Introduction
SunLock uses stainless steel machine screws (also called bolts) in a variety of assemblies. These are usually threaded into aluminium. This technical bulletin describes how the screws are prevented from loosening (i.e. how the thread is locked).
PREVENTING A BOLT FROM LOOSENING
SunLock uses two methods to prevent bolts from loosening.
Correct fastener torque (12 - 14 N·m)
Growth of an aluminium oxide layer
Correct torque
The most effective and reliable method of preventing any nut or bolt from loosening is to tighten the thing properly to start with. Carroll Smith’s nuts, bolts, fasteners and plumbing handbook, 1990, page 116.
For SunLock, please tighten bolts to 12 - 14 N·m, as per the SunLock technical bulletin on fastener torque.
Growth of an aluminium oxide layer
SunLock is fabricated from mill finish aluminium (non-anodised). As a bolt is tightened, the aluminium oxide layer is scraped away by the incoming stainless steel thread. After installation, the oxide layer reforms, bonding slightly to the stainless bolt and “locking” it in place. This has a similar effect to thread-locking fluid.
NOTE ON LOCK WASHERS
Similarly, SunLock does not use helical spring washers, as the spring force created by the washer is far less than the axial tension in the bolt. They effectively act as a flat washer.
REFERENCE
Barrett (1990) Fastener Design Manual, NASA
Smith (1990) Carroll Smith’s nuts, bolts, fasteners and plumbing handbook, Motorbooks International.
Tomotsugu (2008) Bolted joint engineering: Fundamentals and Applications, Beuth.
For Further information
For further information contact SunLock on 1300 655 554 or order@sunlock.com.au.