US3299388A

US3299388A - Electric resistance unit

Info

Publication number: US3299388A
Application number: US436978A
Authority: US
Inventors: Oswald M Bundy
Original assignee: AO Smith Corp
Current assignee: Commander Electrical Equipment Inc; AO Smith Corp
Priority date: 1965-01-27
Filing date: 1965-01-27
Publication date: 1967-01-17
Anticipated expiration: 1984-01-17

Description

3 7 1-967 0. M. BUNDY 2 I v ELECTRIC RESISTANCE UNIT Original Filed April 14, 1961 v 3 Sheets-Sheet l I INVENTOR. OSWALD M. BUNDY BYW ATTORNEY,

in, 173-961). QMBUNDY [3,299, 8

v I I ELECTRIC RESISTANCE mm o i mal Filed April 14, 1961 3 Sheets-Sheet 2 INVENTOR.

OSWALD M. BUNDY m ATTORNEY "Jan. 1.7, 1967 1 o. BUNDY 3,299,388

ELECTRIC RESISTANCE UNIT Ori ginal Filed Aiaril 14, 1961 5 Sheets-Sheet 3 Fig. 3

INVENTOR. OSWALD M. auuov ATTORNEY Unite States Patent fire 3,299,388 ELECTRIC RESISTANCE UNIT Oswald M. Bandy, Cleveland, Ohio, assignor, by mesne assignments, to A. 0. Smith Corporation, Milwaukee, Wis, a corporation of New York Continuation of application Ser. No. 103,067, Apr. 14, 1961. This application Jan. 27, 1965, Ser. No. 436,978

6 Claims. (Cl. 338-284) This invention relates to electrical resistance units of the grid type that are stamped from a sheet of resistance material and more particularly to an improved grid design whereby all of the resistor grids in a resistor bank are made from a continuous single sheet of resistance material. This application is a continuation of applicants copending application entitled Electric Resistance Unit, Serial No. 103,067 which was filed on April 14, 1961, now abandoned.

Heretofore, resistors of the grid type were individually stamped from a sheet of resistance material. The resis tor banks were constructed by utilizing individual grid units and tightly clamping them together at their alternate ends between end frames, in a parallel spaced relationship, by means of suitable insulated bolts. The insulated bolts were passed through suitable mounting means located at or near the opposite ends of the individual grid units. This connected the individual grid units in a series electrical relationship. The electrical connection between two adjacent independent grids was at the ends that were held together by the pressure exerted on them due to nuts threaded onto the ends of the insulated bolts.

One variation from this was to have a metal collar or spacer mounted on the insulated bolt between the two grids so the pressure exerted by the nuts would hold the grids tightly against the opposite ends of the collar. Current would flow from one grid directly to the other if the first method was used, or from one grid through the collar to the other grid if the second method was used.

It is readily seen that trouble would occur whenever one of the connections became loose due to any of a number of reasons.

An improvement over this method was to provide the grids with offset end portions so when they were mounted on the insulated bolts, the offset portion of the adjacent grids would extend towards each other. The ofiset portions of the adjacent grid would then be welded together. While the welding did eliminate the burning at the ends of the grids due to loose connections and the need for periodically tightening the clamping nuts, it was found that the welding itself created additional problems.

Very often the weld between the resistor grids would be faulty, whereby the resistance of the electrical connection of the two grids would be so great to cause the area to become extremely hot during normal use of the resistor. This greatly increased the likelihood of a burnout. Also, resistors of this type are often used in locations where there are many vibrations and jars due to the surrounding operating equipment. If the weld between the adjacent grid units was not strong, it would be caused to separate partially or entirely. If the weld separated only partially, the area would then become one of increased resistance and cause the excessive heating and the probability of a resultant burnout. At times, the welding set up stresses in the material causing excessive heating at spots and which would result in burnout of the material.

Therefore, it is the principal object of my invention to provide a resistor grid which eliminates all of the aforementioned diificulties and faults.

It is anotherobject of my invention to provide a resistor grid which eliminates all of the electrical connections between the grids which form the current path.

Another object of my invention is to provide a resistor which may be readily assembled and inexpensively manufactured.

Still another object of my invention is to provide resistor units in which the heating is reduced to a minimum.

Another object of my invention is to provide a plurality of terminal means so the resistance of the bank may be picked ofl? in small increments.

It is still a further object of my invention to provide terminal means which are an integral part of the grids themselves thereby eliminating the need of separate terminals and the method of mounting them.

The resistor grids of this invention are stamped from sheets of resistance material. The grids themselves are long and narrow having a plurality of slits therein alternately extending through opposite edges of the grid to provide a current path of substantially the same cross section. The grids remain connected to each other by a bridging portion of the sheet, alternately at opposite ends to the grid next adjacent. This is so a continuous current path is formed through all of the grids and the bridging portions stamped from the sheet of resistance material. The bridging portion connecting the grids is of at least the same cross section as the current path in the grid itself.

