JPH03243209A - Grooving method on inner surface of metallic tube - Google Patents

Abstract

PURPOSE:To improve the quality and productivity of a tube with grooved inner surface by limiting the outside diameter of product tube and the ratio of the outside diameter of grooving plug to the outside diameter of product tube in the grooving work of inner surface of metallic tube. CONSTITUTION:In the grooving method of the inner surface of metallic tube that the metallic tube 1 is reduced its diameter with a drawing die 2 and floating plug 3 and, next, expanding and grooving work is performed on the inner surface of the metallic tube with a roll forming member 6 and grooving plug 4 which are supported with a holding ring 7 and the metallic tube 1 is continuously subjected to expanding/rolling press/drawing work by adjusting its diameter with the die 8 for adjusting diameter, the high-quality tube with grooved inner surface and with less internal defect is worked at extremely high productivity by making so that the outside diameter is <=8mm and the ratio of the outside diameter of grooving plug to the outside diameter of product tube is 1.2-1.6.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for forming internal grooves on metal tubes such as copper and aluminum used as heat exchanger tubes for heat exchangers in air conditioners and refrigerators.

(Prior art and problems to be solved) In recent years, metal tubes made of copper, aluminum, etc. with grooves on the inside have been used as heat exchanger tubes for heat exchangers such as air conditioners and refrigerators.
Metal tubes of this type are required to have internal grooves of various shapes.

Conventionally, the manufacturing method for internally grooved tubes has been disclosed in Japanese Unexamined Patent Publication No. 5
As disclosed in No. 4-37059, No. 55-103215, etc., there is a rolling pressure drawing method as one of the so-called tube shrinking groove forming methods in which grooves are formed on the inner surface of a processed metal tube while shrinking it. There is.

As shown in FIG. 8, this tube shrinking compaction method involves gripping the tip of the metal tube 21 with a chuck and pulling it out using a hole die 2.
2 and the floating plug 23 to press the metal tube 21 from the outside to reduce its diameter, and then a grooved plug 25 that has been installed in the tube in advance by rolling rolls or rolling balls 24 arranged around the outer periphery of the metal tube 21. Press the inner surface of the metal tube 21 against the
A groove 26 is formed on the inner surface of the tube.

However, the method of rolling the rolling rolls or rolling balls 24 on the metal tube 21 in the region where the grooved plug 25 is located
Since the grooves are formed by reducing the inner and outer diameters of the metal tube 21 by pressing the metal tube 21, the drawing speed of the metal tube 21 is high.

Immediately after the metal tube 21 passes through a pressing portion formed by rolling rolls or rolling balls, a compression reaction force acts on this portion, which causes a floating phenomenon and tends to distort the metal tube 21.

As a result, when the groove of the metal tube previously formed during grooving is pressed against the grooved plug by the next rolling roll or rolling ball, the groove pitch of the metal tube and the grooved plug may be mismatched (splitting). There is a high possibility that internal defects may occur in the metal tube 21.

Furthermore, the metal tube 21 having an inner diameter larger than the outer diameter of the grooved plug 25 is reduced in diameter and compacted with a rolling roll or rolling ball 24, and is pushed into the groove of the grooved plug 25 to perform groove processing. As a result, the metal flow becomes uneven in the groove and groove crest of the grooved plug, causing defects (fin flaws, groove bottom flaws) on the slope and bottom of the groove of the workpiece. There was a problem with how easy it was. For this reason, when used as a heat transfer tube, there were problems such as a decrease in pressure resistance, a decrease in vibration fatigue strength, generation of metal powder, and generation of slow leakage of refrigerant due to brazing defects.

In order to overcome the inconveniences of the rolling pressure drawing method using the pipe shrinking method, the so-called pipe expansion rolling method was proposed, in which the inner surface of the metal pipe is grooved while expanding its diameter, as shown in Figure 6. (Patent Application No. 169571/1982).

This tube expansion and compaction method involves reducing the diameter of a metal tube 1 with a first die 2 and a floating plug 3, and then expanding the metal tube with a grooved plug 4 having an outer diameter larger than the inner diameter of the metal tube. This method creates grooves on the surface. In addition, in the figure, 1
is an annealed metal tube such as copper or copper alloy to be processed, 2 is a first die with a fixed exit hole diameter, 3 is a floating plug that does not have a bearing part, and 4 is a tie rod 5 and a thrust bearing attached to this floating plug 3 This is a grooved plug rotatably connected to the grooved plug 4, and on the outer surface of the metal tube at a location corresponding to the grooved plug 4, there is a rolled member (rolled ball or rolled roller) 6 that revolves while rotating on its axis. The rolling element 6 is supported by a retaining ring 7. Further, a diameter adjusting die 8 is arranged behind the rolling member 6.

