For every input, there’s output, and in every process, there’s waste.
For metalworkers, waste comes in the form of chips, and other than having them leave your shop in the soles of your shoes, chip handling is a function all shops must consider.
Single-man operations or other small shops know that at the base of the chip handling pyramid is the manual system–shutting down your lathe or mill, cleaning out the machine, and shoveling chips into the appropriate container for scrap hauling. As shops grow, manual systems usually evolve into a better-organized maintenance system. Machines are taken out of production on a regular basis, chip carts are segregated by material, moved across the plant to a staging area where they are allowed to drain, and then are removed by a salvage company.
Chip conveyors are usually thought of as important, but largely commodity add-ons to a machine tool purchase, mainly sold through a machine tool OEM or distributor.
“The majority of the people in manufacturing don’t think of a chip conveyor as something that needs attention until something goes wrong,” says Bruce Kiwala, national product manager for chip and coolant systems at LNS America, Cincinnati, OH. “There’s not a lot of thought about chip conveying up front in a machine tool purchase, and most of that is price-sensitive.”
But much of that is changing, and the machine tools themselves are a big part of the reason why. “Over the recent past, a couple of noteworthy things have changed,” Kiwala says. “With the growth of multiple operations on one machine, turnings generate curling-type chips, sixes and nines, while milling can make finer chips that wash into the tooling coolant tank. Loss of production is another real danger. A coolant tank can fill with chips, necessitating shutting the machine down and cleaning the pumps and tanks.”
Filtration-type conveyors from LNS and other suppliers generally operate by adding a filtration station to a belt conveyor. The hinged belt removes the chips in the same way as a normal hinged-belt conveyor, but the use of filter boxes ensures that all chips greater than a certain size (LNS supplies filters as fine as 50 microns in size) cannot pass into the coolant tank. ”Filtering-type conveyors have grown from five per cent of our product mix 10 years ago to 20 per cent today,” Kiwala notes. “Given indirect labour costs and loss of production time, the benefits of filtering-type conveyors versus traditional hinged-belt conveyors are easy to convey.”
“In some situations the existing chip processing system, operating at design capacity does not adequately remove residual cutting fluids from chips,” says Robert Ennis, executive director, marketing at National Conveyors Company Inc., East Granby, CT. “Chips are too wet, negatively affecting their price (value) in the scrap market. Excess residual cutting fluid leaks from chip collection boxes, creating a wet factory floor hazard and housekeeping problems. A common cause of this situation is a malfunctioning chip wringer (centrifuge) that needs to be repaired or replaced. In other situations, machining operations are expanded, resulting in the production of a higher volume of wet chips without any upgrading of chip handling capabilities. Chip processing equipment such as shredders, chip wringers (centrifuges) and associated conveyors become overloaded, resulting in spillage and poor separation of coolant or cutting oils.”
Also, if machining operations produce bushy, stringy turnings and these are handled with crushing (shredding) so as to produce small “shoveling grade” chips, a poorly performing turnings crusher/shredder can result in troublesome stringy turnings mixed with smaller chips, Ennis adds.
Why invest in sophisticated chip handling capabilities? First, regulations governing the health and safety of employees will dictate that capital must be allocated to a well-maintained chip processing system to provide a clean and safe working environment, Ennis explains. Second, if machining waste is to be sold to independent scrap processors, it must be in a suitable physical condition to obtain the best possible price. Also, regulatory authorities are increasingly prohibiting any leakage of coolants/oils from chip haulage vehicles in transit from point of origin to ultimate destination. Large penalties for leakage on roadways can be levied on the generator of wet metal chip waste and the haulage contractor.
The type (alloy) of metal being machined will also impact the cost/benefit consideration for investment in a chip processing system, Ennis says. Clearly, aircraft grade aluminum scrap, titanium scrap and many other types of specialty metal machining waste can bring attractive income from commercial scrap buyers/recyclers.
Factors for choosing chip handling systems remain work material, volume, chip formation, coolant, and the amount of lights-out manufacturing. Total chip production must be taken into account in an unattended shift. Chip hopper and conveyor discharge height must be adjusted to meet the chip disposal need. Chip formation affecting buildup in the machine and on the tooling must be controlled. An unattended system must be set up with the right robust coolant system, chip handling, and container volume to handle it.