Note: Descriptions are shown in the official language in which they were submitted.
CA 0222~479 1997-12-22
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ELEMENT FOR rUSION WELDING PLASTICS
TF.C~IC~r FIEr.D
The present invention is directed to welding elements of thermoplastic materials.
Elements particularly suitable for joining pipes and buttjoined sections are also
o S ~liccl~ssec~
B~CRGROUND A RT
The joining of thermoplastic materials, or the joining of other materials by thermoplastic
materials, has become relatively common with many construction elements being
constructed of materials amenable to welding using thermoplastic welding techniques.
10 While solvent welding is still commonly used (typically for non-critical joins) greater
strength and reliability may often be achieved by welding techniques--especially for butt-
joined members. For some plastics, such as polyethylene, solvent welding is not
practical due to its inertness with respect to most solvents. Accordingly some often used
plactics must rely on non-solvent welding techniques.
15 Early thermoplastic welding techniques were analogues of traditional metal welding
techniques and relied upon a heat source or element, and a plastic welding rod. In some
in.ct~nCec the welding or filling rod is not required and the welder merely fuses adjacent
areas of thermoplastic materials from the two members together. These techniques are
still acceptable for many situations though suffer several drawbacks.
20 For most thermoplastic materials, the heat of fusion is relatively critical. Inadequate, or
excessive, te~ .dlul~s can both lead to joints which may fail. In most cases the skill of
the welder is relied upon, though even the most experienced welder may have difficulty
in maintaining an even welding temperature, especially where joints are difficult to
access.
25 A solution of the art was to rely upon heating filaments. One technique was to place a
bare wire or metal strip bel~n the two m.omhçr.c to be joined. Passing a current through
the wire heated the ;~ ce~t ends of the members to be joined and allowed fusion.However it was found that it can be tlifFiclllt to obtain acceptable results and that the wire
can actually bum holes in the members being joined.
30 The invention of US patent specification No. 5410131 partially addresses this problem
by providing a 3-~lim~cional mesh. However, this invention relies upon the mesh
embedding itself into the plastic of the pipes being joined, and requiring the pipes to
continue being forced together during the welding process as the mesh imbeds itself
within the ends of same. There is also a further problem that it is possibl~or air pocksts
~UBSTITUTE SHEET (RULE 26)
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to form, resulting in a joint prone to failure should jointing be performed under less than
ideal conditions. Due also to the porous nature of the mesh prior to welding, it may be
difficult to keep foreign matter from entering sarne when joining is performed on site.
A further solution of the art was to coat a wire or strip in a thick layer of thermoplastic
5 material though, due to the thickness of the thermoplastic material of the rod which
surrounds the wire, it could be difficult to adequately soften the outer surface regions (ie.
the surfaces which form the weld) of the rod without burning the plastic surrounding the
wire or strip.
To address this a further modification of the art was to provide a multi-filament welding
10 rod in which the filaments were arranged in a helical fashion and embedded just under the
surface of the rod. However the present applicants have found difficulties in using this
type of product. For instance, as the filaments are distributed in a helical fashion which
substantially describes a cylinder, central regions of the rod may not be heated at the
same rate as the outer surface. This can be a problem in some situations. A further
15 difficulty is that the round nature of the helical filament rod is not suitable for all welding
situations. For instance, when welding steel pipe with a thin polyethylene outer layer, it
is preferable that there is good surface contact between the welding element and the thin
layer of polyethylene. Heating a cylindrical welding rod to the extent that it softens and
flows out to make contact and fill any voids is more likely to burn holes in the thin layer
20 of polyethylene, as well as resulting in inadequate fusion in other regions.
A further problem with much of the existing art is that it is very difficult to produce a
continuous circular weld for butt jointing ends of pipe. Using welding rods, such as the
helical filament welding rod, comprises forming a loop from the rod. However there still
remains a point where each end of the loop must be angled perpendicularly outwardly to
25 allow subsequent connection of an electrical supply. The problem arises ;3t this point
where the ends angle outwardly as it is a small region which is not heated to the same
extent as the remainder of the loop. It is at this point that the weld is most likely to fail or
have problems.
It will be appreciated that this problem cannot be overcome using sections of rod formed
30 into loops. Concentric or inwardly spiralled loops must still have a gap as the ends
terminate, while side by side loops are too thick and non-planar- the result is a side-by-
side spiral rather than a circle. Other configurations have been proposed though it
remains that it is virtually impossible to provide an evenly heated circular welding
element from sections of known welding rod.
35 Some of the art has resorted on the use of sleeves into which the ends of pipe sections are
fitted. Examples include the inventions of the specifications of US4224505, and
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US5229581, US5320697, US5364130, and US5306377 as well as the invention of
New Zealand patent specification No's NZ212786, and NZ247195. However, for many
sleeve like embodiments special heating devices or clamping arrangements are required -
for instance, the subject matter of US5037500, US5241157, US5290387, US4927999,
or US5141580. The use of such devices adds to the expense and ease of jointing and are
not always suitable for use on site - e.g. pipes already laid in a trench.
The use of sleeves also has drawbacks. For instance, they are much more expensive to
manufacture than non-sleeve type devices. They also rely on a significant area of the
outer surface of the pipes being satisfactorily cleaned prior to use - which may be
difficult in an outside environment. Furthermore, they are especially sensitive to
variations in the outside diameters of the pipes which they join. If one of the pipes is of a
slightly different outside diameter, which may for instance result from a different supplier
or batch, then a sleeve may not be able to be used unless the complex adaptor
arrangement of NZ247195 is relied upon.
