tube diameter. A method has been adopted to do so. Normally, heat exchanger tubes with internal spiral grooves are processed by inserting a grooved plug into the tube and drawing the tube while reducing its diameter using planetary rotating rolls.This method is used for heat exchanger tubes with an outer diameter of up to 8m++. It can be manufactured smoothly using processing means. However, in this method, when the outer diameter becomes 7 mm or less, the phenomenon of pipe breakage tends to increase.

In order to solve this problem, the outer diameter of the tube is reduced to 7 mm or less by rolling the inner surface of the tube with a grooved plug in advance to form a groove, and then performing dry drawing. A method for diameter machining has been developed (
JP-A-62-98200).

[Problems to be Solved by the Invention] However, in the above-mentioned diameter reduction method, in order to compensate for the fact that the grooves become close to each other during dry drawing and the groove width and groove depth become small, There is a problem in processing design that the groove width and groove depth of the raw pipe must be increased by the amount reduced by processing, taking into account the degree of drawing.

The present invention solves these difficulties and provides a method for manufacturing a small-diameter, thin-walled heat exchanger tube without complicating the design.

[Means to solve the problem]

That is, the method for manufacturing a small-diameter thin-walled heat exchanger tube according to the present invention is as follows:
Outer diameter (DO) 3~7I, groove depth (h) 0.1~0.3
mm, groove width (Wl) 0.05-0.45III11,
When manufacturing a heat exchanger tube with 25 to 70 grooves in a spiral shape or continuous in the tube axis direction, the outer diameter (D, )
Groove depth (h) within the above range on the inner surface of the pipe beyond the
The outer diameter of the tube ( D0) to 3
It is characterized in that the diameter is reduced to ~6III11.

In the present invention, D+1 in FIG. 1 is the outer diameter, D.

is the inner diameter, W is the groove width, W2 is the peak width, h is the groove depth, t is the bottom wall thickness, r is the peak angle of the peak, and the degree of processing is the rate of change in the outer diameter of the pipe before and after dry drawing. Point.

The rear tension applied during the dry drawing process must be set in the range of 30 to 60%; if it is less than 30%, the bottom wall thickness will increase significantly due to the drawing process, while if it exceeds 60%, the drawing will fail. The pipe is more likely to break during the process.

Further, it is important to keep the working ratio to 16% or less; if this ratio is exceeded, the drawing process will result in an increase in the bottom wall thickness and a decrease in the groove depth. However, when the degree of processing is made smaller than 5%, the working efficiency decreases significantly. Therefore, the desirable working degree range is 5 to 16%.

[Effect]

According to the present invention, the rear tension of 30 to 60% and the working degree of 16% or less per time act synergistically against the breaking force of the pipe applied during air drawing, and the outer diameter is reduced to 7 mm. Even with the following small diameter pipes, 3.
It becomes possible to reduce the diameter extremely smoothly to ~6 mm. Therefore, there is no need for complicated processing design before dry drawing.

〔Example〕

The inner surface of the tube is rolled using a grooved plug to increase the outer diameter (
Do ) 7.94mm, inner diameter (D + ) 6.92
mm, groove width (Wl) 0.30mm, groove depth (h)
A copper tube with an internal spiral groove (helix angle of the spiral groove of 18 degrees) was manufactured, having dimensions of 0.20 mm, bottom wall thickness (t) of 0.31 mm, peak angle (r) of 56°, and number of grooves of 50. .

For this inner spiral grooved copper tube, air drawing was performed without applying any backward tension by changing the conditions of the backward tension relative to the breaking force of the tube (backward tension/breaking force) and the processing degree.

Figure 2 shows the relationship between rear tension/breaking force and bottom wall thickness change.
FIG. 3 shows the relationship between rear tension/breaking force and groove depth change. Further, Table 1 shows the results of determining the rear tension/breaking force and the shape of the peaks between the grooves using enlarged cross-sectional photographs. Among the codes in Table 1, Q indicates a normal peak shape, Δ indicates a low peak shape,
Items with slightly bad shape (2-3 fins/60 fins), ×
indicates a shape that has been deformed from its original shape and is missing in some cases (2 to 3 fins/60 fins).

Table 1 穢方1αL0LL Welfare Works M Name LID Work 20% ■1 degree 25%o o o.

20 0 Δ × 40 0 Δ × 60
0 △ × 80 0 Δ Fracture 1000 Fracture 140 Fracture -- From the results in Figure 2, the increase in wall thickness can be reduced by applying rear tension, and when the rear tension is equal, the degree of processing is below a certain level (16%) It can be seen that the thickness becomes noticeably thinner as the thickness increases, and that thickness fluctuations are hardly recognized in the range of rear tension/rupture force of 30 to 60%.

FIG. 3 shows that the groove depth decreases as the degree of machining increases, without being influenced by the rear tension.

In examples where the degree of processing is 16% or less, it is recognized that there is little variation in groove depth in the region where the rear tension/breaking force is 30 to 60%.

In addition, the results in Table 1 show that the shape of the mountain deteriorates as the degree of work increases, regardless of the increase or decrease in rear tension;
It is found that in 2% of cases, the normal shape is always maintained up to the breaking limit.

〔Effect of the invention〕

As described above, according to the present invention, a high-performance, narrow-diameter, thin-walled heat exchanger tube can be manufactured with extremely good workability. Therefore, it is industrially useful as a technology that can be mass-produced at low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing a small-diameter thin-walled heat exchanger tube of the present invention,
FIG. 2 is a diagram showing the relationship between the rear tension/breaking force and the amount of change in bottom wall thickness according to the embodiment, and FIG. 3 is a diagram showing the relationship between the rear tension/breaking force and the amount of change in groove depth according to the example. Do...Outer diameter D+...Inner diameter W,...
Groove width W2...Mountain width h...Groove depth
t...Bottom thickness r...Apex angle of mountain Applicant Sumitomo Light Metal Industries, Ltd.

Claims (1)

[Claims] Outer diameter (D_0) 3-7mm, groove depth (h) 0.1-0.
3 mm, groove width (W_1) 0.05 to 0.45 mm, and groove number 25 to 70 in a spiral shape or continuous in the tube axis direction.
Groove depth (h) and groove width (within the above range) on the inner surface of the tube exceeding
W_1) and the number of grooves are provided, and 30
Processing degree 16 per run while applying ~60% rear tension
% or less, and the outer diameter (D_0) of the tube is 3~
A method for manufacturing a small diameter thin-walled heat exchanger tube characterized by reducing the diameter to 6 mm.