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The Care Of Carburizing Compounds
Of all the opportunities for practicing economy in the heat-t...

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

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

Corrosion
This steel like any other steel when distorted by cold worki...

Annealing Alloy Steel
The term alloy steel, from the steel maker's point of view, r...

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

Non-shrinking Oil-hardening Steels
Certain steels have a very low rate of expansion and contract...

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

Annealing
ANNEALING can be done by heating to temperatures ranging from...

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

Hardness Testing
The word hardness is used to express various properties of me...

Gears
The material used for all gears on the Liberty engine was sel...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

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

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



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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