Cooling under ambient conditions – the cooling diagram to determine air requirements
Prepared moulding materials with temperatures significantly above 40 °C pose a number of processing problems:
- Drying of the moulding materials until processing
- Increased mould scrap rate
- Condensation and sticking tendency on the pattern surface
- Condensation on the cores and moulding aids
The high thermal stress on the bentonite bonded moulding material requires various process steps to cool the moulding material in moulding material processing systems. These are usually combined with homogenising and pre-moistening the moulding material. Cooling is achieved primarily through the evaporation of water.
The cooling diagram illustrates the physical relationships of used sand cooling as a planning tool for the practitioner.
The evaporation of water, meaning the change from the liquid to the gaseous aggregate state below the boiling temperature under normal pressure conditions, removes energy from the system. It produces water vapour that has to be absorbed by the air. The water absorptive capacity of air depends on the temperature and relative humidity.
The 3 conditional equations
The volume of water that needs to be evaporated and the volume of air that has to be discharged can be formalised using three calculation steps of a combined energy-water balance and ultimately represented in a diagram.In the first step, the energy balance is used to determine how
much heat energy has to be removed. The water requirement for evaporation can be determined from this information in the second step. The third step determines the air requirement to remove the evaporated water.