General
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Laboratory
tests were performed to determine the effect of five commonly used
carbonaceous additives on new sand mixes. The additives evaluated were
seacoal, pitch, petroleum asphalt, Gilsonite of a "coarse"
and "fine" grind, and blown asphalt. Physical sand
properties developed with non-seacoal carbonaceous materials were
equal to or superior to seacoal at significantly lower additive
levels. Gilsonite and asphalt mixes appeared to improve physical
properties of density, water requirements and green, dry, baked and
hot strengths. An even greater improvement in foundry sand green,
baked, and hot strength was obtained by increasing the fineness of
grind of the Gilsonite. It is postulated the finer material provides
better sand coating. The higher strength may be attributed to improved
sand wetting by the thermoplastic asphalt materials.
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For
technical and economic reasons, molds and cores for metal casting are
composed of a combination of sands and additives. In the green-sand
molding process. additives include a small percentage of bentonite,
which acts as a binder, and combustible additives such as seacoal. In
the shellmolded or chemically bonded casting process, small amounts of
organic material and chemicals are added.
Technology
- Sand is used to
modify soils and construct turf systems for various sports turf
applications to promote proper air and water management. Without a
doubt sand is the most extensively used amendment on a weight basis to
modify turf systems. The use of sand has been extensively reviewed by
the United States Golf Association (USGA) in regards to putting green
construction. A wide range of sports turf applications such as
football, baseball, race tracks and soccer, are utilizing the concepts
of the USGA putting green construction guidelines to design and build
turf systems for high performance demands. Not all sports programs
have the budget for sand based sports fields and will utilize sand in
other ways to improve the performance of a field.
- Sand is often used
in conjunction with the native soil in what is known as a by-pass
system. The Cambridge™ system is a commercially available system
that uses sand in trenches and for creating a permeable sand cap over
the trenches to remove water during periods of high rainfall. There
are several designs that use a by-pass approach with sand. We are
often approached about mixing sand with native soils to improve
permeability and to lower excessive water holding values. The mixing
of sand with soil is not as effective as some are led to believe. If
the proper sand particle size is used and the correct amount of sand
is added, some benefit can be realized.
- Developments in
core-making technology and binding agents have resulted in an increase
in specific strength. Aside from a low content of binding composition
in the core moulding material, there has also been a raft of
technological and economic advantages leading to the cost-effective
achievement of the required strength levels – such as improved
shake-out and reclamation performance and a reduction in emissions and
gas-induced defects.
Report
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Feedstock
for the green sand process consists of high-quality silica sand; about
10% bentonite clay (as binder), 2 - 5% water and about 5% coal dust or
starch (which improves the casting finish). The type of metal being
cast determines which additives and what gradation of sand is used.
Chemically bonded sand cast systems require one or more organic
binders (usually proprietary) in conjunction with catalysts and have
different hardening/setting procedures. Typically, about 1 ton of
foundry sand is required for each ton of iron or steel casting
produced.
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