Heat pipe and method of manufacturing the same

Abstract: A wick layer (21) is attached and fixed to one sur­ face of a metal tape (1) without forming a gap (k) with the metal surface, and thereafter, the tape (1) is rolled so that the surface having the wick layer (21) serves as an inner surface, thus forming a pipe shape, then the pipe wall is corrugated (4). According to the above process, the wick layer (21) is completely and uniformly attached to the inner surface of the heat pipe (41).

Description: The present invention relates to a method for manufacturing a heat pipe according to the first part of claim 1 and to a heat pipe according to the first part of claim 8. Such a method and heat pipe are known for example from JP-A-57-100 91. Conventionally, in order to manufacture a heat pipe, a wick such as a metal gauze is attached through an open end portion from the outside to an inner wall of an elemental heat pipe formed into a hollow shape. However, this method is cumbersome; it is difficult to uniformly attach the wick to the entire inner wall surface; it is not easy to check whether or not the wick is correctly attached; it is difficult to attach a wick to the inner wall of a corrugated pipe due to its corrugated surface shape, which results in deterioration of heat characteristics; and more specifically, as shown in Fig. 1, gap K is present between diameter D of inner crest portion and diameter d of inner root portion, thus causing deterioration of the heat characteristics. (in Fig. 1, a cross-hatched portion indicates a wick). Applicant's JP 57-10091 discloses forming a heat pipe tube from a strip of metal and an overlying strip of wick. Partition members secured to the metal strip stand on the wick at given distances. Applicant's JP 58-11387 discloses forming a heat pipe tube by welding together the long edges of a metal tape, and then drawing the tube over a ribbed plug to make axial grooves on the inside wall of the tube. In this invention, a wick layer is attached and fixed to one surface of a metal tape without forming a gap with the metal surface, and thereafter, the tape is rolled so that the surface having the wick layer serves as an inner surface, thus forming a pipe shape, then the pipe wall is corrugated. The present invention has been made in consideration of the above situation, and has as its object to provide a heat pipe, to an inner surface of which a wick is completely and uniformly attached, and a method of manufacturing the same using a simple process. According to a first aspect of the present invention, there is provided a method of manufacturing a heat pipe, which is characterised by the corrugating step of the characterising part of claim 1 below. According to a second aspect of the present invention, there is further provided a heat pipe, corrugated with grooves as defined in the characterising part of claim 8 below. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 shows a conventional corrugated heat pipe; Fig. 2 shows a known apparatus used for manufacturing a heat pipe, Figs. 3 to 5 show structures used for forming a wick layer on a metal tape; Fig. 6 shows a grooving machine for a groove-like pattern on a heat pipe; and Figs. 7 to 10 show groove-like patterns formed on a heat pipe. Referring to Fig. 2, a known apparatus for manufacturing a heat pipe is shown, whereby a metal tape 1 is unwound from a roll in a conventional feeding apparatus (not shown). Metal tape 1 is formed into a heat pipe as a final product. Metal tape 1 is made of copper, aluminum, iron, or stainless steel, and has a width of 30 to 450 mm, and a thickness of 0.2 to 2.0 mm. Reference numeral 2 denotes a wick member comprising a tape to which a fibrous wick material is adhered. Wick member 2 is brought into close contact with and attached to one surface of metal tape 1 to form wick layer 21. Wick layer 21 has a capillary action, and the wick material includes an organic or inorganic metal fiber, glass fiber, animal/vegetable fiber, synthetic resin fiber, or the like. Wick layer 21 may be prepared by disposing the fibrous wick material on the tape. Wick layer 21 may also be prepared by forming the above-mentioned fiber into a net, nonwoven fabric, or porous material. In order to attach wick member 2 to one surface of metal tape 1, wick member 2 is wound into a roll shape in a feeding apparatus (not shown) in the same manner as in metal tape 1, and is fed therefrom at the same speed as the feeding speed of metal tape 1 to be brought into tight contact with and adhered to one surface of metal tape 1. In order to adhere wick member 2 to tape 1, adhesive 23 is sprayed and applied from nozzle 22 onto the surface of metal tape 1. When wick member 2 is attached, press roller 24 is preferably used. Reference numeral 3 denotes forming rollers, each of which forms metal tape 1, after being subjected to the above-mentioned process, into a pipe shape, so that wick layer 21 serves as an inner surface. Each forming roller 3 has an arcuated shape in order to form metal tape 1 into a pipe shape. A plurality of pairs of opposing forming rollers 3 are arranged along the moving direction of metal tape 1. Each of the rollers 3 has an arc configuration and is vertically rotatable around the axis. However, the roller 3 can be arranged in other forms, for example, in a staggered form. The arcs of the pairs of forming rollers 3 can be the same, but are preferably changed in accordance with the progress of metal tape 1 in the pipe forming process. For example, the first stage of forming rollers 3 may have a large radius of curvature, and the radius is gradually decreased to a size