US2639360A - Electric resistance unit - Google Patents

Description

May 19, 1953 R. G. wmnows 2,639,360

ELECTRIC RESISTANCE UNIT Filed July 2, 1951 5 Sheets-Sheet 1 I I I Hm ||nm-Q INVENTOR. -//('//,4P0 6 h waan s.

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May 19, 1953 R. G. wlbbows 2,639,360

ELECTRIC RESISTANCE UNIT Filed July 2, 1951 *5 Sheets-Sheet 5 INVENTOR. Ha /4P0 6.. Wmaaws.

ATTOFNA-KS May 19, 1953,v R. G. wmmows ELECTRIC RESISTANCE UNIT Filed July 2, 1951;

5 Sheets-Sheet 4 s S V K MM p W N 7 WW $7 W an a Q m May 19, 1953 R. G. wionows 2,639,35Q

ELECTRIC RESISTANCE UNIT Filed July 2, 1951 5 Sheets-Sheet 5 l I I Il -Ill:

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121 5 a 2 Z x Patented May 19, 1953 ELECTRIC RESISTANCE UNIT Richard G. Widdows, Shaker Heights, Ohio, assignor to The Electric Controller & Manufacturing Company, Cleveland, Ohio, a corporation of Ohio Application July 2, 1951, Serial No. 234,745

10 Claims.

This invention relates to electric resistance units or resistors of the grid type and more particularly to an improved grid resistor in which the electric circuit between the grids within the resistor is completed only through spot-welded joints.

Heretofore, electric resistors have been constructed by tightly clamping together between end frames in parallel spaced relationship a plurality of sheet metal resistance elements by means of suitably insulated supporting bolts which pass through perforations in lug portions formed at or near the opposite ends of the elements. The resistance elements are generally in the form of grids thereby to provide a relatively long current path within a relatively small area. In series connected resistors of this type, electric connections are made between adjacent grids alternately on opposite sides of the resistor through metal collars on the supporting bolts between the ings of adjacent grids. Each of the collars is forced against its contiguous grid lugs by pressure exerted by nuts threaded on opposite ends of the supporting bolts.

More recently, as described in David C. Wright Patent No. 2,378,056, issued on June 12, 1945, the opposite end portions of a sheet metal resistance element or grid have been offset in opposite directions from the plane of the intermediate portion of the grid so that they lie in planes which are spaced from but parallel to the plane of the intermediate portion. When such grids are properly assembled in parallel spaced relation on the supporting bolts, the oif-set end portions of adjacent grids that are to be connected together electrically extend toward each other and are spot-welded together at welding areas formed by tongue-like extensions of the end portions, and the off-set end portions of adjacent grids that are not to be connected together electrically extend l away from each other and are held in spaced relation by insulating collars on the supporting bolts between the grids.

The spot-welded connections in the resistor of the Wright patent stabilize the resistance value of the unit and eliminate burning at the end portions of the grids and the need for periodic tightening of the clamping nuts. However, the construction of the resistor of that patent requires that a forming operation be performed on the of the off-set lug portions of each grid be difier- Ill ent from the relative direction of the offset lug portions of the next adjacent grids. Thus it is necessary to use separate stamping and forming dies for each size of grid, to stock two forms of rids for each size of resistor, and to select the grids alternately during assembly of the resistor. Also, since welding areas can be provided only by providing suitable tongue portions, the prior construction is somewhat wasteful of the resistive sheet metal which is an expensive alloy. Furthermore, if two or more of the individual grids are to be connected in parallel, the end portions of each grid are off-set in the same direction from the plane of the grid instead of in opposite directions, and jumpers must be used to connect the paralleled groups of grids in series with each other.

It is an object of the present invention to provide an improved welded resistor.

Another object is to provide a resistor comprising a plurality of planiform resistance elements held together in flatwise spaced relationship and having its electric circuit completed from element to element through spot-welded joints.

Another object is to provide an improved welded resistor comprising a plurality of resistance elements arranged in fiatwise spaced relationship on a pair of insulated mounting bolts passing through perforations in respective opposite end portions of the elements.

