The foundry return sand cooler is designed to improve the sand quality especially for automatic molding lines with high sand capacities. Cool sand and controlled moisture help to reduce failure on the castings surfaces and shape.
The return sand after the shakeout is very inhomogeneous in temperature and moisture, the flow rate changes a lot and inhomogeneous particles bigger than lumps cannot be equalised in the sand cooler. Therefor a centrifugal lump breaker is recommended before the sand cooler. Metallic residuals like trump iron should be separated and hard lumps or core pieces should be screened off the sand flow before cooling.
Function of the fluid-bed cooler without integrated feed bin
The sand coolers charging system (by buyer) consists of a feed bin with an extracting belt conveyor. The stop and go operation of the conveyor ensures always a constant sand-flow into the cooler - even at fluctuating sand supply to the feed bin. The cooler is designed for maximum capacity. The operation of the feeder can be reversed to bypass the cooler.
The extracting belt conveyor can be speed controlled during operation by means of a solid state frequency converter maintaining the feed bin level. The addition of spraying water will be adjusted automatically. Using this option the cooler can be continuously operated in a range from 40-120 % of nominal capacity without interruption. So the cooler has not to be calculated for maximum capacities and can be designed for a lower nominal capacity as an average figure, assuming that maximal sand throughput and maximal sand temperature will not appear at the same time.
Function of the fluid bed cooler with integrated feed bin
The level of the feed bin integrated to the sand coolers hood, is adjusted by a speed controlled roller-type feeder using signals from material level detectors. So the cooler has not to be calculated for maximum peak capacities and can be designed for nominal capacity as an average figure assuming that maximal sand throughput and maximal sand temperature will not appear at the same time.
The material transport in the fluid bed cooler is realised by vibration over a perforated steel sheet. Air is blown by a medium pressure fan into the coolers bottom chamber passing the perforated steel sheet to fluidize the sand. A temperature controlled dosis of water is injected by special designed nozzles, is evapurated by the hot sand and is captured by the heated air flow passing the bed. By the effects of the vibrations and the blown air intensive mixing of sand and injected cooling water can be realised.
By a special design of the cooler's vibrating part, the choice of the corresponding frequency, the stroke and line of vibration transmissions of vibrations to the surroundings are mostly avoided.
The stationary hood is designed as a tranquillising chamber to reduce the removal of fines by the exhaust air. Maintenance can be easily done through the inspection doors.
It is recommended to install a cyclone between cooler and bag house to reclaim as much fines as possible. Cyclones are available as high performance unit with high pressure drop and as medium performance unit with moderate pressure drop. For final gas cleaning bag houses are used normally, the cyclone should be adapted to the bag-house.
After sand cooling and conditioning the return sand has almost homogeneous conditions like temperature and moisture. The temperature will be in the range of 35-40 °C depending on temperature at sand supply. The average moisture will be adjustable in range of 1,6-2,2 %, + 0,3 %.
If during winter time less cooling effect is desired, an operation with circulated air from the bag-house and a temperature monitoring should be taken in account as an option. Or cooling air should be taken from inside or outside the foundry depending on the season.