New core technology for light metal castingWednesday (08.11.2017) 12:40 - 13:00 Part of:
Lost cores are used to generate cavities in components produced by means of gravity casting. For light-metal and especially aluminium castings sand cores with organic binders (e.g. phenolic resins) are commonly used. Those cores meet most of the technological requirements: stability against the thermal and mechanical loads of the casting process, limited detrimental chemical reactions and easy demoulding. However, there are serious environmental concerns and strong limitations for small and delicate cores. In order to approach latter problem a new core material and demoulding concept have been developed. For conventional cores the easy demoulding is achieved by a thermal breakdown of the binder strength limiting the range of suitable binders. In contrast, the new concept is characterized by the substitution of the sand filler by hollow filler material with specific compression strength. After casting the core is subjected to a high water pressure, leading to immediate collapse of the hollow filler and loss of the structural strength of the core which can afterwards be flushed out easily.
In the present study phosphate and plaster bonded cores with additions of hollow glass microspheres and cenospheres were produced and tested. Bending strength and surface quality of the cores were determined. The core behaviour during the casting process was evaluated using gravity and low pressure aluminium casting experiments performed in permanent moulds, showing that the removal of the cores is in fact possible as envisaged.
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