A further object is to provide an improved resistor in which perforated end portions of adjacent planiform resistance elements are spotwelded to a metal collar interposed therebetween and surrounding a boltby which the elements are supported.

A more detailed object is to provide a resistor in which perforated end portions of adjacent resistance elements are held in fiatwise spaced relationship on bolts by metal collars interposed therebetween and formed to provide welding areas so exposed and accessible that contiguous resistance elements may be spot-welded thereto after assembly.

A correlative object is to provide a resistor in which metal collars on bolts and between flatwise spaced resistance elements have terminal flanges thereby to provide exposed and accessible areas to permit spot-welding between the collars and the resistance elements contiguous thereto.

Another object is to provide a resistor in which lug portions of a row of resistance elements are held in spaced relation on a supporting bolt by collars, the collars between elements of certain groups being metal and the collars between said groups being insulating material, and the metal collars being of such relative size and shape that resistance elements in contact with opposite ends of the metal collars may be spotweldeol thereto in a single operation.

In an electric resistance unit or resistor in accordance with this invention, a plurality of resistance elements, each having a perforation at one end portion, are arranged in a row in groups and are in flatwise spaced relation to each other with the perforations aligned and are supported at the end portions by a bolt passing through the perforations. Metal spacing collars on the bolt are interposed between the resistance elements of each group, and insulating collars on the bolt are interposed between each of the groups. Each of the resistance elements and each of the metal collars has a contact area directed endwise of' the row and spaced radially outwardly beyond the outer surface of the insulating collars and also has an area generally aligned endwise of the rows with its contact area and directed in the opposite direction. One of the areas of each of the resistance elements which is contiguous toone of the insulating collars is located radially outwardly beyond the surface of the insulating collar a distance sufficient so that it is exposed sufficiently to be engaged with a jaw of a spot welder. After the resistance elements and collars have been assembled on the bolt, the resistance elements of each group are spot-welded to the collars of that group at contiguous contact areas.

In the preferred embodiment of a resistor in which the resistance elements are in series, the elements are arranged in groups of, two and are similarly supported at opposite ends by respective bolts, and the collars on each bolt are. alternately of insulating material and of metal so that a continuous current path extending through the elements in series repeatedly back and forth across the resistor is formed. In this preferred embodiment, each of the metal collars has outwardly extending radial flange portions which engage the resistance elements, respectively, of a group and which define an area for engagement with the jaw of a spot welding machine. Similarly, a resistor may be constructed. with two or more of the individual grids inparallel with 4 each other electrically, the paralleled sets of grids being connected in. series. In a. modification, the metal collars are of larger diameter than the insulating collars thereby to provide exposed areas for the jaws of a spot-welding ma- Other objects and advantages of this invention will become apparent from the following. description; wherein reference is made to the drawings, in which Fig. l is a fragmentary side elevation of a preferred embodiment of the invention,

Fig. 2 isa sectional view of the resistor of Fig. 1 taken along thelineZ-Z of Fig. 3,

Fig; 3: is a sectional view taken along the line 3.--3=of Fig. 2,

Figs. 4 and 5 illustrate modified conducting collars which may be used in place of the collars of Figs. 1, 2, and 3,

Figs. 6 and '7 are fragmentary side elevations of resistors using further modified forms of conducting collars, respectively,

Fig. 3 is a fragmentary top plan view of a resistor in accordance with Fig. 7, and

Fig. 9 is a fragmentary top plan view of a resistor having resistance elements connected in parallel.

Referring principally to Fig. 2, an individual resistance element Ill suitable for use in a resistance unit or resistor 18 in accordance with this invention may comprise an integral planiform piece of sheet metal of suitable mechanical, thermal, and electrical characteristics, preferably a high resistance alloy of chromium, aluminum, and steel, shaped in the form of a grid and having a pair of enlarged end portions or lugs H and E2 of identical configuration with circular perforations or openings M therein, re spectively. If desired, each of the perforations 14 may be in the form of a slot or open eye opening through the edge of the grid, but a sufficient margin of metal should be provided adjacent each perforation 14, particularly the portion of the margin exposed. endwi-se of the grid, to insure adequate welding areas, as hereinafter described.

lhe lugs H and 52 are interconnected by an intermediate flat sinuous strip portion l5 defining a suitably arranged coplanar series of convolutions forming a circuitous current path between the lugs H and H2. The grids Hl'may be formed directly from sheet metal to the shape shown by a stamping operation or may be formed by edgewise bending of a long straight strip. The sinuous strip portion l5 may be of any suitable configuration, the convolutions as shown being merely illustrative of, a preferred embodiment which provides a relatively long current path within a relatively small area with only a small amount of metal being wasted in the stamping operation.

