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Патент USA US2128222

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Aug. 30, 1938.
M. A. DU Bols
2,128,222
RESISTANCE GRID
F'iìled Dec. 2, 1935
2/20
2 Sheets-Sheet l
£20
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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.
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