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Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Rate Of Cooling
At the option of the manufacturer, the above treatment of gea...

Placing The Thermo-couples
The following illustrations from the Taylor Instrument Compan...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Composition Of Transmission-gear Steel
If the nickel content of this steel is eliminated, and the pe...

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

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Annealing Of Rifle Components At Springfield Armory
In general, all forgings of the components of the arms manufa...

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

High Speed Steel
For centuries the secret art of making tool steel was handed ...

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

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

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

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

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

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

Bessemer Process
The bessemer process consists of charging molten pig iron int...

Conclusions
Martien was probably never a serious contender for the honor ...

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



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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