Патент USA US2107187код для вставки
Feb. 3, 1938. c)' M. OTTE 2,107,187 METHOD OF‘ MAKING GRID RESISTQRS Filed March 20, 1935 2 Sheets-Sheet 1 Feb. 1, 1938. ETHOD OF MAKING GRID RESISTORS Filed March 2Q, 1955 __ .. 2,107,187 o. M. OTTE _ 2 Sheets-Sheet 2 Patented Feb. I, 1938 ZJQ'LES'T UNITED STATES PATENT OFFlCE 2,107,187 METHOD OF MAKING cam RESISTORS Otho M. Otte, Tarentum, Pa., assignor to Al legheny Steel Company, a corporation of Pennsylvania Application March 20, 1935, Serial No. 12,011 5 15 , 25 _ 6 Claims. (Cl. 29-—155.5) This invention relates to current limiting re current path of each of the grid resistors dis sistors, such as used for example in the starting closed for purposes of comparison. Throughout the drawings and the speci?cation, circuit of an electric motor, and more particu larly to a new and improved type of grid resistor like reference characters indicate like parts. and to a method of making the same. In many industrial plants and in mines, for UK An object of this invention is the provision of example, where electric locomotives are employed an improved grid resistor. or where electric cranes are used, it is sometimes Another object of the invention is the provi» di?icult to ?nd sufficient mounting space for the sion of a method of making grid resistors from grid resistors which will permit the grid resistors resistant strip material. to clear walls, posts or pillars and to allow the 10 passage of workers between the resistor frames A further object of the invention is the provi sion of a method of making resistor grids from and such walls, posts, or pillars. In many cases, strip material. Without scrap loss and without the available space for mounting the grid resist ors is so small that it is di?icult to accommodate causing any substantial variation in the resist the bulk of the grid resistors that is required by ance thereof at any point in its length. A still further object of the invention is the the motors with which they are used. vMany provision of a grid resistor that shall have a attempts have been made to make resistors of high space factor, whereby for a given space in such shape and form that the required resistor capacity in a given case will occupy only'a rela which gridresistors may be mounted, more re sistance per grid and per group of grids may be tively small space. In other words, the trend has been for manufacturers of grid resistors to obtained. Other objects of the invention will in part be improve the space factor, that is, the ratio of apparent, and will in part be obvious from the resistance in ohms (the proper current carrying following description taken in conjunction with capacity of the resistors being assumed) to the volume of the space occupied thereby. the accompanying drawings, in which: 25 Figure 1 is a View in front elevation of a grid As will be apparent hereinafter, resistors made resistor representing an embodiment of this in in accordance with the method of this invention will make possible an increase of from ?fty to vention; ninety percent in resistance per grid and a cor Fig. 2 is a vertical edge view of the resistor; Fig.3 is a top plan View of a strip of resistor responding increase in the space factor. That is, for a given mounting space resistor grids having material from which a resistor grid such as shown in Figs. 1 and 2 may be made in accordance with from ?fty to ninety percent more resistance per grid, but the same current carrying capacity per the method of this invention; Figs. 4, 5, and 6 are fragmentary top plan, edge, grid, may be mounted in that space. In Fig. 12 of the drawings a prior art resistor and top plan views, respectively, of a portion of grid 9 is shown which is made from a wide strip the resistor strip, showing successive steps em ployed in the development of the resistor grid of of resistance material and which has a relatively good space factor compared to the space factor Figs. 1 and 2; Figs. 7, 8, and 9 are enlarged fragmentary top of prior art grid resistors, say for example the plan, edge, and top plan views, respectively, of a portion of the resistor strip showing steps similar to those depicted by Figs. 4, 5, and 6, but modi?ed cast grid type. Resistor I is made by punching slots 2 which extend from opposite edges and transversely of the strip and in staggered rela to accommodate the method to Wider strip ma tion so as to provide a grid comprising parallel return bends or legs 3. The ends of these return bends are punched as at 4 to receive the mounting 45 bolts 5 and 6 of the support frame (not shown) on which a plurality of grids are supported and which make up the grid resistor unit. The re sistor grids are insulated from the support bolts by tubes 5' and 6' which are slipped on over the bolts. In this form of resistor unit, bolts or rods 5 are of relatively large diameter and these con stitute the main supports for the grid resistor unit. Bolts 6 which are of smaller diameter serve also to support the resistor grid unit, but their 55 terial; ' Fig. 10 is a fragmentary front view in elevation of a modi?ed form of resistor made in accordance with the method