US2870308A - Resistance grids - Google Patents

Description

Jan. 20, 1959 L. SATCHWELL RESISTANCE GRIDS 3 Sheets-Sheet 1 Filed May 25, 1956 Inventor LEONARD SATCHWELL Attorneys 3 Sheets-Sheet 2 L. SATCHWELL' RESISTANCE GRIDS a G mm m H m fmfiifi m 1L1; i: L m m g? w k H I" m l 2 1 I M WW6 1 s I a Jan. 20, 1959 Filed May 23, 1956 Inventor LEONARD SATCHWELL by Attorneys Jan. 20, 1959 L. SATCHWELL 2,870,308

RESISTANCE GRIDS Filed May 23, 1956 3 Sheets-Sheet 3 Inventor LEONARD SATGHWELL b 4%,Mm

Attorneys United States Patent RESISTANCE GRIDS Leonard Satchwell, Theule-sur-Mer, France Application May 23, 1956, Serial No. 586,836

Claims priority, application Great Britain May 24, 1955 Claims. (Cl. 201-69) This invention relates to grid resistances and more particularly to electric resistance grids formed of plates which may be plain or may be slit or slotted to provide a zigzag path for the current, the grids being supported by insulating members imparting rigidity to the grids and preventing the possibility of assembled grids touching one another.

To a considerable extent the design and arrangement of banks of such resistance grids are controlled by the heating to which the insulating supports are subjected by the current flowing in the grids. An object of the present invention is to provide an improved construction in which substantially no part of the grid carrying electric current is enclosed by the insulating supports. A further object is to provide a grid structure, which, while firmly held is free to expand due to rise in temperature.

' A still further object of the invention is to provide an improved grid construction permitting economies in the cost of supports, thereby allowing the use of better resistance grid material in the interest of the known technical requirements both physical and electrical.

In a grid resistance in accordance with the invention the insulating support for the grids comprises a block of insulating material assembled from a series of blocks held together by reinforcing rods or the like while the grids each consist of a plate which may be plain or slit or slotted in well known manner to provide a zigzag path for the current, the plate being folded transversely of the slits about midway of its length to substantially U-form presenting two parallel planes. The free edges of the U-shaped grids are arranged to be wider than the horizontal zigzag bars and are disposed respectively at each side of a block and between alternate insulating blocks, the blocks being of dimensions such as to splay the freeends of the grids to impart a triangular form and rigidity to the grids.

It will be appreciated that all of the grids may extend from one face of the blocks but in a preferred form the grids are arranged in pairs symmetrically of the assembly of blocks and are retained in position in the block which they embrace by the free edges of the grids being deformed by bending, bruising or burring over in conjunction with grooves, or the like on the opposite faces of individual blocks, the grids being clamped in position by the abutting insulating blocks. As aforesaid, the clamped edges are wider than the bars of the grids to avoid enclosure of the current carrying parts and to reduce the wattage at the point of enclosure.

Suitably, connections from one grid to the next are provided in known manner by the spot welding of connecting strips of metal, which may be made in such form as to provide terminals at the same time, such terminals being stabilised by attachment to the adjacent supporting blocks.

The invention is illustrated in the accompanying drawing in which Fig. 1 is a perspective view of the imice proved grid resistance in a simple form while Fig. 2 is a perspective view of one of the grid elements shown in Fig. 1, Fig. 3 is a side elevation of a preferred embodiment, Fig. 4 is a plan view partly in section of a portion of the grid resistance shown in Fig. 3 and Fig. 5 is an end elevation of the construction illustrated in Figs. 3, and 4. Figs. 6, 7, and 8 are detail views illustrating the mode of construction of the grid elements shown in Figs. 3 to 5 while Fig. 9 shows different views of one of the insulating blocks shown in Figs. 3 to 5.

In the simple form shown in Fig. 1 the grid resistance comprises a series of insulating blocks 10 held together by reinforcing rods 11 and grids proper each consisting of a plate 12 slit or slotted in well known manner to provide a zigzag path for the current, plate 12 being folded transversely of the slits about midway of its length to substantially U form as shown in Fig. 2. The free end portions 13 of the U-shaped grids are arranged to be wider than the zigzag bars thereof and are disposed each side of a series of blocks 10 and between alternate insulating blocks, shown as of a slightly different form, the blocks 10 being of dimensions such as to splay the free ends of the grids 12 to impart a triangular form and rigidity to the grids. In the assembly shown in Fig. 1 the grids 12 are arranged in pairs symmetrically of the blocks 10 and are retained in position on the blocks which they embrace by bending, burring or turning over the free end edges of the grids as shown at 12a in Fig. 2, which end edges extend into grooves 10:: in the opposite faces of individual blocks 10. The grids are clamped in position by the abutting insulating blocks and rods 11. The portions of the grids being clamped are wider than the bars of the grids so as to avoid substantial enclosure of the current carrying parts and thus reduce the wattage at the point of enclosure.

The connections (not shown) from one grid to'the next may be provided by spot welding between the grids of connecting strips of metal.

In Fig. 1, merely for convenience of illustration, each of the blocks 10 and each of the intermediate blocks is shown as in a single piece but in practice each block may be constituted by a number of abutting small blocks. Obviously, although the intermediate blocks are shown without grooves or channels, all of the blocks may be alike and interchangeable.

