An inline UV cure station rarely fails outright. It drifts: parts that cured fully at the start of a shift come off soft by the end, and nothing on the controller looks wrong. A structured fault checklist finds the cause faster than adjusting settings by feel.
Q: Why Does an Inline UV Cure Degrade Over a Shift?
A: Because Delivered Dose Changed, Even If the Settings Did Not
Dose is irradiance multiplied by time. Either factor can shift without anyone touching a control: output falls as the lamp or lightguide ages, working distance changes as fixtures wear, or belt speed deviates under load. The first diagnostic step is always to measure irradiance at the part position with a radiometer. For the planning side of integration, see Incure’s guide to specifying and automating cure stations; this page covers faults after commissioning.
Fault Group 1: Sensor and Trigger Handshake
When the cure never fires, or fires at the wrong moment, suspect the signal chain before the lamp.
- No exposure: check that the part-present sensor still sees the part, since a dirty or shifted sensor looks like an empty belt.
- Double firing: a bouncing trigger can start two cycles. Add a debounce window in the PLC.
- Short exposure: if the lamp runs in continuous mode and the PLC drops the signal early, dose falls without any alarm. Compare commanded and actual exposure time.
- Mode mismatch: a lamp left in timer mode when the program assumes continuous (or the reverse) produces exactly this symptom.
Incure’s L-Series™ lamps and the CDM™ LED heads accept foot-switch, PLC, and RS-232 inputs, so verify which input is active before blaming wiring.
Fault Group 2: Dose Drift Across Shifts
Gradual loss points to the light path. LED output decays slowly, rated at 20% or less over 20,000 hours on CDM™ LED heads, so a drop inside one shift is almost never LED aging. Look for contamination instead: adhesive vapor or overspray film on a lamp window, or a darkened connector face. For spot systems, lightguide degradation is the usual suspect, a topic Incure covers in what causes UV light guide degradation over time. On mercury-arc heads, rated above 1,000 hours with up to 45% decay, a bulb late in its life can explain a sag that appears slowly across weeks. Warm-up matters too: an arc lamp read before it stabilizes (1–2 minutes on an S20™) gives a low first-hour reading.
Fault Group 3: Belt Speed Versus Irradiance
On the CDM™ conveyor, belt speed is the dose control, running 1.5 to 12.0 ft/min with 6.0 ft/min nominal. Doubling speed halves exposure time, so a throughput push without a matching intensity or lamp change halves dose. Check the displayed speed against a stopwatch over a known belt length, since a worn belt or drive can deviate from the set value. Also confirm the curing height: heads are specified for set working heights, and irradiance falls steeply with distance. On the L9000™, for example, reading drops from 7,500 mW/cm² at 9 mm to 2,300 mW/cm² at 17 mm, so even a few millimeters of tooling wear changes the cure.
Email Us with your belt speed, lamp model, and the symptom you are seeing, and Incure’s team can help narrow the fault.
A Diagnostic Order That Saves Time
- Measure irradiance at the part position and compare it to the commissioning baseline.
- Confirm working distance and part height against tooling.
- Verify belt speed and exposure time independently of the controller display.
- Inspect lamp windows, lightguides, and connectors for film or discoloration.
- Check trigger logic, mode, and sensor condition.
- Only then adjust dose, and record the change.
Preventing a Repeat
Take a radiometer reading at shift start and again at mid-shift, logging both. A small, trending decline is visible weeks before parts fail. Add cleaning of lamp windows to the preventive-maintenance schedule, and keep belt-speed and timer values under change control so a throughput adjustment cannot quietly cut dose.
Reading a Radiometer Trend
A single reading says little; a log says a lot. Plot each shift-start and mid-shift reading against date. A steady slope over weeks indicates lamp or lightguide aging. A sawtooth that recovers after cleaning points to contamination. A sudden step usually follows a physical event such as a tooling change, a bumped lamp head, or a replaced bulb. Matching the shape of the curve to these patterns tells you whether to clean, replace, or re-fixture before parts are affected.
When the Fault Is the Material
If irradiance, distance, speed, and triggers all verify, look at the adhesive or coating itself. Material that has aged past its shelf life, been applied thicker than qualified, or picked up a different pigment load needs more dose than the validated setting provides. Compare the current lot’s cure result against the retained baseline sample before touching the equipment.
Final Thoughts
Inline cure faults usually trace to one of three places: the trigger, the light path, or the belt. Measure first, then work through the checklist. Contact Our Team to review a recurring cure problem on your line.
Visit www.incurelab.com for more information.