US2235504A - Ignitron starter - Google Patents

Description

March 18, 1941. R, F. RENNIE IGNITRON STARTER Filed April 19. 1939 www2 Re Y

w OM E M mw m W 2 m Y B Patented Mar. 18, 1941 UNITED STATES PATENT OFFICE IGNITRON STARTER Robert F. Rennie, Little Falls, N. J., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of My invention relates to starting electrodes and especially to the make-alive type of starting electrode utilized with mer-cury pool devices.

An object of the invention is to provide a make-alive electrode made from compressed materials having a uniform shape and uniform sintering.

Another object is to provide a method of forming make-alive electrodes that can be produced in quantities with uniform characteristics.

Other objects and advantages of the invention Will be apparent from the following description and drawing in which:

Figure 1 is a vieW in front elevation of a discharge tube having a make-alive therein;

Figure 2 is a view mainly in cross-section illustrating one of the initial steps in forming the make-alive; I

Figures 3, 4, 5, 6, 7 and 8 are views mainly in cross-section illustrating subsequent steps in the formation of the make-alive.

The invention relates to the formation of a make-alive and in Figure 1 is illustrated a typical discharge tube which utilizes such a makealive. The tube illustrated in Figure 1 has a glass'envelope I0 with a mercury pool II in the lower portion thereof. A contact pin I2 has a connection I3 to the mercury at I4. At the upper end of the tube is an anode I5. A connecting pin I6 at the base of the tube has a connection I'l, and this connection passes through the press I8 to an arbor I9 that makes a supporting contact with the shaft or connectying pin upon the lower end of which is the make-alive 2|.

As is well known, this make-alive 2| consists of a high resistance material and in operation a voltage is applied to this make-alive, and a series of tiny sparks or discharges will be created along the lower surface of the make-alive at the surface of the mercury. These discharges will ionize the mercury vapor and make the tube break down if a suitable voltage is applied across the anode I5 and the mercury pool I I.

45 It is necessary, of course, that the make-alive 2| be of such composition 'as to be able to Withstand the corrosive action of these tiny discharges for initiating the current. The makealives heretofore constructed have been very ex- 50 pensive to manufacture. My invention provides a cheaper method suitable for quantity production and at the same time provides for uniform shape and consistent characteristics of the makealive.

The material from which I prefer to construct the make-alive is from to '60% silicon and ythe rest principally silicon carbide or boron carbide or a mixture of both. In place of 60% silicon, ferro silicon may be utilized, or a combination of ferro silicon and silicon. Small amounts of iron oxide such as 1 to 10% may be used. Other silicides, carbides, nitrides, or borides may also be used. I prefer, however, to use ferro silicon of the 85% grade which consists of FeSiz and free Si. The grade consisting of FeSiz and 10 FeSi could be used. The 40% boron carbide (BiC) is preferably of the 320 grain. These percentages may, of course, be varied.

` My tests have especially covered silicon carbide with the remainder of varying percentages of 10 to 60% silicon; 10'to 60% ferro silicon of the 85% silicon grade; 10 to 60% ferro silicon of the 50% silicon grade; .10 to 60% ferro silicon of the 25% silicon grade and 10% cobalt. They have also covered boron carbide with 10 to silicon, 10 to 60% ferro silicon of the grade; 30 to 60% ferro silicon 0f the 50% grade; 30 to 60% ferro silicon of the 25% grade, and 10% cobalt. Other proportions included 40% boron carbide, 20% silicon carbide, 40% silicon; 45% boron carbide, 45% silicon carbide, 10% silicon; 40% boron carbide, 50% silicon, 10% ferro silicon (85% grade); 45% boron carbide, 45% silicon carbon, 10% ferro silicon (85% grade); 40% boron carbide, 55% silicon, 5% iron 30 and 40% boron carbide, 52% silicon, 8% iron oxide.

The mixture of silicon or ferro silicon and boron carbide is well mixed by ball milling. 'I'he mixture is then ready to be placed in the die. 35 Figure 2 illustrates a preferred form of, apparatus for forming the make-alive. This. consists of a die 25 formed as a cylinder with a conical shape desired for the pointed end 22 of the makealive illustrated in Figure 1. ing of the die continues into a cylindrical opening 21 extending through the remaining portion of the die. In this opening is located a rod 28. The die and rod are placed in the die block 29 which has a cylindricn opening therethrough 4 corresponding with the outer diameter of the die 25 and the desired cylindrical diameter of the make-alive.

For the purpose'of compressing the conical point of the make-alive as hereinafter described, 0 it is desired that the rod 28 in the die project a little from -the die and accordingly the die and die block' are. placed on a supporting plate 30 perforated to/accommodate the projecting portion 3| of the rod. The whole assembly rests` D 'I'he conical open- 40' upon a suitable support 32. The desired quantity of the boron carbide,'silicon, or ferro silicon or other mixture, is then placed inthe die and die block, as illustrated at 33. The connecting rod 20 for the make-alive is then inserted in this mixture. This connecting rod 20 is preferably of molybdenum, and at its lower end is pointed or tapered at 34 to correspond somewhat with the conical taper ,o/f the make-alive.

