Composite metal nipple

A tubular metal nipple for joining with the end of a copper tube by means of solder to readily produce a reliable joint in refrigeration plumbing system. The nipple has a inner copper sleeve concentrically spaced from the inside wall of a steel outer casing with an impervious intervening layer of brazing material filling the space and bonding the sleeve to the outer casing. The distal end of the sleeve is tapered or flared outwardly to produce an annular solder well when a tube end is inserted into the nipple.

SUMMARY OF THE INVENTION 
This invention relates to a composite metal fitting or nipple into which 
the end of a copper tube can be soldered. More specifically, it relates to 
a nipple which can be integrally connected to a steel vessel or other 
steel component of a refrigeration system by copper brazing in a furnace 
and subsequently soldered to a copper tube at a remote installation site 
with a solder having low or no silver content. The composite metal nipple 
comprises a tubular outer casing made of steel and a concentrically 
disposed inner thin copper sleeve extending inwardly from beyond an end of 
the casing to a depth of more than one diameter. Preferably the nipple has 
a relatively large diameter outer end for connection to an insertable 
copper tube and a smaller diameter inner end for insertion into an inlet 
or outlet aperture of a steel component, such as a suction accumulator, 
receiver or compressor unit, of a refrigeration system. The outer end 
section of the casing containing the thin tubular copper sleeve has an 
inside diameter that is slightly greater than the outside diameter of the 
sleeve to provide a narrow annular space therebetween. An intervening 
layer of fused impervious copper brazing material fills this annular space 
and integrally bonds the adjoining sleeve and casing sections together. 
The outer end of the sleeve may be flared or angled outwardly to provide 
an annular solder well in cooperation with an adjacent end of a copper 
tube when the tube is inserted in the nipple. A reliable gas-tight 
soldered connection having the required strength and resistance to fatigue 
can be made readily and economically with a low silver content solder or 
even one without any silver. 
At present unlined steel nipples are being used and reliable 
steel-to-copper solder connections which meet the refrigeration industry 
requirements are achieved only by using a solder having a high silver 
content. Silver solder is not only expensive but its use requires higher 
temperatures than are necessary with ordinary solders used in making 
copper-to-copper connections. 
The features, advantages and details of this invention will be understood 
best if the following description is read in conjunction with the 
accompanying drawings showing the preferred embodiment of this invention.

DETAILED DESCRIPTION OF THE INVENTION 
The preferred embodiment of the composite metal nipple 10 of this invention 
comprises a tubular steel casing 12 having a cylindrical midsection 14 of 
a certain diameter with a larger diameter section 16 at one end and a 
smaller diameter section 18 at the other end thereof. The larger diameter 
end 16, designated as the outer end for the sake of description, has a 
concentrically disposed copper sleeve 20 which extends from beyond the end 
to an annular shoulder 22 located at the transition between the outer end 
section 16 and the midsection 14. The smaller diameter end section 18 of 
the composite metal nipple 10 is sized for a press fit with respect to an 
inlet or outlet aperture of a steel object, such a pressure vessel into 
which it may be brazed. It has an annular shoulder 23 where it joins the 
midsection 14. The shoulder functions as a tapered stop which limits how 
far the nipple may be pressed into its vessel aperture. The nipple 10 may 
be foreshortened by eliminating the smaller diameter end section 18 and 
sizing section 14, which had been designated as the midsection, for a 
press fit in an aperture. 
The end portion 24 of the copper sleeve 20, which extends beyond the steel 
casing 12, is angled or flared outwardly such that an annular recess or 
solder well 26 is formed in cooperation with an adjoining portion of a 
copper pipe or tube 30 when the end of such a tube is inserted into the 
sleeve end of the nipple, as shown in FIG. 2. Preferably the end portion 
24 of sleeve 20 extends radially outward a sufficient distance to cover 
the edge of the steel casing completely. The sleeve is relatively thin and 
has a wall thickness of about 0.005 of an inch or more. Preferably it has 
a wall thickness of between 0.008 and 0.015 an inch. Its outer diameter is 
0.010 of an inch or less than the inside diameter of the outer end section 
16 of casing 12 leaving a thin annular space therebetween so the sleeve 
can be inserted into this end without the need of a mechanical force. 
The outside of the copper sleeve 20 is bonded to the inside of the steel 
casing by an impervious layer 28 of fused copper brazing material. A 
brazing material having a melting point below that of the thin copper 
sleeve is used. Preferably the brazing material has a melting point above 
1830.degree. F. such as any of the following commercially available 
compositions. 
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Copper Alloy Brazing Compositions 
CDA CDA CDA CDA 
510 521 655 542 
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Copper 94.8 91.9 95.8 89.75 
Tin 5.0 8.0 10. 
Phosphorous .2 .1 .25 
Silicon 3.4 
Tin and Manganese .75 
Melting Point 
1922.degree. F. 
1880.degree. F. 
1866.degree. F. 
1832.degree. F. 
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The preferred method of brazing is by means of a brazing furnace utilizing 
a protective atmosphere. 
While the composite metal nipple of this invention has been described with 
respect to a specific embodiment it is to be understood that modifications 
or other alternatives will become apparent to those skilled in the art 
without departing from the scope of this invention which is defined 
primarily by the appended claims.