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Chuck Pease of MMI Tank on
October 16, 2012:
Friction between the blast media and the structure being blasted is the cause. The risk is, as the accumulation of suspended blast fines accumulates in the atmosphere, the potential for explosion increases. Control is typically achieved by having both the blast hose and equipment grounded, as well as the structure being blasted. A good dust collection system to help control the accumulation of blast fines helps also. Use of the required blast/spark-proof lighting is also essential.
Dan Ruark of IDS Blast on
October 16, 2012:
Static electricity while blasting stems from the part being blasted not being grounded. (Don't use rubber mats in blast cabinets and try to keep part always in contact with the blast cabinet floor.)
Richard McLaughlin of Marco Group International on
October 18, 2012:
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What causes static electricity during blast is an effect known as “triboelectric generation” or “tribocharging." You can see a small scale demonstration of the effect when you balloon on a sweater and hold it near your hair. Common static electricity is a form of triboelectric charge. It occurs when certain materials come in contract through extended friction and each picks up an electric charge. The polarity and strength vary greatly due to factors such as duration of contact, speed of contact, material making contact, surface roughness, humidity, and the list goes on, so the potential charge is not very predictable. Ironically, the use of smooth-bore, semi-conductive hose, high velocity fluidizing with dry air, and metallic or metallic base fine granular particles flowing in that air stream, which are all desired conditions for abrasive blasting with compressed air, create a near perfect condition to create large potential charges. The only solution is as Dan mentioned, making sure your system is entirely bonded and grounded. This includes the use of blast hose with a significant amount of carbon black to make it semi-conductive, metal hose couplings, a good connection to your blast pot and a grounding object. If you use nylon hose couplings, you will have to employ a set of jumper wires to complete the ground circuit.
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