Welding plastic

There are many different, cost-effective welding methods suitable for industrial mass production of plastics engineering components including ultrasonic, laser, spin, hot plate, linear and orbital vibration welding. Here we will deal with inexpensive manual methods for low quantities which can be carried out in small workshops or on site. 

This is a manual welding process which consists of heating and softening the two surfaces to he joined and a filler rod, usually of the same material, until complete fusion takes place. It is a similar process to welding metal, except that a naked flame is not used as this would burn the plastics material. Instead a stream of hot gas is used, directed from a special welding torch. The heat source may be electric or gas, at a temperature around 300 °C. 

The surfaces to he welded have to be prepared to accept the filler rod. For butt joints the edges are chamfered to an included angle of about 60°. For fillet joints an angle of 45° is used, as shown in Fig. 14.2. The surfaces to be welded must be clean and free from grease. Filler rods are generally cir- T cular in section and for small work are usually 

The surfaces to be joined should be clamped together. The hot air is then directed at the surfaces and the filler rod, which is pressed into the joint as the area becomes tacky. The downward pressure of the filler rod makes the weld, which fuses and solidifies as welding proceeds, Fig. 14.3. Depending on the thickness of the material, more than one weld run may be necessary. 

This method is used with good results to weld rigid PVC, PP and PE (polythene) sheet to fabricate tanks, vessels, pipes for all types of fluids, and ducting. 

The surfaces to be joined should be clamped together. The hot air is then directed at the surfaces and the filler rod, which is pressed 

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Plastic welding Joining of finished plastic components by fusing materials either with or without the addition of plastic from another source. 

Plastic welding. When irregular particles are in contact, the forces between the particles will be borne on extremely small surfaces and the very high pressures developed may give rise to plastic welding. 

Fig. 1.2. ultrasonic plastic welding machine (photo courtesy of Kerry Ultrasonics, UK). 

Fig. HI.2. Plastic welding practice, (a) Some typical welds. (b) Technique for feeding rod into weld. With the rod bent back into a 45° angle, it is easy to heat and the rod is forced into the seam. The torch should be fanned between the rod and the parts being welded, with somewhat greater concentration on the latter, (c) An edge seal accomplished on a hot plate.

For lead sheet, or sheet elastomer or plastic, welds (or laps) not padded, brick not notched. (2)... 

OTS Selective Bibliographies. Approximately 150 Selective Bibliographies have been prepared for areas considered to be of special interest, such as plastics, welding, and transistors. The cost is usually 10 cents per copy and a free list of these bibliographies may be obtained from OTS. 

Isopropyl lanolate Isocetyl salicylate PPG-2 lanolin alcohol ether PPG-5 lanolin alcohol ether PPG-20 lanolin alcohol ether Propylene glycol myristate plasticizer, weather-stripping Dinonyl phthalate plasticizer, welding rod coatings Algin Alginic acid plasticizer, wire coatings Dioctyl terephthalate plasticizer, wire insulation Trimellitic anhydride plastics... 

High-frequency (1892) n. Pertaining to the part of the electromagnetic spectrum between 3 and 200 MHz, employed in plastics welding, sealing and preheating operations. Frequencies of 30 MHz and below are the most used. 

It is possible to strip undercuts for parts molded of these processes in some cases and threads can be molded-in. However, side actions or split cavities, as would be required for details A and G, are more commonplace. Threaded inserts, like those at E and H, can also be molded-in. However, it may be more advantageous to emplace them after molding with adhesives since the molding cycle will be shorter and the risk of one misplaced insert ruining an entire moldment is ehminated. The other common methods of assembling compression, transfer, and thermoset injection-molded parts are self-tapping screws (holes can be tapped), adhesives, snap-fits, press-fits, and the usual screw and bolt techniques. None of the plastics welding techniques can be used with thermoset parts. 

EN 13067 2003 Plastics Welding Persoimel - Approval Testing of Welders - Thermoplastics Welded Assembhes... 

Welding of thermoplastics Mechanical movement based plastic welding... 

Glass fibers sized with polyurethane and polyvinyl acetate formed different interfaces. This was due to the differences in reactivity and miscibility. Polyurethane forms a stronger interface because it is reactive and miscible with epoxy resin. " Surface tension of glass surface in a molten state correlates with the interface formation with polymer. The diffusion at interface contributes to a complex structure controlling properties of the interphase. The analysis of the diffusion at the interphase has helped to develop an understanding of the formation of metal-polymer interfaces and plastic welding. 

A common cause of RF contact burns is from the metal electrode jigs of dielectric heating and plastics welding apparatus, operating at radio frequencies. Unless the output is pulsed there is unlikely to be a shock risk, but an accidental hand contact, for example, will draw out an arc when the hand is removed and a high frequency burn will result. The burning is a function of the arc energy, and for low power apparatus only a minor burn is likely. More powerful equipment, above about 1 kW, can inflict more serious burns. 

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