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Plastic welding

Plastic welding designates the joining of two components made of similar or dissimilar thermoplastics by applying heat and pressure. For welding, the surfaces to be joined are first transferred to a plastic state. Next, the surfaces are joined under pressure and the joint so obtained is allowed to cool to provide a high-strength bond.

The most common plastic welding techniques comprise:

- heating element welding

- hot gas welding

- extrusion welding

- friction welding

- infrared welding

- high-frequency welding

- ultrasonic welding

- vibration welding

- hot gas riveting

- laser beam welding

- induction welding

- injection welding

Of the above welding techniques, extrusion welding is one of the most widely applied methods. This is due to its suitability for universal use whether for shop welding or field welding. Moreover, this process is also excellently suited for deposit and repair welding.

Extrusion welding is a process used for joining (welding) thermoplastic polymers. It is a manual or semi-automatic welding process using a hand-held welding extruder, for instance. The filler material in the form of plastic welding rods or granulate is fed to the extruder (plastifier) where it is melted and plastified before being forced under pressure into the prepared joint of the parts to be welded together. In parallel, the joint is preheated to its softening temperature by a stream of hot air to ensure that the extrudate and the parts fuse together, thus producing a homogeneous continuous weld seam.

Welding shoes matched to the weld geometry are used to apply the extrudate to the welding zone at the required contact pressure. The required bonding pressure is generated by the extrudate expelled from the extruder and the pressure exerted by the welder.

A distinction is made between continuous and discontinuous extrusion welding processes.

In the continuous extrusion welding process, the extrudate exiting the extruder is continuously applied to the plastified weld groove by the welding shoe. Welding extruders used for this purpose may be hand-held or automated.

The welding work can be facilitated by suitable jigs and clamping devices.

The welding speed is governed by the extrudate output and the joint cross-section to be filled. The welding speed and extrudate output must be matched to one another.

Preheating of the components to be joined is accomplished by an on-board hot air blower and hot air nozzles which allow controlled plastification of the parts to be joined.

In the discontinuous extrusion welding process, the plastic melt exiting the extruder is collected batchwise in a suitable vessel and pressed into the joint with the aid of a pressing tool. This process as well uses a hot air blower to preheat and plastify the surface of the welding zone.

Munsch hand extruders consist of a high-performance drive specifically developed for this application, a hot air blower, an extrusion nozzle or a welding shoe.

The hand extruders meet the requirements of the DVS guidelines.

For details of the execution of the welded joints and components, reference is made to DVS Guideline 2205.

To produce a perfect weld seam, the welding shoe must be matched to the specific weld geometry. Standard welding shoes are available for the following weld geometries:

- V-weld

- Double V-weld also known as X-weld

- Fillet weld

- Corner weld

- Lap weld

Special welding shoe designs are available on request. The same applies to the extrusion nozzles.

For plastic welding techniques to be applicable, the thermoplastic must be suitable for welding. Weldability criteria are defined in the DVS guidelines.

Required equipment:

- operable welding extruder

- suitable welding shoes

- flow meter for welding gas

- temperature measuring instrument to measure the extrudate temperature

- diverse measuring tools for checking the welded joint

- machine stand

- scraper, deburring tool

- personal protective equipment

- dust protection for the weld seam

- lighting

- weather protection

- suitable cleaning agents

- welding parameters

- welding report

Proper weld preparation is of key importance to the weld quality.

Plastics most commonly joined by welding - also known as high-performance plastics, include:

PP, PE, PE-HMW, PVDF, PFA, PVC-C, ETFC, ECTFE.

All the above materials can be welded using Munsch plastic welding machines.

High-performance plastics designates thermoplastic polymers exhibiting high temperature stability, superior resistance to aggressive and abrasive media and high mechanical strength.

These plastics are normally used as liner materials to provide protection against abrasion, mechanical damage as well as chemical and thermal degradation. They are typically used as liners in tanks fabricated from metals or mineral materials but also for the fabrication of solid plastic components.

Munsch Plastic Welding Machines in the Training Sector

Training centres specializing in plastic welding technology are equipped with Munsch welding machines

As plastic welding is finding its way into ever broader applications, the vocational education and training curricula and further training programs have to be extended to include corresponding skills for the most diverse trades such as road construction, plant construction, heating, plumbing, air conditioning, landfill construction, tank fabrication, water and gas supply and waste water disposal, to name only a few.

The broad application spectrum translates into special requirements for the plastic welding machines so that these must be optimized for the specific use to ensure maximum efficiency.

On the other hand, cost aspects make it necessary to rationalize the technical equipment pool of the vocational schools and training centres.

Besides the technical equipment, the proper and job-oriented training of the personnel operating the welding machines is crucial to quality welding.

For this reason, both vocational education and training courses and further training programs for welder qualification are based on demanding curricula. Achieving the training objectives is a key prerequisite for the proper execution of the welding work which frequently involves the handling of hazardous substances.

Taken together, these requirements and constraints pose a challenge to the schools and training centres and their highly qualified trainers. The challenge is to train the trainees on technical equipment that meets the requirements for field application while at the same time keeping the equipment pool within limits.

Compounding the problem is that the welding extruders are operated by a continually changing team of beginners. In addition, welding extruders used for training purposes are operated for short periods resulting in frequent load changes and frequent startup and shutoff operations.

To meet these requirements, training centers frequently choose the well-matched welding extruder series of Munsch Kunststoff-Schweißtechnik for developing plastic welding skills. These machines, which are tried and proven in demanding field applications without exception, also meet the requirements in the training sector.

Not only are these machines available in an adequate capacity grading which allows the entire welding speed spectrum of hand extruders to be covered, but their broad range of application also puts schools and training centres in a position to cover the required training applications even with a small equipment pool. Thus, the Munsch mini-extruder allows the welding of virtually all common plastics right through to the high-performance plastics PVDF, PVC-C and PFA with a single unit.

Munsch welding extruders are easy to operate so that operators can be instructed in their use within a short time and faults are minimized. Thanks to their robust design and their reliable operation, the welding extruders can also tolerate frequent changes in the welding personnel.

Many vocational schools and training centres opt for tried-and-tested Munsch technology which is being constantly further developed and optimized into the bargain.

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Worldwide distribution

Munsch Company is a worldwide operating business. Here are our worldwide contacts that are responsible for your application with plastic welding extruders.