United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S2-88/026 June 1988
&EPA Project Summary
Development of Proposed
Standard Test Method for Spray
Painting Transfer Efficiency
K.C. Kennedy
The two-volume report describes
the development and verification,
respectively, of a standardized
spray-painting transfer-efficiency
test method. The result of the
research was determined to be viable
for laboratory evaluation.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to an-
nounce key findings of the research
project that is fully documented in two
separate volumes of the same title
(see Project Report ordering infor-
mation at back).
Introduction
This research program was initiated
with the objective of developing a
standardized spray-painting transfer-
efficiency test method. Both review of
the literature and laboratory research
were conducted. Transfer efficiency
measurement methods presently used
by industry were evaluated and
compared. The best characteristics of
these methods were incorporated into
the final proposed standard method. The
resulting method was determined to be
viable for laboratory evaluations. It still
awaits adaptation and verification for
production line applications.
Phase I. Method Development
Phase I of the transfer efficiency
development program involved the
formulation of a practical procedure.
Many methods used by industry were
reviewed and evaluated. The best
characteristics of these methods were
assembled, resulting in a testing
procedure suitable for extensive
laboratory evaluation of the accuracy and
precision of the results.
Based on ASTM 691-79, the first
requirement for the "existence of a valid,
well-written test method [is that the test
method] has been developed in one or
more competent laboratories and has
been subjected to a screening procedure
or to ruggedness testing." To fulfill this
requirement, the test method was
developed at three painting laboratories
which specialize in paint and painting
equipment testing and evaluation.
In the initial tests, the standardized
laboratory method consisted of three
major equipment types, two paint types,
and specially designed spray targets.
Paint was applied to the targets under
rigidly specified conditions. The amount
of solids deposited on the target was
divided by the net solids sprayed at the
target to arrive at transfer efficiency.
The results of the initial evaluations
within each laboratory were tightly
grouped and exhibited a high degree of
precision. The standard deviations for the
series of tests were defined as 2.5 or less
transfer efficiency points for each site.
Phase II. Method Verification
The Phase II program involved
extensive testing of the transfer efficiency
procedure at eight laboratory sites in
accordance with ASTM 691-79. These
evaluations were to verify the method's
accuracy, precision, and ruggedness; i.e.,
the repeatability of the method and how
well it defines the actual site's transfer
efficiency, six replicate transfer efficiency
measurements were made for each
equipment type at each laboratory.
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Results
In classical interlaboratory programs,
there are two measures of the quality of
the method: accuracy and precision.
Precision is the measure of variability.
The precision goals based on Phase I
results were established as a standard
deviation of 2.5 transfer efficiency units.
Accuracy is the measure of how far off
the observed values of transfer efficiency
are from the true transfer efficiency. In
this research, there is no known true
measure of transfer efficiency; therefore,
accuracy cannot be addressed. Since
accuracy is a measure of the bias
encountered in estimating the value of a
parameter (and because there is no
reason to believe that the spray system,
laboratories, and targets examined have
a significant bias), the proposed transfer
efficiency test method should be
reasonably accurate. The absence of
statistical evidence regarding bias may
be interpreted as an absence of bias.
Therefore, it can be assumed that the
true value determined represents the
actual transfer efficiency exhibited at the
specified site.
The results of these experiments
document the maturity of the proposed
transfer efficiency test method and the
expected ruggedness of the results to
differences within and between
laboratories. As anticipated from earlier
research efforts, the transfer efficiency
results for each spray system were
different. However, the results for ea<
spray system demonstrated exception
consistency when expressed as withii
laboratory standard deviation. Standai
deviation is expressed in units of transf
efficiency. It can be used for estimatir
precision at various confidence interval
The within-laboratory standard deviatic
across eight laboratories was:
Conventional air spray 1.5<
Electrostatic air spray 1.91
Airless spray 1.K
These within-laboratory standai
deviations clearly demonstrate th
capability of the test method to produc
consistent results within a particul
laboratory. The within-laboratoi
standard deviations were well below tt
2.5 predicted at the onset of this project
K.C. Kennedy is with Centec Corp., Reston, VA 22090.
Charles H. Darvln is the EPA Project Officer (see below).
The complete report consists of two volumes, entitled "Development of
Proposed Standard Test Method for Spray Painting Transfer Efficiency:"
"Volume I. Laboratory Development" (Order No. PB 88-204 2431 AS;
Cost: $19.95)
"Volume 2. Verification Program," (Order No. PB 88-204 250/AS; Cost:
$19.95)
The above reports will be available only from: (cost subject to change)
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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Penalty for Private Use $300
EPA/600/S2-88/026
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