HEAT RECOVERABLE METALLIC COUPLING

ACCOUPLEMENT METALLIQUE THERMORETRECISSABLE

English Abstract

ABSTRACT
A novel coupling member which comprises a hollow,
generally tubular metal member which is heat-shrinkable or
can be rendered heat-shrinkable in the radial direction,
and which is provided on its inner surface with at least
three teeth in the form of radially extending rings, the
distance (t) between any pair of adjacent teeth being less
than 0.95 d and less than 4 w, where d is the internal
diameter of the tubular member, and w is the wall thickness
of the tubular member, there being at least one tooth
either side of the tooth nearest the center of the tubular
member, the distance from the center of the member to the
tooth nearest the center of the member being from 0 to 0.3 d
and the distance between the two teeth adjacent the tooth
nearest the center of the member being more than the.
smaller of 0.4 d and 3 w. Such a coupling member can be
expanded by mandrel expansion methods without danger of
damaging the teeth.
- 1 -

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A coupling member which comprises a hollow,
generally tubular member composed of a memory metal, which
member is heat-shrinkable in the radial direction or can be
rendered heat-shrinkable in the radial direction, and which
is provided on its inner surface with at least three teeth
in the form of radially extending rings, the distance (t)
between any pair of adjacent teeth being less than 0.95 d
and less than 4 w, where d is the internal diameter of the
tubular member and w is the wall thickness of the tubular
member; there being at least one tooth either side of the
tooth nearest the center of the tubular member; the distance
from the center of the member to the tooth nearest the
center of the member being from 0 to 0.3 d; and the distance
(p) between the two teeth adjacent the tooth nearest the
center of the member being more than the smaller of 0.4 d
and 3 w.
2. A coupling member according to Claim 1 wherein
w is 0.1 d to 0.4 d, t is at most 0.7 d and p is at least
0.75 d.
3. A coupling member according to Claim 2 wherein
w is 0.2 d to 0.35 d, t is at most 0.6 d, p is at least 0.8
d and the height of each of the teeth is 0.015 d to 0.02 d.
4. A coupling member according to Claim 3 wherein
w is 0.23 d to 0.33 d, t is at most 0.6 d and p is at least
0.9 d.
-6-

5. A coupling member according to Claim 1, 2 or 3
which has a tooth at the center thereof and at least two
teeth either side of the central tooth.
6. A coupling member according to Claim 1 wherein
said memory metal is an alloy comprising nickel and
titanium.
7. A method of making a heat-shrinkable coupling
member as defined in Claim 1 which comprises driving a
tapered mandrel through a coupling member as defined in
Claim 1, 2 or 3 which can be rendered heat-shrinkable,
thereby effecting radial expansion of the member while the
memory metal thereof is in the martensitic state.
8. A method of coupling together a pair of
substrates which comprises placing the ends of the
substrates within a heat-shrinkable coupling member as
claimed in Claim 1, 2 or 3 and heating the coupling member
to cause it to shrink and engage the substrates.
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Description

1463
This invention relates to heat-recoverable metallic
couplings as described in, for example, U.S. Patents Nos.
j 4,035,007 and 3,805,567 and German Offenlegungschrift
No. 2,448,160. The known monolithic couplings comprise
a heat-recoverable tubular member which recovers directly
onto the substrates to be coupled. The member is preferably
provided on its inner surface with at least two teeth which
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~ are in the form of radially extending rings. The function of
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; these teeth is to grip and/or seal to the substrates when the
member is recovered, and they are therefore spaced away from
~; the centex of the~member, leaving the center section of the
inner surface free of teeth (indeed the center section has
often been provided with a recess such that the ends of the
tubings being coupled to not touch the coupl~ing at any
;~15 point).
The conventional method of preparing such
monolithic couplings is to drive a tempered mandreI through
the~coupling while the metal is in the martensitic state.
Howe~ver, a disadvantàge of this method is that the mandrel
20 ~ can;score or otherwise damage one or more of the teeth in a
way which allows the ~nstaIled coupling to leak. We have
now~discovered a novel coupling member in which teeth are
so disposed on the inner sur~ace of the member that the
kelihood of damage to the teeth by the mandrel is
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substantially reduced. In particular we have discovered=
that, contrary to the accepted teaching in the art as
; represented by U.S. Patènt No. 4,035,007, lt is advantageous
that the center section of the coupling member should be
` provided with a tooth, especially when the distance between
- 30 the innermost gripping teeth defining the center section is
relatively large.
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i - 2 -

