Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION:
This invention relates to -twist on wire connectors
and the insulating caps that form the outer shell of the
connector. More particularly, this invention relates to
insulating caps having a relatively thin circumferential wall,
and having a configuration that is adapted to resist
considerable forces -- including especially bursting forces in
a radial direction.
BACKGROUND OF THE INVENTION:
It is common in the electrical wiring industry --
such as domestic or industrial wiriny and the like -- to
connect a plurality of wires `in electrically conductive
relation by using a twist on wire connector. 'I'ypically,
twist on wire connectors comprise a plastic insulating cap and
a coil of wire contained therein. The cap acts as a
insulating housing around -the coil and also provides a means
for gripping the connector in order to twist it onto the
wires. The coil comes into contact with the plurality of
wires being connected. The gripping forces necessary to
retain the wires in electrically conductive relation inside
the coil are provided by both the coil and the cap. If the
forces are provided by the capj they are transmitted to
the wires through the coil.
Some caps for twist on connectors used in
the electrical industry today, may be made of thermosetting
resin. Such types of material have a low modulus of elasticity
and thus are not easily elastically deformable, together
with a high resistance to plastic deformation --
desirable characteristics of wire connectors. However,
more recently it has become desirable to use thermoplastics,
such as nylon, as the material used in the manufacture of
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connector caps for a variety of reasons, such as cost
consideration in the production process and colour choice.
Thermoplastics, however, are relatively elastic and
therefore are easily deformed when tightened onto a pair of
wires, ,generally tending to bulge around the periphery. It
is possible to make such caps using an injection
moulding process, but a cap configuration not
specifically designed to be injection molded may provide
problems for such manufacture, primarily due to cooling
considerations.
Many presently available thermoplastic caps are
thick walled ~7ith either small raised lines for gripping
purposes, or thick walled with a plurality of thick ribs for
gripping and twisting purposes. Most thin walled
thermoplastic caps that are available employ an internal
expansion coil which applies most of the retaining force used to
bind the plurality of wires together. Such coils only contact
the plastic connector cap at the ends of the coil and
therefore transmit onlv a small fraction of the bursting
forces to the cap. As a result, the cap does not need to be of
high strength since the e~pansion coil bears the stresses
involved. Thus -the expansion coil needs to be of high quality,
and therefore higher cost, than if it did not need to absorb the
bursting forces.
DESCRIPTION OF THE PRIOR ART:
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, U.S. Patent 4,150,251 issued April 17, 1979, to
SCOTT discloses a twist-on wire connector having a thin walled
insulating cap that may be made from one of a variety o plastic
insulating materials, including thermoplastic materials. This
type of cap, however, requires a sheet metal retainer or cup
to be used in conjunction with it. The bursting forces
exerted by the wirès being compressed when they are connected,
are absorbed by the plastic deormation o the sheet metal
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retainer. These forces are not transmi-tted to the insulating
cap, thus the cap does not need to be of substantial strength.
U.S. Patent 4,112,251 issued September 5, 1978, to
SCOTT discloses a twist-on wire connector made of a
thermoplastic material, and having an expansion coil. The
bursting forces exerted by the wires are absorbed by the
elastic deformation of the coil. Such expansion does not
place bursting forces on the cap since the coil and the cap
contact only at the ends of the coil.
Canadian Patent 1,033,432 issued June 29, 1978 to
NORDEN discloses a screw-on electrical connector made of a
deformable insulating material suitable for injection moulding
from a wide variety of plastic. The coil inside the
connector is a non-expansion spring however, and the cap is
not relatively thin walled.
These previous thermoplastic material caps for
use with expansion coils are necessarily very specific in their
sizes, and hence are quite restricted in the number and
combination of wires and wire sizes which they may be used to
connect.
Canadian patent application No. 540,005
; copending herewith and assigned to the same assignee, describes
and claims a relatively thin walled thermoplastic material
cap having external ribs for rigidity and having a coil
substantially in intimate contact with the cap wall. Such a
cap is useful with non-expansion coils.
SUMMARY OF THE INVENTION:
In order to produce the caps in an economical
manner, it is desirable to have them cool as quickly as
; possible in the injection mould. For this to occur, there
; must be no large masses of plastic within the cap. It is
therefore desirable to design the cap such that it has a
relatively thin circumferential wall and that any associated
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integral portions thereof, such as those used for gripping or
guiding the wire into the connector, are also relatively
thin. Such a cap is made possible by the invention described
and claimed in copending Canadian patent application No.
