Note: Descriptions are shown in the official language in which they were submitted.
1093Z 76
The invention relates to a novel moulding composition
or masses for production of cores and casting moulds.
Moulding compositions or masses according to the
invention finds its application in production of casting cores
and moulds by methods known to the foundry industry.
Core sands and moulding sands, generally applied in the
industry, are most often produced from quartz sand as well as
binding agents. Binding agents can be of various types, e.g.
traditional oils, starches, clay and different combinations, such
as urea-formaldehyde resin possibly stabilized with amines or
phenol-formaldehyde-furfuryl resin. As a binder there have been
known coal slime as well as mixture of water glass with urea
resin and kaolin. From among binders having the character of
oils there have been known e.g. pine oil with addition of paste
starch or dextrin, vegetable oils or organic solvents possibly
turpentine oil with resin-fatty acids as well as combinations of
solid products of oxidation of drying oils and elemental sulphur.
There has also been known a binding agent for cores and casting
moulds comprising per 100 parts by weight 50-30 parts by weight
of bentonite, 50-80 parts of Portland cement, 3-12 parts of
sodium carbonate, 1.5-6.5 parts of hydrated lime and 0.5-2 parts
of aluminium hydroxide. The considerable variety of binders
added to the grain base indicates how extremely important their
proper selection is, since both further treatment of the masses
e.g. hardening of cores and moulds made of it, as well as
mechanical and technological properties depend on the type of
binder used. Some of the hitherto applied binding agents are
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l~g3276
expensive, low efficient or require a long time to harden in
the core and moulding sand. Cores and moulds produced from the
known masses are characterized either by a small abrasion
resistance or are very difficult to remove, particularly cores.
The hitherto applied methods of removing cores from castings
consist of a mechanical shaking-out by means of e.g. grating
shake-out, pneumatic jumpers and other devices. These methods
produce noise and dusting in the air of the foundry. Moreover
all core sands and some moulding sands presently used cannot
be recycled and are discarded, since their regeneration by
existing methods is unprofitable.
The present invention is aimed at elimination of the
disadvantages of known core and moulding sands by providing
novel compositions, so that cores and moulds made from them
reveal high abrasion resistance and can be easily removed by
non-mechanical means at minimum cost without creating a noise
problem or putting dust in the air.
Moulding compositions or masses for production of
cores and casting moulds according to the invention comprises
per 100 parts by weight of grain base, quartz sand, 0.5-30 parts
of alkaline metal hydroxides, preferably sodium hydroxide
and/or potassium hydroxide, 1-40 parts of alkaline metal carbon-
ates, preferably sodium carbonate and/or potassium carbonate,
1-15 parts of water as well as 0.2-10 parts of known hydrophilic
binders, preferably dextrin. Cores and moulds produced from
the masses according to the invention, as the conducted tests
prove, reveal high abrasion resistance and are durable for a
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1093276
period of about 4 weeks without decreasing their properties.
After production of cores or moulds from moulding
and core sand according to the invention, the core in the casting
or mould are subjected to the action of a solvent, particularly
water. The preferred method is by dipping e.g. in a tank. The
core or mould undergoes spontaneous crumbling within 2-6 minutes.
Cores or moulds, produced from masses according to the invention,
under the action of temperature in a mould develop a capacity
to absorb solvents. The absorbed solvent destroys bonds within
the masses in the core or mould. The removal of cores from
castings by this solvent method is extremely simple, inexpensive
and safe operation. It does not cause noise or emit dust into
the air. The surfaces of castings made by this method are
characterized by exceptional cleanliness, free of residual core
sand grains. The core and moulding sand when kept in the water
or solvent undergo regeneration and can be reused.
The following examples are preferred embodiments of
the invention but are not intended to limit the scope of the
invention.
Example I. Composition of the masses:
100 kg of quartz sand
1 kg of pale dextrin
6 kg of sodium carbonate
1.5 kg of sodium hydroxide
4.5 kg of water
The moulding composition or masses is prepared in a
roll mixer. The said mixer is loaded with 100 kg of quartz sand,
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1093Z76
1 kg of pale dextrin and 6 kg of sodium carbonate. This com-
bination is mixed for 2 minutes. Separately there is prepared
a solution comprising 1.5 kg of sodium hydroxide and 4.5 kg of
water. This solution is added into the mixer without stopping
the mixing. The operation of mixing is continued for a further
3-4 minutes.
From the prepared moulding composition or masses there
is produced by the known methods, a core consisting of inner
shapes of the head. The core is hardened by blowing in a core
box for 15-30 seconds with carbon dioxide. To the tank filled
with water there is inserted a cast of the head, produced from
the aluminium alloy together with a core reproducing the inner
shape of the head. After 5 minutes of maintaining the head
and core in the water there occurs a complete crumbling of the
core and the cast is taken out of the tank. The core sand
remaining in the tank will be separated from the binding agent.
Thus the cast does not require further any cleaning of the
inner surfaces.
Example II. Composition of masses:
100 kg of quartz sand
1 kg of pale dextrin
10 kg of sodium carbonate
3 kg of sodium hydroxide
5 kg of water
The masses is prepared as in the Example I.
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In the table below there are presented properties of
the core and moulding sand according to the invention. The given
properties relate to top and lower values for the quoted examples.
10932~76
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1093276
The content of hydroxides and carbonates has a sub-
stantial influence on the technical properties of the masses.
An increase in these components in the masses improves the
technical properties, however, permeability of the masses
decreases and the time for crumbling of the masses in solvent
is slightly longer.
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