High Level Sand Reclamation
Friday, 10 March 2017
Richard then introduced Andy Pickering and his subject “High Level Sand Reclamation”.
Andy began by saying that environmental pressure, ever more demanding regulations and increasing costs of purchasing and disposing of sand were key drivers in the move for better sand reclamation in foundries. The benefits of good reclamation were seen in lower mixed sand costs, less waste to landfill, improved mould and core quality leading to better casting quality. All these attributes had a positive impact on the bottom line.
Before discussing reclamation Andy stated that no aspect of the no-bake moulding process should be considered in isolation. Binder selection is often influenced not just by the metal to be cast, or a foundries historical preference but for a given country their industry choice. Andy then gave examples of different binder choices seen on his travels around Europe and beyond in relation to steel casting production. Whatever binder system is chosen it is still essential to optimise the mould and core production process. Quality of the new sand is just as important as that of the reclaimed material. Maintaining the mixer to give efficient mixing and then ensuring that sand is used within its bench life are key to consistent good casting quality.
Primary Sand Reclamation
Using a vibrating deck, primary sand reclamation relies on sand on sand scrubbing to break the mould and cores back down to individual sand grains. Loading the vibrating deck is a matter of choice which is dependent upon several factors. For example moulds may be pushed or conveyed from casting lines directly onto the deck. In some foundries castings are stripped from moulds and the broken moulds loaded by bucket loader or skip onto the deck of the reclamation unit. The design is therefore determined by how the unit is to be fed, the size and weight of mould or sand load, and the throughput demanded by the foundry.
Should cooling of the sand after the primary reclaimer be necessary then a fluidised bed cooler-classifier could be built integral with the reclaimer or alternatively a separate unit positioned to take the sand directly from the primary reclaimer. The size of cooler is designed to give the longest practical sand retention time by having it pass through a series of baffles and cooling tubes. Good extraction is fitted to pull off the maximum amount of dust during the cooling process.
If using primary sand reclamation only, with or without a cooler classifier then there will still be some organic product on the sand and dilution with new sand is essential.
The options for secondary reclamation are secondary attrition and / or thermal reclamation.
Passing the sand from the cooler classifier through a secondary attrition unit with good extraction removes much more of the organic matter plus it further rounds off the sand grains. As a result higher amounts of reclaimed sand can be used in the mixed sand. Omega units operate by having sand falling between ceramic rollers and a ceramic drum. The feed system must incorporate tramp metal removal to prevent damage to the ceramics. Controlling the depth of sand between roller and drum and the pressure from the rollers will determine the effectiveness of the attrition process.
Thermal Reclamation burns off all the organics. The high capital cost and running costs of these units is offset by being able to utilise very high reclaim percentages in the mixed sand. The only new sand required is that lost at various stages of the process e.g. shot-blasting. Very little needs to go to land fill.
Alkaline phenolic sands will need a liquid additive to the sand in the thermal reclaimer to prevent glazing of the sand grains.
In the thermal reclamation of alkaline phenolic sands, changing the chemical added to the thermal unit from liquid to a powder has benefits in the transporting of product and also in the handling at the foundry. Water is still necessary for the process but this can be added by the foundry instead of being bought as part of the product.
Optimising the quality of thermally reclaimed alkaline phenolic sand can be achieved by passing the reclaimed sand through a secondary reclaimer thereby removing any adhering organic matter from the sand grains. This then allows very high levels of reclaimed sand to be used at the sand mixer. Less sand to land fill as a result has additional financial and environmental benefits.
Darren Pritchard gave a vote of thanks to Andy for his talk and then members and guests enjoyed a splendid buffet sponsored by Omega Foundry Machinery Ltd.