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Steel Making

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

Open Hearth Process
The open hearth furnace consists of a big brick room with a l...

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

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

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

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

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

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

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

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

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

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

Annealing
There is no mystery or secret about the proper annealing of d...

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

Standard Analysis
The selection of a standard analysis by the manufacturer is t...

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

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

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

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

Hardening
Steel is hardened by quenching from above the upper critical....



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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