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Steel Making

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

ANNEALING can be done by heating to temperatures ranging from...

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

Classifications Of Steel
Among makers and sellers, carbon tool-steels are classed by g...

The Theory Of Tempering
Steel that has been hardened is generally harder and more br...

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

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

Critical Points
One of the most important means of investigating the properti...

Drop Forging Dies
The kind of steel used in the die of course influences the he...

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

Care In Annealing
Not only will benefits in machining be found by careful anne...

Protectors For Thermo-couples
Thermo-couples must be protected from the danger of mechanica...

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

Mushet And Bessemer
That Mushet was "used" by Ebbw Vale against Bessemer is, perh...

Hardness Testing
The word hardness is used to express various properties of me...

The Quenching Tank
The quenching tank is an important feature of apparatus in c...

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

Steel Before The 1850's
In spite of a rapid increase in the use of machines and the ...

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

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



Armor plate makers sometimes use the copper ball or Siemens' water
pyrometer because they can place a number of the balls or weights on
the plate in locations where it is difficult to use other pyrometers.
One of these pyrometers is shown in section in Fig. 109.

SIEMENS' WATER PYROMETER.--It consists of a cylindrical copper vessel
provided with a handle and containing a second smaller copper vessel
with double walls. An air space a separates the two vessels, and
a layer of felt the two walls of the inner one, in order to retard
the exchange of temperature with the surroundings. The capacity
of the inner vessel is a little more than one pint. A mercury
thermometer b is fixed close to the wall of the inner vessel,
its lower part being protected by a perforated brass tube, whilst
the upper projects above the vessel and is divided as usual on the
stem into degrees, Fahrenheit or Centigrade, as desired. At the
side of the thermometer there is a small brass scale c, which
slides up and down, and on which the high temperatures are marked
in the same degrees as those in which the mercury thermometer is
divided; on a level with the zero division of the brass scale a
small pointer is fixed, which traverses the scale of the thermometer.

Short cylinders d, of either copper, iron or platinum, are supplied
with the pyrometer, which are so adjusted that their heat capacity at
ordinary temperature is equal to one-fiftieth of that of the copper
vessel filled with one pint of water. As, however, the specific heat
of metals increases with the temperature, allowance is made on the
brass sliding scales, which are divided according to the metal used
for the pyrometer cylinder d. It will therefore be understood that
a different sliding scale is required for the particular kind of
metal of which a cylinder is composed. In order to obtain accurate
measurements, each sliding scale must be used only in conjunction
with its own thermometer, and in case the latter breaks a new scale
must be made and graduated for the new thermometer.

The water pyrometer is used as follows:

Exactly one pint (0.568 liter) of clean water, perfectly distilled
or rain water, is poured into the copper vessel, and the pyrometer
is left for a few minutes to allow the thermometer to attain the
temperature of the water.

The brass scale c is then set with its pointer opposite the
temperature of the water as shown by the thermometer. Meanwhile
one of the metal cylinders has been exposed to the high temperature
which is to be measured, and after allowing sufficient time for
it to acquire that temperature, it is rapidly removed and dropped
into the pyrometer vessel without splashing any of the water out.

The temperature of the water will rise until, after a little while,
the mercury of the thermometer has become stationary. When this
is observed the degrees of the thermometer are read off, as well
as those on the brass scale c opposite the top of the mercury.
The sum of these two values together gives the temperature of the
flue, furnace or other heated space in which the metal cylinder
had been placed. With cylinders of copper and iron, temperatures up
to 1,800 deg.F. (1,000 deg.C.) can be measured, but with platinum cylinders
the limit is 2,700 deg.F. (1,500 deg.C.).

For ordinary furnace work either copper or wrought-iron cylinders
may be used. Iron cylinders possess a higher melting point and have
less tendency to scale than those of copper, but the latter are
much less affected by the corrosive action of the furnace gases;
platinum is, of course, not subject to any of these disadvantages.

The weight to which the different metal cylinders are adjusted is
as follows:

Copper 137.0 grams
Wrought-iron 112.0 grams
Platinum 402.6 grams

In course of time the cylinders lose weight by scaling; but tables
are provided giving multipliers for the diminished weights, by
which the reading on the brass scale should be multiplied.

Next: The Thermo-couple

Previous: Pyrometry And Pyrometers

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