Spiralräder

Spiralräder are a form of cylindrical gear in which the teeth are shaped along a spiral on the pitch cylinder, producing a helical engagement even for gears with parallel axes. The geometry is defined by the helix angle, pitch, and pressure angle; the tooth flank gradually engages and disengages, giving a higher contact ratio than spur gears and smoother torque transmission. They can be single-start or multi-start (double or triple) to adjust torque capacity and axial thrust.

Compared with straight-cut gears, spiralräder offer quieter operation, less vibration, and greater load capacity for a given face width and module. However, the axial component of the load increases with the helix angle, requiring thrust bearings and more precise alignment. They are generally used for gears with parallel shafts; for non-parallel shafts, bevel or worm gears are used, not spiral cylindrical gears.

Manufacturing methods include gear hobbing, shaping, and milling with a helical cutter or hob set to the desired helix angle; precision finishing by grinding improves surface finish and accuracy. Materials are typically alloy steels, possibly hardened and ground; corrosion-resistant variants exist.

Common applications lie in industrial gearboxes, machine tool transmissions, automotive gearboxes, and robotics where quiet operation and high torque density are advantageous. The term may also appear in older literature as a synonym for helical gears, though some sources reserve spiral to a specific tooth geometry with a curved profile.