Weld factor

In the supplier s catalog, all the readily available 3" tube has a wall thickness of 0.065". This is thicker than my minimum needs, but this extra thickness will leave plenty of allowance for welding factors and stress concentration. 

The strength of a weld joint is determined by a comparison of the tensile or yield strengths of the plastic part at the joint to those of the bulk of the part. The weld factor (WF) is defined by Eqs. 7.1 or... 

Figure 7.14 shows a comparison of the stress-strain curves of a conventional and a modified PTFE for the original and welded material. The weld line in conventional PTFE when welded to itself, at best, fails at very low strains. In the case of a modified resin welded to itself, the weld factor attains value of 0.80-0.85. The weld factors for welding of conventional to modified PTFE have been reported in the range of 0.66-0.87.F 1... 

The weld factor, which is generally defined as the relation between the strength of the weld and the strength outside the welded zones, determined by tensile stress tests, will give values between 0.7 and... 

Rotation speed can be increased, in which case the heating period should be reduced. A practical check is that it changes from opaque to transparent when it melts. Welding factors thus obtained are between 0.7... 

The mechanical testing conducted on high-quality infrared welds has shown that the welding factors achieved for PVDF when tested at -40°C were greater than 0.9. 

The ultrasonic welding of ETFE can be achievedl" with a weld factor of 0.8. The success of this technique is dependent on joint design and welding parameters such as the contact time and pressure. Typical welding conditions include a contact pressure of 170 kPa and a cycle time of 2 secs. 

The strength of a weld joint is determined by a comparison of the tensile or yield strengths of the plastic part at the joint to those of the bulk of the part. Weld factor (WF), is defined by Eqs. 14.1 or 14.2 as the ratio of tensile strength (F) or yield strength (Y) of the welded specimen (w) to the tensile strength of the parent material (p). The weld faetor is defined for the weakest polymer, if two different polymers are welded together. The closer the weld faetor is to unity the better the weld quality. 

A weld factor of 1 or greater indicates that the joint is as strong or stronger that the parent pipe. Joints in polyethylene pipes are qualified ranging from bad to excellent, according to Table 2 [10]. 

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