GB2055060A - Heat exchanger and method of making - Google Patents

Abstract

A method of making a rigid stainless steel, corrosion resistant. welded, tubular heat exchanger and the resulting heat exchanger for exchanging heat between fluids in which a pair of steel tubes 12, 13 with stainless surfaces are arranged in internested spaced relationship, providing a pair of cylindrical steel fillings 15 with stainless steel surfaces at each end 20 of the outer tube and welded to the outer tube on a shoulder of the outer tube by projection welding in which the contacting surfaces of the fitting and the tube are electric resistance welded, the ends of the inner and outer tubes being similarly welded together. Turbulators 14 are fitted between the tubes. <IMAGE>

Description

SPECIFICATION Heat exchanger and method of making BACKGROUND OF THE INVENTION Tubular heat exchangers, which are widely used as oil coolers for internal combustion engines, are customarily made of brass or copper parts joined together to provide one fluid space between the tubes and an internal core through which the heat exchange fluid is passed with the space between the tubes ordinarily having a turbulator therein for turbulizing flow of the liquid through this space to improve the heat exchange relationship between the fluids.

A fitting is provided at each end of this space between the tubes to pass the first fluid in one fitting through the space and out the other fitting. A heat exchanger of this type is illustrated in patents 2,752,125 and 3,959,867, both assigned to the assignee hereof, and patent 3,001,767. Such heat exchangers have also been made of aluminum as well as copper and brass, all of which are relatively lightweight and weak metals and alloys.

The heat exchanger of this invention is made of strong, corrosion resistant steel parts at least the surfaces of which are stainless steel. The invention also comprises a novel method of making such a tubular heat exchanger that is rigid, corrosion resistant and is a weldment construction of the stainless steel parts.

SUMMARY OF THE INVENTION The parts of the tubular heat exchanger of the present invention are either solid stainless steel or steel with surface coatings that are stainless and these may be produced by procedures well known in the art such as those described in U.S. patents 3,093,556 and 3,184,331 and many others of similar nature.

Although the heat exchanger of this invention is preferably made of chromium containing stainless steel, other types of strong yet corrosion resistant steels may be used including Monel and Inconel. These steels are all very strong and, in addition, the heat exchanger of this invention is a weldment structure in that all joints between the internested tubes and between the external fittings and the outer one of the internested tubes are welded. This welding is by projection welding in which an electric current is passed between the contacting surfaces of the stainless steel parts, thereby resistance heating the parts to a molten condition while they are pressed together to produce the welded joint. Then the parts are cooled to provide a weldment heat exchanger.

A stainless steel heat exchanger of a different type is disclosed in U.S. patent 4,159,034, issued June 26, 1979, and assigned to the assignee hereof.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a collection perspective view of each of the parts comprising the specific embodiment of the tubular heat exchanger of this invention.

Figures 2-7 are successive sectional views illustrating successive steps of a method embodying the invention and producing a heat exchanger embodying the invention.

Figure 8 is a side elevational view of the completed heat exchanger embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODI MENT As illustrated in the collective view of Fig.

1, the heat exchanger 10 parts 11 comprise a pair of tubes consisting of an outer tube 1 2 and an inner tube 1 3 of different diameters and a pair of semicylindrical expanded metal turbulator 14 halves. The parts 11 also include a pair of cylindrical fittings 1 5. Each fitting 1 5 is generally cylindrical and has an axial, fluid flow passage 1 6 through it and a circular contact area ring 1 7 having a small, sharp surface for contact with a shoulder 1 8 at each end of the large or outer tube 1 2.

Fig. 2 illustrates the step in the formation of the shoulders 1 8 on each end of the tube 1 2 and, simultaneously, an opening 1 9 surrounded by a shoulder 1 8. In the forming step of Fig. 2 and end 20 of the tube is clamped between forming die members 23 and 24 to form each shoulder 1 8 and a cylindrical punch 25 is forced through the center of the shoulder 1 8 while so clamped to displace a disc 26 of metal frorn the tube 1 2 and thereby form the fluid flow opening 1 9. A similar step is performed at each end 20 of the larger or outer tube 1 2 to provide a shoulder 1 8 and corresponding opening 1 9 in each of these ends.

