Problem of Solids Buildup in Sumps
Solved for Specialty Machine Shop

Bradford Machine Co. (Brattleboro VT), a precision specialty shop making medical components and other close-tolerance products, faced a time-consuming and expensive problem with buildup of chips and sludge in the sumps of the machines. Bradford operates 14 CNC’s, 6 mills, 5 lathes, and 3 EDM machines, cutting primarily aluminum and exotic steels. John Therrien, shop manager, says, “On the milling machines, chip buildup in the coolant caused the pump to clog and cut off coolant flow. Also, chips packing in the sump could result in coolant overflow onto the floor. On the smaller sumps, it takes four hours to pump out the coolant, shovel muck from the bottom of the sump, wipe down the machine, and pump back fresh coolant. On the large mill it’s an eight hour project. Since the mills are operated two shifts, five days per week, shutting down for 4 to 8 hours for a complete cleanout was done only when absolutely necessary. On the lathes, the buildup of fines in the coolant adversely affected the surface finish and required replacing the coolant every few months. Plus, the cost of waste disposal is constantly increasing.”

Therrien’s objective was to find a method for cleaning out the solids without the need for shoveling out the sumps. He tested an air-driven vacuum head fitted on a 55 gallon drum. Although the device removed the coolant from the sump, it left behind a considerable quantity of solids in the corners of the sump. In addition, it used so much compressed air that the air pressure at the machines fell below the low pressure alarm level. Therrien also considered a large portable filter and vacuum tank system, but decided that it would be impractical in the tight spaces of his shop. The problem of buildup of solids in the sumps remained unsolved until Therrien learned that Keller Products, Inc. (Lexington, MA), who previously supplied an efficient tramp oil separator to Bradford, had introduced a new pump/filter unit, PFA-1002, which looked promising as a practical solution to the problem.

The PFA-1002 incorporates a high capacity bag filter and a high flow rate air-operated diaphragm pump, mounted on a compact (20” x 30”) cart. The mixture of coolant and solids is pulled through a large diameter inlet hose into the bag filter, which removes all solids as fine as 5 microns. The filtered coolant is returned to the sump under pump pressure at 20 gallons per minute. The force of the pressurized liquid discharge scours the bottom of the sump and keeps chips and sludge suspended in the sump for pickup by the inlet hose. The PFA-1002 can clean settled and suspended solids from a typical sump in 15 to 30 minutes. The machine tool is shut down during the brief cleaning period, but there is no need to take it off line, in contrast to the 4 to 8 hours of machine downtime required to pump the sump dry and shovel out the solids. With only a 1/4-inch compressed air line connection (no electricals), the cart-mounted PFA–1002 may be moved to another sump and set up to operate in minutes. The only maintenance required is to empty or change the filter bag when the pumping rate slows. When filtering relatively dry solids, such as aluminum chips, the filter bag may be emptied and reused multiple times. A new filter bag costs $7.00. Bradford is using water soluble coolants, but the PFA-1002 is equally effective removing solids from cutting oils.

Bradford has been using the Keller PFA-1002 to maintain the sumps in all the mills and lathes since last year. John says, “We now clean each of the sumps in rotation as needed, usually once in three or four weeks, during scheduled Friday afternoon maintenance. We can do a quick cleaning in 15 minutes, or a more complete cleaning in about 30 minutes by pulling the conveyor. The cleaning operation is usually a one man job.” Because there is essentially no holdup volume in the PFA-1002, the unit may be rotated among different coolants without mixing. John Therrien has concluded, “The use of the PFA-1002 has eliminated machine inefficiencies caused by excessive solids in the coolant, eliminated unscheduled machine downtime for sump cleanouts, greatly reduced the man hours devoted to coolant maintenance, and completely eliminated the unpopular task of shoveling solids from the sumps.” Needless to say, both shop management and shop operators are very pleased with the performance of the PFA-1002.