U.S. patent number RE32,103 [Application Number 06/615,378] was granted by the patent office on 1986-04-01 for welding of plastics material.
This patent grant is currently assigned to Gundle Holdings Limited. Invention is credited to Friedrich Struve.
United States Patent |
RE32,103 |
Struve |
April 1, 1986 |
Welding of plastics material
Abstract
Welding surfaces of thermoplastics material together by
depositing a continuous layer of molten thermoplastic welding
material over adjacent areas of the surfaces to be joined, the
deposition of at least part of the molten welding material being
effected with a smearing action in which the material is subjected
to shear forces acting across the surfaces, and allowing the
deposited material to solidify.
Inventors: |
Struve; Friedrich (Kingwood,
TX) |
Assignee: |
Gundle Holdings Limited
(Edenvale, ZA)
|
Family
ID: |
25575261 |
Appl.
No.: |
06/615,378 |
Filed: |
May 30, 1984 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
287978 |
Jul 29, 1981 |
04377429 |
Mar 22, 1983 |
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Foreign Application Priority Data
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Mar 13, 1981 [ZA] |
|
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81/1667 |
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Current U.S.
Class: |
156/153; 156/157;
156/244.11; 156/244.23; 156/273.3; 156/304.1; 156/322; 156/380.9;
156/499; 156/500; 156/509; 156/535; 156/546; 156/574; 156/575;
156/578 |
Current CPC
Class: |
B29C
65/40 (20130101); B29C 66/022 (20130101); B29C
66/1122 (20130101); B29C 66/43 (20130101); B29C
66/836 (20130101); B29C 66/0242 (20130101); B29C
66/71 (20130101); Y10T 156/1798 (20150115); Y10T
156/1788 (20150115); Y10T 156/14 (20150115); Y10T
156/179 (20150115); Y10T 156/172 (20150115); B29C
66/71 (20130101); B29K 2023/06 (20130101) |
Current International
Class: |
B29C
65/00 (20060101); B29C 65/40 (20060101); B29C
027/02 (); B65H 069/08 () |
Field of
Search: |
;156/73.1,73.4,73.5,82,153,157,244.11,244.23,273.3,304.1,380.9,499,500,502,508 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wityshyn; Michael
Attorney, Agent or Firm: Arnold, White & Durkee
Claims
Having now particularly described and ascertained my said invention
and in what manner same is to be performed, I declare that what I
claim is:
1. A method of welding together surfaces of thermoplastic material
comprising:
(a) depositing a continuous layer of molten thermoplastic welding
material over adjacent areas of the surfaces to be welded
together;
(b) substantially simultaneously with the deposition of the welding
material, circularly smearing a boundary layer of the welding
material which is in contact with the surfaces to be welded onto
the adjacent areas of the surfaces so that the welding material
being smeared is subjected to shear forces transverse to the
direction of deposition of the layer of welding material; and
(c) allowing the layer of deposited thermoplastic welding material
to solidify.
2. A method as claimed in claim 1 in which the adjacent areas of
the surfaces are preheated prior to the deposition of the molten
welding material.
3. A method as claimed in claim 2 in which the preheating of the
adjacent areas of the surfaces to be welded is effected by at least
one of radiation and conduction heating.
4. A method as claimed in claim 2 in which the adjacent areas of
the surfaces to be welded are superficially damaged during at least
one of preheating of the adjacent areas of the surfaces to be
welded and deposition of the welding material.
5. A method as claimed in claim 1 in which the molten welding
material is continuously mixed immediately prior to deposition.
6. A method as claimed in claim 1 in which the surfaces are formed
by a pair of overlapping sheets of thermoplastic material.
7. A method as claimed in claim 1 in which the adjacent areas of
the surfaces include the areas adjacent to an edge of one of the
surfaces.
8. An apparatus for the continuous welding together of surfaces of
thermoplastic material, comprising:
means for depositing a continuous layer of molten thermoplastic
welding material onto adjacent areas of the surfaces; and, smearing
means for circularly smearing a boundary layer of the welding
material which is in contact with the surfaces to be welded onto
the adjacent areas of the surfaces during the deposition of the
welding material, so that the welding material being smeared is
subjected to shear forces transverse to the direction of deposition
of the layer of welding material.