7 Referring now to Figs. 1, 2, and 3, the series connected resistor l8 comprises a plurality of the grids it supported in fiatwisespaced relation in a rowbetween a pair of identical end frames is and 2611. In assembling the resistor l8, elongated bolts 2! and 22 for supporting the grids it! are inserted through respective horizontally spaced perforations near the opposite top. corners of one of the end frames such as 85. Preferably, the perforations in the end frames are elongated horizontally, as indicated in Fig. 3, to allow for thermal expansion of the grids Hi; Each of the bolts 2i and 22 is preferably insulated from the end frame !9 by an outer Washer 24 of suitable insulating material having a centrally disposed annular boss 25 (Fig. 3) which extends through the perforation in the end frame l9 into a complementary cylindrical recess around a central opening of an inner insulating washer Z6, and each bolt is retained in position by a chock-nut 23 and a clamping nut 29, metal washers 3B serving the usual function as shown. Suitable insulating tubes 3! and 32 are slipped over the bolts 2'! and 22, respectively, against respective metal washers 34 disposed inside of respective clamping nuts 35. Suitable insulators 36, which may be in the form of stacked mica washers, are then slipped over the tubes 3|. and 32, respectively, and engage the washers 34, respectively, to provide a good insulating barrier between the end frame I9 and the grids III.

A suitable tubular insulating spacer or insulating collar 38 which may be of durable ceramiclike material is slipped over the tube 3| against one of the insulators 36 and a similar insulating collar 38 is slipped over the tube 32 against the other insulator 36. The first of the grids I8 is then mounted on the bolts 2| and 22 by slipping the perforations I4 in the lugs II and I2 over the tubes 3| and 32, respectively.

After the first one of the grids I is in place, a terminal member 39, formed from a fiat strip of conducting metal and having a rectangular perforation 40 near one end for the attachment of a lead-in conductor (not shown), is mounted on the bolt 2| in electric contact with the lug II of the first of the grids III by slipping a circular perforation in an upwardly extending portion 4| (Fig. 2) over the tube 3|. Preferably, the terminal 39 is shaped, as shown, so that the perforation 40 is positioned materially below the center line of the bolt 2|.

After the first one of the grids I0 and the first one of the terminals 39 are in place, another of the insulating collars 38 is slipped over the tube 3| and the first of a plurality of flanged tubular metal spacers or conducting collars 42 is slipped over the tube 32, and then another of the grids I9 is mounted on the bolts 2| and 22 by slipping the perforations I4 in the lugs I I and I2 thereof over the tubes 3| and 32, respectively.

Each of the collars 42 has annular flanges 44 and 45 extending radially outwardly at opposite ends of a cylindrical intermediate portion 46 of reduced diameter. The diameter of the outer surface of the portions 46 is preferably substantially the same as the diameter of the outer surface of the collars 38. The difference in diameter between the outer periphery of the flanges 44 and 45 and the outer surface of the portion 46 and of the collars 38 is such that contact areas facing endwise of the grid are provided which are exposed sufliciently to be engaged by a jaw of a spot-welding machine.

After the first two of the grids ID are in assembled position, a longer insulating collar 43, but of substantially the same diameter as the collar 38, is slipped over the tube 32 and a conducting collar 42 is slipped over the tube 3|. In like manner, a suitable number of additional grids ID are mounted on the bolts 2| and 22 with the insulating collars 38 and 43 and the conducting collars 42 alternated to provide a back and forth path for the current through the resistor.