of this invention; Fig. 11 is a fragmentary view in front elevation 5 O of another form of resistor made in accordance with the method of this invention; and Fig. 12 is a fragmentary view in front elevation of a prior art resistor, the prior art resistor being disposed between Figs. 10 and 11 and having lines 55. superposed thereon showing theyaverage length of 2 2,107,187 primary function is to hold the return bends of the resistor in place. In a resistor of this type the average length of the current path is indi cated by broken line 7. In making a resistor of this type much mate rial is wasted as is apparent by inspection of Fig. 12. That is, all of the material which is punched out to form the holes through which the insu the radii of the bends. After slitting the mate-r rial this way, the ribbons l2 and 13 are deformed and overlapped as shown in Fig. 6 to reduce the major axes and the section moduli of the strip at the places where the bends. are to be made. This operation may be performed by bending one ribbon above or partially above the plane of the sheet or strip and the opposite ribbon below or partially below the plane of the strip, see Fig. 5. lated rods or bolts pass and to form the return bend loops or legs, represents Waste material. It After the material has been formed as in Fig. 5, 10 the ribbons may be gripped in a suitable die and is not uncommon in the manufacture of grid re squeezed toward the center of the strip until they overlap at the middle portions thereof and only partially overlap from the middle towards the opposite ends thereof (see Fig. 6). The major sistors such as disclosed by Fig. 12, that as much as 43 percent of the material is wasted. Grid resistors of this type are usually made from alloy material which is expensive and where so much material is wasted, the cost of producing such axes of the strips are therefore, as shown, re resistor grids is greatly affected. duced approximately ?fty percentum at these In accordance with the present invention no material is wasted so that the ratio of gross sections. Having thus completed the preliminary steps in the forming of the resistor, the next steps in the 20 formation thereof involve the edgewise bending of the strip at the points where the major axes weight of material employed to the net weight of grid produced is, for all practical purposes, equal to unity. Also, the material is more ef?~ ciently utilized so that a greater average length of current path may be realized which means have been reduced. higher resistance per grid. certain amount of elongation takes place at the outer ?bers of the bends, it is preferred to make the ?rst bend at the middle of the strip and to then work towards the ends, for by so doing the elongation will be equally distributed through 30 out the length of the strip. To make resistor grids that will ?t the frame bolts on which the resistor grid of Fig. 12 is In Fig. 1 of the drawings a resistor 8 is shown which is designed to ?t exactly the mountings of the prior art grid resistors shown in Fig. 12, and for that reason the support bolt apertures 3O or holes are shown to be in the same positions and of proportionate size (note-the resistor of Fig. 1 is drawn to larger scale than the resistor of Fig. 12). The resistor grid 8 is made from strip material having the necessary cross section required to Since a mounted, it is necessary to vary the distance be tween slits Hi and H because the vertical dis tance between the centers of the large bolts 5 is less than the vertical distance between the small carry the current which it must handle in any bolts 6, and to make the slits of the sections which are bent to the radii of the insulating tube 5' for the large bolts, longer than those which are bent to the radii of the insulating tubes 6' for 40 given case. Transverse sections of this mate rial have relatively large major axes and rela tively small minor axes, but the material is bent - edgewise, that is about its major axis, at pre determined points to form a plurality of return bends having substantially parallel legs ii, the major axes of which are in substantially the same plane. In making this resistor, the material is so manipulated that it may be bent edgewise at the places where the bends are formed, while at the same time maintaining the same current con ducting area or section throughout the full length of the resistor. The bending may be done on mandrels of the proper diameter. ' The alloys from which grid resistors are made have physical properties which make it dif?cult to edgewise bend such material when in strip form, without fracturing the same. In accordance with this invention, the major axes of the strip at the points where the bends are to be made are reduced without changing in any material way, the cross section at these points. By reducing the major axes of the ma terial at these points, the section moduli at these 60 points are reduced and therefore the maximum ?ber stresses are reduced. The maximum ?ber the small bolts. Because of the arrangement of the large and small bolts, the longer slits ID are located at the center and the