BBBBflt] «BlJIUrIrlr - Clpdigital.org

8 Forging- Stamping - Heat Treating February, 1925
Temperature.
deg.
Cent.
300
400
500
f,(KI
700
800
900
1000
TABLE VII-THERMAL ELECTROMOTIVE FORCES OF VARIOUS METALS AND ALLOYS AGAINST
STANDARD PLATINUM
Cold Junction, 20 deg. C.
N'icke l-Chromium Alloys
10% Cr
8.35
11.78
15.27
18.61
21.99
25.17
28.30
31.23
Alloys Positive to Platinum
15% Cr
6.20
8.88
11.72
14.56
17.39
20.42
23.50
26.53
20% Cr
4.20
6.18
8.47
10.76
13.34
16.07
18.80
21.68
Iron
3.30
4.28
5.12
6.06
7.34
8.82
10.20
11.58
Iron
Chromium
Alloy
25% Cr
3.25
4.86
6.52
8.11
9.87
11.58
13.50
15.47
It is, however, not feasible to produce such material
on a commercial scale. The metal must be melted in
large quantities, cast into ingots, forged and drawn
into wire. The effect of manganese additions used
for deoxidation at the end of the melting operation
was found to be as follows:
Manganese Added, Temperature
Per cent Coefficient
0.25 0.00460
0.63 0.00452
100 0.00357
The time of melting is a material factor. A succession
of small melts were made in an electric furnace.
For the first melt the furnace required 45 minutes
to reach the melting point of nickel. The second,
third, and fourth melts required progressively shorter
times; the last melt was cast 12 minutes after the introduction
of the cold charge. The following results
were obtained from the separate melts:
Time of Specific
Melting, Resistance, Temperature
Melt No. Minutes Michormcm. Coefficient
1 45 9.75 0.00448
2 20 8.80 0.00462
3 8.67 0.00484
4 8.64 0.00484
5 12 9.12 0.00490
An analysis of the material from melt No. 5 showed
the following constituents: Nickel 99.22 per cent, manganese
0.59 per cent, iron 0.14 per cent, copper 0.03
per cent, and carbon 0.00 per cent. This material
should be somewhat purer than those from the four
preceding melts, since it was exposed for a shorter
time to furnace gases and crucible lining.
TABLE VIII.—THERMAL ELECTROMOTIV
Temperature,
deg. Cent.
300
400
500
600
700
800
900
1000
Ni90%.
Cr 10%,
with
Alumel
11.45
15.74
20.15
24.50
28.85
32.93
37.00
40.80
Iron
with
Advance
14.30
20.10
26.20
32.30
38.80
45.30
51.55
57.90
Cold Junction
Ni 90%,
Cr 10%,
with
Advance
19.35
27.60
36.25
44.90
53.45
61.65
69.65
77.60
A
4.38
5.20
5.96
6.72
7.58
8.48
9.56
10.62
All. ays Negat ive to Platinum
Nickel Alloy! • 1
D
4.38
4.78
5.14
5.46
5.80
6.14
Alumel
3.10
3.96
4.88
5.89
6.86
7.76
8.70
9.57
Copper -Nickel All oys
Advance Advance Advance
(60% Cu, + +
40% Ni) 15% Cr 10% Cr
11.00
15.82
21.08
26.24
31.46
36.48
41.35
46.32
3.60
5.22
7.10
9.24
11.53
13.78
15.70
17.12
4.64
6.74
9.10
11.62
14.38
17.32
20.50
23.76
These experiments indicate the conditions to be observed
in order to secure nickel wire with the highest
possible temperature coefficient of electrical resistance.
The nickel should be the purest available. The additions
of manganese (or magnesium) must be as small
as is compatible with subsequent forgeability. The
time taken to melt should be a minimum in order that
the molten material should be exposed for as short a
time as possible to the effect of the furnace gases. If
these conditions are met, a high-grade nickel wire can
be produced.
Materials With Zero Temperature Coefficients.
Advance and manganin have been mentioned as
alloys which have special applications as materials for
precision resistances by reason of the fact that they
have temperature coefficients which approximate to
zero over restricted ranges of temperature.
Advance contains as major constituents approximately
55 per cent of copper and 45 per cent of nickel.
An alloy containing these materials only has a pronounced
negative temperature coefficient at 20 deg. C.
The material as commercially produced, however, contains
small amounts of impurities such as iron, manganese,
carbon and silicon which are present either in
the raw materials used or are taken up during the
melting. The general effect of these impurities is
to increase the temperature coefficient of the material.
The extent of this change, as produced by the above
impurities, is now under consideration and will be reported
on at a later time.
Manganin is a ternary alloy having as its major
constituents 84 per cent of copper, 12 per cent of
E FORCE OF VARIOUS COMBINATIONS
20 deg. C.
Ni 85%,
Cr 15%,
with
Advance
17.20
24.70
32.80
40.80
48.85
56.90
64.80
72.85
Ni 80%,
Cr2C%
with
Advance
15.20
22.00
29.55
37.05
44.80
52.55
60.15
68.00
Nichrome
with
Advance
13.90
20.40
27.40
34.55
41.90
49.25
57.60
64.20
Ni 90%,
Cr 10%,
with
Advance
+ 15% Cr
11.95
17.00
22.37
27.85
33.52
38.95
44.00
48.35