Method of manufacturing heat exchanger tube and heat exchanger

The present invention provides a method of manufacturing a heat exchanger tube in which a tube for a heat exchanger formed by brazing is manufactured using a sheet material, wherein a filler metal melted during brazing can be prevented from entering an opening formed in an opposing portion or a parallel portion formed when bending a sheet material into a tube shape or an opening facing toward the outside of the tube. The opposing portion, the parallel portion, or the opening facing toward the outside of the tube is sealed. As the sealing means, friction welding is preferable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a heat exchanger tube in which a tube for a heat exchanger formed by brazing is manufactured using a sheet material, and a heat exchanger in which a tube obtained by the manufacturing method is incorporated and integrated by brazing.

2. Description of Related Art

An extruded flat multi-channel tube has been used as a tube for automotive aluminum heat exchangers. In order to reduce the weight of heat exchangers, tubes obtained by forming a sheet material have been proposed. Examples of such tubes include tubes1aand1eshown inFIGS. 1 and 5formed by bending an aluminum sheet material into a tube shape so that the end portions are oppositely positioned, tubes1b,1c,and1fshown inFIGS. 2,3, and6in which the end portions are disposed in parallel, a tube1dshown inFIG. 4in which the end portion and a portion other than the end portion are disposed in parallel, and the like.

Another example is an inner fin tube1gshown inFIG. 7formed by bending a sheet material (in particular aluminum sheet material) into a tube shape so that the end portions are disposed in parallel, inserting a corrugated fin2(in particular aluminum fin) into the tube shape so that the end portion of the fin2is placed between the end portions of the sheet material, and closing (hemming) the end portions to form an end portion G as a temporarily secured portion3(see JP-A-2003-336989, for example).

A heat exchanger is manufactured by stacking the tube1a,1b,1c,1d,1e,or1for the inner fin tube1gand a corrugated fin, assembling a header (not shown), and integrating the components by brazing. When using the tube1a,1b,1c,1d,1e,or1f,a filler metal enters the tube through the opening formed in the opposing portion or the parallel portion or the opening facing toward the outside of the tube. When using the inner fin tube1g,a filler metal enters the tube through the gap in the temporarily secured portion3formed by closing the tube. As a result, the amount of filler metal becomes insufficient for the necessary portion, whereby insufficient brazing occurs. In particular, measures to solve this problem have been demanded when brazing an aluminum heat exchanger.

Specifically, a filler metal enters the tube1athrough an opening11in the opposing portion and an opening13facing toward the outside (portion A). A filler metal enters the tube1bthrough an opening12in the parallel portion (portion B). A filler metal enters the tube1cthrough an opening12in the parallel portion (portion C). A filler metal enters the tube1dthrough an opening12in the parallel portion of the end portion and a portion other than the end portion and an opening13facing toward the outside (portion D). A filler metal enters the tube1ethrough an opening11in the opposing portion (portion E). A filler metal enters the tube1fthrough an opening12in the parallel portion (portion F).

SUMMARY OF THE INVENTION

As means for preventing entrance of a filler metal, when using the tube1a,1b,1c,1d,1e,or1f,the opening11in the opposing portion, the opening12in the parallel portion, or the opening13facing toward the outside of the tube may be sealed by welding before brazing. When using the inner fin tube1g,the opening in the end portion G (temporarily secured portion3) may be sealed by welding before brazing. A complete joint is formed by known welding means which melts the above portion. However, it is difficult to control welding so that an appropriate joint is formed in such a thin portion. Moreover, a complicated instrument is required.

In recent years, friction stir welding (FSW) has been developed and expected to be applied in various fields. Therefore, a number of welding methods have been proposed. FSW is one type of solid-state welding method in which a hard tool is inserted into a soft metal such as aluminum and rotated therein to produce a plastic flow due to frictional heat, followed by stirring to effect welding. The inventors have attempted to seal the above portion by FSW. As a result, the inventors have found that a portion with a thickness of about 2 mm or more is necessary in order to obtain a strong junction without causing the matrix to buckle, and it is difficult to obtain a strong junction with a large junction depth for a portion with a small thickness.

