Unidrive Pty Ltd was established in the late 1950s and currently has a workforce of over 400. It manufactures drive assemblies and other associated components, such as lower suspension arms, for the Australian automotive industry. The components are manufactured by casting or drop forging, followed by machining to achieve the desired tolerances and surface finish.
In its Melbourne operations, Unidrive has a total of about 800 machines of varying size and capacity, which are used for grinding and machining operations. Coolant is used in these operations to provide a degree of lubrication and to remove heat from the workpiece. Coolant is pumped to the workpiece from sumps, generally located under each machine. As a result of the machining operations, the coolant becomes contaminated with particulate material and 'tramp' oil from a variety of sources. In the case of cast iron machining and grinding, a viscous black sludge builds up in the bottom of the machine sumps.
The contamination from oil and sludge results in deterioration of the coolant. This stimulates the growth of bacteria which feed on additives, such as emulsifiers, present in the coolant, and can cause instability and eventual emulsion splitting if not controlled. Anaerobic bacteria also produce hydrogen sulphide, which is the cause of 'Monday morning odour', and is one of the main causes for dumping coolant.
Approximately 20,000 litres per week of waste coolant was being generated by Unidrive's machining operations. In addition, 6 different types of coolant were being used and this complicated the possibility of recovery and recycling.
Cleaner Production Initiative
In conjunction with Houghton Australia (a supplier of industrial oils and chemicals, including machining coolants), Unidrive has implemented a coolant recycling and recovery system. The systems utilises Hyde technology from the United States. At the same time, the number of coolant fluids used by Unidrive was rationalised from six to two. The system was installed in late 1993.
Contaminated coolant is removed from the individual machine sumps using a portable pump and storage tank unit. The contaminated coolant is then transferred to a coolant recycling unit. The coolant is filtered to remove solids and heavy sludge. Free floating and dispersed oil are then removed in a coalescing separator. The recovered oil is collected for disposal. The cleaned coolant is continually circulated through the recycling unit until it is required in the plant. The coolant is then returned to the machine by a reticulated mains system. This means that a machine can be refilled with cleaned coolant immediately after the dirty coolant has been pumped out, thus achieving minimal disruption to production activities.
Using this system, the coolant in individual machines can be changed before the onset of any significant deterioration of the coolant. This requires monitoring of the quality of coolant in each machine to ensure the integrity of the program.
Total waste coolant generation has been reduced from 20,000 litre per week to 8,500 litres per week. Actual waste generation from the machines has been reduced by 95 per cent (there are other sources of waste coolant such as carryover with swarf).