KR20020013403A - Method of making a tube for a heat exchanger - Google Patents

Abstract

PURPOSE: A method for making a tube for a heat exchanger is provided to reduce the cost of materials for making a tube and to prevent problems caused by flux in a passage and necessity of cleaning work for removing flux. CONSTITUTION: A method of making a heat exchanger tube comprises the steps of: (a) providing an elongated strip of aluminum based material(22) having opposed edges and a braze alloy on only one side thereof; (b) forming dimples(30) in the strip; (c) placing slits(34) extending through the strip at the apexes(44,46) of the dimples on at least one side of the fold line; (d) folding the strip along the fold line and bringing the edges into contact with one another and causing the apexes of aligned ones of the dimples to abut one another; (e) welding the edges to each other to form a tube; and (f) causing the braze alloy to flow from the strip one side through the slits to the interior of the tube and braze the apexes of the aligned dimples together.

Description

Method for manufacturing tube for heat exchanger {METHOD OF MAKING A TUBE FOR A HEAT EXCHANGER}

The present invention relates to a heat exchanger, and more particularly to a so-called elliptical or flat dimple tube used in such a heat exchanger and a method of manufacturing the same.

So-called dimple tubes with flat or elliptical cross sections have long been used in various types of heat exchangers. In such tubes, dimples are formed on the sidewalls of the tube and extend in a direction transversely across the smaller diameter of the tube, partially or entirely across the interior of the tube. In most cases, dimples are used to increase the heat exchange rate by swirling heat exchange fluid flowing through the tube. In other cases, the opposing dimples are joined to each other or the dimples are joined to the opposite side of the tube wall so that the tubes can withstand pressure.

More specifically, weight is the biggest problem in many applications, especially in vehicles, and in order to reduce material costs, this type of tube is made very thin and cannot be supported so that the tube does not twist due to fluid pressure in the tube. Can be. This is particularly problematic when the tube is used for high pressure applications such as condensers for refrigeration systems. In particular, because the tubes are flat, they are likely to "go round" when under pressure if they are not supported against the forces causing this torsion. In some cases, plate fins are used on the outside of the tube to wrap around the tube to prevent this twist, while in other cases the insert is placed in the tube and bonded to the opposite side to prevent the twist. In another case, the inwardly facing dimples are soldered to each other or to the opposite side of the tube to provide the desired strength.

Aluminum is increasingly used as a material for forming such tubes because of its relatively low density and relatively high thermal conductivity. Aluminum tubes are easily soldered to other heat exchanger components such as headers and fins. Thus, generally dimpled aluminum tubes are formed by placing dimples in the strip used to form the tube while the strip is generally flat or flat. With conventional molding techniques the strips are generally molded into round shapes so that the sides of the strips are joined together. High frequency induction welding is performed along the edges of the state where the strips are joined to weld into the blocked tube. This tube is then further sized from a basically round tube into a tube having a conventional flat or elliptical cross-sectional shape. Dimples are formed in the strip while the flat tubes are substantially joined together.

The strip itself is molded from an aluminum based metal and clad with an aluminum based braze alloy on both sides. When the solder flux is injected into the tube and the tube is assembled in a heat exchanger and held in place with a fixture, the braze alloy material inside the tube flows into the dimple and the opposing dimples are joined together.

One problem with forming dimple tubes in this way is that the strips on which the tubes are formed must be clad with solder on both sides. In order to solder clad on one side, a braze alloy must be used during the brazing process where the dimples are brought into contact with each other to join the two together. Also on the opposite side of the strip, which is outside of the tube, it is necessary to allow the strip to be soldered to the header, in particular the pin. Strip clad strip stock on both sides is much more expensive than strip clad strip stock on only one side. However, according to the prior art, both clad clad stocks need to solder the inwardly dimples to each other.

Another difficult problem is that the solder flux must be inside the tube to ensure that the dimples are soldered to each other reliably. Soldering fluxes typically used in aluminum brazing operations, such as the Nocolok ™ process, retain excess after the brazing process is complete. These flux surpluses can be difficult to use in processes that run on tubes with passages of relatively small hydraulic diameters because the passages can be partially or wholly plugged by the flux surpluses. In addition, it may be difficult to inject the flux surplus into the tube and the inside of the tube will need to be cleaned continuously to minimize the build up of solder flux therein.

The present invention seeks to overcome one or more of the above mentioned problems.

It is an object of the present invention to provide a new and improved method of forming a dimple tube. It is also an object of the present invention to provide a tube for a heat exchanger produced according to the method.