9. An apparatus as claimed in claim 8 which includes means for
superficially damaging the adjacent areas of the surfaces during
deposition of the molten material.
10. An apparatus as claimed in claim 9 in which said damaging means
is integral with the smearing means.
11. An apparatus as claimed in claim 8 which includes a delivery
tube for the welding material and which terminates in a nozzle for
depositing the welding material, and the smearing means comprises
at least one rotatable member terminating in a smearing surface
within the nozzle.
12. An apparatus as claimed in claim 8 which includes a rotatable
delivery tube for the welding material, the delivery tube
terminating in a transverse annular smearing surface within a
nozzle.
13. An apparatus as claimed in either of claims 11 or 12 in which
the position of the smearing surface is adjustable with respect to
the surfaces being welded.
14. An apparatus as claimed in claim 11 in which the smearing means
comprises two adjacent rotatable members each terminating in a
smearing surface.
15. An apparatus as claimed in claim 8 which comprises a delivery
tube and nozzle including means for causing the molten material to
swirl transversely with respect to the surfaces being welded during
deposition. .Iadd.
16. A method of welding together surfaces of thermoplastic material
comprising:
(a) depositing a continuous layer of molten thermoplastic welding
material on adjacent areas of the surfaces to be welded
together;
(b) substantially simultaneously with the deposition of the welding
material, smearing a boundary layer of the welding material which
is in contact with the surfaces to be welded onto the adjacent
areas of the surfaces so that the welding material being smeared is
subjected to shear forces transverse to the direction of deposition
of the layer of welding material; and
(c) allowing the layer of deposited thermoplastic welding material
to solidify. .Iaddend. .Iadd.17. A method as claimed in claim 16 in
which the adjacent areas of the surfaces are preheated prior to the
deposition of the molten welding material. .Iaddend. .Iadd.18. A
method as claimed in claim 17 in which the preheating of the
adjacent areas of the surfaces to be welded is effected by at least
one of radiation and conduction heating. .Iaddend. .Iadd.19. A
method as claimed in claim 17 in which the adjacent areas of the
surfaces to be welded are superficially damaged during at least one
of preheating of the adjacent areas of the surfaces to be
welded
and deposition of the welding material. .Iaddend. .Iadd.20. A
method as claimed in claim 17 in which the molten welding material
is continuously mixed immediately prior to deposition. .Iaddend.
.Iadd.21. A method as claimed in claim 17 in which the surfaces are
formed by a pair of overlapping sheets of thermoplastic material.
.Iaddend. .Iadd.22. A method as claimed in claim 17 in which the
adjacent areas of the surfaces include the areas adjacent to an
edge of one of the surfaces. .Iaddend. .Iadd.23. An apparatus for
the continuous welding together of surfaces of thermoplastic
material comprising:
means for depositing a continuous layer of molten thermoplastic
welding material onto adjacent areas of the surfaces; and, smearing
means for smearing a boundary layer of the welding material which
is in contact with the surfaces to be welded onto the adjacent
areas of the surfaces during the deposition of the welding
material, so that the welding material being smeared is subjected
to shear forces transverse to the direction of deposition of the
layer of welding material. .Iaddend. .Iadd.24. An apparatus as
claimed in claim 23 which includes means for superficially damaging
the adjacent areas of the surfaces during deposition of the molten
material. .Iaddend. .Iadd.25. An apparatus as claimed in claim 24
in which said damaging means is integral with the smearing
means.
.Iaddend. .Iadd.26. An apparatus as claimed in claim 23 which
includes a delivery tube for the welding material and which
terminates in a nozzle for depositing the welding material.
.Iaddend. .Iadd.27. An apparatus as claimed in claim 23 which
includes a rotatable delivery tube for the welding material, the
delivery tube terminating in a transverse annular smearing surface
within a nozzle. .Iaddend. .Iadd.28. An apparatus as claimed in
claim 27 in which the position of the smearing surface is
adjustable with respect to the surface being welded. .Iaddend.
