A group of Engineering Physics students has designed a small device that will encourage the recycling of aluminum waste chips from machine shops, and help reduce the release of harmful chemicals in the recycling process.
The device, an automated aluminum chip compressor for a computer numerically controlled (CNC) machine, was designed by fourth-year students Peter Bonac, Jeffrey Chang, Vincent Kwong, David Moffat and Craig Wilkinson as a course project. Their design recently won first prize in the 1997 PATSCAN Environmental Innovation Contest, as well as the 1997 Molson Prize for best recycling concept.
The idea for the project came from student Peter Bonac, whose father operates a machine shop using CNC machines. These automated machines are commonly used to manufacture parts from aluminum blocks, using instructions from a computer system with pre-programmed co-ordinates to guide the machine's tools. In the machining process, small waste chips of aluminum are continually expelled from the machines. These chips, coated in a coolant used to control heat in the machining process, must then be collected and either disposed of or recycled.
Problems associated with recycling the chips include removal of the coolant, which is costly and toxic but can be reused, and storage of a large enough volume of chips to make recycling a financially worthwhile venture. Available compressors are versatile but are also extremely expensive and large, Chang said.
"We set out to design a compressor purely for use in CNC shops," he said. "It had to be small, easy to automate, able to run off power and air pressure already available in the shops, and inexpensive enough that the shops could recover the cost within a couple of years through recycling."
The device, which will be largely finished by early summer, consists of a cylinder less than a metre long and about 25 centimetres in diameter. Within the cylinder a compression chamber increases readily available air pressure from 80 to 100 pounds-per-square-inch (psi) to 8,000 to 10,000 psi. As the chips are compressed, the coolant is forced out of the chamber through small troughs so that it can be collected for reuse. Once compression is complete, a small pellet of compressed aluminum -- about the size of a small stack of loonies -- is expelled from the chamber. These pellets can be easily stored, in far less space than is required for the same amount of loose chips, until a sufficient amount has been collected for recycling.
Recycling of compacted aluminum pellets is more efficient than recycling of loose flakes, as smaller chips will evaporate as the metal is heated, Chang said.
The greatest design challenge the group faced was devising a method of feeding the compression chamber with the loose chips.
"The chips that are expelled from the CNC machines vary in size," Chang said. "But they are often tangled into larger clumps which then have to be fed into a small port in the compression chamber."
To do this the group designed a conical screw drive, a rotating hollow cone resembling a large tapered spring, that would draw the aluminum chips through a narrowing passage and then into the small port in the compression chamber.
The cost of the device, said Chang, will be about $2,000 to $3,000. Savings to the user will come from the ability to collect and reuse the coolant on-site, and through the elimination of an intermediary who would otherwise perform the compression and coolant extraction off-site for a price before delivering the pellets to the recycling facility.
"An inexpensive machine capable of facilitating the recycling process for smaller machine shops would be extremely beneficial to both shop owners and the environment, as the choice to recycle is an easy one if there is money to be made at it," Chang said.