JPH04274816A - Manufacture of inside surface double grooved tube - Google Patents

Abstract

PURPOSE:To manufacture the inside surface double grooved tube for a heat exchanger at the same working speed as a conventional inside surface single grooved tube, to prevent the occurrence of generation of rolling-up and a rupture of the tube on the outside surface of the tube, and also, to form the prescribed groove shape. CONSTITUTION:In the manufacturing method for placing thread rolling tools 6, 7 for executing wire diameter working, while rotating like a planet on a plane being orthogonal to a tube axis in two stages on the same axis as an extrusion die, placing grooved plugs 3, 4 connected to a reduction plug in the corresponding position of each thread rolling tool, and executing grooving doubly and continuously in a pipe 1, this manufacturing method for the inside surface double grooved tube constitutes a characteristic feature of executing the grooving by a grooved plug whose outside diameter is >=7.5mm, and thereafter, executing thin diameter working of 10-50% by sink drawing reduction of once or twice or more, and finishing to 8-4mm outside diameter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing internally grooved tubes used in heat exchangers for refrigerators, air conditioners, etc.

0002

[Prior art and its problems] Generally, heat exchanger tubes used in heat exchangers for air conditioners and refrigerators flow fluorocarbons or the like as a refrigerant inside the tube to perform heat exchange with air conditioning outside the tube. Heat exchangers are becoming more efficient and more compact by using internally grooved tubes with triangular or trapezoidal grooves of .53 and 7.0 mm. However, as there is a strong demand for more compactness and higher efficiency, an inner double grooved tube in which spiral grooves intersect with each other and a method for manufacturing the same have been developed in place of the conventional inner grooved tube. By forming two grooves on the inner surface of the tube, the inner double grooved tube makes the groove shape more complicated than the conventional single groove, activates the turbulent flow effect, and increases the heat transfer area. Furthermore, by forming a cavity on the inner surface of the tube to promote boiling, the heat transfer performance can be greatly improved (Japanese Patent Application Laid-open Nos. 57-150799 and 1-317637). The manufacturing method is to arrange rolling rollers for diameter reduction in two stages on the same axis as the drawing die, and to place a plug for groove processing connected to a floating plug at the position corresponding to each roller. A method of forming grooves is known. However, the problem with such high-performance tubes being that they are not used, especially in small air conditioners that have high demands for compactness and high efficiency, is that the small diameter of 8 to 4 mmφ used in such small air conditioners When internally double-grooved pipes are manufactured using conventional methods, the grooves are double-grooved compared to single-groove processing, so the frictional resistance and plastic deformation resistance at the grooved part is doubled. When the drawing speed exceeds a certain level during continuous drawing and grooving, the tensile strength of the pipe exceeds the resistance applied to the pipe and the pipe breaks. In particular, this tendency becomes more pronounced as the diameter of the tube becomes smaller, and the machining speed becomes significantly lower than that of a conventional single internally grooved tube. For this reason, a method has been devised, as disclosed in Japanese Patent Application Laid-Open No. 15015/1985, in which a continuous pipe drawing device is provided between the first inner grooved part and the second inner grooved part. However, if such a method is used in actual manufacturing, the size of the device will inevitably increase.

0003

[Problems to be Solved by the Invention] As a result of studies on the above-mentioned problems, the present invention has developed a method for manufacturing internally double-grooved pipes that does not reduce processing speed and has excellent performance using a relatively simple method. This is what I did.

