Helical gears help manufacturers go green

A trend gaining ground at industrial plants over the past decade has manufacturers replacing traditional spur and worm gears with high-efficiency helical gears. While sometimes viewed as a pricey alternative, in reality, helical gears save energy, run cooler and quieter, require less maintenance, and last longer.

This can mean big savings for manufacturers. Replacing spur gears with helical gears in a 150,000 ft2 snack-food plant, for example, will save one customer of STOBER Drives, Maysville, Ky. about $1.5 million over the next 15 years.

Despite that kind of savings, an estimated half of U. S. manufacturers rely on outdated worm and spur gears that might have low up-front costs, but waste energy and tend to fail prematurely.

Helical advantages
The problem is worm gears are typically bronze, a soft metal, and the gear’s sliding surfaces generate friction that causes wear. This mandates frequent oil changes and means relatively short gear life. (Ironically, hardening worm gears accelerates wear.) In comparison, helical gears experience minimal wear and are practically maintenance-free.

Spur-gear surfaces have rolling contact, but the teeth are cut straight across on a face; one or two teeth are always in contact with another gear. This incomplete face engagement means spur gears are noisier and vibrate more than helical gears.

Another advantage of helical gears over spur gears is in torque capacity. Spur gears, by design, are weaker than helical gears because loads are transmitted over fewer teeth. Helical gearing is machined with angled teeth, then hardened and ground, which is complex but necessary to achieve a high-efficiency gear mesh. Because teeth are cut at an angle, the gears gradually mesh. Two or three teeth of each gear are always in contact with other gears. This alleviates the load on each tooth and creates a smooth transition of forces from one tooth to the next. The result: less vibration, wear, and noise, and longer life.