Heating effect of nichrome resistance wire - Heanjia Super-metals Co., Ltd.

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Heating effect of nichrome resistance wire

The nichrome wire can be used in the very high temperatures under which the wire color changes to red hot. Its resistance also increases with the increase in temperature. Normally the nichrome wire is classified in different levels according to the applications. In order to insulate it is severely oxidized and given black shade following the special chemical process.

The wire gauges and properties: The wire length is measured in milimeters though commonly its size is measured in gauge. Particularly two gauge systems are used for this purpose such as SWG (standard wire gauge) and second system is B & S (brown and sharp). The most common system is SWG.

In the below table diameter of wire is shown in mm and gauges following the both systems using wire of resistance per hundred meter length and wire length in meters on 50g reel. This table can be helpful in education purpose to help tutors in choosing the right gauges for particular experiments.The nichrome resistance wire is taken in different sizes as shown in the below table:

The nichrome wire is constituted of 80% nickel and 20% chromium.

Diameter mm	SWG	Closest B&S	Ohms / metre	Approx metres on 50g reel
2.03	14	12 (2.05mm)	0.337	1.7m
1.62	16	15 (1.45mm)	0.526	2.7m
1.22	18	16 (1.29mm)	0.934	4.7m
0.91	20	19 (0.91mm)	1.661	8.5m
0.71	22	21 (0.72mm)	2.745	14.1m
0.56	24	23 (0.57mm)	4.441	22.7m
0.46	26	25 (0.45mm)	6.645	34.0m
0.38	28	27 (0.36mm)	9.817	50m
0.32	30	28 (0.32mm)	13.987	71m
0.27	32	30 (0.25mm)	18.486	94m
0.23	34	31 (0.23mm)	25.346	130m
0.19	36	33 (0.18mm)	37.258	192m

Another kind of resistance alloy is Karma that offers larger resistance than nichrome for given length. It is utilized for winding higher value of ohms for resistors and potentiometers. The smaller size like 0.02 mm diameter is lower than the width of human air and it costs almost $10,000 per kg. For given weight of 1 Kg, the length of 1 kg of one of these extremely thin wires can be over 220 kilometers.

Tungsten is one of the popular heating wires, it is used in the incandescent lamps to glow at very high temperatures. Tungsten is a high resistance metal and it cannot be soldered easily and needs to be welded to other metal parts to create electric connections. If we observe the light lamps, we can see its filament is welded to metal to support wires.

With the heating process almost all metal begin to expand and these support wires are used lamps made of various alloys which are not easily oxidized when heated and these are made to expand equally at the same temperature just like when glass is heated. The cause of this design is that these wires should be sealed in the molten glass to take the wires to the electrical connection of wire's socket. During the expansion and contraction of nichrome resistance wire that is different from the glass or if the wire gets oxidized coating upon heating, it is tough to bond the glass and seal precisely to the metal wire.

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