On the other hand, the inventors have found that it suffices that these portions be welded to such an extent that these portions can withstand handling before brazing and thermal strain during brazing and a filler metal does not enter during brazing, and that a joint having such properties can be obtained even if the junction depth is small. Therefore, the inventors have found that FSW is also effective as means for welding these portions.

In order to obtain an easier welding method capable of forming a joint having the above properties, the inventors have conducted tests and examinations based on the idea of friction stir welding (FSW). The present invention has been achieved based on these tests and examinations. An object of the present invention is to provide a method of manufacturing a heat exchanger tube in which a tube for a heat exchanger formed by brazing is manufactured using a sheet material, wherein an opening formed in an opposing portion and a parallel portion formed when bending a sheet material into a tube shape and an opening facing toward the outside of the tube can be easily sealed by welding so that the tube has a sealed portion which can withstand handling before brazing and thermal strain during brazing and can prevent a filler metal from entering the tube during brazing, and a heat exchanger in which a tube obtained by the above manufacturing method is incorporated and integrated by brazing.

In order to achieve the above object, a first aspect of the present invention provides a method of manufacturing a heat exchanger tube in which a tube for a heat exchanger formed by brazing is manufactured using a sheet material, the method comprising: bending a sheet material into a tube shape while oppositely disposing end portions or disposing end portions or an end portion and a portion other than the end portion in parallel; and sealing an opening formed in the opposing portion or the parallel portion or an opening facing toward outside of the tube.

In this method of manufacturing a heat exchanger tube, the sheet material may be formed of aluminum.

In this method of manufacturing a heat exchanger tube, the parallel portion may be formed in three layers in which an end portion of an inner fin inserted into the tube is placed between the end portions disposed in parallel.

In this method of manufacturing a heat exchanger tube, the sheet material may be formed of copper.

In this method of manufacturing a heat exchanger tube, the sealing may be performed by friction welding.

In this method of manufacturing a heat exchanger tube, the sealing may be performed by friction stir welding.

In this method of manufacturing a heat exchanger tube, the friction welding may include restraining the opposing portion, the parallel portion, or the opening facing toward the outside of the tube, pressing a hard tool against the portion, relatively moving the portion and the hard tool to cause the hard tool to slide with respect to the portion, thereby causing frictional heat generation and a plastic flow to occur.

A second aspect of the present invention provides a heat exchanger manufactured by assembling a tube manufactured using the above method, a header, and a fin, and integrating the tube, the header, and the fin by brazing.

According to the present invention, a method of manufacturing a heat exchanger tube in which a tube for a heat exchanger formed by brazing is manufactured using a sheet material, wherein an opening formed in an opposing portion and a parallel portion formed when bending a sheet material into a tube shape and an opening facing toward the outside of the tube can be easily sealed by welding so that the tube has a joint which can withstand handling before brazing and thermal strain during brazing and can prevent a filler metal from entering the tube during brazing, and a heat exchanger in which a tube obtained by the above manufacturing method is incorporated and integrated by brazing can be provided. The method of manufacturing a heat exchanger tube according to the present invention is particularly suitably used when manufacturing a tube for an aluminum heat exchanger formed by brazing by bending an aluminum sheet material.

Other objects, features, and advantages of the present invention will hereinafter become more readily apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

As the sealing method used in the method of manufacturing a heat exchanger tube according to the present invention, sealing by friction welding is most preferable. In friction welding, an opposing portion, a parallel portion, or an opening facing toward the outside of a tube formed by bending a sheet material, or an end portion G of an inner fin tube is restrained. A hard tool is pressed against the portion, and the portion and the hard tool are relatively moved to cause the hard tool to slide with respect to the portion. This causes frictional heat generation and a plastic flow to occur, whereby the opening11formed in the opposing portion, the opening12formed in the parallel portion, the opening13facing toward the outside of the tube, or the opening at the end portion G of the inner fin tube is welded and sealed.

In the method of manufacturing a heat exchanger tube according to the present invention, an aluminum sheet material or a copper sheet material may be applied as the sheet material. The thickness of the aluminum sheet material or the copper sheet material is 1 mm or less, preferably 0.05 to 0.5 mm, and still more preferably 0.05 to 0.2 mm.

