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

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

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

Blending The Compound
Essentially, this consists of the sturdy, power-driven separa...

Application To The Automotive Industry
The information given on the various parts of the Liberty eng...

Annealing Of High-speed Steel
For annealing high-speed steel, some makers recommend using g...

Preventing Decarbonization Of Tool Steel
It is especially important to prevent decarbonization in such...

Heat Treatment Of Milling Cutters Drills Reamers Etc
THE FIRE.--Gas and electric furnaces designed for high heats ...

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

Carburizing Material
The simplest carburizing substance is charcoal. It is also th...

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

Surface Carburizing
Carburizing, commonly called case-hardening, is the art of pr...

The material used for all gears on the Liberty engine was sel...

Crucible Steel
Crucible steel is still made by melting material in a clay or...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

The Modern Hardening Room
A hardening room of today means a very different place from ...

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

A Satisfactory Luting Mixture
A mixture of fireclay and sand will be found very satisfactor...

Correction For Cold-junction Errors
The voltage generated by a thermo-couple of an electric pyrom...

Detrimental Elements
Sulphur and phosphorus are two elements known to be detrimen...

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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