Richard Mahaffey on thu 7 jul 05
While in undergraduate school at San Jose State in the late 60's early
70's in the class titled Design for Ceramic Processes (a class aimed at
Industrial Ceramic processes) we visited
Gladding -McBean who made porcelain and other things. Some of us used
their porcelain for a time. Anyway at the plant they took pugs of
clay that were quite near dry and turned them on a lathe with methods
that were like wood turning on a lathe as well as using a metal lathe
for the same process. They were making porcelain insulators that look
kind of like pagodas with a series of circular ribs stacked on each
other. We were stunned to say the least that the insulators were made
this way. We thought that those were all slip cast, but the properties
were not suitable for insulators.
The coolest part was when the tested the insulators that had been
glazed to cone 12 and fired. They were tested in a cage where wires
were hooked up to the insulators and a huge, I mean HUGE voltage was
fed into the wires (I think it was 40,000 volts - I can not find my
notes from that section of the class) and we were treated to a
lightening storm inside the cage with bolts of electricity arcing
everywhere. After the test the electricity was turned off and the
insulator were examined. The rejects had holes and burn marks in them
sometimes the rejects just broke.
This is what I think of when I hear turning associated with clay.
YMMV
Rick Mahaffey
Helen Bates on sat 9 jul 05
Hi Rick,
I was interested in your comment that slip-casting as a process was unsuited
to the formation of the huge insulators used in electric transmission
installations, so did a little searching.
I didn't find anything specifically answering the question that occurred to
me "Why is slip-casting unsuitable for manufacturing these insulators?" but
I did find some pages that list (relatively briefly) a number of ceramic
forming processes and / or considerations.
The last link is to a discussion of the advantages of an "isostatic" slip
formation process followed by the usual "turning", drying, glazing and
firing, as opposed to the usual extrusion method, which requires two drying
periods of some length besides the turning, glazing and firing.
http://www.worldcyberu.com/samplelessoncp4.htm#cp4tradproc
http://tinyurl.com/77aso
http://www.ppcinsulators.com/page.php?parent=3
There is a huge ceramics world out there...
Helen
(Belleville, Ontario, Canada)
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