The Pyrometer And Its Use

: The Working Of Steel

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 ver
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: