Assembly Planbook - April 2008 - (Page 49) Fastening Tolerance Classes TIGHTENING TORQUE Tolerance Class Class 1 Class 2 Class 3 Tolerance ±10% ±20% ±30% Equivalent Capability ±20% ±40% ±50% Typical Application High dynamic loads Medium loads, high safety margin Part fixing—no external forces Application Example High-pressure sealing Low-pressure sealing Covers, attachments Note: Some companies use a Class 1A: a tolerance of ±15% and an equivalent capability of ±30%. The torque tolerance requirements for bolted joints are commonly classified into three categories: Class 1, Class 2 and Class 3. These classes cover all but the most highly stressed bolts, such as connecting rods. bars. Whatever the reason, the results indicate that tool capability as measured by ISO 5393 is significantly better than can be achieved under practical fastening conditions. The cordless impact tool and the transducerized pulse tool produced similar capabilities. The capability of both tools was in the 20 percent range on the medium joint. Surprisingly, the pulse and impact tools were equal to or better than the shut-off nutrunner on both the soft and medium joints. However, looking at the combined data for both joints, the nutrunner was significantly better than either tool. The nutrunner had a combined capability of 33 percent, compared with 46 percent for the cordless tool and 48 percent for the transducerized pulse tool. This difference in capability between the nutrunner and the pulse and impact tools is due to how the tools respond to variations in joint stiffness. Going from the medium to the soft joint dropped their mean torque values by approximately 25 percent, while the nutrunner dropped only 8 percent. That means that the torque output of the tools, even with the transducerized tool, depends significantly on the joint type. Capabilities vs. Needs How should these capability results be judged? The only practical comparison is against the torque tolerance requirements for bolted joints. These requirements are commonly classified into three categories: Class 1, Class 2 The Original Blue Pipe for Compressed Air Energy Efficient Modular Design Simple Installation Lower Install Cost Push-to-Connect Completely Reusable No Corrosion Available in 1/2”- 4” 7205 E. Hampton Ave. ASB04084Trans.indd 1 Mesa, AZ 85209 Phone: 480-830-7764 www.transair-usa.com www.assemblymag.com April 2008 / ASSE M B LY 49 3/4/08 1:12:14 PM http://www.transair-usa.com http://www.transair-usa.com http://www.assemblymag.com
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