Tungsten wire, a thin wire made by forging and drawing a tungsten bar. Tungsten filaments are mainly used in electric light sources such as incandescent lamps and halogen lamps. The tungsten wire used as a variety of light-emitting bodies in the bulb also needs to be doped with a small amount of potassium, silicon and aluminum oxide during the smelting process. This kind of tungsten wire is called doped tungsten wire (Doped Tungsten Wire), also known as 218 tungsten wire or non-sag tungsten wire (Non-sagTungstenWire). Tungsten wires are generally drawn by various drawing dies. The main purpose is to manufacture filament and high-speed cutting alloy steel, and also used in optical instruments, chemical instruments and other aspects.
|Features||High melting point, high resistivity, good strength||Content||W≥99.95%|
|Density||19.3 g/cm³||Use||Used as various luminous bodies in bulbs|
The resistivity of tungsten wire is 5.3*10^-8. Tungsten has a high melting point, high resistivity, good strength, and low vapor pressure. It is the best material for making incandescent filaments among all pure metals. But tungsten is hard and brittle, and it is difficult to process. When the current passes through the tungsten wire and is heated to a certain temperature, the resistance value of the tungsten wire also increases to a certain value (generally, the resistance value of the metal wire increases as the temperature rises). In 1909, Kulich invented the processing technology of tungsten wire, which played a decisive role in the production and promotion of incandescent light bulbs, and its basic principles have been used to this day.
Features and uses
- WB001: Good winding performance, no sagging, suitable for ordinary incandescent lamps, double-spiral or triple-spiral fluorescent lights, holiday lights, bracket wires, etc.
- WB150: Good high temperature resistance, excellent processing performance, suitable for halogen lamps, double spiral incandescent lamps, etc.
- WB584: High recrystallization temperature, good anti-sag performance at high temperature, suitable for special lamps such as shock-resistant filament and high color temperature filament.
Most production of tungsten wire uses ammonium paratungstate (APT) as raw material. The general process is to calcinate ammonium paratungstate in the air at about 500°C into tungsten trioxide, or slightly reduce it to blue tungsten oxide in hydrogen at about 450°C. Tungsten filaments for incandescent lamp filaments need to be mixed with a small amount of potassium oxide, silicon oxide and aluminum oxide in tungsten trioxide or blue tungsten oxide. The total amount of the three does not exceed 1%. This is the tungsten invented by Buzz in 1922. Silk doping process. The doped tungsten oxide is reduced by hydrogen gas to metallic tungsten powder.
The reduction process is generally carried out in two steps: the first step is reduced to tungsten dioxide (brown tungsten oxide) at about 630°C, and the second step is reduced to metal tungsten powder at about 820°C. The purpose of the two-step reduction is to make the incorporated potassium fully function and control the particle size of the powder. The doped tungsten powder obtained in this way is then pressed into elongated square strips in a special mold. The square bar is energized in hydrogen and sintered by self-resistance heating (the temperature reaches about 3000℃).
After sintering, the density of the tungsten bar can reach more than 85% of the theoretical value. This tungsten rod can be processed into tungsten rods with a diameter of about 3mm by rotary forging, and then further processed into tungsten wires of various thicknesses by die drawing. For example, the diameter of the tungsten filament for a 220V, 15W incandescent lamp is about 15µm, and the diameter of a tungsten filament for a 10,000W bromine tungsten lamp is about 1.25mm. Thinner tungsten filaments, such as 220V, 10W incandescent lamp tungsten filaments, have a diameter of about 12 µm, and they must be produced by electrolytic corrosion.
When the diameter of the tungsten wire reaches the micron level, it is difficult to accurately measure its diameter with a conventional caliper. Therefore, in the world, tungsten wires with a diameter of less than 0.2mm are usually expressed by the weight of a wire section with a length of 200mm. For example, the diameter of the above-mentioned 15W incandescent lamp tungsten wire can be expressed by 0.679mg/200mm.
Including high temperature use performance, room temperature use performance and the consistency of wire diameter.
