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Table 3 COM-A parameters for size distribution and roundness measurements
COM-A Parameters Description of Parameters
Xcmin (b) Breadth, particle diameter, which is the shortest chord of the measured set of maximum
chords of a particle. This is thought to be a good measure of the mechanical sieve opening.
XFemax (l) The particle diameter, which is the longest Feret diameter of the measured set of Feret
diameters of a particle.
Feret diameter The distance between two parallel tangents of the particle at an arbitrary angle.
b/l Sphericity parameter b/l = Xcmin/XFemax.
For an ideal circle, b/l is 1, otherwise it is smaller than 1. The threshold value used for b/l
was 0.83.
SPHT Sphericity parameter SPHT = 4A/U2
U--measured circumference of a particle
A--measured area covered by a particle. For an ideal circle, SPHT is 1, otherwise it is
smaller than 1. The threshold value used for SPHT parameter was 0.9.
submitted roundness data using the roundometer. get percent retained and roundness using t-statistics.
Eight laboratories submitted size distributions and The rejection probability of the computed t-statistics
roundness data using the COM-A device. Four labo- for a 5% level of significance would indicate which of
ratories submitted size distribution and roundness the utilized methods most accurately measured the
data using the COM-B instrument. The data were intended properties of the glass beads.
reviewed to identify possible outliers; confirmed out-
liers were eliminated from the subsequent analyses. Analysis of Results from Traditional
Mechanical Methods
Method of Analysis Sieve analysis and roundness measurements
The ILS test results were analyzed for precision in using mechanical sieves and the roundometer were
accordance with ASTM E691. Prior to the analysis, conducted following the ASTM D1214 and ASTM
any partial sets of data were eliminated by following D1155 test methods, respectively. The following
the procedures described in E691 for determining sections provide the results of the precision and bias
repeatability (Sr) and reproducibility (SR) estimates of analysis of the measurements using the traditional
precision. Data exceeding critical h and k values were methods.
eliminated as described in the method. Once identi-
Size Measurements Using Mechanical Sieve
fied for elimination, the same data were eliminated
from any smaller subsets analyzed. The sieve openings and the corresponding sieve
The data from different analysis methods were numbers for each glass bead type are provided in
also analyzed for bias by comparing them with the tar- Table 1.
Table 4 COM-B parameters for size distribution and sphericity measurements
COM-B Parameters Description of Parameters
Thickness (T) Thickness of particle. This is used for sieve analysis of particles.
Length (L) The largest length of the particle.
TL = T/L Aspect ratio of thickness/length, which is 1 for a perfect circle. Otherwise it is smaller
than 1.
NSP Ratio Average Ratio of Da/Dp of all particles analyzed, which is the same as (SPHT)1/2
Da = Diameter calculated of the imaged area of the particle, as an equivalent circle
Dp = Diameter of perimeter calculated of the imaged circumference of the particle,
as an equivalent circle
Aspect ratio of Da/Dp is 1 for a perfect circle. Otherwise it is smaller than 1.
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Table 5 Statistics of percent retained of Type 1 samples using mechanical sieve shaker
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#30 13 5.0 5.0 0.2 3.7 0.4 7.5
#50 14 50.0 48.4 1.0 2.1 1.7 3.4
#100 14 45.0 46.4 1.1 2.4 1.6 3.5
Type 1 Samples. The results of mechanical sieve e.g., the measured retained value of 58.8% for the
analysis of Type 1 (Y) samples were received from #18 sieve is compared with the target retained value
15 laboratories. The precision estimates of the size of 55%. As indicated in the table, the repeatability and
distribution of Type 1 specimens were determined reproducibility coefficients of variation are signifi-
after eliminating the outlier data. All remaining data cantly larger for sieves #16 and #25 than for sieves
were re-analyzed according to the E691 method to #18 and #20. This is likely due to the smaller mass
determine the repeatability and reproducibility statis- percentage of beads in the #16 and #25 size classes
tics shown in Table 5. As indicated from this table, the relative to the mass percentage of beads in the #18 and
measured percent retained agrees relatively well with #20 size classes.
