Dew point check before belt splicing
Is the belt surface warm enough to cement? Dew point from air temperature and humidity, compared with the measured belt surface.
Result
How it works
If the belt surface is at or below the dew point, a thin film of moisture forms on the buffed surfaces and the cement cannot bond. The splice may look normal and then open in service.
Measure the air temperature and humidity at the splice station and the temperature of the belt surface itself. Use the margin your splice instruction gives; one splicing method requires the ambient to be at least 5 °C above the dew point.
Formula
γ = ln(RH / 100) + 17.62 t / (243.12 + t) Dew point Td = 243.12 γ / (17.62 − γ) [°C] Gap = belt surface temperature − Td Gap ≤ 0 → stop; gap < margin → caution; gap ≥ margin → OK
| Symbol | Meaning | Unit |
|---|---|---|
| t | Air temperature at the splice station | °C |
| RH | Relative humidity | % |
| Td | Dew point | °C |
| margin | Required margin from your splice instruction | °C |
Worked example
Inputs: Air temperature = 28 °C; Relative humidity = 70 %; Belt surface temperature (measured) = 18 °C; Required margin (from your instruction) = 5 °C.
- γ = ln(0.70) + 17.62 × 28 / (243.12 + 28) = 1.4630
- Td = 243.12 × 1.4630 / (17.62 − 1.4630) = 22.0 °C
- Belt surface 18 °C − 22.0 °C = -4.0 °C → stop: the surface is below the dew point
Assumptions and limits
- Measure the belt surface itself (contact or IR thermometer), not only the air.
- Use a calibrated hygrometer at the splice station; conditions change through the day, so recheck before each coat.
- The margin is a value from your splice instruction. This page does not set it.
Screening estimate, not a design approval. Verify measured inputs, current standards, manufacturer limits and site procedures before purchasing, cutting or installation. Isolate and lock out equipment before any hands-on measurement.
Questions
What is the dew point at 28 °C and 70 % humidity?
About 22 °C. A belt surface cooler than that will collect moisture.
Does this apply to hot splices too?
Yes. Moisture on buffed surfaces weakens the bond in both hot and cold splices.
Source notes
- Magnus form with WMO constants: saturation vapour pressure e = 6.112·exp(17.62 t / (243.12 + t)) hPa over water — WMO Guide to Meteorological Instruments and Methods of Observation (WMO-No. 8, 2008).
- Dew-point check before bonding and the 28 °C / 70 % → 22 °C example: Mercurio Manual of Conveyor Belts and Splices REV.08/22, pp.113–116. 5 °C ambient-over-dew-point rule: SANS-based splicing method (Van Staden).
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