CPT International 03/2015

PRESSURE DIE CASTING
core package that can then be inserted
into the mold easier and more quickly.
An oxide layer on the aluminum casing
can cause problems in some applications,
particularly if they involve
temperature control. This layer can be
removed by pickling followed by galvanization,
achieving better binding
to the melt. The cores are not faced,
but used in the state they were delivered
to the foundry by Drahtzug Stein
combicore.
from a single casting
Insertion of the prepared formed core
in the pre-treated and sprayed metallic
mold is carried out by a robot. Whereby
the core is frequently held in the
mold and fixed with blind holes and
slots. In sand casting, chaplets can simplify
fixing of the Combicore core.
In the case of gravity casting a vacuum
should, in most cases, be connected
to the core. There can be air inclusions,
depending on the geometry and
diameter and the corresponding degree
of compaction of the salt core. During
the casting process this air expands. In
order to prevent it penetrating the soft
core casing and causing damage it must
be deliberately suctioned off before and
during the process. As an alternative,
compaction of the salt core can be increased
in some applications.
If necessary, the pipe is pre-heated
before or after insertion to reduce the
cooling effect on the melt. This can
be sensible with voluminous and long
pipes, in particular, with strongly differing
casting wall thicknesses (Figure 6).
After the casting process, the castings
are removed from the mold as usual.
Drawing of the Combicore core can
take place directly thereafter or later
in a separate work process. As already
mentioned, the metal casing remains
as a ‘lost’ form and protective channel
wall in the casting. Removal of the
mold material can, depending on the
application and geometry, be assisted
by a wire helix embedded in the core
as a mechanical drawing aid (Figure 7).
The surrounding mold material can be
segmentally pulled out by drawing.
The starting material is a coiled pipe generally over 1,000 m long
Figure 6: Combicore cores replace complex drilling (with its unwanted openings)
and permit near-net-shape casting
This drawing aid is unnecessary in
most applications. It is usually sufficient
if the mold material is ecologically removed
with a high-pressure jet of water.
In order to prevent corrosion, the water
is targeted so that the rest of the component
remains dry. De-coring generally
only takes a few seconds within the cycle
time defined by the production process.
Whereby there is a very tight positive
and linear correlation between the
flushing-out time and the core size or
quantity of mold material used, and its
geometry (diameter, length, bending
angle). In the case of complex core geometries,
the jet of water very rapidly
reaches the mold material – even with
reduced pressure. In this case, the insertion
of a nozzle, with which the jet of
water is targeted at the point requiring
de-coring, proves useful.
tion
If water is used for de-coring, a tightness
test can be directly integrated into
this process. Whereby the cast channel
is impinged with the desired water
pressure for a previously defined time.
Alternatively, the tightness test can be
carried out with compressed air as part
of a subsequent drying process.
Drahtzug Stein combicore offers
comprehensive solutions with which
30 Casting Plant & Technology 3/2015