How to Choose a Gearbox for a Belt Conveyor: A Practical Selection Guide
How to Choose a Gearbox for a Belt Conveyor
Belt conveyors are the single most common application we quote at WGT, and they are also where most buyers make the same three mistakes: picking the gearbox by output speed alone, ignoring the service factor, and choosing a mounting type that does not match the conveyor head shaft. This guide walks through the five numbers you actually need before you open a catalogue.
1. Start with the numbers, not the brand
Before any model number is discussed, you should be able to write down these five values:
| Value | Unit | Why it matters |
|---|---|---|
| Belt speed | m/s | Sets the required output speed of the gearbox |
| Head pulley diameter | mm | Converts belt speed into output speed |
| Required torque at the head shaft | Nm | Determines gearbox size |
| Duty hours per day | h | Determines the service factor |
| Ambient / site conditions | — | Determines cooling, sealing and paint spec |
If you only have the motor power and the belt speed, that is usually enough to start — but the resulting gearbox will be an estimate, not an engineered selection.
2. Convert belt speed into gearbox output speed
The gearbox output speed is set by the head pulley, not by the belt:
n₂ (rpm) = (60 × belt speed in m/s) ÷ (π × pulley diameter in m)
A conveyor running at 1.5 m/s over a 500 mm head pulley therefore needs roughly 57 rpm at the gearbox output. With a 4-pole motor at 1,450 rpm, that is a ratio of about 1:25.
Ratios in this range are covered by our SMR series shaft mounted reducers and by parallel-shaft helical units such as the F series.
3. Determine torque — and then add the service factor
Torque at the head shaft is:
T (Nm) = (9550 × P in kW) ÷ n₂ (rpm)
Do not stop there. Conveyors are a heavy-duty application with frequent starting torque, uneven loading and possible jamming. Apply a service factor and select the gearbox on the service-factor-adjusted torque:
| Duty | Hours per day | Typical service factor |
|---|---|---|
| Uniform load, intermittent | up to 3 h | 1.0 – 1.25 |
| Moderate shock (loaded belt start) | 3 – 10 h | 1.4 – 1.6 |
| Heavy shock (frequent starts, jams) | over 10 h | 1.7 – 2.0 |
A gearbox rated 10,000 Nm nominal should therefore only be applied to about 6,000 Nm of conveyor load in a heavy-shock duty. Skipping this step is the number one cause of premature gearbox failure in the field.
4. Choose the mounting type
Three families cover almost every conveyor:
- Shaft mounted with torque arm — slips directly onto the head shaft, no foundation, cheapest installation. Best for short, light and medium conveyors. See the SMR series.
- Shaft mounted, parallel shaft (RXG type) — heavier bearings, longer life on bulk material handling. See the RXG series.
- Foot or flange mounted with flexible coupling — used when the gearbox must sit on a base plate, or when the head shaft is not accessible.
A typical example is our SMR-E 55 shaft mounted reducer at 13:1, a standard choice for a 500–600 mm head pulley conveyor.
5. Check the thermal rating, not only the mechanical rating
A gearbox can be mechanically fine and still overheat. Always check the thermal power rating at the actual ambient temperature and duty cycle. In hot climates, or when the unit runs continuously, this is often what forces you one size up — or forces a cooling option such as a fan or oil cooler.
6. The checklist we use when quoting
- Output speed required: ___ rpm
- Service-factor-adjusted torque: ___ Nm
- Mounting: shaft mounted / foot / flange
- Motor: IEC or NEMA, ___ kW, ___ poles
- Site: ambient temperature, dust, corrosive atmosphere, indoor/outdoor
- Spare parts and documentation required: ___ (drawings, test report, packing spec)
Send us that list and you will get a quotation with a specific model number, not a generic price.
Frequently asked questions
Can I use a worm gearbox on a conveyor?
Only for light duty. Worm units lose efficiency at high ratios and generate more heat; above roughly 5 kW continuous on a conveyor, a helical or helical-bevel unit is usually better value.
How much backlash is acceptable?
For a new conveyor gearbox, normal backlash is typically 0.1–0.4 mm depending on size. Any "clunk" on reversing is a sign of wear or wrong assembly, not a normal tolerance.
Do I need a backstop?
If the conveyor is inclined and the load can run backwards when the motor stops, yes. Specify it at order stage — it cannot be added later without a new housing.
Get a selection from WGT
WGT WeiGao Transmission has manufactured gearboxes and gear reducers since 1988. Send your conveyor data through our contact page and we will return a specific model recommendation with drawings, ratio and confirmation of delivery time.
