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Examining cleaning room requirements, Part 4: centrifugal wheel performance.

Examining Cleaning Room Requirements, Part 4: Centrifugal Wheel Performance

This continuing series on optimizing the operation of shotblast equipment focuses this month on centrifugal wheel performance. With the proliferation of centrifugal wheels and the recent trend to run wheels at higher speeds or, in some cases, lower than traditional standard speed, there is some confusion as to the performance characteristics of the different wheel diameters. The effect of high speeds or low speeds on flow rates and cleaning efficiency also should be understood.

There are five factors that affect the cleaning rates of centrifugal wheels: * abrasive velocity; * abrasive flow rate; * abrasive distribution in the wheel pattern; * direction of angle of impact of the abrasive; * size, shape and hardness of the abrasive.

All centrifugal wheels (except for some air fed and batter wheels) used today have basically the same components. The components that affect the performance of a wheel, whether V-belt driven or direct drive, are the feed spout that feeds abrasive into the center of the impeller and the rotating impeller blades that carry the abrasive to the fixed impeller case opening.

There, the abrasive is discharged through the opening to the heels of the rotating vanes, which accelerate the abrasive to a useful velocity. Figure 1 shows the velocity diagram of a 19 1/2 in. diameter straight vane wheel rotating at 2250 rpm. Figure 2 shows the approximate abrasive velocity vs. wheel rpm for the centrifugal wheels most commonly used.

The abrasive flow rate is dependent on the power available to accelerate the abrasive from zero to its discharge velocity after overcoming the idling hp and the power used to overcome friction of the abrasive on the wheel parts as it passes through the wheel. Table 1 rates these power factors to arrive at overall wheel efficiencies for commonly used wheels.

Laboratory tests run on 13 in. curved vane, 18 in. curved vane and 19 1/2 in. straight vane wheels have shown the average flow in lb/hr per net hp to be approximately 1700 lb/hr/hp at an abrasive velocity of 240 fps.

Further, it has been shown that as the abrasive velocity is reduced, the flow per hp increases; and conversely, as the velocity increases, the flow per hp decreases. Knowing the wheel size, type, rpm, hp and the average flow in lb/hr/net hp, the total flow can easily be calculated as follows: Total flow (lb/hr) = [motor hp - idle hp] x lb/hr/hp. [Tabular Data Omitted] [Figure 1 & 2 Omitted]

Thomas A. Briere Pangborn Corp Hagerstown, MD
COPYRIGHT 1989 American Foundry Society, Inc.
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Author:Briere, Thomas A.
Publication:Modern Casting
Date:Oct 1, 1989
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