Method of forming corrugated panel

A corrugated panel in which at least the central corrugated sheet is formed from an elastically deformable material such as polyethylene synthetic plastic or spring steel is disposed and secured between a pair of cover sheets. The method of forming the panel includes stretching out a first of the cover sheets and thereafter attaching the ends of the sheet to be corrugated to the first sheet while maintaining the spacing between the remainder of the sheet. This forms a half sinusoidal shape from the sheet to be corrugated. A compressive force is thereafter applied to the sheet to be corrugated which forms it into a number of corrugations having ridges and furrows. The furrows are bonded to the base sheet and a third sheet is positioned on and bonded to the ridges of the corrugated sheet.

BACKGROUND OF THE INVENTION 
This invention relates to corrugated bodies and more particularly to a 
prestressed panel and a method of constructing such panels from sheets of 
flexible material. 
It is known to form sheets of paper into cardboard wherein a sheet of 
corrugated paper is glued between a pair of paper cover sheets. The 
process for forming the cardboard includes wrinkling the corrugated sheet 
between the nip of a pair of meshing corrugation rollers which permanently 
wrinkles the paper sheet which is thereafter sandwiched between and glued 
to the other sheets of paper. It is also known to form permanently 
corrugated metal sheets by the rolling process for use as roof structures 
on certain buildings and for other purposes. When paper is corrugated, 
since it has substantially little yield strength with no flexibility, it 
is quickly deformed permanently. It thus cannot be prestressed for uses 
where a prestressed material may be required. Metals have a very high 
yield strength with little or no flexibility below its yield strength and 
is permanently deformed when corrugated. Thus, it too is not in a 
prestressed condition if used in a honey comb type structure. Synthetic 
plastics, such as polyethylene plastics and vinyl plastics, on the other 
hand are generally flexible. Unless corrugating rollers are heated so as 
to heat and deform the plastic sheets fed thereto, these materials revert 
to their original shapes or fail so that they have not been utilized as 
corrugated panels or the like. By forming prestressed corrugated panels 
from synthetic plastic materials such as polyethylene or certain metals a 
relatively strong structure can be constructed which can have good 
insulating qualities for use in buildings, especially if the voids between 
the corrugation ridges and furrows are filled with a material having high 
insulating properties such as polyurethane foam. 
SUMMARY OF THE INVENTION 
Consequently, it is a primary object of the present invention to provide a 
corrugated panel from sheets of elastically deformable material and a 
method for forming the panels. 
It is another object of the present invention to provide synthetic plastic 
panels having a corrugated sheet sandwiched between a pair of 
substantially planar sheets, the voids between the ridges and furrows of 
the corrugated sheet being filled with an insulating material. 
It is a further object of the present invention to provide a method of 
forming a prestressed corrugated panel from an elastically deformable 
material by forming a first sheet into a curvilinear form relative to a 
second sheet and thereafter applying a loading to the first sheet in a 
direction toward the second sheet so as to convert the curvilinear form of 
the first sheet into a plurality of such curvilinear forms of smaller 
amplitude. 
Accordingly, the present invention provides a corrugated panel by a method 
including the steps of attaching to a first sheet of material the ends of 
a second sheet of elastically deformable material with the remainder of 
the second sheet spaced from the first sheet in curvilinear fashion and 
applying a compressive force to the second sheet in the direction of the 
first sheet until the second sheet is resiliently or elastically deformed 
so as to contact the first sheet at a number of locations between the 
ends. The force is applied in an amount and direction until the second 
sheet is corrugated into the desired number of curved ridges and furrows 
or the desired amplitude relative to the first sheet. The sheets are 
thereafter bonded together along the points of contact and a third sheet 
is disposed on the second sheet remote from the first sheet and also 
bonded thereto. The panels so formed may additionally be stiffened in the 
direction transverse to the ridges and/or the space between the first and 
third sheets may be filled with insulating material for various 
applications.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, and particularly to FIG. 1, a panel 10 
constructed in accordance with the principles of the present invention 
comprises first and second sheets 12, 14 of flexible elastically 
deformable material preferably a thin sheet of metal such as spring steel 
or a synthetic plastic such as polyethylene between which a third sheet 16 
of similar material is sandwiched. The third sheet 16 is corrugated or 
wave shaped and is secured to the first and second sheets at respective 
peaks or ridges of the waves while in a prestressed state resulting from 
the forces applied to the third sheet when forming the corrugated 
configuration as hereinafter described. The manner of forming the 
corrugation effects a curvilinear configuration throughout the third 
sheet, which configuration is substantially sinusoidal. 