0004

[Means for Solving the Problems] The present invention provides two stages of rolling tools that perform diameter reduction while rotating planetarily on a plane perpendicular to the tube axis on the same axis as a drawing die, and After grooving with a grooved plug with an outer diameter of 7.5 mm or more in a manufacturing method in which a grooved plug connected to a drawing plug is placed at the corresponding position of the forming tool and the inside of the pipe is continuously double-grooved, 1 This is a method for manufacturing an inner double grooved tube, which is characterized by performing a diameter reduction process of 10 to 50% by dry drawing or two or more times to obtain an outer diameter of 8 to 4 mm. That is, the present invention is to manufacture a pipe with double grooves on the inner surface using an apparatus such as that shown in FIG. 1, for example. This device has a floating plug 2 and a first grooved plug 3 for groove processing inside a drawing die 22.
and a second grooved plug 4 are connected by a tie rod 5, and a first rolling roller 6 and a second rolling roller 7 are formed on the outside of the grooved plug. The diameter of the blank pipe 1 is reduced by a floating plug and a drawing die, a groove that is inclined or not inclined in one direction is formed on the inner surface by a first grooved plug and a first rolling roller, and a groove that is inclined or not inclined in one direction is formed on the inner surface by a first grooved plug and a first rolling roller. By forming grooves that cross the above-mentioned grooves using a rolling roller, for example, grooves 9 and peaks 10 as shown in FIG. 2 are formed,
An inner double grooved tube 8 having a cross groove 11 that crosses the groove 9 is manufactured. Further, the present invention can also manufacture an inner double-grooved tube 8 in which the groove portion 9 and the peak portion 10 have an offset portion 12 at the cross groove 11, as shown in FIG. In this grooved tube, the presence of the above-mentioned deviation portion changes the flow of the refrigerant liquid within the groove portion, thereby improving heat transfer performance.

[0005]

[Function] According to the manufacturing method of the present invention, double grooved pipes that could not be processed at high speed in the past, especially small-diameter inner double grooved pipes, can be processed in the same way as conventional single internally grooved pipes. can be manufactured at fast speeds. In the present invention, the outer diameter of the grooved plug is 7.5
The reason why the diameter is set to be equal to or more than mm is that if it is less than that, the outer diameter of the raw tube becomes thinner and double groove processing cannot be performed at high speed. In addition, the empty draw rate after groove machining was set to 10% to 50% because
This is because if it exceeds 50%, creases 13 will frequently occur on the outer surface of the tube as shown in FIG. 4 during empty pumping. Also,
This is because if it is less than 10%, it will not be any different from the conventional method, and it will not be possible to increase the machining speed when grooving a small diameter pipe.

[0006]

[Embodiment] An embodiment of the present invention will be described below. Using a device like the one shown in Figure 1, the outer diameter of the raw tube is 12.7 mm.
Although not shown, a phosphorus-deoxidized copper tube of mm x wall thickness of 0.45 mm is pulled in the direction of the arrow A by a pulling device such as a continuous drawing machine. Then, inside this pipe, a floating plug 2 and a first grooved plug 3 for groove processing are installed with an outer diameter of φ9.9.
The second grooved plug 4 is inserted into the floating plug, and the copper pipe is rolled by first and second rolling rollers 6 and 7 which revolve from the outside surface of the pipe and reduce the diameter of the copper pipe. The diameter was reduced to form double grooves on the inner surface of the tube. Here, the first grooved plug 3 and the first rolling roller 6 form a large number of fine first grooves on the heat transfer surface with a number of grooves of 90, a lead angle (left-handed twist) of 18°, and a groove depth of 0.10 mm. The number of grooves is 60, the lead angle (right-handed twist) is 18°, and the groove depth is 0.16 using the second grooved plug 4 and the second rolling roller 7.
An inner surface with an outer diameter of 10 mm, in which cross grooves 11 are formed by forming grooves of 1.5 mm in diameter so as to crush the first grooves, and the first grooves 11 are crushed by the second grooves 9 as shown in FIG. A double grooved tube was formed. After that, when winding it into a coil shape with a winder, it is empty drawn with a die and the drawing rate is 3.
0%, and the product was finished with an outer diameter of 7.00 mm.

