Note: Descriptions are shown in the official language in which they were submitted.
05~
FIBER--REINFORCED COMPOSITE WEIEEL
CONS TRUCT I ON
_
- The present invention is generally direeted
to vehiele wheels and methods for fabrieation thereof,
and more partieularly to methods for fabrieating
fiber-reinforeed eomposite wheels and the resulting
product,
As utilized herein, ths terms "eomposite
wheel" and "fiber-reinforeed eomposite wheel" refer
to a wheel eonstruetion of fiber-reinforced plastie
resin.
A general ob~eet of the present invention
is to provide a vehiele wheel whieh has the strength
and durability of eonventional steel wheels but is
lighter in weight and yet eeonomieal to manufacture.
More speeifie objects of the .invention are
to provide a method of construeting a fiber--rei.nforced
composite wheel in which rein~orcing fibers are dis-
posed and seleetively oriented in the wheel rim and
dise portions for enhaneed durability and strength,
and/or whieh is more eeonomieal to carry Ollt than are
the reinforced plastie wheel construction techniques
proposed in the prior art. A further object of the
invention is to provide an apparatus for constructing
a wheel in accordanee with such method. Another object
of the invention is to provide a fiber-reinforced com-
posite wheel constructed in aecordance with such method.
.1
11~40S4
A further object o~ the invention is to provide a method
of molding fiber-reinforced composite wheels which minimizes flow
and knit line formation during the molding process, particularlv
in the rim flange area and around wheel disc discontinuities such
as bolt and hand holes.
According to the present invention there is provided a
wheel consisting essentially of fiber-reinforced plastic resin
and comprisin~ a rim portion and an inperforate disc portion in-
tegral with said rim portion and including a plurality of pockets
homogeneously integral with the remainder of said disc portion
and adapted to be removed from said disc portion so as to leave
openin~s in said disc portion which lend a spoked appearance to
said disc portion and to said wheel as a whole.
The invention, together with additional objects, fea-
tures and advantages thereof, will be best understood from the
following description, the appended claims and the accompanying
drawings in which:
FIG. 1 is a schematic illustration of a process for pro-
viding one type of raw fiber-reinforced plastic resin sheet mold-
ing compound utilized in carrying out various embodiments of the
present invention;
FIGS. 2 to 4 collectively illustrate presently prefer-
red method steps for providing a fi.ber-reinforced composite
wheel in accordance with the invention;
FIG. 5 is a fragmentary front elevational view of one
wheel embodiment as molded in accordance with the steps of FIGS .
2-4;
FIGS. 6 and 7 are fragmentary side section and rear
views of the wheel in FIG. 5 taken along the respective section
lines 6-6 in FIG. 5 and 7-7 in FIG. 6;
~ FIG. 8 is a fragmentary front elevational view of a
: finished wheel in accordance with one embodiment of the invention;
- : . .
1154(~54
FIGS. ~ and 10 are fragmentary side section and rear
views of the wheel in FIG. 8 taken along the respective lines
9-9 in ~IG. 8 and 10-10 in FIG. 9;
, 10
'; 20
. 3
~ '
.
- 2a
,
llSg~054
FIGS. 11-17 are schematic drawings illustrating
various constructions of the xim charge for molding
fiber~reinforced composite wheels in accordance with
the invention;
FIG. 18 is a schematic illustration similar
to that of FIG. 1 illustrating another process for
providing sheet molding compound for use in carrying
out various embodiments of the invention;
FIG. 19 is a fragmentary sectional view similar
to a portion of FIG. 7 and illustrating a modification
to the wheel of FIGS. 5-10; and
FIGS. 20-23 illustrate another embodiment of
a wheel in accordance with the invention and respectively
substantially correspond to FIGS. 5, 6, 8 and 9 pre-
- 15 viously described.
In general,- the present invention contemplates
a fiber-reinforced molded resin wheel and method of
construction wherein the wheel rim and disc portions
are formed from respective separate mold charges of
sheet molding compound. The separately formed charges
are molded into an integral composite rim and disc
structure of essentially homogeneous resin reinforced
by the fibers. The disc charge preferably comprises
a stack of precut sheet sectio~ns. The reinforcing fibers
in the disc charge and in the final disc wheel portion
are in substantially random orientation essentially
in planes perpendicular to the wheel axis with each
such plane corresponding to a layer of reinforcing
fibers in the starting sections of sheet molding compound.
