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

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

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

Heavy Forging Practice
In heavy forging practice where the metal is being worked at...

Quenching
It is considered good practice to quench alloy steels from th...

Shrinking And Enlarging Work
Steel can be shrunk or enlarged by proper heating and cooling...

The Effect
The heating at 1,600 deg.F. gives the first heat treatment w...

Effects Of Proper Annealing
Proper annealing of low-carbon steels causes a complete solu...

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

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

Brown Automatic Signaling Pyrometer
In large heat-treating plants it has been customary to mainta...

Application Of Liberty Engine Materials To The Automotive Industry
The success of the Liberty engine program was an engineer...

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

Hardening High-speed Steel
In forging use coke for fuel in the forge. Heat steel slowly ...

Connecting Rods
The material used for all connecting rods on the Liberty engi...

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

Correction By Zero Adjustment
Many pyrometers are supplied with a zero adjuster, by means ...

Carbon Steels For Different Tools
All users of tool steels should carefully study the different...

Heat Treatment Of Steel
Heat treatment consists in heating and cooling metal at defin...

Testing And Inspection Of Heat Treatment
The hard parts of the gear must be so hard that a new mill f...



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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