A method for making a glass-to-metal seal is described. A domed metal enclosure having a machined seal ring is fitted to a glass post machined to a slight taper and to a desired surface finish. The metal part is then heated by induction in a vacuum. As the metal part heats and expands relative to the glass post, the metal seal ring, possessing a higher coefficient of expansion than the glass post, slides down the tapered post. Upon cooling, the seal ring crushes against the glass post forming the seal. The method results in a glass-to-metal seal possessing extremely good leak resistance, while the parts are kept clean and free of the contaminants

Podgorski, T. J.

English

NASA Technical Reports Server

United States Patent [19] 
Fletcher et al. 
[ 111 4,017,959 
[45] Apr. 19, 1977 
[ 541 METHOD OF FORMING SHRINK-FIT 
COMPRESSION SEAL 
Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Ted J. Podgorski, St. 
Paul, Minn. 
[76] 
[22] Filed: Apr. 1, 1976 
[21] Appl. No.: 672,815 
[52] U.S. CI. ............................ 291447; 29/DIG. 35; 
[ 5  11 Int. CL2 ......................................... B23P 11/02 
[58] Field of Search ...................... 291447, DIG. 35; 
5319; 4031273 
350196 R; 4031273; 5319 
[561 References Cited 
UNITED STATES PATENTS 
1,331,091 2/1920 Becker ................................ 29/447 
2,768,475 10/1956 Seelen et al. ........................ 29/447 
3,623,196 11/1971 Bongenaar et al. ............. 29/447 X 
3,963,327 6/1976 Poirier ......................... 350/96 R X 
FOREIGN PATENTS OR APPLICATIONS 
1,31 1,323 10/1962 France ................................. 29/447 
550,126 12/1942 United Kingdom ................. 29/447 
Primary Examiner-Charlie T. Moon 
Attorney, Agent, or Firm-Howard J. Osborn; William 
H. King; John R. Manning 
[571 ABSTRAlCT 
A method for making a glass-to-metal seal. A domed 
metal enclosure having a machined seal ring is fitted to 
a glass post machined to a slight taper and to a desired 
surface finish. The metal part is then heated by induc- 
tion in a vacuum. As the metal part heats and expands 
relative to the glass post, the metal seal ring, possessing 
a higher coefficient of expansion than the glass post, 
slides down the tapered post. Upon cooling, the seal 
ring crushes against the glass post forming the seal. The 
method results in a glass-to-metal seal possessing ex- 
tremely good leak resistance, while the parts are kept 
clean and free of contaminants. 
5 Claims, 2 Drawing Figures 
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US.  Patent ~ p r i l i g ,  1977 Sheet 2 of 2 4,017,959 
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PIG. 2 
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METHOD OF FORMING SHRINK-FIT 
COMPRESSION SEAL 
4,017,959 
ORIGIN OF THE INVENTION 
The invention described herein was made in perform- 
ance of work under a NASA contract and is subject to 
the provisions of Section 305 of the National Aeronau- 
tics and Space Act of 1958, Public Law 85-568 (72 
Stat. 435; USC 2457). 
BACKGROUND OF THE INVENTION 
This invention relates generally to methods for pro- 
ducing glass-to-metal seals and more specifically to 
such seals produced by shrink-fit compression which 
are adaptable to aerospace applications where space 
and weight are primary limitations as are cleanliness, 
simplicity of construction, and superiority of seal per- 
formance. 
Shrink-fit compression seals have been developed 
and used successfully by others in operations involving 
glass-to-metal seals. These were primarily large diame- 
ter seals wherein a metal compressed on ring worked 
against a soft sealing material to form a seal with the 
glass. Obviously, if the necessity of the soft sealing 
material could be eliminated, a lighter, smaller seal, 
having inherent advantages with respect to aerospace 
application, would be produced. There is therefore a 
definite need in the art for a method which will produce 
a superior glass-to-metal seal and which eliminates the 
use of a third medium as a binder. 
It is therefore an object of the present invention to 
provide a glass-to-metal seal method using no other 
material in the seal. 
It is a further object of the present invention to pro- 
vide a method for producing glass-to-metal seals which 
are clean yet does not compromise the cleanliness of 
surrounding parts and structures. 
An additional object of the present invention is to 
provide a method which produces glass-to-metal seals 
of superior leak resistance. 
SUMMARY OF THE INVENTION 
These and other objects of the present invention are 
obtained by providing a method of producing glass-to- 
metal seals which minimizes the disadvantages of prior 
art methods and offers a novel parts preparation and 
attachment method producing glass-to-metal seals of 
superior leak resistance, and characterized by simplic- 
ity and cleanliness. The present invention describes the 
process for preparing a domed metal cylinder and a 
glass post; their subsequent positioning, and the man- 
ner by which they are bonded together. 
Specifically, a domed niobium cylinder is prepared 
with a seal ring. That is, an annulus is cut into the base 
of the cylinder, thereby providing the cylinder with a 
seal edge of desired edge width and surface finish. A 
fused quartz cylinder is machined to a slight taper and 
desired surface finish. The domed cylinder is placed 
atop the quartz post; then placed in a vacuum chamber 
which is subsequently evacuated. The metal dome is 
heated by induction which causes the annulus to ex- 
pand relative to the low expansion quartz block and 
result in the metal dome sliding down the quartz post. 
Heating the dome and quartz post under vacuum to 
high temperatures tends to keep the parts clean and 
free of contaminants while the seal edge tends to soften 
and flow slightly. Upon progression of the dome a de- 