The rim charge preferably comprises one or
more lengths of precut sheet molding compound coiled
li540S~
to form a spiral or hoop having at least one layer.
The sheet layers in the rim charge hoop are referred
to herein as spiral plies. Preferably, the reinforcing
fibers in the rim charge hoop and in the final rim
wheel portion include at least first fibers oriented
substantially randomly of the rim circumference and
second directional fibers in one or more selected
orientations with respect to the wheel axis and cir-
cumference. In various specific emboaiments to be
described, the directional fibers are oriented in-
parallel axially or circumferentially of the wheel
axis. In other embodiments, the directional fibers
are in a double helical array forming an X-like pattern
transverse to the wheel rim.
~ 15 By way of background, a process line for pro-
viding one type of raw fiber-reinforced plastic resin
sheet molding compound or stock utilized in carrying out
the invention is illustrated in FIG. 1. A thermosetting
resin paste 10 is metered as by a doctor blade or dam 12
onto a continuous sheet 14 of polyethylene film as the
latter is drawn onto an endless belt conveyor 16. Paste
10 may include an unsaturated polyester, vinyl ester or
epoxy resin, a thickener such as a Group II oxide or
hydroxide, catalysts such as organic peroxides or
hardeners, inert fillers such as CaCO3 or clay, and a
mold release agent such as zinc stearate. At a first
stage 18, continuous fiber filaments or strands 20 are
pulled over a roller 22 and chopped by a multiple knife
roll arbor 23 to form fibers 24 ~hich fall by gravity
onto the paste layer 25 in a substantially random pattern
essentially in the plane of the resin layer surface. The
115q~VS~
random fiber orientation accomplished at process stage
18 is illustrated in plan view schematically at 26.
Preferably, the strands 20 are drawn from the inside
of a fiber ball or roll (not shown) to promote random
twisting of the fibers 24 in the resin layer. Reinforcing
fibers 24 may be glass, aramid, carbon or graphite.
Glass fibers, specifically E and S type glass fibers,
are preferred.
At a second process stage 28, continuous fiber
filaments 30 are laid upon resin layer 25 in a parallel
equally spaced uniairectional pattern over the random
chopped fibers 24 in a direction parallel to the direction
of travel of conveyor 18. The fiber pattern at stage
28 is illustrated in plan view at 32. To prevent twisting
of continuous fibers 30 in the sheet molding compound,
the fiber strands are drawn from the outside of the roll
34. A second layer 35 of paste 36 identical to paste
10 is metered by a doctor blade dam 38 onto a second
polyethylene film 40 and directed by rollers 42 onto
the traveling film layer 25 to form a sandwich in which
the continuous fiber strands 30 and the chopped fibers
27 are disposed essentially in the middle between layers
25,35 of plastic resin sheet material. At a third process
stage 44, radially protruding blades 46 carried by an
arbor 48 pierce upper film layer 35 and cut the continuous
stranas 30 to forrn the discontinuous parallel and sub-
stantially unidirectional fiber pattern illustrated in
plan at 50. The bl~ades 46 are disposed around the sur~ace
- of arbor 48 so as to pierce the individual strands 30 at
selected intervals, and thereby form a staggered array
li~4()5~
of discontinuous parallel and substantially unidirectional
fiber strands 52 of a desired preselected length. The
sandwiched sheet is then compacted as by rollers 54
and rolled into a roll 56 of continuous sandwich sheet
material molding stock. The resin stock should be
allowed to thicken by maturation to a molding viscosity
in the range of 5,000 to 60,000 Pa-sec. It will be
appreciated that the directional fibers are illustrated
at 30,52 in FIG. 1 as being thicker than the random
fibers 24 for purposes of contrast only, the fibers
normally being of identical thickness and of the same
type in actual practice,
~54l~54
As an alternative and presently preferred
process mode, the step of piercing film layer 35 and
cutting strands 30 can ke performed after formation of
the roll 56 of continuous sandwich sheet material.
