US2890320A - Electric heater and method of making the same - Google Patents

Description

June 9, 1959 Y s. A. OAKLEY ELECTRIC HEATER AND METHOD QOFYMAKING THE SAME Filed July 2a. 1955 4 M my m ZL WA 1f W ELECTRODE uAws CLOSED WELD/NS cweksw ATTORNEYS United States Patent ELECTRIC HEATER AND METHOD OF MAKING THE SAME Sterling A. Oakley, Lincolnwood, Ill.

Application July 28, 1955, Serial No. 525,040

13 Claims. (Cl. 219-58) The present invention relates to electric heaters and particularly to electric heaters of the type which include a high resistance metallic member having a terminal attached thereto and more particularly to an improved method and apparatus for joining together the metallic member and the terminal.

In certain types of electric heaters which are known in the prior art as sheathed heating elements, the electric heater comprises a helix of metallic resistance material having terminals attached to the ends thereof. This helix is surrounded with a compacted mass of heat conducting, current insulating material all enclosed within a tubular sheath of metal. This sheathed heating element may be formed into any desired shape.

Although various methods are known for attaching to the ends of the helical resistance element of sheathed heating elements the necessary terminal structures, none of these methods have proven to be completely satisfactory, leaving much to be desired in the way of quality and economy. For example, a number of these methods relates to various structural arrangements for threadedly engaging the helical resistor to a threaded portion of the terminal, which methods, while effecting a physically strong low resistance electric connection, do not lend themselves to high speed manufacturing operations. Moreover, such methods are obviously unsatisfactory when the resistor element is formed of fine wire. In accordance with other methods, the helix of resistance metal is welded to the terminals, but these methods suffer from the disadvantage that the terminal structure is severely weakened if not altogether broken in the vicinity of the joint between the coil and the terminal so that it frequently happens that after the heating element has been encased in the sheath, the connection between the resistance wire and one or more of the terminals is found to be broken. In such cases the entire heating unit is defective and must be discarded. It would be desirable to provide an improved electric heater of the sheathed type and moreover, an improved method of uniting a terminal to a helical resistance element in a high speed foolproof manner.

Accordingly, it is an object of the present invention to provide a new and improved electric heater and method and apparatus for making such electric heater.

It is a further object of the present invention to provide a new and improved method and apparatus for uniting a metallic conductor to a terminal member.

It is another object of the present invention to provide a new and improved method and apparatus for welding a metallic resistance member to a terminal member.

A still further important object of the present invention is to provide a new and improved method for joining a resistance coil to a terminal structure, which method requires a minimum amount of time and provides a joint wherein the terminal structure is substantially in its original condition.

Further objects and advantages of the present invention will become apparent as the following description proceeds, and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Briefly, the above objects are realized in accordance with the present invention by providing a method of making the bond between the resistance metal and the terminal structure wherein the metallic resistance material is shaped in the form of a helix and one end of the terminal structure is partially inserted therein. Welding current is then provided for a predetermined period of time in those portions of the helix and the terminal which are in interengagement, thereby quickly to weld a number of the turns of the helix to the terminal member while providing a physically strong junction.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following detailed description taken in connection with the accompanying drawing in which:

Fig. 1 is a fragmentary view of a heating element constructed in accordance with the present invention;

Fig. 2 is an elevational view partly in section of apparatus employed in manufacturing the heating element.

of Fig. 1 showing one step in the manufacuring operation;

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 2 assuming the entire structure to be shown in Fig. 2; and

Fig. 4 is a time chart useful in understanding both the method and apparatus of the present invention.

Referring now to the drawing, and particularly to Fig. 1, there is illustrated an electric heating element 10 which is suitable for encasement in a conventional tubular sheath for providing a finalized sheath electric heating unit. The element 10 comprises a suitable metallic wire 12 having a relatively high resistance so that when current is caused to flow therethrough it becomes hot and may be used for heating purposes. A common resistance wire for this purpose may be purchased under the trademark Nichrome. In the embodiment of the unit 10 used to illustrate the invention, the wire 12 is formed into a plurality of contiguous turns in the form of a helix. In order to prevent short circuiting between adjacent ones of the turns in the helix, the wire 12 may be provided with a surrounding layer of insulation 01', as is more common, the helix may be so wound that adjacent turns thereof are spaced apart. Current may be supplied to the resistance wire 12 from any suitable current source through metallic terminal members 14 which, in accordance with the present invention, are electrically connected and mechanically bonded to the resistance wire 12 at its opposite ends.

