The Hot-Box process is very similar to the Croning process. A significant difference dwells in the use of much cheaper binder with liquid thermosetting resin instead of the dry pre-coated aggregates. However, the moulding aggregates exhibit a poorer flowability and require intense compaction. Another difference is that one-sided heating of the shell face from the pattern plate is not enough; the core must be heated from all sides in a fully enclosed core box during the entire production cycle.
The core-box is heated to the temperature usually within the range of 230 °C – 260 °C, and is filled with a moulding aggregate which comprises a quick hot-curing binder. The filling is accomplished by a shooting or blowing process, so that a core box with vents must be provided. The moulding aggregate is allowed to cure for 10 to 30 seconds, until the necessary handling strength is attained; the finished core is then ejected from the core box. Some post-curing is needed outside the box, aided by the exothermic heat provided by the chemical reaction. After the core is released, the whole cycle is repeated. Stripping is assisted by periodic treatment by silicone parting fluid. The core box temperature is commonly maintained by integral gas or electric heating elements. To counter the effect of contact with the hot coreboxes, water cooling can be applied to the core machine blowplate.
Hot-Box process;
a) metal core box is heated, b) moulding aggregate is blown or shot into the core box,
c) after a pre-set time the core box is opened and the core ejected