In this case, arbor 48 is not present in the process
apparatus as shown in FIG. 1, but rather is disposed
in a separate machine (not shown~. The molding stock
is fed beneath the arbor to pierce film 40 and cut
strands 30 after the molding stock has been allowed
to thicken or maturate, i.e., after sufficient time has
elapsed for the polyester resin and Group II oxide or
hydroxiae to enter into a hydroxyl-carboxyl ionic
reaction and for the reaction to progress until the
paste layer 35 reaches the aforementioned viscosity of
5,000 to 60,000 Pa-sec. Piercing and cutting of
strands 30 with the sandwich sheet material molding
stock in this higher viscosity condition insures a
minimum of resin squeeze-out or displacement through
film 40.
i 20 It will be evident that the process illustrated
schematically in FIG. 1 is adaptable for making sheet
molding stock with only random fiber orientation or with
only continuous fiber orientation, for example, rather
than the multi-laminar directional-random orientation
illustrated at 50. For example, process stages 28 and 44
may be deactivated such that the rolled sheet stock will
contain only random chopped fibers 24 in the configuration
illustrated at 26~ Similarly, process stages 18 and 44
may be deactivated such that the ultimate rolled stock
will include only continuous parallel strands 30 in the
configuration illustratea at 32. It has kcen found to be
~- ~15D~S4
advantageous in some instances to cover compacting rollers
54 with an endless belt or the like to help prevent
reorientation or twisting of the fiber strands by
serrations on the roller surfaces. For the fabrication
of wheels, the ranaom fiber configuration illllstrated at
26 and the random-directional configuration illustrated
at 50 possess particular advantages. The random-
continuous fiber configuration illustrated at 32 also
has been utilized in wheel fabrication in accordance
with the present invention, although it is not presently
preferred.
For a discussion of manufacture of sheet
molding compound of the type hereinafter described,
reference may be had to U. S. Patent No. 4,167,130;
"SMC and RIM: Calling up Reinforcements", Automotive
Enqineerinq, Vol. 86, No. 3, March 1978, pages 27-33;
"Structural SMC: Material, Process and Performance
Review", owens-corning Fiberglas Corp., Pub. 5-TM-8364,
1978. Glass fiber reinforcements, including E-glass
and S-glass herein preferred, are discussed in "Evaluating
Glass-Fiber Reinforcements", Plast cs_Co~oundinq, July/
August 1978, pages 14-25. The thickening or maturation
process is discussed more fully in Deis et al, "Magnesium
Oxide and H~droxide for SMC", Modern Plastics, November
1974, pages 94-98; and Lawonn et al, "Fast Maturing of
Unsaturated Polyester Resin Prepregs", German Plastics,
translated from Kunstatoffe, Vol. 65, October 1975,
pages 678_680.
llS~054
A process for molding fiber-reinforced composite
wheels in accordance with the invention is illustrated
in FIGSo 2-4. Referring first to FIG. 2, a continuous
strip of fiber-reinforced plastic resin molding stock
is first coiled to form a rim mold charge hoop 60 of
multiple spiral plies or layers. The molding sheet
stock may be cut from roll 56 (FIG~ 1) and coilea twith
polyethylene films 14,20 removed). Alternatively, the
sheet stock may be cut from the roll 206 in FIG~ 18
manufactured in a manner to be described in connection
therewith.
The particular rim charge embodiment illustrated
at 60 in FIG. 2 comprises three spiral plies coiled
from a continuous length of strip stock and having lapped
ends 61. In actual practice it has been found that sheet
molding compound is not always presently commercially
available in lengths sufficient to form hoop 60 from a
continuous length of strip stock~ In such instances it
is necessary to "dovetail" the ends of shorter sheet
lengths. It is anticipated that sheet strips of desired
length will be made available for high volur~ production
of wheels. It should also be noted that some embodiments
to be discussed include different types of sheet molding
compound, i.e~ having d:iffering fiber orientations,
necessitating multiple lengths of strip stocX. In
j every case, the number of spiral plies required depenas
upon the number of different types of sheet molding
compound needed and the thickness of each sheet. Hoop
60 in FIG. 2 is for illustrative purposes only.
