Self Drilling Screws : Tenn RX Selfdrillers


The trend in recent years towards lighter, more economical - but yet strong - forms of steel construction has led to the wide use of thin-walled elements as purlins, rafters, trusses, beams, floor joists and loadbearing walls.

These elements are used very effectively in combination with flat products such as roof sheeting and floor decking. Due to their stability, high load bearing -to-structural-weight ratios and the advantages of corrosion resistance and fabrication flexibility, light gauge sections are increasingly being used in place of heavier and more costly hot-rolled sections, or substituted for timber.

Self-drilling screws are the primary means of roof sheeting attachment. They have to provide firm anchorage and wealhertight seating around surface fastening points.

Roofing fasteners are subject to a variety of forms of loading. These include installation torques which, if excessive, can easily strip the threads formed in thin-walled support members resulting in partially failed fastenings; and in-service loadings (wind action. sheet expansion/contraction) that transmit tensile and shear loads to the fasteners. These loads may produce an insidious mode of failure called "fastener backout" which leads to rainwater leaks because of loss of clamping force.
  
Fig.1 Example of cold-formed sections

Water leaks are a major cause of early corrosion failures in sheet cladding fasteners.

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