Plastic welding
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Plastic Welding is the process of welding plastic parts together. There are several techniques:
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[edit] Hot gas welding
This is the plastic welding technique equivalent to gas welding. However, the techniques are only vaguely similar. A specially designed heat gun (hot air welder) produces a jet of hot air that softens the parts to be joined, as well as the plastic weld rod. Hot gas welding is a common fabrication technique for manufacturing smaller items including and not limited to chemical tanks, heat exchangers, and plumbing fittings. The materials being welded and the welding rod must be of the same or very similar plastic. Welding PVC to acrylic is an exception to this rule.
[edit] Free hand welding
With free hand welding, the jet of hot air from the welder is played on the weld area and the tip of the weld rod at the same time. As the rod softens, it is pushed into the join and fuses to the parts. Free hand welding is a difficult technique to master, and is slow. However, welds can be made in .
[edit] Speed tip welding
With speed welding, the plastic welder, similar to a soldering iron in appearace and wattage, is fitted with a feed tube for the plastic weld rod. The speed tip heats the rod and the substrate, while at the same time it presses the molten weld rod into position. A bead of softened plastic is laid into the joint, and the parts and weld rod fuse. In some types of plastic such as polyproplyene, the melted welding rod must be "mixed" with the semi-melted base material you are repairing. These techniques were perfected in the early '90's by Scott Koblenz of The Bumper Doctor, Co. Speed tip welding is a much faster technique but cannot be used in tight corners.
[edit] Plastic welding rod
This is the extruded rod that is used to weld plastic. Plastic welding rod can be ABS, PVC, Polypropylene, polyethylene, and many other types of thermoplastic. Plastic welding rod is available in a wide range of colors to match (or contrast) the parts being joined.
[edit] Extrusion welding
Extrusion welding allows the application of bigger welds in a single weld pass. It is the preferred technique for joining material over 6 mm thick. Welding rod is drawn into a miniature hand held plastic extruder, plasticized, and forced out of the extruder against the parts being joined, which are softened with a jet of hot air to allow bonding to take place.
[edit] Contact welding
This is the same as spot welding except that heat is supplied with convection of the pincher tips instead of electrical conduction. Two plastic parts are brought together, and heated tips pinch them, melting and joining the parts in the process.
[edit] Hot plate welding
Related to contact welding, this technique is used to weld larger parts, or parts that have a complex weld joint geometry. The two parts to be welded are placed in the tooling attached to the two opposing platens of a press. A hot plate, with a shape that matches the weld joint geometry of the parts to be welded, is moved in position between the two parts. The two opposing platens move the parts into contact with the hot plate until the heat softens the interfaces to the melting point of the plastic. When this condition is achieved, the hot plate is removed, and the parts are pressed together and held until the weld joint cools and re solidifies, which creates a permanent bond.
[edit] High frequency welding
Certain plastics with chemical dipoles, such as polyvinyl chloride (PVC), polyamides (PA) and acetates can be heated with high frequency electromagnetic waves. High frequency welding uses this property to soften the plastics for joining. The heating can be localized, and the process can be continuous. Also known as Dielectric Sealing, R.F. (Radio Frequency) Heat Sealing.
This is the same concept as induction welding.
[edit] Ultrasonic welding
In ultrasonic welding, high frequency sound waves (20 kHz and above) are used to melt the materials to be joined. Localized melting may be accomplished by designing an energy-directing tip into the one of the parts being welded.
[edit] Vibration or friction welding
In vibration or friction welding, the two parts to be assembled are rubbed together at a lower frequency (typically 100-300 Hz) and higher amplitude (typically 1-2 mm) than ultrasonic welding. The friction caused by the vibration motion combined with the clamping pressure between the two parts creates the heat to melt the contact interface between the two parts, and results in a strong weld. At the completion of the vibration motion the parts remain held together until the weld joint cools and the melted plastic re solidifies. The friction movement can be linear or orbital, and the joint design of the two parts has to allow this movement. Ultrasonic Welder provider.
[edit] Spin welding
Spin welding is another form of frictional welding. With this process, one part is held stationary, while the other one is rotated at high velocity. The rotating part is then pressed against the fixed part with significant force. This welding process is related to Vibration Welding.
[edit] Laser welding
This technique requires one part to be transmissive to the Laser and either the other part absorptive or a coating at the interface to be absorptive to the laser. The two parts are put under pressure while the laser beam moves along the joining line. The beam passes through the first part and is absorbed by the other one or the coating to generate enough heat to soften the interface creating a permanent weld.
[edit] Solvent welding
In solvent welding, a solvent is applied which can temporarily dissolve the polymer at room temperature. When this occurs, the polymer chains are free to move in the liquid and can entangle with other similarly dissolved chains in the other component. Given sufficient time, the solvent will permeate through the polymer and out into the environment, so that the chains lose their mobility. This leaves a solid mass of entangled polymer chains which constitutes a solvent weld.
[edit] Additional techniques
Hot air cold staking, Ultrasonic staking, Ultrasonic spot welding, Infrared welding, Torsional welding
