Note: Descriptions are shown in the official language in which they were submitted.
Applicant: J. Pierre Pottier
For: Welding Device for Thermoplastics
FIELD OF INVENTION
This invention relates to a welding device for
thermoplastics, and more particularly to such a welding
device which extrudes the molten plastic without conventional
extruder mechanisms by melting the forward end of a welding
rod and using the unmelted following portion of the rod to
push out the melted portion.
BACKGROUND OF INVENTION
Conventional thermoplastic welding torches heat the weld
surface and the underside of the welding rod as it is fed
onto the weld surface. The melted side of the rod adheres to
the heated weld surface and becomes anchored so that as the
welding torch is moved along the weld surface more rod is drawn
to ma~e a continuous bead. This approach does not heat the
rod thoroughly and so cold joints can occur. In addition, if
the weld requires a bead greater than afforded by the rod, a
number of passes must be made so that a number of rods are
laid down to create a sufficiently large bead to fill the weld.
Extrusion welders do not use heated rods at the weld.
Rather, pellets, rods or any other form of plastic is heated
and then extruded using a heavy duty motor and stainless
steel or chromium plated drive screw to pressurize and
extrude the molten plastic. These devices, although portable,
are e~tremely heavy due to the powerful screw drive motor
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required and create a great strain on the operator due to the
weight and the strong torquing forces generated which constantly
twist the device in the hands of the operator and increase
his fatigue. Generally, frequent rest stops are needed so
that the extruder is used only a few minutes at a time. These
devices are also large and hard to maneuver in tight places
such as inside and outside corner joints to be welded. Typically
two nozzles are used, one to provide hot air to preheat the
surface to be welded and one to deliver the extruded plastic.
SUMMARY OF INVENTION
It is therefore an object of this invention to provide
an improved portable welding device for thermoplastics.
It is a further object of this invention to provide such
a welding device which is lighter in weight, simpler and less
expensive.
It is a further object of this invention to provide such
a welding device which is more maneuverable, requires less
power and is less fatiguing to the operator.
It is a further object of this invention to provide such
a welding device which produces an extrusion-like weld
without the extruder bulk, weight, expense and complexity.
The invention results from the realization that a truly
effective welder for thermoplastic material can be made by
melting a continuously fed rod to create the welding bead
material and using the incoming unmelted portion of the rod
to push out the melted portion of the rod, and the further
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realization that the same heated gas used to preheat the weld
surface can be used to melt the rod.
This invention features a welding device for
thermoplastics including a chamber for receiving a plastic
welding rod at its inlet and issuing molten plastic at its
outlet. There are means for heating the rod in the chamber
to the melting point and means for feeding the plastic rod
into the chamber to drive out melted plastic rod and replace
it with more rod to be melted.
In a preferred embodiment there are means for preheating
the surface to be welded. The chamber outlet may include a
foot with a first hole in it for issuing the molten plastic.
The foot may include a shoe with an aperture aligned with the
hole for issuing the molten plastic. The shoe may be formed
of a self-lubricating material such as polytetrafluorethylene.
The chamber closely, slidingly receives the rod and the means
for heating ~ay include a heat exchanger surface on the
outside of the chamber. The means for heating further
includes a heating element which may be mounted directly on
the chamber or may be remote from the chamber and used in
conjunction with a source of a nonflammable gas, e.g. air or
inert gases, for moving the gas over the heating element
and then over the heat exchanger at the chamber. The means
for preheating a surface to be welded may include a port
proximate the outlet for issuing the heated gas which is
received after it has contacted the heat exchanger on the
chamber. There is a housing surrounding the chamber and the
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heat exchanger surface includes at least one channel
extending between the housing and the chamber. The gas used
to transfer the heat may be air and the welding rod may be
solid or hollow.
DISCLOSURE OF PREFERRED EMBODIMENT
Other objects, features and advantages will occur to
those skilled in the art from the following description of a
preferred embodiment and the accompanying drawings, in which:
Fig. 1 is a cross-sectional view of a welding device
for thermoplastics welder according to this invention; and
Fig. 2 is an enlarged detail view of the welding rod
drive mechanism of Fig. 1.
This invention may be accomplished with a welding device
for thermoplastics having a chamber for receiving a 3/16-inch
plastic welding rod made of such material as polyethylene,
polypropylene, hybrid polyolefins, or Kynar as well as most
other thermoplastics. The rod is received at the inlet end
of the chamber and after heating within the chamber is issued
as molten plastic at the outlet of the chamber. The chamber
may be heated directly by an electrical element or similar
device or may be heated indirectly, for example by passing
over it heated gas (air or inert gas). The rod is fed into
the chamber to drive out melted plastic rod, and replace it
with more rod to be melted, by a drive wheel driven at low
speed, e.g. 6 RPM, by a motor such as a Hurst Mfg.
