AC SPARK PLUG INVOLVEMENT
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During the early to mid 1950's,
General Motors Corporation developed a procedure using
ball mills, elutriation, and blending to manufacture
test dusts.
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AC Spark Plug division of General
Motors Corporation process specification number 2323
describes the production process procedure to produce
AC Standardized Air Cleaner Test Dust, Coarse Grade,
Part Number 1543637. It outlines a process where 100
pound lots of Arizona Sand are ground a specified number
of revolutions in a ball mill containing steel balls.
Excess fine particles generated during the milling process
are removed using an elutriation process in water. The
coarse material remaining is dried in an oven, remilled
in a Fitzpatrick commuting machine and blended.
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Blending consisted of four milling batches
resulting in a blended lot containing 400 pounds of test
dust. Blended dust was analyzed to determine if specified
particle size distribution was achieved.
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AC Spark Plug division of General Motors
Corporation Process Specification Number 2322 describes
the production procedure involving manufacture of AC
Standardized Air Cleaner Test Dust, Fine Grade, Part
No. 1543094. The procedure specifies a process where
100 pounds of Arizona sand is milled in a ball mill for
a specified number of revolutions. Two mill batches were
blended together to form a single 200 pound batch of
dust. Blended dust was analyzed to determine particle
size distribution.
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Particle size of fine and coarse test
dusts produced by AC Spark Plug originally involved use
of a Roller Particle Size Analyzer manufactured by American
Instrument Company. This apparatus fractionated dust
particles into graded sizes, based upon Stokes Law in
connection with a flow of air. The following table defines
particle size specifications for AC Fine and Coarse Test
Dusts using the Roller Analyzer:
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PARTICLE SIZE DISTRIBUTION BY WEIGHT, %
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Size, microns
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Fine Grade
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Coarse Grade
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0 - 5
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39 ± 2
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12 ± 2
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5 - 10
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18 ± 3
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12 ± 3
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10 - 20
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16 ± 3
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14 ± 3
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20 - 40
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18 ± 3
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23 ± 3
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40 - 80
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9 ± 3
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30 ± 3
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80 - 200
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9 ± 3
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SAE Air Filter Test Code Subcommittee, SAE Filter
Test Methods Subcommittee, Military Standards authors,
and others adopted the above table to define particle
size specifications relative to Standardized Arizona
Test Dusts.
SAE Air Cleaner Test Code Specification
J726C specifies the above particle size distribution
of AC Fine and Coarse Test Dusts using a Roller Analyzer.
In March of 1979 AC Spark Plug decided to begin using
a Leeds & Northrup Microtrac Particle Size Analyzer for
determining particle size distributions of test dusts.
February 1982 AC Spark Plug informed the Air Cleaner
Test Code Subcommittee that particle size limits of Fine
and Coarse Test Dusts would be based on the Microtrac
Analyzer and expressed as follows:
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PARTICLE SIZE DISTRIBUTION BY VOLUME, %
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Fine Grade
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Coarse Grade
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Size, microns
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(% less than)
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(% less than)
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5.5
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38 ± 3
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13 ± 3
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11
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54 ± 3
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24 ± 3
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22
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71 ± 3
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37 ± 3
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44
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89 ± 3
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56 ± 3
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88
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100
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84 ± 3
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176
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100
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Subsequently SAE Air Cleaner Test Code
- SAE J726 Specification was updated to include particle
size specification limits for test dust relative to the
Leeds & Northrup Microtrac Analyzer. AC Spark Plug continued
to use the Microtrac Analyzer until they ceased production
in August 1992.
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