GB2154502A

GB2154502A - Holding a nut and tail conduit fitting within an outer member

Info

Publication number: GB2154502A
Application number: GB08503153A
Authority: GB
Inventors: Malcolm Wheatley Phillipps
Original assignee: Philmac Pty Ltd
Current assignee: Philmac Pty Ltd
Priority date: 1984-02-07
Filing date: 1985-02-07
Publication date: 1985-09-11
Also published as: GB8503153D0

Abstract

The conduit fitting is made in plastics material and has one outer member (11) rotatable over an inner member (12) (for example, a nut and tail), the outer member being first moulded separately to have an axially extending portion with an internal thread (14) and a radially inturned annular flange (16) at one end, the outer member (11) being inserted into a die and the inner member (12) being injection moulded within the outer member so that the inner member, when moulded, has an outer surface of an annular flange (30a) which is in contiguity with the complementary surfaces of the outer member but shrinks away from the outer member as the inner member cools. <IMAGE>

Description

SPECIFICATION Moulding a nut and tail conduit fitting within an outer member This invention relates to a method of production of a conduit fitting which has an outer member rotatable over an inner member (for example, a nut and tail assembly). The invention also extends to a product of that method. Still further, the invention relates to a die for the production of such a fitting.

At the present time nut and tail assemblies, and other similar fittings, are frequently moulded from plastics material, and a typical assembly comprises a tailpiece having an external thread surmounted by a gripping ring, a stem which extends into the tailpiece and which has an outstanding flange at one end, and a nut having an inturned flange which bears against the back of the outstanding flange and is arranged to firmly retain the assembly to a male threaded fitting. Other conduit fittings, such as barrel unions, and fittings on the ends of valves, are made by the same method.

Because of the diameter of the tailpiece thread and its gripping ring being greater than the internal diameter of the inturned flange of the nut, the tailpiece and stem constitute an assembly which, in usual manufacturing practice, is effected by a spin welding operation. This is generally satisfactory from a mechanical point of view, in that ample strength can be achieved, but it is still possible for leakage to occur through the weld zone and consequently an expensive inspection step is required in the process of manufacture to ensure that no such leakage occurs. The presence of a possible leakage zone is of particular importance if the fitting is to be used for gas.

The main object of this invention is to provide improvements whereby the construction of a conduit fitting such as a nut and tailpiece of moulded plastics material can be considerably simplified, improved and reduced in cost.

In one embodiment of the invention, a method of production of a conduit fitting consists of the following steps (but not necessarily in the following order): (a) Moulding the outer member to a shape which includes an axially extending portion having an internal thread, and a radially inturned annular flange at one end thereof, (b) inserting the outer member into a recess in female portions of a moulding die to place the outer surface of the annular flange into contiguity with complementary surfaces of said recess, (c) closing the moulding die with a male portion thereof thereby establishing a moulding cavity part of the surface of which is defined by the inner surface of the annular flange, part of which is defined by inner surfaces of the female die portions, and part of which is defined by a surface of the male die portion, (d) injecting fluent plastics material into the cavity, and (e) opening the die portions and removing the conduit fitting as an assembly comprising the inner and outer members.

Contrary to expectation, the inner surface of the annular flange forms an excellent moulding surface for the inner member, and because of the cooling of the die and the use of a (cold) premoulded outer member, the inner member becomes chilled before sufficient heat can be imparted to the outer member to cause any fusion between the members even if the two materials are identical. Upon cooling the moulded inner member contracts slightly and becomes free-running within the outer member, and there is an excellent surface-to-surface engagement between the inner surface defining the inturned annular flange of the outer member and the outstanding flange which forms on the inner member within the outer member. The spin welding operation is avoided, and therefore the inspection thereof is also avoided.

In another embodiment the invention consists of a die for the moulding of the tailpiece of a fluid flow conduit fitting by the above-defined method comprising two separable complementary female die portions having inner surfaces defining a recess, and at least one male die portion, characterised in that the die moulding cavity is defined partly by the inner surface of the annular flange of a said outer member when inserted into said recess, partly by the recess surfaces of the female die portions, and partly by a surface of the male die portion.

In an embodiment, the invention comprises a nut and tail assembly wherein the nut has an inturned flange at its back end, and the tail has an outstanding flange complementary in shape to the inturned flange and engaging the inner surface of the inturned flange, the tailpiece also having an outer surface with a male thread thereon of larger diameter than the diameter defined by the said inturned back flange of the nut, the tailpiece being a monolithic moulding.

An embodiment of the invention is described hereunder in further detail with reference to and is illustrated in the accompanying drawings in which: Figure 1 is a front end elevation of a nut and tail assembly, Figure 2 is a half-section side elevation of same, Figure 3 is a rear end view of said assembly, and Figure 4 is a longitudinal section through a die.

