SUPERIOR FIBER INSERTS FOR NUTS

A VARIETY OF POLYMERS ARE USED AS INSERTS IN NUTS TO PROVIDE RESISTANCE TO LOOSENING FROM VIBRATION AND SHOCK. FIBER REENFORCED RESINS FORMERLY USED HAVE GENERALLY BEEN REPLACED WITH POLYAMIDES (NYLON) AND POLYIMIDES. IT WOULD BE A LOGISTICS ADVANTAGE IF THESE PREVAILING TORQUE LOCK NUTS COULD BE REUSED AFTER THEY HAVE BEEN DEMATED FROM THEIR BOLT OR SHAFT DURING INSPECTION OR REPAIR PROCEDURES. ALTHOUGH SOME MANUFACTURERS OF THE SMALLER SELF LOCKING NUTS CLAIM THAT THESE ITEMS CAN BE ROUSED UP TO 50 TIMES, MILITARY PROCEDURES REQUIRE THAT NUTS BE DISCARDED AFTER DEMATING; THIS IS PARTICULARLY TRUE OF PRECISION NUTS USED AS RETAINER AND PRELOAD DEVICES FOR BEARINGS. RECENTLY INTRODUCED SHAPE MEMORY PLASTICS (SMP) HAVE A DRAMATIC CHANGE IN MODULUS WHEN HEATED ABOVE THEIR GLASS TRANSITION TEMPERATURE(TG), AND A DEFORMED PART WILL RECOVER ITS ORIGINAL SHAPE WHEN HEATED ABOVE THIS TEMPERATURE. SHAPE MEMORY POLYMERS MAY THUS PROVIDE THE NECESSARY MECHANICAL FEATURES TO SERVE AS ELASTOMERIC LOCKING ELEMENTS IN NUTS OF THESE TYPES, WHILE MAKING POSSIBLE THE RECOVERY OF THE VIRGIN DIMENSIONS OF THE INSERT UPON HEAT TREATMENT AFTER DEMATING. EVALUATION OF SELECTED SMPS WILL BE CARRIED OUT IN BOTH THEIR PURE FORM AND MODIFIED BY FILLERS TO ESTABLISH THEIR TORQUE CHARACTERISTICS AND THEIR REUSABILITY.