Layers of fiberglass cloth, generally forming a circular mass, are prestressed by rotation during the curing of epoxy which surrounds and thereby couples together fibers and layers of the cloth

Weyler, G. M., Jr.

English

NASA Technical Reports Server

United States Patent [191 [111 4,190,626 
Wesler, Jr. [45] Feb. 26, 1980 
METHOD OF MANUFACTURE OF BONDED 
FIBER FLYWHEEL 
Inventor: 
Assignee: 
George M. Weyler, Jr., Huntsville, 
Ala. 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. NO.: 912,276 
Filed: Jun. 5,1978 
Int. Ci.2 .......................... B29D 3/00; GO5G 1/00 
U.S. Ci. ...................................... 264/229; 74/572; 
156/74; 156/161; 156/165; 156/285; 156/294; 
264/231; 264/258; 264/259; 264/311 
Field of Search ................. 156/74, 161, 163, 165, 
156/185, 189, 228,245,285,293, 160,294; 
264/310, 311,258,231,229,259; 74/572 
References Cited 
U.S. PATENT DOCUMENTS 
2,783,174 2/1957 Stephens .............................. 264/311 
2,785,442 3/1957 Boggs ................................... 264/311 
2,999,780 9/1961 
3,296,886 1/1967 
3,354,014 11/1967 
3,966,523 6/1976 
4,002,714 1/1977 
4,036,080 7/1977 
4,098,142 7/1978 
4,102,221 7/1978 
Perrault ................................ 264/3 11  
Reinhart ................................ 74/572 
Schick et al. ........................ 156/285 
Jtikabsen et al. ..................... 264/258 
Usui ...................................... 264/311 
Priedericy et al. .................... 156/74 
Weyler ................................... 74/572 
Hatch ..................................... 74/572 
OTHER PUBLICATIONS 
Post et al., “Flywheels”, Scientific American, pp. 17-23 
(12/73). 
Primaly Examiner-Jerome W. Massie 
Attorney, Agent, or Firm-George J. Porter; John R. 
Manning; L. D. Wofford, Jr. 
is71 ABSTRACT 
The method of manufacture of a fiberglass-epoxy 
flywheel wherein layers of fiberglass cloth, generally 
forming a circular mass, are pre-stressed by rotation 
during the curing of epoxy which surrounds and 
thereby couples together fibers and layers of the cloth. 
7 Claims, 9 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19810020625 2020-03-21T09:39:57+00:00Z
e Patent Feb. 26, 1980 Sheet 1 of 2 4,190,626 
atent Feb. 26, 1980 Sheet 2 of 2 4,190,626 
'4,1190,626 
1 2 
FIG. 4 is an exploded pictorial view, partially broken, 
illustrating the arrangement of flywheel components as 
contemplated by this invention. 
FIG. 5 is m edge view showing a layer of epoxy 
5 between two layers of fiberglass cloth. 
FIG. 6 is a pictorial view of a pre-coated glass fiber. 
FIG. 7 is a pictorial view illustrating a modified form 
of construction to that shown in FIG. I wherein fiber- 
glass fabric is in the form Of concentric 
FIG. 8 is a pictorial view illustrating still another: 
arrangement for fiberglass fabric wherein the fabric is 
simply wound about the axis of the flywheel. 
FIG. 9 is a half sectional view, partly schematic, of 
the overall arrangement of components employed in the 
method contemplated by this hvention. 
DETAILED DESCRIPYTION OF THE 
DRAWINGS 
METHOD OF MANUFACRJRE OF BONDED 
FIBER FLYWBEIEL 
ORIGIN OF THE INVENTION 
ne invention described herein was made by an em- 
ployee of the United States Government, and may be 
manufactured and used by or for the Government of the 
United States for governmental purposes without the 
payment of any royalties thereon or therefor. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the art of construction of 15 
flywheels, and particularly to a method of construction 
of a fiberglass-epoxy composition flywheel. 
