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Steel Making

The Penetration Of Carbon
Carburized mild steel is used to a great extent in the manufa...

Typical Oil-fired Furnaces
Several types of standard oil-fired furnaces are shown herew...

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

Optical System And Electrical Circuit Of The Leeds & Northrup Optical Pyrometer
For extremely high temperature, the optical pyrometer is lar...

Bessemer Process
The bessemer process consists of charging molten pig iron int...

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

Sulphur is another impurity and high sulphur is even a greate...

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

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

Preventing Carburizing By Copper-plating
Copper-plating has been found effective and must have a thick...

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

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

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

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

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

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

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

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 whi...

The Pyrometer And Its Use


In the heat treatment of steel, it has become absolutely necessary
that a measuring instrument be used which will give the operator an
exact reading of heat in furnace. There are a number of instruments
and devices manufactured for this purpose but any instrument that
will not give a direct reading without any guess work should have
no place in the heat-treating department.

A pyrometer installation is very simple and any of the leading
makers will furnish diagrams for the correct wiring and give detailed
information as to the proper care of, and how best to use their
particular instrument. There are certain general principles, however,
that must be observed by the operators and it cannot be too strongly
impressed upon them that the human factor involved is always the
deciding factor in the heat treatment of steel.

A pyrometer is merely an aid in the performance of doing good work,
and when carefully observed will help in giving a uniformity of
product and act as a check on careless operators. The operator
must bear in mind that although the reading on the pyrometer scale
gives a measure of the temperature where the junction of the two
metals is located, it will not give the temperature at the center
of work in the furnace, unless by previous tests, the heat for
penetrating a certain bulk of material has been decided on, and
the time necessary for such penetration is known.

Each analysis of plain carbon or alloy steel is a problem in itself.
Its critical temperatures will be located at slightly different
heats than for a steel which has a different proportion of alloying
elements. Furthermore, it takes time for metal to acquire the heat
of the furnace. Even the outer surface lags behind the temperature
of the furnace somewhat, and the center of the piece of steel lags
still further. It is apparent, therefore, that temperature, although
important, does not tell the whole story in heat treatment. Time
is also a factor.

Time at temperature is also of great importance because it takes
time, after the temperature has been reached, for the various internal
changes to take place. Hence the necessity for soaking, when
annealing or normalizing. Therefore, a clock is as necessary to
the proper pyrometer equipment as the pyrometer itself.

For the purpose of general work where a wide range of steels or
a variable treatment is called for, it becomes necessary to have
the pyrometer calibrated constantly, and when no master instrument
is kept for this purpose the following method can be used to give
the desired results:

Next: Calibration Of Pyrometer With Common Salt

Previous: The Thermo-couple

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