In the case of the tube reduction compaction method, as shown in Figure 1, the grooved plug rotates in the direction of the arrow in the figure (counterclockwise), and the rolled ball rotates in the direction of the arrow in the figure (approximately perpendicular to the plane of the paper). While rotating and revolving around the Earth (rightward), the diameter of the metal tube is reduced with a rolling ball and pressed against the grooved plug to form a groove. At this time, the metal of the metal tube flows as if being rolled up toward the groove bottom of the grooved plug as shown by the arrow in the figure, so the metal flows collide with each other, and that part becomes an uncrimped part and remains on the groove side. There is a defect on the slope of the inner groove (fin defect)
occurs. In addition, since the metal of the metal tube is forcibly reduced in diameter by the rolling balls, the metal on the inner surface of the tube is deformed into wrinkles, which are then compressed by the rolling balls against the groove ridges of the grooved plug. As a result, groove bottom flaws appear at the bottom of the inner groove.

This wrinkle-like defect becomes more noticeable as the degree of diameter reduction increases, that is, as the compressive stress acting on the tube increases.

Incidentally, as is clear from the micrograph of FIG. 2, groove bottom defects have occurred as shown in FIG. 2(a), demonstrating the relationship between the state of metal flow and these defects.

On the other hand, in the case of the tube expansion rolling method, the grooved plug and rolling ball are in a state of rotation or revolution as in the case of the tube contraction rolling method, but the metal pipe is expanded from the grooved plug approach part. When configured in this position, the grooved plug is expanded at the approach portion and at the same time is pressed against the rolled ball to form a groove.

In other words, since the metal tube is compressed while applying a hoop force, the metal of the metal tube becomes a uniform metal flow and is pushed into the groove of the grooved plug, as shown in Figure 3, and as a result, the groove slope is There is no occurrence of uncrimped parts (fin defects) due to metal entrainment, and there are no wrinkle-like defects at the bottom of the inner groove. In particular, as the tensile reaction force inside the metal tube generated by the hoop force increases, that is, as the compressive stress increases (pipe expansion ratio increases), the metal tube will be grooved while being in close contact with the grooved plug. , the effect is remarkable.

(Problem to be solved by the invention) For metal tubes with an outer diameter of 8.0+ m or less, in order to keep the overall machining rate low, the outer diameter of the raw tube must be made smaller, and the outer diameter of the grooved plug should be made smaller in proportion to that. It becomes necessary to do so. In the tube expansion rolling method, the material comes into contact with the grooved plug from the approach section on the entry side, so a greater force in the thrust direction acts than in the conventional method.

In order to produce products with fewer internal defects, it is advantageous to increase the tube expansion ratio, but if the outer diameter of the grooved plug is small, the force acting in the rotational direction at the grooved plug approach groove will be in the thrust direction. The grooved plug loses the force and causes a rotation failure, causing the material to break without being able to come out.

In order to improve this, a method has been proposed in which a groove is formed in a part of the grooved plug taper to convert part of the force in the thrust direction into force in the rotational direction, but the grooved plug becomes expensive and However, since only a portion of the grooved plug can be used, the tool life is short and tool costs are high.

On the other hand, if the outer diameter of the grooved plug is increased to increase the rotational torque force at the grooved plug approach groove to avoid rotational defects, the overall machining rate increases and there is a limit.

Also, once the outer diameter of the diameter-adjusting die is made larger,
Even when performing a two-stage process to reduce the outside diameter and reducing the processing rate, if the diameter reduction rate in the second diameter adjustment process is large, the groove shape and wall thickness will change, causing heat transfer. There were problems such as a decrease in performance and an increase in unit weight.

The present invention was made in order to solve the problems in the above-mentioned tube expansion and rolling method, and it is possible to produce high-quality internally grooved tubes with few internal defects in metal tubes with an outer diameter of 8゜0iu or less with extremely high productivity. The purpose of this invention is to provide a method that can produce the same.

(Means for Solving the Problems) In order to solve the above problems, the inventors of the present invention have conducted extensive research and have found an optimal processing process for small-diameter internally grooved tubes with a product outer diameter of 8.0+w or less, especially The present invention was achieved by discovering the relationship between the outer diameter of the grooved plug and the outer diameter of the product tube.

That is, the present invention reduces the diameter of a metal tube using a drawing die and a floating plug, then expands and grooves the inner surface of the metal tube using a rolling member supported by a retaining ring and a grooved plug, and further In a method for grooving the inner surface of a metal tube in which the metal tube is diameter-adjusted using a diameter-adjusting die and then subjected to continuous tube expansion rolling and drawing processing, when the outer diameter of the product tube is 8.0 W+m or less, the outer diameter of the grooved plug and the product are The gist of the present invention is a method for grooving the inner surface of a metal tube, characterized in that the ratio to the outer diameter of the tube is 1.2 to 1.6.

The present invention will be explained in more detail below.

(Function) The inventor has repeatedly researched processing conditions for producing small-diameter internally grooved pipes with an outer diameter of 8.0 mm or less that have fewer internal defects, are of high quality, and are highly productive, and as a result, the pipe expansion rate has been increased. It has been found that the breakage of the material and the formability of the fins are more influenced by the outer diameter of the grooved plug than by the processing rate in the rolling process.