corresponding to a pipe diameter as the process progresses. Rollers 3 may have a shape other than the above-mentioned shape, and may be axially supported in a direction other than in the vertical direction. Reference numeral 31 denotes a welding means for welding the mating edges 10 at the start of the formation of heat pipe 41. A welding electrode of welding means 31 is arranged immediately above mating edges 10 to weld mating edges 10. Note that a process for cooling the pipe immediately after welding may be added so as not to damage already attached wick layer 21. The pipe obtained after the above process can be used as a finished product, or can further be corrugated. Reference numeral 4 denotes a corrugating machine for forming a groove-like or wave-like pattern. The pattern provides a flexibility on the outer surface of the heat pipe 41 and holds the working fluid in the heat pipe. More specifically, corrugating machine 4 comprises small disc 401 which is rotatably pressed along outer surface 42 of heat pipe 41, and ring 402 which holds the disc therein and is rotated along outer surface 42 of heat pipe 41. Ring 402 is rotated by rotating disc 403 arranged thereon. Small disc 401 has a rounded outer shape. In this case, when ring 402 is rotated, small disc 401 is also rotated while pressing elemental heat pipe 41, thus forming a smooth helically corrugated pattern on the outer surface of elemental heat pipe 41 at a constant pitch. When small disc 401 has a flat outer shape, a groove-like or wave-like pattern can be formed. If a groove-like or wave-like pattern is formed by corrugating machine 4 while moving heat pipe 41 is temporarily stopped, a wavy or groove-like pattern extending in the circumferential direction can be obtained on the outer surface of heat pipe 41. If pressing of small disc 401 is stopped with respect to elemental heat pipe 41, neither wavy nor groove-like pattern can be formed. If pressing is intermittently performed, a wavy or groove-like pattern can be intermittently formed on the outer surface of elemental pipe 41. More specifically, a wavy or groove-like pattern can be formed on an arbitrary portion of the outer surface of pipe 41, as needed. Mode of transferring the elemental pipe can be modified as desired. That is, the elemental pipe may be continuously, regularly, or irregularly transferred. Furthermore, the groove forming means can be transferred in correspondence to the transfer of the elemental pipe. The pipe formed as described above can be subjected to normal processes, e.g., cutting of the heat pipe, injection of working fluid, sealing of both ends, and the like, thus completing the heat pipe. Figs. 3 to 5 show other embodiments wherein wick layer 21 is formed on metal tape 1. Fig. 3 shows an embodiment wherein wick member 2 is made of a metal, e.g., a metal gauze. In this embodiment, wick member 2 is preformed into a tape-like shape, is fed from a state wherein it has been rolled, and is overlaid on moving metal tape 1. Spot welding electrodes 201 are arranged at both sides of the moving path of metal tape 1, so that tape-like wick member 2 is attached and fixed to metal tape 1 by spot welding electrodes 201. In this case, wick member 2 is preferably pressed against metal tape 1 by rollers 24, as in the above embodiment. This applies to the following embodiments. Fig. 4 shows an embodiment wherein wick member 2 is a powder, particles, or very fine fibers. In this embodiment, wick member 2 is accumulated in hopper 202. Wick member 2 can be any one of the powder, particle, or very fine fibers or may be a combination thereof. Prior to attachment of wick member 2 to metal tape 1, an adhesive is applied to the surface of tape 1, e.g. a plastic tape, by nozzle 5. Wick member 2 is fed to the applied surface by, e.g., spraying from hopper 202, thus attaching and fixing wick member 2 on the surface of tape 1. Fig. 5 shows an embodiment wherein wick member 2 comprises an organic or inorganic solid material. In this embodiment, solid wick member 2 is fused, brazed, or welded by nozzle 205 and the powder is attached and fixed to one surface of metal tape 1. Fig. 6 shows a grooving machine for forming a groove-like pattern on the surface of heat pipe 41 along its longitudinal direction. Grooving machine 501 has a hollow ring shape, and has an appropriate number of small discs 502 each having a groove forming function in its hollow portion toward the center. If heat pipe 41 is moved while grooving machine 501 is not rotated, grooves can be formed along the longitudinal direction of elemental pipe 41. If grooving machine 501 is rotated in the lateral direction, helical grooves can be formed. Figs. 7 to 10 are longitudinal sectional views of groove-like patterns formed on elemental pipe 41. Fig. 7 shows an embodiment wherein each corner of the bottom portion of the groove has no radius of curvature, and Fig. 8 shows an embodiment wherein each corner has radius R of curvature. Figs. 9 and 10 show embodiments wherein width E of the crest portion is different from width e of the trough portion. In Figs. 7 to 9, each section extending from the crest portion to the trough portion has a vertical wall, but in Fig. 10, each section has an inclined wall. According to the above embodiments, a wick layer can be uniformly and firmly attached and fixed to the entire inner wall of a heat pipe, thus improving the heat characteristics of the heat pipe. More specifically, since a wick layer is formed on a metal tape before being formed into a pipe shape, the contact state of the wick layer is not influenced even if machining and deformation are performed thereafter.