To accomplish this, one end of each of the terminal members 14 is reduced in size so as to provide an outwardly extending cylindrical portion 14a of reduced cross section which is disposed within the respective end of the helically Wound resistance wire 12. As shown, one end of the Wire 12 is placed in abutment with the shoulder 14b of one of the terminals 14 which separates the extending portion 14a of reduced cross section from the main body of the associated terminal 14. Electric heating elements of this type are well known in the art, and consequently, the structure described thus far does not constitute a part of the present invention.

As pointed out above, it is desirable that a reliable method be provided for bonding the ends of the wire 12 to respective ones of the terminals 14. Because welding provides a convenient method for quickly attaching the wire 12 to the terminals 14 so as to provide a low resistance electrical connection between the joined parts, it is further desirable that a method be provided which Patented June 9, 1959 utilizes welding to make the desired junctions while at the same time insuring a physically strong terminal in the completed structure.

In accordance with the present invention, the resistance wire 12 is formed into a plurality of spaced apart turns, resulting in a helix. Preferably, the inside diameter of the helix is equal to or slightly larger than the diameter of the terminal portion 14a. The extending portion 14a of the terminal 14 is then inserted into one end of the helically wound resistance wire 12 until that end of the helix abuts the shoulder 14b. Heating current is then supplied to a portion of those turns of the helix which are in contact with the extending portion 14a of the terminal 14 until melting of the surface of these turns takes place. Since the mass of the helically coiled resistance wire 12 is considerably less than that of the inserted terminal portion 14a, the wire 12 is sufficiently heated to make a good weld at the time that only the surface of the adjacent portion of the terminal 14 is melted, this melting of the outer surface of a heated member is commonly referred to as wetting. When wetting of the surface of the terminal 14 occurs, current is removed from the wire 12 and heat is removed in a positive manner from the weld so as to prevent any further melting of the portion 140: of the terminal 14.

In accordance with another aspect of the invention, there is provided improved apparatus for carrying the above method into effect in a manner suitable for making such welded terminal joints on a mass production basis. Referring now to Figs. 2 and 3, two sets of relatively movable support jaws 16 and 17 are arranged for relative movement along the longitudinal axes thereof. As illustrated, the jaw 16 is disposed above the jaw 17, but obviously other arrangements thereof can equally well be employed. The jaw 16 is illustrated as supporting a pair of welding electrodes 18 while the jaw 17 is illustrated as supporting a pair of welding electrodes 19. These electrodes 18 and 19 upon relative movement of the jaws 16 and 17 move into and out of operative engagement with a work piece which, in the illustrated embodiment is the concentrically disposed resistance wire 12 and terminal portion 14a. Since each set of welding electrodes 18 and 19 and their associated support jaws 16 and 17, respectively, are substantially identical, only jaws 16 and electrodes 18 are described herein, but the corresponding parts of the other jaws and electrodes are designated by the same reference numerals.

The jaws 16 are substantially rectangular having a tapered nose portion 16a (the jaws 17 have a tapered nose portion 17a) and are provided with rectangular recesses 21 and 22 in the adjacent faces near the electrode supporting ends. The pair of electrodes 18 specifically designated as 18a and 18b are disposed in respective ones of the recesses 21 and 22, and having a thickness equal to the depth of these recesses. Each electrode 18a and 1812 has one face which is flush with the inner face of its respective support jaw 16. Since the electrodes 18a and 18b are considerably longer than the recesses 21 and 22, they extend an appreciable distance beyond the nose of the jaws 16. The set of electrodes 19 includes electrodes 19a and 19b supported in recesses 21 and 22, respectively, of jaws 17.

