The application of factorization in the printing industry has developed rapidly. UV materials are widely used in forms, documents, plastics, lotteries, magnetic cards, labels and other products, and almost all current printing methods and printing models are applied, and these printing machines need to be equipped with UV chemical machines. Due to the complex types of printing machines, there are many types of curing machines. The optional UV curing machine often makes printing manufacturers confused.
The core components of the UV generator are UV lamps and transformers. The key to the curing effect is the selection and matching of the parameters of the UV lamp and transformer, so that the lamp can effectively radiate 365 nm ultraviolet light. The author has been engaged in this research work for many years, and experiments have confirmed that the UV lamp transformer should be a well matched system. It can't be purchased separately. How to match and select its parameters? The author talks about some views based on his own experience and discusses with his peers.
1、 Determination of UV lamp parameters
1. Main parameters of UV lamp: main wavelength (in general, the wavelength of curing lamp in printing is 365 nm); Lamp arc length L (i.e. the effective length of emitting ultraviolet light); Lamp tube specific density P. (output power per centimeter, such as 80 W / cm); Total lamp power p; Lamp voltage U; Lamp current I; Tube diameter; Conductive material in the lamp tube, etc.
2. Determination of UV lamp parameters:
1) Lamp arc length L: Zui of the cured product plus 2 cm in width;
2) Lamp power density P.: When the power density is high, the ultraviolet efficiency of the lamp is high. Therefore, the power density should be selected according to the movement speed of the cured object and the characteristics of the cured material.
3) Lamp current I: generally, the lamp current is less than 10a, because the current is large, the secondary heat loss of the transformer is large, and the thick secondary winding of the transformer results in the large volume of the transformer. But the current can not be too small, generally. The current of the lamp can be adjusted by the transformer. Generally, the output current of the high-speed leakage pin is not adjusted to Zui, and then the current is reduced by the capacitor. Zui can be adjusted to 1-2a, but the current of the lamp can not be adjusted by the capacitor.
4) Total lamp power P = l times P.
5) Tube diameter: experiments show that if the current density in the lamp is large, the output ultraviolet component is high. For example, when the tube wall of 160W / cm is 28mm, the ultraviolet intensity is 390W / cm2, and when the tube wall of 22.5MM, the ultraviolet intensity is 620W / cm2. When P. After determination, the energy load per unit area of the tube wall is large, the tube wall temperature is high, and the lamp life is low. The pipe wall temperature can be reduced by water cooling or air cooling to improve the service life.
6) Conduction in the lamp tube: UV lamps are usually mercury lamps and metal halide lamps. Mercury lamps are generally used for low power density. The mercury lamp has a wide output range of 365 nm. Generally, the energy with curing effect is 18% - 23% of the input energy, which is visible light and infrared light. Metal halide lamps, by mixing several halides, increase the output energy of ultraviolet light, improve the warp fixation efficiency, and reduce the heat radiation. They are generally used in high-power density lamps. Mercury lamps have a long service life, generally 600-2000 hours, while halogen lamps have a short service life, generally 200-1000 hours.
2、 Determination of transformer parameters
When selecting a transformer for UV curing, the following parameters are important: input voltage, output voltage, input current and current. Since the internal conduction of the lamp is that the cathode emits hot electrons to excite mercury molecules to vaporize and conduct electricity, and the ionic conduction in the lamp changes with the vaporization process of mercury molecules, the above parameters also change, and generally reach stability after 3-5 minutes. The following describes the change process and selection method of several main parameters.
1) Input voltage: 380V is generally selected as the input voltage of transformers above 3KW.
2) Output voltage: the output open circuit voltage is 120% - 125% of the lamp design voltage, so that the lamp can be excited to turn on.
3) Output current and output voltage: The voltage of the lamp connected to the transformer is the open circuit voltage of the transformer, and the lamp current is zero at this time. With the emission and conduction of hot electrons, the voltage of the lamp drops sharply, and the current rises accordingly. Electrons collide with mercury molecules to excite them, and the movement of electrons is hindered. The current drops slightly, and the voltage rises. When all the supersaturated mercury is vaporized and conductive, the current rises to a stable state, and the voltage drops to a stable value.
3、 General method of selecting UV lamp and transformer
The purpose of correctly selecting UV lamps and transformers is to effectively radiate ultraviolet rays with a wavelength of 365 nm. The content of the following lecture is to briefly introduce some parameters theoretically, so that practical experience is very important when selecting lamps and transformers. The general selection methods are described below.
1) Determine the lamp parameters and select the power density according to the curing requirements. For example, if the curing speed of the rotary machine is fast, the power should be 120-160w / cm. If the printing speed of the screen machine is slow, the lamp with low power should be selected.
2) Select the lamp current. If the total power of the lamp is 3-12kw, the current is 4.5-10a.
3) Select the voltage, and the total power divided by the current is the voltage value. For example, the total power is 4kw, the current is 5.2a, and the voltage is 770v.
The parameters of the transformer should meet the requirements of the lamp, but the large current of the transformer should be greater than the peak current, which is generally 120% of the working current. The voltage should take more than three groups of taps, because the randomness of the lamp tube in the manufacturing process is large and the parameters are unstable. Try three groups of taps of the transformer to make the output voltage of the transformer close to the actual voltage of the lamp tube.