[0007]Comparing this with the conventional method, if the same product is double grooved and then finished with a drawing ratio of 10% or less, for example, a material pipe of 9.53 mm x wall thickness of 0.40 mm is used. Using the first grooved plug outer diameter of 7.5 mm and the second grooved plug outer diameter of 7 mm, the grooved outer diameter is 7.5 mm.
Compared to the case where a grooved tube of 1.5 mm is wound into a coil while finishing it to an outer diameter of 7.00 mm (at a drawing rate of 7%), the production amount per unit time is 7.0 mm due to the drawing rate of 30% of the present invention. 00 mm was about 2.8 times, which was almost equivalent to the conventional single inner grooved tube. One reason for this is that when grooving, the outer diameter of the tube is thicker, which increases the weight per unit length, and even when grooving is performed at the same processing speed, the production volume per unit time increases. It is. Another reason is that when the inner surface is double grooved, the frictional resistance and plastic deformation resistance at the grooved part are twice as high as those with a single groove. This is because the speed limit for drawing and grooving processing becomes lower, and the production amount per unit time inevitably decreases. However, if the drawing ratio is set too high during dry drawing after grooving, (50%
(Limit)) Bad reviews will occur frequently, and the amount of good products produced per unit time will drastically decrease. Next, when producing an inner double grooved tube in which cut-shaped cross grooves 11 with misaligned portions 12 are formed, as shown in FIG. By forming the gap portion 12, the flow of the refrigerant liquid in the groove portion collides with one side of the peak portion 10 and disturbs the flow, and the liquid refrigerant flow on the other side collides with the flow on the other side. By creating a holding part that causes stagnation and forming a liquid film distribution within the groove, heat transfer performance is improved. Further, the turbulent flow effect of such a misaligned portion has the effect of removing refrigerating machine oil and dirt that adhere to the inside of the cross groove 11 and lead to a decrease in performance. The inner double grooved tube thus obtained was assembled into a double heat exchanger, a refrigerant was flowed through the tube, and water was flowed through the annular portion to perform heat exchange, and the evaporative heat transfer was determined. Table 1 shows the experimental conditions at that time.

[0008]

[Table 1]

FIG. 5 shows the heat transfer coefficient within the tube during evaporation. The figure shows the conventional 7.00 mm as shown in Figure 6.
The results for a single internally grooved tube (number of grooves: 60, helix angle: 18°, groove depth: 0.15 mm) are also shown. According to this, the inner double grooved tube produced by the manufacturing method of the present invention showed twice the evaporation performance than the conventional inner grooved tube.

0010

[Effects of the Invention] As explained above, according to the method of manufacturing the inner double grooved tube of the present invention, compared to the conventional inner grooved tube, the
It is possible to manufacture an internally double grooved tube with twice the evaporation performance and a weight that is almost the same as a conventional single internally grooved tube per unit time.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of an apparatus used for manufacturing the inner double grooved tube of the present invention.

FIG. 2 is a perspective view of essential parts showing an example of an inner double grooved tube manufactured according to the present invention.

FIG. 3 is a perspective view of essential parts showing an example of an inner double grooved tube manufactured according to the present invention.

FIG. 4 is a cross-sectional view of a grooved tube with a bulge portion that occurs during the manufacture of an inner double grooved tube.

FIG. 5 is a diagram showing the relationship between the evaporative heat transfer coefficient and the refrigerant flow rate of the inner double grooved tube manufactured according to the present invention.

FIG. 6 is a perspective view of a main part of a conventional internally grooved tube.

[Explanation of symbols]

1　Main pipe 2 Floating plug 3 First grooved plug 4 Second grooved plug

Claims (1)

[Claims] Claim 1: Two rolling tools are arranged coaxially with a drawing die and perform diameter reduction while rotating planetarily on a plane perpendicular to the tube axis, and a drawing plug is placed at a corresponding position of each rolling tool. In a manufacturing method in which a grooved plug connected to a tube is placed and double grooves are continuously formed inside the pipe, the grooved plug with an outer diameter of 7.5 mm or more is used to groove the pipe, and then the grooved plug is connected to the grooved plug once or twice or more. The diameter is reduced by 10-50% by drawing, and the outer diameter is 8-4 mm.
A method for manufacturing an inner double grooved pipe characterized by finishing the pipe with a double groove on the inside.