Патент USA US2128222код для вставки
Aug. 30, 1938. M. A. DU Bols 2,128,222 RESISTANCE GRID F'iìled Dec. 2, 1935 2/20 2 Sheets-Sheet l £20 l / l l f’ any wup: Patented Aug. so, 193s 2,128,222 UNITED STATES PATENT OFFICE V 2,128,222 RESISTANCE Gam Marvin A. Du Bois, Chicago, Ill., 'assignon by mesne assignments, to ÀThe Post Glover Elec trkògiompany, Cincinnati, Ohio, a corporation of` o ‘ Application December 2, 1935, >Serial No. 52,531 6 Claims. (Cl. B01-89) The p're‘sent invention relatesmtp electrical re- light weight, and designed to have a high degree sìstance grids and electrical resistances contaîn- ‘of practically. uniform self-ventilation. ing the same and has for an object the provision of a novel and relatively inexpensive grid ele- ~ » - A further object is to provide resistance devices of the character described wherein the grid ele 5 ment and, as a further object, the provision of r ments of a given gauge of sheet stock and at a Ui an effectively ventilated, long lived and compact electrical resistance f_or use in various installa- predetermined spacing have a higher continuous carrying capacity than heretofore known grids tions. of similar thickness and width and like spacing - A further object of the invention is to provide 10 a novel method of forming highly eiilcient resistance grids of sheet metal with a minimum of loss that have equal individual resistance. Another object is a simple and inexpensively l0 practiced method of cutting grids of the inven of sheet stock in scrap or waste. ~ tion from an elongated steel sheet. Another object is to provide a stamped sheet metal resistance grid characterized in that each 15 grid, between the terminals thereof, is constituted by a continuous series of angulariy related sections so disposed with relation to each other as to provide for the closer disposition of the sec-- These and other objects are attained by the method and means herein described and dis closed in the accompanying drawings, in which: 15 Fig. 1 is a plan view showing in full lines the resistance grid in relation to the sheet in which it is cut, and in dotted lines, the position of the tions thereof nearest the edges of the grid, and 20 for the wider spacing of certain non-adjacent die to cut a succeeding grid. " Fig. 2 is a cross sectional view of a resistance 20 sections providing for the more ready dissipation oi heat from the more closely spaced sections to the edges of the grid, the said relation of these continuous sections further permitting of the -25 stamping of successive grids from a ribbon or device embodying the grid oi the invention. Fig. 3 is a view taken on line 3-3 of Fig. 2. Fig. ,.4 isa cross sectional view of a resistance device showing a modiiled form'of mounting the grids and of providing additional support there- 25 elongated sheet of electrical steel in a fashion for as may be required in rare instances -of ex productive of a minimum of waste of the sheet stock from which the grids are stamped. Another object of the invention is to provide 30 a resistance grid of stamped sheet electrical steel that is designed to> provide a high continuous carrying capacity factor in proportion to the resistance thereof and which in use in a resistance device will readily combine the desirable factors 35 of very nearly uniform temperature distribution throughout the major portion of each grid with a surprising1y low temperature at the terminals thus. avoiding the destructive action of heat on the insulating supports therefor and upon the cessively close spacing and very thin grids. Fig. 5 is a fragmental schematic view showing a modified form of the mounting of the grids of the invention in multiple banks. 30', Fig. 6 is an enlarged view taken on line 6--8 of Fig. 5. , In the art 0f Constructing reSiStOrS. Practice has been largely with cast metal grid resistors or the so- called ribbon resistors, and although the :3,5`V use of sheet metal is not unknown, previous at tempts to use it have resulted in products infe rior t0 the present device and incurring large Waste Of material» The Present inventien DIO 40 insulation and other parts of the actuators and lead Wires associated with the termina1s_ ~ Vides a new Sheet metal grid which has advan' 40 „ tages over the cast grid resistors in that it gives Another object of the invention is to provide ' _a more even distribution “wheat on the grid and sheet metal resistance grids of relatively thin 1s C00] on the ends of the grid during use' allow' gauge and electrical resistance devices compris- .ing the support to remain C001 and thus retard' 45 y ing the carbonization of the mica tubing. Fur- 45 “11g Íhe sam‘â Wliltîenë ghe gridsf may ibe verá thermore, the 4connecting terminals will therefore Íh‘îls; ì?îsìïêm wovgälèatî‘âëegrobu‘ïgfë nguë‘ràf remain cool and the possibility of destroying insu th 50 id g . ' g e gr S- ’ lation on wires connected to the terminals is reduced. The devices made in accordance with Another object is to provide electrical resist ance deViCeS‘COmpriSing grids the afOI‘eStated the present invention also have specific advan- 50 tages over cast grid resistors in that they are characteristics ilhäi I‘eqilire -a minimum -Of SUD- non-breakable and will withstand high overloads porting meteriel'end Which ere easily end rapidly _without warpirig or drooping o_f the grids whereas assembled and which, in general, provide an 55 ideally eiiicient resistance device of compact form, many cast-grid resistor grids droop when hot so that the loops of the grids will touch each other. 