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Патент USA US2107187

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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.
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