Industry Knowledge
In a high temperature oxidizing environment, does a high temperature resistant special-shaped molybdenum screw need an additional coating or protective layer?
Analysis of high temperature oxidation characteristics of molybdenum
Molybdenum exhibits excellent strength and creep resistance at high temperatures, with a melting point of up to 2610°C. It is widely used in aerospace, semiconductor manufacturing, vacuum metallurgy, quartz glass heaters and other fields. However, molybdenum begins to oxidize in an air environment above 400°C to generate volatile MoO₃ (molybdenum trioxide). MoO₃ is easy to sublimate at high temperatures, causing continuous loss of material on the surface of the screw, thereby reducing the fastening reliability of the threaded connection and even causing structural failure.
Therefore, if molybdenum special-shaped screws are used in an environment with high temperature and oxygen or oxygen-containing atmosphere (such as air, CO₂, H₂O vapor, etc.), their service life will be greatly shortened if effective protective measures are not taken.
Whether a coating is required: depends on the strength of the oxidizing environment
Nantong Rongxin Electrical Control Technology Co., Ltd., as a professional manufacturer of tungsten and molybdenum materials with a history of 40 years, deeply understands the behavior of molybdenum materials in different application scenarios. The company was formerly known as Rugao Shuguang Tungsten Molybdenum Material Co., Ltd. It has been focusing on the manufacturing and application optimization of high-performance molybdenum products for many years and has now become one of the leading domestic manufacturers of molybdenum screws and special-shaped molybdenum parts.
In typical applications, such as:
Vacuum furnace heating area: Since the environment is high vacuum or argon protection, molybdenum is almost not oxidized and no protective layer is required.
Open high-temperature air furnace: Oxygen and water vapor in the air will strongly oxidize molybdenum, and a protective coating or modified alloy needs to be applied.
Semiconductor MOCVD equipment: The process atmosphere is complex. Although it is not a pure oxygen environment, oxidants may still exist. Coatings or Mo-La alloys are required to enhance oxidation resistance.
Common protection measures and coating types
In order to extend the service life of high temperature resistant special-shaped molybdenum screws in high-temperature oxidation environments, Nantong Rongxin provides a variety of protection methods according to the customer's application environment:
1. SiO₂/Al₂O₃ ceramic coating
The high-temperature ceramic protective layer can form a dense barrier on the molybdenum surface to block oxygen and water vapor. The coating has strong stability and good thermal shock resistance, and is suitable for high-temperature atmospheres exceeding 1200°C.
2. Anti-oxidation coating (such as silicide, boride)
For example, molybdenum silicide (MoSi₂) or molybdenum boride can form a protective oxide film on the molybdenum surface, which has good oxidation protection performance between 1200–1700°C. Rongxin's technical team can customize coating treatment according to customer working conditions.
3. Molybdenum alloying treatment
For example, molybdenum-lanthanum (Mo-La) alloy or TZM (titanium-zirconium-molybdenum) alloy can delay oxidation to a certain extent and enhance structural stability, especially suitable for high-temperature assemblies with frequent thermal cycles.
4. Application protection design
In scenarios where coating treatment is not possible, Rongxin can also provide matching graphite-coated components or high-temperature anti-oxidation assembly processes to minimize the risk of molybdenum screws being exposed to oxidizing environments.
Company capability guarantee: comprehensive control from design to testing
As a well-known tungsten and molybdenum product company in the industry, Nantong Rongxin has advanced testing equipment, including:
Metallographic analyzer: can detect the grain distribution of molybdenum organization and evaluate the influence of high temperature;
Spectrometer: analyze the purity of molybdenum materials to ensure the quality of raw materials;
Tensile testing machine: verify the mechanical strength retention of screws at high temperatures;
Ultrasonic flaw detector: ensure that there are no crack defects in special-shaped structures and improve the safety of use.
Relying on the above-mentioned testing methods, Rongxin can provide customers with complete product qualification certificates (such as metal material test report MTR), and conduct high-temperature simulated oxidation tests before leaving the factory to ensure that each high-temperature special-shaped molybdenum screw has stable performance.
What kind of forming process is used for the special-shaped part of high temperature resistant special-shaped molybdenum screw?
Special-shaped molybdenum screws: process challenges behind complex geometry
Different from traditional standard parts, special-shaped molybdenum screws usually have asymmetric geometric structures, multi-axis interference structures, special head shapes (such as flat hexagons, limit slots, conical countersunk heads) and even have additional functions such as through holes and positioning slots. Since molybdenum metal itself has the characteristics of high melting point, low plasticity, high brittleness and high processing hardness, the forming processing of special-shaped parts places extremely high requirements on equipment and processes, and the forging or cutting processes of conventional metal materials cannot be directly applied.
Analysis of mainstream forming processes
1. CNC precision numerical control machining (Computer Numerical Control Machining)
This is the main process most commonly used for the manufacture of high-temperature molybdenum special-shaped screws. Nantong Rongxin has multiple CNC turning and milling composite machining centers, which combine multi-axis linkage and micron-level tool control to perform fine cutting, local chamfering, thread processing and special-shaped shape forming on high-density molybdenum rods.
Advantages:
High precision (machining tolerance can reach ±0.01mm)
Flexible response to complex structures
Suitable for small and medium-sized batch customized production
Application examples: aviation hot end sensor connectors, semiconductor equipment fixtures, precision fixture parts, etc.
