US2247133A - Current supply means - Google Patents

Description

June 24, 1941. M. G. REES CURRENT SUPPLY MEANS Filed Aug, 24, 1956 2 Sheets-Sheet 1 N@ YM @n m m6. .A 1. 1f l W W. i t E YW June 24, 1941. M. lG. REES CURRENT SUPPLY MEANS Filed Aug. 24, 1936 2 Sheets-Sheetr 2 Patented June 24, 1941 UNITED STATES PATENT OFFICE CURRENT SUPPLY MEANS Mackworth G. Rees, Detroit, Mich.

Application August 24, 1936, Serial No. 97,571 s claims. (c1. 171-1'19) My invention relates to methods and apparatus for producing resistance welds and particularly to a method of constructing and arranging a transformer and cable so as to materiallyincrease the efficiency of the Welding operation while providing improved welds.

At the present time, Welding transformers and cables of portable welding outts are operated very inefficiently, primarily because of their poor electrical arrangement of parts. The portable welding outfit referred to is that consisting of a transformer, a circuit, and a welding gun which clamps the elements to be welded while producing a resistance Weld therein. The transformer has a single winding on the secondary which is usually a casting about which the primary winding is disposed, and is sometimes water-cooled to limit its temperature rise. The secondary winding of the transformer is connected to the welding gun through two heavy cables which may also be water-cooled and which may be the means for conducting water to the electrodes of the gun.

The power losses in the transformer,- secondary, and conductors are very large and comprise the ohmic drop which is a. function of the resistance of the copper conductor and the current flowing; E (voltage drop) :L R. (current in amperes :c resistance in ohms). Eddy current losses and reactive volt drop are two additional losses which are present in the system. The ohmic drop cannot be improved but the latter two, the losses due to eddy currents and reactive volt drop, can be materially improved.

In practicing my present invention, I materially decrease the losses in the welding apparatus by decreasing the effect of the eddy current and the reactive volt drop. I accomplish this by employing a plurality of small conductors arranged in predetermined order to minimizefthese losses. The transformer is constructed to have the secondary made up of a plurality of sections providing a plurality of positive and negative terminal ends. A plurality of conductors are connected to the secondary terminal ends and are arranged in alternating positive and negative sequence. The conductors may be braided to produce the positive and negative alternating arrangement, or may be disposed adjacent to each other with the position of the positive and negative conductors predeterminedly arranged or, preferably, the alternating positive and negative conductors are positioned annularly` on the circumference of a circle. The conductors are extended in this relation directly adjacent to the gun where they are separated into two groups, one positive and one negative, and joined to the two electrodes of the gun.

The conductor formed in this manner may be encased in a sheath and a cooling iiuid passed therethrough to limit its temperature rise. The cooling uid may be passed over a portion of the conductors, through the electrodes of the gun and back through the remainder of the conductors to a discharge line. The fluid for operating the gun may pass through the central hollow aperture of the cable which is provided by theannular arrangement of the current carrying cables. In this manner a single flexible element connects the transformer to the gun, making the gun exceedingly portable while increasing its efficiency through the elimination of substantially al1 of the reactive voltage drop and eddy current effects. Longer cables may be provided between the transformer and the gun, which is also of advantage in view of the present necessity of making interior welds on large fabricated elements such as automobile bodies, coaches, locomotives, and the like.

Accordingly, the main objects of my invention are to provide a transformer and circuit for a resistance welding gun which are highly efficient; to provide a transformer. for producing resistance welds which has a plurality of secondary sections interspaced between sections of the primary to produce a plurality of positive and negative secondary terminal ends; to provide a conductor between the secondary of a transformer having a plurality of positive and negative terminal ends which is constructed of light llexible cables arranged in predetermined relation with respect to their connection with the positive and negative secondary terminal ends; to decrease the eddy current and reactive volt drop in a cable by insulating sections of the cable from each other and arranging the sections in a predetermined order; to increase the eiciency of a resistance welding gun by delivering current thereto through a cable having insulated sections arranged in predetermined positive and negative order; and in general, to provide apparatus for producing resistance welds which is exceedingly efficient, portable, and economical to manufacture.

