Apart from dimensional differences ( bigger heads of bolts and bigger nuts on preloaded assemblies), the main difference is in the way how these goods are installed. Non-preloaded bolting assemblies are generally tightened to at least snug-tight. The connected components are drawn together to achieve firm contact without any specific preload. The “snug-tight” is generally referenced as tightening the assembly by one man using a normal-sized spanner without an extension arm until the wrench starts hammering.
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Customers very often ask for torque figures for the installation of non-preloaded structural bolting assemblies . Due to the nature of this type of product, assemblies for non-preload connections, there are no torque figures available. There are various guidances available to calculate theoretical torque figures, but following EN 1090-2 (pt. 8.3), tightening of non-preloaded bolts shall be conducted as follow: EN 1090-2:2008+A1:2011 The connected components shall be drawn together such that they archive firm contact.
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To accommodate the thickness of zinc it is normal practice to over-tap the nut thread. This operation reduces the strength of the nut and the overall strength of the nut and bolt assembly. To improve the strength of the assembly manufacturers use either a thicker nut (increasing the number of threads between the nut and the bolt in the assembly) or a higher-grade nut. BS EN 15048-1: To achieve full tensile resistance, hot-dip galvanized assemblies can require special measures, see EN ISO 10684, Annex F.
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Content with Non-preloaded