A printed web may pass the rub or adhesion check on the operator side and remain soft, mark or block on the drive side. Raising the complete UV unit can improve the weak edge, but it also changes the dose and heat received by the rest of the web. First prove that the fault is genuinely cross-web. Keep left, centre and right samples in their original orientation, then separate a coating or ink-film difference from the lamp, reflector, LED array, cooling and geometry of the curing unit.
Keep the web orientation and map the symptom
Mark operator side, centre, drive side and direction of travel before cutting the sample. Take strips from the same repeat and from several positions through the roll. Record the line speed, UV power setting, unit used, ink or coating, substrate and the time at which the fault began.
Use the approved product tests for the job. Depending on the application, these may include surface rub, adhesion, blocking, scratch or a later resistance test. Apply the same method, pressure and waiting time at each position. A casual finger check can make one side appear better simply because the samples were handled differently.
If the weak area follows one printed colour or coating lane rather than the same machine-side position, inspect laydown and application before blaming the UV unit. Compare ink density or coating weight across the web and confirm that the printed film is reasonably uniform. The cure system cannot correct a heavier ink film on one side by itself.
Repeat the test under one controlled condition
Bring the line to a stable production condition and repeat the left, centre and right product checks at the same speed and power. Record any warm-up procedure required by the installed system. Do not compare a cold startup sample from one edge with a steady-running sample from another.
Then make one controlled speed or power change within the approved operating range. If every position improves by a similar amount but the weak edge remains relatively behind, the cross-web pattern still needs investigation. If only one ink or coating changes, include its chemistry, film thickness and application station in the diagnosis.
Compare the result with an accepted baseline from the same unit and product class. IST Metz advises establishing system-specific UV references on site when the system, lamp and reflector are new. A reference is useful only when the spectrum, speed, electrical power, distance and measuring conditions are recorded.
Use a measurement method that suits the direction
Dose and irradiance are different measurements. Dose is the accumulated energy received as the web passes the source, while irradiance describes the intensity at the measuring point. Both can help, but neither replaces the finished-product test. The required value belongs to the ink or coating, substrate, speed and end use.
Check the limitations of the instrument before placing sensors or strips across the web. IST Metz states that its UV Analyzer reference curves are for measurements in the direction of travel and that the system is not suitable for measurement along the axis of the UV unit. It should not be presented as a cross-web mapping instrument when used outside that stated geometry.
For permanent process control, IST Metz describes stationary UV measuring systems that monitor radiation through a sensor and PLC and can regulate output in relation to speed. Confirm the location and sensitivity of any installed sensor. One fixed reading can show a trend at that position, but it does not automatically prove uniform output across the complete working width.
Inspect the optical path and cooling from edge to edge
Isolate and cool the equipment under the approved maintenance procedure. Inspect the lamp or LED window, quartz plate where fitted, reflector, shutters and surrounding surfaces across the full width. Look for dust, ink mist, coating deposit, fingerprints, damaged sections or a component that is not correctly seated.
IST Metz notes that fine dust can collect on lamps and reflectors, burn into hot surfaces and reduce radiation efficiency. Cleaning intervals depend on ambient dust and cooling-air conditions. Record where contamination is found before cleaning so its position can be compared with the weak side of the web.
Compare filter condition, fan operation, cooling-air path, extraction and alarms. Confirm that the source is aligned with the web and that its distance and angle have not changed. IST Metz notes that a finite light source can show a drop towards its ends, so the installed working width and web position have to suit the application.
Separate a product fault from a source fault
Run the same ink or coating through another verified curing position only when the press arrangement and job procedure allow it. If the weak band follows the product application, inspect ink film, coating weight and the printing unit. If it remains at the same curing-unit position, the source, optics, cooling or geometry needs attention.
For LED systems, do not assume the displayed power proves every part of the array is producing the same result. IST Metz describes LEDcure NX as designed for uniform curing across the working width and with independently connected LED chips. A suspected partial-output issue requires an approved service check, not an improvised electrical test.
After maintenance or adjustment, repeat the marked left, centre and right checks at the agreed production speed. Include the most demanding ink or coating in the job and retain the accepted samples. A light process colour is not a sufficient release test when an opaque white or heavy varnish is the limiting application.
Save the width profile with the job
Record the curing-unit ID, lamp hours or LED service record, power, speed, source-to-web distance, cooling and filter condition, cleaning work and measuring method. Add the ink or coating batch, density or film-weight check, substrate and final product-test result at each marked position.
The record should show whether the correction came from the product application, optical path, cooling, geometry or qualified service. Use the same marked positions for the next periodic check so a new cross-web change can be compared with the accepted baseline.
Royal Coat represents IST Metz UV and LED UV curing technology across India, Bangladesh, Sri Lanka, Nigeria and Kenya. For a cross-web cure review, send the Royal Coat team the press and curing-unit details, working width, web position, ink or coating system, substrate, speed, power, marked samples, product-test results and photographs of the optical and cooling path.
Questions from production and purchasing teams
What to ask about cross-web uv cure control
Why is UV cure weaker on only one side of the web?
First separate uneven ink or coating laydown from the curing unit. Then inspect cross-web contamination, reflector or LED condition, cooling, extraction, source alignment, web position and working-width suitability.
Should I raise UV power to correct one weak edge?
Not before mapping the fault. Raising the whole unit changes dose and heat across the complete web and may hide a local optical, cooling, geometry or coating problem.
Can the IST Metz UV Analyzer measure across the axis of a UV unit?
IST Metz states that its reference curves apply in the direction of travel and that the system is not suitable for measurements along the unit axis. Follow the stated instrument geometry and use an approved method for any cross-web study.
Does one stationary UV sensor prove uniform cure across the web?
It proves the monitored condition at its installed sensing arrangement. It does not by itself establish the full cross-web profile, so combine the reading with marked product tests and the equipment supplier's approved inspection method.
What information is needed for a cross-web UV cure review?
Provide the curing-unit ID and working width, source type, web position, speed, power, ink or coating and substrate, cooling and filter condition, marked left-centre-right samples, measurements and product-test results.