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

Restoring Overheated Steel
The effect of heat treatment on overheated steel is shown gra...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

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

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

A Chromium-cobalt Steel
The Latrobe Steel Company make a high-speed steel without tun...

Preventing Cracks In Hardening
The blacksmith in the small shop, where equipment is usually ...

Highly Stressed Parts
The highly stressed parts on the Liberty engine consisted of ...

Lathe And Planer Tools
FORGING.--Gently warm the steel to remove any chill, is parti...

High-chromium Or Rust-proof Steel
High-chromium, or what is called stainless steel containing f...

Quenching The Work
In some operations case-hardened work is quenched from the bo...

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...

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

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

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

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

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...

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

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



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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