Other objects and features of novelty of my invention will be either specifically pointed ou' or will become apparent when referring, for better understanding of my invention to the following description taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a diagrammatical view of a portable resistance welding device embodying features of my invention;

Fig. 2 is a sectional view of the structure illustrated in Fig. 1, taken on the line 2-2 thereof;

Fig. 3 is an enlarged Sectional view of the structure illustrated in Fig. l, taken on the line 3-3 thereof;

Fig. 4 is a view of structure similar to that illustrated in Fig. 1, showing a commercial form which my invention may assume;

Fig. 5 is a sectional view of the structure illustrated in Fig. 4, taken on the line 5-5 thereof;

Fig. 6 is a sectional view of the structure illustrated in Fig. 4, taken on the line 6-6 thereof;

and

Fig. 7 is a sectional View of a plurality of conductors illustrating a further form which my invention may assume.

Referring to Figs. 1 to 3 inclusive, I have illustrated a portable resistance welding device embodying a transformer I0, a flexible conductor I I, and a welding gun I2 for producing resistance welds. The transformer herein illustrated is of the ring type having primary sections I3 and secondarysections I4 alternatingly disposed in annular arrangement. The primary sections or windings I3 are connected in series .by the conductors I5, while the secondary sections or windings I4 each have a positive terminal end I6 and a negative terminal end I1. ductor II has a plurality of parallelly arranged alternatingly disposed conductors I8 and I9 which are joined, respectively to the ends I6 and I1.

The conductor II, as illustrated more particu- I larly in Figs.. 2 and 3, has the light exible cables I8 and I9 alternatingly disposed and spaced from each other by an insulating element 2I which is of sinuous form and disposed between an inner flexible insulating tube 22 and an outer flexible insulating sleeve 23. The elements 2I, 22, and 23 are preferably made of rubber so as to be exible, insulating-'and fluid conducting. The terminal ends of the sleeve 23, are enclosed by jcaps 24 through which a cooling fluid may be passed through an inlet opening 25 and an outlet opening 26. An air-line 21, for operating the gun I2, may bepositioned within the tube 22 so as to have the outer sleeve 23 encompass all of the conductors to the gun.

The efficiency of the device is materially increased by reducing the losses in the transformer and in the conductor provided between the transformer and the gun. Some commercial portable welding devices are so ineiiiciently designed as to require an open circuit voltage of 25 volts to deliver two volts to the welding electrodes.

Devices requiring an open circuit voltage of from` 12 to 15 volts to produce two volts across the electrodes are themost efficient devices commonly employed today. With my transformer and conductor, an open circuit Voltage of 8 volts will deliver as high as 2.4 volts to the welding electrodes.

It is known that the leakage flux, caused by the loose coupling between the primary and secondary windings, will be greater with a single secondary turn Wrapped around the primary winding than it will be if the secondary is wound in sections interspaced between sections of the primary. Accordingly, by increasing the number of secondary sections (I greatly reduce the leakage ux and materially improve the power factor. 'Ihe transformer having the plurality of secondary and primary sections has a better regu- The flexible conlation than transformers having a single turn secondary and a single primary winding.

With the improved transformer, I employ a conductor having a plurality of light cables arranged lannularly, in parallel relation with the positive and negative conductors alternatingly disposed. Tests were conducted on various types of cables, employed in combination with my above described transformer. Two parallel conductors 33 and 34 such as illustrated in Figs. 5 and 6 of the drawings, separate positive and negative conductor groups 20 and 30 as illustrated in Fig. 7 and a plurality of annularly disposed, parallelly arranged, positive and negative conductors I8 and I9, as illustrated in Fig. 2, were compared. Readings were taken when test welds were made with the various cables, employed in connection with the ring transformer above described.

The results were as follows:

Figs. 5 c and t., lig. 7 F1g.2

Primary input amperes, 230 .260 240 Voltsatwelil .8 1.5 2.4 Opeucircuit volts 8 8 Reactive volt drop ln leads and secondary 3.0 2.8 2.0 Ohmic drop iu leads 3.0 3.6 3.6 Condition of weld No weld Fair (lood 'Ihe duration of the attempted welds was 4 cycles on a 60 cycle current requiring approximately l/Lf, of a second. However, greater or less time may be employed in practice. Readings were taken by recording the swing of the instruments, which, while not of the highest accuracy, were comparative. The actual results above indicated checked very favorably with the values to be expected from computations made from standard tables of reactance volts in parallel conductors.