.Iadd.29. An apparatus as claimed in claim 23 which comprises a
delivery tube and nozzle including means for causing the molten
material to swirl transversely with respect to the surfaces being
welded during deposition. .Iaddend. .Iadd.30. A method of welding
together surfaces of thermoplastic material comprising:
(a) depositing a continuous layer of molten thermoplastic welding
material over adjacent areas of the surfaces to be welded
together;
(b) substantially simultaneously with the deposition of the welding
material, smearing a boundary layer of the welding material which
is in contact with the surfaces to be welded onto the adjacent
areas of the surfaces so that the welding material being smeared is
subjected to shear forces in a direction other than the direction
of deposition of the layer of welding material; and
(c) allowing the layer of deposited thermoplastic welding material
to
solidify. .Iaddend. .Iadd.31. A method as claimed in claim 30 in
which the adjacent areas of the surfaces are preheated prior to the
deposition of the molten welding material. .Iaddend. .Iadd.32. A
method as claimed in claim 31 in which the preheating of the
adjacent areas of the surfaces to be welded is effected by at least
one of radiation and conduction heating. .Iaddend. .Iadd.33. A
method as claimed in claim 31 in which the adjacent areas of the
surfaces to be welded are superficially damaged during at least one
of preheating of the adjacent areas of the surfaces to be welded
and deposition of the welding material. .Iaddend. .Iadd.34. A
method as claimed in claim 30 in which the molten welding material
is continuously mixed immediately prior to deposition. .Iaddend.
.Iadd.35. A method as claimed in claim 30 in which the surfaces are
formed by a pair of overlapping sheets of thermoplastic material.
.Iaddend. .Iadd.36. A method as claimed in claim 30 in which the
adjacent areas of the surfaces include
the areas adjacent to an edge of one of the surfaces. .Iaddend.
.Iadd.37. An apparatus for the continuous welding together of
surfaces of thermoplastic material, comprising:
means for depositing a continuous layer of molten thermoplastic
welding material onto adjacent areas of the surfaces; and, smearing
means for smearing a boundary layer of the welding material which
is in contact with the surfaces to be welded onto the adjacent
areas of the surfaces during the deposition of the welding
material, so that the welding material being smeared is subjected
to shear forces in a direction other than the direction of
deposition of the layer of welding material. .Iaddend. .Iadd.38. An
apparatus as claimed in claim 37 which includes means for
superficially damaging the adjacent areas of the surfaces during
deposition of the molten material. .Iaddend. .Iadd.39. An apparatus
as claimed in claim 38 in which said damaging means is integral
with the smearing means. .Iaddend. .Iadd.40. An apparatus as
claimed in claim 37 which includes a delivery tube for the welding
material and which terminates in a nozzle for depositing the
welding material. .Iaddend. .Iadd.41. An apparatus as claimed in
claim 40 in which the smearing means comprises two adjacent
rotatable members each terminating in a smearing surface. .Iaddend.
.Iadd.42. An apparatus as claimed in claim 37 which includes a
rotatable delivery tube for the welding material, the delivery tube
terminating in a transverse annular smearing surface within a
nozzle.
.Iaddend. .Iadd.43. An apparatus as claimed in claim 37 which
comprises a delivery tube and nozzle including means for causing
the molten material to swirl transversely with respect to the
surfaces being welded during deposition..Iaddend.
Description
This invention relates to the welding of thermoplastic materials
and particularly, but not exclusively, to the welding of
thermoplastic sheeting.
In this specification the invention is described with particular
reference to the welding of thermoplastic sheet material. This
description should not, however, be considered as a limitation on
the scope of the invention or its application.
One known method of welding sheets of plastic material together
comprises overlapping the sheets and covering the joint with a
molten thermoplastic extrudate. When the extrudate solidifies it
attaches to each sheet and effectively bridges the joint in a
sealed manner. Generally the plastic sheet is preheated immediately
prior to contact with the extrudate as this enables an extrudate of
a lower temperature to be used and provides improved weld
characteristics. The preheating is generally done by either hot air
or by radiation from a source such as one or more halogen
lamps.
A disadvantage of the use of hot air or a radiant heat source to
provide the heat required is that they are not easily controlled,
that is, the degree of preheating may vary from place to place with
a resultant change in the strength or other characteristics of the
weld. For example, a puff of wind could momentarily partially
deflect a hot air blast and result in substantially no preheating
at all at that particular location.