2. General Description of the Prior Art 
It has been suggested that flywheels be constructed of 
relatively low mass, but high tensile strength materials, 20 technique employed, as outlined above, the mold 
and in accordance with this suggestion, flywheels have 
it is to be that in view of the construction 
in which a flywheel is being molded must have a constructed Of fibers bonded "gether 
from strength not greatly less than the flywheel itself. Ac- cordingly, and as a first step, illustrated in FIG. 1, a rim with an epoxy Or epoxy resin* However, tests of flywheels so constructed have been disappoint- 
ing, it appearing that structural failures occur at 25 manner on a mandral 12, mmdral B2 having a 
flywheel speeds less than speeds at which failure should 
occur considering the known tensile strength of the 
fibers of the fiberglass. The failures were manifested by 
progressive delamination (from center outward) of the 
flywheels tested. As a result, efforts have been under- 30 frictionally positioned within rim 
rations have appeased. Illustrations of certain of these tion) to the inner surface of rim 10. A fiberglass 
appeared in the December 1933 issue ofScienf$cAmer- beit N, either pre-coated with epoxy or otherwise satu- 
jCacan While Some in performance may 35 rated with epoxy, would be formed of a slightly smaller 
have been achieved by diameter than the h e r  surface of mold release 22 and 
tion, a far as is would be positioned just inside mold release 22. There- 
c o n s t r ~ k d  which will withstand operational forces on after, the whole mold assembly 26 as thus formed would 
the order Of the tende strength of rehforchlg fibers 4o be positioned in a cuing chamber similar or identical to 
employed, an obvious design objective. curing chamber 28, shown in FIG. 9. Thus, for example, 
in place of flywheel mold assembly 30, positioned for 
rotation within curing chamber 23, as will be later de- 
The aPPlicant has determined that the basic problem scribed, mold assembly 26 would be suspended between 
has been that the Previous methods of construction 45 bearing 32 and drive coupling 34. In this manner, shaft 
have dl involved the employment of either unstressed 20 would be driven through coupling 34 by motor 36. 
O r  non-uniformly stressed fibers, and that because of Motor 36 is adapted to drive mold assembly 26 at a 
one or both of these conditions, there is unevenness in selected speed to effect a centrifugal force which causes 
strength, with at least some re8ons of a flywheel being belt 26 to uni fody  go into tension and to uniformly 
reinforced to strengths substantially below the tensile 50 stress the fibers of belt 24 at a desired force level. Cur- 
strength of the fibers. To solve this problem, the appli- ing of epoxy around belt 24 is effected by the frictional 
cant has determined that the fibers should be pre- drag of air on mold assembly 26, and this is regulated by 
stressed, and that this be done by centrifugal force ap- air pressure input 38 and air vacuum connection M, 
plied during the curing and hardening of the epoxy enabling a desired air density to exist in chamber 28 and 
being reinforced by the fibers. 55 to thus frictionally engage mold assembly 26. Accord- 
ingly, by this arrangement, a fiberglass rim 42 is formed 
through the curing of epoxy around fiberglass belt 24 
while it is pre-stressed. 
Rim 42, thus constructed, may be employed directly 
in the forming of a flywheel or may be employed as a 
form for the construction of a stronger rim. In the latter 
case, the rim making process would be repeated using 
fiberglass rim 42 as a form as was rim 10. When this is 
done, curing of a rim form would be accomplished with 
progressively higher rotational speeds for increased 
pre-stressing, and thereby increased rim strength. When 
a series of rims are made in this fashion, it is, of course, 
necessary to properly size the rims so that the final rim 
of fiberglass and epoxy is formed in a conventiollal 
fom 
by round suppofiing plate 16 for supPofie- 
is cured, it 
by means such as an end plate 11, 
as shown, lo an 
ing rim fom p4. 
would be 
Next, as shown in FIG. 2, after rim 
way to improve the construction of fiberglass*poxy 
configu- 
d e  20, and with a mold release or mold release mate- 
rial 22 (shown thicker than normal for ease of illusera- and a number Of proposed 
the structural configura- 
flywheels have not yet been 
SUMMARY OF THE INVENTION 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 11 i s  a sectional view cut through the center of a 
round cylinder and showing the construction of a rim- 
shaped mold form employed in constructing a flywheel 60 
as contemplated by the method of this invention. 
FIG. 2 is a sectional view of one-half of a circular 
mold form employing the rim-shaped form shown in 
FIG. I. 
2, illustrating the construction of top and bottom mold 
forms employed in the construction of a flywheel as 
contemplated by this invention. 
