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While feeders with electromagnetic AC drives have been available for a number of years, they went largely unnoticed until energy costs started to skyrocket and energy sources on the West Coast became scarce. Companies soon began to realize that the electromagnetic AC-drive feeders could offer a significant cost savings in power consumption while also improving process control.
The Magnetic Drive CircuitConventional DC-operated electromagnetic vibratory equipment operates with an inefficient attract-release system. A spring-mounted moving mass is alternately attracted by a rectified pulsating direct current electromagnet (requiring a power-consuming rectifier) and returned to its original position solely by the springs.
The AC-operated, variable-speed electromagnetic drive system, on the other hand, incorporates a lifetime permanent magnet (part of a spring-mounted moving mass). The poles of the magnet are intermeshed with those of an electromagnet, which is powered directly by an alternating current line. This results in the spring-mounted moving mass being both attracted and repelled by the AC electromagnet equally on each half of the AC cycle.
This action has the effect of progressively closing the magnetizing circuit through the electromagnet core, providing a progressively increasing magnetizing force upon the permanent magnet. The demagnetizing force is very minor, since the action described also has the effect of progressively opening the demagnetizing circuit.
On the opposite side of the sine wave, the polarities of the electromagnet are reversed. The armature is driven in the opposite direction, and a net magnetizing force once again acts on the permanent magnet. A predominant magnetizing force is always impressed upon the permanent magnet, which prevents it from losing its strength.
Advantages of AC-Drive FeedersSince the amplitude of the feeder’s vibration depends directly upon the forces applied at the poles, and since these forces depend directly upon the applied AC voltage, a simple variation of the AC voltage from zero to 100% results in a corresponding amplitude variation from zero to 100%. With a DC-drive feeder, a 10% increase in voltage might result in a 40% increase in feed; with an AC-drive feeder, a 10% increase in voltage results in a 10% increase in feed. This level of accuracy makes the feed much easier to control. Additionally, no rectifiers are needed, which means that the units require less maintenance and consume less power. An energy savings comparison is shown in Table 1.
However, while the AC-drive units provide increased feed accuracy, energy savings and lower maintenance requirements, there are no trade-offs in speed or capacity. The feeders can handle light, bulky materials at speeds up to 60 ft per minute, and heavy-duty units offer capacities of up to 550 tons per hour.
The Power to ChooseEnergy costs will continue to be a concern in the coming months and years as demand threatens to exceed the available supply in many areas of the U.S. Fortunately, making even minor changes to a materials handling operation can significantly reduce power consumption. In many cases, using AC-operated, variable-speed electromagnetic feeders instead of DC-drive attract-release feeders can help manufacturers save energy while also increasing feed accuracy.
For More InformationFor more information about AC-operated, variable-speed electromagnetic feeders, contact Eriez Magnetics, 2200 Ashbury Rd., Box 10606, Erie, PA 16514-0608; (800) 345-4946 or (814) 835-6000; fax (814) 838-4960; e-mail firstname.lastname@example.org; or visit www.eriez.com.
*The Hi-Vi system, supplied by Eriez Magnetics.
SIDEBAR: Putting the AC-Drive Feeders to the TestSeveral years ago, an aggregate producer put eight AC-drive vibratory feeders into service. In today’s dollars, the savings in energy approach $36,000—more than the original cost of the feeders themselves.
A company located in the mid-south U.S. was using the maximum amount of electricity they could purchase from their power supplier. With expansion in the company’s future, efficient use of energy was a primary concern. By converting the vibratory feeders in its production lines to AC drives, the company was able to cut power consumption by more than 40% and add another production line without a rate penalty.
Another company was required to increase production but was faced with limited space for expansion. The manufacturer replaced its traditional 125-watt, DC-type drive electromagnetic feeder, which fed 360 cu ft of product per hour, with a high-deflection AC-drive feeder capable of feeding 600 cubic feet of product per hour. The end result was 20% less power consumption and 66% more feed capacity.
A ceramic tableware manufacturer was metering a fine powder to its circular screener to remove lumps. The material often aerated and fluidized on its DC-drive feeder and only fed at 20 ft/minute. The company installed an AC-drive feeder at 30 Hz and effectively doubled its capacity at half the power consumption.