In order to insure uniformity of contact between the welding electrodes 18 and 19 and the cylindrical work piece interposed therebetween, semicircular recesses are provided in the ends of the electrodes 18 and 19. This may be seen in Fig. 3 of the drawing where electrode 18a has a semicircular recess 24 therein and electrode 19a has a semicircular recess 25 therein. It may thus be seen that with the provision of such a recess, when the electrodes 18 and 19 are brought into engagement with one end of the helically arranged resistance wire 12 as shown in Figs. 2 and 3, intimate contact between the electrodes and the work piece is provided.

Although a single pair of welding electrodes may be used to provide a voltage across certain ones of the turns of the helix 12 to provide current therebetween, a stronger and more uniform weld may be provided if a plurality of oppositely polarized spatially disposed welding electrodes are carried by each jaw. It will be understood that the electrodes themselves are not polarized but are connected to a source of welding current such that when one is positive the adjacent one is negative (see Fig. 2). The welding current itself may thus be alternating or polarized, i.e., whichever is expedient under the particular conditions encountered.

Preferably, the jaws 16 and 17 are conveniently formed of a low resistance conductive metal so as to facilitate connection of the welding electrodes to a source of welding current, and in order to prevent short circuiting of this source, a sheet 26 of insulation is disposed between the individual ones of the jaws 16 and their respective electrodes 18a and 18b as well as between individual ones of the jaws 17 and their respective electrodes 19a and 19b. To facilitate replacement of the pairs of electrodes 18 and 19, these electrodes and the sheet of insulation 26 are conveniently sandwiched between the jaws 16 or 17 which jaws are forced together by any suitable means (not shown) thereby to hold the pairs of electrodes 18 and 19 in place. Relative movement of the jaws 16 and 17 may be produced by any suitable means such as solenoids or the like, not shown.

During the welding process, it is preferable to cause a stream of an inert shielding gas such as argon, helium, etc. to be maintained around the parts Where fusion occurs in order to prevent oxidation and to provide other advantages. Since, as pointed out above, fusion occurs in that area of the terminal which is disposed intermediate adjacent ones of the welding electrodes, it is necessary that the shielding gas be provided in this vicinity. To this end a transverse passageway 27 to which a source of inert gas (not shown) is connected, is provided in the jaw 17a for communication with a slot 28 which is provided in the insulation member 26 associated with the jaw 17a and which opens into the space surrounding the work piece. As best shown in Fig. 3, the slot 28 is displaced from the longitudinal axis of the insulating member 26 so that the shielding gas which flows therefrom toward the work piece circulates within the cylindrical space defined by the walls of the semicircular recesses 29 and 30 which are respectively provided in the oppositely disposed insulating members 26. Since the recesses 29 and 30 are slightly larger than the recesses 24 and 25 in the welding electrodes 18 and 19, an annular space is provided around the coiled resistance wire 12 in that area where fusion occurs.

Because the turns of the coiled resistance wire 12 which engage the electrodes 18 and 19 are compressed against the reduced portion 14a of the terminal 14, the shielding gas is prevented from passing axially away from the fusion area. Some gas does leak out through the space which is provided between the opposing ends of the insulating members 26 but this leakage is insignificant because of the swirling action of the shielding gas which is obtained by disposing the slot 28 off center.

In utilizing the apparatus of Figs. 2 and 3 to practice the method of the present invention, the resistance wire 12 is first formed into a helix and the portion 14a of reduced cross section of the terminal 14 is inserted therein. While the jaws 16 and 17 are spaced apart, the end of the coiled resistance Wire 12 and inserted terminal is placed in the recesses such as 24 or 25 in one of the pairs of welding electrodes 18 or 19. The jaws 16 and 17 are then forced together so as tightly to clamp the coiled resistance wire 12 to the terminal 14. This clamping insures a low electric and heat transfer contact resistance between the welding electrodes and the coiled wire 12 and additionally insures a low resistance junction between the turns of the wire 12 and the portion 14a of the terminal 14 inserted therein. Because the semicircular recesses in the electrodes Band 19 conform to the shape of the work piece, the latter is not deformed when the jaws 16 and 17 are clamped together.

