Note: Descriptions are shown in the official language in which they were submitted.
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THERMOPLASTIC ELEMENT FOR PROTECTION AGAINST CORROSION IN
THE THERMOFUSION COUPLING OF A THERMOPLASTIC TUBE
The present invention refers to a thermoplastic element
for the protection against corrosion in the thermofused
splicing of a thermoplastic tube to a thermoplastic
connection.
More particularly, the present invention refers to a
corrosion-inhibiting thermoplastic element at a thermofused
splice of a thermoplastic tube consisting of an intermediate
metal layer placed between two thermoplastic layers, with a
thermoplastic connection.
At present, joints between thermoplastic tubes and
connections are performed by means of thermofusion joining,
whereby during a few seconds tube and connection are subject
to a temperature in the range of from 260 to 270 C and after
the elapsing of the heating time both elements are joined by
introducing the male end of one of them into the female
opening of the other, with an adequate interference grade
between their facing superficial layers, and they are fused,
i.e. they are transformed into a single piece through them.
It is highly inadvisable to join tubes bearing a metal
layer to the connections thereof by means of thermofusion, as
such joining would only be accomplished between the external
thermoplastic layer and the connection wall, the intermediate
metal layer edge thus remaining internally uncovered, whereby
water circulating through tubing would produce an oxidising
process with the consequent deterioration of the metal layer,
which would inevitably result in water leaks and/or
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contamination.
On the other hand, even where an abutting supplementary
union could be done between the internal layer of the tube and
an internal cylindrical surface of such connection, a highly
resistant section would not be possible to obtain due to the
reduced thickness of said internal layer, which section could
not absorb the shearing force which causes bending of the
connection wall upon the expansion due to the pressure of
fluid working at high pressure, which on the other hand is
easily absorbed by the tube without any alteration whatsoever
due to the presence of the intermediate metal layer and which
would obviously produce breakage of this joint and the
resulting water-metal contact.
Consequently, connection between tube and any clas.5 of
connection requires from the later to be provided with a
tubular pin which is tightly inserted into said tube end,
around which an external snap-fastener is applied in order to
tighten same around the pin, thus creating an airtight joint
between the internal thermoplastic layer of the tube and said
pin. Due to said tubular pin thickness, a noticeable reduction
of the tubing internal diameter is produced, giving rise to
several drawbacks.
Further, this kind of connection is very expensive, not
only due to the manufacturing cost of the piece itself but
also due to the tools and labour required for the application
thereof.
It is thence the main object of the present invention the
implementation of a termofused splice or joint, under maximum
and total safety conditions, of a thermoplastic tube with a
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thermoplastic connection, by means of a thermoplastic element
which may be incorporated to the tube end through thermofusion
before the thermofusing operation of this end into the
corresponding opening of said connection, providing such
thermoplastic tube with a fully thermoplastic new with no
metal layer, as through it the three layers end covering is
obtained, inhibiting both internal and external contact of the
metal layer edge with the connection and thus with water and
further, a marked increase of the internal layer thickness is
obtained, providing then a larger cross-section at the tube
end, between its internal surface and said metal layer, which
allows for the absorption of said bending stress which is
normally produced at the joint area due to such connection
expansion upon the high pressure operation of tubing.
Another object of the present invention is the provision
of a clear visual or touch indication that the thermoplastic
element has been included and that the connection to be made
will be safe.
Another object of this invention is the application of
said thermoplastic element by means of the same conventional
tooling used in any thermofused joint of a thermoplastic tube
and connection.
Therefore, in accordance with the present invention,
there is provided a protection element against corrosion in
the thermofused splice of a thermoplastic tube which includes
an intermediate metal layer between two thermoplastic layers,
with a thermoplastic connection, characterized in that said
element has substantially the shape of a tubular sleeve fully
premoulded on thermoplastic material, to be applied into a
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socket mouth formed by the expansion of the end of said
thermoplastic tube, said corrosion-protecting element
exhibiting a single internal diameter and two external
diameters which define: an external cylindrical portion having
a rectangular longitudinal section and exhibiting a side wall
abutting against end of thermoplastic tube, and a tubular
projection which diameter is smaller than that of said
external portion, to be introduced into said socket mouth and
having an internal diameter which is substantially identical
to tube internal diameter, said protection element being
attached to socket mouth of said tube by means of thermofusion
between said abutting lateral wall and the edge of both
thermoplastic layers of said tube, and between said tubular
projection and the adjacent portion of the internal layer of
the tube, in a stage previous to the interfusion between tube
end and thermoplastic connection.