Such computation was made from table 27, page 1657 (Mershon Diagram) Mechanical Engineers Handbook (McGraw, Hill Book Company, Inc.) rst edition 1916 Lionel E. Marks, Editorin-chief. Employing the facts in the table and assuming 6,000 amperes in the secondary conductor comparison may be made between the use of the standard 500,000 circular mill cable in a pair of conductors and the employment of 8 conductors of 66,370 circular mills, the plurality of which totals 520,000 circular mills. In the comparison, it is assumed that the cables are 6 feet long, one for a lead and one for a return, and the transformer secondary is selected as approximately two feet long, making a totallength of 14 feet. The following results were obtained by computation z '-MGOOO- 1.164 vous Total ohmic and reactive drop to be added vectorally.

Ohmc drop 500,000 c. in. l cable.

Reactive drop 500,000 c. m. 2 centres ZDOXS =1.64 volts Ohmic drop 8-#2 in parallelIl Reactive drop on l" centres= eddy current losses were not measured but it is known that these were reduced automatically 2,247,133 by the arrangement of the cables reducing the reactive volt drop. In actual tests as set out above, with an open circuit secondary Voltage of 8 volts, 2.4 volts was delivered through the cable, illustrated in Fig. 2, to the Welding electrodes and exceptionally good welds were produced. When the standard form of cables were employed, there was no welding-.of the material. This disclosed the increased eiliciency of the conductor illustrated in Fig. 2 when employed in combination with my above described sectionalized transformer for producing resistance welds. This increase in efficiency is of great advantage particularly in portable welding devices since a decrease in the weight of the device and an increase in cable length may be had. Portable welding devices are now being utilized commercially for welding Within the interior of automobile bodies, busses, trucks, railway coaches, and the like. When exterior welding only was employed, the short cables and heavy equipment could be utilized without experiencing great fatigue. In producing welds on the interior of a structure, the apparatus must be exceptionally mobile and eflicient. I not only have increased the portability of my welding device but have also increased its eiciency which permits the employment of longer or lighter conductors. When an eiiiciency equal to that of the present welding devices is satisfactory, I increase the portability of my device materially by reducing the weight and diameter of the cable employed. By employing a cable as herein illustrated and described, I am not limited to short cable lengths and may therefore produce welds with a single gun at points spaced much farther apart than is the present practice.

The number of cables employed in the conduc- Y tor I I depends upon the amount of current delivered by the secondary. I preferably employ the 66,370 circular mill cable referred to above sinc'e he reactive volt drop in this size is negligible. It is to be understood that cables of smaller or greater diameter cou1d be employed in the conductor. However, I found this size to have a satisfactory current carrying capacity and I `select the number of cables to be employed to correspond to the amount of current to be carried.

Referring to Fig. 4, I have illustrated a commercial form of my invention wherein the transformer I3 illustrated in Fig. l is shown encased in a housing and suspended from a. support 3|. Current is introduced into the transformer through a pair of leads 32. The'conductor II extends from the secondary of the transformer to the gun where it is split to form a positive conductor 33 and a negative conductor 34 having a coolant conducting sheath thereover. The separation of the cables of the conductor I I occurs as close to the electrodes of the gun as possible.

The gun 35 herein illustrated, is of conventional form having a pair Aof welding electrodes 36 and 31, the former of which is movable by the operation of a piston in a cylinder 38. The terminal ends of the conductors 33 and 34 are connected to the support 39 of the electrode 31 and to the movable terminal 36, respectively. A handle 4I is provided on the gun and an operating trigger 42 controls the flow of uid into the cylinder 38 from a conductor 43 which extends through the tube 22 of the conductor II', passing therefrom adjacent to the transformer, as illustrated in the figure.

