US2242482A - Ignitron starter - Google Patents

Description

May 20, 1941. R. F. RENNIE IGNITRON STARTER Original Filed April 19, 1959 IIL Patented May 20, 1941l 2,242,482 lamanon .STARTER Robert F. Rennie, Little Falls, N.

J., assignor to Westinghouse Electric & Manufacturing Company, East Pittsbur Pennsylvania Original application Ap 268,661. Divided 1939, Serial No. 284,574

(Cl. Z50-27.5)

12 Claims.

This application is a division of my copeniing application, Ser. No. 268,661, led April 19, 1939, for Ignitron starters.

My invention relates to starting electrodes and especially to the make-alive type of starting electrode utilized with mercury pool devices.

An object of the invention is to provide a makealive 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:

Fig. 1 is a view in front elevation of a discharge tube having a make-alive therein;

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

Figs. 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 Fig. 1 is illustrated a typical discharge tube which utilizes such a make-alive. The tube illustrated in Fig. 1 has a glass envelope I 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 co-nnecting pin I6 at the base of the tube has a connection Il, and this connection passes through the press I 8 to an arbor I9 that makes a supporting contact with the shaft or connecting pin 20 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 aseries 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 I and the mercury pool I I.

It is necessary, of course, that the make-alive 2I be of such composition as to be able to withstand the corrosive action of these tiny discharges for initiating the current. The make-alives heretofore constructed have been very expensive 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 make-alive.

The material from which I prefer to construct gh, Pa., a corporation of ril 19, 1939, serial vNo. and this application July 15,

the make-alive is from to 60% silicon and the 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 FeSi could be used. 'I'he 40% boron carbide (B4G) 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 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 60% silicon, 10 to 60% ferro silicon of the 85% grade; 30 to 60% ferro silicon of 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 grade) 40% boron carbide, 55% silicon, 5% iron an-d 40% boron carbide, 52% silicon, 8% iron oxide.

It will be noted that, in the above examples, I have selected two of the materials from the group of boron carbide, silicon carbide, silicon and ferro silicon. The percentages of the materials selected from the group have amounted to to of the make-alive body. The amount of each of the two major materials, by which I mean the two having the largest percentage because there may be more than two from the group, is present in the make-alive body in at least 10%.

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. Fig. 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 make-alive illustrated in Fig. 1. The conical opening of the die continues into a cylindrical opening 2l 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 cylindrical opening therethrough 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, 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 upon a suitable support 32. The desired quantity of the boron carbide, silicon, or ferro silicon or other mixture, is then placed in the 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 of the make-alive.

A plunger 35, having a central opening 36 to accommodate the molybdenum rod 20, compresses the mixture 33 as illustrated in Fig. 3. At the Sametime a press 31 is appliedto 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 38, as illustrated in Fig. 4. The rod 28 has its projection 3i extending above the surface of the die block 29.

A plunger 39, having the Idiameter' of the central opening through the die block, is then applied to the assembly in this central opening of the die block. The rst contact of this plunger 39 is upon the extension 3| of the rod 28. The rst action will be to compress the tip 40 of the boron carbide, silicon, or ferro silicon mixture, as illustrated in dotted lines in Fig. 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 4l. The vise is also screw threaded to receive a turn screw 42 that has a shaft 43 applied against the end of the rod 28 and of somewhat smaller diameter. By turning the screw 42 with the general pressure, the rod 2B 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 some graphite with the silica to furnish a suitable ring 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-firing at 1500 C. in hydrogen and then to regrind it before utilizing it to surround the compressed make-alives. In Figs. 'l 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 5l 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 Fig. 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 finished starter, the prering should be at higher temperatures than 580 C.

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

The 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 Fig. 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:

1. A make-alive starter for mercury pool devices comprising substantially 40% to 60% from the group of boron and silicon carbide and 60% to 40% from the group of silicon and its iron alloys.

2. A make-alive starter for mercury pool devices comprising 90% to 40% boron carbide and the remainder 10% to 60% silicon.

3. A make-alive starter for mercury pool devices comprising 90% to 40% boron carbide and the remainder 10% to v.60% ferro silicon of the grade.

4. A make-alive starter for mercury pool devices comprising '70% to 40% boron carbide and the remainder 30% to 60% ferro siliconof the 50% grade.

5. A make-alive starter for mercury pool devices comprising 60% to 30% boron carbide and the remainder 30% to 60% ferro silicon of the 25% grade and 10%v cobalt.

6. A make-alive starter for mercury pool devices comprising substantially 40% boron carbide, 20% silicon carbide and 40% silicon.

'7. A make-alive starter for mercury pool devices comprising substantially 45%' boron carbide, 45% silicon carbide and 10% silicon.

8. A make-alive starter for mercury pool devices comprising substantially 40% boron carbide, 50% silicon and 10% ferro silicon.

9. A make-alive starter for mercury pool devices comprising substantially 45% boron carbide, 45% silicon carbide and 10% ferro silicon.

10. A make-alive starter for mercury pool` devices comprising substantially 40% boron carbide, 55% silicon and 5% iron.

11. A make-alive starter for mercury pool devices comprising substantially 40% boron carbide, 52% silicon and 8% iron oxide.

12. A make-alive starter for mercury. pool devices comprising a body having at least two of the materials from the group of boron carbide, silicon carbide, silicon and ferro silicon mixed and sintered together and forming from to 100% of said body, the amount of each of the two major materials of the group in said body being at least 10% of said body.

ROBERT F. RENNIE.

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