US3536919A

US3536919A - Infrared radiation source with improved ceramic glower rod mounts

Info

Publication number: US3536919A
Application number: US699488A
Authority: US
Inventors: John W Newman
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1968-01-22
Filing date: 1968-01-22
Publication date: 1970-10-27
Anticipated expiration: 1987-10-27

Description

Oct. 27, 1970 J. W. NEWMAN 3,536,919 INFRARED RADIATION SOURCE WITH IMPROVED -CERAM] (J GLOWI'IR ROD MOUNTS Flled Jun 22, 1968 FIG.|'. k n

FIG.4.

r 5 a I J I 45 53 5! 53 45 I.

INVENTORZ JOHN W. NEWMAN,

BYWQZo HIS A TORNY.

United States Patent Office 3,536,919 Patented Oct. 27, 1970 US. Cl. 250-85 3 Claims ABSTRACT OF THE DISCLOSURE An infrared radiation source is provided comprising a ceramic glower rod connected between a pair of spaced electrical contacts. A preheater heats the glower rod to a temperature level at which it begins to conduct and selfheat. A sturdy mounting structure is provided so that the elements may be precisely positioned and so that the glower rod may be mounted without any insulators for electrical isolation of the points of support thereof. The contacts comprise platinum foil strips which are brazed to the glower rod with a brazing material, such as palladium, having a lower melting point than the contact material at a temperature intermediate the respective melting points of the contact material and the brazing material.

BACKGROUND OF INVENTION This invention relates to infrared radiation sources and, more particularly, to radiation sources utilizing ceramic glower rods.

The use of a glower rod as a source of infrared radiation is well known. Such rods commonly comprise a ceramic material having a composition of approximately mol percent Y O and 85 mol percent ZrO It is the character of such glower rods that they are substantially electrically non-conductive at relatively low temperatures. In operation, a glower rod is normally connected between two contacts in an electrical circuit and is positioned in close proximity to a preheater device. The preheater serves to heat the glower rod to a temperature at which it will begin to conduct appreciable electric current. The passage of current through the glower rod results in substantial production of heat within the rod, such that the glower rod assumes a self-heating state and begins to radiate infrared radiation as long as current passes through the circuit.

A method of attaching the electrical contacts heretofore employed comprises the wrapping of platinum wire around the glower rod as a bundle of wires and then securing the connection with a ceramic cement of essentially the same composition as the rod. This method provides only a good mechanical connection and a rather unsatisfactory electrical connection to the glower rod, the points of actual electrical contact being few in number and of rather small surface area. This problem is accentuated if the glower rod has a comparatively uneven surface texture since the wires will then bear only on the high points and will not contact the rod at the depressions therein. Since a principal cause of failure in glower rods is contact deterioration due to loss of contact metal due to oxidation and subsequent sublimation, one notes a gradual rise of glower operating voltage. The poor contact afforded by the mechanical connection accelerates contact deterioration as a result of the excessively high current densities and temperatures that exist at the few point contact areas.

Another disadvantage of the prior art ceramic glowers has been the method of supporting the ends of the glower rod. Due to the location of the contacts at the ends of the rod, the glower rod will heat up and become conductive throughout the entire length thereof eliminating any portion of the rod for mechanical support. This results in a requirement that electrical insulation be provided to isolate the glower rod at the points of support, therebv increasing the cost of such devices.

SUMMARY OF INVENTION It is therefore an object of this invention to provide an improved method of connecting electrical contacts to an infrared glower rod.

It is another object of this invention to provide a ceramic glower cell wherein contact deterioration is substantially diminished thereby to increase the operative life of the cell.

It is another object of this invention to provide a ceramic glower cell wherein no special insulation is necessary for electrically isolating the glower rod from its supports.

In accordance with my invention in one form thereof, I provide an infrared radiation source comprising a ceramic glower rod supported by a mounting member and in close proximity to a preheater element. Spaced electrical contacts are brazed to the glower rod with a brazing material having a melting point lower than that of the contact material. Brazing is performed at a temperature intermediate the respective melting points of the contact material and the brazing material. The contacts and preheater are positioned sulficiently remotely from the glower rod supporting member that the temperature of the glower rod at the points of support will not promote electrical conduction.

DETAILED DESCRIPTION Other objects and advantages of my invention may better be understood by reference to the following de tailed description when taken in conjunction with the following drawings in which:

FIG. 1 is an axial cross-sectional view of the glower rod of the present invention immediately before brazing;

FIG. 2 is a cross-sectional view along line II-II of FIG. 1 of the glower rod immediately before brazing;

FIG. 3 is a view of the glower rod of FIG. 2 after brazing;

FIG. 4 is a top view of the ceramic glower cell of the present invention utilizing the glower rod of FIG. 1;

FIG. 5 is a sectional view taken along line VV of FIG. 4; and

FIG. 6 is a bottom view of the ceramic glower cell.