FIG. 3 is a sectional view similar to the view of FIG. 65 
4,190,626 
3 
is of a desired sue for a desired dimensioned flywheel to 
be molded within it. 
Once a desired strength rim form is formed, e.g., rim 
form 42 in FIG. 4, identical top and bottom plate forms 
44 and 46 for cylindrical mold 30 may be formed gener- 
ally in the same pre-stressed manner by positioning 
fiberglass cloth-epoxy matrix elements 48 within rim 42, 
rim 42 then being attached (frictionally) to axle 50 by 
bottom mold release plate 52, formed of a suitably 
strong material, such as steel. Matrix elements are sepa- 
rated or engaged by additional mold release plates 54, 
and as illustrated, the two plate forms, which are used as 
top and bottom plate forms 44 and 46 for flywheel mold 
30, are formed at one time. If desired, the entire cavity 
56 within rim 42 may be filled with fiberglass-epoxy 
matrix elements 48, and thus bottom and top plates for 
several flywheel molds may be made at one time. 
As in the case of the construction of rim 42, mold 
assembly 58 would be positioned within chamber 28 
(FIG. 9) and rotated by motor 36. This pre-stresses the 
fibers of the fiberglass of matrix elements 48 and epoxy 
of the matrix elements is hardened by frictional heating 
on rim 42 and bottom and top positioned mold release 
plates 52 and 54. In order to obtain sufficient strength 
for release plates, they may be made of fiberglass and in 
progressive steps as in the case of the rims. 
FIG. 4 illustrates the discrete elements of a flywheel 
60 and case 61 where flywheel 60 is formed utilizing a 
plurality of flat circular sheets 63 of fiberglass cloth 
which have been pierced by axle 64. Top and bottom 
plate form or form members 44 and 46, together with 
rim form 42, as case 61, enclose flywheel 60, the plate 
and rim forms being secured together by means not 
shown, such as by frictionally fitting the plate forms in 
a rim form. Epoxy 62 is applied to saturate sheets 63 
(FIG. 5), being either applied prior to the closure of 
case 61 around flywheel 60 (as from precoated fibers) 
or through an opening or openings 66 formed in top 
plate form 44, enabling epoxy to be applied after the 
flywheel is enclosed. Alternately, some epoxy would be 
applied to fiberglass sheets 63 prior to encasing it, and 
additional epoxy would be applied through opening or 
openings 66 after the flywheel is encased. Various addi- 
tional openings and cavities may be employed as needed 
to fill all voids in case 61, or alternately, some voids may 
be filled subsequent to the curing in chamber 28 and 
thereafter the added epoxy cured. In some instances, the 
employment of pre-coated fibers 67 (FIG. 6) formed of 
an inner strand fiber 59 and outer coating of epoxy 65 
may make unnecessary any separate handling of epoxy. 
After case 61 is filled with a desired quantity of ep- 
oxy, case 61 is placed within chamber 30 as shown in 
FIG. 9 and axle 64 driven by motor 36 to rotate case 61 
at a desired speed to appropriately pre-stress the fibers 
of the fiberglass cloth. As described above, a desired air 
pressure, above or below atmospheric pressure, would 
be effected by means of a vacuum connection 38 and 
pressure connection 40. This thus provides a selected 
density of air mass in chamber 28 and thus a selected 
degree of frictional force between this air mass and case 
61 to provide a desired curing rate. Curing chamber 28 
is totally enclosed by walls 71 and is shock mounted on 
springs 73 and 74. At least one wall section is removable 
or has an opening (not shown) by which molds are 
loaded into and removed from chamber 28. 
