Swarf

August 9, 2002

Almost all screw press applications call for the separation of liquids and solids in organic materials, plant and animal. Consequently we were reluctant to test a sample calling for the separation of coolant oil from swarf. Swarf is the name given to the grinding dust and metal chips generated in a machine shop.

The sample supplied came from American Saw. This firm is a very large producer of saw blades. They produce hacksaw blades, band saw blades, hole drills, demolition blades, jig saw blades, etc. The saw teeth can be either ground or milled, depending on the specific blade requirements, and the cutting tools are cooled with either oil or water. The many tons of swarf and cutting chips generated by the plant are processed in briquetting machines that produce dense steel "pucks". These slugs are about 2" in diameter, 1-1/2" thick; they are sold as scrap metal.

The problem at American Saw was that the swarf from oil-cooled grinders contained too much oil for the puck machines to work properly. A partial solution was found by running the swarf through an Oberlin Pressure Screen. The Oberlin is a belt press type machine that has the belt surface covered with a continuous roll of filter paper. The four Oberlin Pressure Screens at American saw produce a layer of swarf 48" wide, about 3/8" thick. Even after pressing in the Oberlin, the swarf, which is very spongy, retained too much oil.

To our surprise a small Vincent screw press has proven successful in removing the residual oil in the cake from the Oberlin presses. Currently the customer is using a Model KP-6 from the rental fleet. A custom version, with a 52" inlet hopper, has been quoted. For abrasion resistance it will have the screw flighting made of AR alloy with Stellite edges, instead of stainless. The gearbox has been selected to turn the screw at a quarter of the normal rpm; a small 3/4 hp motor has proven to be a suitable drive.

Most of the saw blades produced at American Saw are bi-metal. The manufacturing process starts by drawing a high alloy wire into a square shape. This wire is fused to a base metal strip with electron beam welding. Next, the tooth profile is machined into the edge of the band to which the wire has been welded. This machining cuts through the wire, into the base metal, leaving each freestanding tooth individually welded to the base metal strip. The part is then hardened by heat treating so that the tooth becomes extremely durable. Then the part is annealed so that the base metal strip returns to a soft, pliable condition. Band-saw blades in this fashion bend around the band saw pulleys, without breaking, while still having extremely hard (and brittle) teeth.

Issue 130