In the preferred embodiment illustrated in Figs. 3 to 5 each grid proper consists, as in Figs. 1 and 2, of a slotted plate 12 folded transversely of the slots about midway of the length of the plate but the opposite ends of the plate are set at an angle other than a right angle to the sides so that when the plate is folded about a line parallel to the ends as shown in Figs. 6 and 7 the I one half of the plate is offset in relation to the other for a purpose which will be referred to hereinafter. Moreover the burred over or overturned end 12a at each end is similarly directed to correspond to the interlocking form of insulating block illustrated by way of example in Fig. 9.

As shown in Figs. 3 to 5 each insulating block of the grid resistance comprises a row of abutting blocks 10b. The blocks are channeled on one face 10c and are formed in the opposite face with a projecting surface 10d as shown in Fig. 9 so that blocks in adjacent rows may fit together and grip between them the overturned edges of the plates 12 in the manner indicated in the small portion in section in Fig. 4. The insulating blocks are shown as provided with a central passage for the reinforcing rods but they may be provided on each side with semicircular recesses so that abutting blocks in a row may embrace the rods. The assembly of blocks and grids of the resistance grid are held together by the reinforcing rods 11 and by end clamping plates 20 and 21. As :shown in Figs. 3 and 4 the clamping plate 29 at the right end of the figures embraces the projecting faces 10d of the right hand row of blocks and is pressed by the nuts on the reinforcing rods against the faces of the blocks clear of the projecting surfaces led, while the clamping plate 2; at the left end of the figures is clamped against the face outside the channeled portions 100 of the left-hand row of blocks.

In order to prevent damage to the insulating blocks when the reinforcing rods are tightened, such as might occur due to the fact that the whole of the space betwee' adjacent rows is not occupied because of the offsetting of the sides of the grids, spacer plates are inserted as indicated at 16 in Figs. 3 and 4.

In order to provide continuity of current path through the grids and to the terminal blocks for the grid resistance, plates 22, 23, and 24, shown in Figs. 3, 4, and 5, are provided. As shown in Fig. 5, the plates 22 are L-shaped plates one limb of which is Welded to a bar of the grid and the other of which is welded to the one face of a terminal block 25. The adjacent spacer plate 16 is welded to the opposite face of the terminal block 25, which is shown as being of about the thickness of a block 1%, and as bearing against the outside face of a block 105, so that a rigid anchorage for the terminal blocks is provided. The current paths between adjacent grids on the same side of resistance is provided, in the embodiment illustrated, by the plates 23 bent to U-shape. By virtue of the offsetting of the faces of the grid elements suflicient space is provided between the one face of one grid and an adjacent face of the next grid to permit of spot welding thereto of the plates 23.

The plates 24 are flat U-shaped plates which provide the connection between the lower ends of grids disposed symmetrically of the insulating blocks.

The insulating blocks may be produced from any suitable insulating material and the form may be varied in the interests of strength and weight saving.

in use, the grid resistance is supported in a well known manner by brackets fixed to its reinforcing rods.

In order to increase the insulating effect and also incidentally to prevent the leaving of interstices in which dust or other particles might collect, which would affect the insulation of the grids from the rods, 21 heat resisting and insulating cement might be used between parts of the resistance during assembly which cement could be squeezed into such interstices in tightening the reinforcing rods. The reinforcing rods could of course be covered by an insulating tube in a well known manner or by a coating of insulating material.

I claim:

1. A grid resistance comprising a series of individual plates each folded transversely substantially midway of its length to U-forrn to provide two adjacent free edges,

a separating block embraced by the adjacent free edges of each plate, insulating blocks assembled with the series of plates and separating blocks, and reinforcing rods holding the assembly together.

2. An electric resistance comprising a grid slotted to present a zig-Zag path to the current and formed with parallel sides and free ends, the free ends being disposed at an angle other than a right angle to the sides and being overturned at their edges, said grid being folded transversely about midway of its length parallel to the ends to impart a U-form to the grid, insulating separating means spacing the free ends of the grid to impart to the grid a triangular structure, and clamping means holding the free ends only of the grid against the separating means while permitting the grid to expand freely on heating, whereby substantially no current-carrying part of the grid is enclosed.

3. An electric resistance comprising a grid slotted to present a zig-zag path to the current and formed with parallel sides and free ends, the free ends being disposed at an angle other than a right angle to the sides, said grid folded transversely about midway of its length parallel to the ends to U-form with the free ends offset in relation to one another, insulating separating means serving to convert the grid into a triangular structure, and clamping means holding the ends only of the grid against the separating means while permitting the grid freedom to expand on heating, said clamping means clamping no substantial currenbcarrying part of the grid.

4. A grid resistance comprising a plurality of resistance grid elements bent to U-form with the ends spaced apart by insulating supports and separated from one another by other insulating supports and assembled together by means of rods, characterized by this that the grid elements References Cited in the file of this patent UNITED STATES PATENTS 1,526,649 Waller Feb. 17, 1925 2,059,349 Hertner Nov. 3, 1936 FOREIGN PATENTS 427,218 Italy Nov. 13, 1947

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