1) Selective Oxidation With regard to Ni-Cr alloys containing Fe, if the partial pressure of oxygen is lower than a certain value, Cr, which has a high affinity with O2, will undergo selective oxidation, which is grain boundary oxidation unique to Ni-Cr alloys. If you look at the surface oxide layer with a microscope, you can see green precipitates. This phenomenon is often called "green etch." Especially when the temperature is in the range of 800°C to 1050°C and the system contains CO, H2 and other regenerative gases, the positive electrode of the K type thermocouple is more susceptible to selective oxidation. This low thermoelectric potential due to the reduction in Cr content has become a limiting factor for the long-term use of K-type thermocouples in the heat treatment industry. If the gas used is pure and the system contains no oxygen, it can extend the life of the thermocouple. However, if the thermocouple wire has an oxide layer on its surface, it can still provide enough oxygen for the selective oxidation of Cr. Therefore, when using in a non-oxidizing atmosphere, clean, polished wire should be used. At the same time, the use of inert gases with trace amounts of oxygen or low partial pressure of oxygen should be avoided as much as possible. When the length and diameter of the maintenance pipe is relatively large (ie, the maintenance pipe is very thin), due to poor air circulation, an oxygen-deficient state is formed, and the remaining small amount of oxygen can still provide conditions for the selective oxidation of Cr. 2) Countermeasures for selective oxidation In order to avoid or slow down the degradation of K type thermocouples due to selective oxidation, in addition to improvement in materials, corresponding measures should be taken in the construction of thermocouples: 1 Select a metal with stronger oxygen affinity than Cr as a getter, enclosed in the maintenance pipe to avoid selective oxidation of Cr, and increase the oxygen content by increasing the diameter of the maintenance pipe or by blowing air. 2 Assembled thermocouple solidification. The patented product developed by the author—a thermocouple used in a solid carburizing furnace—developed a fabricated thermocouple with a sealed structure to avoid selective oxidation of Cr attack, through the Wazhou Group, FAW, DCM, and Ipsen industrial furnaces. The use of more than a dozen companies such as Shen, Shen, Shen Qian and Qianjiang Motorcycles has proven that this plan is effective. With an operating life of 12 months or more, users are very satisfied [4]. 3) The influence of the atmosphere on the thermocouple's stability varies depending on the operating temperature and the atmosphere. The maximum operating temperature of the same type of sensor, such as the K-type thermocouple, also varies with the diameter, and K-type thermocouples with the same diameter are also used. Due to the different structures, their stability is also very different. In the choice of thermocouple, it is necessary to consider the following conditions for the use of conditions: 1 commonly used temperature and maximum operating temperature 2 Oxidation recovery and other operating atmosphere 3 Anti-vibration performance As for the assembled thermocouple, the influence of the atmosphere depends on the material of the maintenance pipe and the thermocouple structure. Therefore, it is necessary to familiarize with and control the physical and chemical properties of various maintenance pipe materials. For example: In the powder metallurgy industry, molybdenum tubes are commonly used as thermocouple maintenance tubes. In the 1600 °C H2 atmosphere, the use of better results. However, the molybdenum tube is corroded by oxidation in a short time in an oxidizing atmosphere. Secondly, based on the operating atmosphere, choose a suitable thermocouple, select a platinum-rhenium thermocouple in an oxidizing atmosphere above 1300°C, and use a tungsten-rhenium thermocouple under recovery and vacuum conditions. The K type thermocouple is suitable for working in an atmosphere such as air or O2, but when it is used in H2, its appearance is restored by H2 and has no influence in a short time. If it is exposed to H2 for a long time, it will accelerate recovery and it will The wire grows and breaks when the wire grows. In a regenerative atmosphere such as CO or coal gas, the deterioration will be significantly accelerated and it will be worse. With regard to armored thermocouples, the atomic radius of hydrogen is so small that it easily enters the interior through the jacket. It also accelerates deterioration, resulting in a significant decrease in the thermoelectric value. 4) Effect of insulation resistance Thermocouple insulation, at high temperatures, the insulation resistance decreases rapidly with increasing temperature, therefore, there will be a leakage current, the current through the insulation resistance once fell into the insulation, so that the instrument indicates instability or measurement Inaccuracies may also occur as a result of the chaos of the recorder.
Material Selection:
1. Frame: 2MM thicknesses cold-roll Stainless steel.
2. Motor: Germany SEW brake motor (outer), power 0.75KW, power supply 220V.
3. Control system: Imported Japan Mitsubishi converter and PLC to control of electric box (150%1HZ)
4. Opening & closing speed: 0.6-1.5m/s (adjustable).
5. Safety Device: Korea Photocell Sensor, emergency stopping reaction when sensing obstacles.
6. Curtain: France high-density polyester fiber and the surface coating processing, thickness 0.8MM, variety colors can be chose: Red, yellow, blue, green, orange, gray, white, transparent, etc. Tensile strength: 4000/3500N/5cm, tear strength 600/600N. Fire-proofing level: German standard DIN75200 Usage temperature: -30 ° C +70 ° C.
7. Wind resistant: The Aluminium alloy Reinforce Girder to increase wind resistant effect.
8. Curtain replacement function: Aluminium alloy Reinforce Girder is loaded between 2 pieces Curtain, can be replaced easily if any curtain broken, save your cost.
9. Transparent window: 1.2MM thickness transparent PVC window, size and location is up to your request, more safer.
10. Seal: Seal brush are Installed inside the guides, and the special bottom design, to fit any uneven ground.
11. Cotrolling way: Push button + radar sensor, very convenient.
12. Limiting Switch: Mechanical limiting switch, easily and exactly.
13. Emergency STOP: With emergency stop button on control panel, can stop easily by
Hand once disconnect or accident
14 Fault recovery function: All Hongfa's production is with fault recovery function, system will self-recovery after power cut off.
15. Delivery time: About 7 business days with contract and deposit confirmed.
16. Pyament item: 50% before production, and the other 50% before shipment.
17. Warranty Details: We provide 12 months warranty for all doors and accessories (except man-made disasters, Irresistible natural disasters, ect^).
We have many professional engineers with rich experience, qualified products, perfect service system, and good cooperation relationship with many famous companies.
PVC high speed door, plastic roll up doors, high speed fabric roll up doors, high speed rolling doors, pvc roll up doors SHENZHEN HONGFA AUTOMATIC DOOR CO., LTD , https://www.hongfahss.com
Environmental Impact on the Use of Thermocouples
Many companies in the process of using thermocouples, often ignore the impact of the environment on it, the following on the environmental impact of thermocouples given the appropriate treatment methods, companies in the choice of thermocouple can create their own, hoping to help to use the thermoelectric Even business.