JPH03189072A - Hear exchanger and its manufacture - Google Patents

Abstract

PURPOSE:To facilitate bending, tube expansion and brazing by using a copper tube as a U-shaped tube, using a clad tube of a three-layer structure consisting of a specific material as a straight tube, bringing an end part of the clad tube to tube expansion and bringing the copper tube to insertion brazing. CONSTITUTION:As for a straight tube 2 of a heat exchanger constituted of many straight tubes 2, a fin 7 provided on the straight tube 2, and a U-shaped tube 1 for coupling the straight tubes 2, a clad tube which has a structure of at least three layers in which an inner layer 5 consists of copper, a valve metal is fitted and inserted into an intermediate layer 4, and an outer layer 6 consists of copper, a copper alloy, and nickel or a nickel alloy, and also, each metal is brought to metallic junction without generating an intermetallic compound is used. On the other hand, as for a U-shaped tube 1, a copper tube is used, and also, the copper tube is inserted into a tube expanding part formed by bringing an end part of the straight tube being a clad tube to tube expansion, and brazed and joined.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a heat exchanger that absorbs external heat and transfers the heat to a fluid within a tube, and a method for manufacturing the same.

(Prior art and problems to be solved) Copper, copper alloy, aluminum, and aluminum alloy are mainly used for heat exchanger tubes, and in order to increase the efficiency of the heat exchanger, Fins are formed by joining wire rods or plate materials to increase the contact area with the heat source.

In heat exchangers that absorb gas heat, such as those used to recover various types of industrial waste heat and absorb heat from combustion gas in gas water heaters, condensation occurs on the outside of the copper tubes, but there is no condensation in the exhaust gas and combustion gas. It may contain chlorine-based, sulfuric acid-based, and nitric acid-based compositions, and condensation produces corrosive liquids that cause defects that nullify the function of the heat exchanger, i.e., holes that penetrate through the wall thickness of the tube body. do.

As a countermeasure for this, for example, on the outside of the copper tube.

One possible method is to make a double pipe by adding Ti, which has better corrosion resistance to corrosive substances than Cu, and this type of double pipe itself has been known for a long time (for example, the method of
105990 etc.).

Further, a triple-pipe tube itself in which a Cu layer is provided on the inside of a copper tube via Ti is also known (for example, Utility Model Application No. 63-36889, etc.).

However, among the above-mentioned applications, in particular heat exchangers for domestic gas water heaters, etc., because the overall structure is made compact, the tube body itself has a small diameter and has a large number of flow paths. It has a structure in which a large number of straight pipes are welded together by a large number of U-shaped pipes with a small bending radius.

Moreover, the method of connecting the U-shaped pipe and the straight pipe is to install fins on the straight pipe to perform its function as a heat exchanger, create one assembly of the straight pipe and the fins, and then A method has been established as an efficient method for manufacturing a heat exchanger, in which a section is expanded, and then a U-shaped tube is fitted into the expanded section and welded.

Therefore, first of all, when such a connection method is applied to the double pipe, it is difficult to manufacture a small diameter pipe or a U-shaped pipe with a small bending radius due to the poor workability of Ti. Efficient methods such as creating a composite billet of Ti and Cu and manufacturing a composite pipe by hot isostatic extrusion cannot be adopted, resulting in increased costs. Furthermore, when connecting a U-shaped pipe and a straight pipe, as shown in FIG.
The welding itself becomes difficult because it becomes a dissimilar metal bond to the Cu inside the double tube) 12.

On the other hand, when applied to triple pipes, since the structure is such that both sides of difficult-to-process Ti are sandwiched with easy-to-process Cu, Cu also acts as a lubricant, making it easy to manufacture composite straight pipes by the above-mentioned hydrostatic extrusion etc. can.

However, as mentioned above, the bending radius of the U-shaped tube of a water heater heat exchanger is small, and when bending the U-shaped tube,
There is a limit to reducing the thickness of Ti due to the original intention of increasing corrosion resistance (a certain thickness is required), so processing difficulties inevitably arise due to the difference in the elastic modulus of both Ti and Cu. Put it away.

The present invention was made in order to solve the problems of the prior art described above, and it is possible to easily assemble a heat exchanger, and to avoid the occurrence of through-holes in the pipe wall that impair the function of the heat exchanger. The object of the present invention is to provide a problem-free heat exchanger and a method for manufacturing its tube body.

