Experimental characterization of the ageing behaviour of anaerobic threadlockers

Threadlockers are widely used in threaded connections in order to prevent the preload loss (e.g., due to self-loosening). Threadlockers are commercially available in different formulations, such as liquid (to be applied just before tightening) or semi-solid (pre-applied on the screw). Previous research focused on both the frictional behaviour at tightening of the joint with applied threadlocker, and on the breakaway torque of the joint after complete polimerization of the threadlocker. Nonetheless, threadlocker-enhanced joints are often operated at variable levels of temperature and humidity. A literature survey reveals lack of data about the residual strength of threadlocker-enhanced joints after operation at temperature/humidity levels different by the reference ambient levels. The present research tackles the aforementioned issue, by means of an experimental campaign carried out on a liquid medium-strength anaerobic adhesive applied to metric, 8.8 grade, Zinc-coated screws. Upon complete polimerization of the adhesive, the joints have been aged in an environmental chamber at four different combinations of temperature (RT – 90°C) and humidity (20%–90%) for one week. The joints have then been unlocked, sampling the breakaway torque. Statistical analysis of the data has been carried out to determine the significance of each parameter on the breakaway torque of the aged joint.