Building in oil filtration from the start
Original article date: November 1999
Regular oil filtration may not be enough to protect your machinery: the oil needs to be kept constantly clean. Alan Quinn has been finding out about Koppen & Lethem’s microfiltration systems
More than 70% of spare parts sold for hydraulic plant and machinery are used to replace defective components. The cause of 90% of these defects can be traced to oil contamination – the presence of insoluble materials, such as metals, dust particles, sand and rubber. The smallest particles – those under 2um – better known as silt, are most often responsible for defects.
If these small particles can be removed from the oil, their catalytic action is also neutralised and the chemical tainting of the oil is reduced. If, in addition, water can be removed from the oil, the oxidation process of the oil can be even further reduced.
Take the case of injection moulding machinery. Most operators make a conscious effort to keep the hydraulic oil in their machines clean, but few realise just how clean the oil needs to be. And the machine builders typically place little emphasis on the importance of clean hydraulic oil.
Today, most injection moulding machines come equipped with a 10um return-line filter. This usually has a replaceable element and may or may not have an indicator that signal need for an element change. In addition, many machines are equipped with suction strainers at the pump inlet. These strainers often are sized at around 150um to keep big chunks of contaminant from entering the pump. A finer filter at the pump inlet would greatly increase the probability of pump cavitation.
Hence, by using currently available main line filters, it is impossible to filter all contamination from the oil. The oil is actually directed with an alternating flow speed through the filter, as a result of which, strongly differentiating conditions develop in the filter, so that fine filtration is impossible.
Investigation of contaminated oil demonstrates time after time that it is silt which is unable to be adequately filtered out by most fine filters. It is precisely this silt which affects the chemical composition of the oil, so that it has a shorter useful life and must be changed more frequently.
The use of hydraulic fluid off-line filters, employing the radial micro filtration (RMF) system, is highly effective in the sustained delivery of ultra-clean fluid to the machine’s operating system, greatly reducing premature wear, inadequate performance and failure of the hydraulic system. Only a micro filter is capable of removing the smallest contamination particles, as well as the larger solids over 5um.
Special elements called NTZ microfilters form the basis for the RMF filter models. Because the filtration capability of these filters is down to 0.5um, they are especially suitable for filtering the smallest particles (silt) from the oil.
The micro-filter system works as a fine filter with a radial through-flow. The radial-flow principle prevents channel forming by water or solid particles. It also allows for a positive sealing of the element at the top and bottom, so that no by-pass flow can occur. The filter elements, especially designed for hydraulic applications, consist almost entirely of cellulose and are produced by a special wrapping method.
Application studies undertaken by Koppen & Lethem across a wide range of production machinery provide evidence of major reductions in the presence of contaminant particles within operating fluid, following the installation of RMF. One injection moulding machine with new hydraulic oil had a 5um particle count of 64,631 conforming to ISO 17/13. Following three months with an RMF system, the oil had a 5um particle count of 191, conforming to ISO 08/00. Such major reductions in contaminant levels are commonplace when RMF systems are employed.
- Koppen & Lethern
November 1999