Figure 1. Vacuum filter’s media discharging too soon.
If metalworking coolant filtration equipment produced parts that brought income to a company, it would get the attention it needs to operate like all the other production machines in the plant. However, the filtration systems are considered an indirect function and become a low priority item in an already busy maintenance department’s schedule. The lack of routine maintenance and training are not unusual throughout the metalworking industry. The systems are usually located in an out-of-the-way area, misunderstood in many cases, and are only attended to when the flow to production stops. There is enough evidence in many plants that good filtration properly maintained is an “asset and not a liability.” Properly operating filtration equipment may not produce income but it adds to the profit margin in that income.
The objective of this article is to reveal different case histories where the equipment was not given the attention it needed and the hidden costs of the negligence were very high. The case histories are real and could be typical in a number of installations. The hope is that anyone reading these 3 examples can identify with their message and have the justification to devote the resources to train, assign and schedule filtration equipment programs.
THE $80,000.00 VACUUM SWITCH
This case history involves a filter on a honing application, serving a number of hones with light viscosity oil. At one point it appeared that the media had changed because the filter was indexing with far less cake than it did before. Since no one was following this closely and they were able to keep up with the production needs anyway, the filter’s performance went on for at least a year. For completely separate reasons an outside media supplier who conducts media management surveys was called to review all the installations to assess the media selections. It was then that someone noticed how much was spent on media for that operation in the last year. The plant wanted a different media because they were convinced that something was wrong with the production on the fabric, but the supplier’s survey found another problem. The filter had a faulty vacuum switch, which senses the vacuum level and calls for advancing the media as it becomes loaded with contaminants. The bad switch was calling for the filter to index every three minutes, regardless of the condition of the cake on the media. This went on for at least a year without anyone noticing it. Once it was recognized the vacuum switch was replaced for a cost of $75.00 and the filter went back to its normal operation.
However, the data showed that the faulty switch was responsible for that one filter to have an extra unnecessary cost of $80,000.00 for disposable media that year. That was not the only cost. There were other costs such as disposal of the solid wastes and labor to change all the extra rolls. A routine maintenance monitoring of the system would have caught the problem much sooner and saved a considerable amount of money. Figure 1 shows a typical flat bed vacuum filter with disposable roll media hardly used.
Figure 2: Media usage change
When the operators have the freedom of controlling their own valves, there is a good chance they will increase the flows without really knowing what the increased flow does to filter performance. Flush lines are considered “free” liquid and are randomly opened wider because “more is better.” But the filter has to work beyond its design point to keep up with the higher flow rate.
It has been proven in many cases that a small increase in the flow rate will cost a disproportionate amount of additional money in media consumption. Figure 2 shows the rate of change in media usage versus the increase in flow rate could be significant.
For example, a 25 percent increase (say from 40 GPM to 50 GPM) could result in as much as 50 percent more media consumption. Or an increase by 50 percent (40 GPM to 60 GPM) will increase the media usage by 250 percent. The extra flows of just careless valve adjustment could be expensive. This is just fluid flow; not more machines, which is another issue. Details of this phenomenon have been discussed in previous issues and outlined in the book “Coolant Filtration 2nd Edition — Additional Technologies” Also, the increase in flow demands more labor because of the changing frequency. This goes for automatic self cleaning filters and manually cleaned bag and cartridge filters.
WHAT’S IN YOUR FILTER?
This particular case had two fundamental problems created by misunderstanding the equipment.
While responding to a call for help on a production tool life problem in an automotive plant where deep hole drilling is major operation, it was noticed that one system had a cartridge filter polishing coolant coming from a flat bed media filter. The roll media filter was the primary filter while the cartridges were the secondary filters to further clean the fluid for high-pressure, flow-through, deep-hole drilling stations.
a) The Magical 30-Minute Cartridge Filter
The first part of this situation was in not knowing the operation of the cartridge filter.
The cartridge vessel’s differential gage showed 25 psi but no one was taking the steps to change the elements. When asked about the pressure, the operator stated that the filter works great. He reported that when they put in new elements, “within 30 minutes the vessel gets to its full pressure and one month later when they open it, the solids it intercepted is amazing.”
Figure 3: Secondary polishing cartridge filter supplied by manifold from primary flat bed vacuum filter.
What he did not know is that the cartridge vessel has an internal bypass valve so when the elements are loaded and not changed, the bypass valve opens to allow dirty coolant to flow through. Figure 3 shows that arrangement. The objective of this feature for some applications is to make sure there is always liquid flow to the stations even if it is dirty liquid, since dirty is better than no liquid. They were spending about $200 a day to replace or regrind a number of drills. Plus all the down time! The set up men thought the drill problem was the tool supplier’s “inferior” product. Apparently no one looked at the coolant clarity. They felt that it was not a filtration problem, since they saw the flat bed filter working and thought the cartridges filters were working as well. They did not even think about the frequent work to rebuild the high- pressure supply pumps. That was just a routine cost of doing business with high-pressure pumps.
b) The Wrong Agenda For Primary Filter’s Media Selection
The second part of this case made matters worse when they did not know that the media selected for the flat bed filter was more open than it should have been. There was a significant amount of fine particles migrating through the primary filter to flow into the cartridge filter. This is why the cartridges loaded so quickly. They assumed a larger part of the cleaning function that should have been accomplished by the primary filter.
Someone’s cost reduction and solids waste reduction program for the plant selected the more open media to save money since a roll would last longer. The savings in media costs were negligible when compared to what that “savings” did to the costs of drills.
The irony is that if the cartridge filter did not have an automatic bypass, then they would have saved the costs of tool changing but they would have had high costs in cartridge changing. Once the flat bed filter was fitted with the proper media, and the operators were aware of the bypass valves in the cartridge filters, the system stabilized and broken drills and regrinds costs dropped radically. The savings were thousands of dollars per week.
The common thread in these case histories is that there is a lack of awareness and attention to the equipment’s needs to operate properly to keep coolant clean. They are mechanical devices with all the vulnerability of any other piece of production equipment and should be treated with the same value as if they were actually producing parts.
These points apply to all other coolant cleaning devices such as retention tanks, chip conveyors, hydrocyclones, magnetic separators, and centrifuges. As a consultant in the field of coolant filtration, it is safe to say that most existing coolant systems can be improved and usually any negative impact on operating costs can be reduced without a major renovation program.
|James J. Joseph is a consultant who has also written the book “Coolant Filtration 2nd Edition, Additional Technologies.”
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