Foundry Sand Systems

For a common sand casting, sand is uniformly blended with lubricate or any chemical binder to form cores. These cores are then sited inside a mould cavity forming the inner surface of the cast. The sand containing the chemical binder is consistently assorted with the mould sand, once the casting is made. Also, the sand cores are removed. However, special disposal is required for contaminated sand, and CFA has been authorized for discarding waste foundry sand, which can be used as cover material for landfills and land disposal sites.

Sand castings normally produce a rough surface due to high surface impurities, and surface variations. To rectify this type of defect, a machining (finish) allowance is made.

Sand reclamation working principle involves process of cooling of waste molding sand. This may be achieved with rotating coolers, where water acts as the cooling intermediate. The control of temperature in the coolers is within the range of ±2–3°C. Too high temperature may harden in the box and will not strip out. However, lower temperature can delay the binder’s working process. Hence, temperature control is sensitive for the nobake process, or core or mould making.

A sand reclamation system recycles over 90% of the volume of the “contaminated” sand In order to effectively reclaim sand from a metal casting. This contaminated sand containing dust, organic matter and other wastes, is taken in a hopper to control the flow of materials and augured to a hot bed, and is allowed to enter a special designed fluidized gas reactor, at a temperature of 677°C. The source of this heat comes from heating tubes immersed in the fluidized layer. A fluidized bed-cooling chamber then cools down the processed sand to achieve conditioned temperature. This cooling temperature is controlled by an air-to-water converter. This thermally reclaimed sand has better characteristics rather than the new sand. Ontario foundry has also installed similar system for thermal reclamation of waste molding sand.

With the use of reclamation systems, foundries preserve the quality of used sand without the expenses of 100% new sand. As a reducing process, reclamation starts like a simple method and proceeds as per the production requirements. It generates higher quality sand at each step.

Furthermore, most of the foundries follow reclamation of used sand by bringing it back to the muller which generates less number of broken moulds and casting repairs, lesser sand holes and, less burned-on sand.

Other energy management opportunities includes following:

• Implementing and using a costly landfill can be avoided by negotiating disposal through other nearby company;
• Sand system equipment should be switched on, only when in use;
• Sand system equipments should be powered up and down in manufacture progression, when its parts are no longer required.In order maintain mould and core quality, proper attention is required for the categorization of the retrieved sand.

The total cost on sand reclamation must be less than the costs concerned with acquiring of the new sand. A properly managed plan before implementation helps in significant overall savings. Thus a self-evaluation check by the foundry should be followed before implementing the thermal reclamation program.

Apart from Thermal reclamation process, other reclamation processes used are Mechanical, pneumatic, and wet reclamation systems. They all have varied advantages and disadvantages. The choice of the equipments is based on the factors like casting volume and design, binder system, and extent of processing required to produce reclaimed sand.