High-resistance alloys are a class of alloy conductive materials used to make resistive elements. It is not mainly used to conduct current, but to limit or control the current in circuits with its high resistance, such as resistive elements used in motors, potentiometers, standard resistors, potentiometers, sliding wire resistors, resistance wire etc.; resistance alloys for sensing elements that reflect parameters such as strain, temperature, magnetic field, pressure; resistance elements in temperature compensators and temperature measuring resistors. High resistance alloys can also be used to manufacture heating elements in various resistance heating equipment.
Classification
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High resistance alloys can be divided into the following five types according to their uses: resistance alloys for adjustment elements, resistance alloys for precision components, resistance alloys for potentiometers, resistance alloys for sensor elements and resistance alloys for heating.
adjustment element
Windings for current and voltage regulation and control elements. It is required to have high mechanical strength, good corrosion resistance and good oxidation resistance. The working temperature is generally 500°C. Commonly used are constantan, nickel-chromium, nickel-chromium-iron, iron-chromium-aluminum, and the resistivity ρ (20°C) is about 1Ωmm2/m.
Precision components
Mainly used to make resistive elements in instrumentation. It should have the characteristics of small temperature coefficient of resistance, high stability, and small thermoelectric electromotive force to copper. Resistance alloys for precision components can be divided into manganese-copper alloys for electrical instruments, manganese-copper alloys for shunts, and resistance alloys for miniaturized components with high resistance values. The working temperature of manganese-copper-based alloy for electrical instruments is 5~45℃, and the resistance value is relatively stable when used near room temperature, and ρ(20℃) is 0.35~0.47Ωmm
2
/m. The working temperature of manganese-silicon-copper and manganese-nickel-copper alloy for shunt (pressure) device is 20~80℃, and it is better to use it in the range of 30~50℃, ρ(20℃) is 0.35~0.44Ωmm
/m. Resistance alloys for miniaturized components with high resistance value require high resistivity, and can be processed into thin wires (φ is 0.01mm) or rolled into thin films (thickness <0.01mm). Such as nickel chromium aluminum iron, nickel chromium aluminum copper, nickel chromium manganese silicon, nickel manganese chromium molybdenum alloy, its resistivity is 1.33 ~ 1.90Ωmm
/m; in order to meet the needs of miniaturized components, glass-insulated manganese-copper or nickel-chromium-manganese-silicon fine wires (φ is 2~8μm) with a resistance value above 10~50MΩ can be prepared. In addition, there are nickel-chromium vacuum-evaporated metal film resistance elements, and epoxy resin-pasted resistance alloy foil film-mounted flat resistance elements, which can make the temperature coefficient of resistance reach 1 × 10
-6
/°C or less.
Potentiometer
Small contact resistance, good chemical stability and wear resistance are required. Commonly used platinum-based alloys (platinum-rhodium, platinum-iridium, platinum-copper, etc.), ρ at 20 ° C is 0.19~0.90Ωmm2/m; gold-based alloys (gold-silver-copper, gold-nickel-copper, gold-nickel-chromium, gold-palladium-iron-aluminum etc.), ρ is 0.12~2.30Ωmm2/m at 20℃; silver-based alloys (silver manganese tin); ρ is 0.28~0.53Ωmm2/m at 20℃; palladium-based alloys (palladium-silver, palladium-silver-copper, palladium-molybdenum, etc. ), ρ is 0.42~0.90Ωmm2/m at 20℃.
sensor element
It is mainly used to manufacture sensing elements that reflect parameters such as strain, temperature, magnetic field and pressure. Changes in these parameters are converted into corresponding resistance changes to facilitate their measurement, control or compensation. They are required to have high sensing sensitivity, good reproducibility and interchangeability, fast response, small drift and good stability. Commonly used are iron-based alloys (iron-nickel-chromium-molybdenum, iron-chromium-aluminum), and ρ is between 1.13 and 1.78 Ωmm2/m at 20 °C; nickel-based alloys (nickel-copper, nickel-chromium, nickel-chromium-aluminum, nickel-molybdenum-aluminum), 20 ρ at ℃ is 0.48~1.55Ωmm2/m; and pure metal wires such as platinum, nickel and copper for temperature measurement.
fever
Used in the manufacture of heating elements in various resistance heating equipment. The alloy is required to have good oxidation resistance at high temperature. Commonly used electric heating materials are nickel-chromium alloys. The working temperature of the common heating element is 900~1050℃, and the ρ is about 1.1Ωmm2/m at 20℃; the working temperature of iron-chromium aluminum alloy is 900~1500℃, and the ρ is 1.26~ at 20℃. 1.4Ωmm2/m; high melting point pure metals such as platinum, molybdenum, tantalum, etc., the working temperature is 1300~1400℃, ρ is 10-1~10-2Ωmm2/m at 20℃; silicon carbon rod, the working temperature is 1250~1400℃ , ρ is 10-1~10-2Ωmm2/m at 1400℃; silicon molybdenum rod, the maximum working temperature is 1500~1600℃, and ρ is 0.25Ωmm2/m at 20℃.
The main chemical components of nickel-chromium wire are nickel and chromium, and the shape is filamentous, so it is called nickel-chromium wire. Nickel-chromium wire is also called nickel-chromium element wire.
The grades of nickel-chromium wire are: Cr20Ni80, Cr15Ni60, Cr20Ni35, Cr20Ni30.
Nickel-chromium wire and iron-chromium-aluminum wire are both called heating wires because they belong to electric resistance alloys and are used as electric heating elements, or heating elements; also called resistance wires, because they are often used as resistance elements.
Nickel-chromium wire has high resistivity, good surface oxidation resistance, high temperature level, high strength at high temperature, good processability and weldability, and can be widely used in metallurgy, household appliances, machinery Manufacturing and other heating elements and electrical industry as resistance materials. The service life is long, but the price is relatively high because of the nickel content.
Electric furnace wire is the most widely used and the largest heating material. Its disadvantage is that it is in a very high temperature (hot state) in the working state, and it is prone to oxidation reaction in the air and burns; from the perspective of electrothermal energy conversion, energy is lost due to the production of part of visible light; electric furnace wires often When used in a spiral state, an inductive reactance effect will occur when energized.