FEATURE FLOW, LEVEL & CONTROL Fluid level probes for cutting fluid filtration systems
Users of machining centres rightly expect the cooling and lubrication of cutting tools to continue without interruption or failure. By building new level sensing technology from SICK into their swarf management systems, one of Europe’s leading manufacturers is ensuring high-performance machine tool protection and cutting fluid recycling for its customers
process. Until recently, more conventional technology for controlling levels in the tank were capacitive sensors, usually positioned at the top of the tank to avoid overfill or underfill of the reservoir. However, an alternative technology,
F
rom its base in West Yorkshire, Frederick Crowther & Sons
manufactures a wide range of swarf conveyors and cutting fluid filtration systems under the Cromar brand. Cromar systems are used extensively in machining operations in the engineering, aerospace and rail industries, in the UK, mainland Europe and across the globe. Driven by ongoing product innovation,
as well as customers’ custom design requirements, the engineering team at Cromar’s Brighouse manufacturing centre is always on the lookout for ways to optimise reliability and minimise user maintenance of its filtration systems. Cromar offers a range of free-standing
coolant and filtration management systems for integration into cutting tools and machining centres. Typically a Cromar coolant management system comprises a specially-designed conveyor from under the machining or CNC centre, to carry the coolant towards disposal. For coolant management, a cutting fluid pumping, filtration and recycling unit is combined with the conveyor for pumping filtered fluid back to the machining centre. Swarf from the machining process is carried away with the cutting fluid to the sump at the bottom of the machining centre. From here it is fed through the filtration unit to remove the swarf, before the filtered fluid is returned to the reservoir tank for re-use in the machining process. Ensuring reliable level control in the filtration reservoir is a vital part of the
10 APRIL 2018 | INSTRUMENTATION
Upgrading their system to use a new probe with guided-wave radar technology enabled Cromar to improve reliability and availability
the LFP Cubic from SICK, has offered Cromar a product development opportunity, as SICK’s Industrial Instrumentation product specialist, Nick Hartley explains: “We were approached by Cromar when they heard about our guided-wave radar technology for level sensing, which they recognised could offer their customers some significant additional advantages. Cutting fluids can be a challenging medium for some sensor technologies to operate reliably. The level detection provided by the SICK LFP Cubic probe is not affected by changes in the fluid properties, or other contaminants in the fluid, or by the layer of foam that can sometimes build up over the liquid surface. “Using capacitive sensors, for example,
means the fluid reservoir needs regular maintenance by users to avoid build-up on the sensor which could otherwise lead to false readings. “Some types of fluid create a foaming
SICK LFP Cubic probes can also be easily tailored to different sizes of tank when bespoke sizes are required
layer which could, in some cases, even fill the entire reservoir tank. In this case, if capacitive sensors are used, a reading could indicate that there is fluid present in the reservoir when the actual fluid levels may be very low. The SICK patented foam algorithm is extremely effective. “One SICK LFP Fluid Level Probe regulates high and low levels of fluid
in the tanks. The probe is set to signal a low level, prompting automatic topping up with new fluid as well as high level when refilling is complete. The signal is communicated via the PLC to automatically trigger the appropriate response.” Dave Lister, electrical manager of Cromar
Swarf Management Systems, explains: “Efficient management of the cutting fluid supplied to the machine tool head on a machining centre depends on reliable level sensing in the filtration unit reservoir. The sensor reading must reliably switch the pump system on and off so the level of cutting fluid is maintained between optimum low and high limits to ensure continuity of cutting fluid supply. “If the fluid level in the reservoir were to
drop too low without being replenished, the pumps could fail, and the cutting head and machined component could even be damaged. Equally, the reservoir could overflow if it is overfilled, because the sensor has not triggered the pump to stop. Either way, heavy downtime and wastage costs could ensue if the machining operation is interrupted for unplanned stoppages.”
FILTRATION SOLUTIONS Cromar offers a range of filtration solutions. Depending on the particle size of the customer’s process, the swarf is removed from the contaminated fluid by a succession of graded traps and filters, from coarse grids through to high pressure or cyclone filters. Magnetic traps may also be used. After final filtration, the cleaned cutting
fluid is retained in a reservoir from which a pump recirculates the fluid back to the machining centre spray nozzles at the machine tool cutting head. For a large machining centre, where many different cutting, machining, milling and drilling tasks may be operating at the same time, or in a closely-controlled automated sequence, several pumps may be accessing the tank at once. It is essential that the level of the
fluid in the reservoir is continuously monitored to protect the pumps and the process from running dry. Failure of fluid reaching the machining operation can affect the quality of work, which may have to be rejected, as well as damaging the cutting or milling head which might
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