US1851161A - Resistor grid - Google Patents

Description

March 29, 1932. F. T. COPE ET AL RESISTOR GRID Filed Feb. 6, 1930 2 Sheets-Sheet All Ime/mfom Patented Mar. 29, 1.932-

UNITED STATES PATENT orricE anatra a. corn AND ARTHUR H. VUGHAN, 0F SALEM, OHIO,ASSIGNORS T0 THE ELEC- TRIO FURNACE COMPANY, F SALEM, OHIO, A CORPORATION OF OHIO BESISTOR GRID Application tiled February e, 1930, Serial No.. 428,809.y

relates to metallic resistor cast, rolled or forged constructlon,

rllhe invention grids of for use in electric furnaces or kilns, and

more particularly to the cross sectional shape a of such grids and the means for supporting the saine in the furnace or kiln.

lt is well known that metallic resistor grids of dierent pross sectional shapes have been made and used in electric furnaces and l@ the like with various degrees of satisfaction and success.

ln the severe service'to which such resistor grids are subjected in large industrial furnaces, we have found that the following H properties are important in metallic resistor grids:

First, an eiiicient cross sectional shape for structural strength, so as to prevent sagging and warping under. stresses due to tempera- 2G ture dierences, and to the weight of the rid; v

g Second, proper disposition of the heat radiating surface of the grid so as to liberate heat and radiate it to the work with the least possible interference from adjacent parts of the grid itself and from supporting means;

\ Third, ability of the grid to shed scale which may fall thereon from the material when the grid is placed beneath the material Folirth, such cross sectional shape as will permit of soundness and homogeneity being attained when the grid is made by casting;

Fifth, resistance to oxidation such as to enable grid to withstand the temperatures at which it is operated.

To secure the necessary resistance to oxidation it is customary to employ alloys containing nickel and chromium with varying amounts of iron.

e have found that where the resistor is in the form of rolled'wire or ribbon it is very diiiicult to attain the structural strength necessary for horizontal or inclined mountl" mg, which is very often desired. With such resistors it is customary to employ supporting framework and additional insulators and spacers to prevent displacement which might occasion short circuits.

These additional supporting means are not only expensive but they interfere considerably with free radiation of heat from all parts of the resistor and frequently prevent placing of the resistors in the most advantageous position.

lin order to radiate heat from the surface of the grid, ence between adjacent parts of the grid, we have used grids of the greater part of away from the furnace wall.

At times we have used a T-section with a tapered stem rib or flange, mounted so that t e stem extends toward the interior of the furnace; and also a channel section havin tapered ribs or flanges extending toward the interior of the furnace.

en we mount resistor grids near the licor or beneath the roof of a furnace, we support them at the end portions so that each of the straight portions of the grid is loaded, as a beam, by its own weight. Such a method of mounting the grids has the advantage that there is nothing to prevent the free radiation gf heat from the entire length of the grid ars.

When it is desired to make the grids of cast alloys, it is extremely important that their that the castings will be reasonably homogeneous, sound and free from internal cavities. This can only be attained when thecross section is substantially uniform in thickness at all points, the maximum thickness being necessarily thin enough so that no part solidifies appreciably later than other parts.

The object of the present invention is to 'provide a cross sectional shape of resistor which we have found gives the best combination of the severaldesirable features above referred to. This cross sectional shape is in the form of a true Y, and is intended to be placed with the tail rib of the Y extending toward the interior of the furnace and away from the adjacent wall, preferably at a right angle thereto.

We have found that while other cross sectional shapes may excel the Y in certain respects, they are not suitable in others. For instance, an inverted V-shape, with tapered Gti auv

stantially a true Y- ribs, when placed in the floor of a furnace, possesses ideal scale shedding properties, but has been found to be structurally very weak,

. as compared to the Y-section of substantially Y the same cross sectional area and the same over-all dimensions.

Such a section, when made by casting, is

j also likely to be unsound because of slow coolsurface for radiation, is almost the weakest structurally of all sections which have been tried.

The above and other'objects may be attained by constructing and mounting the improved resistor grid in the manner illustrat- .ed in the accompanying drawings, in which Figure 1 1s a transverse sectional view through a furnace ofconventional type provided with the improved resistor grids, taken substantially on the line 1-1, Fig. 2;

Fig. 2, a longitudinal sectional view through one end portion of the furnace, takenon the line v2--2, Fig. 1; and

'Fig 3, an enlarged cross sectional view through the improved resistor grid.

Similar numerals refer to similar parts throughout the drawings.

