Sacrificial Welding Tape

The product was originally designed for a company manufacturing small sailing boats to assemble the hull and deck sections, made from injection moulded Polypropylene material.

A break through followed with the increasing use of thermoplastic materials in motor car components and very large quantities began to be used by Rover cars in the manufacture of plastic bumpers made from injection moulded components. The back plate is welded to the bumper cover.

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.


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.


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.

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Resistance Technology Limited, 8 Worrall Street, Salford,

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