Sight glass structure and method of installing the same

This invention is directed to a novel method of removably securing a sight glass member to a refrigeration vessel in hermetically sealed relation therewith. In accordance with the method concept, a ferrule or like tubular mounting means is fixedly attached to the vessel through an opening therein, and one end of the sight glass is located within the ferrule. Brazing metal is then positioned in contact with the sight glass member and ferrule, and the metal, member and ferrule are heated by electromagnetic induction to melt the brazing metal and form a hermetic bond between the ferrule and sight glass member. By this method, leakage associated with threaded connections, and damage to the sight glass and extreme difficulty of removing the sight glass member when resistance or arc welding methods are used, are herein substantially entirely eliminated.

BACKGROUND OF THE INVENTION 
It is known in the art to which this invention pertains that sight glasses 
are employed in connection with certain components of refrigeration 
systems in order to obtain visual access to the interior thereof. 
Receivers are illustrative of such refrigeration components, and one prior 
art method of securing the sight glass body to the refrigeration component 
or vessel was to effect a threaded connection therebetween. Leakage of 
refrigerant from between the pipe threads was the inevitable result. In 
substitution for the threaded connection, an expedient employed by those 
skilled in the art has been to effect securement of the steel sight glass 
mounting body to the steel refrigerant component utilizing either 
resistance welding or arc welding techniques. Satisfactory results were 
again not obtained. First, during welding the steel surfaces often reach 
temperatures of approximately 3000.degree. F., and by heat conduction, 
damage to the sight glass itself often occurs. Second, by reason of the 
effective weld bond between the two steel bodies, it is essentially 
impossible to remove the sight glass body if replacement of the sight 
glass portion is required. 
SUMMARY OF THE INVENTION 
The present invention is directed to a process concept productive by its 
practice of an essentially leak-proof seal between a sight glass body and 
a refrigeration component, and further featuring ease of removal of the 
body in the event replacement of the sight glass becomes necessary. 
Briefly stated, by applicant's novel process a preformed ferrule or 
bushing is suitably secured to the refrigeration component, a body or 
member with sight glass mounted therein is positioned in contact with the 
ferrule, brazing metal applied to the ferrule and body, and by 
electromagnetic induction the ferrule and body bonded together through the 
brazing metal, while simultaneously the sight glass is shielded to prevent 
the overheating thereof. 
As the description proceeds in more detail, it will be noted that the sight 
glass body and ferrule are so configured as to be in slidable abutting 
relation, the brazing metal may be a wire annulus in surrounding 
contacting relationship with the body and ferrule, and the shielding means 
may be a heat sink positioned in protective relation to the sight glass so 
as to prevent heat damage thereto.

DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now first to FIGS. 1 and 2 of the drawings, a refrigeration 
component is designated generally therein by the legend C, and this 
illustratively may be a receiver or other vessel for containing a medium 
subject to pressure variations. Component C, wherefrom leaks cannot be 
tolerated, is provided with wall 10 having a hole or opening 10a formed 
therein. Secured to and within component wall 10 is a preformed ferrule or 
bushing 12 generally constructed of steel, and shaped to include at one 
end a radially outwardly directed annular flange or lip portion 12a, an 
annular shoulder portion 12b, and annular neck portion 12c. As shaped in 
the manner shown in FIGS. 2 and 3, ferrule 12 has provided therethrough 
passage or opening 12d communicating with the interior of refrigeration 
component C. 
Various techniques may be employed to effect firm securement of the ferrule 
or bushing 12 to component wall 10. Presently hydrogen copper brazing is 
preferred, although arc welding may also be employed. It is also believed 
apparent that the contours of the ferrule may vary from the specific 
configuration shown. 
Sight glass structures are employed in the refrigeration art and in fields 
generally related thereto for purposes of providing visual access to the 
interior of a particular vessel, and thereby permitting observation of 
specific conditions therein. It has been noted in the preceding 
description that earlier modes of securing the sight glass body to the 
refrigeration component have invariably resulted in either leakage, or 
damage to the sight glass, or the impossibility of removing the sight 
glass body if replacement of the fused glass is necessary. 
These difficulties of prior art approaches are effectively surmounted by 
utilization in the novel process concept of this invention of sight glass 
body constructed as best shown in FIG. 2 of the drawings. The sight glass 
body or member shown therein is designated in its entirety by the numeral 
20, and is preferably of steel composition. The member 20 is exteriorly of 
stepped wall configuration, or stated otherwise, of variable outer 
diameter. As so shaped or formed, sight glass body 20 includes at one end 
a generally cylindrical relatively thin wall reduced diameter portion 20a 
integral with a larger diameter central portion 20b unitary with an 
enlarged diameter head or cap portion 20c. At the juncture of the central 
and head portions 20b and 20c shoulder section 21 is formed thereby, while 
at the juncture of reduced diameter and central body portions 20a and 20b 
shoulder section 23 is provided. 
The sight glass body or member 20 is axially passaged as at 22 throughout 
the length thereof, and affixed within one end of the passage 22 is sight 
glass 30. The glass 30 is of course transparent, and is fabricated in disc 
form of any heat and pressure resistant glass composition. 
In performance of the novel method of this invention, and as is shown in 
FIGS. 2 and 3, a silver brazing ring 40 is positioned in encircling 
relationship with reduced diameter portion 20a of the steel sight glass 
body 20. The brazing metal providing the annulus 40 may be of the known 
nickel-silver type having a composition of about 18% nickel, 55-65% 
copper, and 27-17% zinc. Of course, brazing metals of the silver alloy 
type may also be employed, and generally these are constituted of 5-80% 
silver, 15-52% copper, balance zinc, plus tin and cadmium. The brazing 
annulus 40 is fluxed in conventional manner, and this may be accomplished 
by brushing on a commercially available flux paste. 
Either prior to or after positioning of the brazing ring 40 as described, 
the sight glass body 20 is lowered or moved into the ferrule or tubular 
mounting means 12, that is, from the position of FIG. 2 into the location 
shown in FIG. 3. As appears in the latter view, shoulder 23 on the sight 
glass body 20 then abuts against the top wall of the ferrule annular neck 
portion 12c, and the reduced diameter portion 20a of the sight glass body 
20 is received with the ferrule neck portion 12c. It is to be seen from 
FIG. 3 that the brazing ring 40 is seated upon the top wall of the ferrule 
neck portion 12c, and also wraps the annular body portion 20b of the sight 
glass body 20, thereby assuring accurate metal flow during the bonding 
operation. 
Another step in applicant's novel process is to position an annular 
induction coil 50 in radially spaced and circumferentially surrounding 
relation to the silver brazing ring 40, and spaced a sufficient distance 
from the sight glass 30 as to assure there will be no heat damage thereto. 
However, to assure even further that the sight glass 30 will remain 
relatively cool during the bonding of the steel body 20 the ferrule 12, a 
heat sink device 60 is employed in the method of this invention. Device 60 
shown in phantom lines in FIG. 3 is preferably constructed of copper, and 
may be of cap-like configuration so as to seat upon the head portion 20c 
of the sight glass body 20 in insulative surrounding relation to the sight 
glass 30, to thereby dissipate or absorb radiant energy. 
Stated otherwise, the copper heat sink device 60 is effective to prevent 
the magnetic field of the induction coil 50 from lifting the sight glass 
20 during the silver soldering operation. It is further effective to 
shield the steel in the sight glass body 20 from the magnetic field, which 
also results in keeping the sight glass 30 cooler. Additionally, the heat 
sink device 60 prevents overheating and cracking of the glass 30 by 
absorbing or dissipating unwanted heat. 
The induction coil 50 is preferably constructed of copper tubing, and the 
power supply therefor is conventionally an induction welder. As is the 
practice, a suitable coolant is circulated through the tubing 50. 
Temperatures at the bonding joint generally are 1200.degree. 
F.-1400.degree. F., preferably 1250.degree. F., and a firm bond between 
the ferrule 12 and sight glass body 20 is normally obtained in about 5 to 
6 seconds, due in some measure to the relative thinness of the wall 
portion 20a. 
It may be seen from the foregoing that by applicant's method of assembly 
and the structure produced therefrom the problems associated with prior 
art procedures are effectively eliminated. Leaks associated with threaded 
connections are no longer present, damage to the sight glass from the high 
temperatures associated with resistance or arc welding cannot occur, and 
removal of the sight glass body, in the event the sight glass needs 
replacement, is greatly simplified. It is only necessary that induction 
heating, or electromatic induction again be employed. If desired, this 
same type of heat may be used to remove the sight glass body 20 from the 
ferrule 12 in the event repair or replacement is necessary. In totality, 
very significant cost savings result from practice of the present method. 
Various changes and modifications to the invention have been noted in the 
above description, and these and other variations may of course be 
practiced without departing from the spirit of the invention or the scope 
of the subjoined claims.