There is also provided a turbulator 1 4 which in this embodiment is in the form of two semi-cylindrical halves 27 and 28. Turbulators of this displaced metal construction are well known in the art and are illustrated in the following patents, all of which are assigned to the assignee hereof: 3,688,372; 3,732,921; 3,734,135; 3,734,177 and 3,959,867.

The tubes 1 2 and 1 3 are of the above described stainless steel while the turbulator 14 and the fittings 1 5 are of carbon steel.

In producing the heat exchanger after the end shoulders 1 8 and openings 1 9 are formed, as described and as illustrated in Fig.

2, each fitting 1 5 is a projection welded to its shoulder 1 8 by applying an electric current to the fitting as illustrated in Fig. 3. This current is supplied from a welder 29 through electric leads 30 and 33, one of which 30 is connected to the fitting 1 5 while the other 33 is connected to the tube 1 2. As is customary, a current is thereby passed from the welder 29 through the very small circular ring contact area 1 7. Because the sharp contact area 1 7 is so small, the resistance to current flow is high with the result that the steel in the area of the circular area 1 7 becomes molten, so that pressure 34 applied to this area by way of the fitting 1 5, as illustrated schematically in Fig.

3, causes the molten metal to bond on cooling to form the projection weld. This technique, of course, is well understood in the art.

In the next step in the method of making the turbulator of this invention the smaller tube 1 3 is inserted as indicated by the arrow 35 into the larger tube 1 3 in spaced relationship so as to provide a fluid flow space 36.

The two halves 27 and 28 of the cylindrical turbulator 14 are arranged in this space and both ends of the inner tube 13, as illustrated at 37, are flared outwardly by internal pressure 38 into contact with the inner surface of the outer tube end 20 as illustrated in Fig. 5.

Each pair of contacting ends 20 and 37 are then welded together in either a GTAW (gas tungsten arc welding) or TIG welding with the electric current supplied from a welder 39 through electric leads 40 and 43. The arc space is illustrated in Fig. 6 at 41.

After the welding of the pairs of opposite ends 20 and 37 together in the manner described, the inner tube 1 3 is expanded outwardly by internal pressure illustrated schematically at 45 into tight contact with the turbulator 14 and thereby tight contact of the turbulator with the outer cylinder 1 2.

As can be seen in Fig. 8, the joined ends 20 and 37 of the outer 1 2 and inner 1 3 tubes are in areas outwardly, or longitudinally, beyond the fittings 1 5.

As stated, the parts including the pair of tubes 1 2 and 1 3 are of stainless steel. The pair of fittings 1 5 as well as the turbulator 14 may be of stainless steel but are preferably low carbon steel. Some or all of these parts can either be solid stainless steel or may have only their surfaces of stainless such as occurs when the surface of ordinary steel is impregnated with a steel alloy ingredient comprising chromium.

The preferred stainless steel used in making at least the tubes 1 2 and 13 of the parts 11 of the exchanger of this invention is one that contains chromium in an amount of at least 12%, such as from 12-32%, although other types of stainless alloys may be used. A steel that contains chromium is preferred because the chromium is a strong promoter of hardenability as it decreases the critical cooling rate of steel, and the steel alloy containing the chromium has good creep particularly at high temperatures and pressures.

The completed oil cooler as shown in side elevation in Fig. 8 with certain internal parts shown in broken lines is usually mounted in position as on a tank by attaching means at the projecting ledge 47 which is an integral part of each fitting 1 5. This may customarily be done by providing a copper coating (not shown) to the radial surface of the ledge 47 as by welding, plating or spraying the copper onto the top surface 48 of each ledge 47.

This copper coating, for example, would be essential if the unit 10 were soldered or the like to a brass tank. However, if the tank is plastic or stainless steel no such copper coating would be required and, in that event, the structure would be cheaper to build.

Having described our invention as related to the embodiment shown in the accompanying drawings, it is our intenion that the invention be not limited by any of the details of description, unless otherwise specified, but rather be construed broadly within its spirit and scope as set out in the appended claims.

