Welding and Bonding

This discussion addresses to the finishing operations which combine objects. In principle, thermoplastics may be bonded either by welding (like metals) or by gluing. We will consider the most useful welding methods. 

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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. 

PVC pipe welding and bonding ol other molded ilems... 

Fillers for epoxy adhesives used in weldbonding include silica (Cab-O-Sil, 7% by wt) to prevent run-off, 3% strontium chromate to provide corrosion inhibition, and conductive metal powders. Viscosity of adhesives in paste form has an important effect on the weld and bonded joint. Viscosity must be low enough to allow the force of the electrodes to push the adhesive out of the interface contact area, yet sufficiently high or thixotropic so that it will not flow out of the joint during the cure cycle. 

Fatigue strength comparison of spot welded and bonded aluminum and steel... 

The bonding technique was initially applied, in a pilot study, to the fabrication of the model encastre Warren beam shown in Fig. 1.8(a). This was manufactured consecutively by welding and bonding, the design in both cases being identical. The two beams were tested under static or dynamic load applied at the free end, giving the results in Table 1.1. 

Locating and Bonding when cathodic protection is applied to an existing jointed pipeline, all joints must be located without digging up the pipe. On location, each joint is exposed and an electrically conducting bond (usually galvanised steel strip or copper cable) is welded into position. 

TPEs can be bonded to other materials by adhesive, heat bonding, electromagnetic filling, radio frequency, heat-sealing lamination, friction and spin welding, and ultrasonic welding. For TPUs, the most widely used techniques are radio frequencies, and ultrasonic and hot stamping. A few typical applications include football bladders, valves, and conveyer belts. 

Acetylenes contain at least one triple bond. The triple bond is even more reactive than a double bond and, therefore, acetylene is used industrially to make other compounds used in rubber and plastics. Acetylene burns in oxygen to produce a very hot flame used for welding and metal cutting (oxy-acetylene torch). 

Process temperature is usually 25-75% of the melting point of the lower ( )-melting-point metal in the intended weld or bond. It is to be understood that the purpose of attaining elevated temperature is to promote or accelerate interdiffusion of the atoms at the joint interface and also to provide some metal softening, which, in turn, aids in surface deformation. The purpose of pressure application is to establish a firm, robust mechanical contact of the surfaces to be joined and further to break up surface oxides (hence the frequent use of silver, as mentioned above). This will provide a rather clean surface for bonding. Dwell time required at the elevated temperature is determined according to metallurgical and sometimes other considerations. 

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