540,005. However, in the invention of that patent application,
the coil must be in substantially intimate contact along
its entire length with the inside of the cap, in order to
provide a means for good transmission of forces. It is
therefore desirable to design a cap moldable in thermoplastics
material, which will cool relatively quickly in the mould,and
which has fins to aid heat dissipation and permit good grip by
the fingers for turning, or which is capable of providing
engagement means for twisting by means of an overcap or collar.
Such an~over-cap or collar in combination with a connector
cap is described and claimed in copending Canadian patent
application No. 577,655 filed on September 16, 1988, and assigned
to the same assignee as this application.
It is further desirable that a twist-on connector cap
have a sufficient degree of rigidity to accommodate an
expansion coil suitable for use over a wide range of wire
sizes and number of wires to be connected, thus reducing
the larger number of differently sized connector coils
and moulded caps which have previously been necessary. The
cap should preferably also be so designed to be relatively
thin-walled.
Accordingly, the invention provides a twist-on
insulating connector comprising an expansion coil spring;
an insulating cap substantially shaped as a frustum
having a small.closed end and a larger open end
leading to an axial bore within a peripheral wall
between the ends;
the bore including a wire receiving portion adjacent
to the end and leading to a wire guiding portion,
narrowing to a wire retaining portion containing said
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the spring belng adjacent -the wire re-taining portion
only at the ends thereof and being spaced inwardly
therefrom over at least a major portion of its
length;
the cap lncluding a plurality of longitudinal
strengthening fins extending radially therefrom at
least over the length of the wire retaining portion.
The wire receiving portion may be such that the
spring is constrained thereby, before damage occurs to lt
through expansion.
BRIEF DESCRIPTION OF THE DRAWINGS:
A typical embodiment of the invention will now be
described by way of example, with reference to the drawings in
which:
Figure 1 is a view, partially in section, of a cap
containing an expansion spring connector;
Figure 2 is a top view of the cap;
Figure 3 is a partly cut away section on line 3-3 of
Figure l; and
Figure ~ is a view similar to Figure 1 of a cap
having additional wings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
A twist-on connector 20 comprises a thermoplastics
material insulating cap 22 and a wire expansion coil 24
contained therein. The connector 20 is adapted to receive the
ends of a plurality of wires to be connected electrically. A
; square wire coil, as shown, may be preferable because the edge
o:f the coil is adapted to cut into the wires, but any
conventional expansion coil may be used. The thermoplastics
material may suitably be a polymeric material such as a nylon,
polypropylene, or polyethylene or a copolymer thereof.
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The cap 22 includes a cap body 26 and plurality of
fins 28. The cap 22 has a larger open end 30 to receive wires,
and a smaller closed end 32 -to preclude the passage of any
wlres contained in the interior 38 of wire connector 20 and
to provide insulation for the wires within the cap. The cap
body 26 is generally hollow, having an exterior surface 40
and an interior surface 42, and includes a peripheral wall 44
and the closed end 32. The wall 44, is disposed between the
ends 30, 32. For example, in a cap having a length of
approximately 1.1 inches, and a diameter of approximately
0.0655 inches at the open end 30, the wall thickness nearest
the end 30 may be in the order of .055 inches, with the
wall portion near the end 32 being somewhat thicker.
The interior surface 42 defining a bore in the
cap 22 is divided into three portions: a wire receiving
portion 48, a guide portion 50, and a wire retaining portion
52. These three portions are all substantially co-axially
aligned, seriatim, within the cap body 26.
The wire receiving portion 48 is tapered slightly
inwardly to receive a plurality of wires, and includes threads
54 to help catch any relatively soft insulation of any wires
entering the connector. This can aid in drawing the wires into
the interior 38 of the connector 20 as they are twisted
relative to one another. Additionally, the wires may
be retained better in the connector 20 once they are in
place, if portions of the thread 54 have cut into any
insulation of the wires.
The wire receiving portion 48 leads to the guide 50
which is sloped more sharply as a guide for wire ends, leading
them to expansion coil 24 in the wire retaining portion 52.
The manner in which a plurality of wires is
inserted into connector 20 and subsequently connected, will now
be described.
