Plastic welding
From Wikipedia, the free encyclopedia
 |
This article may require cleanup to meet Wikipedia's quality standards. Please improve this article if you can. (May 2007) |
 |
This article may need to be wikified to meet Wikipedia's quality standards. Please help by adding relevant internal links, or by improving the article's layout. (April 2009) |
 |
It has been suggested that Plastic Sealing/Welding Technologies be merged into this article or section. (Discuss) |
Plastic welding is the process of welding plastic parts together. Heat sealing is one of the primary processes of joining or welding plastics.
There are several techniques with which this can be accomplished:
Contents |
[edit] Hot gas welding
This is a plastic welding technique which is analogous to gas welding of metals, though the specific techniques are different. A specially designed heat gun (hot air welder) produces a jet of hot air that softens both the parts to be joined and a plastic filler rod, all of which must be of the same or a very similar plastic. Welding PVC to acrylic is an exception to this rule.
Hot air/gas welding is a common fabrication technique for manufacturing smaller items such as chemical tanks, water tanks (black, grey, fresh & ballast), heat exchangers, and plumbing fittings. Poly family plastics are used for manufacturing cabinets, medical facility chassis, transport assemblies, etc.
[edit] Freehand welding
With freehand 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 joint and fuses to the parts. Free hand welding is a difficult technique to master, and is slow. However, welds can be made in almost any situation.
[edit] Plastic welding rod
This is the extruded rod that is used to weld plastic. Suitable rod materials include ABS, PVC, Polypropylene, polyethylene, PVDF and many other types of thermoplastic. Plastic welding rods are available in a wide range of colors to match a project's color. It is often used for design.[citation needed]
[edit] Speed tip welding
With speed welding, the plastic welder, similar to a soldering iron in appearance 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. With some types of plastic such as polypropylene, the melted welding rod must be "mixed" with the semi-melted base material being fabricated or repaired. These welding techniques have been perfected over time and have been utilised for over 50 years by professional plastic fabricators and repairers internationally. Speed tip welding method is a much faster welding technique and with practice can be used in tight corners.
[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 where 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 to create 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.
In a ferromagnetic work piece, plastics can be induction-welded by formulating them with metallic or ferromagnetic compounds, called susceptors. These susceptors absorb electromagnetic energy from an induction coil, become hot, and lose their heat energy to the surrounding material by thermal conduction. [1]
[edit] Ultrasonic welding
In ultrasonic welding, high frequency (15 kHz to 40 kHz ) low amplitude vibration is used to create heat by way of friction between the materials to be joined. The interface of the two parts is specially designed to concentrate the energy for the maximum weld strength.
[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 which begins to melt the contact areas between the two parts. At this point, the plasticized materials begin to form layers that intertwine with one another, which therefore 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.
[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 a laser beam and either the other part absorptive or a coating at the interface to be absorptive to the beam. 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.
Semiconductor diode lasers are typically used in plastic welding. Wavelengths in the range of 808 nm to 980 nm can be used to join various plastic material combinations. Power levels from less than 1W to 100W are needed depending on the materials, thickness and desired process speed. [2]
Diode laser systems have the following advantages in joining of plastic materials:
• Cleaner than adhesive bonding • No micro-nozzles to get clogged • No liquid or fumes to affect surface finish • No consumables • Higher throughput • Can access work-piece in challenging geometry • High level of process control
Requirements for high strength joints include:
• Adequate transmission through upper layer • Absorption by lower layer • Material compatibility – wetting • Good joint design – clamping pressure, joint area • Lower power density
Materials that can be joined include:
• Polypropylene • Polycarbonate • Acrylic • Nylon • ABS
Specific applications include sealing / welding / joining of: catheter bags, medical containers, automobile remote control keys, heart pacemaker casings, syringe tamper evident joints, headlight or tail-light assemblies, pump housings, and cellular phone parts.
[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 mingle 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.
This technique is commonly used for connecting PVC and ABS pipe, as in household plumbing. The "gluing" together of plastic (polystyrene or ABS) models is also a solvent welding process.
Dichloromethane (methylene chloride), which is obtainable in paint stripper, can solvent weld polycarbonate and polymethylmethacrylate. It is also a component - along with tetrahydrofuran - of the solvent used to weld plumbing.
[edit] See also
[edit] References
- ^ "Induction Welding". http://www.emabond.com/inductionwelding.html. www.emabond.com
- ^ "Plastic Welding with Diode Lasers". http://www.coherent.com/Downloads/Laser_Spot_Welding_PlasticRev2.pdf. www.coherent.com
