TECHNICAL INFORMATION
Resistance Alloys (India) Ltd. Electric Resistance Heating Alloy RAIL®-NC 80/20 (Brightray® Alloy S) Strip RAIL®-NC80/20 (Brightray® Alloy S) Strip is an austenitic, non-magnetic, Nickel-Chrome alloy. It is used at strip temperature upto 1200°C. RAIL ® -NC80/20 (Brightray ® Alloy S) strip has outstanding characteristics like high uniform electric resistance, excellent heat stability, strong resistance to corrosion, excellent ductility, weldability and mechanical stability. Its austenitic structure gives good toughness allowing it to be easily cold worked. It is an ideal metallic heating element material for use in high temperature industrial furnaces and electric domestic heating equipments. Physical & Mechanical properties Maximum element working temperature (in air)
1200 °C
Nominal composition % Cr Si Fe Mn Ni
… … … …
20 1 1 (Max) 0.4 Balance
Density g/cm3
…
8.43
Electrical Resistivity at 20°C Ohms rinn2/m
… …
1.10
Elongation %
…
Min 30
Melting temperature
…
1400
Tensile strength Kgs/ min2
…
70
•••
Creep limit (1% elongation after 1000 hours)
8.16 … … … …
8.16 1.53 0.408 0.051
Workability
…
Good
Weldability
…
Satisfactory
Magnetic Property
…
Non-Magnetic
2
Kg/ nun 600°C Kg/ mm2 800°C Kg/ mm2 1000°C Kg/ mm2 1200°C
Resistance values are at 20°C & for values at working temperature, multiply by the factor Ct from the table. C 20
100
200
Ct 1.01.005 1.012
300
400 500
600
1.02 1.027 1.032 1.026
700 800 900 1.02 1.019 1.022 1.02
1000 1100 1.035 1.05
A Short note on design of elements using RAIL-NC-80/20 (Brightray*-Alloy S) strips Surface Load Selection of strips size is on the basis of surface load acceptable to different applications. The following data can be general guidance for industrial heating elements, although the actual value to be chosen will depend on the circumstances.
TxW mm
.
Resistance Surface Area Win at 20° C cm2/m
Weight Will
cm2/Ω at 20° C
1.00 1.00 1.00 1.00 1.00 1.00
x x x x x x
10 15 20 25 40 50
0.110 0.073 0.055 0.044 0.028 0.022
220 320 420 520 820 1020
84.30 126.45 168.60 210.75 337.20 421.50
1.20 1.20 1.20 1.20 1.20 1.20
x x x x x x
10 12 15 20 25 40
0.092 0.076 0.061 0.046 0,037 0.023
224 264 324 424 524 824
101.16 121.39 151.74 202.32 252.90 404.64
2435 3474 5311 9217 14162 35826
1.50 1.50 1.50 1.50 1.50 1.50 1.50 1.50
x x x x x x x x
10 12 15 20 25 30 40 50
0.073 0.061 0.049 0.037 0.029 0.024 0.018 0.015
230 270 330 430 530 630 830 1030
126.45 151.74 189.68 252.90 316.13 379.35 505.80 632.25
3151 4426 6735 11622 18276 26250 46111 68667
2.00 2.00 2.00 2.00 2.00 2.00 2.00
x x x x x x x
10 15 20 25 30 40 50
0.055 0.037 0.028 0.022 0.018 0.014 0.011
240 340 440 540 640 840 1040
168.60 252.90 337.20 421.50 505.80 674.40 843.00
4364 9189 15714 24545 35556 60000 94545
2.50 2.60 2.50 2.50 2.50 2.50
x x x x x x
15 20 25 30 40 50
0.029 0.022 0,018 0.015 0.011 0.009
350 450 550 650 850 1050
316.13 421.50 526.88 632.25 843.00 1053.75
12069 20455 30556 43333 77273 116667
3.00 3.00 3.00 3.00 3.00
x x x x x
20 25 30 40 50
0.018 0.015 0.012 0.009 0.007
460 560 660 860 1060
505.80 632.25 758.70 1011.60 1264.50
'
2000 4384 7636 11818 29286 46364
25556 37333 55000 95556 151429
-3Design of strip element To calculate the most appropriate section and length to use as element in a furnace to operate at 1000°C with a total electrical loading of 90KW for operation on 420 Volts, 3 phase supply. 1- Volts per phase
=
240 √3
Electrical loading/phase
=
Resistance Rh
=
Rc
=
90 3 242 2 30.000 1.95 1.035
= 242Volts = 30 Kw = 1.95 Ω =
1.884Ω
2- Maximum surface area loading for a furnace temp. 1000°C is 1.5 Watts/ cm2 3- Quantity cm2/ Ω = 30000 = 10615 cm2 /Ω 1.5x1.884 From the table, the size of the strip is 20 x 1.5 mm 4- Required length =
1.8884 0.0363
= 51.90 meters
- It is necessary to check that .actual surface area loading has not exceeded the maximum, otherwise premature failure due to overheating may occur. Total surface area of chosen element =B x D= E (d is surface area of strip C from table) = 51.90 x 430 = 22317 cm 6- Actual surface loading = 30000 = 1.344 Watts/ cm2 22317 This value is below the maximum permitted value. Brightray® Alloy S is registered trademark of Special Metals Wiggin Ltd.U.K.