Welding tape has since been used
for a number of diverse applications including welding two plastic pallets
together to make one very large pallet and welding a sealed annular tank
of a wet and dry cleaner for Hoover.
The resultant weld is a very
secure load bearing weld in the true sense of the word, not just a join.
Long lengths can be welded together which is not the always practical with
other alternative methods of Plastic Welding.
The foregoing
information is given as an indication of the potential for the product,
there are unlimited possibilities for the use of welding tape in other
applications.
The capital cost of the equipment to apply the
welding tape can be quite small thus making the use of the product very
cost effective.
Application
Welding tape is used to obtain a strong,
homogeneous welded joint between thermoplastic components. It is ideal for
bonding injection moulded parts, especially where long joint faces are
involved.The strength and integrity of the resulting joint is far superior
to that obtained by adhesives or other means. The thickness of each
component can be as low as 1.5 to 2.0 mm with no deterioration of the
outer surfaces of the joint.
The product has been successfully
employed in a variety of commercial applications ranging from the welding
together of dinghy hull/ deck sections to the large scale fabrication of
automotive bumpers.
The product has been used in the white goods
market by a household name manufacturer to obtain a circular waterproof
joint in the reservoir section of a wet and dry cleaner and has been
utilised in a variety of other applications, such as the assembly of Hi-Fi
speaker enclosures.
The product is exported to a number of
countries and can be particularly useful in making short run design stage
components were the cost of injection moulds would possibly make the
initial trials otherwise
impractical.
Construction
Welding Tape is
manufactured as a flat tubular braid, from metallic conductive wire and
thermoplastic monofilament.
The precise mix of these constituent
components depends on the actual welding application and the width of the
tape selected, to suit the components being welded. Normally the
monofilament will be made from the same material as the items to be
welded.
Widths from 4mm to 12mm are produced, the choice being
dependent upon the jointing surface. The tape is supplied as continuous
reels or pre-cut lengths as desired with 250 mts being the minimum
quantity.
Methods of
Application
To obtain the most effective results, the
design of the mating joint faces should be specifically intended to
accommodate the welding tape and therefore the method of jointing should
be considered early in the design process.
An appropriate length of
welding tape is laid along the joint face, sandwiched securely between the
components to be welded, and held under mechanical pressure in a suitable
jig or by clamping. During assembly the tape may be temporarily held in
position by ultrasonic welding, spot welding with a hot iron or stapled.
Alternatively, the joint may be designed so that the tape locates without
any other means of fixing.
The design of the welding jig, including
the degree of automation, will be dependent on the production run (or cost
constraint) requirements. The device must provide a uniform pressure over
the whole joint area during welding. Electrical connections to the tape
must be adjacent to the mouldings and there should be no gaps. Connectors
must be self supporting, to avoid the tape sliding out of the joint area
during welding.
The ends of the tape are then connected across a
low voltage, high current electricity supply, using heavy duty spring
loaded clamps or a similar arrangement. For safety and practical reasons,
the applied voltage will be as low as 8 to 30 volts, provided by a
suitable transformer. When the primary of the transformer is connected to
a single phase AC thyristor power controller using Phase Angle firing
mode, the power supplied to the Weldind Tape, connected to the secondary
of the tansformer, can be adjusted to suit the application.
Where a
circumferential weld is required, both tape ends should be taken outside
the joint area for connection to the electrical supply, ensuring the ends
do not short.The resulting gap in the side of the joint may be plugged
with thermoplastic material, which will be incorporated within the weld.
Any surplus tape may be trimmed off, to make flush.
The required
voltage, the mechanical pressure on the joint and the actual heating /
welding time will all depend upon the application and the materials in
use.
Consistent, high quality results under production conditions
will be obtained after initially determining the operating parameters by
means of experiment.
Welding Current
Manufacturers will require the shortest
welding time possible in order to meet production requirements.
The
duration of the welding cycle, (jig loading, clamping, actual welding,
cooling period, unloading) will be affected by the welding
current.
The value of the welding current will be a compromise
between the highest current values permitting the shortest welding time,
without deterioration of the thermoplastic material characteristics, or
burning out of the welding tape, for the application concerned.
The
value of the current will be affected by the heat transfer characteristics
of the system, i.e., the mass and material thickness of the joint area,
heat conductivity of the welding jig supports in contact with the parts to
be welded and the pressure applied to the joint face.
The many
variables in the situation and the diversity in the types of assemblies
that can be achieved are such, that we cannot recommend specific current
values based on tapes width and length. Therefore, the ideal current value
for a specific application will be determined during development tests
carried out by the customer. However, practical values of the maximum and
minimum welding current are indicated below and as a starting point for
development work.
| Tape
width: |
12mm |
7mm |
4mm |
| Minimum Current |
120amps |
70amps |
40amps |
| Maximum Current |
200amps |
120amps |
75amps |
| Recommended Current
|
150/180amps |
80/100amps |
50/60amps |
Thermoplastic Base
Materials
Our standard welding tapes are designed to
weld PET (Polyester) and PP (Polypropylene) thermoplastic materials. To
this effect they incorporate PET or PP extruded monofilaments mixed with
the conductors.
Whilst PP and PET extruded monofilaments are
readily available, this is not the case for a large number of alternative
thermoplastic materials. We would consider manufacturing sample lengths
using alternative monofilaments if
available. |