A nut and tail asembly 10 comprises three elements, the first being the nut 11, the second the tailpiece 12 and the third an "0" ring 13.

The nut 11 is firstly moulded to a shape which has an internal thread 14 in an axially extending portion 15 and a radially inturned annular flange 16 at an end thereof.

A die 20 (Figure 4) is provided with four parts, there being a front male portion 21, a rear male portion 22 which upon die closure, abuts the front male portion 21, and two female portions 23 and 24 which, upon die closure, abut each other on an axial plane 25. When the portions 23 and 24 close, they define between them a recess 26. However, before closure, a nut 11 is positioned on the front male portion 21, and the end surfaces of the nut are urged into contiguity with surfaces of the female portions 23 and 24 which define recess 26. A moulding cavity 27 is established, which is partly defined by a surface of recess 26, partly defined by the front and rear male portions 21 and 22 adjacent their mutual abutment zone, and partly defined by the inner surface of the annular flange 16.

The die is formed from tool steel and is provided with cooling conduits 28 therein. Die cavity 27 includes a shape 30 in which the tail forms a flange 30a, which itself will have a shoulder recess 30b for retention of "0" ring 13, as shown in Figure 2.

Fluent plastics material is injected into the die cavity 27, but the nut 11 is normally cold, and the die portions are rapidly cooled by the cooling effect of the fluid flowing through the cooling conduits 28 of the die 20. The die portions are then separated, and the nut 11 remains captive on the front end of the tailpiece 12 because of the outstanding flange portion 30a of the tailpiece 12 which, by its moulding, is of complementary shape to the inner surface of the nut flange 16.Surprisingly it has been found that there is no tendency for adhesion or fusion to occur between the surfaces of the flange 16 and the outstanding flange 30a of the nut 11 and tailpiece respectively, and upon shrinkage of the tailpiece, the nut becomes freely rotatable about the tailpiece, and since the surfaces are circular and complementary in shape there is an excellent surface-to-surface contact as the nut is tightened when in use.

The expensive weld and inspection operations are dispensed with, and the final product is one which is more likely to have a satisfactory strength than the product which it replaces. The likelihood of leakage is substantially eliminated, and the total overall cost is considerably less.

The preferred embodiment refers to a nut and tail assembly, but it is clear the invention is applicable to various other conduit fittings, for example, barrel nuts or valve tails.

Claims

1. A method of production of a conduit fitting having an outer member which is rotatable over an inner member comprising: (a) moulding the outer member to a shape which includes an axially extending portion having an internal thread, and a radially inturned annular flange at one end thereof, (b) inserting the outer member into a recess in female portions of a moulding die to place the outer surface of the annular flange into contiguity with complementary surfaces of said recess, (c) closing the moulding die with a male portion thereof thereby establishing a moulding cavity part of the surface of which is defined by the inner surface of the annular flange part of which is defined by inner surfaces of the female die portions, and part of which is defined by a surface of the male die portion, (d) injecting fluent plastics material into the cavity, and (e) opening the die portions and removing the conduit fitting as an assembly comprising the inner and outer members.

2. A method of production according to claim 1 wherein said conduit fitting is a nut and tail assembly.

3. A method of production according to claim 1 or claim 2 wherein the shape of said moulding cavity includes a portion for moulding of a flange on an end of the inner member, said fluent plastics injection comprising injecting the plastics material into the cavity thereby forming that said flange to lie in contiguity with the inner surface of the inturned flange of the outer member.

4. A method of production according to claim 3 comprising forming said inner member flange with a shoulder recess.

5. A die for the moulding of a fluid flow conduit fitting by the method of any one of claims 1 to 4, comprising two separable complementary female die portions having inner surfaces defining a recess, and at least one male die portion, characterised in that the die moulding cavity is defined partly by the inner surface of the annular flange of a said outer member when inserted into said recess, partly by the recess surfaces of the female die portions, and partly by a surface of the male die portion.

6. A die according to claim 5 further characterised that there are two male die portions which abut one another end to end in said moulding cavity upon die closure.

7. A method according to any one of claims 1 to 4 when effected in a die according to claim 6, wherein said insertion of the outer member into said die recess is effected by positioning said outer member on an end of one of said male die portions and closing the die.

8. A conduit fitting comprising an assembly of an inner member and an outer member, each being a monolithic moulding of plastics material, the inner member having been moulded by the method of any one of claims 1 to 4, claim 6 or claim 7.

9. A method of production of a conduit fitting substantially as herein described with reference to and as illustrated in the accompanying drawings.

10. A die substantially as herein described with reference to and as illustrated in the accompanying drawings.

11. A conduit fitting substantially as herein described with reference to and as illustrated in the accompanying drawings.