A cooling circuit may be provided within the cables and gun comprising a conduit 44 for delivering fluid within the space 45 between the element 2I and the inner tube 22. The water or other cooling fluid passes into the sheath of the conductor 33 to be delivered through the conduit 46 to the electrode 3l and then through the iiexible conduit 48 to the electrode 36 where it passes through the flexible conduit 49 into the sheath of the conductor 34. The fluid is then passed through the passage 5I between the insulating element 2I and the sleeve 23 and discharged therefrom through the conduit 52.

When the circuit to the transformer is controlled through the operation of the gun, this may be produced by the drop in pressure in the uid line 43 or may be effected through the actuation of a switch carried by the gun. The conductors to the switch preferably are passed through the interior tube 22 of the conductor II and to a relay which controls the fiow of current to the leads 32. The construction of the transformer and the disposition of the plurality of cables in the conductor I I are preferably the same as that of the structure illustrated in Fig. 1.

The conductor II herein illustrated and described may be utilized to advantage with the transformers commonly employed on portable welding devices. Positive and negative terminal end portions 33 and 34 are provided at both ends of the conductor, one set to be connected to the positive and negative terminal ends of the secondary winding, the other to be connected to the gun. While such a combination is not as eiicient as that of the structure illustrated, a material improvement is obtained over the employment of a pair of solid cables.

Accordingly,`I have provided an exceedingly flexible and portable welding device having a high degree of efficiency. This I have produced by increasing the eflciency of the transformer and decreasing the losses in the conductor which delivers current from the transformer to the Welding gun. connecting cables due to eddy current and-'reactive volt drop have been substantially eliminated in my conductor. This I have produced by the particular arrangement of the positive and negative current carrying cables which go to make up the conductor. A single lighter and more ilexible conductor is thereby provided which is not limited in length and which adds materially to the portability, and extends the uses of such a welding de vice.

The invention in the present vapplication pertains primarily to the specific construction of the body of the cable and to its use between a. source of current and a load device. The specic terminal construction of the cable is shown diagram` matically in Fig. l, and in a commercial form in Fig. 4. For a more detailed teaching of the grouping of the cables and terminal assembly reference may be had to my co-pending application, Serial No. 201,360, filed April 11, 1938, wherein several constructions are illustrated in detail.

While I have described and illustrated but a single embodiment of my invention, it will be apparent to those skilled in the art that various changes, omissions, additions, and substitutions may be made therein without-departing from the spirit and scope of my invention, as set forth in the accompanying claims.

I claim as my invention:

1. A conductor for transmitting heavy current including, in combination, a exible insulating central core, a pair of leads each comprising a. plurality of bare iiexible cablesdisposed annularly 'Ihe losses present heretofore in thev sheet of rubber disposed between and insulating said cables from each other, an outer flexible insulating sheath encompassing said core and cables, said cables having coolant conducting passageways thereabout within said insulating sheath.

3. In a system for conducting current from a transformer to a load device, the combination, including a transformer having a plurality of pairs of secondary terminals, a cable having a pair of leads comprising a plurality of conductors which are alternately disposed in said respective leads, the conductors at one end of the cable being connected to the pairs of rsecondary terminals of said transformer, the said conductors at the opposite end being grouped, a pair of terminals to which said grouped'conductors are secured, and means for connecting said pair of terminals to said load device. i

4. In a system forv conducting current from a transformer to a load device, the combination, including a transformer having a plurality of pairs of secondary terminals, a cable having pairs of leads each composed of a plurality of conductors, with the conductors of one lead alternately disposed relative to the conductors of the other lead, the conductors at one end of the cable being connected to the pairs of secondary terminals of said transformer, and at the opposite end said conductors of like leads being grouped, va pair of terminals to which said grouped leads are attached, said terminals being connected to said load device.

5. A cable for transmitting heavy current4 which includes a pair of leads comprising a plurality of flexible conductors disposed annularly about an axis, alternate conductors being of different leads, an outer flexible insulating sheath covering said conductors, and means'providing a plurality of coolant passageways inwardly of said sheath and disposed annularly about said axis and arranged to conduct coolant through the cable in intimate heat conducting relation with the conductors.

MACKWORTH G. REES.

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