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Steel Making

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Armor plate makers sometimes use the copper ball or Siemens' ...

Vanadium has a very marked effect upon alloy steels rich in c...

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

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

Hardening Operation
Hardening a gear is accomplished as follows: The gear is tak...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

Lathe And Planer Tools
TO FORGE.--Gently warm the steel to remove any chill is parti...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

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

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

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

Compensating Leads
By the use of compensating leads, formed of the same materia...

Refining The Grain
This is remedied by reheating the piece to a temperature slig...

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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