- High temperature performance. The operating temperature of the tungsten filament for incandescent lamps is often between 2300 and 2800°C. Generally, the greater the power of the bulb, the higher the operating temperature of the filament. It can be seen that the operating temperature of the filament far exceeds the recrystallization temperature of the tungsten filament. Under the action of its own weight, the filament section between the two hooks will sag. In severe cases, the filament can sag until it collides with the bulb of the bulb. For the doped tungsten wire that is mixed with a small amount of potassium, silicon and aluminum oxide in the powder metallurgy process of tungsten, although the content of silicon and aluminum in the final finished wire is only a few parts per million, the content of potassium is not too high. Tens of parts per million, but the degree of sagging of the filament made of this doped tungsten wire can be greatly improved. The reason is that the recrystallized crystal structure of doped tungsten wire and undoped tungsten wire is very different. The recrystallized crystal of the undoped tungsten wire is basically an equiaxed crystal, while the recrystallized crystal structure of the doped tungsten wire is a long strip of coarse crystal grains overlapping each other. From the high temperature creep theory of metallic materials, the recrystallized crystal structure of this thick and long lap structure can greatly improve its high temperature resistance to sag. According to a series of transmission electron microscopy and Auger spectrometer research and analysis conducted in the 1970s, the formation of the recrystallized crystal structure of the thick and long overlap structure unique to this doped tungsten wire is related to the formation of the doped tungsten wire. The potassium is closely related. The trace potassium remaining in the doped tungsten rod forms potassium bubbles parallel to the filament axis during processing, which hinders the lateral growth of crystal grains during the recrystallization process, thus forming a thick and long overlap structure.The sagging of the filament of the incandescent lamp is not only related to the content of the added elements in the doped tungsten filament and the processing technology, but also related to the processing technology in the filament manufacturing process. The tungsten wire retains a large amount of internal stress when it is drawn into a finished wire, and when it is wound into a filament, a new non-uniform deformed internal stress is generated on the cross section of the tungsten wire. These internal stresses must be perfectly eliminated before the filament mounting frame enters the bulb, otherwise the filament will be twisted, deformed and sag when the bulb starts to burn. The sagging of the filament will seriously reduce the luminous efficiency of the bulb.
- Room temperature performance. The room temperature use performance of tungsten wire is shown in its winding performance. Because of the long processing flow of tungsten wire, if the process management is not good, it is easy to cause many small cracks or local brittleness of the tungsten wire, so that it is easy to break when the wire is wound. The fracture of the winding wire caused by the crack is hairy, and the fracture caused by the brittleness of the wire shows a flashing crystal surface.
- Consistency of wire diameter. The poor consistency of the tungsten wire diameter is an important reason for the ultra-tolerance of the optical parameters of the incandescent bulb, and some will also affect the service life of the bulb.
The Application Of Tungsten Wire
Except for a small amount of tungsten filaments used as heating materials for high-temperature furnaces, heaters for electron tubes, and reinforcing ribs for composite materials, most of them are used to make filaments for various incandescent lamps and tungsten halogen lamps and electrodes for gas discharge lamps. For the tungsten wire or tungsten rod used as the cathode of the gas discharge lamp, in order to reduce its electron work function, 0.5-3% thorium must be added, which is called tungsten thorium wire. Because thorium is a radioactive element that pollutes the environment, cerium is used instead of thorium to make tungsten-cerium wires or tungsten-cerium rods. But the evaporation rate of cerium is high, so tungsten-cerium wire or tungsten-cerium rod can only be used for low-power gas discharge lamps.
Once the tungsten wire is used for high temperature and recrystallizes, it becomes very brittle and easily breaks under impact or vibration. In some electric light source products that require high reliability, in order to prevent the filament from breaking, 3 to 5% of rhenium is often added to the doped tungsten wire, called tungsten rhenium wire, which can reduce the ductile brittle transition temperature of tungsten to Room temperature or below. This is a very peculiar rhenium effect. So far, it has not been found that an element can replace rhenium and produce the same effect in tungsten.