A very preferred method of manufacturing the heat exchanger according to the invention

a) preparing an elongated strip of aluminum substrate with opposite edges and brazing alloy on only one side,

b) forming dimples in the strip such that the dimples protrude toward the strip opposite one side of the strip and the dimples on one side of the predetermined fold line located between the opposite edges align with the dimples on the other side of the fold line,

c) placing a slit through the strip at at least one dimple vertex of the fold line,

d) folding the strip along the fold line to bring the edges into contact with each other, while bringing the aligned one vertex of the dimples into contact with each other,

e) welding the edges together to form a tube, and

f) soldering the vertices of the aligned dimples to each other by flowing a braze alloy from one side of the strip through the slit into the tube;

It includes.

More preferably, step f) proceeds to applying flux to one side of the strip at least near the dimple with the slit.

Preferably, the dimples are conical in shape.

In some cases, a hole other than a slit may be used while in other cases the dimple may be located on only one side of the fold line and contact the opposite inner wall of the tube.

Also described is a new and improved dimple tube produced by the method according to the invention.

Other objects and advantages will be apparent from the following detailed description set forth with reference to the accompanying drawings.

1 is a side view of a general heat exchanger using a dimple tube manufactured according to the present invention.

2 is a perspective view of an aluminum sheet stock portion to be finally folded over the tube to form a tube;

FIG. 3 is a view similar to FIG. 2 but folded over the tube to form a finished tube portion; FIG.

Figure 4 is an enlarged cross-sectional view of the dimple tube manufactured according to the present invention.

The method of the present invention is to provide an aluminum based tube with a so-called flat or elliptical cross section comprising inwardly facing dimples. This type of tube is ideally suited for use with various types of heat exchangers, especially heat exchangers that induce vortex inside the tube with an inwardly directed dimple, in which case the tube is not subjected to any pressure of the heat exchange fluid passing through the tube. It is necessary to have a degree internal resistance. In general, the tubes are useful for manufacturing heat exchangers for use in automotive radiators, air supply coolers, air conditioners or refrigeration systems. However, it should be noted in particular that there is no restriction on the use of any one of the heat exchangers described above. It will be appreciated that the tube is ideally suited for use in any heat exchanger that uses dimples to provide vortex induction and / or pressure resistance.

Referring to Figure 1, a general heat exchanger made in accordance with the present invention includes headers spaced in parallel opposite one another, which may be of any known form. For example, the headers 10, 12 may be tubular in one or more pieces. In addition, the headers 10, 12 may be in the form of header plates covering the tank in a conventional manner.

As shown in FIG. 1, the schematically illustrated inlet 14 extends into the header 10, and the schematically illustrated outlet 16 extends from the header 12. A plurality of tubes 18, only some of which are shown, extend between the headers 10, 12 to be in fluid communication with the interior of these headers. The tube 18 has a so-called flat or elliptical cross section and extends through the facing slots (not shown) of the headers 10 and 12 to be soldered in place. A serpentine fin is placed between adjacent tubes 18 and soldered to the tube in a conventional manner. However, it should be particularly noted that plate pins can be used if desired.

All members are formed of aluminum-based materials, which can be soldered together in a conventional manner, for example by a so-called Nocolok ™ process using a so-called potassium fluoro aluminate compound.

In addition, although the inlet 14 extends to one of the headers 10 and the outlet 16 extends from the header 12 to appear as a so-called single pass heat exchanger, one or the other or both of the headers 10, 12, or both. Note that baffles can be placed in the to provide as many different passes as desired. Thus, the inlet 14 and outlet 16 may be located in one of the headers 10 and 12 rather than in different headers depending on the number of passes provided.

Referring to FIG. 2, the tube 18 is formed of an elongated strip 22 of aluminum-based sheet stock. The strip 22 has opposing edges 24, 26 that can be rolled up upwards in the same direction at about 90 ° on each of the edges 24, 26 as illustrated.

Generally there is a predetermined fold line 28 at the center of the strip. Indeed, the fold line 28 is an imaginary line that represents the area where the strip 22 is curved along its length such that the edges 24, 26 are in contact with each other. Of course, if desired, the fold line 28 may be actually drawn on the strip by any suitable marking technique that draws ink, and so on.

Between the fold line 28 and the edge 24, a series of dimples 30 are formed in at least one row extending longitudinally of the strip 22. The dimples 30 are spaced apart from each other in the shape of a nominal truncated cone, but are imperforate in the preferred embodiment. The dimples may be formed by any suitable stamping or drawing as the strip 22 passes through the prior art forming equipment used to form the strip 22 in the finished tube. Can be.

