Self-fastening

There are basically two methods of mechanical assembly for plastic parts. The first uses fasteners, such as screws or bolts the second uses interference fiL such as press-fit or snap-fit and is primarily used in thermoplastic applications. This latter method of fastening is also called design for assembly or self-fastening. 

Self-fastening joint designs generally produce very high stresses in the plastic part during the assembly operation. With brittle plastics, such as thermosets, press-fit assembly may cause the plastic to crack if conditions are not carefully controlled. In addition, certain plastics, especially thermoplastics, are subject to cold flow under stress. Under continued stress, which is the fundamental adhesive that holds self-fastened parts together, the plastic may relax, causing the joint to fad. 

Another important point to consider when designing joints for self-fastening is the thermal coefficient of expansion. For example, most metals have a thermal expansion co-... 

These materials can be joined by mechanical self-fastening methods or by mechanical fasteners. However, polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) parts are generally joined by adhesives. 

These materials can be joined by mechanical self-fastening methods or by mechanical fasteners. 

These materials can be joined by mechanical self fastening methods or by mechanical fasteners. Polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) parts are generally joined by adhesives. Surface treatments recommended specifically for PBT include abrasion and solvent cleaning with toluene. Gas plasma surface treatments and chemical etch have been used where maximum strength is necessary. Solvent cleaning of PET surfaces is recommended. The linear film of polyethylene terephthalate (Mylar ) surface can be pretreated by aUcahne etching or plasma for maximum adhesion, but often a special treatment is unnecessary. Commonly used adhesives for both PBT and PET substrates are isocyanate cured polyesters, epoxies, and urethanes. Polyethylene terephthalate cannot be solvent cemented or heat welded. 

Are locks, tags, and other protective materials and hardware for securing machines (e.g., chains, wedges, key blocks, adapter pins, self-locking fasteners) provided by the employer [OSHA Reference 147(c)(5)]... 

Mark a center line on the top rear of the 8 tube. Measure 5/8 down each side from the center line and mark the tube. Measure 1 from the rear of the tube and mark again,intersecting the first 2 lines. These two points are the location for the tube support screws They can be drilled and tapped for machine screws or simply drilled for self tapping screws or pop rivets. Be sure that whatever fasteners used do not extend through the collar into the barrel itself. This allows the collar/ tube assembly to be removed from the barrel by loosening the bottom screw only. 

Special care should be exercised in systems where previous experience has indicated tray vibration problems. When tray vibration is expected, bolted-through tray connections should be used, along with lock washers or self-locking nuts, rather than frictional fastening. 

As human beings developed tools and weapons, sharp stones had to be fastened to handles to make axes and spears. Some of these were bound with vines, fibers, pieces of animal skin, or tendons or other body parts, and some had natural self-adhering properties to supplement the use of knots. To enhance the joining process, observing users soon smeared on sticky materials found locally. 

Thread locking. The first applications for anaerobic adhesives were for locking threaded fasteners. Filling the inner space between a nut and bolt with a hard, dense material prevents self-loosening. 

A manufacturer of restaurant appliances fastens a stainless steel top to a combined counter/refrigerator/stove imit. The standard attachment technique included both welding and the use of self-tapping screws. An aerobic acrylic adhesive has replaced these techniques resulting in a lower cost assembly requiring less skilled labor. 

This description applies equally to assemblies using threads tapped in the plastic or to self-tapping screws. Screws are generally used for larger assemblies, such as enclosures for electrical apparatus, etc., and for any size assembly that must be taken apart for servicing or into which are fastened other components which may have to be removed fm servicing, etc. 

A remarkable special property of nitrate esters is the ability to catalyze some additional polymerization reactions [42]. In nitroglycerine, both styrene and methyl methacrylate can be self-polymerized. If the amount of nitroglycerine is up to 5-20 portion (weight fraction), equals to 10 % of polymers, the polymerization rate will be fastened. The molecular weight of polymers is less than that obtained through slowly polymerization or in situ anionic polymerization. 

The cost of riveting is lower than that of most other methods of fastening, due to the absence of plain washers, locking washers, nuts or split pins also, the use of self-piercing rivets eliminates the need to predrill holes. Rivets are available in steel, brass, copper and aluminium in a variety of types. The more standard head types used are shown in Fig. 12.11. 

A large variety of mechanical fasteners can be used for joining plastic parts to themselves and to other materials. These include machine screws, self-tapping screws, rivets, spring clips, and nuts. In general, when repeated disassembly of the product is anticipated, mechanical fasteners are used. 

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