Why Thermally Reclaim?
Today’s modern foundry using one of the many chemically bonded sand systems available is under increasing pressure to reduce costs, reduce it’s impact on the environment but at the same time improve and maintain it’s casting quality. One of the ways of meeting these requirements is to invest in sand reclamation. Whilst most foundries now have mechanical reclamation, many are looking to further reduce costs and invest in Thermal reclamation.
Thermal Reclamation
The ultimate in sand reclamation is of course thermal, whereby 100% of all binder and other organic material are removed.
Firstly, the sand from the mechanical reclamation plant will pass through a cleaning tower which basically removes any metallic particles prior to entry into the furnace. The furnace itself is a fluidised bed design with a gas and air mixture providing the fluidising medium and igniting on the sand bed surface via pilot gas nozzles.
Typically a Thermal unit will run on natural gas or LPG and operate at temperatures of between 670C and 720C depending on the type of binder used. The sizes on offer from Omega range from 250kg/hour up to 12 tonnes per hour with a unique 3-year warranty on the burners and lining.
The patented ‘Dead Bed’ system from Omega ensures total heat insulation and therefore lower running costs but also a longer life for the ceramic fibre insulation. This is due to the ‘Dead Bed’ providing protection for the insulation from sand erosion caused by the moving processed sand.
Low running costs are achieved through a combination of the excellent insulation of the furnace with the ‘Dead Bed’ system as well as a heat recovery module after the furnace that takes the heat from the hot sand as it leaves the furnace and reintroduces that heat as warm air into the fluid bed section of the furnace. This means that the fluidising air is always warm, leading to lower gas consumption.
Safety is also of prime concern so multiple safety systems are employed to monitor fluid bed ignition, temperatures for every component (including dust collector) and level of sand available for processing. Also, a full touchscreen HMI with status and fault finding indications is provided.
Emissions from the thermal plant is guaranteed to be lower than the local regulations permit as Omega has sufficient temperature and retention of gasses in the furnace hood to ensure that the air leaving the furnace is clean.
For the Alkaline Phenolic system, a special inhibitor must be pre-mixed with the sand to prevent the Alkaline salts causing low temperature fusing of sand grains.
It is also now possible to thermally reclaim Green Sand for re-use in the core shop. A mechanical scrubbing system is employed before and after the furnace to ensure that all clay is removed, but essentially the thermal reclamation is the same as the no-bake system.
Conclusion
Thermal reclamation has been around for many years but it has now reached a point where it is cost effective, economic, reliable and therefore viable for most foundries to consider.