2. Spark discharge machining (EDM)
For some special-shaped molybdenum screws with complex internal structures or difficult to access with traditional tools, the Nantong Rongxin technical team uses electric spark forming processing technology. EDM uses the good conductivity of molybdenum material, uses tungsten wire or copper wire as an electrode, and uses pulsed arc to erode fine grooves, countersunk holes or complex contours.
Advantages:
No contact force, low processing stress
Can process high-hardness and high-melting-point metals
Can achieve fine and precise structures
Nantong Rongxin, with the cooperation of multiple discharge forming machines, is particularly suitable for processing slotted screws, split nested structures, and slender through-hole shaped parts.
3. Hot Isostatic Pressing (HIP) + Finishing
In some products with extremely high requirements for strength and density, Nantong Rongxin uses hot isostatic pressing to form molybdenum blanks. After directional pressure is applied to the mold, a preform with fine grains and extremely high density is obtained. Then it enters the CNC or grinding finishing process to achieve special-shaped structures and functional details.
Advantages:
Dense material structure, strength increased by more than 20%
High forming efficiency, suitable for large-scale products with uniform structure
Reduce internal microcracks and holes, significantly improve high-temperature fatigue life
This process is particularly suitable for special structural parts such as MOCVD reaction chamber fixing screws and vacuum heat treatment clamping screws that require high cycle and high load conditions.
4. Powder metallurgy pre-pressing + machining
For some special-shaped screws with complex geometric shapes, Nantong Rongxin uses molybdenum powder to form preforms through isostatic pressing or compression molding, and then sintering densification to obtain the general shape before fine processing. This process route makes full use of the isotropic properties of molybdenum materials, while maintaining the integrity of the special-shaped structure, taking into account thermodynamic uniformity.
What kind of high temperature environment is high temperature resistant special-shaped molybdenum screw commonly used in?
Vacuum heat treatment equipment
In vacuum heat treatment furnaces, high-temperature sintering furnaces, vacuum annealing furnaces and other equipment, the internal temperature of the furnace chamber often exceeds 1400°C, and because the environment is vacuum or inert gas, molybdenum becomes one of the main structural materials. Special-shaped molybdenum screws play the following main roles in these devices:
Fix and support the furnace frame
Connect and fix the graphite element and the heating element
Positioning parts of the hot zone loading system
The high-purity molybdenum special-shaped screws provided by Nantong Rongxin are CNC machined and finely polished to ensure that they will not deform or oxidize during repeated thermal cycles. They are widely used in many vacuum furnace manufacturers and are stably used in high-end equipment exported to Europe.
Semiconductor manufacturing equipment (MOCVD/PECVD/diffusion furnace)
The semiconductor process equipment needs to perform thin film deposition, oxidation diffusion, ion implantation and other operations under ultra-high temperature conditions. The operating temperature is often between 1100°C and 1300°C, and the thermal stability requirements of the internal structural parts of the equipment are extremely high.
The uses of special-shaped molybdenum screws in such equipment include:
Clamping quartz glass/sapphire substrates
Fixing heating elements/thermal field structures
Stable supports for gas distribution systems
The molybdenum screws produced by Nantong Rongxin have been widely used in the semiconductor industry, especially in the design of complex head structures (such as limit type, countersunk type, T-slot matching). Nantong Rongxin uses CNC multi-axis machining technology to achieve integrated adaptation of screw structure and equipment design, greatly improving the assembly accuracy and thermal field stability of the equipment.
Aerospace and military hot end structures
In aerospace engines, rocket tail nozzle structures and aircraft thermal protection systems, special-shaped molybdenum screws are fasteners and interface connectors for high-temperature components. They need to withstand ultra-high temperature, high vibration and thermal shock alternating working conditions, and the temperature in some areas even exceeds 2000°C.
Molybdenum's high melting point (2610°C), low thermal expansion coefficient and creep resistance make it an ideal material for such extreme environments. Nantong Rongxin combines years of military supporting experience and develops various forms of special-shaped connection screws through Mo-La alloy and TZM molybdenum alloy material solutions, which have the following features:
Strong thermal fatigue resistance
Not easy to get stuck due to thermal expansion
Stable holding force after tightening
Currently, Nantong Rongxin has become a long-term partner of high-temperature connection structures for many domestic scientific research units and military industrial groups.
High-temperature glass and quartz melting industry
In equipment such as quartz crucible manufacturing, high borosilicate glass melting, and electric melting furnaces, the internal temperature often exceeds 1600°C, and is often accompanied by a highly corrosive atmosphere (such as water vapor, chlorine, oxygen, etc.), which places extremely high demands on the corrosion resistance and thermal stability of fasteners.
The high-density special-shaped molybdenum screws produced by Nantong Rongxin adopt the refined powder metallurgy densification process, and SiO₂ ceramic coating or MoSi₂ anti-oxidation coating can be applied on the surface, which significantly improves its service life in high-temperature oxidation environment. It is often used for:
Electrode positioning and fixation
Hot zone packaging component connection
Glass guide plate support structure
Nuclear industry and radioactive environment
Molybdenum material has the characteristics of low neutron absorption rate, high irradiation stability and good thermal conductivity. It is an important component material for nuclear reactor structural parts and experimental equipment. Special-shaped molybdenum screws are often used in high-temperature testing devices for nuclear materials:
High-temperature tensile/compression specimen fixation
Radioactive container internal component connection
Nutrone source target packaging structure
Nantong Rongxin molybdenum screws use vacuum sintering + full inspection and flaw detection technology in the nuclear industry, and are accompanied by metallographic and elemental analysis reports to ensure their safe operation in irradiation and high-temperature cross-environment.
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