opposite ends of the strip, and the shorter slits H are located between them. 45 After having slitted the strip and reduced the major axes thereof at the places where the bends are to be made, the bending of the strips to form the return bend loops is done. The first bend is made at the center of the strip about a mandrel 50 having a diameter D as indicated in Fig. 1; the sections on each side of the middle are bent about mandrels having a diameter DI as indicated in Fig. l; and the ends of the strip are bent about a mandrel or mandrels having a diameter D. The bends on each side of the middle of the re sistor strip are made progressively from the middle to the outer ends thereof, so that the elongation above mentioned will be equally dis tributed between the two halves of the resistor 60 grid. stresses can be more or less limited to values far A resistor such as shown in Fig. 1, having the below the ultimate strength of the material by maintaining the proper relation between the radii of the bends and the major axes of the material at these bends. In a preferred form of this invention, the major axes of the material are reduced at the same dimensions X and Y as the resistor of Fig. 12, has a current carrying section at any point points of bending by ?rst slitting the strip lon by broken line H‘: and he average or mean length 70 gitudinally at spaced points or sections as at I0 and H, thereby forming narrow ribbons l2 and I3 on each side of the slits. The distance be tween slits and the length of these slits are de termined by the length of the return bend loops, 75 or the distance between the mounting rods and along its length which is uniform and for all practical purposes equal, but has a longer mean or average current path. The average or mean length of current path of resistor 8 is indicated of path of resistor I (Fig. 12) is indicated by 70 broken line I'B. A visual comparison of these paths shows that the resistors of Fig. 1 has about 48.25 percent longer path than the resistor of Fig. 12 and therefore, it has about 48.25 percent more resistance than the resistor of Fig. 12, but 75 2,107,187 3 both occupy the same amount of space.‘ It is will depend largely upon 'the Width of the strip therefore apparent that a resistor grid such as shown in Fig. l and having the same resistance as the resistor in Fig. 12 will occupy less space than the latter, and that therefore, the former and on the radii of the bends. has the higher space factor. ’ By utilizing more insulated supporting bolts, By comparing the'grid resistors disclosed as embodying'this invention to the grid resistor of Fig. 12, it will appear that the latter has more heat dissipating surface in the regions of the sup port bolts or rods. However, if this is a de support bolts 23 and 24 are grouped in parallel ?ciency in the former, the rate of heat dissipa tion of the resistors of this invention may be adequately increased at the bends by mounting 10 large washers for example on the support bolts on either or both sides of the grid but in contact therewith, in which‘cas'e insulation would be placed between adjacent washers for reasons well 15 understood by those skilled in this art. Although a convenient procedure has been dis closed whereby the section moduli with respect vertically spaced planes, with the larger bolts 24 to the major axes of the material may be re of the same or different diameter, resistor grids may be made in accordance with this invention 10 that will have the same overall dimensions X and Y with about 91 percent more resistance. Such a resistor is shown in Fig. 11 and is numbered l'l. This resistor has three relatively long legs l3, l9, and 29, the middle leg it! being double, and 15 two relatively short double legs 2i and 22 in terposed between the longer legs. The insulated at the four corners of the resistor grid. The bends 20 in this resistor are made in accordance with the duced to the amount required for bending edge wise to a given radius, it will be apparent that 20 procedure described in connection with Figs. 1 to 6, inclusive, except that the end bends are the section moduli may be reduced in other ways without changing the current conducting sec tion of the strip or without departing from the spirit or scope of the invention. In some cases it may be necessary to stretch 25 the grid resistors made in accordance with this turned “in” instead of “out” as in Fig. 1 in order to keep all parts of the resistor within the bound 25 ary of dimensions X and Y. The increase in resistance which a resistor such as indicated in Fig. 11 aiiords over the resistor of Fig. 12 is readily apparent by comparison of lengths of the mean current paths thereof, broken 30 line 25 indicating the mean current path of re sistor of Fig. 11, and broken line ‘i indicating the mean current path of the resistor of Fig. 12. By increasing one of the overall dimensions of the space occupied by the resistor of Fig. 12, say 35 dimension X, the number of full length loops of a resistor made in accordance with this inven tion may be increased and with a corresponding increase in resistance per grid, and all this