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Steel Making

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

The Electric Process
The fourth method of manufacturing steel is by the electric f...

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Sulphur is another impurity and high sulphur is even a greate...

MANGANESE is a metal much like iron. Its chemical symbol is M...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Annealing Work
With the exception of several of the higher types of alloy s...

Tungsten, as an alloy in steel, has been known and used for a...

The Modern Hardening Room
A hardening room of today means a very different place from ...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

Chromium when alloyed with steel, has the characteristic func...

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

Furnace Data
In order to give definite information concerning furnaces, fu...

It is considered good practice to quench alloy steels from th...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

Calibration Of Pyrometer With Common Salt


An easy and convenient method for standardization and one which
does not necessitate the use of an expensive laboratory equipment
is that based upon determining the melting point of common table
salt (sodium chloride). While theoretically salt that is chemically
pure should be used (and this is neither expensive nor difficult
to procure), commercial accuracy may be obtained by using common
table salt such as is sold by every grocer. The salt is melted in
a clean crucible of fireclay, iron or nickel, either in a furnace
or over a forge-fire, and then further heated until a temperature
of about 1,600 to 1,650 deg.F. is attained. It is essential that this
crucible be clean because a slight admixture of a foreign substance
might noticeably change the melting point.

The thermo-couple to be calibrated is then removed from its protecting
tube and its hot end is immersed in the salt bath. When this end
has reached the temperature of the bath, the crucible is removed
from the source of heat and allowed to cool, and cooling readings
are then taken every 10 sec. on the milli-voltmeter or pyrometer. A
curve is then plotted by using time and temperature as cooerdinates,
and the temperature of the freezing point of salt, as indicated
by this particular thermocouple, is noted, i.e., at the point
where the temperature of the bath remains temporarily constant
while the salt is freezing. The length of time during which the
temperature is stationary depends on the size of the bath and the
rate of cooling, and is not a factor in the calibration. The melting
point of salt is 1,472 deg.F., and the needed correction for the instrument
under observation can be readily applied.

It should not be understood from the above, however, that the salt-bath
calibration cannot be made without plotting a curve; in actual
practice at least a hundred tests are made without plotting any curve
to one in which it is done. The observer, if awake, may reasonably
be expected to have sufficient appreciation of the lapse of time
definitely to observe the temperature at which the falling pointer
of the instrument halts. The gradual dropping of the pointer before
freezing, unless there is a large mass of salt, takes place rapidly
enough for one to be sure that the temperature is constantly falling,
and the long period of rest during freezing is quite definite.
The procedure of detecting the solidification point of the salt
by the hesitation of the pointer without plotting any curve is
suggested because of its simplicity.

Next: Complete Calibration Of Pyrometers

Previous: The Pyrometer And Its Use

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