Claims: A method of manufacturing a heat pipe, comprising the steps of: feeding a tape (1) from a tape roll; forming a wick layer (21) on one surface of the fed tape; forming the tape having the wick layer thereon into a form of pipe (41) in which the wick layer is fixed to the entire inner wall of the pipe; and characterised by corrugating the pipe wall to create on the wall of the pipe a plurality of longitudinal or helical grooves each of which takes the form of a trough, having walls and a trough bottom, and a corner between each wall and the trough bottom. A method according to claim 1, characterised in that the wick layer (21) comprises a net, fabric, or non-woven fabric made of organic or inorganic fibre as a major component, and is attached and fixed to the fed tape by adhesion, fusing, brazing, or welding. A method according to claim 1, characterised in that the wick layer (21) comprises an organic or inorganic powder or particle, and is attached and fixed to the fed tape by adhesion or fusing. A method according to claim 1, characterised in that the wick layer (21) comprises an organic or inorganic fine fibre, and is attached and fixed to the fed tape by adhesion or fusing. A method according to claim 1, characterised in that the wick layer (21) comprises a mixture of an organic or inorganic powder and a fine fibre, and is attached and fixed to the fed tape by adhesion or fusing. A method according to claim 1, characterised in that the wick layer (21) comprises an organic or inorganic solid linear member or powder or a combination thereof, and is attached and fixed to the fed tape by spraying. A method according to claim 1, characterised in that mating edges of the tape having a wick layer formed thereon are bonded together by welding or adhesion to form the pipe. A heat pipe comprising a pipe (41) consisting of a tape (1) joined at its mating edges, and a wick layer (21) provided on and fixed to the inner surface of the pipe, characterised in that the pipe is corrugated to provide a plurality of longitudinal or helical grooves on the wall of the pipe, each of which grooves takes the form of a trough, having walls and a trough bottom, and a corner between each wall and the trough bottom. A heat pipe according to claim 8, characterised in that the tape (1) is a metal tape. A heat pipe according to claim 9, characterised in that the tape (1) is a tape of copper, aluminum, iron, or stainless steel. A heat pipe according to claim 8, characterised in that the wick layer (21) comprises a net, fabric, or non-woven fabric made of organic or inorganic fibre as a major component, and is attached and fixed to the fed tape by adhesion, fusing, brazing, or welding A heat pipe according to claim 8, characterised in that the wick layer (21) comprises an organic or inorganic powder or particle, or fine fibre. A heat pipe according to claim 8, characterised in that the wick layer (21) comprises a mixture of an organic or inorganic powder and a fine fibre. A heat pipe according to claim 8, characterised in that the wick layer (21) comprises an organic or inorganic solid linear member or powder or a combination thereof.

Inventors: MASHIKO KOUICHI, MOCHIZUKI MASATAKA, OKIAI RYUICHI, SAKAYA MASUJI, MASHIKO, KOUICHI, MOCHIZUKI, MASATAKA, OKIAI, RYUICHI, SAKAYA, MASUJI
Applicants: FUJIKURA LTD, FUJIKURA LTD.
Application year: 1988
Main classification: F28D15
IPC codes: F28D15