How to Select a Gear reducer Box

Posted on Sep 8, 2020

How to Select a Gear reducer Box

The starting point for most gearbox manufacturers is to define a service factor. This tool is used to correct issues such as the type of input, hours of use per day, and any shock or vibration that may be present in the application.

The most frequently requested information includes:

• Input speed and power

• Desired output speed or desired output torque (will determine the gear ratio)

• Characteristics of use; hours per day, a type of shock or vibration in the system

• The degree of shear force

• Unit configuration, shaft entry or hollow bore entry, shaft exit or hollow bore exit

• Unit orientation, e.g. for a worm gear at right angles, worm above or below worm, horizontal or vertical shafts

• Special materials; corrosion resistant paints, stainless steel housing and shafts

• Service factor

The starting point for most gearbox manufacturers is to define a service factor. This tool is used to correct issues such as the type of input, hours of use per day, and any shock or vibration that may be present in the application. An application with irregular impacts, such as grinding, will require a higher duty factor than one that is loaded evenly. Likewise, a device that is used occasionally will have a lower factor than that that is used 24 hours a day.


Service class

After determining this factor, it will define the service class. A unit powered by an ordinary AC motor driving a uniformly loaded constant speed conveyor for 20 hours a day would normally be Service Class 2.

Gearbox manufacturers provide graphs based on service class. To use this graph, you need to know the input power, class of service, and desired ratio. Our example is for a 2hp motor and the need for a 15: 1 ratio. To use the chart find the point where 2 hp and 15:1 ratio intersect. In this case, a size 726 unit is selected.

Following the manufacturer's product number system, unit size 726 defines a unit that has 2.62 center spacing. To confirm the selection and confirm a specific torque or speed level, manufacturers will provide graphs showing these values.

A diagram will show the values ​​for the input of a C-type front motor (flange) or directly coupled (without flange) motors. This verifies that, with a 15: 1 reduction, the 726 flange gearbox will deliver 116.7 RPM of power, and when used with a 2hp engine, it will provide up to 994lb of torque.


Transverse load

After selecting the unit size, the catalog or website of the gearbox manufacturer will indicate the value of the maximum lateral load that is acceptable for that unit of the specified size. If the application load is greater than the allowable value, the gearbox may need to be enlarged to account for lateral load.



At this stage, the size and capabilities of the unit have been defined, so the next step is to define the assembly properties of the unit. While there are several common mounting configurations, gearbox manufacturers offer a wide range of options for each unit size. The most common mounting may be a flanged entry with a hollow hole for a C-frame motor in combination with an output shaft extending to the left, but there are many other possibilities. Options such as mounting feet above or below the gearbox body, empty outputs, and input and output configuration are possible. All gearbox manufacturers provide their mounting options as well as information on dimensions in catalogs and on websites.


Grease, seals and motors

Most manufacturers provide the option to ship the gearbox filled with lubrication (in most cases, the units are shipped empty by default and allow customers to refill them on site). seal. Finally, as many gearboxes are ultimately mounted on a c-frame engine, many manufacturers will also offer the service of integrating the engine into the gearbox and shipping the assembly as a single unit.


Types of gears

Worm gears that use slipping feedback reduce speed, cause greater tooth contact, and increase friction. This greater friction generates more heat and a thicker (higher viscosity) lubricant would be appropriate for this application. On the other hand, a helical gear using a rolling coupling is more efficient and less viscous lubricants are more suitable. Note that higher speeds (units with a lower coefficient) produce more heat, and viscosity numbers may need to change accordingly.

For any gear type, the operating environment and ambient temperature will have an effect on changes that will affect the selection of the appropriate lubricant viscosity. Higher operating temperatures require greases with higher viscosities as the resistance to flow decreases as the oil warms up.


Choosing the right one

All manufacturers provide instruction manuals with their products. These manufacturers conducted laboratory tests to determine the appropriate oil viscosity for operating conditions. Generally, most helical gear units operating in an industrial 40 ° C (104 ° F) environment will perform well with SAE10W for higher speeds (3000 rpm) to SAE 40 for lower speeds. Lower ambient temperatures would shift this range from SAE 10W to SAE 20W.

For worm gear units, SAE140 (600W) would be suitable for ambient temperatures of 40 ° C, while higher weights would be required for higher temperatures.

When looking at a speed reducer versus a gearbox, the terminology is often the only difference. This is because all speed reducers are gearboxes. However, not all gearboxes are speed reducers. It may seem a bit complicated, but it's actually quite simple.

Speed ​​reducers are gear transmissions between the engine and the machine. The purpose of the speed reducer is to reduce the speed of rotation transmitted between these two end points. Speed ​​reducers take the torque generated by the motor (input) and multiply it. Second, the speed reducers, as the name implies, reduce the speed (output rotation speed) of the input so that the output is at the correct speed.

The term “gearbox” is simply a generic term for a gear train between a motor and a piece of machinery. Hence, all speed reducers are gearboxes.

However, not all gearboxes reduce the speed of the input. While not common, gearboxes can actually be tooled to increase the speed of the input. By far the most common type of gearboxes are speed reducers, but it wouldn’t be correct to say all gearboxes are speed reducers.


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