As refractory metals, molybdenum and molybdenum alloys have been widely used in high temperature with its good performance and low cost. The high-temperature applications of molybdenum and molybdenum alloys are as follows:
The filament is made of tungsten with aluminum, potassium, and silicon, and is fixed in the bulb with molybdenum wire. In some cases, the hard molybdenum wire is used as the wick for winding filament.
There are some special difficulties in making light bulbs with quartz glass. The expansion coefficient of quartz glass is too small to reach the seal that matches any known metal material.
On the contrary, the thin edge molybdenum strip with a thickness of 0.025mm and a certain length can be used as a contraction seal and has been applied to mercury vapor lamp and quartz halogen lamp.
Heat treatment of metal, ceramic and composite materials should be carried out under increasingly strict conditions in order to meet the requirements of modern processing technology.
Although the sintering process of various metals and their alloys requires a great deal of control over the atmosphere, it is generally believed that annealing, hardening, and brazing treatment have many advantages in a vacuum or protection atmosphere.
The furnace used for these processes has special requirements for internal structural materials, including high-temperature resistance and high purity and low vapor pressure. Refractory metals (molybdenum, tungsten, and niobium) are suitable for high-temperature furnace components, the main applications of which are as follows.
First, a resistance heating element made of wire, rod, strip, board or mesh; second, heat shield parts for furnace wall protection; third, the burden filling and stacking of the boat, material tray, sliding frame and support; fourth, as temperature monitoring and control and so on.
The propulsion furnace is a special kind of hot wall furnace, which usually used in the protection or reduction atmosphere of sintering metal and ceramic powders. Its heating zone has a ceramic hearth, while the rest is lined with firebrick. The outside of the furnace is a sheet metal shell. A continuous heating element of molybdenum wire or molybdenum is placed in the heating area, and sometimes the heating element is fixed on the furnace cover with the molybdenum hook.
A cool wall furnace has a larger volume than a hot wall furnace and can be heated and cooled more quickly. Therefore, it is ideal for batch heat treatment including program heating, heat preservation, and cooling.
The outer wall of a cool wall furnace is a vertical or horizontal cylindrical shell, which must be protected by a set of heat-shielding metal plates to protect it from thermal radiation. The wire or stick heating element is commonly used in this furnace, and the strip or mesh heating element is often used, too.
The material of the heating element and heat shield is chosen according to the working temperature and design requirement of the furnace. If you’re considering an economic benefit, you should first choose molybdenum, because it is suitable for continuous work under 1825 ℃ temperature.
Facts show that the sintering or casting withstand the pressure of 200MN/m2 and high-temperature synthesis of 2000℃can greatly improve its organization and performance. It is known that this is the hot isostatic process (HIP). In HIP equipment, several large molybdenum or TZM alloy thermal shielding can be used.
In addition, the lower part of the pressure vessel is equipped with a large ventilation fan to speed up the flow of gas in some HIP devices. The contra-rotating axial and balance rotor of the fan are made of TZM alloy.
The high-temperature mechanical properties of molybdenum and molybdenum alloys have been widely used in various thermal processes.
For example, the TZM alloy forging hammer is used to process other refractory metals; the TZM alloy die for extrusion brass has a long life, while other materials cannot meet these requirements; TZM alloy is used as the die material in isothermal forging, which can forge titanium and its alloys and nickel-based superalloys which are difficult to be processed by traditional methods; compressor and rotor is the key parts processing by this way, the processing temperature of which is about 1130℃. If the temperature of the tools and parts is kept constant during the forging process, the best mechanical properties can be achieved.
Besides the high cost, the application of electricity to melt glass has become increasingly important in the last 30 years as it has many advantages over fossil fuels. Compared with burning oil or natural gas, the electric furnace is easier to control and produces less pollution, and it also prevents volatile substances such as boron from evaporating from molten glass.
In addition, the thermal loss of the electric melting process is significantly reduced, and the glass itself is more pure and even.
Molybdenum has good conductivity and thermal conductivity as well as a small thermal expansion coefficient, which makes it suitable as the electrode material to melt most of the glass. The corrosion resistance of molybdenum is very strong, and the glass melting electrode made of which can withstand a high current load of 1~3A/cm2.
However, the surface of the molybdenum electrode is often coated with a layer of molten glass to avoid oxidation loss.
Ceramic fiber products have replaced asbestos in many applications requiring insulation. As insulation materials, ceramic fiber is widely used in the construction industry, and also in the cool wall furnace and hot isostatic pressing equipment.
Ceramic fibers are produced in large tank furnaces made of molten alumina and kaolin, which is electro fused with a submerged molybdenum electrode. The diameter of the cylindrical molybdenum electrode is 75~100mm and the length can reach 360mm.
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