The bridging portion connecting the grids together at one of their ends is the terminal portion and is bent, in effect, to bend to grids back upon themselves. The other bridging portion is left straight so the grids, when mounted, will form a plane alternately above and below each other.

With one of the bridging portions serving as a terminal, a plurality of terminals are provided. Also, since the terminal is an integral part of the grid, there is no need for a separate terminal or means of mounting it, or to insure a good electrical connection exists between the terminal and the grid.

When the grids are stamped to form the described grid configuration, suitable holes are punched in the material to provide means for the insulating mounting means and for connection to the terminal.

After being bent, the grids are made into banks by passing the insulating mounting means or bolts through the respective holes punched in the grids for the mounting of the resistors. Metallic collars or spacers are placed between the resistor grids and over the insulating bolts to keep the grids physically spaced from each other. Nonconducting spacers may be used, if desired. An insulating washer is placed between one end of the metallic collars and one of the adjacent grids to prevent an electrical connection by this means between the adjacent grids.

Other objects and advantages of my invention will become apparent to those skilled in the art when the following disclosure is read in light of the accompanying drawings in which:

FIGURE 1 is a view of the grid configuration stamped in the flat metal sheet;

FIGURE 2 is an exploded view of the grids after hav- With reference to FIGURE 1, individual grid units are shown generally at A, B, C, D and E.

A sheet of resistance material is stamped to provide a single current path at the left side of grid unit A, which also serves as a terminal 10, and ends at the other end of grid E.

The grid unit A is separated from grid unit B by cuts made along lines 11.

Slits

12A and 12G are stamped alternately into grid A from opposite edges to form the current path throughout its length and terminates in a bridging portion 13. Terminal has a square aperture 14 and a round hole 15 punched therein. Bridging portion 13 has a hole 16 punched therein.

As mentioned, grid B is separated from grid A by cuts 11 and grid B is likewise separated from grid C by cuts 17. Grid B has slits 18A to 186 stamped alternately in opposite edges to form the current path and terminates into a bridging or terminal portion 19.

Terminal 19 has

square apertures

21B and 21C and a round hole 22 punched therein. Terminal 19 is separated from terminal 10 by slit which connects by a portion of cut 11 to slit 12A.

Terminal 19 connects to grid unit C which is separated from grid unit B by cuts 17 and grid unit D by cuts 23. Grid unit C has the alternate slits 24A to 24G stamped in opposite edges to form the current path which terminates into bridging portion 25.

Bridging portion 25 is separated from bridging portion 13 by a cut 26 which connects to slit 18A. Bridging portion 25 has a hole 27 therein.

Bridging portion 25 forms the current carrying path from grid unit C to grid unit D, which is separated from grid unit E by cuts 28. Grid unit D has the series of alternate slits 29A to 29G stamped into the opposite edges to form the current path which terminates into bridging or terminal portion 30.

Terminal 30 is separated from terminal 19 by a slit 31 which connects by a portion of cut 23which connects to slit 24A.

Terminal 30 has two square apertures 32D and 32B and a round hole 33 stamped therein.

Terminal 30 is connected to grid E, which is separated from the next succeeding grid (not shown) by cuts 34. Grid E has the alternate slits 35A to 35G stamped into opposite edges to form the current path and terminates to a bridging portion 36.

Bridging portion 36 is separated from end portion 3 by a cut 37 which connects to slit 29A. Bridging portion 36 has a hole 38 in it.

The current paths of the individual grids are formed by the stamping out of the alternate slits to form the longest possible current path from a minimum of overall grid length and still maintain a uniform cross section throughout the entire current path.

A triangular shaped aperture 48 is stamped in grid C and connected to slit 18G to facilitate bending.

A triangular shaped aperture 49 is stamped in grid E and connected to slit 29G to facilitate bending.

FIGURE 2 illustrates and shows the resistor section after the bending has taken place. It is seen that the terminal portions are bent back on themselves so the two connected grids end up in the same plane. The bridging portions at the other end of the grid are left straight thereby placing the two connected grids in different planes.

The terminal portions are alternately bent in the opposite direction so that the grids will be placed in two horizontal planes, one above the other. It also makes

holes

16, 27 and 38 line up with each other and-

holes

15, 22 and 33 line up with themselves, see FIGURE 5.

