ASME B18.16.6-2008 pdf – Nylon Insert Locknuts(lnch Series).
The hanleiwd washer shall be prevented from turning during nut tightening. The nut shall then be backed off by the appLica tion of reverse torque until the tensile load in the bolt or mandrel has been reduced to zero. The Iwet nunwrical torque occurring while the nut is being backed off throughout the nest 360 deg of rotation shall be recorded as the minimum first removal torque. This minimum torque shall not be less than the first removal prevailing- torque value as specified in Table 2 or 3. 11w nut shall then be backed off until the prevailing-torque element Is disengaged from the bolt or mandrel thread. 11w nut shall be reasseiiihled and removed four more tinies. On each reassembly, the nut shall be assembled to the initial first removal position hut no clamp load shall be induced in the bolt or mandrel. The test washer shall not be removed during these additional cycles.
At no time during the four additional installations and removals should the prevailing-torque exceed the maximum, first install prevailing-torque value as specified for the applicable grade and thread series in Table 2 or 3. During the fifth removal, the minimum torque occurring while the nut is being backed off throughout the first 360 deg of rotation shall be recorded. The minimum torque shall not be less than the filth removal value as specified in Table 2 or 3. Sufficient time shall elapse between torquing cycles to prevent oveitteating of the test assembly.
The speed of installation and removal of the nut shall not exceed 30rpm and shall be continuous and uniform.
12.3.1 Torque-Measuring Device. The torque- measuring device shall be capable of measuring the torque while the test nut is in motion Test results may be reconled by an analog or digital device that is capable of forming a permanent record. The measuring system shall have a measurement uncertainty at the point of measurement of ±2%. Test equipment may be handheld or electronic, provided that accuracy and speed restrictions as noted above are observed. A manual wrendi and manual recording device may be used if it meets the above calibration criteria.
12.3.2 Load-Measwlng Devke. The load-measuring device used in the prevailing-torque test shall be an instrument capable of measuring the actual tension induced in the test bolt as the nut is tightened. The device shall be accurate within ±5% of the lest damp load being used. The bolt clearance hole in the backing pLate behind the washer shall have the same diameter and tolerance as the test washer.
12.3.3 Test Bolt. The test bolt in the prevailing- torque test shall have a zinc phosphate and oil finish (dry to the touch).
The bolt shall have threads conforming to Class ZA tolerances as specified in ASME BI.1. Threads on all bolts I in. in diameter and smaller shall be produced by rolling. In those instances in which a test mandrel is used, the threads may be produced by rolling., cutting. or grinding. Inspection of test bolts shall be conducted using a basic size GO and NO GO thread ring gage set. Bolt length shall be such that a minimum length equivalent to six thread pitches, as measured from the end of the bolt, will protrude through the nut when the nut is seated against the test washer. Thread length shall be such that a minimum of two lull threads are within the grip after the nut is seated. The bolt shall be pointed in accordance with the dimensional requirements for hex cap screws as given in ASME B18.2.1. The thread surface shall be free of burrs or other contamination that might affect an accurate determination of the prevailing- torque developed by the nut.
The bolt shall have an ultimate tensile strength not less than the specified prorsf load of the nut to be tested. The threads of heat-treated bolts shall have a metallurgical surface condition equal to Class B as specified in SAE 1121. When test bolts less than 3 in. in diameter are used, a new bolt shall be used for testing each nut. Bolts in. and larger in diameter may be reused if upon inspection the thread condition is acceptable In those instances in which a test mandrel Is used, the mandrel may he reused if upon inspection the thread condition Li acceptable.