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The method of joining thermoplastics using a hot plate under contact heat and pressure as well as infrared radiation is an excellent choice for large-surface plastic parts and parts with a spatially shaped geometry of the joining area.
The welding tool used during hot plate welding is heated by the electrical warming of a coated or non-coated hot plate. During this process, the surfaces of the components to be fused are heated on contact or by radiation and subsequently joined and cooled off under a specific pressure. Since the heating of the components is selective and performed only as appropriate for the workpiece, hot plate welding ranks among the most reliable and safest welding techniques available for thermoplastics.
The methods that can be applied fall into three different categories: low temperature range, high temperature range and infrared radiation.
The low temperature range method requires a hot plate that heats up to a temperature of up to 250° as well as a welding mirror that has been given a non-stick coating. The use of contact heat allows this technique to be exceptionally robust and reliable and to deliver tight joints that are free of particles. On the flip side, the lower temperature produces longer cycle times than the high-temperature technique.
The high temperature technique requires the hot plates to heat up to a temperature between 300° and 450°, which puts them within or above the temperature range where the component to be welded will decompose. When used for this technique, the hot plate does not need to have a coating. While offering shorter cycle times, this technique has a few distinct disadvantages compared to the low temperature method due to the high temperature, which increases the probability of fume formation and necessitates the use of an extraction system.
The technique involving the use of infrared heat / radiation heat joins the components without them coming into contact with one another. This non-contact joint cannot be established, however, unless the components have been made with the necessary precision. The warm-up time varies with the permissible distance between component and radiating body.
Similar to ultrasonic welding, this technique can theoretically be applied on all thermoplastic materials as well as all amorphous and semi-crystalline polymers.
An important prerequisite for the welding process to begin and for the five phases of the joining process to commence is that the components are clean. The process starts by inserting the components into the corresponding holders and by checking their correct placement. Next, the welding surfaces are moved up evenly to the hot plate at the specified pressure and hot plate temperature until the appropriate melting temperature / melting degree of the joining areas has been reached. Afterwards, the feed units move apart while the hot plate returns from the machining position to its home position. Next, the joining process proceeds by pressing the components together along their joining areas. The joining time and the subsequent cooling time vary with the type of material used and with the wall thickness. The fully hardened component can be removed once the cooling time has elapsed.
This technique offers tremendous benefits as it allows for
Compared to ultrasonic and rotation welding, this technique requires a longer cycle time, which, however, can be reduced to an efficient minimum by specifying the appropriate temperature and by designing the process accordingly.
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