The invention consists primarily in the provision of a metallic resistor formed of a plurality of spaced parallel bars 10, ofsuitable heat resisting alloy suc-h as nickel-chromium containing varying amounts of iron, which may be connected together at alternate ends, as b-y the return loopsor bends 11 to provide a continuous resistor.

The entire resistor may be cast in a single piece, each straight bar thereof being of subhaped cross section, as best shown in Fig. 3, and including the angular fork or V-portion adapted to face toward the adjacent furnace wall and comprising the ribs 12 extending toward the wall at equal angles thereto, and the tail rib 13 preferably of greater length than theribs 12 and extending away from the adjacent furnace Wall at a right angle thereto.

The ribs 12 forming the V-portion may be of substantially the same thickness throughout their length and preferably have the an gular rear edges 14 arrangedto be located parallelto the adjacent furnace wall while the tail rib 13 is preferably tapered from the junction of the V-portion to its e'dge which may be rounded as at 15. I

rl`he sides of the ribs 12" of the angular fork or V-portion as well as the sides of the' tail. portion 13 are preferably flat -as` shown in Fig. 3 of the drawings.

It will be seen that the effect of shaping the resistor substantially as a true Y in cross section is to reduce the thickness and consequently the mass of metal at the junction of the V-portion and tail rib with the result that there is very little difference in the thickness of the metal at the junction of the ribs as compared with the thickness of the several ribs themselves.

As above ointed out, a substantial uniformity in tie thickness of the sections is very important in the casting of the metals usually employed for resistor grids because of the considerable shrinkage of such metals when cooling from tendency to produce shrinkage cavities in any portion of the casting which cools at a much slower'rate than the other portions.

In applying the improved resistors to a furnace, such as illustrated conventionally in Figs 1 and 2, the resistors may he located adjacent to the top, bottom and side walls 16, 17 and 18 respectively, as illustrated in these figures.

The upper grids may be located adjacent to the top wall 16 and supported as by means of the ledges' 19, forme near the upper ends of the side walls, and by the refractory blocks 20 supported in any suitable manner, as by the bolts 21.

The'side grids may be supported adjacent to the side walls 18 as by the hooks or hangers 22 which engage the upper loops or bends of the grids, guides 23 being carried in the side walls for guiding the lower ends of the grids and permitting expansion and contraction thereof under changing temperatures.

The hearth 24 may be supported upon spaced piers 25 having ledges 26 at their bases for supporting the lower resistors spaced from the bottom wall or floor. It will be seen that the upper and lower resistors are both supported as a beam.

From the above descri tion and the illustration in the accompanying drawings it will be seen that-a resistor grid is provided havin a true Y cross sectional shape, the tail rib of the Y facing toward the work while the open side or fork thereof is faced toward the adjacent greater portion of the cross section of the resistor toward the interior of the furnace and directing the major portion of the' heat radiated therefrom toward the work or interior of the furnace at an angle to the adjacent furnace wall.

Where the Y-shaped grids are mounted beneath the work or beneath the hearth, the Ys are inverted with the tail ribs extending upward so that scale falling from the work or hearth and striking of the grids will slide therefrom,preventing short-circuiting of the grids by scale piling upon the same.

From the a ove it will be seen that a resistor grid is produced which has the best the molten state and the furnace Wall, thus disposing the' combination of lateral and beam strength, efficient disposition of surface for heat radiation, and ability to shed scale and dirt, and which can be cast satisfactorily if it is de- 5 sired to make the grid in this manner.

v We claim:

1. A resistor grid including a straight bar of substantially Y cross sectional shape and having an angular fork portion and a straight tail rib each having flat sides.

2. `A resistor grid including a straight bar of substantially Y cross sectional shape and having an angular fork portion and a tail rib, each having Hat sides, the tail rib being tapered toward its edge.

3. A resistor grid including a straight bar of substantially Y cross sectional shape and having an angular fork portion and a tail rib, each having fiat sides, the ribs of the fork portion being of uniform thickness throughout aid the tail rib being tapered toward its e ge.

4. A resistor grid including a straight bar of substantially Y cross sectional shape and having an angular fork portion and a tail rib each having fiat sides. the tail rib being provided with a rounded edge.

5. A resistor grid including a straight bar of substantially Y cross sectional shape and having an angular fork portion and a tail rib, each having flat sides, the ribs of the fork portion being of uniform thickness throughout and the tail rib being tapered toward its edge and having its edge rounded.

6. A resistor grid including a straight bar of substantially Y cross sectional shape, and having an angular fork portion and a tail rib each having Hat sides, the ribs of the fork portion being of uniform thickness throughout.

In testimony that we claim the above, we

have hereunto subscribed our names.

FRANK T. COPE. ARTHUR H. VAUGHAN.

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