Additional terminals 39 may be placed over the tube 3| in contact with the grids I!) at suitable intervals as desired. Preferably, the terminals 39 are alternated endwise of the resistor with terminal members 59, similarly supported on the bolt 2| and having a rectangular perforation 5|, but so shaped that the perforation 5| is horizontally disposed with respect to the mounting bolt 2|. Consequently, lead-in conductors can be more easily fastened to closely adjacent terminals 39 and 59 since the respective openings 48 and 5| are not in horizontal alignment. The conducting collars 42 and the insulating collars 43 are made slightly longer than the insulating collars 38 to compensate for the space occupied by the terminals 39 and 50 thereby to permit the grids I8 to be parallel with each other. Such terminals, wherever used in contact with the grids IIJ, serve not only as terminals but also as spacing collars in the same manner as the collars 42. Thus the terminals 39 and 50 and the collars 42 each serves as a spacing element for the grids 9.

After a sufficient number of resistance grids I9 has been assembled to provide the total resistance, additional insulators 36 are slipped over the tubes 3| and 32 and additional washers 34 and clamping nuts 35 are grouped on the bolts 2| and 22 which are then inserted in horizontally spaced, elongated perforations in the end frame 28 and held by additional washers 24, 25 and 38 and nuts 28 and 29. Thus the grids I 0 are spaced and insulated from the frame 20 by the same type of spacing, insulating and clamping arrangement used for the end frame I9. The dispositions of the nuts 38, 29, and 35 at opposite ends of the bolts 2| and 22 may be selected so as to provide uniform spacing between the end frames I9 and 28 of the resistance units irrespective of the number of grids, the spacing therebetween, and the thickness of the metal forming the individual grids. By properly positioning of the nuts 28, 29, and 35, space for thermal expansion may be provided so that all deleterious thermal strains are prevented.

As mentioned, the flanges 44 and '45 of the conducting collars 42 define contact areas which face endwise of the row of grids of the resistor, are spaced outwardly beyond the outer surface of the portion 46 of the collars 42 and beyond the outer surface of the insulating collars 38 and 43, and are aligned endwise of the row with areas defined by the margin of metal of the lugs I I and I 2 around the perforations I 4. Similarly, the terminals 39 and 50 have areas aligned endwise of the row with the other areas. Consequently, adequate space is provided for opposing jaws of a spot welder (not shown) to engage any two exposed areas which are oppositely facing. In this manner, one or more spot welds 52 between juxtaposed areas through the respective lugs II or I2, flanges 44 or 45, and terminals 39 or 50, if any, are made to form the stack of grids into an integral resistance structure. If the flanges 44 and 45 were not provided in the resistor I8, there would be no areas on the collars, aligned with accessible contact areas on the grids, which could be engaged by the jaws of a spot-welding machine.

The grids I8 of the assembled resistor I8 are all in series with each other and define a current conducting path through the grids II] which is alternately back and forth across the resistor. As seen most clearly in Figs. 1 and 3, a circuit through the resistor I8 extends from the terminal 39 closest to the end frame I 9 through one of the spot-welded joints 52 to the lug II contiguous thereto, the first one of the grids I8, another of the spot-welded joints 52 from the lug I2 of the first one of the grids to the flange 44 of the first one of the conducting collars 42 on the bolt 22, the first collar 42, another of the spot-welded joints 52 from the flange 45 of the first collar 42 to the lug I2 contiguous thereto, the second of the grids I0, and another of the spot-welded joints 52 into the flange 44 of the first of the conducting collars 42 on the bolt 2|. The circuit continues in like manner until a final one of the terminals 39 (Fig. 1) closest to the end frame 20 is reached.

The conducting collars 42 of the resistor I8 are preferably a screw machine product with the intermediate portion 46 of reduced diameter cut away from a thick walled tube. If desired, flanged conducting collars 53, such as shown in Fig. 4, may be substitutedfor the collars 42. .The r collar 53 comprises a short metal tube M with washer-like elements 55 of larger diameterspotwelded to opposite ends thereof, the central openings in the tube a l and the washers 55 being in alignment. The outwardly extending portions of thew'ashers 55 are of such size that adequate flange areas are provided for accommodating welding jaws to make the spot welds with the grids Ill after assembly of a resistor.