f 1-15~05~
Hoop 60 may be formed by coiling about a rotatable
mandrel tnot shown) to a diameter approximating the
ultimate desired median diameter of the wheel rim. Where
the wheel rim is of a type which includes bead retaining
flanges at one or both of the opposite rim edges, it has
been found to be advantageous to flare outwardly the
axial hoop edges prior to placing the hoop in a
wheel mold. Accordingly, the hoop 60 is preferably
placed on a rotatable die 62 having an outer surface
64 which cooperates with a rotatable roll follower 66
to give a slight outward flare to the hoop eages 68 to
thus provide a first preform 69. The flared rim charge
hoop preform 69 is then placed between two radially
outwardly opened rim mold half sections 72 and 74 such
~ 15 that the iower flared end 68 rests upon the upper face
of a lower disc mold section 84. Mold sections 72,74
are connected ~y push rods 73,75 to hydraulic cylinders
77,79 (FIG. 3) and are slidable inwardly on guideways
76,78. Cylinders 77,79 are operatively coupled to a
suitable hydraulic control 85. The radially inner or
forming surfaces 81 and 83 of mold sections 72 and 74
respectively are preferably contoured to form a rim
well, bead retaining flanges and suitable tire bead
seats on the outer rim surface. After flared charge
hoop preform 69 is placed on disc mold section 84 between
rim mold sections 72,74, the rim mold sections are closed
and the preform 69 is captured therein in slight radial
compression. In a continuous production process, mold
sections 72,74 are maintained at an elevated temperature
in the range of about 270F (132C) to about 320F
(160C).
10 .
1~5~0S~
Referring next to FIG. 3, a plurality of
flat sheet sections 80 of fiber-reinforced ~plastic)
sheet molding compound, suitably cut from a roll of
stock similar to roll stock 56 after stripping films
14 and 40 therefrom,
~ .
. ' .
11 .
1154054
are then stacked one upon another to form a disc mold
charge. The roll of stock preferred for use in making
these disc charge sections 80 is made in the manner
described in connection with FIG. 1, except that continuous
fibers 30 are omitted, as is the step of piercing and
cutting thereof by arbor 48. This disc charge stack is
then placed in the mold on the forming surface 82 of
a lower disc mold section 84 coaxially within the rim
mold charge 69. As shown in FIG. 3, disc charge stack
80 is supported in the mold by the horns 90 extending
upwardly therefrom to cooperate with corresponding
cavities 100 in the upper disc mold section 94 to form
pockets for the disc hand holes, as will be described
hereinafter. Preferably, the disc charge sections 80
are each substantially square and are stacked with
section corners circumferentially staggered in a rosette
pattern so as to obtain maximum coverage of the disc mold
face 82. This particular configuration ha~ been found
.to result..in minimized material flow and re5ulting knit
lines in the final aiSc. Mold parts 84, 94 and 120,
(in addition mold parts 72,74) are continuously maintained
. at an elevated temperature in the aforementioned range
¦ of about 270F (132C) to about 320F (160C) during
and between the molding sequence or cycle of operation.
Where the eventual wheel is of a type which
` is to include a hub extending axially from the main portion
of the disc, a number of smaller square hub char~e sheet
sections 86 are disposed between the disc stack 80 and
_ mold face 82 over the cavity 88 formed in the mold face.
Cavity 88 cooperates with a horn 98 mounted on the opposing
surface g9 of upper disc mold section 94 to form a hub
11 54054
pocket in the wheel disc. Sections 86 help displace
air that may otherwise become entrapped in cavity 88
upon closure of the disc mold sections. The outwardly
directed radial surface 101 and 103 of disc mold sections
84 and 94 respectively cooperate with surfaces 81,83
to aefine in a mold cavity contour the rim well, flange
and bead seat rim portions of generally uniform thickness.
It should be noted that the number of plies in disc
charges 80,86 and rim charge 69 in FIG. 3 depends upon
the desired wheel thickness and upon sheet stock density.
As indicated above, it is desirable to lay disc charge
sections 80 in a pattern which substantially covers the
mold face and thereby approximates the eventual disc
geometry to reduce material flow auring the ensuing
- 15 compression molding operation. Given any particular
density of sheet molding compound and the desired wheel
.~
size, the number of plies, etc. may readily be determined
i~ by persons skilled in the art to fill the mold volume
ii with minimal overflow. It is also envisioned that disc
~ .
