Two-stage gearboxes that are a more efficient alternative speed reducer to worm gears in applications with high gear ratios
Worm gears are widely used in packaging machinery, conveyors, materials-handling applications, and in pharmaceutical and food processing plants. Huge numbers of right-angle worm gear motors are in use. Worm gears are specified because they have a low initial cost, are compact, deliver high speed reductions, offer fine speed control with a long service life, feature quiet operation, and can withstand high overloads. However, worm gears have low efficiencies at high gear ratios and are not the best choice from an energy efficiency standpoint.
Worm gears may have efficiencies of 55% to 75% at high gear ratios. Available helical/bevel gears are about 95% efficient. Combination gears (two-stage gearboxes) achieve a high gear ratio while maintaining an efficiency of about 90%. Improving gear efficiency from 80% to 95% results in a15.8% reduction in baseline energy use.
High-efficiency gear reducers should be specified for new projects or existing process retrofits. In-service worm gear replacements are difficult to accomplish because product familiarity is needed to identify worm gear drives. Physical constraints can present obstacles, such as mounting configurations, couplings, shaft size, and gear reducer centerline-to-centerline distances. Retrofits should focus on applications with high gear ratios. In some cases, a gearbox can be replaced. In other cases, an integral right-angle gear drive motor is recommended. Increasing the gear reducer efficiency may provide an opportunity to downsize the replacement motor. Additional energy savings are obtained when an old standard efficiency motor is replaced with aPremium Efficiency model. .
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Baseline Description: Worm Gear Baseline Energy Use: 3385 kWh per year per hp
Worm gears may have an efficiency of 55% to 75% at high gear ratios. Helical/bevel gears are about 95% efficient. For very high gear ratio applications, two-stage gearboxes can be provided that use two sets of gears and achieve a high gear ratio while still maintaining an efficiency of about 90% (95% x 95%). Improving gear efficiency from 75% to 90% results in a 16.7% reduction in baseline energy use. Assume a 3 hp driven equipment load---with a 75% gear efficiency, the load imposed on the drive motor is 4 hp. A 5 hp drive motor would typically be installed and operate at its 80% load point. Given a 90% combined gear efficiency, the load on the motor decreases to 3.33 hp. The 5 hp motor is now only 66.6% loaded. Assuming an energy efficient motor and 5000 hours per year of conveyor operation, the baseline energy use is 16,924 kWh/year with an energy savings of 2798 kWh given installation of the more efficiency combination gear. Energy savings are 16.5% of the baseline use (note 16.7% as the drive motor efficiency is slightly decreased at the reduced load point).
"Typical" Savings: 17% Energy Savings Reliability: 4 - Extensive Assessment
Energy Use of an Emerging Technology is based upon the following algorithm. Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.
Jennifer Werger, 01/01/2009. Food Processing Machinery: Improving Energy Efficiency FoodProcessing.com
John Lytle, 01/01/2011. Switching Gears to Save Energy Costs Material Handling & Logistics News
Tejindar Singh, 11/01/1994. Motor and Drive Application Notes: The Mechanical System Pacific Gas & Electric Company
Sadrul Ula, 01/01/1992. Energy Efficient Drivepower: An Overview Office of Conservation and Renewable Energy
Bernd Stoeber, 07/01/2000. Gear Efficiency -- Key to Lower Drive Cost Motion System Design
Hermann Siebert, 05/01/2011. Worm Gears -- Higher Energy Efficiency and Less Strain on Resources Gear Technology
John Malinowski, 05/01/2009. Maximizing Energy Savings by Replacing Motors and Reducers Plant Services