Plastics joining

The largest market for elastomer-based adhesives is that of lamination (see Laminates). Modem office furniture having Formica as a surfacing material is made with an elastomer-based adhesive. Tile adhesives for ceramic or carpet tile are also elastomer-based and usually solvent appHed. Paper adhesives and shoe manufacture also use substantial quantities of mbber-based materials. Solvent-weld adhesives are used to join plastic plumbing and to repair vinyl sheeting. 

A variety of techniques is available for joining plastics to themselves or to other materials—mechanical fastening, welding, and bonding with adhesives—and all are used extensively. Each method has both advantages and drawbacks for plastics, bonding might be said to be preferable when they are to be joined with dissimilar materials. 

However, even with these potential difficulties, adhesive bonding can be an easy and reliable method of fastening one type of plastic to itself, to another plastic, or to a nonplastic substrate. Pocius et al. provides an excellent treatise on the use of adhesives in joining plastics.51... 

Plastic foams are manufactured from thermoplastic and thermoset resins in various forms. The main pitfall in joining plastic foam is that of (1) causing the foam to swell or collapse by contact with a solvent or monomer and (2) having the adhesive alter the properties of the foam through its absorption into the foam. Adhesion and joining are usually not a serious problem because of the porous nature of the foam. 

Handbook of Plastics Joining, Plastics Design Library, Norwich, NY, 1997. 

In addition to the various welding techniques, adhesives may join plastic parts. Both thermoplastic and thermosetting resins may be bonded and parts made of different resins are often treated in this... 

Heat sealing A method of joining plastic films by simultaneous application of heat and pressure to areas in contact. Heat may be supplied conductively or dielectrically. 

The reactive hotmelt adhesives retain a high level of flexibility and dynamic load-bearing capacities even after crossUnking and are used to join plastics to one another as well as to wood (furniture industry), glass (construction industry), aluminum (sandwich elements), and painted surfaces. Typical applications include window casement sheathing, foil laminations, clip fasteners, bookbinding, textile... 

Welding methods are listed in Table 7.1. Ultrasonic welding is one of the most efficient methods of joining plastic parts, and different materials can be welded so long as they have a common monomer. While particularly useful for hard rigid materials, it may generate particles. 

Often it is necessary to join two or more components of plastics to produce a particular setup or to repair a broken part. For some thermoplastics solvent welding is applicable. The process uses solvents which dissolve the plastic to provide molecular interlocking and then evaporate. Normally it requires close-fitting joints. The more common method of joining plastics, however, is to use heat, with or without pressure. Various heat welding processes are available. Those processes in common commercial use are described here. 

O Rinda Trauernicht, J. 1970. Bonding and joining plastics. Plastics Technology, Reinhold Publishing, New York. 

Table 7.5 Pretreatments and adhesive types used by the plastics industry to join plastic components ...

State two types of we Iding used to join plastics materials. 

Press-fitting is used to join plastic parts to each other or to metals, especially to fit wheels on to shafts. The interference /, defined as the difference between the internal diameter of the hub and the outer diameter of the shaft, is given by... 

The joining processes that can be used will be dependent on the type of polymeric resins used to manufacture the parts to be assembled. However, there are also certain assembly opportunities for the designer because the material is a plastic material. Generally, plastics can be joined by more processes than other materials. The following processes are normally used for joining plastic materials ... 

TABLE 7.1 Bonding or Joining Plastics What Techniques Are Available, and What Do They Offer ... 

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. 

Mechanical fasteners provide an economical and reliable means of joining plastic parts to themselves and to other materials. However, mechanical fasteners are generally not employed in high-volume, fast-production operations because of the added inventory requirements. Also, the time required to join parts with mechanical fasteners relative to other processes is substantial, especially for larger parts that require multiple fasteners. 

How to Fasten and Join Plastics, Materials Engineer, March, 1971. 

R. J. Wise, Thermal Welding of Polymers, Abington Publishing, Cambridge, 1999. Anon, Handbook of Plastics Joining, Plastics Design Library, New York, 1997. 

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