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

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

For Milling Cutters And Formed Tools
FORGING.--Forge as before.--ANNEALING.--Place the steel in a ...

Steel Can Be Worked Cold
As noted above, steel can be worked cold, as in the case of ...

The Effect Of Tempering On Water-quenched Gages
The following information has been supplied by Automatic and ...

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

Manganese
MANGANESE is a metal much like iron. Its chemical symbol is M...

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

Hardening High-speed Steels
We will now take up the matter of hardening high-speed steels...

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

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

Liberty Motor Connecting Rods
The requirements for materials for the Liberty motor connecti...

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

Protective Screens For Furnaces
Workmen needlessly exposed to the flames, heat and glare from...

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

Heat Treatment Of Punches And Dies Shears Taps Etc
HEATING.--The degree to which tools of the above classes shou...

Robert Mushet
Robert (Forester) Mushet (1811-1891), born in the Forest of D...

Using Illuminating Gas
The choice of a carburizing furnace depends greatly on the fa...

Carburizing By Gas
The process of carburizing by gas, briefly mentioned on page ...

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



The Quenching Tank






Category: CASE-HARDENING OR SURFACE-CARBURIZING

The quenching tank is an important feature of apparatus in
case-hardening--possibly more so than in ordinary tempering. One
reason for this is because of the large quantities of pieces usually
dumped into the tank at a time. One cannot take time to separate
the articles themselves from the case-hardening mixture, and the
whole content of the box is droped into the bath in short order,
as exposure to air of the heated work is fatal to results. Unless
it is split up, it is likely to go to the bottom as a solid mass,
in which case very few of the pieces are properly hardened.



A combination cooling tank is shown in Fig. 38. Water inlet and
outlet pipes are shown and also a drain plug that enables the tank
to be emptied when it is desired to clean out the spent carburizing
material from the bottom. A wire-bottomed tray, framed with angle
iron, is arranged to slide into this tank from the top and rests
upon angle irons screwed to the tank sides. Its function is to
catch the pieces and prevent them from settling to the tank bottom,
and it also makes it easy to remove a batch of work. A bottomless
box of sheet steel is shown at C. This fits into the wire-bottomed
tray and has a number of rods or wires running across it, their
purpose being to break up the mass of material as it comes from
the carbonizing box.

Below the wire-bottomed tray is a perforated cross-pipe that is
connected with a compressed-air line. This is used when case-hardening
for colors. The shop that has no air compressor may rig up a
satisfactory equivalent in the shape of a low-pressure hand-operated
air pump and a receiver tank, for it is not necessary to use
high-pressure air for this purpose. When colors are desired on
case-hardened work, the treatment in quenching is exactly the same
as that previously described except that air is pumped through
this pipe and keeps the water agitated. The addition of a slight
amount of powdered cyanide of potassium to the packing material
used for carburizing will produce stronger colors, and where this is
the sole object, it is best to maintain the box at a dull-red heat.


is necessary.]

The old way of case-hardening was to dump the contents of the box
at the end of the carburizing heat. Later study in the structure
of steel thus treated has caused a change in this procedure, the
use of automobiles and alloy steels probably hastening this result.
The diagrams reproduced in Fig. 39 show why the heat treatment of
case-hardened work is necessary. Starting at A with a close-grained
and tough stock, such as ordinary machinery steel containing from 15
to 20 points of carbon, if such work is quenched on a carbonizing
heat the result will be as shown at B. This gives a core that is
coarse-grained and brittle and an outer case that is fine-grained
and hard, but is likely to flake off, owing to the great difference
in structure between it and the core. Reheating this work beyond
the critical temperature of the core refines this core, closes
the grain and makes it tough, but leaves the case very brittle;
in fact, more so than it was before.





Next: Refining The Grain

Previous: Quenching The Work



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