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

Affinity Of Nickel Steel For Carbon
The carbon- and nickel-steel gears are carburized separately...

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

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

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

Carburizing Low-carbon Sleeves
Low-carbon sleeves are carburized and pushed on malleable-ir...

Silicon
Silicon prevents, to a large extent, defects such as gas bubb...

Temperature Recording And Regulation
Each furnace is equipped with pyrometers, but the reading an...

The Leeds And Northrup Potentiometer System
The potentiometer pyrometer system is both flexible and subst...

Hardening Carbon Steel For Tools
For years the toolmaker had full sway in regard to make of st...

The Pyrometer And Its Use
In the heat treatment of steel, it has become absolutely nece...

Heat Treatment Of Axles
Parts of this general type should be heat-treated to show the...

Pyrometers For Molten Metal
Pyrometers for molten metal are connected to portable thermoc...

Oil-hardening Steel
Heat slowly and uniformly to 1,450 deg.F. and forge thorough...

Heat Treatment Of Gear Blanks
This section is based on a paper read before the American Gea...

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

Annealing In Bone
Steel and cast iron may both be annealed in granulated bone. ...

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...

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

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



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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