In the production process of fluorescent lamps, exhaust gas is an important production process. Whether the process is reasonable or not is important for ensuring the quality and yield of the product. The exhaust process is completed by degassing the tube and the lamp. Internal surface degassing, cathodic decomposition activation, mercury injection, argon gas filling, etc. In the process of completing these processes, if it is improper, it may directly affect the quality of the lamp, light degradation, yellowing, blackening and other quality problems.
1, the role of fluorescent lamp exhaust stage
The surface and inside of the baking tube glass of the lamp are adsorbed with a gas containing many impurities. The surface of the tube and the internal adsorption gas are due to the following reasons:
Gas adsorption on the glass surface
1. Impurity gas molecules collide with the glass surface and condense on the surface of the object like a liquid.
2. The object has a surplus chemical valence force due to the surface molecules, and the electrical attraction force causes the impurity gas molecules to adhere to the surface of the object.
3. The gas pressure around the solid surface is strong, the amount of gas adsorbed on the solid surface is large, the pressure is reduced, the amount of gas adsorbed on the solid surface is small, and the excess impurity gas is released back into the space.
Internal gas suction of glass tube
The glass tube contains gas. The structure of the glass is the same as other substances. The molecules are not completely dense. There are actually many voids. The pores in the glass are not less than 3.22 angstroms. The porosity is the physical property of all solids. The pores often contain compatible gas molecules. These gas molecules increase or decrease due to changes in external pressure and temperature. Therefore, it is extremely effective to reduce the gas pressure in the tube and increase the temperature in the lamp.
Selection of glass degassing temperature and time relationship
For general electric vacuum glass, it is reasonable to choose a baking temperature of 350 degrees Celsius, but in order to improve production efficiency,
When possible, increase the baking temperature and shorten the pumping time. Generally, it can choose about 500 degrees Celsius for 12-15 minutes. At the same time, it is required to raise the temperature to 500 degrees in the shortest possible time, and strive for the inside of the glass tube. Degas completely, and at the same time require that the lamp should maintain a fairly high temperature throughout the exhaust process, so that the degassed lamp is no longer inhaled.
Cathode decomposition
The decomposition of the fluorescent lamp cathode during the exhaust process has a decisive influence on the performance and life of the lamp. The decomposition of the alkaline earth metal ternary carbonate is caused by the Joule heat generated by the cathode decomposing a certain current in the cathode during a higher vacuum. MeCO MeO+CO ↑ (Me means 钡, 锶, )) The rate of decomposition of carbonate (the height of the applied current and the length of time) is compatible with the pumping speed, otherwise the cathode carbonate decomposition will not be complete. Decomposed too much, affecting the quality of the lamp.
The role of mercury in fluorescent lamps
Fluorescent lamp is a low-pressure mercury vapor discharge lamp. When the lamp is discharged, mercury produces a wavelength of 2537 angstroms in the lamp. The phosphor absorbs 2537 angstroms of ultraviolet light to emit visible light. To achieve the purpose of illumination. The purity of mercury is not high, too much and too little. Or the improper lamp making process, the formation of mercury compounds, will cause mercury adsorption in the lamp, which affects the light and decay of the lamp.
The role of argon in fluorescent lamps
Argon is a well-known gas. It does not chemically react with any metal to form an argon compound. Since the argon steady potential of argon is slightly higher than the ionization potential of mercury, it can produce a Penning effect, which is beneficial to help mercury. The ionization, so as to achieve the purpose of helping the jump. On the other hand, the cathode in the vacuum hot state is easy to evaporate, and the filling of the argon increases the gas pressure in the lamp tube, greatly reducing the evaporation speed of the cathode, and also Reduce the energy of positive ions, reduce the sputtering of the cathode, protect the cathode, and improve the service life of the cathode.
The effect of fluorescent exhaust on quality
In the process of exhausting, due to factors such as poor equipment, improper operation, and raw materials that do not meet the requirements, the quality of fluorescent lamps will be affected, resulting in various ills. The following analysis and production of several common ills caused by fluorescent lamps during venting Reason to talk about the solution.
Poor jump
After the lamp is exhausted and experienced, the 190-220 volt power supply can not work normally in the next minute. It is a bad start. The bad jump is due to the low vacuum in the lamp, the rare cathode electronic powder, and the argon pressure charged in the lamp. Improper cause.
The effect of low vacuum on the take-off of the lamp
The so-called low degree of vacuum means that the produced lamp is mixed with impurity gas (meaning that the Penning effect cannot be formed with mercury, and the gas that does not contribute to mercury ionization is called impurity gas), such as oxygen, nitrogen, carbon monoxide and Water vapor compounds, etc. Because oxygen and nitrogen are present in the lamp, it affects the ionization of argon and mercury because the excitation of oxygen and nitrogen does not promote the ionization of mercury because their excitation potential is much lower than the ionization potential of mercury ( The excitation potential of oxygen is 6.1 electron volts, nitrogen is 7.9 electron volts, and mercury is 10.4 electron volts. Its presence hinders the collision probability of argon and mercury atoms. The more their content, the greater the hindrance effect, hindering the mercury discharge. Due to the presence of water vapor and hydrocarbons, they decompose and ionize into oxygen, hydrogen, and carbon atoms under electric and high temperature conditions. Oxygen and hydrogenation cause the cathode's surplus cesium atoms to be oxidized and evaporated, and migrate to the cathode. On the wall of the attachment (becoming a yellow black block), carbon is adsorbed on the surface of the cathode, causing poor cathode emission and affecting the establishment of discharge.