Although the above method works relatively well on plastic
materials such as polyvinyl chloride (P.V.C.) considerable
difficulty has been experienced in the welding of polythene for
example. Thus, so-called "peel tests" carried out at elevated
temperatures on polythene sheeting which has been welded indicate
that the extrudate may simply peel off the polythene substrate as
proper welding often does not take place. Peel tests comprise
subjecting the weld to controlled peeling forces (as opposed to
shearing forces) and these tests carried out at normal ambient
temperatures frequently do not demonstrate that proper fusion has
not taken place.
The inventor of this invention is also the inventor of the
invention of South African Patent Application No. 81/1427. That
invention relates to the heating by conduction of, and the damaging
of, the thermoplastic surfaces prior to the deposition of the
molten material.
It has been found that although the aforementioned invention works
well, in some applications it has certain disadvantages of a
practical nature.
An object of this invention is to provide a method and apparatus
for the improved welding of thermoplastic material.
According to the invention a method of welding together surfaces of
thermoplastic material comprises:
(a) depositing a continuous layer of molten thermoplastic welding
material over adjacent areas of the surfaces to be joined, the
deposition of at least part of the molten welding material being
effected with a smearing action in which the material is subjected
to shear forces acting across the surfaces to be joined; and,
(b) allowing the deposited material to solidify.
Further according to the invention the adjacent areas of the
surfaces may be preheated prior to the deposition of the molten
welding material; the preheating is provided by radiation or
conduction or both and the adjacent areas may be superficially
damaged during preheating or during deposition of the welding
material or both.
Still further according to the invention the surfaces are formed by
a pair of overlapping sheets of thermoplastic material, and the
adjacent areas of the surfaces are the areas adjacent to an edge or
one of the surfaces or those areas as well as areas between the two
sheets and adjacent to the edge.
Further according to the invention the molten material is
continuously mixed immediately prior to deposition.
The invention also provides an apparatus for the continuous welding
of surfaces of thermoplastic material comprising:
means for depositing a continuous layer of molten thermoplastic
welding material onto adjacent areas of the surfaces; and,
smearing means for subjecting the material to a smearing action
relative to the surfaces during deposition.
Further according to the invention the apparatus includes means for
superficially damaging the surfaces during deposition of the molten
material, and said damaging means is integral with the smearing
members.
According to a first aspect of the invention the apparatus includes
a delivery tube terminating in a nozzle for the welding material
and the smearing means comprises at least one rotatable member
terminating in a smearing surface within the nozzle.
According to a second aspect of the invention the apparatus
includes a rotatable delivery tube for the welding material, the
delivery tube terminating in a transverse annular smearing surface
within a nozzle.
Further according to the first and second aspects of the invention
the position of the smearing surfaces is adjustable with respect to
the surfaces being welded and the smearing surfaces include
projections for superficially damaging the surfaces during use.
According to a third aspect of the invention the apparatus
comprises a delivery tube and nozzle including means for causing
the molten material to swirl transversely with respect of the
surfaces being welded during deposition.
Three embodiments of the invention, described by way of example
only, follow with the reference to the accompanying drawings in
which:
FIG. 1 is a sectional elevation of a first embodiment of welding
apparatus according to the invention;
FIG. 2 is a sectional elevation of a second embodiment of welding
apparatus according to the invention;
FIG. 3 is a sectional elevation of the delivery tube of a third
embodiment according to the invention, and
FIG. 4 is a sectional elevation of the shearing surfaces of a
fourth embodiment.
In the first embodiment of the invention as shown by FIG. 1, an
apparatus 1 for use in the welding of overlapping sheets 2 of
thermoplastic material such as polythene, for example, comprises an
extruder indicated generally by numeral 3. This extruder 3 includes
a barrel portion 4 which tapers down at its lower end 5 via a
conically-shaped shoulder 6 into an elongated delivery tube 7 which
is concentric therewith.
Within the barrel 4 is a screw-feeder 8 which is adapted to force
molten thermoplastic welding material 9 through the delivery tube
7. Integral with this feeder 8 and at its lower end 10, is a
rotatable member 11 of circular cross-section. This rotatable
member 11 is concentric with the screw-feeder 8 and extends down
the centre of the delivery tube to provide an annular passage 12
for the molten welding material between it and the inner wall of
the delivery tube.
