Steel Castings Pty Ltd operates a foundry located in Port Melbourne, Victoria. The foundry produces high integrity steel, alloy and stainless castings from 50 kg to 3,800 kg in size. It also produces forging ingots to 2 tonnes in alloy, stainless and Duplex grades, and offers Shaw ceramic method castings for close tolerance parts up to 100 kg in size.
Its customers include manufacturers of heavy earth moving equipment for the mining industry, pumps and valves for the oil and gas industry, mills and crushers, parts for the steel, sugar and paper industries and mooring equipment for the offshore oil and gas industry.
The casting process is achieved by pouring molten metal into a mould. Steel Castings uses sand mixed with binders and a catalyst to produce the moulds. After cooling, the casting is removed from the mould and the sand is discarded. All this discarded sand, which is 97 per cent pure silica sand and 3 per cent sodium silicate, is sent to landfill.
Steel Castings used a 6 tonne per hour continuous cold setting sand mixer, plus core making facilities for the production of moulds. In the preparation of moulds, sand is mixed with sodium silicate and an ester-based setting agent. As well as sand discarded from the final moulds, waste sand was generated because of:
- variations in sand temperature, which resulted in moulds either curing too quickly or too slowly and therefore being scrapped;
- excessive catalyst usage on small moulds;
- drift in the calibration of the pump settings causing variations in sand quality between calibration checks; and
- use of larger moulds than required to allow for the non-optimal sand properties, especially on critical castings.
The single largest cause of sand wastage was the temperature variation in the new sand. If the sand had only recently been processed (screened and dried) by the supplier prior to delivery, its temperature could be up to 100 degrees Celsius. When the catalyst addition rate was set for a temperature of between 10 and 30 degrees Celsius, this could cause significant problems, including setting of the sand inside the mixer. Conversely, during periods of cold overnight temperatures the sand cooled significantly, resulting in insufficient setting and consequent sagging in the middle of large moulds.
Cleaner Production Initiative
Steel Castings installed a computerised ‘Autocat’ system, for metering catalyst and binder to the sand in the mixing machine, at a cost of $22,700. The Autocat system utilises computer control for dosing of additives, to achieve the optimal ratio of catalyst to binder for the current operating temperature (sand and ambient), and the required curing time to suit the specific mould being prepared.
The system continuously monitors parameters such as sand temperature, ambient temperature, and catalyst flowrate, and changes the catalyst-to-binder ratios and flowrates as required to maintain cure times. The system also blends slow and fast catalysts to give a mix with the correct set time at the correct strength.
Advantages of the Process
Steel Castings has realised a number of benefits from the installation of the Autocat system, including:
- a significant reduction in mould losses due to variations in sand temperature, which has avoided the generation of
- an estimated 140 tonnes of waste sand per annum;
- saving of approximately 8 per cent in catalyst usage because of the more precise control over catalyst dosing; and
- reduced environmental impact from any waste sand because of the lower content of unreacted catalyst.