The decision to use worm gears in an application is a question of cost, space and efficiency. Even though worm gears can have low efficiency and are designed to wear, there are many benefits that make worm gears a practical solution for machine manufacturers and users.
How Worm Gears Work
A worm gear unit consists of two primary parts: the worm gear and the worm wheel. The worm gear is often made of steel, while the worm wheel is typically made of bronze.
These gears operate with a sliding action rather than the rolling action which is common in other gear types. The sliding generates friction which contributes to their low efficiency. 40% to 90% efficient is the normal range for worm gears. This means that worm gears often require more power to do the same job than if another more efficient type of gear set were used.
Worm Gears and Low Efficiency
Worm gear efficiency is affected by the sliding of the worm gear and worm wheel. The amount of friction can be reduced with optimized lubrication. NORD Drivesystems uses only synthetic oil in worm gearboxes, which reduces friction, heat and energy loss. With less friction comes greater efficiency.
The use of two different metals for the worm gear and worm wheel also helps improve efficiency. The bronze worm wheel is softer and therefore produces less friction against the steel worm gear. However, the softness of bronze means it will wear quicker, which is a compromise for improved overall efficiency.
Advantages of Worm Gears and Reasons to Use Them
While worm gears aren’t the most efficient, there are some benefits that make them a practical solution:
- Quiet Operation: The sliding action of the gears is quieter than other gear types.
- High Ratios: Worm gears can have a low number of teeth (threads), which allows higher ratios to be accomplished with fewer gears.
- High Shock Loads: The softness of the bronze worm wheel helps to better absorb shocks.
- Compact Size: Since fewer gear sets are required to achieve the desired ratio, therefore worm gearboxes can be smaller in size.
- No Backdriving: Worm gears can be self-locking and have braking characteristics. It's sometimes not possible to backdrive worm gears, which is an excellent advantage for lifts, cranes and other applications where braking is critical.
- Inexpensive: The smaller housing size and fewer required gears means worm gearboxes are typically cost effective to manufacture and purchase.
NORD Drivesystems has a large product portfolio that includes worm gearboxes that are optimized for many industrial applications. Contact a NORD representative today and work with a Sales Manager or NORD Engineer to select a complete drive system to enhance efficiency and performance of your operations.
Machine Design: http://machinedesign.com/mechanical-drives/gear-efficiency-key-lower-drive-cost
MEAD Info: http://www.meadinfo.org/2008/11/gear-efficiency-spur-helical-bevel-worm.html