Claims (16)

1. The method of making a rigid stainless steel, corrosion resistant, weldment, tubular heat exchanger for exchanging heat between fluids, comprising the following steps: (a) providing a pair of steel tubes of different diameters each having stainless steel surfaces; (b) forming a fluid flow opening with a surrounding shoulder adjacent each end of the larger tube; (c) arranging said pair of tubes as spaced inner and outer tubes; (d) providing a pair of cylindrical steel fittings each having a fluid flow passage through the fitting and a circular contact area ring on one end of the fitting surrounding the flow passage, said ring having a contact surface of small area for contact with said shoulder;; (e) projection welding each fitting to a said shoulder by applying an electric current to the fitting and the outer tube for current flow therebetween by way of said contact ring while pressing a said fitting against its said shoulder, thereby melting said fitting and said shoulder at said contact area to a molten condition and then cooling to provide a resistance electric weld of each said fitting to said outer tube; and Q fusion welding the ends of said inner and outer tubes together.

2. The method of claim 1 wherein said pair of tubes are solid stainless steel.

3. The method of claim 2 wherein said stainless steel is No. 409 stainless.

4. The method of claim 1 wherein said spaced inner and outer tubes define a fluid flow space therebetween and a steel liquid turbulator is inserted within said space.

5. The method of claim 1 wherein said spaced inner and outer tubes define a fluid flow space therebetween and a steel liquid turbulator is inserted within said space after which said inner tube is expanded outwardly to force said tubes and turbulator into perma nent pressure contact.

6. The method of claim 1 wherein the ends of said inner tube are expanded outwardly into contact with the inner surface of said outer tube in areas outwardly of said fittings, the welding of the tubes to each other being at these contacting ends.

7. The method of claim 1 wherein said spaced inner and outer tubes define a fluid flow space therebetween and a steel liquid turbulator is inserted within said space and the ends of said inner tube are expanded outwardly into contact with the inner surface of said outer tube in areas outwardly of said fittings, the welding of the tubes to each other being at these contacting ends.

8. The method of claim 1 wherein said pair of tubes have steel surfaces impregnated with a steel alloying ingredient comprising chromium.

9. A rigid stainless steel, corrosion resistant, weldment, tubular heat exchanger for exchanging heat between fluids, comprising: (a) a pair of spaced inner and outer tubes having a fluid flow opening with a surrounding shoulder adjacent each end of the larger outer tube; (b) a pair of cylindrical steel fittings each having a fluid flow passage through the fitting, a circular contact area ring on one end of the fitting surrounding said passage and a continuous projection weld at said contact ring joining each fitting to a said shoulder; and (c) a continuous weld joining the ends of said inner and outer cylinders together, each said weld joining a said fitting to said outer tube and joining said cylinders together having as weld metal essentially only solid, previously molten metal from adjacent portions of said tubes.

1 0. The heat exchanger of claim 9 wherein said pair of tubes are solid stainless steel.

11. The heat exchanger of claim 10 wherein said stainless steel is No. 409 stainless.

1 2. The heat exchanger of claim 9 wherein said spaced inner and outer tubes define a fluid flow space therebetween and there is provided a steel liquid turbulator within said space.

1 3. The heat exchanger of claim 9 wherein said spaced inner and outer tubes define a fluid flow space therebetween and there is provided a steel liquid turbulator within said space in permanent pressure contact with said tubes.

1 4. The heat exchanger of claim 9 wherein the ends of said inner tube are enlarged and in contact with the inner surface of said outer tube in areas outwardly of said fittings, the welding of the tubes of each other being at these contacting ends.

1 5. The heat exchanger of claim 9 wherein said spaced inner and outer tubes define a fluid flow space therebetween and there is provided a steel liquid turbulator within said space and the ends of said inner tube are enlarged and in contact with the inner surface of said outer tube in areas outwardly of said fittings, the welding of the tubes to each other being at these contacting ends.

16. The heat exchanger of claim 9 wherein said pair of tubes have steel surfaces impregnated with a steel alloying ingredient comprising chromium.