We have compiled a list of Frequently Asked Questions for your benefit:
- How can you tell if your UV lamps need to be replaced?
- How does a lamp start?
- Why do you need to wait for lamps to cool before restarting?
- What is the optimum operating temperature for lamps?
- How often should reflectors be changed?
- Why do we make our discharge tubes out of fused quartz?
- What is devitrification?
- How does an atom/ion emit electromagnetic radiation?
- Why do we use molybdenum foil?
- Why do we use/make electrodes out of tungsten?
- Why do we use UV inks/coatings/adhesives?
- What are the advantages and disadvantages of an electronic power supply?
- What is the difference between aluminium reflectors and dichroic reflectors?
- What is electromagnetic radiation?
- How to pack a UV lamp?
If you have a question that has not been listed feel free to email it to us – firstname.lastname@example.org
Q. How can you tell if your UV lamps need to be replaced?
A. 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.
Q. How does a lamp start?
A. 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.
Q. Why do you need to wait for lamps to cool before restarting?
A. 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.
Q. What is the optimum operating temperature for lamps?
A. Mercury Lamps = 700 °C Metal-Halide Lamps = 800 °C
Q. How often should reflectors be changed?
A. 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, so should be checked and maintained regularly since most of the curing power of the lamp comes from the reflected radiation.
Q. Why do we make our discharge tubes out of fused quartz?
- It has high UV transmission at 90% UV transparency
- It has high thermal stability (up to as high as 1665 °C)
- It has a low coefficient of thermal conductivity
- It has a low coefficient of thermal expansion
A. Devitrification is a process where fused quartz of the lamp body begins to change its structure to a crystalline form. This can start to occur when:
- The lamp is submitted to excessively high temperatures
- run lamps with sufficient cooling
- ensure powers and currents are no higher than those recommended
- catalysed by chemical impurities on the lamp body such as oils secreted by the skin
- wear gloves whilst handling lamps
- clean the lamp body with an alcohol wipe such as isopropyl 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.
It is very poor at transmitting UV. It also has 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.
Q. How does an atom/ion emit electromagnetic radiation?
A. 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.
Q. Why do we use molybdenum foil?
- It has a similar coefficient of thermal expansion to the quartz
- It forms a tight vacuum seal and prevents cracking of the quartz
- It is a good electrical conductor
- It has a high resistance to corrosion
Q. Why do we use/make electrodes out of tungsten?
- It has the highest melting point of any metal
- It has good thermal conductivity and stability
- It has a low thermal expansion coefficient
Q. Why do we use UV inks/coatings/adhesives?
- 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
Q. What are the advantages and disadvantages of an electronic power supply?
Q. What is the difference between aluminium reflectors and dichroic reflectors?
A. 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:
- Ultraviolet (UV)
- visible light
- radio waves
Q. How to pack a UV lamp?
A. When sending a UV lamp you must ensure that the lamp is packaged securely to avoid damage in transfer. To show you how to do this correctly our own Chloe Rees and Zach Rambaldini show you how to securely pack a UV lamp for shipment below.