UV Lamp Troubleshooting

UV Lamp Devitrification / Clouding

Problem: The basis of natural “devitrification” occurs when quartz converts back into a crystalline structure which acts as a very poor UV transmitter. This process occurs after surface contamination and is accelerated when the UV lamp becomes too hot. Devitrification appears as many white spots on the surface of the quartz body, which causes a reduction of quartz transparency to UV light.

Prevention:

• Ensure lamp is clean before running the lamp and operated in a dust free environment.

• Ensure lamp is run at correct volts and amps and that the UV system is properly cooled.

UV Lamp Mirror Coating

Problem: Over-cooling results in a combination of tungsten from the electrode and mercury, condensing onto the inside of the lamp ends giving it a mirror coated effect.

Prevention:

• Alpha-Cure's UV lamp ends are coated with heat reflective materials such as; gold, platinum, silver & white paint, to keep the lamp shoulders hot. Contrary to popular belief white paint is actually the best reflective coating to retain heat within the lamp.

• The system is producing too much cool air that isn't being properly circulated evenly along the length of the lamp. Remember to keep lamp shoulder temperature above 600 °C.

• The UV lamp is not running at the correct power for prolonged periods, UV lamp operators should seek professional advice in this instance

Problem: Although tungsten has a high melting point, natural “blackening” occurs during the lifetime of a UV lamp, due to very high arc temperatures operating between each electrode. During normal operation the electrodes start to erode and the tungsten material starts to sputter depositing on the inside of the quartz body. When the transparency of quartz body is compromised, UV output potential is significantly reduced.

Prevention:

• Manufacturer uses a “special material” coating on the end of the electrode to prolong the life of the electrodes.

• This process can be avoided by simply not switching the UV lamp on and off in between print runs, the biggest surge of current (increased loading) on the electrode happens at ignition. To avoid this most UV system manufacturers design a standby mode, which means keeping the lamp running at 50% (and increasingly lower than this) even when not in use during the production shift, to avoid switching the lamp on and off (power cycling).

UV Lamp Deformation (top) & Bowing (bottom)

Problem: The UV Lamp has overheated due to poor air circulation within the UV System, this is more common with longer lamps due to increased requirement for airflow across a larger surface area. Overheating of the lamp body softens the quartz which starts to sag under gravity or deforms from pressure differences.

Prevention:

• Keep lamps below 850 °C

• Adjust airflow and cooling around the lamp, ensure your cooling system is fully functioning.

• If possible to do so, rotate the UV lamp by 180 ° weekly.

Problem

External contamination of a UV lamp happens when foreign contaminants such as finger prints or spray from powders, paper dust and ink, stick onto the outside surface of the quartz body. Sometimes contamination even occurs where the system reflector itself has come into direct contact with the lamp. These contaminants cause devitrification (recrystallization) on the quartz body, as such UV radiation is no longer able to pass through.

Prevention

• Clean UV lamps frequently using isopropanol wipes.

• Always wear gloves when handling lamps and exert caution whilst cleaning and changing them.

• Ensure lamps are placed with sufficient clearance away from the lamp housing, avoiding contact with system reflectors and shutters.

Problem

If a UV lamp is exposed to a current overload or excessively high temperatures, the electrical connection can break down. Overcurrent situations are generally due to power supply faults, not a fault in the lamp design itself. The electrical connections at the end of each UV lamp are designed to withstand temperatures of no more than 250 °C. This problem causes electrical arcing between the lamp and the lamp holder, which can result in a hole being burnt through the cap, destroy the lamp and potentially even damage the UV system.

Prevention

• Ensure the right UV lamp is chosen for your power supply and that the power supply is operating correctly

• Keep ceramic cap and seal below 250 °C

• Ensure the lamp is correctly placed within the lamp head

• Inspect caps for damage before placing them into the system