After the jaws 16 and 17 have been brought together so as to clamp the coiled resistance wire 12 to the terminal 14, a voltage is impressed across the welding electrodes to provide welding current in the turns of the resistance wire 12 and shielding gas is forced into the passageway 27. As shown, the spacing between the electrodes in each jaw is relatively close so that only a few turns of the helically coiled wire 12 are disposed therebetween when the jaws 16 and 17 are clamped together, and therefore, the mass of those turns which are intermediate the welding electrodes 18a and 19a are appreciably less than the efiective mass of those turns which are in contact with the welding electrodes. Consequently, only the intermediate turns are heated to the fluid state to effect a weld between the terminal 14 and coiled resistance wire 12. Current is then removed from the resistance Wire 12, and the jaws 16 and 17 are maintained in a clamping position for a predetermined short period of time thereafter to prevent the fluid outer surface of the terminal portion 14a from migrating further into or along the surface thereof. Once the weld has hardened, the jaws 16 and 17 are opened and the work piece is removed. In a successful commercial embodiment of the invention, the entire cycle of operation beginning with closing of the jaws until they are again opened required less than three seconds. It will be appreciated that the spacing between the electrodes such as 18a and 19a will determine the number of turns of the wire arranged in the form of a helix which are welded to the terminal.

Referring to Fig. 4, there is shown a time chart which indicates the relative time periods involved in this welding operation. Values are not provided on this chart since the exact times required will vary with the current used and with the particular material of which the helically coiled wire 12 is constructed.

In describing the operation of the welding apparatus of Figs. 2 and 3, no mention has been made as to whether these steps are performed manually, automatically or semi-automatically. It should be understood, however, that both the method and apparatus of the invention may be used in the most expeditious manner for satisfactorily mass-producing electric heater terminals. For example, each of the steps of the method may be manually performed by an operator using the apparatus of this invention, or the entire operation may be performed by automatic fabrication machinery.

It has been found desirable, however, to utilize automatic timers for controlling the sequence and the duration of times that the jaws 16 and 17 are closed and the time that the welding current is permitted to flow, since if the current is supplied for too long a time this may result in excessive melting of the portion 14a of terminal 14 to produce the tear-drop effect common with prior art arrangements which adversely affects the strength of the terminal and the reliability of the completed unit. The control system for this automatic operation does not constitute a part of this invention but may suitably include a pair of timers for determining the periods when the solenoids are energized movably to position the jaws 16 and 17 between a clamped and an unclamped position, and when welding current is provided between the electrodes 18 and 19. Specifically, a first timer may control the jaw solenoid and preferably a spring is interposed between the solenoid and jaw so that after the jaws are in clamped position the solenoid may continue to stress the spring. During this final solenoid operation after the jaws are closed a switch may be actuated to start the flow of welding current which may be controlled by a second timer. The welding current is cut oflf by the second timer and then after a short delay the first timer permits the jaws to move out of welding position.

While the invention has been described by means of a particular embodiment thereof, it will be understood by those skilled in the art that many changes and modifications may be made without departing from this invention. Therefore, the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

l. The method of making a terminal structure for an electric heater of the type having a high resistance metallic conductor and a metallic terminal therefor, comprising, forming a portion of said conductor in a helix, inserting a portion of said terminal into said helix in engagement therewith whereby said helix and a portion of said terminal are concentrically arranged, and welding said helix to said terminal by providing current for a predetermined period of time in that portion of said helix which is in engagement with said terminal, the magnitude of said current and the period of its application being such as to cause only wetting of the surface of said terminal without appreciably melting the interior of said terminal.

2. The method of making a terminal structure for an electric heater of the type having a high resistance metallic conductor and a metallic terminal therefor, comprising, deforming a portion of said conductor to form a helix, inserting a portion of said terminal into said helix in engagement therewith, connecting welding electrodes to spaced turns on said helix, and providing welding current between said electrodes.

3. The method of making a terminal structure for an electric heater of the type having a high resistance metallic conductor and a metallic terminal therefor, comprising, forming a portion of said conductor in a helix, inserting a portion of said terminal into said helix in engagement therewith, said engagement being throughout an appreciable length of the inner surface of said helix, connecting welding electrodes to spaced positions on said helix, said turns being disposed within said appreciable length, and providing welding current between said electrodes.

