How Does Operating Temperature Affect Worm Gearbox Choice?
2026-10-23
A design engineer specifies a Worm Gearbox for a conveyor drive in a steel mill. The gearbox is rated for 5 kW at 40°C ambient. The actual installation is beside a reheating furnace, where the ambient temperature reaches 65°C. Within four months, the gearbox overheats and the lubricant degrades. The engineer replaces the unit with the same model and the same problem occurs. The root cause is not the gearbox quality. It is the temperature. The thermal power rating of a Worm Gearbox is based on a specific ambient temperature, typically 40°C. Above that temperature, the gearbox must be derated or a different cooling method must be used. This guide explains how operating temperature affects every aspect of worm gearbox selection.
1. How Does Temperature Affect Lubricant Viscosity and Film Thickness?
The lubricant in a Worm Gearbox forms a film between the worm and the wheel. The film thickness depends on the viscosity of the lubricant at the operating temperature. At high temperatures, the viscosity drops, and the film becomes thinner. If the film is too thin, metal-to-metal contact occurs, which causes wear and scuffing. At low temperatures, the viscosity increases, and the lubricant may not flow to the contact zone. The table below shows the viscosity of a typical ISO VG 460 gear oil at different temperatures.
| Temperature (°C) | Viscosity (cSt) | Film thickness | Recommended action |
| -10 | 5,000 – 8,000 | Very thick; poor flow | Use low-temperature oil (ISO VG 220) |
| 0 | 1,500 – 2,500 | Thick; slow flow | Warm up before operation |
| 20 | 400 – 600 | Optimal | Standard operation |
| 40 | 150 – 250 | Optimal | Standard operation |
| 60 | 60 – 100 | Thin; risk of contact | Use high-temperature oil (ISO VG 680) |
| 80 | 30 – 50 | Very thin; scuffing risk | Use synthetic oil; add cooling |
In our factory, we recommend the lubricant based on the operating temperature range. For temperatures between -10°C and 40°C, ISO VG 460 mineral oil is suitable. For temperatures between 40°C and 60°C, ISO VG 680 or a synthetic oil is recommended. For temperatures above 60°C, a synthetic oil with a high viscosity index is required, and the gearbox may need an oil cooler. Saifu has been manufacturing Worm Gearbox units for over 15 years and provides lubricant selection guidance for each application.
2. How Does Temperature Affect Seal Material Selection?
The seals in a Worm Gearbox are made from elastomers. Each elastomer has a specific temperature range. Above the upper limit, the elastomer hardens and cracks. Below the lower limit, the elastomer becomes brittle and loses its sealing ability. The table below shows the temperature range for common seal materials.
| Seal material | Temperature range | Oil resistance | Typical application |
| Nitrile (NBR) | -30°C to +100°C | Good | Standard industrial |
| Fluoroelastomer (FKM) | -20°C to +200°C | Excellent | High temperature |
| Silicone (VMQ) | -60°C to +180°C | Moderate | Low temperature |
| PTFE | -100°C to +260°C | Excellent | Extreme temperature |
| EPDM | -40°C to +120°C | Poor (not for oil) | Water-based applications |
Design engineer's note: The seal material must be matched to the temperature at the seal location, not the ambient temperature. The seal at the output shaft is heated by the gearbox itself, so it operates at a higher temperature than the ambient. In a gearbox running at 60°C ambient, the output shaft seal may reach 80°C. In this case, NBR is marginal, and FKM is the safer choice. In our factory, we measure the seal temperature on our test gearboxes and provide a temperature map for each model. Saifu Vietnam Company Limited recommends FKM seals for ambient temperatures above 50°C.
3. How Does Ambient Temperature Affect Thermal Power Rating?
The thermal power rating is the amount of power the Worm Gearbox can transmit without exceeding the maximum allowable oil temperature. The rating is based on a specific ambient temperature, typically 40°C. If the actual ambient temperature is higher, the thermal power rating must be reduced. The derating factor depends on the temperature difference between the ambient and the maximum allowable oil temperature. The table below shows the derating factors for different ambient temperatures.
| Ambient temperature (°C) | Derating factor | Thermal power (relative to 40°C rating) | Recommended action |
| 20 | 1.15 | 115% | Can overload slightly |
| 30 | 1.08 | 108% | Standard operation |
| 40 | 1.00 | 100% | Standard operation |
| 50 | 0.88 | 88% | Reduce load or add cooling |
| 60 | 0.75 | 75% | Reduce load; add fan or oil cooler |
| 70 | 0.60 | 60% | Oil cooler required |
In our factory, we provide a thermal power rating chart for each Worm Gearbox model. The chart shows the allowable power at ambient temperatures from -20°C to +70°C. For ambient temperatures above 40°C, we recommend adding a fan or an oil cooler to maintain the thermal power rating. Saifu can supply the gearbox with a factory-installed fan or a separate oil cooler kit.
4. What Are the Special Considerations for Low-Temperature Applications?
Low-temperature applications present different challenges. The lubricant becomes viscous and may not flow to the bearings at startup. The seal material may become brittle and leak. The housing material may become brittle and crack under impact. The table below shows the considerations for low-temperature applications.
| Consideration | Effect of low temperature | Mitigation |
| Lubricant flow | High viscosity; poor flow at startup | Use low-temperature oil (ISO VG 220); add heater |
| Seal flexibility | Elastomer hardens; leaks | Use silicone or PTFE seals |
| Housing impact strength | Cast iron becomes brittle | Use ductile iron or steel housing |
| Condensation | Moisture forms inside gearbox | Install breather with desiccant; use heater |
| Starting torque | Higher due to viscous oil | Use a larger motor or a soft-start drive |
In our factory, we offer a cold-climate package for Worm Gearbox units that includes low-temperature oil, silicone seals, a ductile iron housing, and a breather with a desiccant. We also offer an optional sump heater for applications that start at temperatures below -20°C. Saifu Vietnam Company Limited provides a cold-climate specification sheet for each gearbox model.
Frequently Asked Questions About Operating Temperature and Worm Gearbox Selection
Summary for Design Engineers
Operating temperature affects every aspect of Worm Gearbox selection: lubricant viscosity, seal material, thermal power rating, and housing material. The standard gearbox is rated for 40°C ambient. Above that temperature, the thermal power rating must be derated, and the lubricant and seals must be upgraded. Below -10°C, a cold-climate package is required. The design engineer should specify the ambient temperature range, the startup temperature, and the duty cycle so that the gearbox manufacturer can select the correct configuration. Saifu Vietnam Company Limited has been manufacturing Worm Gearbox units for over 15 years and provides full temperature specification support for our customers.
Saifu Vietnam Company Limited manufactures Worm Gearbox units for ambient temperatures from -30°C to +70°C, with mineral or synthetic oil, NBR, FKM, or silicone seals, and optional cooling fans, oil coolers, and sump heaters. We provide temperature specification sheets and derating charts for all of our products.
