Note: Descriptions are shown in the official language in which they were submitted.
Back~round of the Invention
This invention relates to electrical devices the
operation of which takes place in a vacuum environment and,
more particularly, to a structurally sound, vacuum sealed joint
between the structural elements of the envelope surrounding
that vacuum environment.
The types of electrical devices in which this
invention may be used are varied, e.g. vacuum interrupters,
vacuum switches, vacuum fuses, and the like. The element of
commonality in these devices is that they achieve their
operation in a vacuum environment.
Brazing and welding have been recognized as
acceptable methods of making the necessary joints and
connections in such devices, with brazing having been
recognized as perhaps the most suitable because it is readily
incorporated in the overall manufacturing process and provides
both a mechanically sound and vacuum-tight seal.
_/_
~, ..
. . ' . ~ : . . .. , . , .:
- -: . . . . . , ~ .-
,,,:
- , . :
- . . : . -
: . . ~ ': ' .. :
~04~352
01 This invention is concerned with providing an
02 improved joint for use in such devices.
0 3 SUMMARY OF THE INVENTION
04 Among the general objects of this invention are to
05 provide an improved slip joint between inter-fitting housing
06 portions which define an envelope for an evacuated area in
07 an electrical device; to provide a joint which readily
08 accepts an amount of brazing alloy adequate to result in a
09 mechanically sound and vacuum-tight joint; and to provide
such a joint without requiring either complicated operations
11 on those portions which define the joint or complicated
12 processing steps to admit the brazing alloy into the joint.
13 For the achievement of these and other objects,
14 this invention provides a joint between mating portions of a
vacuum area defining envelope wherein the edge of one
16 portion makes line contact with the surface of the other.
17 The portions overlap over a limited length but are spaced
18 apart other than at the line contact area to define a space
19 into which a connecting medium such as brazing alloy can be
admitted. The connecting medium mechanically joins the
21 first and second portions and provides the vacuum-tight seal
22 at the joint. This space is formed by a flare provided on
23 the end of one portion, the end edge of the flared portion
24 making the above mentioned line contact.
Preferably the area so defined comes substantially
26 to a point at the line contact and may be generally
27 triangular in transverse cross section. It is further
28 preferred that the end with which the flared end makes line
29 contact be offset and the line contact be made within the
offset portion.
31 Other objects and advantages will be pointed out
32 in, or be apparent from, the specification and claims, as
33 will obvious modifications of the embodiments shown in the
34 drawings, in which:
. , ,:
.~ ' .
104635Z
Fig. 1 is a general illustration of a vacuum fuse
embodying a joint formed in accordance with this invention;
Fig. 2 is an enlarged section view through a portion
of the envelope and illustrating a preferred embodiment of the
05 joint;
Fig. 3 is an enlarged section view of a portion of
the envelope illustrating an alternative joint arrangement; and
Fig. 4 is a section through a typical section of
brazed alloy.
Description of Preferred Embodiment
With particular reference to Fig. 1 of the drawings,
the improved joint of this invention is illustrated as embodied
in a vacuum fuse 1. The actual interior structure of the vacuum
fuse is not necessary to an understanding of this invention and
therefore has not been illustrated and will not be described.
Bell shaped housing portions 2 and 3 are part of an
outer housing, or envelope, which surrounds and defines an
interior area 4 in which a vacuum is drawn so that the operation
of the fuse, in a conventional manner, takes place in a vacuum
environment. Overall, the elements of the vacuum fuse which
make up the outer housing or envelope are all generally
circular in radial cross section. Portions 2 and 3 are made of
a suitable metallic material, such as copper-nickel, iron-
nickel, copper, or stainless steel.
Portions 2 and 3 are separate members connected at a
joint 6. The joint 6 must be mechanically sound to preserve the
structural integrity of the outer envelope and also must
provide a vacuum-tight seal to maintain the integrity of the
vacuum in area 4. This invention is concerned with the
construction of this joint.
~,
-3-
A preferred joint hill be described with reference
being made to Fig. 2 as well as Fig. 1. Portions 2 and 3
include ends 7 and 8, end 8 being positioned radially inside of
end 7. End 7 includes an offset portion 9, i.e. offset radially
05 relative to the remainder 11 of end 7, so that the end 7
includes an offsetting shoulder 12 which is disposed at an
angle, preferably an oblique angle, to the portions 9 and 11 of
the end of member 2.
