UV Curing FAQS

Over time the running voltage of a lamp will drop. Once the lamp falls beneath the voltage set by the Voltage Relay, it will fail to send a “Lamp ready” signal to the press.

If a lamp becomes swollen due to overheating, this will reduce the running voltage of the lamp. Swollen lamps will also not be as effective at curing.

If all other components within the UV system are operating correctly, lamps should be changed when:

• they fail to start
• they fail to reach “ready”
• they fail to cure
• are significantly discoloured
• are swollen

99% of failures are commonly misdiagnosed as lamp failure. In fact, these are often actually failures caused by other components in the system such as capacitors, ballasts, reflectors or ignitors.

Initially a high voltage is applied to the electrodes and the starting gas is ionised. The temperature and pressure begins to increase allowing the mercury/metal halides to vaporise. Energetic collisions involving mercury/metal halides lead to a high temperature plasma arc being generated. This principally emits UV, as well as other electromagnetic radiation.

When a lamp is turned off, charge carriers are lost when ions and electrons recombine.  However, when the lamp is still hot, atoms in the lamp are moving around quickly and this leads to high impedance of the electrons when trying to restart the lamp.

Mercury Lamps = 700 °C

Metal-Halide Lamps = 800 °C

Lamp Seal = 250°C max

It is recommended that reflectors should be changed whenever the lamp is changed, or sooner if they are dirty or damaged. Reflectors are extremely important, generating around 70% of the usable UV so should be checked and maintained regularly.

Devitrification is a process where fused quartz of the lamp body begins to change it’s structure to a crystalline form. This can start to occur when:

• The lamp is submitted to excessively high temperature. To avoid this from happening we suggest:
  • To run lamps with sufficient cooling
  • Ensure powers and currents are no higher than those recommended
• Devitrification can also happen when a UV lamp is catalysed by chemical impurities on the lamp body, such as oils secreted by the skin. We recommend the following:
  • Wear gloves whilst handling lamps
  • Clean the lamp body with an alcohol wipe such as isopropanol alcohol before use

Devitrification is visible once the lamp has cooled down to room temperature as white spots or patches. This is due to the different optical properties of the crystalline form: it refracts and transmits electromagnetic radiation such as light.

The lamp becomes very poor at transmitting UV. There is a different density, causing micro cracks in the body and loss of vacuum. This can lead to lamp failure. Thus, once devitrification begins to occur, it may be necessary to replace the UV lamp.

A collision with a moving particle excites the atom/ion, causing an electron to jump to a higher energy level. The electron then falls back to its original energy level, releasing the extra energy in the form of a ‘photon’, a particle of electromagnetic radiation.

Because:

• UV substrates do not contain solvents and volatile organic compounds (conventional substrates have 40%)
• They prevent drying/sticking to printers overnight
• They are space efficient, with a low starting/cleaning time
• Traditional solvent-based inks take a long time to dry; curing with UV is instant
• UV lamps are more energy efficient than heaters/driers
• They give an improved quality of ink/polymer/resin substrate and cure

Advantages

• Better efficiency — energy savings
• Lighter and smaller
• Instant step-less variable power switching and voltage output
• Extended lamp life

Disadvantages

• Shorter life-span
• More heat sensitive — requires cooling

Electromagnetic radiation is a form of energy emitted by charged particles. It is transmitted as a wave or packet of energy, and travels through vacuum (cf.  radiation from the sun). There are 7 types of electromagnetic radiation. These are:

• Gamma-rays
• x-rays
• Ultraviolet (UV)
• visible light
• infrared
• microwaves
• radio waves

Watch our video to find out how to safely and securely pack a UV lamp to avoid damage in transit. Click Here