A plunger 35, having a central opening to accommodate the molybdenum rod 29, compresses the mixture 33 as illustrated in Figure 3. At the same time a press 31 is applied to the upper end of the molybdenum rod 20 to press its lower pointed end down to the desired location within the mixture 33. The press and plunger are then removed, and I prefer to turn the die block 29 upside down upon a lower die block 39, as illustrated in Figure 4. The rod 2l has its projection 3i extending above the surface of the die block 29.

A plunger 39, having the diameter of the central opening through the die block, is then applied to the assembly in this central opening of the die block. The first contact of this plunger 39- is upon the extension 3l of the rod 2l.' The first action will be to compress the tip 40 of the boron carbide, silicon, or ferro silicon mixture, as illustrated in dotted lines in Figure 4. The plunger 39 will then enter the central opening of the die block and push out the die 25, rod 28, pressed make-alive mixture 33 and connecting rod 20 from the die block 29.

The pressed make-alive can then be removed from the die in any convenient manner. I have found it convenient to use the apparatus in Fig- 6 for this purpose. This apparatus comprises a vise 40 for holding the die 25 by means of a screw 4I. The vise is also screw threaded to receive a turn screw 42 that has a shaft 43 applied against the end of the rod 29 and of somewhat smaller diameter. By turning the screw 42 with the general pressure, the rod 28 will gently force the compressed make-alive 33 out of the die.

To obtain a uniform sintering temperature, the starters are buried in a powdery medium that will not sinter together too hard at the temperature employed. Silica has been found to answer /,the,purpose. It has been found desirable to mix "sorne graphite with the silica to furnish a suitable iiring atmosphere. Fifteen to seventeen per cent. has been found to be especially suitable, although this percentage may be varied.

I have also found it advisable to give this mixture a pre-ring'at 1500 C.`in hydrogen and then to regrind it before utilizing it to surround the compressed make-alives. In Figures 7 and 8 I have illustrated the combination of the starters and the mixtures in a portion of one type of furnace. The furnace, which may be electrical, is illustrated by the walls 50 and upon the lower wall is resting the so-called furnace boat 5I having the mixture of silica and carbon therein. The

compressed make-alives 33 with their connecting` molybdenum rods 20 are illustrated buried in the mixture.

In Figure 7 is illustrated the first step of prering in air anywhere from 200 to 600 C. I prefer to preheat at approximately 570 to 580 C. If it is desired to reduce the resistance of the nnished starter, the pre-firing should be at higher temperatures than 580 C.

In Figure 8 I have illustrated the second step in which hydrogen is applied through the rurnace and this hydrogen is preferably at a temperature between 1500 and 1600 C. 'I'he hydrogen is preferably dried over P205 and the gas now is kept preferably as low as possible. about 11/2 cubic feet per hour. The firing is preferably of the order of eight minutes.

'I'he boat is then removed from the furnace and the uniformly sintered make-alive removed from the silica carbon mixture. After the silica carbon mixture is removed, the make-alive is then ready for insertion in a discharge device, such as that illustrated in Figure 1, which of course is for purposes of illustration and not to limit the invention.

It is apparent that many modifications may be made in the order of the steps and the particular shape of the apparatus utilized and also the composition of the materials specified without departing from the spirit and scope of the appended claims.

I claim:

l. 'I'he method of making an auxiliary startl ing electrode for contact with a mercury pool which comprises packing under pressure, a powdered mixture of material with a conductor, burying the packed mixture and conductor in a loose second mixture and sintering the first packed' mixture on said conductor in a gas furnace.

2. The method of making an auxiliary starting electrode for contact with a mercury pool which comprises packing under pressure a powdered mixture of material with the end of a conductor including the step of forming a substantially conical tip to said material, burying the packed mixture and conductor in a loose mixture and sintering the first packed mixture on said conductor in a gas furnace.

3. The method of making an auxiliary starting electrode for contact with a mercury pool which comprises packing under pressure a'powdered mixture of material with a conductor, embedding in a powdered mixture diilicult to sinter, providing a suitable hot gaseous atmosphere and uniformly by sintering the packed mixture on the conductor.

4. 'Ihe method of making an auxiliary starting electrode for contact with a mercury pool which comprises placing material in a die with a conical depression, compressing said material and inserting a conductor therein, removing said compressed material and conductor, embedding them in a mixture difiicult to sinter and sintering said compressed material on the conductor in a gaseous atmosphere.

5. The method of making an auxiliary starting electrode for contact with a mercury pool which comprises placing material in a die with a conical depression, compressing said material and inserting a conductor therein, removing the compressed material and conductor and embedding them in a mixture of silica carbon and sintering the compressed material in a gaseous furnace.

6. Means for uniformly sintering a. compressed powder on a conductor for an electrode, which comprises an enclosing powdered silica carbon mixture for the electrode, a container for the mixture and a hot gaseous atmosphere to sinter the compressed powder.

ROBERT F. RENNIE.

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