Helical Gear

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Helical or "dry fixed" gears present an improvement over spur gears as they feature teeth angled at a set angle to the axis of rotation, forming a helix shape. These gears can be paired in parallel or crossed orientations with the former being more common. The angled teeth offer a gradual engagement, resulting in smoother and quieter operation compared to spur gears. In parallel helical gears, contact between teeth starts at one side, grows across the face, then recedes on the opposite side, preventing sudden line contact stress and noise. Spur gears are typically used in low-speed applications or where noise control isn't a concern, while helical gears find use in high-speed applications, large power transmission, and noise-sensitive scenarios. However, helical gears generate thrust along their axis and have greater sliding friction, necessitating appropriate bearings and lubricant additives respectively. High speed is considered when pitch line velocity exceeds 25 m/s.