J 20 mold charges other than the presently preferred rosette
stack-up may be used to form discs of other configurations,
such as a square charge to form a four-spoke disc.
As a next step in the compression molding
operation bridging FIGS. 3 and 4, lower disc mold
!~ 25 section 84 is displaced upwardly from its rest position
on lower stops 92, and upper mold disc section 94 is
simultaneously displaced downwardly by hydraulic control
.~ .
; 85 until the disc mold sections are in axially opposed
;i initial forming positions within the closed rim mold 72,
74, which are very close to the fully closed and final
compression molding positions illustrated in FIG. 4,
~ , .
:
.. . : 1 ~
(^ 1~54054
Preferabiy, motion of mold sections ~4,94 is controlled
such that the mold sections move together and reach
their final positions (FIG. 4) substantially simultaneously.
Since upper mold section 94 must be initially positioned
away from mold sections 72,74 and 84 to permit placement
of the mold charges, this necessitates a greater controlled
rate of travel for the upper mold section. Mold section
84 is guided by a surrounding sleeve 120 having an axial
stop shoulder 122 thereon to cooperate with a lip 126
:~,
on mold section 84 to limit upward motion of the disc
section, and is connected by a rod 124 to a suitable
hydraulic cylinder (not shown). A sleeve skirt 96
axially projecting from the radially outer edge of upper
mold 94 captures rim mold sections 72,74 as mold 94
is lowered thereby to clamp the rim mold sections and
simultaneously guide disc mold section 94 into position.
: ,~
Horn 98 on upper mold surface 99 initially
forms the hub charge 86 into opposing cavity 88 in lower
mold section 84. At the same time, horns 90 initially form
the disc charge 80 into corresponding recesses 100 in
` the upper mold surface so as to mold initially a circular
array of pockets 102 (FIGS. 4-7) offset from the wheel
disc 104 but integrally connected thereto by the narrow
circumferentially continuous bridging section 106 around
each pocket. The closed mold is then subjected to high
;~ pressure on the order of 1500 psi (10.3 megapascals)
~ at an elevated temperature of 132C to 160C for on the
;;~ order of 5 minutes to form by compression molding an
integral rim and disc structure of essentially homogeneous
resin reinforced by the dispersed fibers. The mold sections
. ' , .
,.
: . . .
,
~` 1154054
are then opened in an order reverse to that previously
described and the molded wheel 116 (FIGS. 5-7) is
removed for finishing.
It may be noted at this time that a particular
advantage of the molding process thus far described is
thought to lie in the provision of a movable lower disc
mold section, particularly in combination with the step
of flaring the ends of the rim charge to form the open
flanges 68 as previously described. As will be appreciated
from FIGS. 2-4, the slightly retracted position of lower
disc mold section 84 at the time when flanged rim charge
69 is placed in the mold permits the lower flanged portion
of the rim charge which will ultimately become the out-
board rim flange 122 (FIG. 6) to be located closely
adjacent the flange-forming surfaces of rim mold sections
72,74 when the latter are closed. This, in turn, means
that the mold material will not be "pushed" into the
flange area as the disc mold sections are closed. This
feature results in a more uniform distribution of reinforcing
fibers in the flange than would be the case if ~old section
84 were fixed, This is particularly important when
directional ~ibers transverse to the wheel rim are utilized,
a~ in FIGS. 13-17 to be discussed. In molds for production
wheels, rim molds possessing more than two mold sections
may be utilized without departing fro~l the invention.
The wheel 116 as molded includes a rim section
120 with integral bead retaining flanges 122,123 and a
center drop well 124 ~FIG. 6) coupled to flanges 122 by
the bead seats 126,127. As best seen in FIG. 6, drop well
124 is offset or asymmetric with respect to the rim center-
line, which is to say that drop well 124 is located nearer
1-5.
: .
,--` llS~05~
outer flange 122 than inner flange 123 tllouterll and
"inner" being taken with reference to the preferred
orientation of the finished wheel mounted on a vehicle).
