There are four basic types of gear reducers on the market today:helical gears,parellel shaft helical gears,helical bevel gears,and helical worm gears. The latter three types of gear reducers are often used in the theatre industry. Both parallel shaft and helical bevel gear reducers are very efficient in transmittting power from the motor to the output shaft. The helical worm gear reducer is inefficient in its transmission of power from the motor to the output shaft. The helical worm design is the mostly widely used gear reducer type, offering long service life overload and shock tolerance.
Efficient gear reducers are used on most of today’s packaged winch systems. They are also used on most fire curtain motor systems as they are easy to back drive, which is the reverse of the normal operation. The output shaft is used to turn the input shaft. Many fire curtain release systems release the brake on the motor, using the weight of the fire curtain to turn the output shaft of the gear reducer, which turns the motor. A hydraulic dampener attached to the motor controls the descent speed of the fire curtain.
An inefficient gear reducer design does, however, have advantages in the threatre world. A helical worm gear reducer with a gear ratio greater than 60:1 statistically cannot be back-driven. This means that a load on the output shaft will remain staionary even if the motor brake is released. Most line shaft, drum, and counterweight assist winches use this type of gear reducer because of this feature. Helical worm gear reducers are a simple design that is very cost-effective to produce. This design lends itself to the lower output RPM and higher gear ratios used in the theatre industry.
Gear reducers are filled with oil and are vented because the oil will expand as the reducer is used. The oil helps to keep the reducer cool. The reducer will have breather vent and a drain plug. While it may look like as if they can be mounted or oriented in any position, it is very important to be certain that the vent is at the top and drain at the bottom when the reducer is mounted in its final position. The amount of oil with which the reducer is filled varies with the orientation that is used. The orientation is also important regarding the bearings that are installed into the reducer. The manufacturer will install different bearing depending on whether the bearing is below or above the oil level in the reducer. Thus it is important to order a gear reducer for the specific orientation for which it will be used.
Gear reducers also have their own service factor, which is defined by the American Gear Manufactures Association (AGMA). AGMA adjusts a reducer’s ratings relative to the individual load charateristics of the reducer. AGMA’s ratings are based upon time duration. For winches used for between three and ten hous per day the service factor is 1.25. For winches used for more than ten hours per day the service factor is 1.5.