In order to facilitate understanding of this invention
and for a better appreciation thereof, the thermoplastic
element and its incorporation to the thermoplastic tube has
been illustrated as follows, according to one of its preferred
embodiments, wherein:
Figure 1 shows a longitudinal cut view R-R of figure 2
and an exploded view of the splicing thermoplastic element and
the end of tube, before attaching one to the other by means of
thermofusion;
Figure 2 is a side elevational view of the splicing
element;
Figure 3 is the same view as in figure 1, showing
interconnection of splicing element and the end of the tube
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once fused;
Figure 4 is a schematic view showing the splicing element
and the tube end applied to the corresponding nozzles of a
thermofusing machine, during prior heating stage of the
5 surfaces through which fusing of both elements is to take
place;
Figure 5 shows a longitudinal section illustrative of
fusion between the splicing element and the tube end,
according to figure 3;
Figure 6 is the same as figure 5, but showing splicing
element after it has been applied and attached by means of
thermofusion to the tube end, and ready to proceed with the
final stage of thermofusion of this tube end to the
thermoplastic connection;
Figure 7 shows behaviour of the element already applied
to the tube end, when it is introduced in order to be heated
into the corresponding nozzle of a second thermofusing
machine, for the end stage of tube to connection thermofusion;
Figure 7' is the same view as in figure 7 once the
introduction of tube with the splicing element into the second
thermofusing machine is completed;
Figure 8 shows the end of the tube with the splicing
element and connection once heated, at the beginning of said
thermofusion final stage;
Figure 8' is the same view as figure 8 once the final
thermofusion stage is completed;
Figure 9 is an illustrative sketch from a practical
example of how the thermofusion between tube end and abutting
splicing element and connection has been accomplished.
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In figure 1 thermoplastic tube A exhibits a wall with two
thermoplastic layers, an external a and an internal a', made
of, for instance, polypropylene or polyethylene, with an
intermediate metal layer a" made of, for example, aluminum
foil adhered to both faces a and a', exhibiting, for example,
a total wall thickness of 2 mm, i.e. 0.7 mm represented by
external layer, 1.0 by internal layer and 0.2 by intermediate
aluminum foil, both faces being provided with an adhesive
cover 0,05 mm thick, all these dimensions being given by way
of example.
Splicing element C has been developed as an injection
pre-moulded fully thermoplastic tubular sleeve, for example,
which diameter is larger that that of the tube itself, so that
in order to be applied at the tube A end a socket mouth e,
which is obtained by expanding end I of said tube A, should be
previously formed.
It is the purpose to attain said expansion of tube end in
a range of from 10% to 20% of the diameter of intermediate
metal layer a" diameter, for all of the tubing diameters, and
up to 15% in the particular case of an aluminum layer
exhibiting the above mentioned dimensions.
This splicing element C which form is substantially that
of a tubular sleeve exhibits only one internal diameter and
two external diameters, which define a cylindrical external
portion c which exhibits a rectangular longitudinal section
which external diameter is the same as that of the expanded
end I of thermoplastic tube A and which exhibits a side wall P
abutting against tube end 2 and a height such that it covers
the three layers of said tube, and a tubular projection c'
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which external diameter slightly larger than the internal
diameter of expanded end I of tube and an internal diameter
which is substantially equal to the internal diameter of tube
A. Interference between said diameters is of from about 0.4 to
0.5 mm.
As regards length of c' dimensioning thereof has been
considered according to a length smaller than that of expanded
end I.
It is to be noted that above mentioned drawings
illustrate said splice element C and a supplementary ring C',
which will be described below, as integral part thereof, not
participating in this application stage of splice element C of
tube A end, it merely remaining incorporated to the latter in
order to be used at the end of the process of thermofusion
between said tube and the connection piece in the manner and
to the end to be explained below.
External portion c of element C exhibits a rear lateral
wall P' which will become tube A new end itself upon
completion of the operation of element C fastening onto said
socket mouth e as shown by Figures 3 and 6.
Such fastening will be accomplished by means of the
direct and simultaneous thermofusion of abutting side wall P
of element C to the joint end 2 of both thermoplastic layers a
and a' and from said tubular projection c' to said internal
thermoplastic layer a', according to the typical thermofusion
technique, by heating on the one hand said abutting side wall
P, external surface 4 of tubular projection c' and its
external edge 4', and on the other hand said joint end 2 of
tube and internal socket e internal layer, then introducing
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said tubular projection c' into socket e until said side wall
P abuts against said joint end 2, all of the above under the
required pressure and interference degree in order to obtain a
firm interfusion between facing surfaces of both elements
(Figs. 4, 5 and 6).
