Effects of aging temperature and humidity on the response of medium and high strength threadlockers

To prevent the preload loss, threadlockers are frequently used in threaded connections (e.g. to avoid self-loosening). Threadlockers are generally anaerobic adhesives and are commercially available either as semi-solid (pre-applied) or as liquid (to be applied just before tightening). Previous research deals with the frictional behavior of threaded joints with applied threadlocker. However, fasteners with applied threadlocker may sometimes operate at variable levels of temperature and humidity. A literature survey indicates there is a lack of data about the strength of joints with added threadlocker when they operate at different temperature/humidity levels with respect to conventional environmental conditions. In this research, the aforementioned issue has been tackled by means of an experimental campaign performed on liquid medium/high strength anaerobic adhesives (respectively, Loctite 243 and Loctite 270) applied to M10, 8.8 grade, zinc-coated screws. Following complete adhesive polymerization, the joints were aged in an environmental chamber, accounting for four combinations of temperature (room temperature–90°C) and humidity (20–90%) for one week. The joints were then untightened, sampling the breakaway torque. Statistical analyses of the data were carried out, to assess the influence of each parameter on the breakaway torque of the aged joint, thus deriving useful data for design.