That is, when manufacturing a small-diameter grooved tube and trying to maintain the same processing rate as before, the outer diameter of the grooved plug becomes smaller. However, if the force required for forming the groove is the same, the rotational torque at the outer circumference of the grooved plug approach will be smaller due to the smaller outer diameter of the grooved plug, resulting in a 5-turn failure. -There is a limit to the processing rate that can be applied to processing.
Furthermore, even if a step is taken in which the outer diameter is increased, that is, the processing rate is kept low, and the outer diameter is separately reduced, problems such as a change in the groove shape and an increase in wall thickness occur when reducing the outer diameter.

Therefore, we searched for appropriate conditions taking these relationships into account, and found that the ratio of the outer diameter of the grooved plug to the outer diameter of the product tube was 1.2 to 1.
They found that a range of 6 is good.

If the ratio of the outer diameter of the grooved plug to the outer diameter of the product tube is less than 1°2, the processing rate can be lowered for products with an outer diameter of 8.0 wm or less, but the outer diameter of the grooved plug The diameter becomes relatively small. In that case, the rotational torque acting on the grooved plug becomes smaller, causing the grooved plug to malfunction.
The material will not come out and will break easily.

On the other hand, if the ratio of the outer diameter of the grooved plug to the outer diameter of the product tube exceeds 1°6, the outer diameter of the grooved plug will become relatively large, which can prevent rotation failure of the grooved plug, but the machining rate will be high. Therefore, it becomes difficult to process a shape with a wide groove bottom and a small fin top, or a shape with a deep groove depth. - In order to reduce the machining rate, if the outer diameter is machined to a larger size and then the outer diameter is scraped off separately, the groove shape changes, and the slope becomes thicker and the groove becomes narrower (see Figure 9). In addition, the phenomenon that the unit weight increases as the wall thickness increases becomes noticeable, and even if processing conditions are set that takes this into account, it becomes difficult to obtain the desired shape.

Note that the grooved plug is not particularly limited as long as it has a groove and at least an approach portion.

For example, typical examples include a shape in which a groove is provided in a part of the approach portion as shown in FIG. 4, and a shape in which a groove is provided in the entire approach portion as shown in FIG.
These have parallel parts. The angle of the ablative portion, that is, the approach half angle θ, is set, for example, in the range of 5 to 13 degrees.

Of course, other configurations may be the same as those of the conventional tube expansion and rolling system shown in FIG.

Next, examples of the present invention will be shown.

(Example) When internal groove processing was performed using a grooved plug with a grooved plug outer diameter of 9.8 mm in the internal groove processing apparatus using the tube expansion and rolling method shown in Fig. 6, the following dimensions were obtained. It was possible to manufacture an internally grooved tube with an expansion allowance of 0.04 mm.

Outside diameter near, 02+am Bottom thickness: Q, 26m5+ Fin height: Q, 16mm Lead angle = 17° Summit angle = 45° Groove bottom width: 0.24mm Approach half angle = 9.5° (Effect of the invention) Details above As mentioned above, according to the present invention, the outer diameter is 8°011
- Among the following metal tubes, high-quality internally grooved tubes with few internal defects can be processed with extremely high productivity.

[Brief explanation of drawings]

Figure 1 is a diagram illustrating the concept of the fin formation mechanism in the grooved state by the tube reduction method, and Figure 2 is a micrograph showing the metal structure of the groove of the internally grooved tube obtained by the tube reduction method. So, (a) shows the cross section (X 200), and (b)
shows the plane (x 38) of the groove forming start part, Figure 3 is a diagram explaining the concept of the fin forming mechanism in the grooved processing state by the tube expansion and rolling method, and Figures 4 to 5 are the grooved plug Figures 4(a) and 5(a) show the shape of
a) is a longitudinal sectional view, and FIGS. 4(b) and 5(b)
4(a) and 5(a), respectively, as seen from the X direction, FIG. 6 is a diagram showing the internal groove machining state and equipment in the conventional tube expansion rolling method, and FIG. 7 is Figure 6 is an explanatory diagram showing the phenomenon of poor rotation of a grooved plug that occurs when thick inner material is rolled using the conventional tube expansion rolling method, and Figure 8 is the internal groove machining state and equipment in the tube shrinking rolling method. FIG. 9 is a micrograph (xloO) of the metal structure of the groove where the groove shape has changed significantly due to scraping. 1...Metal tube, 2...No. ↓ die, 3...Floating plug, 4...Grooved plug, 5...Tie rod, 6...Rolled member (rolled ball or rolled roller)
, 7... Holding ring, 8... Diameter die, 9...
Groove forming part, 10... Grooved plug part where groove is not formed, ■... Unfilled area, ■... Uncrimped defect (fin flaw), ■... Wrinkle-like defect, ■...・Groove bottom flaws.

Claims (1)

[Claims] The diameter of the metal tube is reduced using a drawing die and a floating plug, and then the inner surface of the metal tube is expanded and grooved using a rolling member supported by a retaining ring and a grooved plug. In the method for grooving the inner surface of a metal tube in which the tube is diameter-adjusted and then expanded continuously by rolling and drawing, the outer diameter of the product tube is 8.0 mm or less, and the ratio of the outer diameter of the grooved plug to the outer diameter of the product tube is A method for grooving an inner surface of a metal tube, the method comprising grooving the inner surface of a metal tube so that the groove becomes 1.2 to 1.6.