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sired distance down the post, the parts are permitted to 
cool causing the seal edge to crush against the glass 
post forming the desired seal whereupon the assembly 
is removed from the evacuated chamber. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a cross section of the niobium dome and 
quartz post; and 
FIG. 2 is a plan view perspective of the niobium 
dome and quartz post placed inside a vacuum chamber, 
a portion shown cut away, and surrounded by an induc- 
tion coil also having a portion shown cut away. 
DETALED DESCRIPTION 
Referring now to the drawings and more particularly 
to FIG. 1, the present method consists in the first stage 
of the preparation of a domed niobium cylinder gener- 
ally designated by reference numeral 10 and prepara- 
tion of a fused quartz cylinder generally designated by 
reference numeral 20. 
The domed niobium cylinder 10 is manufactured 
with a niobium seal ring 11 defining its base. The inner 
surface of seal ring 11 slopes downwardly and inwardly 
at an angle of 45 degrees to an annulus 12 machined at 
its base defined by a seal edge 13 of known width. The 
annulus is centered in the base of domed niobium cylin- 
der 10 and posseses a k n o w  diameter, which, in the 
case of the preferred embodiment, is 0.375 inches. 
In the preferred embodiment, seal edge 13 has a 
width of .004 inches. While this dimension is variable, 
a seal edge of lesser dimensioa, for example, less than 
0.001 inches a “knife-edge”, will result in small frac- 
tures in the quartz cylinder upon attachment of the 
niobium cylinder thereto. This condition reduces the 
leak resistance of the seal and may result in component 
failure. On the other hand, a seal edge width of too 
great a dimension, for example, greater than 0.008 
inches, will reduce the leak resistance of the desired 
seal. Therefore, in the preparation of the seal ring the 
seal edge width is restricted to between 0.002 and 
0.006 inches. This range has been found to practically 
eliminate the small fracture problem and to provide the 
best leak resistance. 
The fused quartz cylinder 20 is machined such that it 
possesses a diameter slightly smaller than the annulus 
of the seal ring 21, in this instance less than 0.375 
inches at its top and a 2’ downward and outward taper 
along its length. The outer surface 22 of quartz cylinder 
20 is then polished transparent, that is, fine ground to a 
surface finish of better than 116 microinches. 
As shown in FIG. 2, following preparation of the 
niobium dome and quartz cylinder, the parts are posi- 
tioned upright with the seal ring 11 of niobium dome 10 
resting on tapered outer surface 22 of quartz cylinder 
20. The assembly is then placed in a vacuum chamber 
30 and surrounded by an induction coil 40. Vacuum 
chamber 30 is then evacuated and power applied to 
induction coil 40 so that the: niobium seal ring 11 is 
heated to a bright red at which point the niobium dome 
10 slides down the tapered quartz cylinder 20. As soon 
as the niobium dome stops dropping, heating is 
stopped. The parts are allowed to cool to room temper- 
ature, approximately 68’ F., under vacuum, at which 
time the parts are removed from the vacuum chamber 
30. 
Heating to very high temperatures under vacuum 
tends to keep the parts clean and free of contaminants 
and, at high temperatures, the seal edge 13 tends to 
4,O 17,959 
3 4 
soften and flow slightly, In operation, the resulting seal 
is capable of sustaining a leak rate of less than 1 X lo-@ 
standard cubic centimeters of helium per second. 
It is to be understood that the preparatory steps 
taken, materials used and annulus configuration are 5 
merely the preferred embodiment of the present 
method. Various changes can be made in the shape, 
size and material as will be readily apparent to those 
skilled in the art without departing from the spirit and 
scope of the present invention. 
What is claimed as new and desired to be secured by 
Letters Patent of the U.S. is: 
1. A method of making a noncontaminated glass-to- 
placing said opening of said metal enclosure over said 
small end of said post so that the metal enclosure is 
supported by said post; 
heating Said metal enclosure thereby causing it to 
expand and Slip down Said Post; and 
cooling said metal enclosure whereby the seal edge of 
said metal enclosure crushes against said glass post 
forming the desired seal. 
2. A method according to claim 1 including the steps 
of shaping the periphery of said opening in the metal 
enclosure such that the width of said seal edge is be- 
tween o.oo2 and o.oo6 inches. 
3. a method according to claim 1 including the step 
of placing A d  metal enclosure and said post 
under vacuum then performing the steps of heating said 
being a seal edge of controlled dimensions, comprising form the desired seal then removing said metal enclo- 
the steps of: sure in conjunction with said glass post from said vac- 
shaping said glass post such that its cross section is in uum. 
the shape of said opening and such that it is tapered 4. A method according to claim 1 wherein said glass 
along its length with the resulting smaller end being 2o post is a fused quartz post and the metal enclosure is a 
slightly smaller than said opening; and such that its 
surface has a desired surface finish; 5. A method according to claim 1 wherein heating is 
placing said shaped glass post in an upright position 
with said smaller end up; 
between a glass post and a , having an Opening therein, the periphery ofthe opening metal enclosure and cooling said metal enclosure to 
domed niobium cylinder. 
obtained through an induction coil. * * * * *  
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Method of forming shrink-fit compression seal

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