This invention relates to the joining together by brazing

or soldering of metal tubing.

Lengths of metal tubing are frequently joined together by

soldering or brazing in which joining means, commonly known in the art as fittings, unions or couplings (herein simply

referred to as "couplings") are utilised. Such couplings usually

comprise two or more sockets with each socket formed to receive, with marginal clearance, an end portion of a length of tubing

and carrying in an annular groove or recess around its inner

surface a. brazing alloy or a soldering alloy. In use, an end

portion of tubing is inserted into a socket and upon heating of

the coupling and the said end portion, molten brazing alloy or

soldering alloy flows by capillary action between the inner

surface of the socket and the outer surface of the tubing

(the "jointing surfaces") to produce, on cooling a strong and

durable joint.

In one simple embodiment, a coupling may be used for joining two sections of tubing in a substantially straight line,

both sections of tubing having the same nominal external diameter.

More complex couplings may involve the use of bends or elbows

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and/or reducing bores and/or means for joining more than two

sections of tubing, for example, take the form of tee, cross

or "Y" pieces.

We have now found that the brazing alloy or soldering

alloy may be replaced with thermoplastic brazing or soldering

material.

According to one aspect of the present invention, therefo

a coupling (as hereinbefore defined) comprises at least two

sockets, each socket having one or more indentations, for exam

grooves or recesses formed in its inner surface with each inde ation (groove or recess) carrying a deposit comprising a therm

plastic brazing or soldering material.

The internal diameter of each socket should generally be such that it fits over a section of tubing with a tolerance so

that the brazing or soldering composition will, when molten,

flow by capillary action between the "jointing surfaces".

Naturally, the brazing or soldering composition should not

project from the groove or recess into the socket to an extent

greater than that which will permit the entry of a section of

tubing of the appropriate size.

Each groove or recess may take the form of a peripherally

continuous or discontinuous annulus, that is to say, an endles

or broken groove or recess, or it may take another form, for

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example that of a continuous or discontinuous helix or a spiral

or a series or pattern of recesses may be used. Furthermore,

we have found that the internal cross-sectional profile of the

groove or recess may have a significant effect on the ease of

carrying out the jointing operation and on the quality of the joint when formed. Under certain ^' circumstances, it may be necessary or desirable to have a groove which is relatively broad aid shallow whereas a relatively deeper and/or narrower

groove or, for example, a groove having an arcuate inner cross- '-

sectional profile may be preferred. Each indentation may have

a part circular cross-sectional shape selected from the group

consisting of a semi-circular segment of a circle having a chord

coterminus with the inner surface of the socket andhaving- a

length less than the diameter of the said circle. Other

modifications to the internal cross-sectional profile are within

the scope of the invention. One factor which may limit the

choice of profile is the desired thickness of the socket walls. Where the socket walls are insufficiently thick to accept a

groove or recess formed therein by removal of metal, the groove or recess may be rolled or otherwise formed in the socket wall. In such a case the existence of a groove or recess will be re¬

flected in the external shape of the socket wall.

Thermoplastic brazing compositions suitable for use with

couplings according to the present invention are described in

our co-pending British patent application No. 36655/78 filed

on 13th September 1978 claiming priority from British Patent

Application No. 38738/77 filed on 16th September 1977, and

comprise θ-aiixture of particulate brazing alloy and a thermo¬ plastic material, optionally with the addition of flux. Therm

plastic soldering compositions suitable for use with couplings according to the present invention are described in our co-

pending British patent Application No. 8010889 filed on 1st April 1980 and comprising a particulate soldering metal- or

alloy or oxide(s) reducible to said metal or alloy, a flux

which may have tϋermoplastic properties and, if necessary, a

thermoplastic binder.

In more detail, couplings according to the present invent

consist essentially of one or more short, hollow, open-ended

cylinders forming a ring, tee, "Y", or cross, for example,

defining two or more sockets adapted to receive with marginal

clearance the end portions of sections of tubing which it is desired to join together, the extent to which a section of

tubing can be inserted into a socket being limited by an inter annular shoulder, each socket having in its inner surface and

between its open end and said shoulder one or more essentially

annular grooves or recesses, each of said grooves or recesses

carrying a deposit comprising a thermoplastic brazing material

or thermoplastic soldering material.

Couplings according to the present invention may very

simply be made by assembling and/or machining a blank(that is,

devoid of brazing or soldering material) coupling and then

inserting into each groove or recess thermoplastic brazing

material or thermoplastic soldering material by extrusion

moulding for example.

Brazing or soldering operations may be carried out in a similar fashion to that using prior art couplings, that is

to say, by inserting the ends of sections of tubing into the

coupling, suitable cleaning and other preliminary operations

having first been carried out and applying heat, for example

from a blowlamp, to melt and burn away the thermoplastic

material, melt flux if used, and melt the brazing or soldering

alloy which then flows by capillary action between the"jointing ^'

surfaces" to form, on cooling a strong and durable joint. The

need for any separate fluxing operation is thus avoided. We

have found that the thermoplastic material is very satisfactorily

"chased out" from the grooves or recess and away from the"joint- ing surfaces" on application of heat and does not in any way

interfere with the successful formation of a jo.int.

The temperature to which it is necessary to heat the

coupling is generally in the range 200-300 C for soldering an

greater than about 450 C for brazing operations.

One form of straight coupling in accordance with the

invention is shown by way of example in the accompanying

drawing. The drawing shows a straight coupling partially

sectioned having a copper tube 1 formed with two semi-circula

cross-sectioned annular grooves 2. Each groove is filled

with a thermoplastic brazing or soldering material 3. The

copper tube 1 is divided longitudinally into two sockets by

an internally extending flange 4 which limits the distance a

length of tube can be inserted into the tube.

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