The method is described below in detail with reference to the drawings. An example of sealing the end portion G of the inner fin tube by welding is described below. Note that the opening12in the parallel portion of the tube1cshown inFIG. 3may be welded in the same manner as the end portion G. The opening13of the tube1a shown inFIG. 1, the opening12in the parallel portion of the tube1bshown inFIG. 2, the opening12and the opening13in the parallel portion of the tube1dshown inFIG. 4, or the opening12in the parallel portion of the tube1fshown inFIG. 6may be welded in the same manner as the end portion G by restraining the portion from the inside.

In a first embodiment, as illustrated inFIGS. 8 to 9showing the side surface of the end portion G, the end portion G is restrained from both sides, and a cylindrical hard tool4which rotates in a direction X1is pressed against the side surface of the end portion. The hard tool4is caused to slide with respect to the width direction of the end portion G to cause frictional heat generation and a plastic flow to occur to effect welding. The hard tool4is moved along the width direction of the end portion G of the sheet material bent into a tube shape while being rotated to weld the end portion G over the entire width.

As shown inFIG. 9, when the diameter of the hard tool4is smaller than the total thickness of the end portion G, friction stir welding may be performed in which the hard tool is inserted into the end portion G by rotation and pressing, and is moved in the width direction while being rotated to cause a plastic flow to occur around the rotating tool4, whereby the end portion G is welded to fill the path of the tool.

In a second embodiment, as shown inFIGS. 10 to 11, the end portion G is restrained from both sides, and a spatula-shaped hard tool5is pressed against the end portion G The hard tool5or the end portion G is moved in a direction Y1to cause the hard tool5to slide with respect to the end portion G. This causes frictional heat generation and a plastic flow to occur to effect welding. In this case, in order to prevent the plastically flowing matrix from forming a burr toward the outside, a lower end face6of the spatula-shaped hard tool5preferably has a shape which is internally depressed when viewed from the side surface, as indicated by6A,6B, and6C inFIGS. 15 to 17. When the amount of protrusion of the end portion G is small in a state in which the end portion G is restrained from both sides using a roll or the like, the lower end face6of the hard tool5may have a convex shape, as indicated by6D inFIG. 18.

Since the edge portion of the aluminum sheet material forming the tube is cut using a slitter or the like, a depression may be formed in the end portions disposed in parallel. In this case, as shown inFIGS. 15 to 17, a hard tool is used in which a depression is formed by causing both sides of the lower end face to protrude with respect to the center portion so that the matrix is introduced into the depression, whereby a stable junction state without a gap can be obtained.

In a third embodiment, a roller-shaped hard tool7may be used as the hard tool, as shown inFIGS. 12 to 14.FIG. 12shows the side surface of the end portion G The roller-shaped hard tool7which rotates in a direction X2is pressed in the direction indicated by the arrow in a state in which the end portion G is restrained from both sides, and is moved in the width direction of the end portion G The end portion G (matrix) to be welded may be moved relative to the hard tool7. It is preferable that the roller-shaped hard tool7have grooves8in the circumferential direction, as shown inFIG. 12. This promotes frictional heat generation and a plastic flow due to partial pressing and sliding, whereby the junction state can be improved.

FIG. 13shows an example in which frictional heat is generated by strongly rubbing the end portion G by rotating the hard tool7in the direction opposite to the direction Y2in which the hard tool7is moved along the end portion G (or, rotating the hard tool7in the direction opposite to the moving direction of the end portion G (matrix)) to effect welding. A matrix9is discharged in front of the hard tool7to form a burr. However, formation of burrs is minimized by selecting the moving speed and the rotational speed, whereby a sound junction state is obtained. Moreover, a stable junction state is obtained by controlling the pressing force of the hard tool7at an appropriate value.

FIG. 14shows an example in which frictional heat is generated by rotating the hard tool7in the same direction as the direction Y2in which the hard tool7is moved along the end portion G (or, rotating the hard tool7in the same direction as the moving direction of the end portion G (matrix)) to effect welding. In this case, since a stirred matrix10is discharged behind the hard tool7, it is preferable to apply a press jig (not shown) in order to prevent the matrix10from being discharged.

