July 2007 Edition

Coolant/Filter

Cast Iron Waste No Longer Wastes Time

Cleaning cast-iron fines from its machines was putting a dent into this shop’s process, the solution minimized the downtime needed to clean the machines

The magnetic chip disc of the Hennig Cast Iron Chip Disc Filtration System used at Paul Precision Machine assists in the removal of cast-iron fines

At Paul Precision Machine, Inc., Tulsa, OK, a machine shop specializing in oil and gas equipment, machining cast iron created recurrent and costly problems.

In machining cast iron, a large volume of fines – small particles in the 25µ to 100µ range – are produced, owner Chuck Paul said. These particles are often smaller than the typical machine tool filter system’s capabilities. The result is a sludge that accumulates in the chip conveyor’s coolant tank as well as in the filter vessel. When clogging occured, the machines required substantial downtime and production was lost as the sludge was shoveled out of the system.

“Every 80 to 100 hours, our big machining centers were going down due to filter clogging from cast iron fines,” Paul said. “We’d stop production, completely break down the system, clean and replace parts, reassemble, and get back to business. This process usually took anywhere from eight to 12 hours and that represented substantial loss of revenue, in addition to pushing back our production scheduling, every two weeks or so.”

A Show Trip Pays Off

In a trip to a machine tool show, Paul found a magnetic chip disc filtration system designed to handle cast-iron fines. He returned to Tulsa and further investigated the system using the website of the manufacturer, Hennig, Inc., Machesney Park, IL.

Within 60 days of discussions and drawing exchanges, Paul purchased his first Hennig Cast Iron CDF Filtration System – CICDF – and installed it on one of the shop’s 600mm Okuma machining centers. Through the first four months of operation, there was no downtime due to canister filter clogging.

With the CICDF, the contaminated coolant is channeled to a conveyor, where the big chips and larger particles move up the incline and discharge into a chip hopper. Smaller cast-iron fines are collected by a magnetic drum that rotates across a stainless steel scraper blade. As the sludge accumulates on the scraper blade, it drops the fines onto the conveyor for delivery to the chip hopper.

The small particles that escape the magnetic field of the drum migrate to a disc filter made from a stainless steel micronic weave mesh that intercepts particles as small as 25µ. A continuous backwash of coolant blasts the particles collected in the filter back to the magnetic drum, where they are scraped off as sludge, eventually dropping onto the conveyor, and carried out with the chip load.

The disc filter is sealed with an inverted lip seal on the clean side of the conveyor wall, ensuring a tight and long seal life.

There is less heat build-up and longer coolant life, Paul said, as well as other benefits from the filtration system. Only clean coolant returns to the reservoir or is diverted to the system’s self-cleaning spray nozzles.

 Paul admits to some “sticker shock” at the cost of the first system, until he calculated the payback time to be 14 to 16 months on a machining center running one 10-hour shift per work day. That took only the billing rate for the machine tool into account.

 Staying Clean

 With the additional uptime and better predictability on his work schedule, Paul improved turnaround time on jobs and avoided the almost bi-weekly income loss caused by cleaning downtime. As a result, Paul purchased a second CICDF and a third is scheduled for installation on the shop’s Daewoo machining center.

Kevin Paul, Lisa Davis, and Chuck Paul of Paul Precision Machine with typical cast iron cylinders the company machines

 Compared to the alternatives of a vacuum cleaning system or the changeover and disposal problems of conventional paper media, Paul said the magnetic drum systems savings and benefits are substantial.

 The filter system installation was a low-impact process since the system used the machine tool controls – interconnected to a manual auto-switch – to run the filtration system whenever the machine tool operates.

 Paul Precision Machine, founded in 1978, targets large parts with 10" to 30" diameters for processing on its CNC machining centers. The company, with 12 employees, machines tool steels, stainless, cast iron, and aluminum. Paul said the CICDF system performs well on all materials, even non-ferrous materials.

 A particular specialty of this shop is the machining of ductile-iron cylinder castings, steeple cylinders, and crosshead guides for natural gas compressors. High-pressure coolant flushing is required, as the machining centers accommodate large work envelopes. This means coolant nozzle clogging causes immediate problems when machining large workpieces. .

Hennig, Inc www.rsleads.com/707mn-202

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