In brief
A helical gearbox transmits torque via externally toothed gears on parallel shafts and is considered a robust, highly efficient type of gearbox.
Contents
What is Helical gearbox?
Cylindrical gears are toothed around their circumference. In a helical or spur gear unit, pairs of gears mesh on parallel shafts. Several stages in series produce higher ratios. This design has high efficiency per stage, a simple construction and is easy to maintain. Coaxial versions keep the output in line with the input, while shaft-mounted designs with parallel offset shafts save installation space in length.
Straight-cut spur gears are easy to manufacture but run more noisily. Helical gears have more teeth in mesh at the same time, run more quietly and carry more load, but generate axial forces that have to be absorbed by the bearings. Key ratings are ratio, number of stages, rated torque, service factor, centre distance, mounting position and shaft design. In geared motors, the helical gearbox is connected directly to the electric motor.
It is used in conveyor belts, pumps, agitators, hoists, mixers and many other machines. Wear parts are bearings, shaft seals and gaskets; damage to the gearing is mainly caused by overload, lack of lubricant or contaminated oil.
In practice: maintenance and procurement
For replacement or repair, nameplate data, ratio, mounting position and the shaft or flange design must be stated. Stocking seal kits and bearings for installed gearbox types shortens repairs, because the gearing itself fails less often than these components.
Synonyms and abbreviations: spur gearbox · helical gear unit · helical geared motor · gear reducer
Frequently asked questions
What is the difference between straight and helical gearing?
With straight gearing, the teeth run parallel to the axis; with helical gearing, they run at an angle to it. Helical gears engage gradually, run more quietly and transmit more load for the same width. In return, an axial force acts on the bearings. Straight gearing is easier to manufacture and produces no axial force.
When is a helical gearbox better than a worm gearbox?
When energy efficiency is important and the machine runs for long periods, because the helical gearbox has significantly lower friction losses. A worm gearbox makes sense when a right-angle output, a high ratio in a single stage or particularly quiet running is required. For right-angle drives with high efficiency, a helical-bevel gearbox is often chosen.
What information is needed to replace a helical gearbox?
The manufacturer’s type designation, size, ratio, mounting position, shaft design and, where applicable, flange dimensions are important. If the gearbox is part of a geared motor, the motor data are also needed. If the nameplate is missing, photos, centre distance, shaft diameters and mounting dimensions help in the search for a dimensionally identical gearbox.
How can damage to a helical gearbox be recognised?
Signs include changed noise, higher vibration, rising temperature, oil loss and metal particles in the oil. Vibration analysis and oil analysis often reveal gearing and bearing damage long before a failure. During inspections, the gearing can be checked for pitting and wear through the inspection opening or with an endoscope.