CA1123423A

CA1123423A - Heat exchanger and method of making

Info

Publication number: CA1123423A
Application number: CA349,895A
Authority: CA
Inventors: Zalman P. Saperstein; Jeffrey A. Logic
Original assignee: Modine Manufacturing Co
Current assignee: Modine Manufacturing Co
Priority date: 1979-08-03
Filing date: 1980-04-15
Publication date: 1982-05-11
Also published as: JPS5623390A; ES8105177A1; BR8003603A; IT8048930A0; ES493947A0; ES252388Y; ES252388U; SE8004532L; GB2055060A; FR2462679A1; DE3021240A1; IT1146180B

Abstract

ABSTRACT OF THE DISCLOSURE

A method of making a rigid stainless steel, cor-rosion resistant, weldment, tubular heat exchanger and the resulting heat exchanger for exchanging heat between fluids in which a pair of steel tubes with stainless surfaces are arranged in internested spaced relationship, providing a pair of cylindrical steel fittings with stainless steel surfaces at each end 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-heated to a molten condition, the ends of the innter and outer tubes being similarly projection welded together.

Description

-HEAT E~CHANGER AND MET~IOD OF ~hING

BACKGROUND OF THE INVENTION
Tubular heat exchangers, which are widely used as oil coolers for internal combustion engines, are cus-tomarily 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 ex-changer of this type is illustrated in U.S- patents 2/752~l25 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 alloysO
- The heat exchanger of this invention is made of strong, corrosion resistant steel parts at least the sur-faces 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.

SUl~ARY 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 ispreferably made of chromium containing stainless steel, ~ ~.Z3423 other types of strong yet corrosion resistant steels may be used including Mone~ and Incone~. These steels are all very strong and, in addition, the heat exchanger o~ 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.
~ us, i~ onc broad aspcct, the invention comprchends a rigid stainless steel, corrosion resistant, weldment, tubular heat exchanger for exchanging heat between fluids.
The heat exchanger includes 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, a pair of cy~
lindrical steel fittings each having a fluid flow passage through the fitting with a circular contact area ring on one end of the fitting surrounding the passage and a continuous projection weld at the contact ring joining each fitting to the shoulder. A continuous weld joins the ends of the inner and outer cylinders together. Each weld joins a fitting to the outer tube and joins the cylinders together and has, as weld metal, essentially only solid, previously molten metal from adjacent portions of the tubes.
The invention further includes a method of making a rigid stainless steel, corrosion resistant, weldment, tubular heat exchanger for exchanging heat between fluids.
The method comprises the steps of providing a pair of steel tubes of different diameters each having stainless steel surfaces, forming a fluid flow opening with a surrounding shoulder adjacent each end of the larger tube, and arranging the pair of tubes as spaced inner and outer tubes. A pair of cylindrical steel fittings are provided, 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. The ring has a contact surface o~
small area for contact with the shoulder. Each fitting is projection welded to a shoulder by applying an electric current to the fitting and the outer tube for current flow ~herebetween by way of the contact ring, while pressing the fitting against its shoulder. The fitting and the shoulder are thereby melted at the contact area to a molten condition and then cooled to provide a resistance electric weld of each fitting to the outer tube. The ends of the inner and outer tubes are fusion welded together.
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 il-lustrating 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 com-pleted heat exchanger embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in the collective view of Figure 1, the heat exchanger 10 parts 11 comprise a pair of tubes consisting of an outer tube 1~ ànd an inner tube 13 of different diameters and a pair of semicylindrical expanded metal turbulator 14 halves. The parts 11 also include a pair of~cylindrical fittings 15. Each fitting 15 is generally cylindrical and has an axial, fluid flow passage 16 through it and a circular contact area ring 17 having a small, sharp surface for contact with a shoulder 18 at ., .; ~,,~ , 23~23 each end of the large or outer tube 12.
Figure 2 illustrates the step in the formation of the shoulders 18 on each end of the tube 12 and, simul-taneously, an opening 19 surrounded by a shoulder 18.
In the forming step of Figure 2 the end 20 of the tuhe is clamped between forming die members 23 and 24 to form each shoulder 18 and a cylindrical punch 25 is forced through the center of the shoulder 18 while so clamped to displace a disc 26 of metal from the tube 12 and thereby form the fluid flow opening 19. A similar step is per-formed at each end 20 of the larger or outer tube 12 to provide a shoulder 18 and corresponding opening 19 in each of these ends.
There is also provided a turbulator 14 which in this embodi~ent 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 U.S. 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 12 and 13 are of the above described stainless steel while the turbulator 14 and the fittings 15 are of carbon steel.
In producing the heat exchanger after the end shoulders 18 and openings 19 are formed, as described and as illustrated in Figure 2, each fitting 15 is a projection welded to its shoulder 18 by applying an electric current to the fitting as illustrated in Figure 3. This current is supplied from a welder 29 through electric leads 30 and 33, one of which 30 is connected to the fitting 15 while the other 33 is connected to the tube 12. As is customary, a current is thereby passed from the ~elder 29 through the very small circular ring contact area 17.
Because the sharp contact area 17 is so small, the resis-tance to current flow is high with the result that the steel in the area of the circular area 17 becomes mo]ten, so that pressure 34 applied to this area by way of the - , .` . , , . ~ , . ~. ' .

:~23~23 fitting 15, as illustrated schematically in Figure 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 maklng the turbulator of this invention the smaller tube 13 is in-serted as indicated by the arrow 35 into the larger tube 13 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 Figure S~ Each pair of contacting ends 20 and 37 are then welded together in either a GTA~ (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 Figure 6 at 41.
After -the welding of the pairs of opposite ends 20 and 37 together in the manner described, the inner tube 13 is expanded outwardly by internal pressure illustrated schematically at 45 into tight contact with the turbulator 19 and thereby tight contact of the turbulator with the outer cylinder 12.
As can be seen in Figure 8, the joined ends 20 and 37 of the outer 12 and inner 13 tubes are in areas ~ ; -outwardly, or longitudinally, beyond the fittings 15. ~ ~
As stated, the parts including the pair of tubes -12 and 13 are of stainless steel. The pair of fittings 15 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 in-gredient comprising chromium.
The preferred stainless steel used in making atleast the tubes 12 and 13 of the parts 11 of the exchan~er ~ lZ34~Z3 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 con-tains 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 con-taining the chromium has good creep particularly at high temperatures and pressures.
The completed oil cooler as shown in side ele-vation in Figure 8 with certain internal parts shown inbroken 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 15. 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 e~bodiment 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

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

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 sur-rounding 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 sur-rounding the flow passage, said ring having a contact sur-face 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 f) 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 permanent 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 in-gredient 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, pre-viously molten metal from adjacent portions of said tubes.

10. 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.

12. 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 tur-bulator within said space.

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

14. 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 to each other being at these contacting ends.

15. 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 tur-bulator 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.