~ 1463
;.`
.~ In one aspect, the invention provides a coupling
member which comprises a hollow, generally tubular member
composed of a memory metal, which member is heat-shrinkable
in the radial direction or can be rendered heat-shrinkable in
the radial direction, and which is provided on its inner
~: surface with at least three teeth in the form of radially
:~ ~ extending rings, the distance (t) between any pair of
adjacent teeth having a value which is less than 0.95 d and
less than 4 w, where d is the internal diameter of the
~ 10 tubular member and w is the wall thickness of the tubular
:~ member, there being at least one tooth either side of the
tooth nearest the center of the tubular member, the distance
~ from the center of the member to the tooth nearest the center
; : of the member being from 0 to 0.3 d, and the distance (p)
: 15 between the two teeth adjacent the tooth nearest the center
~; of the member being more than the smaller of 0.4 d and
: 3 w (i.e. p is greater than 0.4 d if 0.4 d is less than
3 w, and p is greater than 3 w if 0.4 d is more than 3 w).
The term "memory metal" is used herein to denote a
metallic material which exists in an austenitic phase at a
first temperature and in a martensitic phase at a second
temperature lower that the first temperature, which
material, when cooled from a first temperature at which it
is in a first configuration and is in the austenitic phase
to a temperature at which it is in the martensitic phase,
~; can be deformed to a second configuration which it will
maintain until it is reheated to a temperature at which it
is in the austenitic phase, whereupon it will recover
towards the first configuration. The memory metals used in
the present invention are preferably alloys comprising
nickel and titanium.

~ - "
11~1463
In another aspect, the invention provides a method
of preparing a heat-shrinkable coupling member as defined
above, which method comprises driving a tapered mandrel
through a coupling member as defined above which can be
5 rendered heat-shrinkable, thereby effecting radial expansion
of the member while the memory metal thereof is in the
martensitic phase.
_ .
In a further aspect, the invention provides a
method of coupling together a pair of substrates which
comprises placing the ends of the substrates within a heat-
shrinkable coupling member as defined above, and heating the
coupling member to cause shrinkage thereof. The substrates
should of course be positioned and sized so that when the
coupling member has shrunk, at least one of the teeth grips
each of the substrates.
'
The less the distance (t) between any pair of
; adjacent teeth, the less is the danger that the mandrel will
damage the teeth. The distance t is generally at most
0.8 d, preferably at most 0.75 d, especially at most 0.7 d,
particularly at most 0.6 d. The internal diameter of the
; member between the teeth is generally less than 3 inches
e.g. 1 to 2.5 inches, but can be much greater. The height
of the teeth (h) is generally from 0.015 d to 0.02 d. The
wall thickness (w) of the member is generally not more than
0.45 d, for example 0.1 d to 0.4 d, preferably 0.2 d to
0.35 d, e.g. 0.23 d to 0.33 d.

1~1463
The distance (p) between the two teeth adjacent
the tooth nearest the center of the member ls usually at
least 0.6 d, preferably at least 0.75 d, for example at
least 0.80 d or 0.9 d. The couplings will usually comprise
at least two teeth either side of the tooth nearest the
center of the member, and will usually be symmetrical about
the mid-point thereof (i.e. have a tooth at the center
thereof).
The invention is illustrated in the accompanying
~ 10 drawings in which the Figure is a cross-section of a
:' ~ .
~ coupling member according to the invention.
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