Tungsten has good acid and alkali resistance at room temperature, but it is easily oxidized in humid air, so fine tungsten wires cannot be stored in a humid environment for too long. In addition, tungsten begins to react with carbon to form tungsten carbides at around 1200°C. Therefore, attention should be paid to this problem in the hydrogen burning treatment of the filament, otherwise the tungsten reacts with the graphite lubricant on the surfa
The heat radiation of the object will produce electromagnetic waves of various frequencies (wavelengths). For tungsten wire, almost 100% of electromagnetic waves incident on the surface will be absorbed. (Absorption and emissivity coefficient is 1) For tungsten wire, almost 100% of the electromagnetic waves incident on the surface will be absorbed (absorption and emissivity coefficient is 1), so its thermal radiation is close to the black body radiation whose spectrum is only related to temperature. Therefore, its thermal radiation is close to the black body radiation whose spectrum is only related to temperature.
Tungsten Wire Lamp
The two poles of the energy-saving lamp are ordinary tungsten wires. After heating, electrons can be emitted. A relatively high voltage is applied to both sides of the lamp tube to form an electric field. These electrons will be accelerated in the lamp tube to form a The electron flow of a certain speed and energy, the lamp tube is evacuated into a vacuum, and it is filled with mercury, that is, the electrons in the mercury electron flow hit the mercury atoms at a certain speed, so that the mercury atoms are excited and become an excited state of electricity. The ion is said to have undergone a step, and the mercury in the excited state will spontaneously fall back to its original state after a short period of time. At the same time, ultraviolet light is emitted, which cannot be used for illumination. Common energy-saving lamps include ordinary ordinary lamps and three-primary-color lamps that have become mainstream. Compared with incandescent bulbs, they have the advantage of saving electricity. The difference is that the color rendering of ordinary tubes is low, while the three primary colors of tubes show natural sunlight colors, and are better than ordinary tubes in terms of color rendering and light efficiency. Energy-saving light sources all contain mercury. Because the boiling point of mercury is very low, it can evaporate at room temperature. After the waste fluorescent tube is broken, mercury vapor will be emitted to the surroundings immediately, which can instantly make the mercury concentration in the surrounding air reach 10-20 mg per cubic meter, which is regulated by the state. The maximum allowable concentration in the air is 0.01 mg per cubic meter. After mercury enters the human body, it is difficult to be eliminated.
- Mercury pollution occurs during the production process and after use and disposal. Western countries attach great importance to mercury pollution.
- Since it is a glass product, it is easy to break and difficult to transport. It’s not easy to install.
- The power consumption is still too large.
- It is easy to damage, short life span, and energy saving without saving money. This sentence is the best portrayal of it.
The simplest method: There is a big difference between the lamps made of two materials. The color temperature of the dysprosium lamp is about 5600, and it will fluctuate up and down. Because of the aging of the bulb, it is generally around 5600K. The color temperature of the tungsten lamp is 3200K! This is the biggest difference between the two, the dysprosium lamp is white light, the tungsten lamp is yellow light, the dysprosium lamp is more used, and the models are different, subject to ARR lamps. Dysprosium lamps include: 200W, 575W, 2000W, 2500W, 4000W, 6000W, 12000W and new PAR lamps, which also belong to the dysprosium lamp category, 200PAR, 575PAR, 1200PAR, 4000PAR, 6000PAR, 12000PAR tungsten lamps include: 50W, 300W, 650W, 1000W, 2000W, 5000W, 24000W!
The development of the tungsten filament industry has been closely linked with the lighting bulb industry from the very beginning. After nearly 30 years of research, British electrical engineer Joseph Swan made a vacuum bulb with carbon filaments that emit light in December 1878.  But this kind of bulb has serious shortcomings, mainly because of its short life. In October 1879, Edison successfully made an incandescent bulb with carbon fiber as the filament.  Nearly 20 years later (1897), carbon wire was replaced by osmium wire and tantalum wire, but due to the low melting point of Os and Ta, the working temperature and light efficiency were low.
Edison tried carbon filaments in 1879 and used them for hundreds of hours. Although “carbon” has a very high melting point (3550°C), it has a low “sublimation” temperature. It is directly sublimated from solid to gaseous state at low temperature, so it is easy to consume and has a short service life. And it must be completely isolated from the air (it will burn in the air). At present, almost all tungsten wires with a melting point of (3410°C) are used. The advantage is that the rate of sublimation is lower when the melting point is lower. Therefore, it can be heated to a higher temperature than “carbon wire”. Tungsten filaments will burn in the air, so the bulb needs to be evacuated.