These units can now be assembled in a zigzag manner into a bank (see FIGURE 3) by placing a bolt 39 with an insulating sleeve 40 thereon, through

holes

15, 22 and 33 in the terminals. Likewise, a second bolt 41 having an insulating sleeve 42 thereon, is inserted through

holes

16, 27 and 38 in the bridging portion. While the

bolts

39 and 41 are being slid through their respective holes, large spacers, preferably metallic, are slipped over the insulating sleeve 40. These spacers 43 are placed between the respective grids to maintain their separation in the desired zigzag manner. If spacers 43 are made of metal, they serve to aid the dissipation of heat from the resistor, and require insulating washers 44 between one grid and a spacer to prevent the short circuiting of the current path.

The

bolts

39 and 41 are fastened at their opposite ends to

side plates

45 and 46 by means of nuts 47. Spacers 43 are positioned between the grid units and the

end plates

45 and 46. Insulating washers 44 are placed between spacers 43 and the

side plates

45 and 46.

When assembled, the grids form two horizontal planes as it is shown by FIGURES 4 and 5, one above and one below the plane formed by the insulating'mounting means or

bolts

39 and 41.

In operation, a wire is connected to terminal 10 and current flows through the current carrying path of grid A, up bridging portion 13 and back through current carrying portion of grid B. Terminal 19 presents a point at which a second wire may be connected and the current taken off, see FIGURE 5. However, if this is not desired and since grid C is directly connected to grid B, the current will flow through the current carrying path of grid C, down bridging portion 25 to grid D and back through the current carrying path of grid D to terminal 30. Here is another terminal or point where the second wire can be connected by a wire if desired. If not, the current can go through the current carrying path of the next two grids in the same manner as described for grids C and D, see FIGURE 4.

Thus, it is seen that by utilizing a grid of this construction, the bank has a terminal available every time the current path reaches the front portion of the bank.

Further, it is seen a continuous unbroken current conducting path is available through the entire bank. By this means, all of the troubles and faults encountered with the pressure type resistor construction and the welded tab type construction have been completely eliminated. Thereby, any possibilities of hot spots throughout the resistor and its terminals have been completely eliminated.

Also, by this design, it is seen that the current carrying path for each grid unit is at its optimum for its overall length. This allows the resistor to have a higher resistance for a given length.

Further, it is seen that the grids zigzag back and forth between the two mounting bolts such that in a vertical direction one grid does not cover the other. This allows for the maximum convection of heat away from the grids, thereby allowing them to have a higher current carrying capacity.

An even greater advantage is that the terminal is an integral part of the grid, thereby eliminating the need for a separate terminal, means for mounting or securing it to the bank, and making positive the electrical connection between the terminal and the grid. Further, the

terminal provided by this design utilizes only a minimum of space and eliminates the necessity of taking the grid assembly apart to change the location of the terminal when a new value of resistance is required.

Although I have described my invention with a certain degree of particularity, it is understood that the above disclosure has been made only by way of example, as is required by law, and that many changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of my invention as hereinafter claimed.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which is regarded as the invention.

I claim:

1. A resistance grid assembly comprising a pair of spaced insulated support members, a plurality of platelike grids formed of a sing-1e piece of fiat metal to provide a continuous current path throughout the grid assembly, said grids being connected to one end bya terminal portion formed by bending the grids to different planes so the grids extend in a zigzag manner between the support members, every other grid having an integral mounting projection forming a part of the corresponding grid terminal portion and secured to the adjacent support member in spaced relation to a contact connecting portion of the terminal portion.

2. A resistance grid assembly comprising a pair of spaced frame members connected by spaced apart insulated support means; a plurality of grids connected at one end to an adjacent grid by an integral end terminal portion which is bent back on itself and connected at the other end to the other adjacent grid by a bridging portion, said terminal portion having a wire connecting opening therein, and said grids being made from a single continuous piece of resistance material to provide a continuous current path throughout the grid assembly with the current transfer from the one grid to the other at the terminal portion, each grid having a plurality of slits therein alternately extending through opposite edges of the respective grids to define a current path through the grid; said grids being connected to one insulated support means spaced inwardly of the wire connecting opening in the terminal portion and the bridging portion connected to the other insulated support means so the grids extend in a zigzag manner between the support means with pairs of the grids on opposite sides of the plane of the support means.

3. A multipler resistor grid comprising a single piece of resistor material cut and formed into a plurality of interconnected similar grids disposed in a pair of parallel planes, the grids in one plane being joined to each other at one end by simliarly folded bridging portions and the grids in the second plane being joined to each other at the corresponding one end by similarly and opposite folded bridging portions, said folded bridging portions being provided with integral terminal means, alternate grids in each plane having mounting tabs spaced from the terminal means in overlapping relationship and having aligned integral mounting means, and the opposite ends of the grids being connected by bridging sections having similar mounting means in alignment with each other.

