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

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

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

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

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

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

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

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

An Automatic Temperature Control Pyrometer
Automatic temperature control instruments are similar to the ...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

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

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

Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

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

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

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

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

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Temperatures To Use
As soon as the temperature of the steel reaches 100 deg.C. (...



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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