(Means for Solving the Problem gA) In order to achieve the above object, the present inventor has conducted extensive research into ways to facilitate assembly of the tube without the occurrence of through holes.

As a result, when both a straight pipe and a U-shaped pipe are made into a three-layer structure, it becomes difficult to bend the U-shaped pipe with a small bending radius as described above. Since the parts do not touch each other, there are fewer problems and there is no need to use a three-layer structure.Therefore, by using a single copper tube as a U-shaped tube, it is possible to form a U-shaped tube. We found that processing problems can be solved. Furthermore.

It has been found that by forming a straight pipe into a three-layer structure made of a specific material, corrosion resistance and processing by hot isostatic extrusion can be easily achieved, and the present invention has been made based on this finding.

That is, the present invention provides a heat exchanger comprising a large number of straight pipes, fins provided on the straight pipes, and U-shaped pipes connecting the straight pipes, wherein the straight pipes are made of copper as a base. Composite pipe, the inner layer of which is made of copper, the middle layer of the thick inner layer with a layer of valve metal inserted therein, and the outer layer of which is made of at least three layers of copper, copper alloy, nickel, or nickel alloy. The U-shaped tube is a copper tube, and the ends of the clad tube are made of copper. The gist of the present invention is a heat exchanger characterized in that the copper tube is inserted into an expanded tube portion and brazed and joined.

Further, the present invention relating to the production of the clad pipe provides that after the materials of the inner layer, intermediate layer, outer layer, etc. of the clad pipe are combined in a mechanically fitted state, the valve metal and copper or copper alloy form an intermetallic compound. The feature is that hot isostatic extrusion is carried out in a temperature range where no metallurgical bonding occurs.

The present invention will be explained in more detail below.

(Function) Many materials are known as materials with excellent corrosion resistance, such as valve metals such as tantalum, niobium, titanium, and zirconium, nickel-based alloys, stainless steel, and even nonmetals. It is essential that the material has the following functions 1 to 4.

1. Good thermal conductivity.

2. It has an airtight and liquidtight structure, making it easy to join the pipes together.

3. It is easy to join plates and linear members (fins) to the outer circumference of the pipe for the purpose of improving heat absorption efficiency.

4. It should have excellent corrosion resistance and should not have holes penetrating the thick part.

There are other factors that are necessary for heat exchanger tubes, but after narrowing it down to the four items listed above as essential items, we came to the conclusion that it would be difficult to meet the requirements with a single material. As a result of careful consideration of the combination of functional materials and processing methods, we have created a 3-layer clad pipe as described below.

First, as a tube body for a heat exchanger, it has a corrosion-resistant function that makes it easy to connect the built-in tube body to the heat exchanger by arranging various functional materials in the appropriate places to reduce the contact thermal resistance of different materials to an ideal state. As shown below, it is necessary to use a clad pipe having copper as a base and having at least three layers as a straight pipe.

That is, copper is used as an inner layer on the inner surface of the clad pipe. This is because copper has good thermal conductivity, and the pipes can be joined by brazing, which is easier than before.

On the other hand, the outer surface (outer layer) of the clad pipe body is preferably made of copper in order to facilitate bonding with plates and wire materials (fins) for improving heat absorption efficiency, and copper alloy or copper alloy to further add corrosion resistance. Nickel or nickel-based alloys are also applicable as bondable materials. In this case, although it may be difficult to join copper alloys and nickel-based alloys to the fins using the same level of construction technology as in the past, this is within the technical range that can be achieved.

Further, in order to maintain corrosion resistance, a layer of valve metal is inserted into the thick wall as an intermediate layer of the clad pipe.

The valve metals shown are tantalum, niobium, titanium, zirconium, etc., all of which have excellent corrosion resistance, and each material has its own characteristics, so they are selected and used depending on the purpose. For example, tantalum has excellent corrosion resistance but is expensive. Although titanium is cheaper than tantalum and niobium, its crystal structure is a close-packed hexagonal crystal that is relatively difficult to work with, and is prone to defects when its thickness is reduced. Furthermore, since these metals do not exhibit excellent corrosion resistance against all corrosive substances, they are used depending on the corrosive substance, purpose, etc.

From the viewpoint explained below, such a three-layer clad pipe is made by combining the materials of the inner layer, intermediate layer, and outer layer in a mechanically fitted state, and metallurgically bonding them in a specific temperature range by hot isostatic extrusion. Manufacture.