~T 2602-013. The heater may be a 1000 watt cartridge heater
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through whlch air or inert gas (nitrogen) at approximately 3
psi is driven at the rate of about 2 cubic feet per minute.
A preheater is used to warm the surface to be welded. The
preheater may be pressurized air driven through the heater
and first used to heat the chamber to melt the welding rod.
The chamber outlet may include a foot with a hole in it
for issuing the molten plastic that creates the welding bead.
The foot may include a shoe having an aperture that is
aligned with the hole for issuing the molten plastic. The
shoe may be fitted with a sole made of a self-lubricat~ing
material such as Teflon, or a polytetrafluorethylene
composition. The sole comes in several configurations. Thc
chamber, which may be a steel tube, closely, slidingly
receives the rod. The chamber may have a heat exchanger on
its outside surface for transferring the heat from the heated
moving air to the chamber to melt the welding rod. That same
air may be expressed through a port proximate the chamber
outlet to preheat the surface to be welded.
The heat exchanger on the chamber may include a single
channel or a number of channels through which the heated air
flows. The heat exchanger may include a helical channel or a
helical channel plus an annular channel, or it may include
vertical, inclined or various other arrangements of channels
or fins just so long as there is enough time for an amount of
heat sufficient to melt the welding rod to be transferred
from the heated air to the chamber.
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There is shown in Fig. 1 a welding device for
thermoplastics according to this invention including a hollow
stainless steel tubing 12 which holds an interchangeable
electrical heating element or cartridge 14 that engages with
electrical socket 16 in handle 18. Typically 110/120 volt 60
cycle or 220-240 volt 50 cycles power is fed on cable 20
through a non-corrosive vinyl hose 22, through the hollow
area 24 of handle 18, through the heating element 14, and
thence through housing 12 to heat exchanger 26 mounted on
chamber 28. Pressurized air or nitrogen is delivered through
hose 22. Air heated by heating element 14 transfers heat
through heat exchanger 26 to chamber 28 containing welding
rod 30, which is solid up to approximately point 32 ~n~
melted beyond that. Heat exchanger 26 has a generally
tapered or conical shape and contains a helical channel 34
through it as well as an annular channel 36 of decreasing
radius between it and the wall of housing 12. Heat exchanger
26 need not be tapered and need not provide annular chamber
36: it may be expanded to closely contact the walls of
housing 12 so that a single helical channel is provided.
Alternatively, heat exchanger 26 can be formed wit;n one or
more vertical or inclined channels.
After the air passes through heat exchanger 26 to melt
the rod in chamber 28, that heated air passes out of preheat
port 40 in foot 42. Foot 42 may include a stainless steel
shoe holder 44 and a Teflon shoe 46. Preheat port 40 is
formed by an aperture 48 in shoe 46 which mates with hole 50
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in shoe holder 44. The outlet end 52 of chamber 28 passes
through shoe holder 44 and shoe ~6 to provide the molten
plastic in a bead right at the joint to be welded. The
molten plastic 54 below point 32 is forced out of chamber 28
by means of rod 30 , which is solid above point 31, and which
is driven by drive mechanism 60. Mechanism 60 sits atop
support plate 62 mounted by collar 64 on housing 12 at one
end and at the other end is mounted by standoff 66 which
rises from the curved elbow area of housing 12 and supports a
second, forward handle 68. This handle is adjustable for
right or left-handed use.
Drive mechanism 60 include!a drive wheel 70 mounted on
shaft 72 driven by 110/120 volt low-speed electric motor 74.
Shaft 72 is supported in bearing block 76. The drive
mechanism also includes a spring loaded idler wheel 78, Fig.
2, which may have a shallow groove for aligning rod 30 and
providing a pinching action against which the friction
surface 80 of drive wheel 70 can act. Motor 74 is driven
slowly at approximately 6 RPM to feed rod 30 downwardly
through chamber 28 at a rate that permits the rod to be
melted in the lower portion of chamber 28 and pushed out by
the constantly delivered unmelted portion of rod 30 being
driven down by drive wheel 70. Motor 74 is interconnected by
leads 86 to electrical terminals 88 energized from cable 20
to drive motor 74 and electric heating element 14.
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Although specific features of the invention are shown in
some drawings and not others, this is for convenience only as
each feature may be combined with any or all of the other
features in accordance with the invention.
Other embodiments will occur to those skilled in the art
and are within the following claims:
What is claimed is:
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