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234 Fbrging-Stamping - Heat Treating
Water or brine tanks are sometimes arranged for
continuous circulation by having the supply enter
through a perforated pipe in the bottom, with a side
overflow connection to a storage tank.
Modern practice provides for continuous rapid circulation
of the quenching oil and for cooling external
to the tanks. Hot oil passes out from the side of each
tank, near the surface of the bath. Cold oil is pumped
into the opposite side near the bottom. The two connections
are located as far apart as possible to prevent
short circuiting of the oil. In some installations the
oil enters the bath through perforated pipes laid on
the tank bottom, leaving through numerous outlets
near the top, connected to a common return pipe. The
bottom pipes arc protected against damage by gratings.
The rate of oil flow is regulated by a valve on the
inlet line to each tank. The tanks are located directly
opposite the furnaces in a central position for convenience,
and to shorten the time between heating and
quenching operations.
Cooling Systems.
The methods used to cool quenching oil are:
(a) Water circulation through coils in the
quenching tanks or through jackets surrounding
the tanks.
(b) Circulating the oil through the atmospheric
cooling pipe coils with or without water.
(c) Circulating brine through coils immersed in
the tanks and cooling in a refrigerating machine.
(d) Circulating the oil through coils immersed
in large water volumes such as a pond, river, etc.
(e) Circulating the oil in a closed circuit
through an external oil cooler.
Modern practice undoubtedly favors the last method.
The others are all either unreliable, insufficient in
effect, bulky, expensive to operate and maintain, or introduce
a fire hazard. A leak in a water coil or jacket
on a tank containing oil would float the oil out of the
tank, flooding the quenching room floor with great
danger of a serious fire. In the last method this is
not possible where the pressure on the oil is in excess
of that on the cooling water.
Advantages of Oil Circulation.
The four principal advantages derived from continuous
circulation of the quenching oil are: Reduced
cost for oil. uniform hardening, reduced fire risk' and
time saved in continuous operations.
By keeping the temperature of the bath low at all
times, it is possible to use an oil having a low flash
point. A smaller quantity can be used because large
capacity quenching tanks are unnecessary with artificial
cooling. Evaporation losses and the formation
of oil sludge in the bottom of the tanks are reduced
with cool oil.
Uniform hardening results are possible in quantity
production when oil is circulated because of the close
control of the bath temperature, and the maintenance
of constant quenching speed. The formation of vapor
bubbles on the hot steel, causing soft spots, is prevented
with cool oil.
Fire risk is reduced if the oil is kept at all times at
a temperature well below the fire point regardless
of the weight of metal quenched. This also prevents
the danger of igniting oil vapors above the baths in
a poorly ventilated hardening room.
July. IMS
Time saved. In continuous operations when forced
cooling is not used it is invariably necessary to discontinue
quenching periodically in order to prevent overheating
the oil. This is unnecessary when adequate
cooling is provided.
Standardization of Drawings and Practices
The American Engineering Standards Committee
has been requested by the A^merican Society of Mechanical
Engineers to authorize the organization of
a sectional committee whose duty it would be to develop
standards for drawings and certain drafting
room practices. The society signifies its willingness
to act as sponsor or joint sponsor for this project.
At the main committee meeting of the A. I'.. S. C
on June 11. \'->25. the chairman was authorized to
call a general conference or to appoint a special committee
to consider the proposed standardization.
Drawing is the universal graphical language of the
industrial world. It has its "grammar", and uses
varied forms of expression, varied styles, all matters
of importance on which it is evidently advantageous
to have general agreement. As an example of the
present day diversity not less than 34 different methods
exist to represent the most common standard
American form of screw threads, and this is only one
among the innumerable details considered in mechanical
drawing.
A^nuing the organizations in this country which
have been carrying on standardization work in this
field and have prepared manuals of unusual significance,
are :
The Bureau of Ordnance, LI. S. ANavy Department;
the General Electric Company; Kempsmith Manufacturing
Company; Reed-Prentice Company; Barber
Coleman Company; Gurney Ball Bearing Company;
Walworth Manufacturing Company; Union Tool
Company; The Jeffrey Manufacturing Company; Connersville
Blower Company and B. F Sturtevant Company.
These drafting room manuals are more or less
elaborate and complete as to the field covered by the
standard practice. They standardize the conventions
used on drawings, give the sizes of paper or cloth
used, the size or style of lettering and grouping of
notes, the arrangement of views, dimensioning, methods
of expressing tolerances, instructions for alterations,
classification of drawings and much other valuable
information.
What is needed now is to come to a definite understanding
as to the best practice to be recommended
as a national standard.
Standard Specifications
The tenth edition of its book, "Standard Specifications,"
has just been issued by the Carnegie Steel
Company, Pittsburgh. The specifications contained are
those of the Association of American Steel Manufacturers,
American Society for Testing Materials, American
Society of Mechanical Engineers, Carnegie Steel
Company and American Bridge Company, and cover
steel for bridges and buildings, locomotives and cars.
boilers and boiler rivets, commercial and forging bars,
reinforcement bars, forgings, railway and industrial
wheels and axles and shafts. The book is concluded
with a list of products made by the Carnegie Steel
Company and a list of the company's plants.