A spaced dimple 32 in a second row is formed between the fold line 28 and the edge 26. The dimples 32 are arranged to align with the dimples 30 when the strips are folded about 180 ° on the fold line 28. Dimples 32 are also generally truncated in shape and are provided with openings 34 at their vertices.

The strip 22 is an aluminum-based material, as described above. The upper surface 36 of this strip 22 is not covered with aluminum. That is, the top surface 36 can be oxidized to some extent as is known, but without the braze alloy. The opposite side of the strip 38 is clad with a braze alloy, which is a generally aluminum-based compound containing some silicon or other material that lowers its melting point slightly below the melting point of the base aluminum on which the strip 22 is formed. This allows the base strip 22 aluminum to flow into the braze alloy liquid before it softens and flows. The metallurgy of such systems is well known and will not be further described herein.

The finished tube portion is illustrated in FIG. 3. Here, the edges 24 and 26 abut each other and are joined to each other by, for example, high frequency induction welding. In addition, the vertices of the dimples 30 and 34 are in contact with each other and joined to each other by means to be described later in more detail. Of course, the tube 18 is generally substantially longer than the tube shown in FIG. 3 where only a short portion of the finished tube 18 is shown.

Next, referring to FIG. 4, a strip 22 is illustrated with a tube made up of welds 40 formed at their junctions, with edges 24 and 26 joined to each other. On 38, a braze alloy layer 42 is also located. Note that there is no solder clad alloy on the side 36.

One vertex 44 of the dimple 32 abuts one vertex 46 of the dimple 30.

Thus, it can be seen that the opening 34 of the vertex 44 is aligned with the vertex 46. Fillets 48 of brazing material not only bond the vertices 44, 46 together but also seal the opening 34. The fillet 48 is formed by the brazing material from the layer 42 on the side face 38 of the strip that enters the interior of the tube through the opening 34 to wet the vertices 46 of the dimple 30.

In the general case, the strip 42 is unwound from a coil or the like and passed through a stamping or drawing machine to form curls at the edges 24, 26 as well as the dimples 30, 32. Through roll forming techniques or the like, the strip 22 is generally bent around a fold line such that the edges 24 and 26 are in contact with each other and welded here to form a weld 40. The shape of the tube obtained is generally round and flattened near the weld 40 and the fold line 46 so that the dimples 30, 32 are in contact with each other generally in the configuration illustrated in FIG. 3. In some cases, the holeless dimple 30 may be omitted and the holed dimple 32 may be in direct contact with the facing inner wall of the tube 18. The welding operation is generally carried out before the dimples 30 and 32 are contacted but may be carried out simultaneously or after contact if desired.

At this time or any subsequent time, flux may be applied to the dimples 30, 32 that have been brazed outside of the tube and at least in the vicinity of the tube. The brazed cladding material on the tube surface 38 liquefies, with the flux flowing through the opening 34 into the interior of the tube to wet the vertices 46 of the dimple 30 and finally form the fillet 48. However, prior to this, it is desirable that the tubes be assembled to the fixture with the headers 10 and 12 depending on the fluxing and soldering temperatures to achieve a final heat exchanger with dimples 30 and 32 bonded to each other.

The opening 34 may be of various shapes in a circular to elliptical shape and in other configurations, but is preferably formed of a slit such as the slit 34 shown in the drawing. In the process of forming the strip 22 as described above, the slit is formed substantially more than the circular opening so that the molding process does not need to substantially remove the material so as to slow down by any need to form the opening 34. It is easy. That is, the slit opening is basically an opening that completely penetrates the strip 22 of the vertex 44 of the dimple 32 without removing any material. However, if the assembly line speed can be slightly reduced, the opening 34 can be formed by a method other than slitting with the material substantially removed from the vertex 44.

Thus, the opening 34 can access the interior of the tube near the vertex 46 of the dimple 30 so that the braze alloy can enter the exact point where the junction between the dimples 30 and 32 is made from the layer 42 and the flux. . Thus, the strip 22 only needs to be solder clad on one side, not on both sides. As a result, the material cost of the tube is reduced.

In addition, the flux inside the tube is completely prevented because the flux flows from the outside of the tube to the junction. Thus, problems due to the flux in the passage and the need for the flux removal cleaning operation are also prevented.

The resulting tube thus offers the advantage of providing a known flat dimple tube while being able to be manufactured at low cost and avoiding any problems with the flux surplus. Dimples in the tube provide the desired resistance and / or pressure resistance for numerous applications.