In summary there are a number of problems associated with the art. At least one of the
problems is that many of the prior art welding rods and elements do not evenly heat the
thermoplastic material of the rod, or adversely affect the thermoplastic members being
joined. Another problem is that the many of the welding elements are not of the ideal
shape for welding flat surfaces and may not evenly fuse with flat sections to be joined. A
further problem is that existing thermoplastic welding elements are, as a whole, unable to
provide an ideal closed or circular element for joining pipe sections.
It is an object of the present invention to address the foregoing problems or at least to
provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the
ensuing description which is given by way of example only.
DISCLOSURE OF INVENTION
According to one aspect of the present invention there is provided an article whose body
portion includes an annular or arcuate modified weld interface comprising ~ contact face
for cont:-~ting a second surface to which said article is to be welded,
the weld interface comprising a thermoplastic material including at least one filament
arrangement in turn comprising one or more filaments aligned substantially lengthwise
with respect to the weld interface, and wherein the filaments of the filament arrangement
are substantially parallel to the contact face of the weld interface;
and wherein said filaments terminate at terminal portions not forming part of the weld to
said second surface.
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According to a further aspect of the present invention there is provided an article
comprising a welding element for the end-to-end joining of pipe sections, said welding
element comprising an annular or part annular body portion of a thermoplastic material
positionable between the ends of said pipe sections;
5 there being distributed along sub~t~nti~lly the entire length of said body portion at least
one substantially planar filament arrangement comprising one or more filaments aligned
sllhst~nti~lly lengthwise with respect to said body portion;
and wherein the end of a provided filament or filaments terminate at terminal portions
directed inwardly or outwardly of said body portion.
10 According to another aspect of the present invention there is provided a welding element
substantially as described above in which the two pipe contacting faces of the body
portion are substantially parallel to each other.
According to another aspect of the present invention there is provided a welding element
substantially as described above wherein there are at least two provided filament
l S arrangements, one each at or near a said pipe contacting face.
According to another aspect of the present invention there is provided a welding element
substantially as described above which comprises filaments starting at a terminal portion
for the first said filament arrangement, and which then extend along said first filament
arrangement, then cross to said second filament arrangement, extend along same to a
20 terminal portion associated with second filament arrangement.
According to another aspect of the present invention there is provided a welding element
substantially as described above in which when viewed in frontal projection, the filament
tracks of the said two filament arrangements as they divert to their terminal portion.
appear to cross over~ or overlap.
25 According to another aspect of the present invention there is provided a welding element
substantially as described above in which the filament tracks of a particular filament
arrangement are arranged such that when viewed in frontal projection, any radial line
extending outwardly from the annular centre will either intersect at a plurality of tracks,
or pass a filament track within a distance of half the average separation distance of said
30 filament tracks along the annular body.
According to another aspect of the present invention there is provided a welding element
substantially as described above in which a filament arrangement comprises more than
one set of filaments~ each set being part of a different electric circuit.
According to a further aspect of the present invention there is provided a method of
35 joining thermoplastic articles, comprising the use of at least one article including an
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annular or arcuate modified weld interface comprising a contact face for contacting a
surface of the second surface to be welded,
the weld interface comprising a thermoplastic material including at least one filament
arrangement in turn comprising one or more filaments aligned substantially lengthwise
5 with respect to the weld interface, and wherein the filaments of the filament arrangement
are snhst~nti~lly parallel to the contact face of the weld interface;
and wherein said filaments terminate at terminal portions not forming part of the weld to
said second surface,
and wherein electricity or an RF field is applied to cause said filaments to heat thereby
lO softening surrounding thermoplastic material to an extent sufficient for welding of the
articles.
According to another aspect of the present invention there is provided a method,substantially as described above, in which an intermediate welding element is employed
for the end-to-end joining of pipe sections. said welding element comprising an annular
15 or part annular body portion of a thermoplastic material positionable between the ends of
said pipe sections;
there being distributed along substantially the entire length of said body portion at least
one substantially planar filament arrangement comprising one or more filaments aligned
su~st:-nti:llly lengthwise with respect to said body portion;
20 and wherein the end of a provided filament or filaments terminate at terminal portions
directed inwardly or outwardly of said body portion;
and wherein said welding element is positioned between the ends of pipe sections to be
joined.
An article suitable for fusion welding, according to the present invention. may take a
25 number of forms. Typically the article will include at least one fil~m~n~ arrangement (see
later) embedded or adjacent a thermoplastic material at a weld interface - this is generally
a face for contacting another article to which it is to be welded.
In some embodiments the article may comprise a length of pipe or a fitting therefor~ with
an end being modified to include a preferred filament arrangement at the weld interface.
30 In other embodiments the article may be a shorter intermediate item~ termed a 'weld
element', with typically a weld interface at each end. The same principles apply to both
the larger, end modified articles and the (normally) shorter weld elements. There may be
little difference other than the nature of the article to which the weld interface and its
associated body portion is attached--eg it may a pipe length, or it may be only the body
35 portion itself (in a weld interface).