Referring now to FIGS. 1 and 2, there is shown a glower rod 1 of ceramic material. The composition of the ceramic material for the rod may be 15 mol percent Y O and mol percent ZrO It is to be understood, however, that while this may be the usual composition for such rods, the invention is not limited to such composition, all Well-known equivalents being equally well utilizable with this invention. As has been pointed out already, the prior art mechanical connection of contacts to the glower rod has promoted undesirable contact deterioration and the resultant early failure of such glowers. A better electrical coupling of the contacts to the rod is elfected through the novel brazing method which is a feature of the present invention.

It has been found that a better electrical coupling can be obtained by using a brazing material which has a lower melting point that that of the contact material. As seen in FIGS. 1 and 2, there is shown a strip of contact material 3, platinum, in this case, which has been wound around the glower rod 1. Wound around the rod 1 in a similar manner, and interposed between the rod 1 and the platinum contact strip 3 is a strip of brazing material 5, palladium, for example, which has a lower melting point (1554 C.) than the melting point of the platinum (1773 C.). The strips are so wound that a tab 7 is formed which may be spot, resistance or otherwise, welded to secure the contact and brazing strips for the brazing operation.

Brazing is accomplished at a temperature intermediate the respective melting points of the platinum contact ma terial and the palladium brazing material, that is, at a temperature in the range of 1554 C.-1773 C. The alloy formed from the two metals wets the ceramic glower rod to form a desired large area reactive seal. As can be seen by the cross-hatched lines in FIG. 3, the alloy surrounding the glower rod comprises a palladium rich alloy 9 at the interior portion thereof and at the rod seal, and a platinum rich alloy 11 at the exterior portion thereof.

The seal is such that all depressions, ridges and other surface irregularities are filled in and around with the alloy. Thus, a large, uniform contact area is obtained, reducing current densities and temperatures and increasing the life of the contact structure. Another feature of this brazing method is that the exterior 13 of the alloy, being rich in platinum, which has a higher melting temperature than that at which brazing is accomplished, does not become liquid during brazing. This means that the material will hold its shape and that no deformation will occur.

It is also feasible to eliminate the contact cement used in prior art techniques since its primary function of anchoring the contact and increasing electrical coupling to the rod is now fulfilled by the contact itself. Of course, the use of such cement with the brazing technique of the present invention will serve to further enhance the anchoring of the contacts, and tend to reduce oxidation thereof when the cement material is caused to encapsulate the brazed contact.

Live tests were performed with four glower rods having contacts brazed thereon in accordance with the present invention and operating at hot-spot color temperature of 1700" C., as determined by an optical pyrometer. The tests revealed that the first failure occurred after 1700 hours had elapsed. Other units were all still performing satisfactorily after 2000 hours of operation.

Referring now to FIGS. 4 and 5, there is shown a ceramic glower cell 15 utilizing glower rods having contacts brazed thereon in accordance with the above-described feature of the present invention. Broadly stated, the structure of this glower cell is such as to eliminate the necessity for electrical isolation of the glower rods at their respective points of support. Also, the arrange ment shown allows for precise positioning of the glower rod and, importantly, the glow zone thereof, within the support structure. In a preferred form of this feature of the invention, two separate glower assemblies are provided which operate independently of each other so that one glower assembly is available immediately to replace the other glower assembly which may have failed.

More particularly, there is shown in FIGS. 4 and a ceramic glower cell comprising a header assembly 17 including a cylindrical metal outer shell 19 having one end thereof closed off by an apertured ceramic header 21. The ceramic header 21 includes a series of contact pins 23 projecting through apertures therein for connection with a suitable electrical current source (not shown).

A mounting assembly 25 is provided which is interconnectable with the header assembly 17 to provide the completed glower cell. The mounting assembly 25 supports two glower assemblies, 27, 27 each of which includes respective glower rods 29, 29' and preheaters 31, 31 in close proximity thereto. The preheaters comprise respective

ceramic bars

33, 33 about which

wire heaters

35, 35, respectively, are wound. The glower rods and preheaters are supported horizontally and in generally parallel relation to each other within the outer shell 19 by means of a pair of spaced support plates 37, 37' secured to a positioning ring 39 retained by the outer shell 19 of the header assembly 17 to which it is connected as by welding. Aligned openings are provided in the support plates 37, 37' for reception of the glower rods 29, 29' and the preheater bars 33, 33'. Another pair of aligned openings are provided for reception of a sublimation shield 41 which separates the two

glower assemblies

27, 27.

