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Steel Making

Effect Of Different Carburizing Material
[Illustrations: FIGS. 33 to 37.] Each of these different p...

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

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

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

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

Compensating Leads
By the use of compensating leads, formed of the same materia...

Uses Of The Various Tempers Of Carbon Tool Steel
DIE TEMPER.--No. 3: All kinds of dies for deep stamping, pres...

Properties Of Alloy Steels
The following table shows the percentages of carbon, manganes...

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

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...

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

Heat-treating Equipment And Methods For Mass Production
The heat-treating department of the Brown-Lipe-Chapin Company...

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

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

William Kelly's Air-boiling Process
An account of Bessemer's address to the British Association w...

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

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

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

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

Calibration Of Pyrometer With Common Salt


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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