For simplicity of description, the specification shall refer predominantly to an
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intermediate welding element--the general principles can be readily applied to sections of
pipe and fittings given the description herein. Accordingly, a welding element (or the
weld forming portion of an article) of the present invention can generally be characterised
into two main portions - the body and terminal portions. The body portion can beS generally characterised as that portion forming the active part of the welding element
involved in joining the members being welded. The terminal portion, of which there may
be one or more, are typically regions to which a power supply may be connected, or RF
field applied, for activating the heating filaments. These are usually positioned in a
manner allowing the ready access of a power supply. but without interfering with the
10 weld. Depending on the embodiment, the terminal portion(s) will be typically (but not
necessarily) be provided at the end of the welding element. For looped and annular
embodiments of a welding element, terminal regions are generally~ but not necessarily,
provided in a manner extending inwardly and/or outwardly from the loop.
Most embodiments of the present invention are characterised by the arrangement of the
15 provided filaments. In most embodiments the preferred configuration and disposition of
the filaments is applicable to the body portion (which may comprise more than one
portion). The same disposition may also exist in the terminal portions though as this
region typically has a different function, the same preferred arrangement of filaments is
not generally necessary.
20 Before proceeding further, several terms which will occasionally be used shall be
explained. The first term is "welding interface" which shall refer to surface and near-
surface portions of the welding element which contact, or are meant to contact, members
to be joined. The welding interface will fuse with parts of the members being welded
that it contacts.
25 The term 'filament' shall generally refer to a conducting element, typically a heating
filament which will heat when subjected to an electrical current or RF field (RFgeneration techniques to induce heating are well known and shall not be described further
herein). The filament may comprise a single wire strand, a strip, or in some instances
several strands which are typically braided, woven or twisted.
30 The term "thermoplastic" shall be used in its normal sense and refers to a material which
softens upon heating though will return to its original state upon cooling. Typical
thermoplastic materials which are used in welding elements of the present invention will
comprise plastics materials though other types of thermoplastics materials may also be
employed.
35 The term "filament track" shall refer to the path that a filament follows. In some
examples the term shall be used to describe the path that a filament shall follow in the
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finished product. For instance, in some methods of manufacturing various
embodiments, a track may be formed into the body portion into which a filament is
subsequently inserted.
The term "filament arrangement" will refer to a filament track, or set of tracks, which lie
5 substantially within a single plane. More than one filament arrangement may be provided
in the body portion, and will often be positioned at or near the weld interface.
Preferably, the welding portion according to the present invention will comprise a
combination of thermoplastic material and filaments~ wherein the filaments are disposed
such that when activated they substantially evenly heat the thermoplastic material.
10 Preferably this should be without localised overheating to the extent that holes or burning
of thermoplastic material occurs. The exception would be remote, non-critical points
such as the terminals for connection to a power source.
Similarly there should not be any cold spots in regions which could interi'ere with the
integrity of any formed weld. In various embodiments it may be acceptable to merely
15 provide substantially even heating, at least in the body portion. in at least one of the
following manners:
- throughout the cross-sectional area of the body portion;
- on a face of the body portion;
- across the entire surface of the body portion;
- through the weld forming portion of the body portion, and
- across the weld interface of the welding element.
Various embodiments of the present invention may take different forms. In a number of
preferred embodiments, the welding element can be further characterised by comprising
at least one filament set in turn comprising a plurality of conducting elements or tracks
25 which are substantially parallel to each other, and which lie (at least in the body portion)
in a filament arrangement substantially within a single plane.
A welding element may comprise one or more filament arrangements and may comprise
any number of filaments in addition to provide more even heating of the thermoplastic
material in the body portion. These may be electrically conducting and appropriately
30 connected. Thermally conducting filaments and elements may be provided to distribute
he~t generated from the main filament arrangements. Where the body of the welding
element has a relatively simple cross-section (eg. rectangular), then additional filaments
may not be required. For more complex shapes, additional filaments may be needed. In
more complex embodiments, such as the flanged elements to be described later, sets of
35 filaments may be provided in the flanged or other depending portions.
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In preferred embodiments of the present invention the body portion is generally created
from a thermoplastic material formed to the desired shape. When joining pipe sections in
an end to end manner, the body portion will generally comprise a loop or ring
corresponding to the cross section of the pipe sections. As a variation the present
5 invention also includes body portions which comprise an arc and which may be
assembled to form an annular ring or loop. This variation will typically be used for
larger pipe diameters where it is difficult to m~nllf~rture or transport large diameter rings.
For embodiment used for connecting end sections of pipes, the weld interface will
generally be distributed along the pipe contacting faces of the body portion. It is at, or
10 near, these faces that there will be a filament arrangement capable of heating the
thermoplastic material of the body portion. To a certain extent, these filaments will also
heat the end sections of the pipe sections, or other articles to be joined.
Typically the filament arrangement will be substantially parallel to the weld face that it is
near. As, for the jointing of pipes, the end sections of each pipe is substantially planar,
15 so too will the filament arrangements in preferred embodiments of the present invention.
In a preferred embodiment, two filament arrangements are provided, one being at or near
each pipe contacting face of the body portion. Additional filament arrangements may be
provided, typically interme(li~l~ between the outer two filament arrangements. These
may be part of the same electrical circuit, or separate thereto.