The above described operation may be carried manually
using female t and male t' nozzles provided on both sides of a
first thermofusing machine T-I.
This operation of splice end C heating and subsequently,
its application to the end of tube .A could be carried out
manually, maintaining splice element C applied on female
nozzle t of the thermofusing machine in order to get a maximum
contact between abutting lateral wall P of external portion c
of element C, and the respective seat 8 of this nozzle t, and
of external surface 4 of splicing element C against wall 9 of
female nozzle t and its external edge 4' against the
corresponding back step 9', in order to be sure that all of
the element surface which is to actively act during the
interfusion process with the joint end 2 and internal layer a'
but maintaining the internal face of the projection and the
splice element adequately "cold" in order to avoid collapsing
of piece.
On the other hand, on male nozzle t', internal layer a'
of the wall of expanded end I of tube A tightens laterally on
a corresponding projection 10 thereof, and at the same time
joint end 2 of tube A tightens at its base, obtaining the
heating required for its interfusion with tubular projection
c' and abutting lateral wall P of splice element C.
Subsequently, both are removed from the thermofusing
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machine, in order to be mutually faced and to gradually
introduce element C into mouth socket e of tube end I,
applying said element as if it were a stopper into a bottle,
first forcing entering of tubular projection c' into tube A
internal wall a' according to the established interference
degree, wherein its external edge 4' proceeds at the
superficial portion of the internal layer forming a lip 11
which aids in sealing the joint between both walls until
abutting wall P of splice element reaches the bottom and fuses
against the joint end 2 of the three layers of tube A (Fig.
6).
Thus a firm union by thermofusion is obtained between
element C and tube A end which comprises an abutted joint II
with both thermoplastic layers, and which continues with a pin
joint III between internal layer of tube A and said tubular
projection c' of element C, virtually wedged inside same, as
illustrated by Figure 6, such that behaviour of said element
as an integral part of tube A is assured, with said metal
layer fully enclosed by thermoplastic material.
At the same time, tube end is internally reinforced,
offering a larger annular section between metal layer a" and
tube internal surface at the union sector where bending stress
is to be present upon tubing working at high pressure, due to
the fact that the connection tends to expand, whereas the tube
remains unaffected, because of the contention granted to its
metal layer, as already mentioned.
As may be appreciated from what has been described and
illustrated, incorporation of this splice element introduces
no reduction of tube conduit, as the inner diameter of tubular
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projection c' is substantially equal to tube original
internal diameter, and is fully within the expanded end I
thereof (Fig. 6)
It is clear that by the incorporation of this element,
5 tube A end is conformed as a single layer conventional tube,
which external and internal surfaces end at a thermoplastic
front which comprises all of the wall thickness and,
accordingly, may be thermofused within a connecting piece as
per the usual technique, heating said end and the interior of
10 the corresponding nozzle of the connection and introducing one
into the other with an interference extent between its lateral
surfaces as required for the obtention of a sound welding
between same, without any risk of its intermediate metal layer
being exposed.
According to a preferred embodiment, inclusion within the
scope of this invention has been contemplated of a control
element which upon completion of the final stage of the
thermofusion process between tube end, already bearing
splice element C, and connection piece B, will provide a clear
physical and external indication that said tube end
incorporates said splice element and that this joint is safe,
i.e. there is no risk for water to contact tube metal layer.
Accordingly, and as a supplementary element to the above
arrangement, it has been contemplated the temporary inclusion
at splice C of a supplemental ring C', initially formed as an
integral part of said element C (Figs. 1 and 2), shaped as an
annular piece incorporated as a collar of larger diameter than
said element C and which surrounds same concentrically, with
an appreciable gap between them, they being joined only by a
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very thin intermediate wall 12 as a membrane arranged at the
place where sweeping by the thermofusing machine nozzle is to
take place. Said thin intermediate wall 12 thickness is such
that such sweeping may only take place if the thermofusing
machine provides an adequate thermofusing temperature. Thence,
said auxiliary ring C' acts as a control of the minimum
necessary temperature of the thermofusing machine nozzle.
This auxiliary ring C' has an internal diameter which is
noticeably larger than the external diameter of the expanded
wall of the tube, such as to fulfil a second auxiliary
function, i.e. as a control of splice element C positioning,
as we will see hereinbelow.
