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Question We have a dry powder barrel filling application where the powder is elevated by an auger type conveyor then drops through a metal detector in a 3' long, 6" diameter stainless tube. When the operator touches the filling lid he gets a static discharge. We've tried bonding all metal components to a single electrical ground point and placed an anti static mat on the floor. Operators wear cotton coveralls and move about freely so wrist straps are not a possibility. Any suggestions? - Anonymous, Manitowoc, WI
Answer As the dry powder travels through the tube and fills the barrel, both the powder and barrel are undergoing triboelectric generation. The static discharge the operators feel most likely is caused by this generation process. You've tried (bonding) grounding all metal components to a single ground point (CPG) and employed an antistatic mat. You've taken some important ESD control steps, but haven't solved your problem yet. You need to check the following: The filling lid is conductive and grounded to the same CPG. The barrel is conductive and also grounded to the same CPG. If either of the above are not conductive, ionization is a candidate. The antistatic mat is either conductive or dissipative and grounded to the same CPG. All operators should be wearing a pair of 2 Megohm foot grounders in conjunction with the conductive grounded mat to ensure they are not the source of the ESD event at the filling lid. Having properly implemented all the above steps, your problem should be controlled.
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