55 2 2,128,222 In addition to this the resistance banks of the present invention will require a lesser amount of space than required for a cast grid resistor of equal resistance and carrying capacity because of the thin cross section of the grid which allows a higher ratio ofY airspace to space .taken up by grids. In addition to this the entire struc ture is lighter in weight for equal carrying capac ity and resistance. Furthermore, the present de vice offers a lower thermal coefficient of resist ance. The device furthermore has advantages over ribbon type resistors in that no porcelain need be used so that the resistor may be heated and drenched with water without danger of dam age. Furthermore, the number of supporting bolts is less and of those used a portion can be arranged for floating mounting so as to allow for ings I1 and the irregular openings I9. With each stroke leaving the forward profile of the grid with tongues shaped like opening I4 on the sheet and. on the next succeeding operation of the die, cutting a similar outline which severs the said tongues. The shape of the grid thus formed is, as before indicated, not only productive of a maximum number of grids with a minimum amount of waste from a given quantity of sheet material, but it 10 also affords the utilitarian features of a substan tially even distribution of the heat over the major area of the grid and a comparatively low tempera ture at the terminal lugs thereof. It will be fur ther noted that there is for all practical purposes 16 uniformity of cross section of resistance metal in the circuitously shaped strip between the end lugs. expansion. The type of terminal necessary may` The relatively close proximity of the sections il be such as can be firmly attached but easily of a given loop is compensated by the fact that around all sides and ends of the said sections Il moved when desired. The individual grid of the invention indicated there is an enlarged Ventilating area communi eating with the outside atmosphere and tending generally by the reference numeral i0 is an in tegral stamping from suitable electrical sheet steel to effect relatively uniform distribution and dissi having a pair of end lugs ii with perforations I2 pation of heat. It has been found that in use this uniform heating and efficient ventilation pre therein connected by a dat strip forming a cir cludes warping of the grids when carrying rated cuitous path and comprising a succession of op positely extending open ended loops connected in current and that when the current is increased to a series between said lugs. The shape of the bring the grids to a white heat, there is but a loops is such that a pair of closely spaced sections slight amount of warping which is not sufficient II which are of uniform cross section and size and having a narrow space I4 between, are con nected together at a common end Il and each of these sections i3 in turn connects at its remaining end with an angular-ly divergent portion i6. The portions i6 in turn connect the sections I3 of the next adjacent oppcsitely extending loops or with the perforate end lugs Il. Thus it will be noted that the narrow opening Il between the sections I3 of each loop communicates with a wider open? ing I1 which is bounded by sections i3 on adjacent oppositely extending loops and the intervening portions Il. It will further be noted from a fur ther inspection of Fig. 1 that each of the larger openings Il is occasioned by the cutting out of the loops of a preceding or succeeding grid. Hence, the amount of scrap or waste stock occasioned by the production of these grids according to the present invention is very small. and in practice represents a seventy-?ve per cent saving‘of scrap 50 metal over heretofore known methods‘of forming stamped sheet metal resistance grids. This fac tor of saving is deemed important because the nature of electrical sheet steel is such as to render the value of its scrap very low as compared with 'l Si its initial cost because this type of metal does not have a wide field of utility for other purposes. Furthermore, a greater number of grids can be stamped from a given piece of metal than by heretofore known methods. The method of forming these grids consists in feeding a steel sheet or strip i8 endwise beneath a punch and die, the sheet Il in Fig. 1 being in dicated in full lines and exclusive of the com pleted grid shown in position prior to the next operation of the die, the position of which is shown in dotted lines. Thus a complete grid is struck from the sheet at each operation of the die and the outline of half of the succeeding grid is cut from the sheet in the same operation. This affords a very rapid and inexpensive fabrication of the metal into grids with a minimum of scrap which will be readily apparent from an inspec tion of Fig. 1. The method of forming the grids may be stated to be constituted by the steps of successively stamping out the point shaped open to cause even the more closely spaced grids to touch at any point. Furthermore, when the grids are allowed to cool. they return to practically original position. The warping just referred to obtained only under extreme conditions and under conditions wherein both of the lugs Il were rigidly fixed. As will be hereinafter de scribed in greater detail, it is possible to eliminate observable warping by mounting the lugs of a bank of grids on a fixed through bolt at one end and on a floating through bolt at the other end so that when the grids are excessively overheated, e. g., to a white heat, the grids are allowed to expand so that the distance between the fixed and floating bolts would increase slightly but sutil ciently to accommodate the elongation due to 45 expansion. The grids of the invention adapt themselves to the mounting in banks as illustrated in Fig. 2 or in a connected series of- banks as suggested in Fig. 