According to the above, element C is thermofused at the
tube end as shown and illustrated by Figures 4, 5 and 6,
bearing this auxiliary washer C', which has remained separated
around same, wherein thermofusion between said splice element
and tube is limited to joint end 2 of tube and stop P of this
element C and though this auxiliary ring C' will receive some
heat, indirectly radiated by splice element and its proximity
to the thermofusing machine mouth socket, it is subject to no
stress, as the fusion pressure is exerted only between one and
the other, leaving aside this auxiliary ring, as shown by
Figure 4 schematics, wherein respective nozzles t and t' of
the first thermofusing machine T-I employed during this
preparatory stage for the heating of the parts which are to be
joined: end I of tube A and element C.
Thus, element C is applied to end of tube bearing said
auxiliary ring C' around same, as illustrated by Figure 6,
such that when at the stage of heating tube end, upon the
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introduction thereof into nozzle t" of the second thermofusing
machine T-II (Figure 7), at the final stage of the process,
this auxiliary ring C' abutts against mouth 13' of end 13
thereof and intermediate wall 12 which joins same to splice C
yields, provided temperature of nozzle t" of thermofusing
machine T-II is the adequate one, it ruptures and thus freely
slides on the tube easily and, pushed by this end of said
nozzle t", is finally at the distance of tube A end
corresponding to penetration length thereof in the latter
(Fig. 7'), all in such a way that, upon retrieving tube from
this nozzle t" of thermofusing machine, this auxiliary ring C'
is applied around its expanded end I as a "control", showing
that same bears element C, which is schematically illustrated
by Figure 8 at the beginning of tube penetration into female
portion b of connection B.
It is clear that this auxiliary ring C' is an accessory
means that protects operator who may have omitted application
of splice element according to the invention, without
participating thence in the formation of the new thermoplastic
end which seals the union between external and internal layers
caps, over the edge of the aluminium cap.
When carrying out this final stage of thermofusion
introducing end of tube A into female part b of connection B,
auxiliary ring C' follows (Fig. 8) until it is virtually
applied on socket 14' of female part b, gradually tightening
around said tube wall due to the natural, albeit reduced,
expansion produced under the compression stress between both
elements which is required by its forced insertion and also to
the natural outwards creepage of both facing superficial
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layers 15-16 on the side of element C and tube A and 17 by
connection B and as a consequence thereof this auxiliary ring
C' tightens over the material which tends to flow forming the
classic external curl 18 which it contains, all of which may
be appreciated on Figures 8 and 8".
Lastly, reference must be made to the design adopted for
this auxiliary ring C', depicted by figures 1 and 2, with
which it has been the intention to reduce thickness and
amplitude of intermediate wall 12 which joins same to element
C body, providing at the same time a configuration such that
it contributes in maintaining it away from heat originated
from the thermofusing machine at the end of the tube (Fig. 4),
thus reducing any possibility of the degradation thereof.
On the other side, and in order to assure that this
auxiliary ring C' is clearly and easily seen, around union,
between tube A and connection B, once thermofusion is
completed between both elements thus assuring that the
coupling element has been applied at the end of the tube, not
only has it been provided with an ample diameter, but it has
further been equipped with several cylindrical projections 19
which protrude from the external periphery thereof underlining
the presence of this washer, providing an easy tactile
detection in those cases in which such detection is not
visually possible. Also, it may be provided with colours
contrasting that of the thermoplastic tube, so as to
facilitate its visual detection.
Regarding the above mentioned final stage of the
thermofusion process between connection B and new end of tube
now formed by element C, it has been foreseen the
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establishment of an axial abutting joint, again by
thermofusion, between element and internal step 20' of
connection wall 20, incorporating between them melted material
which flows into the interior of the connection as an effect
of the interfusion of facing lateral surfaces of the tube wall
with splice element included and the connection wall, as
schematically depicted by Figure 8' as an attempt to contain
this creepage and thus increase contact pressure between said
surfaces, reducing size of typical curl 21 formed inside the
connection so it does not protrude within the tubing conduit.
In order to better understand how it is done in the
practice, the referred thermofusion union between the wall of
the tube end, including element and connection wall, it is
included as Figure 9 depicts a reproduction of a sketch from a
digital image obtained from a partial longitudinal section of
a sector of said union, where it can be seen the deformation
and creepage of surfaces of either element.which are mutually
fused, establishing a perfect sealing between them, with the
intermediate metal layer of the tube being isolated from any
internal or external contact.