At the lower end of the delivery tube 7 there is a nozzle which
enables the molten welding material to escape in a direction
substantially transverse to the axis of the delivery tube. This
nozzle is formed by making the trailing edge 13 of the delivery
tube somewhat shorter than the leading edge 14.
The rotating member 11 terminates in a circular smearing surface 15
at a position midway between the leading and trailing edges of the
delivery tube.
Along the major part of its length the delivery tube 7 is encased
in an insulating sheath 16 of suitable heat resisting material as
for example, that sold under the trade name "Teflon". At the
trailing edge 13 of the delivery tube 7 the sheath 16 extends
rearwardly to form a pair of guides 17 which bridge the molten
material 28 extruded from the nozzle and support the apparatus on
the sheets 2 being welded.
Forwardly of the leading edge 14 of the delivery tube 7 is a
preheating device 18 for preheating the sheet material prior to
welding as is well known in the art.
In use a pair of sheets of thermoplastic material, such as
polythene for example, are overlapped by a small amount and the
welding apparatus 1 is passed centrally along the overlapping edge
of the uppermost sheet. As the apparatus moves along this edge, the
areas of the sheet surfaces immediately adjacent the edge are
preheated to just above the melting point of the thermoplastic
material by the heating device 18. Immediately after preheating a
layer of molten thermoplastic material is deposited onto these
areas and over the aforementioned edge by the extruder.
From the drawing it will be appreciated that the screw-feeder 8 of
the extruder 3 forces the molten thermoplastic welding material
down through the delivery tube 7. As the material passes down this
tube it is constantly mixed by the rotatable member 11 so that
there is substantially no temperature gradient between the inner
part of the mass of molten material and that part of the material
immediately adjacent the delivery tube wall. This ensures that a
relatively cool layer of molten material is not deposited
immediately onto the sheet material as is the case with known
machines.
As the molten material is extruded from the delivery tube 7 a large
portion of it is subjected to the shearing forces caused by the
rotating smearing surface 15. In this way some of the material is
smeared onto the surfaces of the sheets and in all directions
parallel thereto. It has been found that this smearing action
provides a particularly good bond between the welding material 28
and the material being welded.
In a second embodiment of the invention as shown in FIG. 2. the
apparatus has a hollow delivery tube 21 which rotates about its
axis and terminates in a flat annular smearing surface 23 having
projections 24 thereon.
The rotatable delivery tube 21 is encased in an insulating sheath
of the same general type as that described in the first embodiment.
This sheath however forms both the leading edge of the apparatus as
well as the guide 25 at the rear thereof.
The apparatus of this embodiment is used in the same manner as that
of the first embodiment and as it moves along the upper edge of the
sheets of material 26 to be welded, molten thermoplastic welding
material passes down the tube which in turn rotates about its axis.
When the welding material is emitted from the delivery tube it
passes the smearing surfaces 23 and is thus smeared across the
adjacent preheated areas of the sheets which are damaged by the
projections 24.
A third embodiment is shown in FIG. 3 of the drawings. In this
embodiment there are no rotating parts but the internal
configuration of the delivery tube 29 includes means in the form of
helical guides 27 which act on the molten material and provide it
with a swirling action as it passes therethrough.
Because of this swirling motion the material is again smeared
across the surfaces of the sheets being welded as it is emitted
from the nozzle at the end of the delivery tube.
A fourth embodiment of the invention is shown in FIG. 4 and is
similar to the first embodiment. Instead of a single shearing
surface, two adjacent rotating shearing surfaces 30 and 31 are
provided, the one 31 being slightly lower than the other 30. This
embodiment is intended to cater for the side action where
relatively thick plastics sheets 32 are being welded together.
As indicated each of the surfaces 30 and 31 includes projection 33
for damaging the thermoplastic sheets.
Although the use of the apparatus of the above embodiment has been
described in the welding of the upper surfaces only of the sheet
material, it will readily be appreciated that welding material
could easily be deposited simultaneously between the two sheets
utilising an apparatus made in accordance with the invention.
Furthermore, it is envisaged that where the apparatus incorporates
a smearing surface the distance between this surface and surfaces
being welded could be adjustable so as to either decrease or
increase the smearing and shearing action. The surfaces could also
be on a rotatable member driven independently of the extruder of
the apparatus.
* * * * *