It has been previously determined that radial stresses 
are minimum at the periphery and center of io flywheel 
and highest mid-way between the center and periphery 
4 
and that circumferential stresses are highest at the cen- 
ter. In keeping with these findings, the curing process 
would be sequenced wherein initially curing would be 
effected in the outer peripheral region utilizing a less 
5 than maximum rotational speed (at peripheral speeds as 
low as 300 feet per minute) for curing, but with a rela- 
tively high air pressure whereby outer peripheral cur- 
ing would occur fwst because of this combination. This 
then would, in effect, provide a cured and thus rein- 
10 forced case hardening for the flywheel, and thereafter 
the speed of rotation of it might be significantly in- 
creased (to peripheral speeds as high as 60,OOO feet per 
minute for some glass fibers) to increase the stressing of 
fibers to a greater extent in the mid region and inner 
15 region of the flywheel as required. At the same time, the 
gas pressure in chamber 28 would be proportionately 
decreased. While in the two-step procedure of curing 
there would be a difference in stressing between the 
outer peripheral region and region inner to it, there 
20 would be uniformity of stressing at like radial distances 
from the center of the flywheel. In addition to obtaining 
a desired stressing pattern in this manner, there may be 
instances where the outer peripheral region of a 
flywheel may be cured in this fashion without the re- 
25 quirement of an outer rim as a mold, and thereafter the 
cured outer peripheral region serving as a mold for the 
inner regions of the flywheel as required by the higher 
speeds during its curing. 
After the epoxy applied to fiberglass sheets 63 has 
30 hardened, case 61 is removed. A flywheel 60, thus con- 
structed, is removed after curing, and having been pre- 
stressed prior to and during curing, will provide an 
overall strength commensurate with the tensile strength 
of the fibers of the fiberglass cloth. 
The actual arrangement of fiberglass cloth may be 
varied as desired and still appropriately achieve a se- 
lected degree of prestressing of fibers. Thus, FIG. 7 
illustrates a flywheel wherein instead of flat sheets of 
fiberglass, the fiberglass is formed in concentric belts 68 
40 about axle 69. As still another arrangement, FIG. 8 
illustrates the fiberglass cloth being in the form of a strip 
70 wound around axle 72. 
While the term epoxy is used to describe a bonding 
agent commonly employed with fiberglass, it is to be 
45 appreciated that other suitable bonding materials may 
be employed. 
Equally significant, because of the nature of the pre- 
stressing technique employed, the fibers tend to be 
stressed naturally and as would the finished product be 
50 stressed in operation. Accordingly, the fibers are pre- 
stressed as needed for maximum reinforcement 
strength. 
Having thus described my invention, what is claimed 
is: 
I. The method of constructing a flywheel comprising: 
forming a desired dimensioned, round, cylindrically- 
shaped, matrix of layered, glass fiber cloth within a 
cylindrical case, and there being an uncured fiber- 
glass bonding material covering the fibers of the 
cloth and between layers of cloth and filling the 
case; 
placing a vertically positioned axle concentrically 
through said round matrix; 
while said bonding material is still in an uncured state, 
placing said case within a curing chamber with said 
axle rotably supported; 
rotably driving said axle, whereby fibers of said ma- 
trix are stressed by centrifugal force; and 
35 
55 
60 
65 
4,190,626 
5 
while said matrix is so rotably driven, applying a 
desired degree of heat to said matrix and effecting 
the curing of said bond material with fibers of said 
matrix in a stressed state, and fibers of said matrix 
becoming bonded together and to said axle. 
2. The method as set forth in claim 1 wherein said 
layers of said matrix are formed of generally flat, round 
sheets of fiberglass cloth lying generally normal to and 
pierced by said axle. 
3. The method as set forth in claim 1 wherein said 
layers are formed of concentrically formed and posi- 
tioned belts of fiberglass cloth arranged concentrically 
about said axle. 
10 
15 
20 
25 
30 
35 
40 
45 
6 
4. The method as set forth in claim 1 wherein said 
case is formed of pie-stressed fiberglass impregnated 
with a bonding material. 
5. The method as set forth in claim 1 wherein said 
matrix is positioned within a chamber, and gas pressure 
within said chamber is selectively regulated to provide 
a,selected degree of frictional force between gas and 
said matrix, and thereby selectively regulating the 
amount of heat applied to said matrix as it is rotated. 
6. The method as set forth in claim 5 wherein initially 
the curing is effected, utilizing a combination of a se- 
lected speed and gas pressure, and thereafter a combina- 
tion of higher speed and lower gas pressure. 
7. The method as set forth in claim 1 wherein fibers of 
the fiberglass cloth are pre-coated with a bonding mate- 
rial before said cloth is formed into said matrix. * * * * *  
, 
50 
55 
60 
65 


Method of manufacture of bonded fiber flywheel

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