Many processes are developed in a laboratory and operating parameters are established for each application before carrying the process out to the production floor. Quite a number of variables must be studied, one of which is the UV level necessary to effect a proper cure. A radiometer is used to quantify the dosage and intensity required and numerous tests are run to assure that the product being cured has all the right properties. After laboratory studies have been performed, the real test is to try it in a production environment. Sometimes a direct transfer can be made, but more often there are conditions in the production setting that are different from the lab setting which have an affect on curing. The operating temperature may be higher in production than in the lab; the production UV curing system may have multiple lamps while the lab studies were conducted using just one; it may not be possible to duplicate the high production line speeds in the lab; and a host of other variables may exist that must be measured to fully quantify and transfer the process from the laboratory to the production floor.
In use, a UV radiometer measurement is taken after product has been produced which is determined to be at optimal cure. This becomes the benchmark value for "good" product. If the process is developed thoroughly, the UV exposure time is gradually decreased until the product is undercured and undesirable results are obtained. A measurement is taken that becomes the minimum "cure window" value. Conversely, the exposure time is also gradually increased until undesirable results from overcuring are obtained. A measurement is taken that becomes the maximum "cure window" value.
Once a process has been established and control parameters are measured, it is necessary to routinely measure the operating parameters to assure that they fall within the satisfactory range. Now the operator has established parameters within which to operate. A UV radiometer is used to stringently monitor the UV component. Some applications simply require that an equivalent UV dosage be repeated from one work order to the next to achieve a good cure.
As a production tool, the UV radiometer is typically used to take a reading or a series of readings at the beginning of each day, each shift, each work order, or even each hour to assure that the UV curing system is operating within established guidelines. The production radiometer may or may not be the exact same model that was used to establish the process in the lab.
Often the lab will use a more sophisticated instrument, such as a UVIMAP, and the production crew will use a simple, easy to use dosage radiometer such as a UVICURE Plus. The production foreman is given a strict window to operate within. If he gets a reading that falls outside the window, either the lab radiometer is brought in for verification and to troubleshoot the curing system or adjustments are made to the curing system to bring the operating parameters back into line; e.g. change the UV lamp, clean the reflectors, adjust the lamp focus.
Any variance outside the cure window is reported to the QA manager for resolution. Quite often the QA manager will have a UV radiometer of his own which he uses periodically to monitor production conditions and to verify that the production radiometer is still operating within the calibration specifications. The QA unit is also used in production while the production unit is being returned for service and calibration re-certification.