20 For alternative embodiments of the present invention intended for other uses than the end
joining of pipe sections, each filament arrangement may not nt-c~ rily be planar. though
will typically be parallel to the contacting surface of the body portion where a weld is to
be formed. However, for simplicity, the present description shall be restricted to loop
and annular embodiments for joining pipes - the same principles may be applied to other
25 configurations.
It is possible that each filament arrangement comprises a single electric circuit, and it is
possible that different filament arrangements may also form part of the one circuit. As a
variation, each filament arrangement may comprise several sets of filaments. each of
which may belong to a different electric circuit. In one arrangement, adjacent parallel
30 filament tracks may belong to different circuits, while in another arrangement the length
of the welding element may be divided into several segments, each of which may
comprise a different set of fil~m~ntc and tracks.
It is also typical that the filaments, or tracks of a filament arrangement, will generally
follow, or be parallel to. the length of the body portion. Where the body portion is
35 linear, it can be said that the filament tracks of the set are parallel to the longitudinal axis
of the body portion. Where the welding element is non-linear, for instance an annular
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embodiment to be described later, then the tracks of the filament set are substantially
concentric with the annular body - it can also be seen to be substantially parallel to the
length of the body portion, which in this case would be a ring.
While the fil:lmf~ntc or tracks of the fil~m~nt set should m~int:~in their relative disposition
5 throughout a substantial proportion of the body length, occasional deviations from the
preferred arrangement may be tolerable in some situations, such as the welding of
complex shapes. It is also considered that deviations, when present, are likely to occur
within the terminal portions, or within the body portions which approach these terminal
portions.
10 In the terminal portions the filaments are generally oriented to become exposed or to
contact terrninals to which an electrical power source may be connected. The orientation
of the filaments in these portions is primarily one of function to enable a power source to
be connected. However, the transition from body portion to terminal portion should not
be such that weld integrity in those regions is significantly compromised - this was a
15 problem with loops formed from rods in the prior art. For relatively simple embodiments
comprising a body portion having a terminal portion at one or both ends, any welding
problems can generally be overcome by ensuring that the transition portion to the terminal
portion does not form part of the weld. However, this is not practical for closed loops
where the transition region is still involved in forming a weld. Accordingly, the general
20 criteria for the filaments in the body portion (of which it forms a part) are also generally
applied to this region so as not to overly co~ unlise the weld in this portion.
In a preferred embodiment, the filament tracks preferably form substantially concentric
rings about the centre of the annular body (in an alternative cylindrical body arrangement
the filaments may be co-axial). The terminal portions comprise one or more extensions
25 which typically extend inwardly or outwardly of the ring. The manner by which they
extend from the annular body portion may vary though radially outward extensions will
often be employed.
In preferred annular embodiments of the present invention it is desirable that there is
substantially even heating throughout the entire length of the annular body portion for
30 weld consistency. This may be achieved in a number of manners.
One such manner is to extend the filament tracks substantially tangentially (or at a slight
angle there to) outwardly to the terminal portions. Travelling in a direction about the ring
which begins at the angled lead-in, leading from a terminal portion, any track will
eventually re-encounter the side of the lead-in where it, or another member of the parallel
35 set of tracks, has entered the ring. At this point the filaments may be altered in direction
to travel inwardly and parallel to the lead-in filaments or, outwardly and parallel to the
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lead-in filaments. The filaments could then be directed to terminal regions. and/or
bndged to provide a return path for the electrical current.
In another alternative. a single filament can be wound spirally about the ring to provide a
number of parallel and substantially concentric tracks. Each end of the filament may be
5 directed to the app~up~iate terminal. A plurality of spirally wound filaments may also be
provided.
In a preferred embodiment, several filament arrangements are provided. When the
filament track encounters the lead-in where it or another member of the parallel set of
tracks has entered the ring, may divert to the edge of the body portion. At or near the
10 edge the tracks then divert and travel deeper into the body portion. They may at this
stage connect to another parallel filament arrangement (which may be the arrangement
present on the opposite pipe or article contacting face of the body portion near the
tangential filament tracks for that particular filament arrangement) - or to a terminal
portion.
15 The tracks from the other parallel filament arrangement may then parallel these angled
tracks before performing a concentric path about the annular portion to become the angled
tracks leading to a second terminal portion. As a variation, rather than leading to a
second terminal portion, the tangential filament tracks may then jump to yet another
filament arrangement provided within the body portion. As can be appreciated. in such
20 arr~ngem~nts a single electric circuit may comprise more than one filament arrangement.
A further significance of annular embodiments such as described above is that there is a
substantially even distribution of filaments around the entire length of the body portion.
When viewed in frontal projection. it can be seen that the fil~lment~ tracks of the provided
arrangements appear~ as they divert to their terminal portions. to cross over or to overlap.
25 Unlike much of the prior art, which must rely on rods of straight welding elements
formed into a loop, there is no point along the length of the loop which has a less dense
distribution of filaments, as is the case for prior art where the rod must be bent at a right
angle inwardly or outwardly to a terminal portion. Most welding elements of the present
invention can be characterised such that when the ring is viewed in plan, any radially
30 extending ray from the centre of the ring, in any direction, will pass through at least one
filament track. In contrast, at least one ray extending from the annular centre and
between the terminal portions of prior art welding elements, will cross the ring without
encountering any tracks - this being where the rod is diverted to form the terminals or
where a double~ concentric loop is used.
