Chromel NiCr10 Wire

Composition

Thermocouple nickel alloy consists of nickel (89−91%), chrome (8,7−10%), residual elements of ferrum, mangan, silicon, carbon, cobalt, which does not ecxeed in summation 1,4%. Nichrome alloy, which has similar composition, is often called chromel alloy A.

Advantages

Nickel conduces to increasing of an origin, a plasticity, and a corrosion resistance. (A surface obtains a resistant greenish oxide film of nickel). This alloy is relatively light-weight and heat resistant. It has an effective combination of thermoelectric properties and heat resistance. Its density equals 8,71 g/cm³ and melting point reaches 1440 °C. Annealing performs at a temperature of 800−900°C, and a hot working at 1000−1200°C. A coefficient of alloy electrical resistance is 0,66 Ohm-mm2/m, and a linear thermal expansion is 12,8·10−6/°C. When heated, in a contact points with other metals, this alloy produces a current potential, which can be changed almost directly at a large range of temperatures. For instance, a thermoelectric power of a fume with platinum at a temperature from 1000 °C till 0 °C equals about 33 millivolts. Chrome thermocouple is capable of keeping a constant thermo-electromotive force on air at t ° 20−1000 ° C. Higher temperatures increase an error.

Demerits

Production of nickel in a pure form is associated with a number of problems that affect its value. Disadvantages include a decrease of a thermal emf in a process of rapid cooling after annealing below 600 ° C. Depending on alloy cooling time, there can be changed its thermal electromotive force — the faster it cools, the lower its thermal emf becomes. An application of chromel wire for measuring instruments with a stationary source of heat in excess of 600 ° C, increases inaccuracy of measurements up to 10 °C. It can be fixed by partial and artificial inhibitor effect of cooling in the range of 250−600 ° C, thereby allowing to stabilize a thermo-electromotive force of chromel and to obtain more accurate indications. By impact of oxygen-rich and by reducing gases hotter than 1000 °C, chromel corrodes as long as by an impact of sulfur and hydrogen (a surface becomes greenish, that significantly changes a thermo-electromotive force and leads to embrittlement of alloy).

Usage

Through all products of nickel alloy (rod, strip, wire), a wire is the most required. It is widely used in a manufacturing thermocouples, rheostats, compensating lead wires (wires for hitching thermocouples), heating units. A property of wire to maintain a stable thermal emf at temperatures up to 1000 ° C in the air, allow using it as a positive thermal electrode of thermocouple alumel-chromel (due to its heat resistance it can withstand «heat strokes» up to t ° 1300 ° C), therefore it is applied in a form of temperature gauge for welding. Electrodes of chromel-alumel alloy are made of wire, a diameter of which ranges from 1.2 mm to 3.2 mm. They are isolated from each other and from a protective cover with porcelain single-channel insulator kits.

NiCr10 is the most popular grade. A delivery of chromel can be done in the following forms:

A rod (Ø 12,0 — 100,0 mm);
A wire (Ø 0,10 — 12,00 mm);
A strip (0,1−5,0 mm of thickness; 3−600 mm).

Percentage composition:

Physical characteristics at a temperature 20 °C