5. They are further adapted to mounting in double banks as suggested in Fig. 4 and in the latter embodiment when the grid thickness is #18 gauge or thinner and the grid spacings are very small, it has been found desirable to use the center bolts and spacers illustrated in Fig. 4 in order to preclude warping and possible touching of the rigidly secured grids under continued over load heating. The device of Fig. 2 may have a center bolt and spacers applied thereto if the grids are thin and are closely spaced. It is well understood in the art that resistors of various types, for example, such as illustrated herein, are adapted for use upon electric loco~ motives such as mine locomotives, in mills. and in various environments. and that in the design and construction of the various devices and apparatus employing these various resistors. it frequently happens that the design or lay out has been made with compactness as an important object and that no particular provision has been made for the exact location of the necessary resistors. For all such conditions. it is particu larly desirable and useful to have a fully efficient resistor as small and compact as possible so as to permit the installation of the resistors if need 3 2,128,222 be in restricted remaining. space or spaces. In It will have been noted from the foregoing that the following detailed description, the resistors ' the shape of the stamped grids of electrical sheet will be considered only from the viewpoint of metal has been designed to afford a relatively the necessary end supports for the through bolts uniform heating of the grids throughout the area which carry the grids and these latter elements. thereof so that by the use of floating bolt sup Referring now to Figs. 2 and 3 a resistor of ports it is possible to simply and inexpensively construct resistors with only two supports for the present invention employing the grids here -tofore described, comprises essentially suitable the bank in cases where the grid spaciny is three end supports or frames 20 and 2l. One of these eighths of an inch (%") or more and the gauge of the grids is of #18 or thicker. When it is de 10 end frames such as 20 has a pair of elongated supporting bolts 22 inserted through it and upon sired to use closer spacings'and thinner grids these bolts are mounted insulating tubes 2l of than the foregoing, it is possible to use a center bolt with spacer washers entered through one of mica or the like. A suitable number of insu lating washers or spacing collars 24 are then the spaces I1 between the loops oi' the grid. This 15 placed over the tube and in abutment with the would be provided essentially as a matter of safety against extreme and continued overheat inner face of wall 20 to establish the spacing be tween said wall and the first grid lli, a terminal ing due to difllculties in the electrical system or lug 25 which may constitute a mere perforated the load. The use of additional supports inter conductor plate contacting the ilrst grid and mediate the ends of the grids and the necessary 20 suitably arranged for connection with a ter? spacing washers effects some restriction of the escape of heat although not to the degree en minal 26 of a lead wire 21 being mounted in posi countered in resistors now on the market and -tion at this point. Thereafter, successive wash ers orl groups of washers or spacing collars 24 ‘ of metal and of insulation are added to the stack 25 and the additional grids ill mounted as shown by passing the insulated supporting rods through the perforations in the terminal lugs Il of the grids to attain the requisite spacing and the elec trical connection betweengrids as is well known 30 in this art. The necessary additional terminal vlugs are placed at desired intervals to secure the desired different resistances for the Several taps and the entire stack is finally bound as a rigid unit in this case by drawing the remaining end 35 frame 2| tightly upon the stack by means of nuts 28 on the threaded ends _of the bolts. This par ticular form of mounting may be -used when the grids are stamped from relatively heavylgauge sheet metal, e. g., thicker than #18 gauge, and 40 with relatively wide spacing. A structure so ar ranged may,- when overloaded to a degree that brings the grids to a white heat, show some slight warping of the grids while at that heat but this has been found insuilicient to cause the grids to touch and short circuit and it has been found furthermore that upon cooling, the grids will re in which a multiplicity of supports are utilized. As shown in Fig. 4 it is possible to assemble resistors employing double interleaved banks of 25 grids wherein the composite bank will have the same resistance per unit of length as a single bank of similar grids at half the spacing of either the top or bottom section. Under some conditions such a double bank may be found ad-` 30 vantageous even though, by reason of the fact that the air temperature will reach its permitted maximum before the grids have reached their maximum permitted temperature, the carrying capacity value is somewhat reduced. This is 35 apparently due to the restriction of air ilow caused by the use of additional center supports 220. A_s shown somewhat diagrammaticallyin Fig’. 