with out materially increasing the overall dimensions thereof. Fig. 10 shows a resistor 26 of this type, its dimension X, for example, being shown as be ing approximately twenty percent greater than the same dimension of the resistor of Fig. 12, but its dimensions Y is the same. The resistance 45 of the grid of Fig, 11 however is approximately invention, in a direction lengthwise of the loop legs in order to accurately size the grids and make them fit the frame bolts. While several forms of the invention have been shown, each having the same-with the exception of resistor grid 26—over all dimensions as the prior art resistor of Fig. 12, it is to be under stood that the relative dimensions and propor tions have been given merely for the purpose of 35 accentuating the advantages of and the results that may be gained from this invention. What I claim as new and desire to secure by Letters Patent is: 1. Method of making resistor grids of the re turn bend loop type from strip material which consists in slitting the strip lengthwise at pre determined points in the length thereof to form narrow ribbon portions, deforming strip at the slitted portions so as to cause the ribbon portions 101 percent higher than that of the grid of Fig. 12. This increase is shown by the relative lengths ing the strip edgewise at the overlapped portions of the average or mean current paths 2? and 1, so as to form the return bend loops of the grid. respectively, of these two resistors. In order that a ready comparison in regard to 50 the values of resistance per grid, may be made between the resistor grids of Figs. 1, 2, 10, and 11, and the grid of Fig. 12, the lengths of average 2. The method of making resistor grids of the character described, from strip material which consists in subdividing lengthwise spaced sec or mean current paths of these resistors are su perimposed on Fig. 12 and identi?ed in accord ance with the legends thereto appended. The method of producing resistors as depicted by Figs. 3, 4, 5, and 6 applies more particularly to the making of resistor grids from relatively 60 narrow strip material, but where wider strip material is used, the method may be modi?ed in accordance with the procedure depicted by Figs. 7, 8, and 9. The strip material shown in Fig. '7 is approximately one-half wider than the strip 65 shown in Fig. 3 and in order to reduce its section moduli about the major axes thereof, at the points where the bends are to be made, the strip is slit longitudinally, say twice at each section, thereby dividing the strip into three narrow ribbons, 70 which, when superimposed one on the other as indicated, the strip may be bent edgewise to a relatively sharp radius without rupturing the material at the points where the maximum ?ber stresses occur. Thus, it is apparent that the 75 number of slits which are made in the material on opposite sides of the slit to overlap, and bend tions of the strip into ribbons which are unitary at their ends with the strip, displacing the rib bons transversely of the strip to at least par tially overlap the same, and then bending the 55 strip edgewise at said ribboned sections to form the return bends of the resistor grid. 3. The method of making resistor grids, of the character described, from strip material which consists in subdividing lengthwise spaced sections of the strip into ribbons of substantially equal width which are unitary at their ends with the strip, displacing the ribbons transversely of the strip to at least partially overlap the same, and then bending the strip edgewise at said ribboned 65 sections to form the return bonds of the re sistor grid. 4. A method of making a resistor grid having a substantially constant resistance throughout its length which comprises reducing the Width of a 70 strip of suitable material at spaced points along its length without reducing the current conduct ing section of the strip material at such points and bending the strip edgewise at such spaced points to form the return bend loops of the grid. 75 4 Lil 2,107,187 5. A method of making a resistor‘ grid having a substantially constant resistance throughout a substantially constant resistance throughout its length without the production of scrap which comprises subjecting a strip of suitable material its length which comprises reducing the width of to such operations as will cause partial over lapping of the material of the strip at spaced points thereof Without removing material and Without reducing the current conducting section of the strip material at such points and bending the strip edgewise at such overlapping points in such manner as to form the return bend loops of the grid. 6. A method of making a resistor grid having a suitable ?at strip of resistance material and proportionately increasing the thickness thereof at spaced points along the strip, thereby main taining the current conducting section of the strip uniform, edgebending the strip at the points of reduced Width and increased thickness in such manner as to distribute equally any elongation re sulting from such bending and then adjusting 10 the loops to size. OTHO M. OTTE.