Method for producing a heat pipe

Abstract

A method for producing a heat pipe comprises the following steps, performed on a first tube made from a malleable material: the diameter of the tube is swaged at a first end, and the end thus swaged is sealed closed; a second tube, of a smaller diameter than the first, is inserted into the second end of the first tube the second end of the first tube is swaged around the second tube and the interface between the two tubes is sealed the pipe thus created is partially filled with a heat-transfer fluid the air contained in the pipe is removed; and the free end of the second tube is sealed closed.

Claims

1. A method for producing a heat pipe comprising the steps: swaging a diameter of a first tube, at a first end, and sealing the first end closed; inserting a first end of a second tube, of a smaller diameter than the first tube, into a second end of the first tube; swaging the second end of the first tube around the second tube, and sealing an interface between the two tubes to form a heat pipe; partially filling the heat pipe with a heat-transfer fluid; removing air contained in the heat pipe; and sealing a second end of the second tube closed, wherein the first tube and the second tube are made from annealed copper.

2. The method according to claim 1, wherein the first end of the first tube is sealed by brazing.

3. The method according to claim 1, wherein the swagings are performed using a three-jaw or four-jaw chuck.

4. The method according to claim 1, wherein the swagings are performed using a shutter-shaped swaging tool.

5. The method according to claim 1, wherein the removing step is performed by connecting a vacuum pump to the second end of the second tube and sucking out the air until a partial air pressure of between 0 and 70 mbar is obtained in the heat tube.

6. The method according to claim 1, wherein the removing step is performed by heating the closed end of the first tube until the heat-transfer fluid boils.

7. The method according to claim 1 further comprising the following steps to seal the second end of the second tube: crushing a part of the second tube which is situated outside of the first tube until it seals; and cutting the second tube at the crushed part.

8. The method according to claim 7 further comprising the following step to seal the second end of the second tube: welding the cut end of the second tube to strengthen sealing.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other objectives and advantages of the invention will become clearly apparent in the following description of a preferred, but non-limiting, embodiment, illustrated by the following figures, in which:

(2) FIGS. 1a and 1b show the ends of a heat pipe produced according to one embodiment of a method according to the invention, employing a star-shaped swage.

(3) FIGS. 2a and 2b show the ends of the heat pipe produced according to one embodiment of a method according to the invention, employing a ring-shaped swage, and

(4) FIG. 3 shows a tool employed in one particular embodiment of a method according to the invention.

DESCRIPTION OF THE BEST EMBODIMENT OF THE INVENTION

(5) As previously described, a heat pipe produced using a method according to the invention comprises two tubes which are assembled to form the pipe. The pipe thus formed comprises two ends, a first which could be described as “ordinary”, and a second end that can be referred to as “composite”, because it comprises the second tube inserted inside the first tube.

(6) One particular embodiment of the present invention will be described hereinafter. The first tube, which can be seen in FIGS. 1 and 2, comprises a first end 10, 10′, and a second end 20, 20′. A second tube 30, 30′ is inserted in this second end 20, 20′.

(7) The first tube is preferably made of annealed copper. It has a diameter of the order of 10 millimetres, and a length of a few centimeters. The second tube is also preferably made of annealed copper and has a diameter of 4 millimetres. It is also emphasized that the wall of the second tube needs to be thick enough, for example of the order of 1 millimeter thick, that it does not become damaged during the crushing step. It also needs to be stiff enough that it remains in place after crushing, so as to prevent the tube from opening back up again, as this could lead to tube sealing problems.

(8) At the ordinary end, a total swage needs to be achieved so that a braze can later be performed in order to seal the pipe. At the composite end, the swaging is performed around the second tube. As previously described, there are a number of solutions considered for performing this swaging. Thus, in a first embodiment shown in FIGS. 1a and 1b, a three jaw or four jaw chuck is used to perform the swaging, yielding a star-shaped swage. As can be seen in FIGS. 1a and 1b, use may for example be made of a three jaw chuck, as shown in FIG. 1b for the ordinary end, and of a four jaw chuck or other type of chuck. This solution may be advantageous for large-diameter tubes but makes the subsequent operations of achieving sealing, for example by brazing or welding, more complicated because the shape that has to be welded is complex.

(9) In the case of heat-pipes which are intended to be installed in a battery unit, the number of chuck jaws used will, for example, be selected according to the desired architecture and notably according to the number of battery cells that are to be installed around each heat-pipe.

(10) The second solution, shown in FIGS. 2a and 2b, is to make a ring-shaped swage. Advantageously, in order to do this, use will be made of a swaging tool as shown in FIG. 3. The ring-shaped swage makes a production method according to the invention easier to industrialize since the sealing operations performed for example by welding are easier and more readily repeatable on long production runs.

(11) The swaging tool shown in FIG. 3 is created according to the same principle of operation as a photographic shutter. Thus, this tool comprises an outer disc 40, having a circular opening 41 at its centre. Installed within this circular opening are leaves 42 and an activating ring 43. The leaves are secured, at one of their ends, to the activating ring 43. Rotating the ring 43 causes the leaves to move into a position in which the orifice 41 is smaller.

(12) Thus, if a tube is inserted into the orifice 41 and the ring is activated, the pressure applied by the leaves to the tube leads to circular swaging of the tube shape. This leaf geometry makes it possible to obtain swaging that is uniform over the entire circumference of the tube. The choice of the number and size of the leaves will be made carefully in order to make it possible to swage the entire tube without damaging the wall of the tube.

(13) Once the swaging operations have been performed, the second tube has been inserted inside the first tube and the brazing and/or welding steps have been performed, a method according to the invention comprises the step of filling the pipe thus created with a heat-transfer fluid and of then removing the air contained in the pipe.