Nichrome (NiCr, nickel-chrome, chrome-nickel, etc.) is any of various alloys of nickel, chromium, and often iron (and possibly other elements). The most common usage is as resistance wire, though they are also used in some dental restorations (fillings) and in a few other applications.
Video Nichrome
History
Patented in 1905, nichrome is the oldest documented form of resistance heating alloy. A common nichrome alloy is 80% nickel and 20% chromium, by mass, but there are many other combinations of metals for various applications. Nichrome is consistently silvery-grey in colour, is corrosion-resistant, and has a high melting point of about 1,400 °C (2,550 °F). Because of its low cost of manufacture, strength, ductility, resistance to oxidation, stability at high temperatures, and resistance to the flow of electrons, nichrome is widely used in electric heating elements in applications such as hair dryers and heat guns. Typically, nichrome is wound in coils to a certain electrical resistance, and when current is passed through it the Joule heating produces heat.
Maps Nichrome
Uses
Almost any conductive wire can be used for heating, but most metals conduct electricity with great efficiency, requiring them to be formed into very thin and delicate wires in order to create enough resistance to generate heat. When heated in air, most metals then oxidize quickly, become brittle, and break. However, when heated to red-hot temperatures, nichrome wire develops an outer layer of chromium oxide, which is thermodynamically stable in air, is mostly impervious to oxygen, and protects the heating element from further oxidation.
Nichrome is used in the explosives and fireworks industry as a bridgewire in electric ignition systems, such as electric matches and model rocket igniters.
Industrial and hobby hot-wire foam cutters use nichrome wire.
Nichrome wire is commonly used in ceramic as an internal support structure to help some elements of clay sculptures hold their shape while they are still soft. Nichrome wire is used for its ability to withstand the high temperatures that occur when clay work is fired in a kiln.
Nichrome wire can be used as an alternative to platinum wire for flame testing by colouring the non-luminous part of a flame to detect cations such as sodium, potassium, copper, calcium, etc.
Other areas of usage include motorcycle mufflers, in certain areas in the microbiological lab apparatus, as the heating element of plastic extruders by the RepRap 3D printing community, in the solar panel deployment mechanism of spacecraft LightSail-A, and as the heating coils of electronic cigarettes.
The alloy price is controlled by the more expensive nickel content. Distributor pricing is typically indexed to market prices for nickel.
Properties
Nichrome alloys are known for their high mechanical strength and their high creep strength. The properties of nichrome vary depending on its alloy. Figures given are representative of typical material and are accurate to expressed significant figures. Any variations are due to different percentages of nickel or chromium.
Table 1: Resistance per inch (?), closed helix, 80/20 alloy.
Table 2: Current (A) vs. temperature characteristics, straight wire.
Showing approximate current (in amperes) necessary to produce a given temperature. Applying only to straight wires stretched horizontally in free air. Values for diameters from 0.040" through 0.010" are based on coiling on an arbor 0.12" diameter and stretched to twice the close-wound lengths.
Table 3: Cold resistance (? at 75°F) and wire gauge vs. power output (W) at operating voltage (V).
In the following table, the alloy named nichrome V is specified as: 19-21% Cr, 2.5% Mn (max), 1.0% Fe (max), 0.75-1.6% Si, 0.15% C (max), balance Ni.
Resistance of nichrome flat/strip and weight table
- The effective cross sectional area = Width × Thickness × 0.98
Additional properties
- NiCrA
- Chemical Composition: 80% Ni, 20% Cr
- Approx. Melting Point: 1400°C
- NiCrC
- Chemical Composition: 61% Ni, 15% Cr, 24% Fe
- Approx. Melting Point: 1350°C
See also
- Chromel
- Kanthal
- Inconel
- Hastelloy
- Constantan
References
Source of the article : Wikipedia
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