Chromel - 2.4870 - Nicrosil® wire

Chromel — 2.4870 — Nicrosil® wire

Every miracle must find its explanation stated Karel Capek.

Composition Hromel

Chromel based on nickel. consists of: 89−91% Ni, 8,7−10% Cr, the balance being iron, alloyed with manganese, silicon, copper, cobalt. Known nichrome alloy similar composition also sometimes called chromel A.

dignity

Nickel gives Hromel ductility and high resistance to corrosion. Resistant surface film of nickel oxide protects the alloy in aggressive medium density = 8.71 g / cm³. It is relatively hard and heat-resisting alloy. melting t ° — 1450 ° C. Hot deformation is made at t ° 1200−1000 ° C, and annealing at 800−900 ° C. The coefficient of linear expansion chromel 12,8 · 1010−6 / ° C, resistivity = 0.66 ohm mm2 / m. This alloy has the best combination of thermoelectric properties and heat resistance. In contact with another metal alloy when heated generates thermal electromotive force, which has a linear progression in a wide temperature range. 20−1000 ° C. At higher temperatures, the accuracy of the readings is reduced. For example, the thermo emf of the thermocouple-based Chromel and platinum in the range from 0 ° to 1000 ° C = about 33 millivolts.

disadvantages

Production of nickel in its pure form is associated with a number of difficulties, therefore it belongs to the expensive metals. The disadvantages of chromel are to reduce thermal emf by rapid cooling below 600 ° C after annealing. The faster the alloy is cooled, the lower the thermal emf. Using hromelevoy wire for instruments with a stationary heat source of 600 ° C gives significant measurement error (10 ° C). Partly this can be corrected by means of artificial braking process cooling in the range of 250−600 ° C, which allows to stabilize the thermoelectric power chromel and to obtain more accurate readings. At t ° to 1000 ° C and exposure to the oxidizing and reducing gases, sulfur or hydrogen, this alloy corrode. This surface is formed greenish patina that significantly changes the thermoelectric voltage and promotes embrittlement of the alloy.

application

Wire — the most in demand of the whole line of products (round, ribbon) of the nickel alloy Widespread use of wire found in the manufacture of thermocouple, compensation wires, resistors, heaters. With the ability to maintain a stable thermal emf in the air up to 1000 ° C, this wire is used as a positive thermoelectrode thermocouple chromel-alumel (due to the heat resistance stands «thermal shocks» up to 1300 ° C). It is used for welding, as the temperature sensor is used for compensation wires (wires joined by a thermocouple). The electrodes pair chromel-alumel made of wire Ø 1,2 — 3,2 mm. They are isolated from each other, and — a protective cover of the single-channel porcelain insulators. In turn, the working end is protected by a pair of porcelain tip from contact with the metal cover.

Features thermocouples

All chromel-alumel thermocouple types in addition to TCA-In-XV and TX-VII of, have high inertia. The mechanical stability of all types of ordinary couples, except for TXA-430 and TXA-420, which are vibration resistant. Thermocouples chromel-alumel demonstrate excellent work in an oxidizing environment, but in the absence of aggressive gases. This is made possible by the formation of a thin protective oxide film that prevents the destructive action of oxygen. Linear characteristic TEDS makes it relatively easy to calibrate such a thermocouple.

In the USSR produced Chromel NH9 and NH9,5 brands. Chromel NH 9.5 is available in the following forms:

• wire (Ø 0,10 — 12,00 mm);
• circle (Ø 12,0 mm — 100.0 mm);
• ribbon (thickness of 0.1−5.0 mm, the width of 3−600 mm).

The physical properties of the alloy NH9.5 at 20 ° C

Buy at the best price

In stock «Elektrovek-steel» company offers a wide range of thermocouples. Our offices are located in Russia and Ukraine. Lead times are minimal. When wholesale purchases discounts.

Characteristics of the alloy Chromel NH9,5