35 A variation of the preceding annular examples is to have the filament tracks to divert
substantially perpendicularly outwardly (or inwardly) to the terminal portions. While this
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bears some similarity to prior art devices, a distinction is that the tracks are brought into
close proximity to each other before being diverted substantially perpendicularly inwardly
or outwardly. For outwardly extending terminal regions, the perpendicularly directed
tracks which most closely approach are those of the innermost annular filament track (in
5 the set). For inwardly extending terminal regions, it is the outermost track - other
variations in track patterns are possible. In the embodiments of the preceding
paragraphs, it has been stated that no portion of the body portion is void of filament
tracks for any great distance. While there is one point through which a ray extending
from the annular centre may extend without touching a filament track (for the described
10 arrangement of this paragraph), it can be further stated that when passing through this
region, it is no further away from one of the filament tracks leading to the terminal
portion than the distance of one half of the average separation between filament tracks
about the annular body portion. Accordingly a gap where filament tracks do not
completely encircle a ring is acceptable providing that the gap is small. However, even
IS then it is desirable that the tracks are angled away from the perpendicular to avoid
possible flaws extending radially through the weld thickness.
While it is possible that continuous or overlapping filament tracks can be provided about
the annular body portion, and which extend outwardly to the terminal regions in a
manner overlapping other concentric tracks, such embodiments have inherent problems.
20 One problem is that the concentration of overlapping filaments leading to the terminal
portions can cause overheating of the thermoplastic material in this region. Thicker
filaments or conducting elements which do not warm to the same extent as the main
filaments, may be used in this region to connect the main filaments to the terminal. This
may be used to address possible overheating due to a larger number of filaments in a
25 localised region, though adopting track patterns such as described or illustrated herein
should reduce any such need.
B RIEF DESCRIPTI~N ~F D RA WINGS
Further aspects of the present invention will become apparent from the ensuing
description which is given by way of example only and with reference to the
30 accompanying drawings in which:
Figure I is a perspective diagrammatic cut-away view of a portion of a possible- flat, linear embodiment of the present invention;
Figure 2 is a perspective diagrammatic cut-away view of a portion of a another
possible flat. Iinear embodiment of the present invention;
35 Figure 3 is a perspective diagrammatic cut-away view of a portion of a possible L-
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shaped embodiment of the present invention;
Figure 4 is a perspective diagrammatic cut-away view of a portion of a an
alternative to the complex shaped embodiment of Figure 4;
Figure 5 is a perspective diagrammatic cut-away view of a portion of a planar
annular welding element;
Figure 6 is a perspective diagrammatic cut-away view of a portion of a possible
embodiment of an annular welding element with flanges;
Figure 7 is a perspective diagrammatic cut-away view of a portion of an alternative
embodiment of an annular welding element with flanges;
Figure 8 is a front diagrammatic view of an embodiment of an annular welding
element;
Figure 9 and 10
a front diagrammatic views of multiple filament set embodiments of the
present invention as having filament sets which contribute to more than
one filament arrangement;
Figure 11 is a front diagrammatic view of a further embodiment having a single
fil~m(~nt set fil~ml~nt arrangement;
Figure 12 through 14
are embodiments of single and multiple filament set embodiments
characterised in that the terminal portions for each filament set are on the
same face of the body, said body comprising a length of pipe:
Figures 15 and 16
are front diagrammatic views of arcuate segments which can be used to
form closed loop assemblies;
25 Figure 17 is a perspective diagrammatic view of the embodiment of Figure 10.
Figure 18 is a side cross sectional view of two pipe lengths being joined~ one of
which lengths has been modified to include a weld interface such as in the
embodiments of Figures 12 to 14, and
Figure 19 is a side cross sectional view of two standard pipe sections which are
being joined through the use of an intermediate welding element, such as
in the embodiment of Figure 8.
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~F.~T M OD~S FOR CARRYING OUT THE INVENTION
With reference to the drawings and by way of example only there is provided a welding
element (generally in-lic~t.o~ by arrow 1) comprising at least one filament arrangement 2,
in turn comprising a plurality of conducting elements 3 which are sub~st~nti,llly parallel to
5 each other, and (at least for other than at or near the terminal regions) substantially within
a single plane. which are embedded within a thermoplastic material 4.
Figure 1 illustrates a portion of a linear welding element which is substantially
rectangular in cross-section. A plurality of filaments 3 are provided which lie within a
single plane and make up the filament arrangement '. While a variety of materials may
10 be used for the filaments, it is envisaged that they will comprise a stainless steel wire.
The filaments 3 are spaced substantially equidistantly and substantially parallel to the
length of the body portion of the welding element.
The diagram of Figure I is not to scale and the thickness of the body portion of the
welding element will typically be less than that illustrated. This is to avoid problems with
15 localised overheating when attempting to attain the correct welding temperature at the
surface of the welding element. As can be appreciated, the relatively even distribution,
and number, of the wires can allow for reasonably rapid and even heating of the entire
weld interface (top and bottom surfaces) of the embodiment of Figure I without the
problems of cold regions and localised overly hot spots.