The reason why the degree of vacuum is not high and the reaction on the tube
(vacuum is not high)
a, the mechanical pump itself has a small pumping rate, the ultimate vacuum is not high, the pump has less oil or the temperature is too high.
b. The vacuum system has poor air tightness and slow leakage.
c, the vacuum system is not clean, such as oil, mercury and other dirt to form too much vapor source
d, the vacuum pipe is too long, the inner diameter is too small or there are plugs in the pipe.
e, baking temperature is not enough or time is not enough.
f, the electronic powder decomposition is not complete or not exhausted after decomposition (including the glow is not thorough).
g, the baking tube is not thorough, the cotton glue is not baked.
The reason why the above seven points of vacuum is not high, the most important thing is that in the exhausting process, especially the baking temperature, time, the electronic powder is not completely decomposed and decomposed after the decomposition (including the incomplete glow). The vacuum is not high. Reflected on the finished lamp, the following phenomena will occur:
The first four (when you feel the pumping slow, the pumping is not clean) appears in the initial refining and aging
1. It is difficult to take off the lamp;
2, the pipe pressure is high (in the case of a certain amount of inflation);
3, the extinguishing voltage is high;
4, the lamp is dark (whole lamp);
5. The tube is red in the middle;
6, the gas appears gas rotation phenomenon (filament)
The first five are reflected in the lamp
1. The middle of the lamp is dark or the lamp is dark;
2. There is a gas rotation phenomenon;
3, the tube pressure drop begins to be high, normal after the old refining.
The first six are reflected in the lamp (in the initial refining)
1, when the 220 volt filament, the color is purple;
2. After 220 volts is lit, there is a gas discharge phenomenon at the filament, which is extinguished when it is severe;
3. Pulling high pressure (260 volts) has more gas to be released, and the phenomenon of turning is more serious, and the pipe pressure rises;
4. When looking at the filament (after lighting), the number of red circles is more than 1-1.5 turns, even purple;
5. If the filament is lit, the glow color at both ends is good, and no gas is turned into decomposition after lighting.
The first seven are reflected in the lamp: during the ignition process, the cotton gel decomposes the impurity gas such as nitrogen and oxygen, causing the light to decay quickly, the early yellow circle appears, and the inner lead wire and the lamp die appear serious carbon black matter.
The solution is not high vacuum
The first to fourth items are equipment problems. They should be inspected and maintained regularly. The glass and rubber systems should be replaced regularly. The mechanical pump and the foreline pump (Roots pump) should be changed regularly and refueled. The vacuum is measured with a vacuum gauge before use. According to the process requirements, the baking time and temperature are guaranteed. According to the pumping speed and vacuum state of the mechanical pump, the specification of the electric current decomposition is appropriately adjusted. The baking tube should be thorough to ensure the full decomposition of the rubber. In order to improve the vacuum degree of the lamp, the flushing method can be used. ensure product quality.
In theory, all the inflation tubes can use the "flushing" method to reduce the partial pressure of the impurity gas to the required degree. The limit of this degree depends mainly on the purity of the "flushing" gas used. "It is to "flush" (dilute) and replace the residual impurity gas in the lamp with the working gas required by the lamp itself.
Since the flushing method keeps a large amount of gas in the whole exhausting process, it is often between ten to 10 Torr, so the pumping effect (pumping speed) of the mechanical pump is faster than that of the diffusion pump. Because the diffusion pump only draws faster when it enters the molecular state of lower pressure, and the pumping speed is slower when the pressure of the gas is higher.
In the ideal state, the residual pressure before rinsing is 3*10 Torr (this can be achieved by a general mechanical pump), filled with 10-15 Torr of high purity argon, and then pumped to a pressure of 3*10 Torr. It is equivalent to reducing the molecular weight of the impurity gas to 1/300-500, which is equivalent to increasing the vacuum by two orders of magnitude. If the flushing is twice, the vacuum equivalent to four orders of magnitude can be increased, so that the vacuum of the fluorescent lamp It is completely satisfactory. Therefore, the exhaust station using the charging process can be completely without the diffusion pump.
However, considering the diffusion between the argon gas and the impurity gas requires a certain time and the vacuum performance of the mechanical pump is stable, whether to cancel the diffusion pump is determined according to actual needs.
Argon is charged into the lamp to help the jump, but it can only achieve the desired purpose when it is filled with a certain pressure. Too high or too low will produce undesirable results. The pressure of argon is too high, and the density of argon atoms is too high. The free path is small, and the energy of the atom is small. When the atoms collide with each other, it is not enough to ionize the mercury atom. The argon pressure is too low and the mean free path is large. The probability of collision between the argon atom and the mercury atom is small, and the ion atomization of the mercury atom is also affected. The probability of unfavorable discharge. Generally speaking, the argon pressure is too high and the argon pressure is too low.
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