Green sand is one of the oldest foundry moulding mediums known to the industry, its use in the foundry can be traced back to the early times. But do you know how to get the best from it. While it's use in commercial foundry operations has diminished somewhat, green sand still has its place in the hobby foundry. Green sand can be made up using quite basic materials, and is still being used to produce sound quality aluminium, bronze, and grey iron castings in many hobby foundries scattered across the globe. Green sand is also ecologically friendly in that it can be recycled & reused almost indefinitely, before being discarded in favour of a newly mulled batch. When green sand was the preferred commercial moulding material, special machines were used to reprocess the sand to remove foreign objects and to break down the dry sand lumps and recondition the sand again for the moulding shop. Because green sand is reconditioned or re-tempered by the addition of water, it requires quite a bit of processing work to make it suitable again for moulding work. Unfortunately, the hobby foundry worker does not have the luxury of automatic processing machines, so the reconditioning task for the hobby foundry worker is reduced to a laborious manual process, which can soon become tiresome if a large quantity of sand has to be processed. When we speak about reprocessing green sand, we are not talking about the mulling or milling of a new batch of green sand, which is quite a different issue. To recondition green sand it is normally fed into a sand slinger to break the lumps and clods, which form naturally in the green sand mould during solidification of the metal castings, much of the moisture content of the sand is also driven off during this stage. One option for the hobby worker to recondition and retemper green sand is to use the slow manual hand sieving method whereby the operator manually processes the sand through a wire riddle in order to break up the lumpy sand, then the retempering can be done by slowly adding water and cutting, turning and dumping the sand with a shovel. Yes, it is hard work and a slow process, and one in which most hobby workers will rapidly lose interest. If you want to use green sand in the hobby foundry, but don't want to retemper the sand by this hard labour manual system, then, there is another way. The quickest, easiest way to retemper small batches of green sand such as the hobby worker would require, is to use a motorised gyratory riddle. The riddle is capable of processing a large quantity of sand in 10 to 15 minutes, which includes the fluffing and the retempering process, it is virtually a simultaneous three way process. The quality of green sand produced through this method is second to none, and the motorised gyratory riddle greatly reduces the back breaking labour to virtually zero. Anyone with general metal fabricating skills could easily build a riddle, the material costs are not expensive and are readily available. The main requirements are: A small electric motor, a wire sieve, some square tubing to build the frame, plus the instructions to build an efficient machine. Solid plaster and cement rendering workers in the building trade could also use this type of machine to prepare mortars and wall-finishing materials applied by the baggin |