A fourth embodiment is an example in which the opening formed in the opposing portion such as the opposing portion of the tube1ashown inFIG. 1or the opposing portion of the tube1eshown inFIG. 5is welded. As shown inFIG. 19, the opposing portion of the tube (circular tube inFIG. 19) T is restrained by providing a backing jig14from the inside and providing forming rollers15from the outside. A hard roller16which rotates in the direction of the arrow is pressed against the restrained opposing portion. The opposing portion (opening11in the opposing portion) to be welded is moved relative to the hard roller16using the forming rollers15to promote frictional heat generation and a plastic flow due to partial pressing and sliding, whereby the opening11in the opposing portion is welded. After welding, the tube T may be subjected to roll forming into a cross-sectional shape as shown inFIG. 5.

In the above friction welding and friction stir welding, the junction depth is set at 0.5 mm or less, and preferably 0.3 mm or less. Friction welding is a method in which a plastic flow is caused to occur in a minute portion due to frictional heat generation. A sufficient frictional heat generation to cause a plastic flow to occur may not be obtained when welding at high speed, for example. In this case, it is preferable to preheat the weld target portion. As the preheating method, a method of heating the weld target end portion by high frequency induction heating, arc heating, laser heating, resistance heating, or the like can be given. The weld target portion is preheated to a temperature of 50 to 90% of the melting point of the weld target portion. As the preheating atmosphere, an inert atmosphere is preferable. It is effective to weld the opposing portion, the parallel portion, or the like utilizing friction welding or friction stir welding when applying an aluminum sheet material as the sheet material.

Friction welding and friction stir welding have been described above as the sealing means by preferable welding in the present invention. It is also possible to apply known welding means under sufficiently controlled conditions.

EXAMPLES

Examples according to the present invention are described below to demonstrate the effects of the present invention. Not that the following examples illustrate one aspect of the present invention, and should not be construed as limiting the present invention.

An Al—Mn aluminum alloy sheet (thickness: 0.2 mm) in which a sacrificial anode material Al—Zn alloy was clad on its outer surface was bent into a flat tube shape as shown inFIG. 3, and a parallel portion of the end portions was formed. An inner fin (thickness: 0.1 mm) formed of a corrugated Al—Mn aluminum alloy (Al—Si alloy filler metal was clad on both sides) was inserted into the flat tube. The end portion of the inner fin was placed between the aluminum alloy sheet portions forming the parallel portion to form an end portion in which the three portions were stacked.

The parallel portion and the end portion in which the three portions were stacked were restrained using steel plates with a thickness of 5 mm. A cylindrical steel rotating tool with a diameter of 0.5 mm was pressed against the side surfaces of the parallel portion and the end portion while rotating the tool at a rotational speed of 1500 rpm. The tool was moved in the longitudinal direction (width direction of the flat tube) at a speed of 8 m/min to cause frictional heat generation to occur due to sliding, thereby welding the end portion.

The resulting tube and inner fin tube were inserted into a header tube, and subjected to Nocolok brazing (brazing using fluoride flux) in which the tube was heated at a temperature of about 600° C. for three minutes. As a result, the filler metal did not enter the joint during brazing, and the amount of filler metal for the header tube did not become insufficient, whereby sound brazing could be performed.

An Al—Mn aluminum alloy sheet (thickness: 0.2 mm) in which a sacrificial anode material Al—Zn alloy was clad on its outer surface was bent into a flat tube shape as shown inFIG. 5, and an opposing portion of the end portions was formed.

As shown inFIG. 19, the opposing portion was restrained using a steel backing jig and forming rollers. A disk-shaped steel roller with a diameter of 200 mm and a width of 0.5 mm was pressed against the opposing portion while rotating the roller at a rotational speed of 3000 rpm. The opposing portion was moved at a speed of 100 m/min to cause frictional heat generation to occur due to sliding, thereby welding the opening in the opposing portion.

The resulting tube was inserted into a header tube, and subjected to Nocolok brazing (brazing using fluoride flux) in which the tube was heated at a temperature of about 600° C. for three minutes. As a result, the filler metal did not enter the joint during brazing, and the amount of filler metal for the header tube did not become insufficient, whereby sound brazing could be performed.