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208 forging - Stamping - Heat Treating
Heat Treatment.
Defects due to the heat treatment of forgings is
one subject which would demand many pages for its
consideration, even in very rough outline. However.
there are several major points of caution which can
well be mentioned.
Any heat treatment should lie applied only after
all forging operations have been completed.
The heating and cooling should be uniform and
applied to the entire mass, eliminating all possibilities
of local heating or cooling of any part.
In large forgings the effect of mass must not be
considered, and time must be allowed for the complete
penetration of the heat. It should be appreciated
that there is a certain amount of inertia present
which resists structural changes, and that the
larger the mass, the greater will be the length of time
necessary to accomplish any change.
Any heat treatment that obtains high physical
strengths but leaves the materials in a highly stressed
condition, should be avoided.
A uniform distribution of the microscopic constituents
in as fine a size as possible should be the
desire, in order to prevent cleavage planes of
weakness.
The Allis-Chalmers Company has found that to
secure good large forgings the following precautions
must be taken, not on one or two forgings, but on
each and ever)- forging.
The ingots used for making the forgings must Inmade
under careful supervision as to material melted,
method of melting, temperatures obtained, pouring
conditions, and mechanical handling.
The forging operations are closely controlled as
to the heating and forging. The forge department is
apprised of the stresses under which the finished
piece will operate, in order that it may get the maximum
results attainable by reduction and heat treatment
before making the forging.
The physical tests are so made as to be representative
of the forging, and in such a manner as to check
the operating stresses in the finished machine.
FIG. 5—Periscope used for examining the bore of a shaft.
The heat treatment and chemical characteristics
are checked by careful microscopic examination and
analysis before the forging is released by the metallurgical
department.
All laps, cracks, seams, or surface defects are completely
chipped out before the piece is machined.
Great care is used to see that all traces of the defect
are removed, even to the extent of etching and examining
with the microscope. In defects of this kind
there is great danger that the metal at the base of
the visual crack will be found to be distorted or microscopically
ruptured, and if such material were allowed
in service, there would be risk of fatigue failure.
June, 1925
All shafts over 9 in. in diameter have an exploratory
hole (iy in. in diameter or larger) for use in periscopic
examination.
There are several types of periscopes for this work,
but the one which has been used with success for the
past ten years is shown in Figs. 5 and 6.
This instrument consists of a brass tube, the inner
end of which contains an electric light for illuminating
the bore, and a reflecting prism. The outer end
has a focusing telescope, the object of which is to bring
the image up to the eye, and not to magnify it. This
equipment allows the slightest flaws to be detected
within the bore of the shaft.
FIG. 6—Periscope of Fig. 5 in use.
It is believed that with the careful observations
as outlined above, large forgings today offer the best
means of securing homogeneous material. However,
a full understanding of the nature of defects and their
reference to operating stresses should be thoroughly
understood by all operating and designing engineers.
It is this neglect to realize the limitations of large
forgings which has caused them, through failures, to
fall into disrepute; while in reality they are today one
of our most uniform materials of construction.
Mr. M. K. Epstein has discontinued the business
of the Heat Treating Equipment & Supply Company,
Hartford, Conn., to accept the position of District
Manager for Gilbert & Barker Manufacturing Company,
Springfield, Mass., at their New York offices
located at 26 Broadway. Mr. Epstein represented the
Gilbert & Barker Manufacturing Company in the
Philadelphia District from September 1912 to March
1920. _ _ _ _ _
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COMING MEETINGS
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June 22-26—Annual meeting of the American Society
for Testing Materials at Chalfonte-Haddon Hall,
Atlantic City, X. J. Secretary-treasurer, C. L. Warwick,
Engineers' Club Building, 1315 Spruce Street,
Philadelphia, Pa.
* * *
September 14-18—Annual convention of the American
Society for Steel Treating, and Seventh National
Steel Exposition, to be held at the Public Auditorium,
Cleveland, Ohio. Secretary, W. H. Eisenmann, 4600
Prospect Avenue, Cleveland, Ohio.