End 8 of member 3 is provided with a portion 13 which
flares radially outward relative to the basic axis of the
vacuum fuse. End 7 also includes a radially flared end 10.
Flared portion 13 terminates in an end edge 14 such that, with
end 8 positoned inside of end 7 and overlapping a limited
length of end 7, the end edge 14 engages the interior surface of
end 7 and within offset portion 9. The remainder of end 8 and
offset portion 9 of the members 2 and 3 are spaced apart
relative to each other and define an area 16 therebetween.
With this arrangement, end edge 14 makes line contact with the
inner surface of end 7, specifically within offset portion 9,
and with area 16 coming to a point at the line contact. This
insures a good sealing contact between the overlapping ends of
members 2 and 3 and, moreover, so defines area 16 that it
effectively receives a suitable brazing alloy to achieve the
mechanical connection between the two members and a vacuum-
tight seal at the joint.
With the envelope members 2 and 3 arranged as justdescribed, a brazing alloy can be positioned at area 16 so that
when the fuse is subjected to a brazing temperature, e.g. the
bake-out temperature for the overall fuse, the brazing alloy
melts and is drawn, by capillary action, into area 16. The line
contact insures a close engagement at that point so that the
-4-
:
- .
1046352
brazing alloy does not flow out of the area 16 at the line of
contact between the ends 7 and 8. The brazing alloy bonds with
the surfaces of ends 7 and 8 and provides a vacuum-tight seal
and acceptable mechanical connection at the joint.
05 The resulting brazed alloy 15, is illustrated in Fig.
4 and can be seen that it takes on a shape which is
substantially to a point and is generally triangular in
transverse cross section. This is because the area 16 itself
has that general shape in cross section due to the relative
arrangement of ends 7 and 8 as a result of the flare provided on
end 8. This triangular shape readily admits the brazing alloy
during the brazing operation and in amounts sufficient to
provide the mechanical connection and the vacuum-tight seal.
In a preferred embodiment, the amount of overlap between end 8
and end 7 is generally in the neighborhood of 1/4-3/8 inch and
the distance between end 7 and end 8 at the open end of area 16
is generally approximately .010 inches. The .010 inch
dimension, which forms the base of the triangle, is preferred
for effective capillary action but the practice of this
invention is not necessarily limited to these dimensions which
are merely preferred relationships. Spacings at the open end
greater than .010 inches may detract somewhat from the
capillary action but still provide for movement of an adequate
volume of brazing alloy into the area to provide an acceptable
mechanical and vacuum-tight seal.
Fig. 3 illustrates an alternative joint 6'. In this
embodiment, end 7' does not have the offset 9. However, end 8'
retains flared portion 13' which terminates in end edge 14'.
In this embodiment, end edge 14' engages the inner cylindrical
surface of end 7', again establishing effective line contact.
This arrangement also defines an area 16' having generally the
C
--5--
- . - : ~ .................... . . . :
-
1046352
same configuration as area 16, i.e. coming substantially to a
point at the line contact and being generally triangular in
transverse cross section, for effective entry of the brazing
alloy into the joint to make a good seal along the line contact.
05 In practice, members 2 and 3 are formed by being
drawn and rolled, or they may be spun, rolled, or drawn to
whatever configuration is desired. The outward flares 13, 13'
and 10, 10' are found to occur normally when the members 2 and 3
are drawn and/or rolled. By providing the offset portion 9 in
one of the envelope forming members, both members can be made
from the same tooling. Both are drawn on the same tooling and
one is then rolled to provide the offset so that the members can
overlap one within the other. In the embodiment of Fig. 3,
members 2' and 3' have different diameters so that end 8' can
fit within end 7', this requires two sets of tooling.
As to the brazing alloy, with sections 2 and 3 made
preferably from Monel 404 or stainless s~eel 304, a copper
silver alloy has provided adequate results.
Although this invention has been illustrated and
described in connection with particular embodiments thereof, it
will be apparent to those skilled in the art that various
changes and modifications may be made therein without departing
from the spirit of the invention or from the scope of the
appended claims.
:
~ -6-
