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Steel Making

Tempering Colors On Carbon Steels
Opinions differ as to the temperature which is indicated by t...

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

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

Chromium when alloyed with steel, has the characteristic func...

Piston Pin
The piston pin on an aviation engine must possess maximum res...

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

A combination of the characteristics of nickel and the charac...

Quality And Structure
The quality of high-speed steel is dependent to a very great ...

Effect Of A Small Amount Of Copper In Medium-carbon Steel
This shows the result of tests by C. R. Hayward and A. B. Joh...

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

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

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

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Carbon In Tool Steel
Carbon tool steel, or tool steel as it is commonly called, us...

Vanadium has a very marked effect upon alloy steels rich in c...

Carbon Tool Steel
Heat to a bright red, about 1,500 to 1,550 deg.F. Do not ham...

Protectors For Thermo-couples


Thermo-couples must be protected from the danger of mechanical
injury. For this purpose tubes of various refractory materials
are made to act as protectors. These in turn are usually protected
by outside metal tubes. Pure wrought iron is largely used for this
purpose as it scales and oxidizes very slowly. These tubes are
usually made from 2 to 4 in. shorter than the inner tubes. In lead
baths the iron tubes often have one end welded closed and are used
in connection with an angle form of mounting.

Where it is necessary for protecting tubes to project a considerable
distance into the furnace a tube made of nichrome is frequently used.
This is a comparatively new alloy which stands high temperatures
without bending. It is more costly than iron but also much more

When used in portable work and for high temperatures, pure nickel
tubes are sometimes used. There is also a special metal tube made
for use in cyanide. This metal withstands the intense penetrating
characteristics of cyanide. It lasts from six to ten months as
against a few days for the iron tube.

The inner tubes of refractory materials, also vary according to
the purposes for which they are to be used. They are as follows:

MARQUARDT MASS TUBES for temperatures up to 3,000 deg.F., but they will
not stand sudden changes in temperature, such as in contact with
intermittent flames, without an extra outer covering of chamotte,
fireclay or carborundum.

FUSED SILICA TUBES for continuous temperatures up to 1,800 deg.F. and
intermittently up to 2,400 deg.F. The expansion at various temperatures
is very small, which makes them of value for portable work. They
also resist most acids.

CHAMOTTE TUBES are useful up to 2,800 deg.F. and are mechanically strong.
They have a small expansion and resist temperature changes well,
which makes them good as outside protectors for more fragile tubes.
They cannot be used in molten metals, or baths of any kind nor
in gases of an alkaline nature. They are used mainly to protect
a Marquardt mass or silica tube.

CARBORUNDUM TUBES are also used as outside protection to other
tubes. They stand sudden changes of temperature well and resist
all gases except chlorine, above 1,750 deg.F. Especially useful in
protecting other tubes against molten aluminum, brass, copper and
similar metals.

CLAY TUBES are sometimes used in large annealing furnaces where they
are cemented into place, forming a sort of well for the insertion of
the thermo-couple. They are also used with portable thermo-couples
for obtaining the temperatures of molten iron and steel in ladles.
Used in this way they are naturally short-lived, but seem the best
for this purpose.

CORUNDITE TUBES are used as an outer protection for both the Marquardt
mass and the silica tubes for kilns and for glass furnaces. Graphite
tubes are also used in some cases for outer protections.

CALORIZED TUBES are wrought-iron pipe treated with aluminum vapor
which often doubles or even triples the life of the tube at high

These tubes come in different sizes and lengths depending on the
uses for which they are intended. Heavy protecting outer tubes
may be only 1 in. in inside diameter and as much as 3 in. outside
diameter, while the inner tubes, such as the Marquardt mass and
silica tubes are usually about 3/4 in. outside and 3/8 in. inside
diameter. The length varies from 12 to 48 in. in most cases.

Special terminal heads are provided, with brass binding posts for
electrical connections, and with provisions for water cooling when

Next: Steel Before The 1850's

Previous: Pyrometers For Molten Metal

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