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

Critical Points
One of the most important means of investigating the properti...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

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

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

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

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

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

Tempering Round Dies
A number of circular dies of carbon tool steel for use in too...

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

Quenching Tool Steel
To secure proper hardness, the cooling of quenching of steel ...

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

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

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

Judging The Heat Of Steel
While the use of a pyrometer is of course the only way to hav...

Short Method Of Treatment
In the new method, the packed pots are run into the case-har...

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

Take Time For Hardening
Uneven heating and poor quenching has caused loss of many ve...



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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