Inline Speed Reducers

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Apparatus Repair & Engineering, Inc.

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Inline Speed Reducers

Inline Speed Reducers are used primarily when we're looking for efficiency and high reduction ratios. Inline reducers are generally comprised of 1 or more sets (stages) of helical or helical bevel gears. And based on the laws of physics, when we "add" stages to a gear train, we MULTIPLY the ratios. Doing the math, if the first gear set ratio is 5:1, and we add a second gear set whose ratio is also 5:1, the resulting final speed will be based on a total reduction ratio of 25:1. And that's the beauty of multi-stage gear reduction in speed reducers... of ANY design, not just inline reducers.


So it's not uncommon to see an inline gear reducer with 3 stages of reduction and an overall ratio of 100:1 or even 200:1. The box simply gets physically larger, and while the speed decreases, the torque INCREASES like the ratio. That means that while a 200:1 reducer may have an input shaft of 1" diameter, the output shaft may have to be more like 3 or 4" in diameter to handle all of the torque that is produced.

An inline gearbox can come in a multitude of configurations when we consider the "prime mover". I believe it's safe to say that most gear reducers are driven by electric motors, and these motors are attached to the input shaft of the reducer by various means. One might even connect the motor and reducer by way of a belt and sheave system, or a chain and sprocket system, as one example. But the most common methods are direct connected with a shaft coupling, "quill" mounted (meaning the motor shaft inserted into a hollow bore input shaft), direct connected with the motor being an integral part of the gearbox case itself, and lastly, a "shovel" mount where a platform is attached to the input side of the gearbox and the motor sits on that platform. The motor is then connected to the input shaft with a shaft coupling. The use of a "shovel" base eliminates the fabrication of a special base to align the gearbox and motor shafts, vertically. There is even a "top" mount platform for some applications where a platform type base is mounted on the top of the reducer. The motor is mounted on this base and attached to the input shaft of the reducer by a belt and sheave arrangement.


Now that we've discussed the "input" side of the reducer, let's turn our attention to the "output". The photos above show all of the reducers as "base" (or foot) mounted devices. Meaning that the reducer casting has drilled holes by which it is mounted to it's operating location. But there are other methods by which an inline reducer is mounted. One is a "C-Face" output. This is a reducer whose output casting has a standard "NEMA C-Flange" adapter attached. Just like the "C-Flange" adapter used to mount the motor on the input side, this flange mounts the adapter to it's DRIVEN load by way of the same type adapter. The second type is a "hollow shaft" output. With this type, the shaft of the "driven" equipment is extended and the "hollow bore" of the reducer slides over the shaft. There is commonly some type of flange on the reducer which is fastened securely to the driven equipment to hold the reducer in place.

Shaft Mount Reducers

The last type of inline helical reducer we're going to discuss is the true "Shaft Mount Reducer". These reducers are used in specific instances, especially on conveyors and heavily in the aggregate industry in quarries and on applications using "screw conveyors". These reducers are limited in their reduction ratings due to the actual "thin" characteristic of the casting and being available in a maximum of 2 stages. The reduction ratios available from manufacturers vary widely and has a lot to do with what the manufacturer can pack into the cramped confines of the reducer casting. For instance, one manufacturer has single reduction ratios of 4.857:1, 4.91:1, 4.23:1, and 5.67:1, as well as a number of other ratios. In Double Reduction units, the ratios include 14.79:1, 15.23:1, 23.544:1, and 39.68:1, in addition to others.

These reducers are usually driven with an electric motor and the motor is attached to the input shaft of the reducer by a belt and sheave arrangement. So in selecting your reducer. you pick one close to the ration you want, and then "tweak" the final ratio through the belt and sheave combination to arrive at your exact output RPM based on combined ratios and motor input speed. The motor is usually mounted to the top of the motor by a "platform" mount like we indicated is available in the inline helical reducers above.

Since the reducer is mounted on the "shaft of the conveyor", it is free to spin around if not fastened securely in some manner. That's where an accessory called a "torque-arm" comes into the picture. The torque-arm attaches to the casting of the reducer and extends to some portion of the frame of the conveyor. When attached in this manner, the reducer is held in place securely allowing it to do its' job. In many cases, the torque-arm attachment contains an "electrical limit switch". This switch acts like an overload safety. In the normal operation of the conveyor, the limit switch is closed and allows the motor to run. If the conveyor becomes overloaded, the reducer casting will attempt to "twist" further, pulling on the torque-arm. If this extra pull causes the limit switch to move, the contact breaks and the motor stops. Protecting both the motor from an overload and the conveyor/gearbox from physical stress and damage.

So that's about it for the Inline Helical gearbox topic. If you've got questions about a particular application you're thinking about, and would like a "second" opinion, give us a call. We're ready to help, whenever we can.