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Niles, Donald E. (ed.) / The Wisconsin engineer
Volume 48, Number 7 (March 1944)

Graham, Walt
Mathematical morsels,   pp. 12-21


Page [17]


STANDARDS LAB ...
                (continued from page 10)
ments, illumination, photometry, and some of the funda-
mental required courses. Professor Larson also often
prepares specifications and plans for large state institu-
tions. This work has been assumed by the laboratory in
order to keep abreast of the practice in wiring large pub-
lic buildings. The work is done under the direction of
Mr. Charles A. Halbert, State Chief Engineer, and Mr.
Roger C. Kirchhoff, State Architect. The specification
work includes illumination design, signal systems of all
kinds, as well as the regular systems for power. Current
examples include the electrical layouts for a 300-bed hos-
pital at King, Wisconsin, and design of control mech-
anismn circuits at the Waupun state prison.
  In spite of the achievements of the laboratory, the lab-
oratory itself presents many handicaps and "headaches."
Crowded conditions and lack of fireproofing offer a con-
stant hazard to the $20,000 worth of equipment, and lack
of sufficient help is slowing up the work. Air-condition-
ing is another urgently needed improvement to keep deli-
cate equipment and parts free from the dust and dirt in
the air.
  The University, and the engineering school in particu-
lar, may rightfully be proud of the splendid work the
Electric Standards Laboratory is doing. The value of
such service to scientific and public advancement goes un-
questioned.
SHRINK FITS...
                 (continued from page 7)
of operation and adaptability to mass production, which
has made it the more important method in use today.
  A very illustrative example of experimentation with
refrigerants is in the Dodge Division of Chrysler Corp.,
in Detroit, where shrink fits were first practiced with the
use of dry ice back in 1932. Today Dodge reports that
deep-freeze units are used entirely, at a reduced operat-
ing cost of 17 to 1. That is, $175 spent for electric cur-
rent will do the same as $3,000 formerly spent for dry
ice.* Apparently this does not take into account the high-
er initial cost of the freezer unit, but it is quite obvious
that this cost would soon be offset by the reduction in
operating costs. The Ford Motor Co., on the other hand,
reports that shrink fitting valve seats in cylinder blocks
has been a standard operation for 10 years, and they
apparently use liquid air as the refrigerant with satisfac-
tory cost reports.*
  Examples such as these only go to show that shrink fits
are still in their experimental stage. Only a few com-
panies had done much work along this line before the
war, but today the majority of companies in war indus-
tries are employing this method, either singly, or in some
few cases along with expansion by heating. It is from the
reports of these companies that this information has been
gathered, and it is only reasonable that the methods in
use are based chiefly on a few experiments, or satisfac-
tory results, rather than thorough experimentation. These
facts lead one to believe that the method of tomorrow
will be an efficient refinement of the methods in use
today.
  Finally may I summarize some of the advantages and
disadvantages of shrink fitting as compared to expansion
and press or drive fitting. First, in the case of shrink vs.
expansion, we note that negative temperatures do not in-
volve the danger of change in metallic structure, nor the
chances of warping and scaling found in higher tempera-
tures. At the same time the newer designs in mechanical
refrigerators enables automatic devices for feeding and
removing parts from the machine, without large furnaces
and heated working condition. In the case of press fits,
the mechanical strains and fatigue failure often produced
by pressing or driving are reduced to a minimum, at the
same time reducing bending, springing, and scoring trou-
bles almost entirely. The cost factors, at present, are
about on even terms, with the future pointing in the
direction of the mechanical freezing unit. The chief dif-
ficulties center around the rate of cooling, the tempera-
ture differential necessary and obtainable, and the high
rate of expansion involved the minute the metal is ex-
posed to room temperatures. Precautions must also be
taken against flesh burns, as these are as bad if not worse
than those obtained from high temperatures.
   "'Metals & Alloys, July 1943.
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