Wet Chip and Coolant Recycling
Aluminium machined component
Supercraft operate over 25 CNC milling and turning machines. Many milled components are machined from a solid billet of aluminium, producing a huge quantity of wet chip wasteage. Formerly, this material was sent for recycling, fetching only a low price due to the weight of coolant within the chips, and also, the coolant was lost upon the disposal of wet chips. Coolant remaining within the CNC machines was disposed and renewed upon end of life, producing many drums of waste coolant, requiring expensive collection for specialist disposal.
The objective of the recycling initiative was to remove the coolant from the wet chip material, thereby producing a clean compressed pellet of aluminium waste, then clean and recycle the coolant for re-use within the CNC machines.
The need for coolant and lubricant
Liquid coolant removes heat, reduces friction and tool wear, and permits higher cutting speeds
Production work requires heavy cutting over long time periods and typically produces more heat than air cooling can remove. Rather than pausing production while the tool cools, the use of liquid coolant removes heat rapidly, thereby reducing friction and tool wear, and permits higher cutting speeds. However, it's not just the tool which heats up but also the production piece work surface. Excessive temperature in the tool or work surface can ruin the temper of both.
Besides cooling, cutting fluids also aid the cutting process by lubricating the interface between the tool's cutting edge and the chip. This lubrication helps to prevent heat generation and avoid the chip from being welded onto the tool. Extreme pressure additives are often added to cutting fluids to further reduce tool wear.
Cutting fluid degredation
Compressed pellets of aluminium ready for recycling
Cutting fluids degrade over time due to contaminants entering the lubrication system. A common type of degradation is the formation of tramp oil, also known as sump oil, which is unwanted oil that has mixed with cutting fluid. This contamination provides an ideal breeding ground for bacteria and fungi, which quickly degrade the coolant.
Old, used cutting fluid must be disposed of when it is fetid or chemically degraded and has lost its usefulness. As with used motor oil or other wastes, its impact on the environment needs to be mitigated.
To clean the coolant, Supercraft installed a Cardev T700 Portable Trampoil Removal unit. Supercraft also installed a chip pelletizing machine, which succeeded in squeezing virtually all the coolant from the chips. The coolant recovered from the chip pelletizer contains fine aluminum particles plus tramp oil, both of which must be removed before the recovered coolant can be recycled.
Cardev T700 portable trampoil removal unit
The coolant recovered in the pelletizer drains into a collection sump where some of the entrained tramp oil is removed. The coolant is then pumped through a bag filter, which removes particles down to 25 microns, and then into a holding tank.
Once the coolant has been cleaned and trampoil contamination removed, an anti-bacterial agent is added to the coolant before being mixed with fresh coolant and supplied back to the CNC machines.
Coolant loss is now a fraction of what it was prior to installation of the pelletizing and recycling system. The environmental gain is a 75% reduction in coolant disposal with associated cost saving and the corresponding purchase of new coolant. The compressed pellet of aluminium also receives a better price for recycling and avoids the waste of coolant.
Coolant samples before and after cleaning
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