Many metal finishers perform welding and other secondary operations on parts they process. Welding of stainless steel parts produces hex chrome fumes, resulting in yet another potential headache for finishers already worried about their chrome plating operations.
But fumes and dust from welding, plasma cutting, and other operations can be handled relatively easily compared with airborne hex chrome from plating operations, according to one company.
United Air Specialists Inc. (UAS; Cincinnati) is a supplier of air-filtration and dust collection equipment for commercial and industrial applications. According to UAS, media filtration collectors with separate hoods and ducting are the best way to meet the U.S. Occupational Safety and Health Administration’s (OSHA’s) new hex chrome permissible exposure limit (PEL) of 5µg/m³. The company says it reached this conclusion after a study of the two main types of dust/fume collection systems: electrostatic precipitators (ESPs) and media filtration collectors.
“We looked at the effectiveness of ESPs and media filtration collectors in light of the new OSHA 5µ/m³ hex chrome exposure limit,” explains senior application engineer Ed Ravert. “ESPs have long been ideal for the collection of submicronic dust/fume particles. Typically, they are used for source-capture systems or ambient-air systems, because they require very little maintenance and are not subject to periodic media filter replacement costs.
“However, our review clearly showed that ESPs cannot match the overall efficiency of a media filtration source capture system for hex chrome dust/fumes, especially if the air is to be returned into the work space,” Ravert says.
“If the work generates hex chrome dust/fumes and ambient air collection is desired, we found that the worker must be required to wear personal respiratory protection at all times,” he adds. “Even then, a monitored HEPA after-filter would be required if the air was to be returned to the workspace.”
According to UAS, media filtration units can collect hex chrome dust and fumes with 99.9% efficiency, and, depending on the manufacturing process, source-capture systems do the best job of capturing contaminants using the lowest air flow. Source-capture systems include hoods, ducting, an air-cleaning device and air-moving devices (fans). The air-cleaning device can include swing arms and hoods. “With separate hoods and ducting, the cartridge collector is ideal for hex chrome dust/fumes because the dust/fumes are captured before they can escape into the ambient air,” Ravert says.
UAS recommends its SFC series of downward-flow cartridge dust collectors combined with either a hooding or ducting as the ideal solution for hex chrome dust/fume collection in welding, cutting and other operations. The modular units can be placed in a factory or outdoors, and use patented pulse-jet cleaning technology to continuously clean filters during operation. Systems are available for air volumes from 510 to 62,280 cfm.
Unfortunately, says Ravert, such systems are not applicable for any airborne hex chrome that may be generated by plating or other wet processes. “Platers have a much tougher nut to crack when it comes to hex chrome control and abatement,” he says.