The panel 10 may be utilized for various purposes such as for packaging, 
but since the corrugations can be of a large size, the panels have 
application for wall structures and partitions. Moreover, as illustrated 
in FIG. 2, especially where the sheets are of synthetic plastic, the voids 
between the waves of the third sheet and the respective first and second 
sheets may be filled with an insulating material such as polyurethane foam 
18 and the resulting product may be used as insulating wall panels in 
buildings. Because of the prestressed state of the third sheet the panels 
have substantial strength, but if desired they may be reenforced to 
provide a more rigid structure by the addition of stiffeners (not 
illustrated) between the first and second sheets extending substantially 
perpendicular to the plane of the waves formed, i.e., substantially 
parallel to the longitudinal axis of the panel. 
The method of forming the panel 10 comprises securing the first sheet 12 
substantially at its ends 20, 22 on a flat surface 23 or at least in a 
stretched disposition so that it forms a substantially planar surface. 
This may be accomplished by holding the ends by clamping means 24, 26. 
Thereafter the third sheet 16 is disposed on the first sheet and the ends 
thereof secured by clamping to the first sheet. The third sheet may be the 
same size as the first sheet in which case the third sheet is clamped to 
the first sheet at a disposition spaced from the ends of the first sheet 
or the third sheet can be longer than the first sheet and clamped at or 
adjacent the ends of the first sheet. In either case, the ends 28, 30 of 
the third sheet may be clamped by clamping means 32, 34. The length of the 
third sheet or the spacing of its ends 28, 30 relative to the ends of the 
first sheet is dependent upon the number of waves desired in the 
corrugation of the third sheet. This forms a curvilinear member from the 
third sheet in a single wave form of a substantially one-half sine wave as 
illustrated in FIG. 3. 
Thereafter a gradual compressive force F is applied equally upon the third 
sheet at the crest thereof and directed toward the first sheet. This can 
be applied by a platen or other substantially flat beam 36 or the like 
applied to the top of the third sheet in a planar direction toward the 
first sheet. Due to the resiliency of the third sheet this force initially 
results in the third sheet being deformed to form a two wave curvilinear 
configuration as illustrated in FIG. 4. Continued application of the 
compressive force to the third sheet results in an increasing number of 
wave forms, each of which is substantially of a sine configuration. The 
number of curves appears to be exponentially related to the force applied 
to the third sheet. 
When the desired number of curves are formed, or stated differently, when 
the desired amplitude of the crest of the third sheet relative to the 
first sheet is attained, the first and third sheets are bonded together at 
the contact point 38. The second sheet 14 may thereafter be disposed on 
the peaks of the third sheet remote from the first sheet and bonded 
thereto. Alternatively, the second sheet may be disposed on the third 
sheet prior to application of the compressive force intermediate the third 
sheet and the platen 36 and bonding of the third sheet to the first and 
second sheets may occur substantially simultaneously in the process. In 
either case when the platen is released the third sheet has been 
prestressed by an amount substantially equal to that of the compressive 
force and has large load bearing capacity. 
A modification of the process may be utilized to form curved bodies and 
cylindrical members by utilizing a complimentary shaped member against 
which the first sheet is disposed and a platen also of that shape can be 
compressed toward the first sheet. For example, as illustrated in FIG. 6, 
to form a cylindrical body a mandrel in the form of a central member 123 
having the size and shape of the inner diameter of the cylindrical body 
has the first sheet 112 fastened thereto. The third sheet 116, which in 
this case has a greater circumferencial size than the first sheet, can be 
attached to the first sheet at its ends and a platen 136 in the form of a 
number of sectors 137 may be disposed about the third sheet and the 
sectors forcibly drawn radially inwardly to corrugate the third sheet. The 
second sheet can thereafter be attached to the third sheet to form the 
corrugated cylindrical body. 
Numerous alterations of the structure herein disclosed will suggest 
themselves to those skilled in the art. However, it is to be understood 
that the present disclosure relates to the preferred embodiment of the 
invention which is for purposes of illustration only and not to be 
construed as a limitation of the invention. All such modifications which 
do not depart from the spirit of the invention are included within the 
scope of the appended claims.