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York Machine Shop Ltd. (Campbel1 River, British Columbia) cuts aluminum-bronze tube for a specialized paper industry application. Since 1983, the company has served a diverse collection of customers in the logging, pulp and paper, fishing and mining industries. The company machines new parts and repairs old ones with versatile programmable equipment. A DoALL model C1216A automatic bandsaw is assigned a mix of cutting tasks in cast iron, steel, brass, aluminum and other metals.
"We use bi-metal blades for 90 percent of what we cut here," says York president Dennis Cambrey. However, one manufacturer has placed repeat orders for parts cut from aluminum-bronze tube, which is especially tough on bi-metal blades, tying up a bandsaw for 16 hours with a batch of parts.
Bronze alone is a difficult alloy to bandsaw. It produces fine dust instead of chips and the dust mixes with saw coolants to make the fluid abrade the saw blade rather than lubricate it. It also generates more heat under the blade than bronze alone. While recommended blade speed on 4 inch diameter solid bronze bar stock is 180 sfm, the recommended speed on aluminum-bronze stock is just 80 sfm.
Aluminum-bronze is commonly specified for bearings, and it provides the wear and corrosion resistance essential to a papermill accessory used on the Campbell River waterfront. A local longshoreman developed a pneumatic crane head to carry 10 or 12 big paper rolls at a time from loading dock carts to pier-side freighters. The head has an array of paper core probes. York provides more than 20 parts for each core probe, including a four-piece cone made of aluminum-bronze. The cone segments are also subject to routine abrasion as they enter and grip the paper cores. Aluminum-bronze outlasts steel in this harsh environment, but cutting the critical cone segments is a complicated bandsawing task in a difficult material.
The cone-making operation begins by bandsawing 10 foot lengths of aluminum-bronze tube into 4-inch-long sections. The tube has a 3-inch outside diameter and 1-inch inside diameter. The short pieces are machined with an external groove to accommodate the rubber bands that will later collapse the probe. They return to the bandsaw in a special fixture, enabling the saw to slice the tube lengthwise and roll the piece 120 degrees for another cut. Each tube stub is therefore cut into three rectangular pieces.
A separate machining operation, more accurate than bandsawing, tapers the rectangular pieces into 90-degree cone segments. Each segment tapers from 1 3/4-inch wide at one end to 1-inch wide at the other. Four such pieces make a gripping cone that expands and contracts inside the paper roll as a pneumatic wedge is inserted and withdrawn.
Cutting the probe cone components with a common bi-metal bandsaw blade required five cuts and three bi-metal blades per piece, with typically 96 pieces. "Aluminum-bronze just wears blades out," says Mr. Cambrey. "The abrasion takes the set right off the blade."
Aluminum-bronze stock also requires relatively low cutting speeds to limit the destructive heat created by abrasive swarf. An order for 96 finished pieces took the bandsaw 16 hours to complete.
Around 18 months ago, Dean Richardson, the local salesman for Sandvik Saws and Tools (Scranton, Pennsylvania) distributor Thomas Skinner & Son, told Mr. Cambrey about the carbide-tipped 3868 TripleSet Xtra blade. Carbide teeth resist abrasion far better than even hardened steel, and the strong-set blade is meant to penetrate hard metals. Having just finished another set of probe parts with bi-metal blades, Mr. Cambrey asked for feed and speed information on the carbide blade.
Based on data provided by York Machine Shop, Sandvik technical specialists formulated new machine settings for the carbide blade to cut aluminum-bronze. Blade speed for the carbide blade is 90 surface feet per minute while bi-metal blades typically ran around 60 surface feet per minute. Once the carbide blade was broken in, the higher cutting speeds available paid productivity dividends. "The carbide blade really cuts through the tube," says Mr. Cambrey, "The bi-metal blades sort of rubbed their way through it." Bandsawing time to produce 24 probe pieces fell from 16 hours with bi-metal blades to just five hours with carbide.
Significantly, the first carbide blade lasted through four sets of parts—96 pieces, outlasting 12 bi-metal blades. This longer carbide blade life reduced blade cost by more than 70 percent per cut.
York Machine Shop still uses bi-metal blades for most jobs, and switches to the carbide-tipped 3868 only when cutting aluminum-bronze or stainless steel. "I tend to put it in the machine if we're cutting more than 30 parts in stainless," says Mr. Cambrey.