Periodic validation and maintenence of a light-curing process is critical to its success.
The basic components of a UV/LED light-curing process consist of a light-curable adhesive, dispensing system, and curing equipment (spot, flood, or conveyor). Depending on the curing source chosen, each unit must be qualified prior to manufacturing start-up and consistently maintained during actual production. Specifying the exposure time and acceptable intensity range of an energy source used is essential to the success of the light-curing process, so periodic validation and maintenance of it is critical.
The three types of equipment that require these routine performance checks are spot-curing, flood-curing, and conveyor curing systems. Each one needs to be regularly tested to ensure that the light intensity being emitted hasn't degraded or fallen out of range, which is very important to the overall curing process.
A spot-curing system is comprised of a power supply and lightguide or emitter head that emits UV/LED high-intensity concentrated light. The wavelength and type of light-delivery option chosen is dependent upon the application requirements. This type of equipment is typically used manually by an operator as a bench-top unit to cure a small area of adhesive or coating very quickly on a component, or multiple components if using multiple lightguides or emitter heads. Spot-curing lamps can also be integrated into high-speed automated assembly lines. The light generated is applied in an optimized, precise manner to the bond line, providing cures in as little as 1-to-10 seconds.
When using a traditional UV broad-spectrum spot-curing system with a lightguide, where the light-curing bulb is situated within the power supply, there can be some loss of intensity as the light travels from inside the unit to the end of the lightguide. In newer LED-equipped emitter heads, the LED array is placed at the end of the curing mechanism, so the chance of light degradation is less. Frequent bending of lightguides can be another factor detrimental to the loss of intensity being transmitted because lightguides are less flexible and more susceptible to damage from constant movement.
Flood-curing systems operate similarly to spot-curing systems but have a much larger curing area and generate moderate to high-intensity light energy. They are comprised of a power supply and a reflector housing equipped with a metal-halide bulb or LED array, rather than a lightguide or emitter head. This equipment is ideal for users that need to cure multiple parts or trays of parts at the same time. They can be used as stand-alone units, be incorporated into assembly lines, or used in conjunction with a conveyor system.
LED arrays can provide more even curing across a surface compared to traditional broad-spectrum bulbs that emit greater intensity toward the middle of the curing area due to their central placement within the reflector housing. Poor uniformity of light delivery can result in more frequent process adjustment or replacement of equipment.
Conveyor Curing Systems
For manufacturers that require consistent, fast, and safe cures of UV/LED curable adhesives, coatings, and inks, conveyorized curing systems might be a suitable choice of equipment. This type of system consists of a moving belt that passes through a chamber area with curing lamps mounted above and/or on each side for fast curing of parts. Conveyor systems utilize high intensity flood lamps for curing and typical models include the mounting of one, two, or four UV or LED lamps onto the unit.
Even though improvements have been made to the overall uniformity of the light being emitted from a flood lamp to reach the edges of the curing area, there can still be some drop-off of curing intensity, especially when two flood lamps are placed side-by-side, as in a conveyorized system. Since conveyor systems are outfitted with flood-curing lamps, they are also susceptible to light-intensity drop off, bulb degradation, and decreased light uniformity.
The type of light-curing system specified for an assembly process is unique to its application. However, no matter which system is selected, each one must be validated on a regular basis to ensure that the exposure time and intensity range don't fall out of the recommended parameters for the overall curing process.