Evanohm® R is a unique resistance alloy with high electrical
resistivity and very low temperature coefficient of resistivity
(TCR). The alloy is produced by melting and conditioning
practices which result in a low level of pinholes at ultra-thin
thicknesses. This combination of attributes with inherent
corrosion resistance makes it suitable for a variety of
strain gauge,
foil heaters and
airbag igniters.
The alloy is supplied with 90% cold reduction which has
a positive TCR of about 70 PPM/ºC. A stabilizing heat
treatment (approximately 475ºC) during manufacture of
finished parts adjusts the TCR to a desired value. The heat
treatment virtually eliminates any drift tendency of the
resistivity. A heat-treat curve for each melt is developed at
Hamilton and is made available as a guide in regulating
TCR.
Sizes
Evanohm® R is available from Hamilton Precision Metals as
foil and strip product in thicknesses from 0.0005” to 0.010”
(0.0127 mm to 0.254 mm) and in widths up to 12.0” (304.8
mm) maximum. It is available in foil as thin as 0.000100”
(0.00254 mm) in widths of 4.0” (101.6 mm) maximum.
Nominal Composition
| NOMINAL COMPOSITION |
| Chromium |
20.0% |
| Aluminum |
2.8% |
| Copper |
2.0% |
| Silicon |
1.0% |
| Manganese |
0.90% |
| Zirconium |
0.08% |
| Nickel |
Balance |
Typical Mechanical Properties of Evanohm® R Alloy
|
ANNEALED |
COLD ROLLED |
HEAT TREATED |
| Ultimate Tensile Strength |
120,000 PSI |
200,000 PSI |
240,000 PSI |
| Yield Strength (0.2% Offset) |
70,000 PSI |
195,000 PSI |
235,000 PSI |
| Elongation in 2” * |
30% |
1% |
1% |
Physical Properties of Evanohm® R Alloy
| PHYSICAL PROPERTIES |
| Density |
0.293 lbs/cu.in. |
| Melting Point (Approx.) |
1350°C |
| Electrical Resistivity @ R.T |
133 Microhm·cm |
Temperature Coefficient of Resistivity (TCR)
(-55°C to 105°C) – Heat Treated |
± 10 PPM/°C |
| Thermal Expansion Coefficient (20°C to 100°C) |
13 x 10-6/°C |
| Thermal EMF vs. Copper (0°C to 100°C) |
<1.0 Millivolts/°C |
| Thermal Conductivity R.T. |
14.6 W/m·K |
| Magnetic Attraction |
None |
| Specific Heat |
0.104 gram·cal./°C |