20 Figure 2 illustrates an alternative embodiment of the welding element of Figure 1. In this
embodiment there are intersecting cross filaments also provided. It is not envisaged that
these cross filaments 5 will make electrical contact with the conducting elements 3 though
this is a possibility. It is envisaged that the cross filaments S can be used to add
additional strength to the weld region (ie. acting as a reinforcing element) though may
25 also serve the purpose of conducting heat through the thermoplastic material to aid heat
transfer and thus even heating. In this latter instance they may be acting more as a
thermal conductor rather than an electrical conductor. While there may be advantage in
their being electrically connected to conducting elements 3 and acting as further heating
filaments, the electrical connection and inclusion of these cross-wire connectors
30 introduces other problems. Accordingly it is preferable that electrically heated filament~s
are restricted primarily to those extending lengthwise with respect to the body portion.
Figure 3 illustrates an L-shaped embodiment of the present invention which may be used
in a number of different types of joins. In the embodiment of Figure 3, cross filaments
5 have been included though these may be absent in other embodiments of this general
35 configuration. As can be readily appreciated from Figure 3, there are two sets of
filaments provided, one set for each arm of the body.
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Figure 4 illustrates a further complex shaped element which may be used for various
types of connections. Other configurations are also possible - the configurations of
embodiments of Figures 1 through 4 are also meant to be illustrative of a range of
possibilities for forming different welding elements according to the present invention.
5 Figure 5 through 7 illustrate some annular embodiments of a welding element. Figure 5
illustrates a substantially planar annular embodiment 7, though for clarity only a cut away
portion is shown. In many respects the embodiment 7 of Figure 5 is very similar to the
embodiment 1 of Figure 1, though has been formed into an annular ring. In the body
portion of the element the filaments 3 remain substantially parallel and concentric with the
10 annular centre. To prevent localised overheating, the body portion is relatively thin so
that the filaments are new each welding face 15 (contacting each end of a pipe section).
Figure 6 illustrates a further embodiment 8 of an annular welding element though with
outwardly extending fianges 9. This type of embodiment 8 is also envisaged for use in
joining sections of pipes, with the flange providing additional reinforcing and sealing for
15 the joined pipe sections.
Figure 7 illustrates a similar embodiment but wherein a second filament set is provided
for heating material in the flange. This is more likely to be used where the pipe ~sections
are of thermoplastic materials, or have thermoplastic coatings with which the fianges can
interact.
20 Figure 8 illustrates from a frontal view, an annular embodiment of a welding element
such as those of Figures 5 through 7. The outwardly extending tcrminal portion 11 has
fittings 12 for the connection of an electrical supply. In electrical contact with these
fittings 1'' are the filaments which enter the annular body portion tangentially (or at an
angle approximating ~same) and follow concentric fïlament tracks 13 about the annular
25 portion. When the filament tracks 13 re-encounter the tangential portion of the filament
tracks, they are redirected to run parallel to the tangential lead-in portions, then encounter
the edge (20), cross or fold to the other side (21 ) perform another loop before connecting
to the alternate terminal portion (12a). The terminal portion (12a) and the tangential
tracks leading to it on the opposite face have been partially shown in dotted outline.
30 In Figure 8 there is one electric circuit and this extends twice about the entire
circumference of the annular body portion through tracks which lead through two parallel
filament arrangements, each at or near the pipe contacting face of the body portion. In
some situations, especially for larger pipe diameters, electrical problems may arise if
significant lengths of filament are used between each terminal. This may, for instance.
35 impose excessive requirements on voltage and current generating equipment connected to
the terminals. Accordingly, in some situations it may be desirable to divide the filaments
14
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into two or more filament sets, each set being identified by the fact that it corresponds to
a different electrical circuit (though it may share terminals) rather than the fact that the
filament tracks lie substantially within a single plane (which characterises a filament
arrangement).
Figure 19 illustrates the use of an annular welding element 80 for joining two lengths of
pipe or fittings 81, 82. In figure 19 the two filament arrangements 83~ 84 can be seen. as
well as some of the crossover wires 85. Also visible is the terminal portion 86 and
contacts 87. Optional covers 88 are provided to act at least partially as a heat sink due to
the greater concentration of fil~ment.s in this area. Also in the embodiment illustrated in
figure 19, one of the terminal covers houses a thermocouple device 89 which can be
externally monitored to provide an indication of the temperature at the weld interface (or
at least a value which is proportional thereto). This may also be incorporated in
equipment controlling the electrical supply for contacts 87. to ensure that a preferred
temperature range is mnintnined during a welding operation.
Also illustrated is a piezo electronic pressure device 90 which can be used to provide an
indication of the applied pressure at or near a weld interface. This can be used to ensure
that adequate pressure is applied during a welding operation.
Figures 9 and 10 illustrate annular embodiments which comprise more than one set of
filament tracks. In Figure 9 there are two filament sets, generally indicated by arrows 30
and 31. The filaments of set 30 begin at terminal contact 32, travel halfway around the
length of the body portion until near terminal post 33. At that point the tracks divert
substantially tangentially inwardly and cross to the alternate face of the body portion. At
that point they complete the return portion of their path underneath the top filament tracks
(in the illustration) of filament set 31 until near contact 3~. At that point they divert
substantially tangentially outwardly and connect to terminal contact 3''a. on the opposite
hidden face of the body portion (shown in outline only). The filament of the second
filament set 31, performs substantially the same path but beginning at terminal contact 33
and terminn~ing at terminal contact 33a. The result is that each filament arrangement (of
each pipe contacting face) comprises approximately 50% of the filament tracks of each
filament set 30, 31.
