The names given to the various lines of a tooth on a gear-wheel are as follows: In Figure 233, A is the face and B the flank of a tooth, while C is the point, and D the root of the tooth; E is the height or depth, and F the breadth. P P is the ... Read more of Drawing Gear Wheels at How to Draw.caInformational Site Network Informational
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Steel Making

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

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

Suggestions For Handling High-speed Steels
The following suggestions for handling high-speed steels are ...

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

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

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

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

Composition And Properties Of Steel
It is a remarkable fact that one can look through a dozen tex...

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

Crucible Steel
Crucible steel is still made by melting material in a clay or...

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

Tensile Properties
Strength of a metal is usually expressed in the number of pou...

The Packing Department
In Fig. 56 is shown the packing pots where the work is packe...

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

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

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

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

Sulphur
Sulphur is another impurity and high sulphur is even a greate...

Ebbw Vale And The Bessemer Process
After his British Association address in August 1856, Besseme...

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



Temperatures To Use






Category: HARDENING CARBON STEEL FOR TOOLS

As soon as the temperature of the steel reaches
100 deg.C. (212 deg.F.) the transformation begins, increasing in intensity
as the temperature is raised, until finally when the lower critical
range is reached, the steel has been all changed into the ordinary
constituents of unhardened steels.

If a piece of polished steel is heated in an ordinary furnace, a
thin film of oxides will form on its surface. The colors of this
film change with temperature, and so, in tempering, they are generally
used as an indication of the temperature of the steel. The steel
should have at least one polished face so that this film of oxides
may be seen.

An alternative method to the determination of temper by color is
to temper by heating in an oil or salt bath. Oil baths can be used
up to temperatures of 500 deg.F.; above this, fused-salt baths are
required. The article to be tempered is put into the bath, brought
up to and held at the required temperature for a certain length
of time, and then cooled, either rapidly or slowly. This takes
longer than the color method, but with low temperatures the results
are more satisfactory, because the temperature of the bath can
be controlled with a pyrometer. The tempering temperatures given
in the following table are taken from a handbook issued by the
Midvale Steel Company.

TABLE 23.--TEMPERING TEMPERATURES FOR STEELS
----------------------------------------------------------------------------
Temperature Temperature
for 1 hr. for 8 min.
--------------- Color --------------- Uses
Deg. F.Deg. C. Deg. F.Deg. C.
-----------------------------------------------------------------------
370 188 Faint yellow 460 238 Scrapers, brass-turning tools,
reamers, taps, milling cutters,
saw teeth.
390 199 Light straw 510 265 Twist drills, lathe tools,
planer tools, finishing tools
410 210 Dark straw 560 293 Stone tools, hammer faces,
chisels for hard work, boring
cutters.
430 221 Brown 610 321 Trephining tools, stamps.
450 232 Purple 640 337 Cold chisels for ordinary work,
carpenters' tools, picks, cold
punches, shear blades, slicing
tools, slotter tools.
490 254 Dark blue 660 343 Hot chisels, tools for hot
work, springs.
510 265 Light blue 710 376 Springs, screw drivers.
----------------------------------------------------------------------------

It will be noted that two sets of temperatures are shown, one being
specified for a time interval of 8 min. and the other for 1 hr. For
the finest work the longer time is preferable, while for ordinary
rough work 8 min. is sufficient, after the steel has reached the
specified temperature.

The rate of cooling after tempering seems to be immaterial, and
the piece can be cooled at any rate, providing that in large pieces
it is sufficiently slow to prevent strains.





Next: Knowing What Takes Place

Previous: The Theory Of Tempering



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