Nichrome

Nichrome (Ni Cr, nickel-chrome, chrome-nickel, etc.) generally refers to any alloy of nickel, chromium, and often iron and/or other elements or substances. Nichrome alloys are typically used in resistance wire. They are also used in some dental restorations (fillings) and in other applications.

History

Patented in 1905, it is the oldest documented form of resistance heating alloy. A common alloy is 80% nickel and 20% chromium, by mass, but there are many others to accommodate various applications. It is silvery-grey in colour, is corrosion-resistant, and has a high melting point of about 1,400 °C (2,550 °F). Due to its resistance to oxidation and stability at high temperatures, it is widely used in electric heating elements, such as in appliances and tools. Typically, nichrome is wound in coils to a certain electrical resistance, and current is passed through it to produce heat.

Uses

Nichrome is used in a very wide variety of devices where electric heating is required.

Almost any conductive wire can be used for heating, but most metals will be rapidly oxidized when heated in air. When heated to red hot temperatures, nichrome wire develops an outer layer of chromium oxide,^[1] thermodynamically stable in air, 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, as the heating coils of electronic cigarettes.

The alloy price is controlled by the relatively more-expensive nickel content. Distributor pricing is typically indexed to market prices for nickel.

Properties

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.

Material property	Value	Unit
Modulus of elasticity	2.2 × 10¹¹	Pa
Density	8400	kg/m³
Melting point	1400	°C
Electrical resistivity at room temperature	(1.0—1.5) × 10⁻⁶	Ω·m
Specific heat	450	J/(kg·K)
Thermal conductivity	11.3	W/(m·K)
Thermal expansion	14 × 10⁻⁶	K⁻¹
Standard ambient temperature and pressure used unless otherwise noted.

Table 1: Resistance per inch (Ω), closed helix, 80/20 alloy.

^[2]

Wire Gauge (B&S No. / AWG)	Outside Diameter of Helix (inches)
Wire Gauge (B&S No. / AWG)	³/₄	⁵/₈	¹/₂	³/₈	¹/₄	⁷/₃₂	³/₁₆	⁵/₃₂	¹/₈	³/₃₂	¹/₁₆	¹/₃₂
14	0.446	0.365	0.283	0.202	0.121	0.101
15	0.638	0.523	0.408	0.293	0.178	0.148	0.120
16	0.895	0.735	0.575	0.415	0.255	0.215	0.175	0.135
17	1.32	1.08	0.851	0.617	0.383	0.325	0.266	0.208	0.150
18	1.89	1.56	1.22	0.891	0.559	0.475	0.392	0.309	0.226
19	2.60	2.14	1.69	1.23	0.779	0.665	0.551	0.438	0.324
20	3.72	3.07	2.42	1.78	1.13	0.967	0.805	0.644	0.482
21		4.53	3.58	2.63	1.68	1.45	1.21	0.971	0.733	0.496
22			4.98	3.67	2.36	2.03	1.70	1.37	1.05	.719
23			7.02	5.18	3.34	2.88	2.42	1.96	1.51	1.05
23			7.02	5.18	3.34	2.88	2.42	1.96	1.51	1.05
24					4.69	4.05	3.41	2.78	2.14	1.60	0.865
25					6.87	5.94	5.02	4.10	3.17	2.25	1.32

^[2]

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.^[2]

Wire Gauge (B&S No. / AWG)	Diam. (inches/mm)		400 °F 204 °C	600 °F 316 °C	800 °F 427 °C	1000 °F 538 °C	1200 °F 649 °C	1400 °F 760 °C	1600 °F 871 °C	1800 °F 982 °C	2000 °F 1093 °C
12	0.081	2.057	11.34	15.91	20.27	25.53	31.77	39.03	46.73	54.80	63.01
13	0.072	1.829	9.73	13.53	17.21	21.61	26.89	33.06	39.60	46.41	53.31
14	0.064	1.626	8.34	10.50	14.59	18.30	22.76	28.01	33.56	39.31	45.11
15	0.057	1.448	7.15	9.78	12.38	15.50	19.26	23.73	28.44	33.30	38.17
16	0.051	1.296	6.13	8.31	10.50	13.11	16.30	20.10	24.10	28.20	32.30
17	0.045	1.143	5.31	7.18	9.13	11.30	13.90	16.90	20.30	23.60	27.00
18	0.040	1.016	4.66	6.26	7.90	9.75	11.96	14.51	17.37	20.48	23.08
19	0.036	0.914	4.09	5.46	6.84	8.41	10.30	12.45	14.87	17.78	19.73
20	0.032	0.813	3.58	4.77	5.92	7.25	8.86	10.69	12.72	15.43	16.87
21	0.0285	0.7239	3.14	4.16	5.13	6.26	7.63	9.17	10.88	13.40	14.40
22	0.0253	0.6426	2.76	3.63	4.44	5.40	6.56	7.87	9.31	11.63	12.33
23	0.0226	0.5740	2.42	3.16	3.84	4.67	5.65	6.76	7.97	10.09	10.54
24	0.020	0.508	2.12	2.76	3.32	4.01	4.86	5.80	6.82	8.76	9.01
25	0.0179	0.4547	1.84	2.42	2.90	3.44	4.15	4.97	5.86	6.96	7.72
26	0.0159	0.4039	1.58	2.09	2.52	3.00	3.61	4.31	5.06	5.97	6.63
27	0.0142	0.3607	1.34	1.80	2.19	2.62	3.14	3.73	4.37	5.12	5.69
28	0.0126	0.3200	1.18	1.55	1.90	2.28	2.73	3.23	3.77	4.39	4.88
29	0.0113	0.2870	1.02	1.34	1.65	1.99	2.37	2.80	3.25	3.76	4.39
30	0.010	0.254	0.875	1.16	1.43	1.74	2.06	2.43	2.81	3.22	3.59