4. The method of attaching a metallic conductor to a terminal, comprising, forming said conductor into a plurality of turns, inserting said terminal at least partially within said turns, providing at least two welding electrodes supported in opposing jaws, clamping said helix to said terminal by means of said electrodes, supplying current between said electrodes for a predetermined period of time, and releasing said electrodes from said helix and said terminal only after a predetermined delay following the termination of said period.

5. The method of forming a terminal connection for an electric heater of the type comprising a helix of resistance wire and a cylindrical terminal, which method comprises, inserting a portion of said terminal into a portion of said helix, providing a pair of welding electrodes, utilizing said electrodes to clamp said helix to said terminal at spaced locations on said portion of said helix, providing welding current between said electrodes for a predetermined period of time, and maintaining said electrodes in contact with said helix for a predetermined time after the expiration of said period of time.

6. The method of forming a terminal connection for an electric heater of the type comprising a helix of resistance wire and a cylindrical terminal, which method comprises, inserting a portion of said terminal into a portion of said helix, connecting a source of welding current between spaced apart locations on said portion of said helix for a period of time to weld said helix to said terminal, and extracting heat through said helix on opposite sides of the welded portion thereof for a predetermined time after the welding current is terminated.

7. The method of welding a tubular metallic structure to a cylindrical metallic structure, which method comprises, inserting said cylindrical structure into said tubular structure, connecting recessed Welding electrodes to locations longitudinally spaced apart on said tubular member with said tubular structure disposed in the recesses in said electrodes, and providing welding current between said electrodes.

8. The method of electrically welding a cylindrical metallic structure to a tubular metallic structure, which method comprises, inserting said cylindrical structure Within said tubular structure so that said structures contact one another, applying a high current in said structures in the vicinity of the area of contact, and removing heat from said structures on longitudinally opposite sides of the welding area in a manner to prevent excessive melting of said structures.

9. Apparatus for welding a terminal to a coil of resistance metal, comprising, a pair of oppositely disposed electrode support jaws, a plurality of electrodes carried between said pair of jaws, an insulating member disposed between adjacent ones of said electrodes in said support jaws, said electrodes having contact faces with cylindrically defined recesses therein, said recesses substantially conforming to a portion of a cylinder defined by the envelope of the outer surfaces of said coil, and means for supplying Welding gas between adjacent ones of said electrodes.

10. Welding apparatus comprising means for supporting a plurality of pairs of oppositely disposed welding electrodes, insulating means positioned intermediate adjacent ones of said electrodes to space said electrodes apart, and means for supplying shielding gas between adjacent ones of said electrodes.

11. The apparatus of claim 10 wherein said last mentioned means comprises a passageway in said insulating member.

12. The apparatus of claim 10 wherein said last mentioned means comprises a passageway in said insulating member and said passageway is displaced from the longitudinal axis of said insulating member.

13. The apparatus of claim 10 wherein said last mentioned means includes means for causing said shielding gas to swirl in the space intermediate adjacent ones of said electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 1,123,624 Thomson Jan. 5, 1915 1,361,652 Wetrnore Dec. 7, 1920 2,025,744 Hathorn Dec. 31, 1935 2,137,718 Friberg Nov. 22, 1938 2,354,313 Harris July 25, 1944 2,409,636 Little Oct. 22 1946 2,504,338 MacLatchie Apr. 18, 1950 2,546,315 Oakley Mar. 27, 1951 2,550,090 Schnepp Apr. 24, 1951 2,712,048 Huetten et al. June 28, 1955 2,766,983 Taylor Oct. 16, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.) 2,890,320 June 9, 1959 Sterling An Oakley It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 41, for "positions" read an turns Signed and sealed this 29th day of March 1960.,

{SEAL} Attest:

KARL H AXLINE ROBERT C. WATSON Attesting Ofiicer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE F CURRECTION Patent No, 2,890,320 June 9, 1959 Sterling A Oakley It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 41, for "positions" read turns Signed and sealed this 29th day of March 1960.,

(SEAL) Attest:

ROBERT C. WATSON KARL H. AXLINE. Attesting Officer Commissioner of Patents

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