Machine Coolant Maintenance Leading to Waste Reduction Barb Loida Donna Peterson Terry Foecke. University of Minnesota Minneapolis, MN ABSTRACT

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1 Machine Coolant Maintenance Leading to Waste Reduction Barb Loida Donna Peterson Terry Foecke a r t University of Minnesota Minneapolis, MN ABSTRACT The volume of machine coolant waste can be reduced through maintenance. Coolants are generally considered a waste due to rancidity, not due to a loss of their cooling properties. Through a grant study and intern projects administered by MnTXP the steps for maintaining coolants and the means to implement them were uncovered. Maintenance involves the removal of tramp oils from the machine's coolant sump, control of bacterial growth in the coolant and maintenance of the proper coolant to water ratio INTRODUCTION There are approximately 14,000 companies performing machining operations in the United States, generating sales of $20 billion per year. Machine shops make parts from metal stock for a wide variety of industrial products, using processes such as drilling, turning, lapping, grinding, and broaching. Machine tools used in these operations are cooled by fluids, generally referred to as "coolants", in order to extend tool life and enhance product quality. When these coolants reach the end of their useful life, their disposal may be regulated as a hazardous waste in some states. Spent coolants may contain contaminants which can pollute groundwater, surface waters, and upset wastewater treatment 509 plant (WWTP) operations. These contaminants may include tramp oils, high levels of biocides, heavy metals and nitrates. In addition, they are generally a high strength waste as measured in biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solids (TSS). Preliminary studies on the treatability of coolants indicate that the material is biodegradable if sufficient acclimation time is provided (acclimation time is the length of time between the addition of a substance and a noticeable change in the oxygen uptake by the organisms), It should be noted that these results are believed to be plant specific and the acclimation time will vary depending on the exposure to high strength industrial waste the organisms have received in the past. In addition, the acclimation time may exceed the

2 detention time of the WWTP and result in the material passing through the WWTP into the receiving water. The Minnesota Technical e MR-ThPf became involved with this wastestream when a number of generators called regarding proper coolant management and disposal. A company approached MnTAP in 1986 for an intern to help them establish an acceptable management strategy for their coolant waste. The early part of the intern project focused on treatment methods (chemical splitting technologies) which would break the emulsion for each of the two brands of coolants the company used. Treatment would generally result in the water portion being sewered and the coolant/oil portion recycled through used oil haulers. After repeated efforts at treatment it was determined that the ability to split the coolant emulsion by chemical treatment was coolant specific and therefore not broadly applicable. During this project, information about coolant maintenance as a means to reduce the volume of waste generated was also emerging. Since the factors affecting coolant life were not coolant specific, the steps required for coolant maintenance and implementation were identified as areas which needed to be further explored. PURPOSE MnTAP wanted shop based data which would indicate the steps required to accomplish maintenance and show how they -1d be ~mpic.,.-.rted. I ne literature indicated that coolant life could be prolonged by removing the tramp oil which accumulates in the machine s coolant sump, controlling the bacterial growth in the coolant and maintaining the proper coolant to water ratio. Two opportunities were presented to MnTAP to test these principles in a shop setting. Washington Scientific Inc. conducted a year long grant study which was administered by MnTAP, and Midwest Electric Products was selected as a company for a 1988 MnTAP intern project. The details of these projects and their results are outlined in the next section. APPROACH AND RESULTS It is important to note that both companies listed above approached the projects with the following elements in mind: 1) Starting with the lowest cost techniques and expanding them as needed. 2) Examining the site specific problems of implementation and modifying the operations if feasible where needed. 3) Starting with simplest (or easiest) equipment to operat e. 510

3 I. I, Washinzton Industries, Inc. Background Scientific This machine shop has anorox ima t elv 150 employees doing precision machining and assembly of motors and drives for the computer industry and other specification manufacturers. A wide variety of machine tools are used which have in the past generated as much as gallon drums per year of waste water-soluble coolant. The research project was designed to study the effects of maintenance practices and coolant type on coolant life. Baselines were established for coolant maintenance practice, coolant life, and tool performance. Coolant life was found to be as short as two weeks in some machine sumps, due to the formation of hydrogen sulfide by anaerobic bacteria and, in some cases, reduced tool performance. Maintenance involved coolant removal and sump cleaning as required because of excessive hydrogen sulfide odor. A specific water-soluble coolant which does not require the labor and expense of biocide - add tions for bacterial control was substituted for the coo ants used in all operations except grinding and magnesium machining. The performance of this coolant was evaluated throughout the project for tool performance, resistance to bacteria 1 con t am i na t ion, and health effects on operators. Development and Implementation It took several months to characterize current practice and coolant performance. Oil skimmers, a centrifuge, and coolant changing/coolant sump cleaning practices were evaluated for oil removal efficiency and effect on coolant life. Use of the mobile centrifuge was tested by cleaning the coolant in the sumps of a group of 25 machines. It was found that this is the maximum size group for one person to maintain, i.e., the first sump required cleaning by the time the 25th was done. Even though the coolant was cleaned adequately, this was judged to be an inefficient use of labor. At the same time that the centrifuge was being evaluated, disk andbelt oil skimmers (see Figure 1) were installed on Disc Skimmer Figure 1 511

