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Properties Of Steel
Steels are known by certain tests. Early tests were more or l...

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

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

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

Furnace Data
In order to give definite information concerning furnaces, fu...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

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

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

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

Flange Shields For Furnaces
Such portable flame shields as the one illustrated in Fig. 1...

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

PHOSPHORUS is an element (symbol P) which enters the metal fr...

SULPHUR is another element (symbol S) which is always found i...

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

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

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

Leeds And Northrup Optical Pyrometer
The principles of this very popular method of measuring tempe...

Reheating for machine ability was done at 100 deg. less than ...

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

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

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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