UV Curing calculator

UV Dwell Time Calculator

Dwell is the lever between belt speed and dose: dose = irradiance × dwell. When the belt speed is set by an upstream constraint (a packaging line, a robot cell, a coater), you back into dwell to see whether the dose math works. This calculator does that conversion plus a margin so you have headroom before lamp aging shortens the effective cure window.

What this calculator does

  • Convert belt feet-per-minute and the lamp's effective cure-zone length into seconds the part spends under UV per pass.
  • Use it on a conveyor line when the belt speed is fixed (paced by upstream equipment) and you need to know the dwell you actually have for dose math.
  • Reports seconds the part spends inside the lamp's effective cure zone per pass, with and without your dwell margin.

Formula used

  • Base dwell (sec) = (cure-zone length ÷ 12) ÷ belt speed × 60
  • Recommended dwell = base dwell × (1 + dwell margin)

Inputs explained

  • Lamp cure-zone length: Effective UV-emitting length along the belt — measured with a profiling radiometer at ~80% of peak.
  • Belt speed: Actual belt speed at the lamp position (verify with a tach — drive readouts can drift).
  • Dwell margin: Cushion for irradiance falloff and reading variance; 15–25% is typical.

How to use the result

  • Use it any time belt speed is fixed and you need the dwell number to feed UV Dose calculations, or after a focal-distance change that resized the cure zone.
  • Single-pass only and assumes the part lays flat across the cure zone. For multi-lamp tunnels, sum dwells across each lamp using the UV Multi-Lamp Dose calc; for tilted or 3D parts, the projected dwell on inclined surfaces is lower — model that with the UV Shadowing Risk calc.

Common questions

  • Why does cure-zone length matter more than lamp housing length? The lamp housing is mostly hardware. The cure zone is the length over which irradiance is high enough to actually contribute to dose. On focused mercury lamps the cure zone is often half the housing length; on diffuse LED arrays it's closer to housing length. Always measure with a radiometer pass.
  • Belt speed dropped — is the part overcured now? Possibly. Slower belt = more dwell = more dose. If the chemistry is dose-tolerant (most coatings, many adhesives) it's harmless; if it's a heat-sensitive substrate or an oxygen-inhibited chemistry, more dose can mean substrate distortion or surface effects. Re-run UV Dose with the new dwell to confirm.
  • What dwell margin is reasonable? 15–25% on production lines with weekly radiometer checks; 25–40% on lines monitored monthly or less. Margin here protects against the gap between scheduled radiometer passes — it's not the same as the dose safety margin in UV Exposure Time.
  • How does dwell relate to dose? Dose (mJ/cm²) = irradiance (mW/cm²) × dwell (sec). Use this calc to get dwell, then multiply by the irradiance you measured at the belt to confirm dose. The UV Dose calculator does that math directly.

Last reviewed 2026-05-12.