Guide to UV Measurement
3-D Radiometry
3-D Processing presents some new and different problems for radiometry. Parts have complex surfaces, so the irradiance levels will vary by location. For optimized lamp positioning and process verification, this could require irradiance and energy measurements at almost every point on the surface. The motion can range from the straight-through linear travel of a paint line past a fixed set of lamps, to compound motion of chain-on-edge conveyors, to combinations of part motion and limited lamp motion, and to totally robotically-controlled motion of lamps themselves. The exposure (irradiance profile) at any point will result from the combined effects of part geometry, relative surface velocity, and lamp configuration.
Radiometry and the Steps in the 3-D design process:
- The coating is characterized in its response to UV Exposure variables – this yields the maximum and minimum exposure required by the coating. This step is done with flat, linear processing – in the lab. Radiometry is used to quantify the exposure specifications (irradiance, profile, wavelength, and temperature) and to evaluate the optimum or minimum exposure required for a photo-curable material to develop its ideal properties. The exposure conditions must be within the range achievable by a production system.
- The mechanics of the line are identified – degrees of motion, surface velocities, lamp organization, total power, etc., and lamps are positioned for maximum effectiveness.
- Radiometry is used to verify the process design. Dry parts are instrumented with radiometers (or dosimeters) to verify that the exposure is within specified limits on all surfaces. The spectral exposure (wavelength distribution) must be the same as used in the development phase (step 1). It is often difficult to use the same instruments that were used in the laboratory. This raises serious issues of measurement with different instruments.
- Finally, radiometry is used to monitor the process over time.