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Turning from water wheels to abrasive saws.

Turning from water wheels to abrasive saws

In 1934, W J Savage Co was still producing steel and wood overshot water wheels - designed to withstand years of uninterrupted service. Things still go around today, but the product line consists of spindle saws that use abrasive, diamond, or carbide blades - in horizontal, vertical, and chop-stroke configurations. The saws cut ferrous materials including high-density alloys, nonferrous alloys, and nonmetallic materials such as composites, plastics, natural stone, glass, and refractory products. Cutting rates reach 120 to 130 [in.sup.2]/min, up from typical competition a few years ago of just 40 to 50 [in.sup.2]/min.

Technology is more complex than that required in the water-wheel era. In the founding days of the 1880s, Savage told users to use the Weir method of measuring water level with a stake. Today, for abrasive-cutoff wheels, the firm offers optical beam measurement of wheel diameter after each pass, so machines can maintain speeds of 10,000 sfm as wheels lose diameter.

Other systems include integral water scrubbers to eliminate smoke and fumes. Here, water flows through the spark stream and draws smoke and oxidation products out of the air. Also, a filtration system is available to filter out swarf and clean the coolant.

Steel producers are among users of these big saws. For example, Latrobe Div, Timken Bearings Co, Latrobe, PA, employs a Savage computerized saw with system components that include electronic weighing stations with digital readouts, length gages that control length of material being cut, and conveyor systems.

The machines use blades up 54" dia, and can cut 4" to 18" rounds or squares. Variable-speed hydraulic motors produce up to 250 hp and mount directly on spindles to eliminate drive belts and gearboxes.

Foreign correspondence

Perhaps the most exotic application came from overseas during WW II. Kiousin Shipbuilding and Engineering Works, Shanghai, China, sent Savage a piece of hard steel with a request for a machine to cut it. The tough material shattered most tools that tried to penetrate it, and it probably was armor steel originating in Germany, according to a newspaper report. There was speculation that the steel was to serve on bullet-proof army trucks using Ford V8 engines. Savage never knew what the steel was really used for in China, but they did find how to cut it with abrasive saws.

Today, Savage engineers explain that cold sawing has two definitions, depending on the source: (1) Carbide-tipped blades turning at slow rpm's and working like milling cutters, and (2) Abrasive saws with flood coolant. Neither type is to be confused with friction sawing. The friction saw is in another category. It turns fast enough to provide 21,000 sfm cutting rates and actually cuts with heat.

Jack Elkins, a vice president at Savage, says "Friction sawing is like rubbing hands together to get heat. But it's noisy. That's why OSHA put most of these saws out of business. They create a noise level of 140 dB to 160 dB, requiring operators to stay inside `telephone booths' for protection. We still make friction saws, but there's little demand for them."

Late models ease

wheel-maker's job

Historically, conventional abrasive cutoff machines put the burden of quality cutting on blade manufacturers. Early machines had single-speed AC main motors and recirculating coolant systems with nozzles that distributed coolant in much the same manner as garden hoses. They had fixed-speed oscillation mechanisms, and relay-logic controls with only manual and semi-automatic capabilities.

Given these factors, it was the responsibility of the tool manufacturer to develop blade specifications that would do an effective job of cutting the user's particular materials. It took a long time to pick the best grits, grit sizes, concentration, bonds, etc. And then the user would change the material or type of cut!

Today, with new equipment such as that produced by Savage, engineers don't have to start all over. They simply vary wheel speed, feed, angles, etc with computer controls - obtaining optimum results with existing wheels.

The photo shows a Model 1300 SASS (Savage Abrasive Super Saw) machine with 300-hp motor. An industrial computer controls all sawing functions, such as constant peripheral wheel speed, oscillation, length of cut, clamping, applied horsepower, coolant application, swarf collection, and smoke abatement. Cutting rates up to 2 [in.sup.2]/sec are possible now, even on super alloys and titanium, and blade life is three times historical averages, according to the firm.
COPYRIGHT 1990 Nelson Publishing
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Copyright 1990 Gale, Cengage Learning. All rights reserved.

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Title Annotation:cutting machine development
Publication:Tooling & Production
Date:May 1, 1990
Words:736
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