4 study group of five machines which represented a spectrum of machining operations and raw materials. All machines are a common size, one to four years old, and used on two-four week product ign rili1s-. material and processes were held constant as much as possible. The project also evaluated different coolant change procedures for labor requirements and effectiveness. When coolant is changed or cleaned (oil removal, solids removal), it is important to clean the coolant sump to minimize carry over of bacteria and other contamination. The ideal method is to vacuum and clean the sump until all contaminants are removed. However, this can be difficult in practice because of limited sump access. Therefore, the objective of the project was to determine the best combination of effectiveness and efficiency. Results The selected coolant, even after being recycled for over seven months, met or exceeded all performance requirements. There was no incidence of dermatitis among the operators. It is important to note that no biocide additions were required to maintain this particular coolant. The combination of normal pumping agitation and oil skimming was sufficient to control bacterial growth. A coolant change and sump cleaning practice was developed which standardized a procedure to be used with any machine. It was found that some sumps are easier to clean than others, especially when access covers can be fully removed and 512 corners (along bottom and sidewalls) are rounded. It is believed that this change routine, which requires approximately five hours per sump, extends coolant life. I..~~ mt -Imte& Lc. in isolation from other changes. Both disk an d be 1 t skimmers effectively reduced coolant oil and grease concentrations. It proved necessary to install timers and pumps to reduce the amount of coolant carried out with the oil, but these were simple changes. It was also necessary to modify several sumps to provide access for the skimming equipment. In some cases, a skimmer was moved from sump to sump; on other machines, the installation was permanent. Both modes of operation were equally effective in extending coolant life. The results of tests conducted during this project show that it is possible to extend the life of machine oil coolant. Simple skimming of tramp oil using any of several different methods was costeffective and controlled oil and grease concentrations well. Midwest Electric Products Project Background This company, with approximately 250 employees manufactures weatherproof electrical boxes. Many of the machine operations use a watersoluble coolant. The company had asked for assistance in reducing this waste because of concerns over increasing

5 I I. I I * charges for BOD/COD levels, and the uncertainty about the continued acceptance of the wastewater by the city. The intern pro.ject started with a waste survey, in which the sites of waste generation were identified and the waste quantities from each site were measured. There were seven machine sumps generating batch dumps ranging from gallons. In most cases machine operators dumped the coolant when it became rancid. The total annual waste coolant was estimated to be about 2000 gallons. Development and Implementation At one site in the plant, several machines already were situated close to each other, which made the idea of plumbing their sumps together attractive as that would reduce the time required for maintenance. At the same time that plans were being made to do this, the student conducted tests to evaluate.the effectiveness of the methods identified in the literature on prolonging coolant life. While results were not always conclusive, preliminary findings supported the validity of these methods (removal of tramp oil, bacteria control, maintaining proper coolant to water ratio). Therefore, plans were developed for a central sump, shown in Figure Two, to service the eleven drilling and tapping machines. The system was designed to include periodic oil skimming, removal of metal fines and agitation of coolant once oil skimming was completed. The central sump was fabricated at the company site, starting with a purchased cattle trough for the holding tank. Baffles were welded into the center of the tank so that an oil skimmer could remove the oil at one end of the tank before the coolant flowed over the weir to the other end of Central Sump Figure 2 513

6 the tank where it is agitated by 9 pump prior to recirculation to the machines. Agitation was incorporated into the design so as to discourage the growth of anaerobic bacteria. A programmable timer was purchased so that the disc oil skimmer would operate only periodically, thus reducing quantities of coolant removed with the oil. Stainless steel screens were fabricated to collect fines at each worktable. In addition a bag filter placed over the inlet to the central sump also removes metal fines. The cost for the components purchased and the labor needed to install the tank was approximately $800. While agitation, removal of fines and oil happen automatically in the central sump, ph control and bacteria level require manual monitoring. Strips are used to read ph and also bacterial count weekly. When these parameters register outside the expected operating range, caustic and/or biocide are added. In addition, coolant concentration is monitored with a refractometer, and adjusted as needed. Results In late August, the new system became operational. Four months later, the same coolant was still being used in the sump. Weekly, the operator monitors ph, bacterial count and coolant concentration and makes the necessary changes. While this involves some effort on the part of the operator, the bonus is that employees have a more pleasant machining environment as dermatitis is not a problem nor is there a rotten egg smell associated with hydrogen sulfide formation. In addition the wastewater strength has been reduced by discharging less results indicate that both the BOD and COD of the total wastewater from the company have been reduced by approximately 50 percent since the centralized sump became operational. SUMMARY AND CONCLUSIONS The Department of Energy has estimated that proper maintenance has the potential to reduce the volume of emulsified oil waste by 80 percent. The steps for maintenance for one type of emulsified oil, coolan.ts, are briefly outlined below: Properly designed sumps to give ac ces s for skimming/cleaning equipment. Sumps should also be constructed out of material easily cleaned and should allow the coolant to circulate freely. Routine sump cleaning (either chemically or with steam) needs to be performed when coolant is rep laced to remove residual sump bacteria. Oil skimming should be performed routinely. The two most practical skimming devices for coolant maintenance are disc and belt skimmers. 514