4. A multiple resistor grid comprising a single piece of resistor material cut and formed into a plurality of interconnected similar fiat grids disposed edgeways in a pair of parallel planes, the grids in one plane being joined to each other at one end by similarly folded bridging portions and the grids in the second plane being joined to each other at the corresponding one end by similarly folded bridging portions, said folded bridging portions in said two planes being oppositely folded and being provided with terminal openings, alternate grids in each plane having mounting tabs projecting toward the opposite plane and having a mounting opening aligned with the other mounting openings, the grids between said alternate grids having cut away portions aligned with said tabs to allow unobstructed communication between said mounting openings, and the opposite ends of the grids being connected by planar bridging sections having mounting openings in alignment with each other.

5. In a thin planar rectangular blank having a substantially greater longitudinal length than width, said blank being of a metallic resistor material, a plurality of equally spaced parallel zigzag cuts extending laterally between the side edges and terminating in spaced relation to said edges, and defining a terminal and mounting portion to one side and a mounting portion to the opposite side of the zigzag cuts, each out being formed of similar rectilinear portions, mounting openings formed in said mounting portion in alignment with alternate zigzag cuts, transverse separation slots in the mounting portion in alignment with alternate zigzag cuts between said mounting openings and extending from the adjacent side edge to the end of the adjacent zigzag out, said terminal and mounting portion having second mounting openings in alignment with the mounting openings in said mounting portion in spaced relation to the adjacent end of the corresponding zigzag cut and to the side edge of the blank, transverse separation slots in the terminal and mounting portion extending from the ends of the zigzag cuts outwardly to the blank edge in alignment with the alternate zigzag cuts aligned with the first and second mounting openings, terminal openings similarly spaced to opposite sides of said last-named separation slots whereby said blank may be folded longitudinally in aocordian fashion on the lateral line including said first-named separation slots with the mounting openings and terminal openings in the terminal and mounting portion being aligned and the mounting openings in the mounting portion being aligned and said folded blank can be sepread to separate the adjacent grids.

6. In a thin planar rectangular blank having a substantially greater longitudinal length than width, said blank being of a metallic resistor material, a plurality of equally spaced parallel zigzag cuts extending laterally between the side edges and terminating in spaced relation to said edges and defining a terminal and mounting portion to one side and a mounting portion to the opposite side of the zigzag cuts, each out being formed of similar rectilinear portions, slits formed at each junction of said rectilinear cuts and at the end of each zigzag cut, said slits extending longitudinally alternately in opposite directions from the zigzag cut, transverse slots in the mounting portion in alignment with the zigzag cuts between said mounting openings and extending from the adjacent side to the end of the adjacent zigzag cut, second mounting openings formed in said terminal and mounting portion in alignment with the mounting openings in said mounting portion and in spaced relation to the adjacent end of the corresponding zigzag cut and to the side edge of the blank, a lateral slot in the terminal and mounting portion extending outwardly to the blank edge from adjacent said second mounting openings, a cut from said lateral slot about the second mounting opening to the adjacent zigzag cut, and terminal openings similarly spaced to opposite sides of said last-named slots whereby said blank may be folded longitudinally in aocordian fashion on the lateral line including said transverse slots with the mounting openings in the terminal and mounting portion aligned and the mounting openings in the mounting portion aligned and with the terminal openings aligned.

References Cited by the Examiner UNITED STATES PATENTS 1,719,179 7/1929 Haydon 338284 1,861,434 6/1932 Campbell 338387 1,962,673 6/1934 Wilms 338-291 X 2,769,885 11/1956 Charbonneau 338287 2,969,516 1/1961 Du Bois 338284 ANTHONY BARTIS, Primary Examiner. RICHARD M. WOOD, Examiner. V. Y. MAYEWSKY, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 299 ,388 January 17 1967 Oswald M. Bundy It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 27, for "to grids" read the grids column 4, line 74, for "to" read at column 5, line 27, for "multipler" read multiple column 6, line 22, for "sepread" read spread Signed and sealed this 14th day of November 1967.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. A RESISTANCE GRID ASSEMBLY COMPRISING A PAIR OF SPACED INSULATED SUPPORT MEMBERS, A PLURALITY OF PLATELIKE GRIDS FORMED OF A SINGLE PIECE OF FLAT METAL TO PROVIDE A CONTINUOUS CURRENT PATH THROUGHOUT THE GRID ASSEMBLY, SAID GRIDS BEING CONNECTED TO ONE END BY A TERMINAL PORTION FORMED BY BENDING THE GRIDS TO DIFFERENT PLANES SO THE GRIDS EXTEND IN A ZIGZAG MANNER BETWEEN THE SUPPORT MEMBERS, EVERY OTHER GRID HAVING AN INTEGRAL MOUNTING PROJECTION FORMING A PART OF THE CORRESPONDING GRID TERMINAL PORTION AND SECURED TO THE ADJACENT SUPPORT MEMBER IN SPACED RELATION TO A CONTACT CONNECTING PORTION OF THE TERMINAL PORTION.