Joseph Herbert on wed 31 oct 07
Sher wrote: Can anyone tell me about mesh sizes? I use sieves With 100 and
80 mesh. I saw on ebay metal sieves that I would be interested in, but they
give the sizes in decimals of an inch, I think, and mm sizes, even micron
sizes. What does the 100 and 80 measure on the glaze sieves? I never
thought of it before, just took it for granted. Sher morrow
Ah! Basking in the golden light of the ancient age...
My favorite story about "Standards" involves the collapse of the Tay river
Bridge (or some other 19th century British bridge collapse). It may just be
a story and unrelated to the actual failure of the bridge but it is this:
The examination of the remains of the bridge showed some examples of
startling metal failure in the Wrought Iron members. Closer examination
showed lots of carbon and slag inclusions, generally not too good metal for
railroad bridge construction. The engineering company was of course alarmed
because the investigation was looking at them as displaying inadequate
performance. So they went to the metal supplier and said, "What is this
rotten metal you sold us, we specified your best wrought iron for these
bridge members?" The supplier replied, "Oh, you should have asked for our
"Best Best Best" wrought iron." So, being unfamiliar with the "standards"
of the supplier, the engineering company unintentionally asked for the worst
of their products for their critical use.
There was a time when people would just make stuff up. Companies who were
large suppliers of something would make up some term or designation for
their particular product line and that would then, if the company was large
and influential, become a "Standard" for smaller companies working in the
same industry. This still happens but in a more organized way when industry
task forces or working groups get together to define something like "the
HTML protocol" or some such. They still make stuff up but they think about
it and sort of agree at the start. There are also the governmental and
quasi-governmental standards and testing entities that have attempted to
make sense of the proliferation of methods and materials that have
accompanied the industrial revolution and follow-on development.
The sieve sizes stated are a result of activities in the previous age of
making stuff up. The numbers you refer to, #80 or #100, generally refer to
the numbers chosen for a series of screens used by the U.S. Bureau of
Standards in 1919. The sizes of the openings seem to bear no relation at
all to the numbers assigned to the particular sieve, nor do the number of
wires per inch, nor the size of the wires... A table showing the numbers
and the sizes of the openings can be found on the internet by entering
"Sieve Sizes" in an internet search engine. In the case of the mentioned
sieve sizes, the #80 sieve passes particles smaller than 0.0070 inches; the
#100 passes particles smaller than 0.0059 inches.
The bureau of standards is no longer called by that name - National
Institute of Standards and Technology (or NIST) - but the sieve sizes linger
on.
There is also a Tyler standard screen scale sieve set. This "Standard" also
has a sieve numbered 80 and one numbered 100. They pass particles of 0.0069
and 0.0058 respectively, pretty close. In addition, there is a British
Standard sieve size series that does identify itself by meshes per inch.
That series has no #80 sieve but does have #85 sieve which passes 0.007 inch
particles, and a #100 that passes 0.006 inch particles, again close.
Metric sieves are numbered (I think) by the size of opening in microns or
thousandths of a millimeter.
Other examples of the arbitrary method of "standards" generation may
include: Letter and number drill sizes, numbered wire gauges, Some**
pyrometric cone numbers, names of olive sizes, graphite content of pencil
lead, food can sizes, envelop sizes, names of larger paper sheet sizes,
Screw sizes, and the list goes on.
One thing about the sieves is that the changes in the sizes of the openings
are, perhaps, related to the kind of work the sieves were (are) used for.
One of the major uses is the classification (that word is used to describe
the process of running an unsorted sample through a set of sieves) of soils
and aggregates by determining the relative amount of a particular
particulate size in a sample. If the material is intended to be used for
road building, a set of three sieves might be used with a pan to collect the
fine material. A researcher might find that material with too much fine
stuff (passing all the screens) could not be used unless washed. A person
looking at a natural material for use as concrete aggregate would look for a
wide distribution of sizes and might use several screens to see how the
particle sizes are distributed. In a more esoteric setting, a person might
look at particle size distribution to discover the depositional environment
of a sediment. The size distribution of a wind blown beach sand is
different from that of a water deposited sand bar.
** Finally, cone numbers as arbitrary standards. The cone numbers between 4
and 10 have Silica parts by weight that match their cone number. This could
be a coincidence but I would think not. The irregularity of the maturing
temperature gaps (ranging between 10 and 25 degrees C) indicate to me that
the composition was driving the choice of number. The Alumina parts by
weight through this range and above (up to cone 27) is consistently one
tenth of the Silica. The fluxes are of constant parts by weight ( at 1)
through the range (up to cone 27). All this is from the Lange's handbook of
chemistry, 1946 edition. I assume that the research of cone formulation
started with the arbitrary selection of flux amount and alumina/silica
ratio, probably based on a glaze or clay body composition in the temperature
range of interest. I then expect that the temperature gap between the
single part increase was thought to be too small above cone 10 and they went
to a two part increase per cone number. Going to lower cone numbers shows
no discernable pattern.
Joe
Joseph Herbert
Technical Writer
Irving, Texas
214-725-8305 (Cell)
Randall Moody on wed 31 oct 07
Sieve Number Opening Size( mm) (Nominal)
60 0.250
80 0.180
100 0.150
140 0.106
200 0.075
270 0.053
On Oct 31, 2007 11:53 AM, Joseph Herbert
wrote:
> Sher wrote: Can anyone tell me about mesh sizes? I use sieves With 100
> and
> 80 mesh. I saw on ebay metal sieves that I would be interested in, but
> they
> give the sizes in decimals of an inch, I think, and mm sizes, even micron
> sizes. What does the 100 and 80 measure on the glaze sieves? I never
> thought of it before, just took it for granted. Sher morrow
>
>
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