Instead of using the washer-like elements 55 of Fig. 4, the desired exposed welding areas may be provided as shown in by spot welding eccentric perforated elements 56 to opposite ends,

respectively, of the short tub 54 to form a conducting collar '59 with outwardly extending tongue portions. When the collars so are used in place of the collars 42, the tongue portions thereof p-referabiycxtend outwardly of the resister from the supporting bolts 28 and 2.2 thercby to provide exposed and accessible areas for forming spot welds between the tongue portions and the grid lugs contiguous thereto.

Fig. 6 shows how the resistor iii of Figs. 1, 2, and 3, may be modified by use of a further modifled form of conducting collar. In Fig. 6, a plurality of grids it are shown as held in flatwise spaced relation on an insulated supporting bolt 6i], similar to the bolt 28, by the insulating collars 3S and conducting collars ti. The collars iii are thick-walled cylindrical metal tubes having a uniform outside diameter sufiiciently greater than the outside diameter of the insulating collars 38 to form accessible areas directed endwise of the resistor for making spot-welds or. As clearly seen in Fig. 6, aligned spot welds 62 may be made between a pair of grids it, one of the collars Bl therebetween, and one of the terminals 39 or fail in a single operation alter the resistor is assembled.

Referring now to Figs. 7 and 8, a further modifled resistor comprises a plurality of the grids l8- held in fiatwise spaced relation by insulating collars iii and cooperating pairs of flanged conducting collars "ll. Each of the collars ll comprises a tubular portion '12 of relatively small diameter and an outwardly extending terminal flange portion i l of relatively larger diameter. Before the grids iii are assembled in the resistor of Fig. 7 and Fig. 8, the unflanged ends of a pair of collars 7! are spot-welded to the opposite end. lugs ii and i2, respectively, on opposite sides of each of the grids lil as shown most clearly in. Fig. effect, oi i set end portions of the grids which are parallel to the plane of the grid. In assembling the resistor of Figs. 7 and 8, the collars 12 that are welded to those end portions of the grids it which are to be electrically connected to each other extend toward each other, and the collars E2 that are welded to those end portions of the grids it which are not to be electrically connected to each other extend away from each other. After the resistor has been assembled, the flange portions i l of the collars 72 which extend toward each other are either spot-welded to each other directly or to opposite sides of a suitable terminal member such as the terminal 5%.

In the resistor l3 and the modified forms thereof shown in Figs. 6, '7, and 8, all of the grids it] are connected in series with each other. In order to provide increase thermal capacity, it is sometimes desirable to connect two or more of the individual grids in parallel with each and the paralleled sets of grids in series. A resistor constructed in this manner is illustrated in Fig. .9.

The flanges l l thus constitute, in

Referring to Fig. 9, the grids it) are arranged in parallel connected pairs to, ill, B2, and 83 and the several pairs of grids are connected in series with each other. Assuming that current enters the resistor of Fig. 9 through the terminal 39 in the upper right hand corner of the drawing, the current divides and passes through the grids H! of the pair 88 in parallel, the lugs H of these grids being spot-welded as at 52 to respective flanges of a first one of the flanged conducting collars 42 received on the bolt 2i and the lugs i2 thereof being spot-welded as at 52 to respective flanges or a first one of the conducting collane 42 received on the bolt 22. The first of the insulating collars 43 received on the bolt 2! in sulates the lugs H of the pair of grids to from the lugs H of the pair of grids 8! along the bolt 2|, but a conducting collar 84 received on the bolt 22 and similar to but longer than the collars t2 electrically connects the lugs 52 of the pair of grids lit to the lugs it of the second pair of grids iii through spots welds t2 as indicated, the latter lugs l2 being Spot-welded to another collar n! received on the bolt 22. Current there fore i lows through the pair of grids 8-4 in the direction indicated by the arrow adjacent thereto. The lugs ii of the pair of grids iii are connected to each other through a second collar lE received on the bolt iii and to the lug ii of one of the pair of grids .82 through a third one of the insulating collars 32 received on the bolt 29. A terminal {:36 is preferably welded to the lug ii of the pair of grids 8i closest to the of grids and a terminal 39 may be welded to the lugof the pair of grids t2 closest to the pair of grids Bl. An insulating collar similar to but longer than the collars it, is received on the bolt 22 and separates and insulates the lugs ii: of the pair of grids 8! from the lugs l2 of the pair of grids Current flows from the pair of grids as to the pair of grids 8.3 through another of the collars 8'2 recefu/ed on the bolt 22 and thence as indicated by the arrow adjacent the grids 33 towards the lugs H thereof.

