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Worm gears need specialist lubrication

11th June 2021

     

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Worm gears are specifically designed to transmit motion and power between nonintersecting shafts, such as shafts at right angles to each other. Because worm gears work differently to other gears, they require specialist lubrication.

Unlike other gears, the worm can easily turn the gear, but the gear cannot turn the worm. High-performance lubricant manufacturer Lubrication Engineers (LE) South Africa national marketing manager Callum Ford explains that this is because the angle on the worm is so shallow that when the gear tries to spin it, the friction between the gear and the worm holds the worm in place. This feature is useful for machines such as conveyor systems, in which the locking feature can act as a brake when the motor is not turning.

“However, this static action can cause massive pressures on the film of oil, often rupturing the film and allowing metal-to-metal contact, which is why we recommend specialist lubrication,” says Ford.

In a worm gear, he explains, there are two components: the worm and the worm wheel or gear. While the worm is usually made of a hard, wear-resistant steel, the worm wheel should be made from a good bearing bronze.

Ford says that worm gears are often used where space is very limited. “High gear ratios may be obtained. However, at high ratios the efficiency can be as low as 40% to 50%. The worm drives by its threads sliding into contact with the teeth of the worm wheel. This constant sliding action generates heat and, therefore, adequate cooling and superior lubrication must be provided.”

The bronze, from which most worm wheels are made, is sensitive to active sulphur, which is found in most extreme pressure gear oils.

“When activated this can etch the gears, so steer clear of options that include active sulphur. It’s important to choose an oil that adheres to the metal surfaces, provides an excellent film strength and prevents surfaces from welding to each other from the sliding action,” says Ford.

There are three basic types of worm gears, and each requires specific lubrication. Cylindrical (nonthroated) worm gears are similar to a rack and pinion, with straight teeth. Ford suggests this type of gearing be lubricated with a high-quality gear oil, such as LE’s Almasol Vari-Purpose Gear Lubricants.

A single enveloping, or a single-throated worm gear is helical cut with a parallel-sided gear mating with a curved worm wheel. “This type of gear is more forgiving for position and alignment to tolerance problems,” says Ford. He suggests lubricating these types of worm gears with either a high-quality gear oil, or a specialist worm gear lubricant, such as LE’s Almasol Worm Gear Lubricants, depending on the manufacturer’s specifications.

A double enveloping, or a double-throated worm gear is helical cut and with a curvature of both gears that increases the surface of contact between the gears. Because of the constant friction, we recommend only using specialist worm gear lubricants designed for this application, such as LE’s Almasol Worm Gear Lubricants,” concludes Ford.

Edited by Nadine James
Features Deputy Editor

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