Metallic Fume Emission and Operator Exposure During WC-10%Co-4%Cr Spraying by HVOF

The increasing use of HVOF (high-velocity oxy-fuel) coatings to replace hard chrome plating was initially motivated by the environmental and health risks associated with hexavalent chromium (Cr⁶⁺) emissions during the plating process. Following performance optimization and proper coating selection, it has been found that the potential increase in performance and the cost/process-time reduction offered by the HVOF process often justifies its application. Recently, the use of Cr-containing alloys processed by HVOF has drawn attention to the potential release of Cr⁶⁺ during heating of metallic chromium. For instance a new California regulation for airborne toxic control measures to reduce emission of hexavalent chromium from thermal spraying is in preparation. The present study focused on monitoring operator exposure during the HVOF spraying of WC-10%Co-4%Cr. The spraying was performed using a JP-5000 HVOF gun in a spray room in which a ventilation flow rate of 10,000 scfm was imposed. Air sampling was taken in the spray room as well as in the adjacent control room in accordance with the NIOSH 7300 and 7600 standard methods. A portable sampler attached on the operator’s chest was also used to monitor the operator exposure during a typical workday. Results indicate that even though metallic fumes of Co and Cr are present in the spray room during spraying, the hexavalent form Cr⁶⁺ is not detected. It was concluded that an operator entering the spray room for a limited amount of time with the gun in operation would be exposed to only low fume levels that can still be reduced by wearing an appropriate respiratory mask.