The connector cap is placed over the ends of the
wires to be connected, until the wires and the coil 24 contact
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one another. The connec-tor cap, which is grasped between
the thumb and fingers, is turned in the appropriate
direction -- clockwlse when viewed from the distal end of the
connector. When -the connector cap is turned, the group of
wires is tapped according to the helix of the coil 24 in
the expansion chamber, and they advance into the connector.
The coil expands into space 51 of -the cap and tends to absorb
bursting forces, and the coil may ultimately contact the wall of
the cap 22 within the expansion chamber 51 to preven-t
further expansion. This may allow for the use of expansion
coils of lesser quality than has heretofore been possible,
since excessive forces on the coil may be limited by the cap.
The expansion coil 24 may be made, when undeformed, to
be slightly narrower adjacent its mid point of length so that it
may be of "waisted" shape. This allows better initial grip on
the wires and optimizes use of expansion chamber 51. This is
because unlike conventional connector caps, cap 22 does not
deform with the coil 24 but the plurality of fins 28 acts
to preserve rigidity. It has been found that from about 14
to about 18 fins is an optimal number.
The combination of features including the waisted
shape oE the spring, the expansion space within the cap, and the
rigid walls containing the bursting forces may make it possible
to use a single connector according to the invention with a
greater number of wires of different thicknesses than has
heretofore been possible. At least partially, the reason for
this is that the connectors according to the invention may be
less critical in performance due to the inventive features.
The radially extending fins 28 are moulded as an
integral part of the cap; and are generally at right angles
to the wall 44. The fins 28 extend longitudinally from the
end 32 substantially along the entire length of the wall 44 to
the area corresponding to the wire guide portion 50 on the
interior surface 42. The fins 28 are preferably spaced
substantially equally around the wall 44, with the dis-tance
be-tween any two adjacent ribs being below the two-point
threshold for a typical human finger, which is usually in
the order of three to six millimetres. This means that the
pressure transmitted to the fingers and thumb is distributed
fairly evenly thereto, and there are no small local areas of
high force due to a small part of the cap digging into the
fingers or thumb. This results in a more comfortable grip
for the user. Alternatively, an over-cap or collar as
described and claimed in copending Canadian pa-tent
application No. ........ Omay be used. Each fin 28 may
have substantially flat parallel side walls joining an outer
wall through substantially 90 degree corners. Thus very good
grip on the cap is possible.
Proper electrical connection requires a tight
physical connection between the wires being connected and
between the wires being connected and the conductive coil
part of the connector. It is very important that these
connections be tight enough that gaps cannot develop between
the contacting surfaces. If a gap develops, there may be
a possibility that the surfaces at these points will
oxidize, and result in connections that are relatively
high in resistance. Such high relative resistance
connections may produce a great amount of heat while
conducting electricity, due to the fact that -the power
dissipated by the connection is proportional to the resistance
and to the square of the current.
Figure 4 shows another embodiment in which the
exterior of the cap 22 in the region of the wire receiving
portion is in the form of a smooth band 71 and is provided with
a pair of diametrically opposed wings 73. The roots 75 of the
wings 73 may extend over the height of the band 71 and spread
into wings 73, which may be shaped for conventional manual
manipulation.
The thickness of wings 73 should be sufficient tha-t
they are not unduly flexible under finger pressure, and so that
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they are capable of acting as levers through which additional
torque may be -transmitted to cap 22.
When -the wlres are inserted into the connector
and the connector is turned so as to threadibly engage the
wires, the edges of a square wire coil will cut into the
wires slightly, thus precluding the wires from slipping out
of the connector. However, expansion coils of round wire may
also be used. As the connector cap is turned, the wires and
the connector are drawn inwardly towards one another such that
the ends of the wires move towards the closed end of the
connector. As the connector is tightened onto -the wires, the
wires become pressed tightly together and exert reaction
forces, generally referred to as bursting forces. These
bursting forces cause the coil to expand and also to
shorten.
The present invention provides a structure
which may satisfy the requirements for good moulding
techniques, permitting production of the moulded thermoplastic
caps in an economical manner, as noted above. The use of
generally thin walled sections, not only in the circumferential
wall of the cap but also in respect of the ribs extending
radially outwardly therefrom, assures relatively even cooling
with a short cooling cycle of the moulded part within the
mould. This, in turn, precludes moulding deficiency such as
sink marks, which could materially affect the electrical and
mechanical properties of the cap, as well as make the product
les~ viaually acceptable.
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