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2161 |
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Tuesday, May 04, 2010, Moor Room 10:00 AM Economic and Environmental Aspects |
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Measurement of particle emissions generated by arc spray and flame spray processes |
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Dominique Billières* / SAINT-GOBAIN COATING SOLUTIONS, FRANCE Denis Bemer / INRS, FRANCE Isabelle Subra/ INRS, FRANCE Marie Lecler/ INRS, FRANCE Roland Regnier/ INRS, FRANCE Yves Morelle/ INRS, FRANCE |
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Thermal spray of Zn, Zn/Al, or Al is a technique extensively used to make long-lasting anticorrosion coatings on steel structures. To make such coatings, the two simplest and most practised processes are electric arc spray and wire flame spray. These two processes are generating molten particles by melting and atomizing the tip of the wires, and these particles are then accelerated and impinge the substrate to build the coating. An understanding of fume emissions is important to determine the ventilation air flow rate of the spray booth, or for assessing exposure near the process. It is also a useful parameter in designing a downstream dust filtration unit. Two thermal metal spraying processes were studied to characterize fume emission: flame spraying and electric arc spraying. Fume emission was extracted by a semi-circular hood placed inside a ventilated cabin. Aerosol concentration was measured inside the exhaust ductwork using various instruments: an ELPI impactor (Dekati), a CNC 3022A (TSI), a TEOM microbalance (R&P) and sampling filters, scanning electron microscope (SEM). Electric arc spraying produced much more fumes and fine particles than flame spraying. Aluminum spraying also produces large fume quantities compared to the Zn spraying under the same conditions. The aerosol comprised submicron particles and 95% of the numerical particle size distribution was less than 100 nm. The nanometric nature of the fume particles was confirmed by observations on the SEM. The strong dilution caused by compressed air has the effect of strongly limiting particle coagulation and, in turn, the size of the agglomerated particles. Electric arc spray has taken market share versus wire flame spray for Zn, ZnAl, or Al spraying, due to its higher productivity, but this study shows that it generates much more particle emissions: this should be considered when choosing the process to spray Zn, ZnAl, or Al. |