Table 3: Cold resistance (Ω 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% Ni, 2.5% Mn (max), 1.0% Fe (max), 0.75–1.6% Si, 0.15% C (max), balance Cr.^[2]

Power Output (W) (Upon reaching operating temperature)
	Resistance (Ω), Nichrome V, 75 °F.		Resistance (Ω), Nichrome, 75 °F.		Recommended Wire Gauge (B&S No./AWG)
	110–120 V	220–240 V	110–120 V	220–240 V	110–120 V	220–240 V
100	123.52	494.09	118.10	472.40	Max. 26-30 Min.	Max. 29-33 Min.
150	82.347	329.38	78.732	314.93	26-30	29-33
200	61.761	247.04	59.050	236.20	25-29	28-32
250	49.409	197.64	47.240	188.96	24-28	27-31
300	41.174	164.69	39.366	157.46	24-28	27-31
350	35.291	141.16	33.742	134.97	23-27	26-30
400	30.881	123.52	29.525	118.10	22-26	25-29
450	27.449	109.80	26.244	104.98	20-24	23-27
500	24.704	98.817	23.620	94.479	20-24	23-27
550	22.458	89.832	21.472	85.889	19-23	22-26
600	20.586	83.345	19.683	79.730	19-23	22-26
650	19.004	76.016	18.170	72.679	18-22	21-25
700	17.646	70.584	16.871	67.486	18-22	21-25
750	16.468	65.874	15.745	62.982	18-22	21-25
800	15.440	61.766	14.762	59.055	18-22	21-25
850	14.532	58.128	13.894	55.577	17-21	20-24
900	13.724	54.897	13.122	52.487	17-21	20-24
950	13.002	52.009	12.431	49.726	17-21	20-24
1000	12.352	49.409	11.810	47.240	16-20	19-23
1050	11.764	47.055	11.247	44.989	16-20	19-23
1100	..229	44.918	10.737	42.946	16-20	19-23
1150	10.741	42.964	10.270	41.078	15-19	18-22
1200	10.2936	41.174	9.8418	39.367	15-19	18-22
1250	9.8817	39.527	9.4479	37.792	14-18	17-21
1300	9.5016	38.006	9.0845	36.338	14-18	17-21
1350	9.1497	37.599	8.7480	35.992	13-17	16-20
1400	8.8229	36.292	8.4356	34.743	13-17	16-20
1450	8.5188	34.075	8.1449	32.579	12-16	15-19
1500	8.2347	32.938	7.8732	31.493	12-16	15-19
2000	6.1761	24.704	5.9050	23.619	10-14	13-17
2500	4.9409	19.764	4.7240	18.896	9-13	12-16
3000	4.1174	16.469	3.9366	15.746	8-12	11-15

^[2]

Additional properties

Approximate current (A) to heat a straight oxidized wire to a given temperature^[3]
AWG	Diameter (inches/mm)		400 °F (204 °C)	1000 °F (537 °C)	2000 °F (1093 °C)
8	0.128	3.251	22.4	52	128
10	0.102	2.591	16.2	37.5	92
12	0.081	2.057	11.6	26.5	65
22	0.0253	0.643	2.9	5.6	12.5
32	0.0080	0.2032	0.68	1.36	2.76
40	0.0031	0.0787	0.24	0.43	0.79

Resistivity (ohms per foot) at 20 °C^[3]
AWG	Diameter (inches/mm)		NiCrA	NiCrC
10	0.102	2.591	0.06248	0.06488
12	0.081	2.057	0.09907	0.1029
22	0.0253	0.643	1.015	1.055
32	0.0080	0.2032	10.16	10.55
40	0.0031	0.0787	67.64	70.24

Increase in resistance with temperature^[3]
°F	°C	NiCrA	NiCrC
68	20	0	0
600	315	3.3%	5.2%
1000	538	6.3%	8.6%
2000	1093	6.0%	10.5%

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

References

↑ "Advanced Topic: Oxidation Resistant Materials" (PDF). Sciences Education Foundation. General Atomics. 2002.
1 2 3 4 5 "Wire cable specifications". Pelican Wire. Archived from the original on 2012-09-20. Retrieved 2013-11-24.
1 2 3 "Nichrome 80 & Other Resistance Alloys - Technical Data & Properties". wiretron.com, Wiretronic Inc.

External links

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Nichrome

History

Uses

Properties

Table 1: Resistance per inch (Ω), closed helix, 80/20 alloy.

Table 2: Current (A) vs. temperature characteristics, straight wire.

Table 3: Cold resistance (Ω at 75°F) and wire gauge vs. power output (W) at operating voltage (V).

Additional properties

See also

References

External links