University of Wisconsin Digital Collections
Link to University of Wisconsin Digital Collections
Link to University of Wisconsin Digital Collections
The University of Wisconsin Collection

Page View

Hartnell, June (ed.) / The Wisconsin engineer
Volume 49, Number 6 (February 1945)

Watson, Ralph A.
Wings via mother's pie plate,   p. 8


Page 8


Wings
P
A  LTHOUGH the facts are not yet widely known, it
    may be said that Wisconsin industries are letting no
dust collect in their research labs. Two notable examples
of pioneering in the development of new and better prod-
ucts are the low pressure laminates being developed by
the Consolidated Water Power and Paper Company of
Wisconsin Rapids and the resin faced plywood recently
put on the market by the Kimberly-Clark Corporation of
Neenah. Both of these companies have large research
staffs assigned to the search for new uses for paper and
other wood products.
  The laminates are of paper or fabric impregnated with
phenolic or urea resins. The layers are precut roughly to
final shape by standard dies and shears before the resin
is applied. Forming is done over low cost molds and the
resin is cured by heat at low pressures. Some have strength
weight ratios equal to metal.
  Though they were first developed as a substitute for
the scarce light aircraft metals, these laminates are now
used for many purposes including binocular cases by the
Navy, safety hats for miners and construction workers,
electrical parts (principally housings), jettison gasoline
tanks by the Army Air Forces, and even airplane wing
tips. Many other uses are being studied. The Coast Guard
is testing channel buoys made of laminates. The saving
of 350 lbs. weight giving greater freeboard with conse-
quent increased visibility, coupled with a similar saving
in cost, is very convincing. Machine gun ammunition boxes
made of such laminates illustrate its resistance to abrasion
particularly well. Samples tested fed 1200 continuous
rounds of ammunition without jamming. Metal doesn't
match that performance.
  Laminates now used in the aircraft industry equal and
exceed the strength and stiffness of aircraft aluminum on
a weight basis. Impact strengths of 20 to 25 foot pounds
are obtained as compared with 2 foot pounds for most
molded plastics. Fatigue tests of 10 to 60 million flexes
result in no deformation and virtually no fatigue. They
compare favorably with other plastics in chemical and
electrical properties. Aircraft with fuselage, wing and tail
sections built of low pressure laminates have been as-
sembled and are now being tested. Top tensile strength of
the molded laminates is more than 80,000 pounds per
Via Mother's
ie Plate
-Ralph A. Watson, m&m'46
square inch obtained with fiberglass fabric. Most tests,
however, run about 40,000 to 50,000 pounds per square
inch. Cotton fabrics show low strengths, averaging from
9,000 to 12,000 pounds per square inch, while some paper
laminates equal the strength attained by those of fiberglass
fabric.
  Perhaps the most significant feature to be noted when
considering the use of the laminates is their low cost and
ease of fabrication. It is said that "they mold as easily
as dropping a wet handkerchief over a pie tin". Large and
small, simple and complex shapes are easily formed over
inexpensive, easy to tool-up dies of wood, Kirksite, Form-
rite, cast aluminum, concrete, sheet metal, cast iron, or
even molded laminates themselves. The forming tech-
niques used in production are the autoclave, hot press,
metal to metal, or variations of these. Perhaps the method
most widely known is the autoclave. The layers of resin-
impregnated paper or fabric are placed between the mold
and an inflated rubber bag before the entire assembly is
sealed in the autoclave. Steam, hot air, or even hot water
is forced into the autoclave under pressure to cure the
resin in the laminate. Curing takes only 15 to 30 minutes
after which the cured shape is removed and set aside to
cool. The autoclave has the advantage of being able to
form large complex shapes in one operation thus saving
assembly costs.
  The simple "hot press" principal is used for molding
smaller parts. The press consists of a heated lower die of
aluminum or Kirksite and a rubber bag which is inflated
as the upper die. The resin coated layers are put into the
lower die and the upper die lowered. Air or water is then
introduced into the rubber bag forcing the impregnated
layers to conform to the contour of the heated lower die.
The resin cures in five to nine minutes depending on the
thickness of the material.
  When using a method utilizing a rubber bag as one
side of the die, only that part of the laminate which is in
contact with the formed die is given a smooth finish.
  A third method of low pressure laminating, that of us-
ing presses with heated metal male and female dies, similar
to the conventional compression molding of plastics, gives
both sides of the finished shape a smooth finish.
                 (please turn to page 13)
THHE WISCONSIN ENGINEER
8


Go up to Top of Page