The disc portion of wheel 116, which is generally
indicated at 130, is coupled to rim portion 120 at
the lower outer edge of drop well 124. The outboar~
face of disc 130, best seen in FIGS. 5 and 6, includes
a symmetrical array of five circumferentially spaced
radial ribs 132 alternating with pockets 102 previously
described. Each rib 132 extends wideningly from adjacent
drop well 124 to flare into a central outwardly cupped
hub shell 134. Ribs 132 not only strengthen the wheel,
but also lend an ornamental spoked configuration thereto.
; The outer surface of shell 134 includes an axially ex-
tending channel 138 in radial alignment with the center
of each pocket 102.
Ribs 132 are hollow, which is to say that a
pocket 136 extends into each rib 132 at the inboard face
of the wheel disc, as best seen in FIG. 7. Each rib
pocket 136 i5 straddled by a pair of strengthening ribs
140 tFIG. 7) which flare into the base of drop well 124.
Similarly, each hand hole 110 is surrounded by a continuous
strengthening ledge or bead 141 best seen in FIG. 7. The
radially outer portion of each ledge 141 is separated
from rim well 124 by the pockets 144 (FIGS. 6 and 7).
Between ribs 132 and openings 110, disc portion 130
tapers narrowingly from a thickened re~on 146 (FIG. 6)
aajacent shell 134.
During the finishing operation, flash is removed
-
from the edges of bead retainlng flanges 122,123. The
, ~
115405~
bottom and side edges of each pocket 102 are removed
flush with ledge 141 along the phantom line 108 in
FIG. 6 so as to form a circular array of openings or
hand holes 110 (FIGS. 8-10) in the wheel disc to cooperate
with ribs 132 in lending a spoked configuration to the
wheel as a whole. A hub center hole 114 is bored in
the base of shell 134. A circular array of mounting
holes 112 is drilled or otherwise formed in the thicker
portion 146 of wheel disc 130 coaxially with wheel pilot
surface 113 (FIGS. 6 and 9), one bolt hole 112 in out-
wardly spaced radial alignment with each channel 138
in the hub shell outer surface. An Opening 150 is
drilled in rim 120 for an inflation valve. It has been
found that molding of an imperforate disc as previously
described, although requiring finishing operations on
the molded wheel for removal of the pockets 102 and
drilling of the bolt holes 112, etc., reduces knit line
formation in the molded product and thus enhances
strength and reliability of the finished wheel 114
during operation. The wheel as molded and as finished
is illustrated at 116 (FIGS. 5-7) and 117 (FIGS. 8-10)
respectively~
In construction of wheels in accordance with
the invention to the extent thus far described and
utilizing sheet molding compound per FIG. 1, glass
fiber-to-resin weight ratios from about 45% up to about
75% have been tested, with a fiber/resin weight ratio
of 50/50 being preferred. Fiber/resin ratios below 30%
are considered to contain too little fiber reinforce~ent
ror manufacture of automobile road wheels, while ratios
17.
115405~
above 75/~ exceed the "wetting limit" of the glass fiber
and thereby possess both reduced moldability and poor
resin-glass adhesion. The paste is of about 50% resin
and about 50% filler with small amounts of catalysts, etc.
as previously described. In the construction of wheels
in accordance with one embodiment of the invention, the
random fiber pattern 25 (FIG. 1) and the directional/
random pattern 50 are particularly advantageous in the
disc charge and in the rim charge respectively. Pre-
ferably, although not necessary, the rim charge is
coiled such that the directional fibers lie radially
inward of the random fiber layer in each charge ply.
Random fibers 24 may be from 1.25 cm to 10 cm in length,
all fibers having the same length, preferably 5 cm.
Directional fibers 52 may be between 5 cm and 30 cm in
length, with a 20 cm length being preferred. The usable
range of fiber lengths, as fiber/weight ratios, is
determined by strength and moldability. Using a 50%
glass fiber weight ratio as is preferred, directional/
random fiber weight ratios in the range of 5/45 to 45/5
are envisioned, with a range of 20/30 to 30/20 being
preferred.
In one wheel constructed in accordance with
the invention, a disc charge consisted of multiple plies
of 50% ranaom fibers by weight, with the random fibers
24 being about 2.5 cm in length and being oriented
essentially in planes perpendicular to the mold axis.