Claims (11)

In the manufacturing method of the heat exchanger tube, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming dimples in the strip so that the dimples protrude toward one side of the strip and the dimples on one side of the predetermined fold line located between opposite edges align with the dimples on the other side of the fold line; c) placing a slit extending along the strip at at least one dimple vertex of the fold line, d) folding the strip along the fold line such that the edges are in contact with each other such that aligned one vertices of the dimples abut each other; e) welding the edges together to form a tube, and f) flowing the braze alloy from one side of the strip through the slit into the tube so that the vertices of the aligned dimples are soldered together Containing Method of making heat exchanger tubes. The method of claim 1, Performing the step of f) then applying a flux to one of the strips at least in the vicinity of the dimple with the slit. Method of making heat exchanger tubes. The method of claim 1, The dimple is nominally truncated Method of making heat exchanger tubes. In the manufacturing method of the heat exchanger tube, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming dimples in the strip so that the dimples protrude toward one side of the strip and the dimples on one side of the predetermined fold line located between opposite edges align with the dimples on the other side of the fold line; c) placing a perforation extending along the strip at at least one dimple vertex of the fold line, d) folding the strip along the fold line such that the edges are in contact with each other such that aligned one vertices of the dimples abut each other; e) welding the edges together to form a tube, and f) flowing the braze alloy from one side of the strip into the tube through the perforations such that the vertices of the aligned dimples are soldered together Containing Method of making heat exchanger tubes. In the manufacturing method of the heat exchanger tube, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming dimples in the strip so that the dimples protrude toward one side of the strip and the dimples on one side of the predetermined fold line located between opposite edges align with the dimples on the other side of the fold line; c) placing a perforation extending along the strip at at least one dimple vertex of the fold line, d) folding the strip along the fold line such that the edges are in contact with each other such that aligned one vertices of the dimples abut each other; e) welding the edges together to form a tube, and f) flowing the braze alloy from one side of the strip into the tube through the perforations such that the vertices of the aligned dimples are soldered together Containing Method of making heat exchanger tubes. A tube for a heat exchanger produced by the method according to any one of claims 1, 4 and 5. In the manufacturing method of the tube for heat exchangers, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming projections on both sides of the predetermined fold line located between the edges such that the protrusions on one side of the fold line protrude toward the strip facing one side of the strip in alignment with the protrusions on the other side of the fold line; c) drilling at least one of the protrusions, d) folding the strip along the fold line such that the edges are in contact with each other while the projections abut against each other with one perforation of the projection open toward the other projection, e) welding the edges together to form a tube, f) placing a soldering flux on at least one side of the strip near the perforation, and g) welding the protrusions together by flowing the braze alloy from one side of the strip through the perforations; Containing Method of making heat exchanger tubes. The method of claim 7, wherein The step c) is performed by placing a slit in the at least one protrusion Method of making heat exchanger tubes. In the manufacturing method of the heat exchanger tube, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming projections on both sides of the predetermined fold line located between the edges such that the protrusions on one side of the fold line protrude toward the strip facing one side of the strip in alignment with the protrusions on the other side of the fold line; c) slitting at least one of the protrusions, d) folding the strip along the fold line so that the edges are in contact with each other while the protrusions abut one another with one slit open toward the other protrusion, e) welding the edges together to form a tube, f) placing a soldering flux on at least one side of the strip near the slit, and g) welding the protrusions to each other by flowing the braze alloy from one side of the strip through the slit; Containing Method of making heat exchanger tubes. In the manufacturing method of the heat exchanger tube, a) preparing an elongated strip of aluminum-based material with opposing edges and solder alloys on only one side thereof, b) forming projections on both sides of the predetermined fold line located between the edges such that the protrusions on one side of the fold line protrude toward the strip facing one side of the strip in alignment with the protrusions on the other side of the fold line; c) slitting at least one of the protrusions, d) folding the strip along the fold line so that the edges are in contact with each other while the protrusions abut one another with one slit open toward the other protrusion, e) welding the edges together to form a tube, and f) soldering the protrusions to each other by flowing the braze alloy from one side of the strip through the slit; Containing Method of making heat exchanger tubes. In the manufacturing method of the heat exchanger tube, a) preparing a long strip of aluminum-based material with opposing edges and a braze alloy on one side thereof, b) causing dimples in the strip to protrude toward a strip opposite one side of the strip, c) placing perforations extending along the strip at at least a few vertices of the dimples, d) forming the strip so that the edges are in contact with each other while the apex of the slit comprising the dimple is against the opposite side of the strip, e) welding the edges together to form a tube, and f) flowing the braze alloy from one side of the strip through the slit into the tube such that the vertices of the slits containing dimples are soldered to opposite sides of the strip where these vertices abut each other; Containing Method of making heat exchanger tubes.