Worm gears, used for speed-reduction in tight spaces for various types of automation systems, conveyor belts, industrial machinery and lifting equipment in industrial and mining applications, require specialist lubrication for their unique purposes and operational longevity, reports industrial lubricant supplier Lubrication Engineers (LE) South Africa marketing manager Gavin Ford.

Worm gears are specifically designed to transmit motion and power between nonintersecting shafts, such as shafts at right angles to each other.

There are two components in these types of gears, including the worm and the worm wheel and/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, which is highly sensitive to the active sulphur that is found in most extreme-pressure gear oils, he notes.

When the bronze reacts with sulphur, Ford says the gears can get etched. This is why LE recommends avoiding lubricants that include active sulphur.

“It’s really important to choose an oil that adheres to the metal surfaces, whether the worm is above or below the wheel. [This] provides an excellent film strength and prevents surfaces from bonding to each other from the sliding action,” he adds.

Lubricating Various Worm Gears

Worm gears come in three main variations, each requiring specific lubrication, including a cylindrical or non-throated worm gear, which is similar to a rack and pinion, and has straight teeth.

Ford suggests this type of gear be lubricated with a high-quality gear oil, such as LE’s Almasol Vari-Purpose gear lubricants.

Second is the single enveloping throated worm gear, which has a helical cut with a parallel-sided gear mating with a concave curved worm wheel. For these types of worm gears, he says it is best to use a specialist worm gear lubricant, like LE’s Almasol Worm Gear Lubricants, or a high-quality gear oil.

The third type is the double enveloping (double throated) worm gear. It also has a helical cut but the curvature of both gears increases the surface of contact between the gears.

“This can be very useful for power applications, but also generates the most heat from the sliding motion,” says Ford, adding that the constant friction in this type means only specialist worm gear lubricants should be used.

Ford says a manufacturer’s specifications can also offer helpful guidance on the right product for a specific gear.

However, unlike other gears, Ford notes that the worm can easily turn the gear, but the gear cannot turn the worm. He says 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 for the conveyor 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,” he notes, explaining that proper lubrication becomes critical for preventing this.