Development of a recycling system for metalworking fluids

Wong, Kien Kuok (2012) Development of a recycling system for metalworking fluids. PhD thesis, Universiti Malaysia Sarawak.

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Abstract

Over 2 billion litres straight-oil and water-based metalworking fluids (MWFs) are consumed currently worldwide, portraying a great demand for this non-renewable feedstock. It is a great challenge for the manufacturers, suppliers and end users to develop efficient and effective MWF treatment systems to tackle health and safety issues, as well as preserving the environment. In such the importance of developing a MWF Recycling System (MRS) which primarily consists of 4 operational units; an upflow filtration, enhanced gravity separator, aeration-filtration unit and pasteurization process, are outlined in this thesis The upflow filtration and aeration filtration consists of 5 layers of geotextile with 120 llm pore size for removal of metal chips and oxidized metal chips. The enhanced gravity separator is a circular separator with 4 series of inverted and upright alternating coalescing frustums to enhance gravity separation of metal chips and coalescence of tramp oils. The individual unit processes and treatment performances were evaluated with respect to removal efficiencies of oil and solid particles, status of lubricity as a function of application and microbial contaminant growth Qver time. Experimental results were compared with the existing Computer Numerical Control (CNC) built-in MWF Treatment System. At design flowrate of 1.0x10-5 m3/s, the upflow filtration unit and enhanced gravity separator were observed to achieve particle size removal of ~6.7111m and ~3.28 llm, respectively. The enhanced gravity separator removed approximately 97.25% of tramp oil at 1.0x10-5 m3/s flowrate. This MRS also had experimentally demonstrated to remove significant amount of silt and clay in the MWF, whereby silt and clay particles in the MWF were mainly due to reuse and recycling of MWF. A comparison of MRS with CNC MWF Treatment System with respect to tramp oils and solid particles removal efficiencies reviewed that MRS was able to treat the used coolant to an acceptable quality range, whereby CNC Coolant Treatment System was incapable of effectively treating the MWF. The lubricity tests of spent coolant through recycling process by MRS produced acceptable quality recycled coolant within workable range over a longer period as the friction coefficient (Ps) maintained in the range of 0.1683 to 0.1788, whereby the CNC built-in coolant filtration system showed a rapid drop in lubricity during the fourth and fifth weeks with ps in the range of 0.1929 to 0.1956, and must be disposed off within 4 to 8 weeks times. Microbial contaminant growth in MRS recycled (treated) coolant was approximately 9 times lower than that of CNC filtered recycled coolant. Economic analysis on MRS and CNC filtration system showed that relatively higher initial investment cost of MRS can be offset by its low operation and maintenance costs, whereby the breakthrough period is about 2 years. iii

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