the target percent retained for all sieve sizes, e.g., mea-
sured retained value of 48.4% for #50 sieve agrees Type 5 Samples. The results of mechanical sieve
well with the 50% target retained value. The variabil- analysis of the Type 5 (C) samples were received
ity of the data as indicated by the repeatability and from 14 laboratories. The variability of the size dis-
reproducibility coefficients of variation is relatively tribution of the Type 5 specimens was determined
low. The repeatability and reproducibility coeffi- after eliminating the outlier data. All remaining data
cients of variation corresponding to the #50 sieve size were re-analyzed according to the E691 method to
are lower than those corresponding to the #30 and determine the repeatability and reproducibility sta-
#100 sieve sizes. This may result from the larger mass tistics shown in Table 7. This table indicates that the
percentage of beads in the #50 size class than in other measured percent retained agrees fairly well with
size classes. the target percent retained for all sieve sizes, e.g., the
measured percent retained value of 58.5% for the #14
Type 3 Samples. The results of mechanical sieve sieve is compared with the target retained value of
analysis of the Type 3 (P) samples were received from 55%. As shown in Table 7, the repeatability and
14 laboratories. The precision estimates for the size reproducibility variability values of all except the #14
distribution of the Type 3 specimens were determined size class are rather large. This is likely due to the
after eliminating the outlier data. All remaining data smaller amount of beads in those size classes com-
were re-analyzed according to the E691 method to pared to the amount of beads in the #14 size class.
determine the repeatability and reproducibility statis-
tics shown in Table 6. The table shows that the mea- Summary of Percent Retained by Mechanical Sieves.
sured mass percent retained values agree reasonably The analysis of the traditional mechanical sieve
well with the target percent retained for all sieve sizes, mass percent retained data suggests that in general
Table 6 Statistics of percent retained of Type 3 samples using mechanical sieve shaker
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#16 13 5.0 6.5 0.4 6.9 2.5 38.0
#18 13 55.0 58.8 1.1 1.9 3.4 5.7
#20 12 35.0 30.3 1.2 4.0 1.9 6.3
#25 14 5.0 4.3 0.8 18.2 1.1 26.5
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Table 7 Statistics of percent retained of Type 5 samples using mechanical sieve shaker
No. Target Measured Repeatability Reproducibility
Sieve of % % Retained,
Sizes Labs Retained Average STD, % CV, % STD, % CV, %
#12 14 5.0 5.2 0.6 12.4 1.0 18.9
#14 13 55.0 58.5 2.2 3.7 4.3 7.4
#16 14 35.0 31.4 2.8 9.0 4.1 13.2
#18 13 5.0 5.0 0.7 14.4 1.2 23.6
the measured percent retained in the most preva- of the statistics in Table 8 indicates that the average
lent size classes provides the closest agreement with roundness of the Type 1 samples was overestimated,
the target value. The measured values also yield the e.g., the measured percent round of 74.2% for the #50
smallest repeatability and reproducibility coefficients beads is larger than the target roundness of 70%. Sim-
of variation for the sieves with the largest number of ilar to the observation from the size distribution sta-
beads. Furthermore, the traditional mechanical sieve tistics, both repeatability and reproducibility coeffi-
measures mass percent retained of Type 1 beads more cients of variation of roundness measurement are
accurately and precisely than that of Type 3 and significantly smaller for the #50 beads, which was the
Type 5 beads. most prevalent size in the Type 1 samples.
Roundness Measurements Using Roundometer Type 3 Samples. Nine out of the 14 laboratories that
Type 1 Samples. The results of roundness analysis of conducted mechanical sieve analysis on the Type 3
Type 1 samples were received from 11 laboratories. samples also returned results on the roundness of the
The variability of percent roundness of Type 1 spec- samples. After removal of outliers, all remaining data
imens was determined after eliminating the outlier were re-analyzed according to the E691 method to
data. All remaining data were re-analyzed according determine the repeatability and reproducibility sta-
to the E691 method to determine the repeatability and tistics shown in Table 9. A review of the statistics
reproducibility statistics shown in Table 8. A review in Table 9 indicates that there is a good agreement
Table 8 Roundness statistics of Type 1 samples using roundometer,
target roundness of 70%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#30 9 72.2 2.3 3.2 5.7 7.9
#50 11 74.2 2.5 3.4 3.8 5.1
#100 10 77.7 4.8 6.2 4.6 5.8
Table 9 Roundness statistics of Type 3 samples using roundometer,
target roundness of 80%
No. Measured % Repeatability Reproducibility
Sieve of Round,
Sizes Labs Average STD, % CV, % STD, % CV, %
#16 6 75.1 1.7 2.3 4.1 5.5
#18 8 78.5 2.3 2.9 4.1 5.2
#20 7 73.9 1.6 2.1 4.7 6.4
#25 7 65.6 12.5 19.0 11.8 18.0
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