In order to avoid the sublimation of the filament, inert gas is injected into the bulb. These gases are mainly argon and do not contain oxygen. Through the collision, the partially vaporized tungsten atoms can return to the filament. Although the inert gas increases the service life of the filament, it also pays some price. In the original vacuum bulb, due to the presence of inert gas, heat conduction and convection are increased, and energy is taken away, so the equilibrium temperature is lowered. The sublimed tungsten gas forms weak particles in the inert gas and forms black spots on the inner surface of the bulb by convection.
In 1903, according to the patents of A. Just and F. Hannaman, Hungary produced the first tungsten filament. It heats the carbon filament to a high temperature through an electric current in the oxyhalide vapor of tungsten containing free hydrogen, so that the carbon is completely replaced by tungsten. The incandescent filament produced in this way contains more or less carbon, not only is brittle, but also when the bulb is in use, the filament is continuously densified, so the electrical parameters of the filament will change.
In 1904, Jest and Hannaman realized the effect of carbon on brittleness, mixed them with tungsten compounds with a carbon-free binder, extruded them into filaments, and then heated them in hydrogen to reduce them to metal. The tungsten wire made by this method is very brittle, but because of its much better light efficiency, it has replaced carbon wire, osmium wire and tantalum wire for making light bulbs.
None of the above methods can prepare fine tungsten wires. In order to solve this problem, in 1907, a low nickel content tungsten alloy came out. It was prepared by mechanical processing, but its severe brittleness hindered its application. Until 1909, W.D. Coolidge of General Electric Company of the United States produced tungsten billets through powder metallurgy, and then used mechanical processing to produce tungsten wires that are ductile at room temperature, thus establishing the tungsten wire processing industry. The foundation also laid the foundation of powder metallurgy.
However, this “ductile” tungsten filament shows obvious brittleness after the bulb is ignited. In 1913, Pintsch invented the thorium tungsten wire (ThO2 content of 1% to 2%), which greatly reduced the brittleness of the incandescent filament. At first, the sagging of the filament (see the anti-sagging performance of tungsten wire) was not a problem, because the filament at this time was a straight filament, but after 1913, Langmuir changed the straight filament to a spiral filament. In this way, when a light bulb When in use, the high working temperature and dead weight cause the filament to sag, so pure tungsten and thorium tungsten are difficult to meet the requirements of use.
In order to solve the problems of sagging and short life of tungsten wires, in 1917, A. Pacz invented tungsten wires that “undeformed” at high temperatures. At first, he used a refractory crucible to bake WO3 when preparing pure tungsten. He accidentally discovered that the tungsten wire spiral made from tungsten powder obtained by reduction of this WO3 was unusually mysterious and no longer sag after being recrystallized. Subsequently, after 218 repeated experiments and verifications, he finally found that the tungsten wire made by adding potassium and sodium silicate to tungstic acid (WO3·H2O) after reduction, pressing, sintering, and processing, recrystallized to form equivalent The coarse grain structure is neither soft nor sag resistant. This is the earliest tungsten wire that does not sag. Perth’s discovery laid the foundation for the production of non-sagging tungsten wires. Until now, the United States still calls non-sagging tungsten wires “218 tungsten wires” to commemorate this major discovery of Perth.
However, the earliest non-sagging tungsten wire is more brittle than thorium tungsten wire, so some light bulb manufacturers insist on using thorium tungsten wire as the filament. However, with the continuous development and improvement of the production process of non-sagging tungsten filaments, people have gradually realized that adding K, Si, and Al compounds to tungsten oxide at the same time can make the tungsten filament have good sag resistance at high temperatures, and at the same time, After crystallization, it has satisfactory ductility at room temperature. This is what people often call “AKS tungsten wire”, that is, “non-sagging tungsten wire” or “doped tungsten wire”. T. Millner called this improved non-sagging effect in 1931. “GK effect”.
Link to this article：Tungsten Wire
Reprint Statement: If there are no special instructions, all articles on this site are original. Please indicate the source for reprinting:Tungusten，Thanks！^^