Motor costs are calculated using a US Department of Energy website which identifies a national average industrial power rate of 6.3 cents per kilowatt-hour as of March 2012. This chart shows the potential dollar cost to operate a motor at full-load current for an 8-hour shift using a standard ac motor. Even in this instance, the purchase price differential between a helical and a worm gearbox is high enough that the time to make up the cost difference would be 48,000 hours. For the same 1 HP application, a 30:1 ratio would see a worm gearbox efficiency drop to 81%. At that rate it would take more than 200,000 hours of operation to recover the difference in costs between the two.Īs noted, the higher the ratio, the lower the efficiency of the gearbox. That converts to less than a penny per hour of operation. So, you can use an efficiency of 97% as the best scenario for the helical right angle reducer, as compared with 92% for worm reducers that are manufactured using current technology. Even the most efficient helical reducer will not exceed 97% (more typically it is in the low to mid 90% range). In an application for a 1 HP unit with a 10:1 reduction, you can conservatively expect to pay a $300 or more premium when using a helical right angle gearbox instead of a worm right angle gearbox. The efficiency of the worm gearbox would be 92% compared to a 97% for a helical gearbox. For example, in a simple application for a 1 HP unit with a 10:1 reduction, the cost of a worm gearbox is $840 less than the equivalent helical unit. Motor costs are calculated using a US Department of Energy website which identifies a national average industrial power rate of 6.3 cents per kilowatt-hour as of March 2012.Īs center distance grows, efficiency improves, as seen here where the rise in efficiency for seven center distances is at a 10:1 ratio.īased upon market prices and catalog stated efficiencies, the payback time for low HP applications can be long. To compare the savings in some common lower HP applications, we have calculated the dollar cost to operate a motor at full-load current for an 8-hour shift using a standard ac motor. When the energy dollars saved are compared to gearbox purchase costs, there are strong reasons to consider right-angle worm gearboxes in many lower HP applications. Helical gearboxes are generally more expensive than worm gearboxes for the same HP and gear ratios. As a general statement, the multiple stages required within a helical gearbox add complexity and cost. When comparing the energy savings for a helical gearbox compared to a worm gearbox in the same application, there are many situations where the dollars saved are minimal. The challenge is what is the trade-off between purchase price and cost savings through efficiency? Is it more economical to pay extra for higher efficiency or is the cost of that efficiency too high to recapture through lower operating costs? center distance, for example, efficiency decreases slowly as ratio increases. Larger center distance worm gearboxes are generally more efficient than smaller center distances. Right-angle worm gear reducers tend to lose efficiency as they cross into higher ratios. Similarly, as center distance grows, efficiency improves, as seen here where the rise in efficiency for seven center distances is at a 10:1 ratio. center distance sees efficiency decrease slowly as ratio increases. For example, a standard unit with a 2.6-in. Generally speaking, right-angle worm gear reducers begin to see drops in efficiency as they cross into higher ratios. Some manufacturers have made greater strides in these efficiency improvements than others. Right-angle worm gearboxes that previously had efficiencies of 82 or 83% are now showing ratings in the upper 80% ranges, while units that were in the upper 80% range now 93 to 94% efficient. However, advances in worm gearbox design as well as improvements in lubrication are closing the efficiency gap to the point where the cost-effectiveness of worm gearboxes is more than competitive with helical designs. It may be conventional wisdom that using a helical gearbox design will lead to more system efficiency than using a worm gear design. By Greg Cober, Boston Gear Product Training Manager, Boston Gear
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