Page 18 - GlobalEyes Edition 1 Feb 2011

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The plant operates one of the
largest green sand moulding
units ever made, a Jolt Squeeze
Kunkel-Wagner. It produces
a plate size of 2,400mm x
1,200mm and exerts pressure
on the pattern of more than
1,450 pound per square inch,
resulting in a very hard mould.
The quality of the raw materials
used in the Green Sand
process is critical in producing
high quality castings. High
purity silica sand is mixed
with clay containing sodium
bentonite, the principle bonding
medium, and coated with
the appropriate water based
coating to produce the desired
surface finish.
Technicians at Runcorn run
rigorous tests on the Green
Sand mix to ensure the foundry
sand has the correct chemical
and physical properties to
produce consistent quality
moulds with a low level
of rejects.
The pH level of the sand used in
the process is the most critical
factor in sodium bentonite
systems, as it affects the gelling
ability of the clay. The viscosity
test measures the performance
of clays in acidic and alkali
conditions, testing gel strength,
which ultimately determines
green strength and moisture
absorbance – two key factors
in the success, or otherwise, of
the process.
Also tested are green compression
and green shear strength, moisture
content and the sand’s ‘dry strength’
- its ability to withstand handling and
the forces of casting, as well as the
ease with which the mould can be
knocked out.
Other key measures are friability, the
sand’s ability to resist edge breaking
when inserting cores into their prints
and mouldability, the ability for the
sand to follow the pattern.
This comprehensive testing regime
has contributed to a very low level of
mould related defects, now less than
0.1%. As the entire reject rate for the
plant is below 0.9%. Less than 10%
of those defects are related to the
green sand!
Sand is greener on
the Runcorn side
Twenty thousand tonnes of steel castings are now produced each year at Runcorn
using the environmentally more friendly Green Sand process. The castings produced
with this process are destined for the local, export mining and rail markets.
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