7 , Some additional factors to keep in mind when using skimming devices include: - access to the sump will limit the type of skimmer which can be used - use of timers to intermittently remove oil and reduce the amount of coolant carried out of the sump. - placement of skimmers near the sump s pump since the pumping action will draw the tramp oil towards it. - use of a low speed/ volume pump to reduce the possibility of drawing the tramp oil into the pump. 0 Metal chip removal should be performed routinely to minimize the machine fouling and minimizing sites for bacterial growth. Screens can also be used to prevent the chips from entering the system. 0 Adjusting the pa of the coolant or addition of a biocide to control bacterial growth. 0 Refractometers or coolant proportioners should be used to maintain the proper coolant to water ratio. Both are fairly inexpensive devices. Although the maintenance steps are not coo 1 ant dependent, higher quality coolant did not require the addition of biocides or ph adjustments. In some cases where too,ling machines did not have access for maintenance equipment, the higher grade coolant did have a longer life. The maintenance steps were also found to be more streamlined by usin. a ~ ; v t LJA, shop. At some point waste coolant will still need to be treated for disposal. A number of treatment technologies exist including: high speed centrifuges, chemical splitting processes, ultrafiltration, coalescing and reverse osmosis. These technologies require further research to determine their performance. Field work and other research directed by our office has shown that the volume of machine coolant generated as waste can be reduced by implementation of relatively simple technologies and techniques. Factors important to successful implementation include a limited number of coolants, tolerance of selected coolant to a wide variety of conditions, and careful so lut ion and e qui pme n t maintenance. Barriers to implementation include lack of a willingness to change es tab 1 ished processes, limited availability of shop-based testing data, and initial c ap i ta 1 costs, especi ally machine too 1 modifications. As treatment and disposal costs continue to rise, more attention will be given towards waste minimization. 515

8 ~ ACKNOWLEDGEMENTS MnTAP wishes to acknowledge and thank the following people: 2. "Emulsified Industrial Oils Recycling", U.S. Department of Energy - Division of Energy Conservation, Laura Newcombe - the Joseph, J. J., Coolant the possibility of maintenance in prolonging coolant life for MnTAP. Joe Pallansch of Washington Scientific Industries, Inc. - for his diligent efforts at exploring the maintenance options and means to implement them. Don Neu - the 1988 intern student at Midwest Electric Products for the design of the central sump and for the maintenance informat ion he uncovered. Ed Grazulis of Midwest Electric Products - for his support in showing that maintenance can work and his support of MnTAP. Lee Anne Johnson of the Metropolitan Waste Commission - for the treatability studies she conducted on coolants Marketing, East Syracuse, NY, Newcombe, L. "Reduction ad Treatment Options for kter Soluble Coolants," Minnesota Technical Assistance Program, Intern Report, Neu, D. "Main t a in in g Coolant Quality to Reduce Waste," Minnesota Technical Assistance Program, Intern Report, Pallansch, J., "Machine Coolant Waste Reduction By Optimizing Coolant Life," Grant Funded by U.S. EPA - Administered by Minnesota Technical Assistance Program. "U.S. Industrial Outlook 1988," U.S. Department of Commerce, MnTAP would also like to thank the Minnesota Pollution Control Agency for the program's funding and the University of Minnesota's School of Public Health for its support. REFERENCES 1. Cutting and Grinding Fluids : Selection and App li cat ion, Ame r ic an Society of Tool and Manufacturing Engineers, Dearborn, MI, MnTAP was established at the University of Minnesota in 1984 as a non-profit, nonregulatory program through a grant from the Minnesota Pollution Control Agency. MnTAP's goals are to assist Minnesota businesses with waste management and waste reduction. Assistance is provided through telephone consultations, onsite visits. student internships, the gathering of technical informat ion and actins! as a clearinahouse. 516