5 a plurality of banks maybe arranged by suspending the first bank of grids froma rigidly mounted bolt 22 iixed between the elongated end frames 33, which frames are provided with elon gated lslots 34 at necessary intervals to receive the remaining bolts 22. In such 'installation the intermediate bolts 2_2 would have adjacent sides 45 of adjacent grid banks mounted thereon so that turn to substantially their original shape. It can . the entire assembly is suspended from the up be readily appreciated that the cost of resistors of this type is relatively low and that compara 50 tively little skill is required in the assembly thereof. ' ' '_ ' . It is preferred in general and not only for re sistors employing very thin gauge grids, e. g., from #1.8 gauge to #26 gauge, to rigidly fix one 55 of the bolts 22 in the end frames as speciñcally illustrated in Fig. 3 -and to provide a floating mounting of the » remaining bolt in the end frames as detailed >in Fig. 6. This construction is provided by forming an elongated slot 29 in 60 each end frame in lieu of a perforation which snugly receives the bolt and providing means whereby the stack is rigidly clamped together with the bolt 22 and a means such as a collar 3,0 65 and shoulder-forrning washers.“ which permits the rigidly clamped bolt and grid assembly to move longitudinally relative to the frame when the grids elongate slightly due to high heating. In ordinary construction the heating of a grid to a white heat will increase the distance between 70 the rigidly anchored bolt and the floating bolt support suiiiciently to take care of expansion. Any other suitable mode of providing for the free floating of one of the support bolts may be employed in lieu of the means just illustrated 75 and described. permost rigidly mounted support. One or more of these elongated banks may be of course adapt able to -assemblies which will ñt compactly into 50 long narrow confined spaces but nevertheless with very effective operation. What is claimed is: v l. As a new article of manufacture a resist ance grid comprising an integral sheet stamping having a pair of mounting lugs connected by an intermediate uniform strip forming a cir cuitous resistance path, said strip comprising a succession of parallel legged loops alternately ex tending in opposite directions from the longi 60 tudinal axis of the> grid, the loopsv on each side of said axis being spaced apart by an opening greater than the combined width of the parallel legs of the intermediate loop on the opposite side of said axis, each leg of each loop being offset lat 65 erally from every other leg of the remaining loops, and each of said legs being longitudinally aligned with one of said openings. 2. A a new article of manufacture a resist ance grid comprising` an integral sheet stamping 70 having a pair of mounting lugs connected by an intermediate uniform strip forming a circuitous resistance path, said strip comprising a succes sion of parallel sided loops alternately extending in opposite directions from the longitudinal axis 75 4 2,128,222 of the grid. the loops on each side oi said axis being spaced apart by an opening shaped like the reversed counterpart of one of said loops, the interior openings of the several loops on one side of the longitudinal center of the grid forming a continuation or the loop-spacing openings on the other side, the mounting lugs being disposed be yond the extreme loops of said grid. 3. A resistance grid o! stamped sheet electri 10 cal resistance material and comprising a pair of end mounting lugs connected by an interme diate succession of oppositely‘extending loops, integral portions disposed angularly to the adja cent legs of successive loops and connecting said adjacent legs whereby said legs are offset from one another in staggered parallel relation and form, between alternate loops, enlarged venti-~ lating openings. 4. A resistor comprising spaced end frames 20 having aligned perforations therein at one side and aligned elongated slots in the other side, a pair of suitable support bolts extending respec tively. through the said pair of perforations and the said pair of slots,-a suitably spaced stack of 25 stamped sheet metal grids having perforate lugs at opposite ends receiving the support bolts, said grids each having oppositely extending open loops in staggered relation on opposite sides of the lon gitudinal axis of the grid and enlarged ventilat 30 ing spaces on each side of each loop, means rig idly securing together the perforate lugs on one end of said stack, end frames and the support ing bolts in said perforations of the end frames and means rigidly securing the lugs on the re maining end of the stack on the remaining bolt. said bolt being adapted for movement in the slots in said end frames and permitting expan sion of the grids. > . 5. As a new article of manufacture a resistance grid of stamped sheet material comprising a pair of end lugs and a connected series of spaced loopsdisposed on opposite sides of the longitudinal axis oi the grid in staggered relation whereby enlarged openings are provided between adjacent loops on a common side of said axis, said enlarged open ings communicating with smaller interior open ings of intermediate loops on the opposite side of said axis and providing, upon electrical ener gization of the grid, increased heat dissipation re sulting in uniform heating of all of said loops. 6. A resistor comprising spaced end frames each having aligned pairs of elongated slots, support bolts each having opposite ends extend ing into slots in opposed end frames. a suit 20 ably spaced stack of stamped sheet metal grids having perforate lugs at opposite ends receiving the support bolts, said grids having oppositely extending open loops in staggered relation on op posite sides of the longitudinal axis of the grid 25 and enlarged Ventilating spaces on each side of each loop, means rigidly securing the grids to the bolts and means retaining the bolts against accl dental separation from the end frames, said bolts being adapted for movement in the slots in said 30 end frames and permitting expansion of the grids. MARVIN A. DU BOIS.