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Steel Making

Phosphorus is one of the impurities in steel, and it has been...

Steel For Chisels And Punches
The highest grades of carbon or tempering steels are to be re...

Making Steel Balls
Steel balls are made from rods or coils according to size, st...

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

Hints For Tool Steel Users
Do not hesitate to ask for information from the maker as to t...

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

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

High Speed Steel
For centuries the secret art of making tool steel was handed ...

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

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

Rate Of Absorption
According to Guillet, the absorption of carbon is favored by ...

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

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

Steel Worked In Austenitic State
As a general rule steel should be worked when it is in the a...

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

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

Instructions For Working High-speed Steel
Owing to the wide variations in the composition of high-speed...

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

MANGANESE is a metal much like iron. Its chemical symbol is M...

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

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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