That is, first, since heat exchange involves transferring heat from the outer surface of the tube to the internal fluid, it is preferable to minimize the heat transfer resistance within the thick wall of the tube. To that end, firstly,
It is important to achieve metal bonding of dissimilar metal materials, and secondly, to reduce the thickness of materials with high heat transfer resistance.

Regarding the former metal bonding, based on the knowledge that it can be achieved by applying large deformation processing in a high temperature range, the present invention applies hot isostatic extrusion. In this case, generally speaking, the higher the processing temperature range, the lower the deformation resistance, and the stronger the processing becomes possible. Therefore, metal joining is facilitated by high temperatures and heavy processing.

However, it should be noted that there is an appropriate temperature range depending on the combination of metal materials used. For example, in the case of titanium among valve metals, if it is heated above 900°C, the crystal structure will transform from α to β, the crystal grains will become coarse, and this will hinder the thinning process of titanium. 85
0°C is preferred. On the other hand, for niobium and tantalum, there is no problem even if the temperature is higher than that for titanium, but if the temperature is too high, the copper becomes too soft, so it is preferable to limit the temperature to 1000°C or less.

However, a common problem with these selected metals is that they tend to form brittle intermetallic compounds with copper, and the formation of intermetallic compounds impairs the function of the composite pipe, so the hot isostatic extrusion temperature It is essential that the temperature be below the temperature at which intermetallic compounds are formed.

Regarding the latter wall thickness, since copper is the metal with the highest thermal conductivity, making the corrosion-resistant material with lower thermal conductivity thinner will reduce the thermal conduction resistance of the tube. However, each material of each layer constituting the cladding tube needs to have a certain thickness in order to prevent defects from penetrating through the thick wall portion. The guidelines are as follows.

To inspect for defects in corrosion-resistant materials, the presence or absence of defects can be confirmed by removing the outer covering material by pickling and then immersing it in acid.
Even if the thickness is reduced to a certain extent, the internal copper will not be eluted, and no through-holes will occur in the niobium layer.

On the other hand, tantalum is slightly less workable than niobium;
Copper elution is detected at 0 μm, and through holes are generated. Titanium is a hexagonal crystal that is less workable than the hexagonal crystals of niobium and tantalum, and defects occur at 40 μm in the same way as tantalum at 20 μm.

In this way, it is necessary to select an appropriate thickness for each material, but in general, the total wall thickness of the clad pipe is 0.4 to 1. O
In a tube of about n+m, the thickness of the corrosion-resistant material is 100
It is preferable to use approximately μm as a guide.

The clad pipe having the above structure is used as a straight pipe, but one of the points of the present invention is that a single copper pipe is used for the U-shaped pipe connected to the straight pipe.
These are two characteristics. This is because if a conventional double or triple clad pipe clad with a material other than copper is used as a U-shaped tube in the same way as a straight tube, there is a problem in bending and forming the U-shaped tube. In addition, since the U-shaped tube part is provided with a shell 8 as shown in Figure 1, there is no direct contact with combustion gas, so there is no problem of corrosion, and it is necessary to use a clad tube in the same way as a straight tube. This is because there is no

Next, assembling the straight clad pipe and the U-shaped copper pipe, the end of the clad pipe is expanded, and the end of the U-shaped pipe is inserted into the expanded part, and then the wax-phase welding is performed. and assemble.

In this case, since a single copper tube is used as the U-shaped tube, it is easy to manufacture the U-shaped tube by bending. No problems arise.

Note that the method for providing fins on the straight pipe may be the same as the conventional method.

As shown in FIG. 1, the thus obtained heat exchanger consists of a straight pipe 2 provided with plate fins or wire fins 7, an inner layer 5 made of copper, an intermediate layer 4 made of a corrosion-resistant material, and an outer layer 6.
It has a layered structure, and its expanded portion is brazed to a U-shaped tube 1 made of a single copper tube. In the figure, 53 is a brazing material, and 7 is a shell.

(Example) Next, examples of the present invention will be shown.

311 Example 3 Copper tube for outer layer with inner diameter 143φ and dimension 3, outer diameter 134.
A three-layer structure was prepared in which a copper tube for an inner layer having dimensions of 5φ and an inner diameter of 51φ was inserted into a cylindrical shape with a double winding of a niobium plate having a thickness of Q and a thickness of 5nv inserted between these as an intermediate layer.

Next, the space surrounding the niobium was hermetically sealed in a degassed state, and then extruded by hot isostatic extrusion.

Extrusion heating temperature is 750℃, extrusion dimension is 36mm outer diameter
, the inner diameter is 30mo+. Then, by cold drawing, 12
．． It was machined to size 7φX0.6 and expanded into a bell mouth tube.

A single copper tube was inserted into this expanded section and brazed.

This kind of construction could be done in exactly the same way as conventional copper pipes.

In addition, there were no defects in the niobium layer in the tube expansion section, and no peeling was observed between the metals.

Copper tube for outer layer with inner diameter 143φX3 and outer diameter 122φ
A three-layer structure was prepared in which a copper tube for an inner layer with an inner diameter of 51φ was inserted, and a titanium welded cylinder with a wall thickness of f3.5 mm+ was inserted as an intermediate layer between these tubes.

Next, the space surrounding the titanium was hermetically sealed in a degassed state, and then extruded by hot isostatic extrusion.

Extrusion heating temperature is 750℃, extrusion dimension is 36mm outer diameter
, the inner diameter is 30 mm. Then, by cold drawing, 127
It was machined to a size of φX0.6 and expanded into a bell mouth tube. A single copper tube was inserted into this expanded section and brazed.

This kind of construction could be done in exactly the same way as conventional copper pipes.

Furthermore, there were no defects in the titanium layer in the expanded tube section, and no peeling was observed between the metals.

Copper-nickel alloy tube for outer layer with inner diameter 143φXSt dimensions (
70% Cu, 30% Ni), outer diameter 112φ, inner diameter 51
A three-layer structure was prepared in which a φ-sized inner layer copper tube and a titanium welded cylinder with a wall thickness of 6.5+n+n was inserted as an intermediate layer between these tubes.

Next, the space surrounding the titanium was hermetically sealed in a degassed state, and then extruded by hot isostatic extrusion.

Extrusion heating temperature is 800℃, extrusion dimension is 44mm outer diameter
, the inner diameter is 35 mm. After that, 12.
It was machined to a size of 7φ x 0.6 and expanded into a bell mouth tube. A single copper tube was inserted into this expanded section and brazed.

This kind of construction could be done in the same way as conventional copper pipes. Furthermore, in the expanded tube section, there were no defects in the outer copper alloy layer and the intermediate titanium layer, and no peeling between the metals was observed.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to prevent the occurrence of through holes in the pipe wall thickness, and since the metal layers are metal-bonded, the contact thermal resistance is minimal, so the heat Since the function of the exchanger is not impaired, and since a copper tube is used as the U-shaped tube, bending, expanding, and brazing can be easily performed in the same way as conventional copper tubes. Furthermore, cladding pipes can be manufactured without producing intermetallic compounds. Therefore, it greatly contributes to industrial production.

[Brief explanation of drawings]

1 and 2 are diagrams showing a straight pipe and a U-shaped tube of a heat exchanger according to the present invention, and FIG. 1 is a cross-sectional view of the heat exchanger, and FIG.
In the figure, (a) is a cross-sectional view of the vicinity of the brazed part, (b) is an enlarged view thereof, and Fig. 3 is an explanatory cross-section showing the joint between a straight pipe and a U-shaped pipe using a conventional double pipe. It is a diagram. 1... Copper single tube (U-shaped tube), 2... Clad pipe (straight pipe), 3... Brazing metal, 4... Intermediate layer (corrosion resistant material), 5
... Inner layer (copper), 6... Outer layer, 7... Plate fin (or wire fin), 8... Shell.

Claims (2)

[Claims] (1) In a heat exchanger consisting of a large number of straight pipes, fins provided on the straight pipes, and U-shaped pipes that connect the straight pipes,
The straight pipe is a composite pipe with a copper base, the inner layer is made of copper, the thick middle layer is fitted with a layer of valve metal, and the outer layer is made of copper or copper alloy. , is a clad pipe having a structure of at least three layers made of nickel or nickel alloy, and in which each metal is metal-bonded without forming an intermetallic compound, and on the other hand, the U-shaped pipe is a copper pipe. Furthermore, the heat exchanger is characterized in that the copper pipe is inserted into an expanded part formed by expanding the end of the clad pipe and is joined by brazing. (2) In the method for manufacturing a clad pipe according to claim 1, after the materials of the inner layer, intermediate layer, outer layer, etc. are combined in a mechanically fitted state, the valve metal and the copper or copper alloy form an intermetallic compound. Hot isostatic extrusion is carried out in a temperature range that does not produce
A method for manufacturing a clad tube for a heat exchanger, characterized by metal bonding.