Figure 10 is another multiple filament set embodiment, but with three terminal portions
~ shown. For simplicity, the terminal contacts have been numbered to indicate the
beginning and end points of each filament set e.g. 35 and 35a are the contacts for a first
- filament set, 36 and 36a are the contacts for a second filament set, and 37 and 37a the
35 contacts for the third filament set. The suffix a indicates (for these figures) that the
contact is on the rear, hidden face, of the illustrated device.
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During welding, the use of multiple circuits can reduce the current required for long
filament paths. For embodiments such as shown in Figures 8 through 10, the welds can
be performed ~imult~neously or individually. The number of different filament sets (and
circuits) is up to the user and the equipment being used. As a rough guide, there may be
5 up to 8 segments for a 3 metre diameter pipe.
Figure 11 illustrates an alternative embodiment of a welding element. Here the filament
tracks 36 run substantially concentrically with respect to a body until they near a terminal
portion 37. At this point the tracks divert substantially perpendicularly outwardly to
connect to terminals 38 and 38a. The innermost track should approach itself by a10 distance substantially the same as the average distance between the concentric tracks,
before diverting perpendicularly outwardly. This avoids any large gaps about thecircumference which is not heated to the same extent as the others. It is typical that a
similar filament arrangement is provided on the opposite face of the element.
Figures 12 through 14 illustrate embodiments having similar characteristics to the
15 embodiments of Figures 8 through 10, as well as characteristics of the embodiment of
Figure 11. These characteristics are that there is a semi-tangential angling of the tracks
40-45 to the terminal contacts 46-52. The characteristic of the embodiments of figures 1
through 14 that is shared with that of figure 11 is that each filament set remains on the
same face of the body portion, and does not cross to the opposite side. In one respect
20 this can be an advantage as the crossing of filaments from one side to the other can create
additional heating in this region. As this may, in some instances, be detrimental to the
forming of a uniform weld, it is sometimes necessary to rely on positioned heat sinks
when using embodiments such as shown in Figures 8 through 10. Such heat sinks may
be provided through a provision of extra thermoplastic material positioned inwardly of
25 the ring in the vicinity of the cross over, or, perhaps, removable elements which bear
against same during a welding operation. The applicant has found that an inflated
neoprene bag within the pipe section is sufficient to act as a heat sinL; during a welding
operation, as well as helping to maintain items in the correct position for welding and
.
~olmng.
30 However, the embodiments of Figures 11 through 14, because they lack cross overs
between filament arrangements, do not require such considerations. A limitation
however of the embodiments of Figures 12 through 14 is that it may be difficult to access
the internal contact from the outside of the pipe during a welding operation.
Accordingly, such embodiments are typically only used during connection of short35 sections of pipes bends and other fittings of short length, or at the end of pipe sections.
As a variation, the filament arrangements of Figures 11 through 14 may be applied to the
16
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end of a pipe section. The result is a pipe length, or pipe fitting, having at least one end
pre-fitted with an integral weld interface with fil~m~nt arrangement. In many respects the
result is equivalent to a welding element though with the mid portion of the body of
greater thickness. Filament arrangements may be provided at each end of the pipe or
fitting. Bridging conductors could be provided to link the rearwardly diverted tracks of
arrangements similar to the embodiments of Figures 8 through 10, to terminals so as to
allow similar filament arrangements to be used on pipe end sections.
Figure 18 illustrates, from the side, the use of a pipe length or fitting of which at least
one end has been modified through the inclusion of a weld interface 70 with a filament
arrangement 71. The terminal portion 72 is shown extending from the main body portion
73, as is the electrical contract 74 and optional cover 75. In practice two pipe sections
76, 77 are brought together, and electricity applied to contacts 74. This softens plastic in
the vicinity of a weld interface 70, as well as plastic material at the end of pipe section 76.
This is m~int~ined until an adequate weld is formed.
Figures 15 and 16 illustrate welding elements which are arcuate in configuration. These
segments are intended to be joined together to form a complete loop. Such segments are
typically for use with large diameter pipes where it is impractical to manufacture a single
large loop. These segments 55, 56, may be assembled prior to use, and may make use
of bridging conductor strips to connect termin~tPd filament tracks (e.g. 57-60) to the next
segment in the assembly.
While each segment 55, 56 could comprise its own independent electrical circuit (in
which case filament tracks near each end of the segment would resemble those (37) at the
terminal portion of Figure 11) the illustrated embodiments of Figures 15 and 16 still rely
on the substantially tangential or outwardly angled filament tracks so that the resulting
assembly resembles the embodiments of Figures 8 through 10, or even 12 through 14.
Figure 17 illustrates, in a perspective diagrammatic manner, the embodiment of Figure
10. Here the cross-over (64-65) of some of the filament sets can be clearly seen. It is at
this point that a heat sinking material may be positioned during a welding operation, to
absorb extra heat from increased density of filaments at these particular points.
The terminals (35, 35a, and 36 shown) can be clearly seen~ as are optional terminal
covers 65. These covers also act as heat absorbers and are typically made of the same
material as the ring. These absorb additional heat from the filament as they approach the
terminals and also act as locating members to help maintain the body 66 in the correct
orientation with respect to the pipe ends (not shown).
