Project at a Glance
Title: Final report on the development of a standardized test protocol for determining the relative transfer efficiency of spray guns.
Principal Investigator / Author(s): Joseph, Ron
Contractor: Ron Joseph & Associates
Contract Number: 92-352
Research Program Area: Emissions Monitoring & Control
Topic Areas: Stationary Sources
A Transfer Efficiency Test Protocol has been developed to evaluate the efficiency of a manual or automatic spray gun in comparison with a spray gun that the South Coast Air Quality Management District (SCAQMD) will select as its standard or baseline.
In developing the protocol it was first necessary to understand the sensitivity of transfer efficiency to various parameters, a comprehensive list of which is provided in Table 1.
Because tranfer efficiency is directly or indirectly affected by more than 15 parameters, it was necessary to focus this study on those that were considered to have the most effect. They were:
Coating rheology (solvent-borne coatings)
Spray gun type
Distance between the spay gun tip and the targets (flat panels)
Spray gun design
Water borne coating
The research demostrated that the protocol will yield repeatable results, and can be sufficiently sensitive to differentiate between spray guns of different types and designs. Except with guns for which the efficiency differences are not significant, the work showed that the relative ranking of spray guns, when compared against each other, is preserved even when panel size and coating formulation are changed.
Based on the results of the sensitivity studies, the Draft Protocol was modified to (a) identify a specific panel size, (b) standardize on a coating that can be used to evaluate all existing and future spray gun types, (c) specify parameters and their ranges that will need to be defined during a spray gun evaluation.
It is expected that the protocol can be used by the SCAQMD, industry, and other agencies to identify spray guns that are at least as efficient as a reference spray gun (yet to be chosen) which meets regulatory transfer efficiency requirements. The protocol will also permit the agency to identify spray guns that do not meet a minimum standard of efficiency.
The report provides recommendations for additional work that will further refine the protocol in the areas of (a) the possible use of a pressure pot as the coating reservoir in the fluid delivery system, (b) the effect of ambient humidity on the electrostatic application of the coating, (c) the effect of different solvent blends in the coating formulation on its electrostatic properties, (d) water-borne coatings, (e) the effect of air flow in the booth on transfer efficiency.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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