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Steel Making

Machineability
Reheating for machine ability was done at 100 deg. less than ...

The Thermo-couple
With the application of the thermo-couple, the measurement of...

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Heat-treating Department
The heat-treating department occupies an L-shaped building. ...

Forging High-speed Steel
Heat very slowly and carefully to from 1,800 to 2,000 deg.F....

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Placing Of Pyrometers
When installing a pyrometer, care should be taken that it re...

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

Phosphorus
Phosphorus is one of the impurities in steel, and it has been...

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

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

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

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

Pickling The Forgings
The forgings were then pickled in a hot solution of either ni...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

Manganese
Manganese adds considerably to the tensile strength of steel,...

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...



Calibration Of Pyrometer With Common Salt






Category: PYROMETRY AND PYROMETERS

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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