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Pyrometry And Pyrometers
A knowledge of the fundamental principles of pyrometry, or th...

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

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

Heating
Although it is possible to work steels cold, to an extent de...

Hardening
The forgings can be hardened by cooling in still air or quen...

Separating The Work From The Compound
During the pulling of the heat, the pots are dumped upon a ca...

Introduction Of Carbon
The matter to which these notes are primarily directed is the...

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

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

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

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

Compensating Leads
By the use of compensating leads, formed of the same materia...

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

Alloying Elements
Commercial steels of even the simplest types are therefore p...

Chrome-nickel Steel
Forging heat of chrome-nickel steel depends very largely on ...

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

Annealing Method
Forgings which are too hard to machine are put in pots with ...

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

High-carbon Machinery Steel
The carbon content of this steel is above 30 points and is ha...

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



Protectors For Thermo-couples






Category: PYROMETRY AND PYROMETERS

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
durable.

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
temperature.

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
necessary.





Next: Steel Before The 1850's

Previous: Pyrometers For Molten Metal



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