Builders of production and test equipment often want to ensure that any electrostatic build-up will be safely discharged to earth. This can sometimes be a problem with aluminium profile frames, because the anodised layer is an electrical insulator. The fasteners used usually do not guarantee an electrical connection, particularly over the longer term: once even the smallest amount of corrosion has set into the joint area, any continuity may be lost. Many tests have been conducted by Item over a long period to solve this problem.
Item has now introduced a version of its Standard Fastener (a two-part fastener consisting of a special button-head screw and load-spreading plate), whereby the screw has been subtly altered just under the head. This alteration guarantees that when tightened, the screw destroys and displaces the anodising immediately around it, giving a guaranteed connection to one piece of profile. The other piece is already connected by virtue of the machined thread in the profile. The screw is designed such that the normal function of assembly and ease of fitting the two profiles together before tightening the screw, is not affected.
For the Universal and Automatic type fasteners, which cannot be easily altered, a simple ESD steel pin is available which is lightly driven into the central bore of one profile, making good contact. The pin head then destroys the anodising of any subsequent profile to which the first profile is fitted, making electrical contact.
Both ESD fittings work in such a way that if the profiles are subsequently disassembled, the marks are hardly noticeable, so the increasingly important re-usability feature of the profiles and parts is not compromised.
The ESD fittings are the latest addition to the Item range of electrical discharge related products. These include Potential Equalisers which can be retro-fitted to provide ESD connections, and Earthing Terminals where a safety circuit is needed.