Welding Thermal

Thermoplastics Mechanical Fasteners Adhesives Spin and Vibration Welding Thermal Welding Ultrasonic Welding Induction Welding Remarks... 

Acrylonitrile-Butadiene-Styrene (ABS). ABS plastics are derived from acrylonitrile, butadiene, and styrene. ABS materials have a good balance of physical properties. There are many ABS modifications and many blends of ABS with other thermoplastics that can affect adhesion properties. ABS resin can be bonded to itself and to other materials with adhesives, by solvent cementing, or by thermal welding. 

When solvent welding or thermal welding is not practical or desired, adhesive systems can be used. Adhesive types such as epoxies, urethanes, thermosetting acrylics, nitrile phe-nolics, and cyanoacrylates permit ABS to be bonded to itself and to other substrates. The best adhesives have shown strength greater than that of ABS however, these adhesives provide very rigid bonds. 

Because of their high thermal stability and excellent resistance to solvent, fluorocarbons cannot be joined by solvent cementing, and they are very difficult to join by thermal welding methods. Because of their inertness and low surface energy, they also tend to be difficult materials to join by adhesive bonding. Surface treatment is necessary for any practical bond strength to the fluorocarbon parts. 

Because of their excellent chemical resistance, polyolefins are impossible to join by solvent cementing. Because of their very low surface energy, polyolefins can only be adhesively bonded after surface treatment processes. The most common way of joining polyolefins is by thermal welding techniques. 

Polystyrene is ordinarily bonded to itself by solvent cementing, although conventional adhesive bonding, thermal welding, and electromagnetic bonding have been used. When polystyrene is bonded to other surfaces, conventional adhesive bonding is usually employed. 

Breccias which are shock compressed aggregates of soil (regolith breccias) or thermally welded material (metamorphic breccias). 

Polymer Adhesives Mechanical Fastening Solvent Welding Thermal Welding... 

The membrane envelope consists of two membranes fleeces and spacers between the membranes to provide an open space for an unrestrained permeate drainage. Thermal welding at the outer cutting edges seals the membrane sandwich (Fig. 1.4). 

Spun-bonded composites, on the other hand, are mainly produced from poly(ethylene), poly(propylene), and aromatic polyesters. Area-bound products behave more like paper, but point-bound products are more like fleeces (Table 38-6). In these cases, composites from poly(ethylcne) and poly-(propylenc) arc purely thermally welded without the use of adhesives the resulting products span the whole of the area of application between heavy packing papers to fine writing papers. The poly(ethylene) papers can be... 

With these materials, solvent cementing or thermal-welding methods are often preferable alternatives to adhesive bonding. However, where dissimilar materials are being bonded, or where the thermoplastic is relatively inert to solvents, adhesive bonding is recommended. 

Ordinarily solvent cementing or thermal welding is used with PMMA. These methods provide stronger joints than adhesive bonding. Adhesives used are cyanoacrylates, second-generation acrylics, and epoxies, each of which provides good adhesion but poor resistance to thermal aging. "... 

Solvent cementing and thermal welding use the resin in the part itself as the fastener to hold the assembly together. Adhesive bonding and mechanical fastening use another substance as the fastener. ... 

Thermal welding process can be of two kinds direct and indirect. Each kind of thermal welding may be further classified, as shown below, according to the method used to provide heat. 

Other thermal welding processes that are less common than those described above but still used in industry are infrared welding and laser welding. These are generally used in specialty processes or with applications that require unique methods of heating because of the joint design or nature of the final product. 

When decisions are to be made relative to assembly methods (mechanical fastening, adhesive bonding, thermal welding, or solvent cementing), special considerations mnst be taken becanse of the nature of the substrate and possible interactions with the adhesive or the enviroiunent. The following sections identify some of these considerations and offer an assembly gnide to the varions methods of assemblies that have been found appropriate for specific plastics. 

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