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

S A E Heat Treatments
The Society of Automotive Engineers have adopted certain heat...

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

Cutting-off Steel From Bar
To cut a piece from an annealed bar, cut off with a hack saw,...

Calibration Of Pyrometer With Common Salt
An easy and convenient method for standardization and one whi...

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

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

Plant For Forging Rifle Barrels
The forging of rifle barrels in large quantities and heat-tre...

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

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

Manganese
Manganese adds considerably to the tensile strength of steel,...

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

Knowing What Takes Place
How are we to know if we have given a piece of steel the ver...

Tool Or Crucible Steel
Crucible steel can be annealed either in muffled furnace or b...

Silicon
SILICON is a very widespread element (symbol Si), being an es...

Heating Of Manganese Steel
Another form of heat-treating furnace is that which is used ...

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

Annealing To Relieve Internal Stresses
Work quenched from a high temperature and not afterward tempe...

Process Of Carburizing
Carburizing imparts a shell of high-carbon content to a low-...

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



Pyrometers






Category: PYROMETRY AND PYROMETERS

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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