In the embodiment of Figures 8 through 17, various methods of manufacture may be
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W O 97/01433 PCTnNZ~
employed. In a preferred method of m~nuf~ture the body of thermoplastic material. and
the extending terminal portions, is formed from a suitable technique, such as injection
moulding. Filament tracks will typically be included on any mould or die so that they are
formed during the injection or casting process. It is possible however that the fil~m~n~
5 tracks may be formed after moulding such as by a suitable machining or pressing
method, or that a combination of the various techniques may be relied upon. The
filaments are then laid into these provided tracks, optionally being slightly heated so that
they partially bond to the thermoplastic material so that they do not become loose during
transport of storage. The terminal portions will generally be provided at the same time as
10 the filaments are fitted.
Various other modifications may be made to various embodiments. For instance. a
thermocouple may be incorporated into various embodiments to provide an indication of
the temperature of the welding element. Additional filaments may be included to connect
a thermocouple(s) to an external monitoring device.
15 In other embodiments a pressure sensitive device (eg. a piezo device) may also be
included to provide an indication of pressure being applied to the weld during its
formation. This may be useful where parts being welded are to be forced together during
formation of the weld. Such devices can be made relatively small or thin and can rely on
additional filaments to connect them to external monitoring devices.
20 Another modification may be in the selection of filament material. Materials whose
r~sict~nce increases significantly with temperature may be relied upon as the filaments. If
the characteristics of these material are known, a way exists to limit the maximum
temperature of these filaments when a current passes therethrough. In many instances
this is similar to using nichrome wire for a heating element - at a certain temperature the
25 recict~nce of the nichrome becomes such that a higher current cannot be carried unless the
voltage is also increased. The result of current limiting is also a limitation on the wattage
and therefore heat output and temperature of the filament. Similar principles can be
employed in various embodiments of the present invention - applying different voltages
can be used to control the maximum current carried by the filament set, and thus their
30 heat output and temperature.
The welding fitting is typically made from the same thermoplastic material that is being
welded. Embedded into this welding fitting is a filament wire or wires dependant on the
thickness of the weld area required. The filament wires may be coated either by
extrusion or thin film of the same material that the welding fitting is manufactured from.
35 The thickness of this film can alter according to the heat dispersion required to perform a
weld on a particular object, ie. if, for example, one was welding very thin film
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polyethylene such is present on coated steel pipe, there would be a thicker membrane
covering the fil~m~nt wire/wires so that the thin polyethylene film on the steel pipe did
not get too hot and burn or distort etc.
In practice it is desirable to provide a certain watt~ge of power over a certain area of
5 plastic to get the plastic to a temperature to perform a successful weld. The ideal welding
situation is to have the heat dispersion between two or more wires so that the entire
welding interface is the same temperature, ie the plastic imme~ tely surrounding the
filament wire is the same as the plastic in the middle of the filament wires. When the
filament wires have only a thin film coating the molten plastic at the interface will spread
10 while some of the heat/ener~y dissipates into the member causing a molten mass which
(when a small pressure is applied) becomes one homogenous mass. The fusion is
completed with the two members being welded and the welding fitting still embedded
between them. Preferably the filament wires do not cross and touch in the area of the
actual interface as this usually increases the power requirement to achieve the welding
15 temperature. It can also cause a hot spot where the filament wires touch, although in
some situations this does not overly detract from the weld quality and may in some
situations of filament design be a necessity. For most filament designs however, the
fil~ment wires will run parallel and at no stage touch in the area of the interface.
It is also possible in some instances to make the welding fitting from a very thin
20 membrane itself so that the heat dispersion to perform the weld is obtained from one
single filament element, however it is more likely on the larger welds or welding thicker
members together that there will be two or more fil~m~nt circuits at each interface, even if
the filament element only has one complete circuit.
Typically to perform a weld you apply pressure until the target weld temperature is
25 achieved, then a slight increase in pressure ensures that the members and the welding
fitting have a homogenous amount of plastic.
It is desirable that the same wattage is produced in each of the filament wires, ie. if you
make a fitting using the same wire diameters and same wire material, the filament wires
would ideally need to be the same length. Similarly the gaps between them need to be the
30 same to get the same even heat dispersion across the entire interface. It is possible to
achieve the same resultant even temperature spread by having wires of differing lengths
~ and/or diameters and/or wire types and achieve the same results~ ie. in a circular filament
pattern you could have a smaller diameter wire in the centre of the fitting and a longer,
- larger rli~mt-ter on the outside.
35 If the filament has two or more termination points, it is desirable to have these away from
the weld interface as these points are a potential source of overheating. It is also
_
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desirable to have these termination points covered by material so that any excessive heat
build up is dissipated into the material or some other medium.
The welding fittings may be m~nllf~rtllred in many ways. For example:
1) For pipe "rings" you can mould a plastic fitting with slots in it for the filament
S wires, attach your electrical fittings and then mould a thin coating of material over
the filament wire and a thicker "block" to act as a heat dispersant and to hold the
electrical connectors in place.
2) You can laser cut or engrave the slots for the filament wires into sheet plastic of
the correct thickness. You could then melt thin plastic sheet over the filament
wires to get coverage. The use of coated wire is also a possibility, so that thefitting does need to be coated with the thin plastic sheet. In these types of
embodiments the filaments are virtually at the surface, and for coated wires theactual coated wire will be visible at the surface.
3) For the "straight line" type fittings, you can do the above or have the wires inserted during extrusion etc.
Aspects of the present invention have been described by way of example only and it
should be appreciated that modifications and additions may be made thereto without
departing from the scope thereof as defined in the appended claims.