As was stated previously, the glower cell 15 is adapted to operate only one glower assembly at a time. This is effectuated, in the preferred form of the invention, by provision of

separate sets

45, 45 of contact pins for each preheater, as best seen in FIG. 6. Each set 45, 45' includes respective preheater contact pins connected with the winding wire 35 of a preheater 31 and wire 35 of preheater 31'. There is also provided a pair of contact pins 47, 47 which are commonly connected to each of the

glower rods

29, 29 so that these rods are effectively in an electrically parallel relation. The contact pins 47, 47 are thus connected to respective pairs of leads 49, 49' from the glower rods 27, 27' by the afore-described brazing technique. The spaced

contacts

51, 51 on the

respective glower rods

27, 27 form glow zones 53, 53' therebetween. The glower rod contact pins 47, 47' being common to both glower rods, are always connected in a live socket no matter which glower assembly is operating. Selective operation of the glower assemblies, then, is determined by which pair of preheater contact pins 45 or 45 are connected in the live socket. Thus, a changeover from one glower assembly to the other merely requires rotation of the glower cell to connect the other pair of preheater contact pins 45 or 45' in the live socket.

A particular advantage of the glower cell structure is the elimination of insulation required to isolate electrically the

glower rods

29, 29 from the

support plates

37, 37 at the points of support thereon. This is because the

preheater winding wires

35, 35 and the glower rod contaits 51, 51' which form the

glow zones

53, 53 are sufiiciently remote from the support points that the glower rod 29 does not attain a temperature level which will promote electrical conduction thereat. This allows the

support plates

37, 37 to be constructed of a variety of materials, including metals, and allows electrical interconnection of the support plates without any deleterious effects.

Operation of the ceramic glower cell 15 is initiated by connection of the glower rod contact pins 47, 47' and one pair of preheater contact pins 45 or 45' to a source (not shown) of electric current. After the preheater winding 35 for example has heated up, the temperature of the glower rod 27 in the glow zone 53 will be raised sufliciently to a level which promotes electrical conduction therethrough. Infrared radiation is radiated from the glow zone 53 as the current flows, and the glower rod 27 self-heats to maintain the temperature suificiently high to promote conduction. If desired, means may be provided to cause the preheater 31 to switch off after conduction begins in glow zone.

I have thus described a glower cell utilizing a glower rod and a novel method of brazing contacts thereto. The brazing method comprises using a brazing material having a lower melting point than that of the contact material, and brazing at a temperature intermediate the respective melting points. The glower rod is supported with a preheater therefor by a structure including a mounting assembly that effectively isolates the conducting area of the rod so that insulation need not be provided at the points of support thereof.

While the invention has been described with specificity, it is the aim of the appended claims to cover all such equivalents and variations as come within the true spirit and scope of the foregoing disclosure.

What I claim as new and desire to secure by Letters Patent of the United States of America is:

1. A ceramic glower cell comprising a header assembly carrying electrical contact means connectible with a current source, a glower assembly including a glower rod,

a preheater member including electrical heating means for heating said glower rod to a temperature level at which said rod will conduct electrical current, spaced electrical contacts connected to said glower rod forming a glow Zone therebetween for conduction of electrical currents therethrough, electrically conductive means conmeeting said electrical contact means of said header assembly with said preheater heating means and with said glower rod contacts, and a mounting assembly interconnected with said header assembly for supporting said glower assembly, said mounting assembly including spaced support plates for supporting said glower rod and said preheater member, said heating means of said preheater member and said glow zone of said glower rod being sufiiciently remote from the points of support of said glower rod that said glower rod does not attain a temperature level at the points of support which promotes appreciable electrical conduction.

2. The ceramic glower cell as recited in claim 1 wherein a plurality of glower assemblies are provided each including a glower rod, and a preheater member, said electrically conductive means connecting said glower rods and said preheater members with said electrical contact 6 means, each of said glower rods and each of said preheater members being supported by said support plates of said mounting assembly, and a sublimation shield for separating said glower assemblies.

3. The ceramic glower cell as recited in claim 2 wherein said electrical contact means of said header assembly are so oriented that only one of said glower assemblies may be operated at one time.

References Cited UNITED STATES PATENTS 2,876,361 3/1959 Hutchinson 25085 2,892,119 6/1959 Miller et al. 3l3331 X OTHER REFERENCES Van Nostrands Scientific Encyclopedia, 3rd ed., D. Van Nostrand Company, Inc., Princeton, N.J., 1958, p. 224.

WILLIAM F. LINDQUIST, Primary Examiner US. Cl. X.R.

2925.ll; 2l9354, 553; 313-236, 334