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Steel Making

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

Air-hardening Steels
These steels are recommended for boring, turning and planing...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Drop Forging Dies
The kind of steel used in the die of course influences the he...

Heat Treatment Of Lathe Planer And Similar Tools
FIRE.--For these tools a good fire is one made of hard foundr...

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Fatigue Tests
It has been known for fifty years that a beam or rod would fa...

Although it is possible to work steels cold, to an extent de...

Cyanide Bath For Tool Steels
All high-carbon tool steels are heated in a cyanide bath. Wi...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

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

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Temperature For Annealing
Theoretically, annealing should be accomplished at a tempera...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

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

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

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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