It should be noted that the individual grids iii of each of the pairs Si], Si, 82, and 83 are closer together than are the respective pairs of grids. This is because any engagement between the grids of any one pair due to warping not deleterious whereas contact between grids of separate pairs would be harmful. It should also be noted that the current enters and leaves the pairs of grids at diagonally opposite corners thus insuring proper current distribution between the grids in each pair, and that the terminals 39 or 5B are so located as to maintain such a current path as near as practicable.

I claim:

1 An electric resistance unit of the type in which a plurality of resistance elements, each having an opening at one end portion, are arranged in a row in fiat-wise spaced relation to each other with the openings aligned and are supported at said end portions by a bolt passing through said openings, metal spacing elements having portions received on the bolt, said resistance and spacing elements, at the portions adjacent said bolt, being arranged in groups each of which includes at least two resistance elements and one spacing element, each of the elements of each group being in electrical conductive relation to those next adjacent to it at a contact area at its said portions, the said portion of at least one of said spacing elements or" each group being 111- terposed betweena pair of the resistance-elements of its associated group and in electrical conduc tive relation thereto to provide a conductive path therebetween, insulating collars on the bolt interposed between the groups, certain elements of the group having exposed areas facing away from each other, each of said exposed areas being exposed endwise of the row, spaced radially out- Wardly of the bolt, and spaced endwise of the row from any next adjacent surface of the unit exposed toward it endwise of the row, said contact area of each element facing endwise of the row and being inwardly of the roup endwise of the row from said exposed areas of its associated group, and said spacing of said exposed areas radially of the bolt and said spacing of said exposed areas endwise of the row being sufiicient, respectively, so that a pair of said exposed areas can be engaged concurrently with the respective jaws of a spot welder, whereby the contact areas between said pair of exposed areas can be spotwelded together simultaneously.

2. An electric resistance unit in accordance with claim 1 characterized in that said exposed areas and said contact areas are generally aligned endwise of the row.

3. An electric resistance unit in accordance with claim 1 characterized in that said resistance elements have elongated portions extending in a predetermined direction radially of the bolt and the radial spacing of said exposed areas is in a direction different from said predetermined direction.

4. An electric resistance unit in accordance with claim 1 characterized in that some of said spacing elements are collars each having at least one flanged portion thereon extending radially outwardly from the remainder thereof.

5. An electric resistance unit in accordance with claim 1 characterized in that some of said spacing elements are collars each having flanges extending radially outwardly from the remainder thereof and spaced apart endwise of the row from each other.

6. An electric resistance unit in accordance with claim 5 characterized in that some of said flanges are annular.

7. An electric resistance unit in accordance with claim 1 characterized in that some of said spacing elements are collars which have only contact areas facing endwise of the row.

8. An electric resistance unit in accordance with claim 1 characterized in that each of said resistance elements comprises a single strip of resistive material.

9. An electrical resistance unit in accordance with claim 1 characterized in that each of said resistance elements comprises a plurality of resistive members arranged in a row in flatwise spaced relation to, and connected in parallel with, each other,

10. An electric resistance unit in accordance with claim 1 characterized in that said resistance elements are substantially planar and parallel to each other and the spacing element between a pair of adjacent resistance elements is of sufficient length endwise of the row to space said pair of resistance elements apart the distance necessary for adequate electrical clearance throughout their length.

RICHARD G. WIDDOWS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,471,391 Dunlop Oct. 23, 1923 1,501,638 Weimer et a1 July 15, 1924 2,378,056 Wright June 12, 1945 OTHER REFERENCES Kutcher et a1. Welded Resistors, The Welding Journal, October 1948, pages 827-830.

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