~, The rim charge consisted of a hoop of airectional/random
sheet molaing compound, again 50% fibers by weight.
The rim charge hoop was coiled with the directional
fibers 52 disposed radially inwardly of the random fibers
18.
59t()S4
24 in each ply and oriented in the circumferential
direction. The random fibers 24 were thus disposed
essentially in a spiral pattern of revolution about the
mold axis. Directional fibers 52 were 20 cm in length
and random fibers 24 were 5 cm in length at a directional/
random weight ratio of 30/20.
In the following material specification for
both the disc and rim charge of the aforementioned example
of a wheel in accordance with the invention (see con-
struction B3 in Table III for test results), "SMC" isa trade designation for sheet molding compound. The
particular compounds utilized were manufactured by
Owens-Corning Fiberglas. D refers to directional fikers
of the type illustrated at 52 in FIG. 1, and
.
19 .
li54()S~
R refers to random fibers 24. Thus, SMC-R50 means sheet
molding compound containing 50% random fibers by weight.
(See the above-referenced Automotive Enqineeri~ publication.)
TABLE I
SMC - Sheet Moldinq Compound For Disc Char~
Type SMC-R50
Product Width 46 cm (69 cm, 92 cm or 115 cm
optional)
Product Weight 4.6 kg/m
Product Density 1.9 g/cm3
Package 32 kg minimum - 180 kg maximum/roll
Glass % 50% + 1
Glass Type OCF 433/AB/47 (47 is yield in m/kg)
Glass Source Owens/Corning Fiberglas
~15 Glass Length 2.54 cm
Paste Formulation:
Parts by
Weiqht Source
Resin DERAKANE 790 100 Dow Chemical Co.
Catalyst t~butyl perbenzoate 1% BOR* U.S. Peroxygen Co
Filler Camel Wite (CaCO3) 100 H. T. Campbell &
Sons
Mold release Synpron ABG (Zinc Stearate) 3% Synthetic Product
BOR*
~25 Thickener 40% MAGLITE D/60% DERAKANE
470-45 ~ 4.7%
BOR* MERCK Co/Dow
Chemical
20.
lS'~(lS~`~
Paste Viscosity: '
HBT Brookfield Viscometer, T-F spindle @ 29C
5 days 50,000 Pa-sec
+ Magnesium oxide slurry
* BOR Based on resin
. . ,
Material Specification
Resin
I Traae name DERAKANE 790
I Source Dow Chemical Co.
I 10 Chemical Name Vinyl ester
Non-volatiles 45%
Monomer Styrene
Acid Number 25
: Viscosity 1.. 1 Pa-sec.
Density (gm/ml @
25C)- 1.03
SPI Gel time ~
~j 82C 30 minutes
¦ Time to peak 32 minutes
Peak exotherm 188C
SMC_- Sheet Moldinq Com~ound For Rim Ch_rg~
Type SMC-D/R
Product Width . 38 cm (76 cm or 115 cm optional)
Product Weight 2.88-3.16 kg/m2
Package 32 kg - 13S kg/roll
Glass Length D - 20 cm; R - 5 cm
Glass % D - 30%; R - 20%
Glass Type OCF 433/AB/47 (47 yield in m~kg)
Source ~ens/Corning Fiberglas
Color CM-1003 Black (variable) Plasticolor~
: Added to Paste Formulation
Paste formulation and paste viscosity (same as for S~IC-R50
~!
llS40S~
A number of different wheel constructions
have been constructed and tested to the following 1978
orlginal equipment fatigue test specifications for
intern~diate size car body styled wheels:
S TABLE II
Dynamic Cornerinq Fatique
Disc Fatigue Blo ~ 30,000 cycles
No failure below 20,000 cycles.
- Bending Moment 2263 N m
SAE J 328a requires 18,000 cycles.
Dynamic Radial Fatique
Rim Fatigue Blo - 1,000,000 cycles
No failure below 800,000 cycles.
Radial Load 12,910 N
Test Tire Pressure 448 kPa
SAE J 328a requires 400,000 cyclec
All of the tested wheels (with the exception of one con-
struction D wheel) embodied SMC-R50 material in the
disc charge pattern as previously described, and all
of the wheels as finished were identi.cal to that shown
to scale at 117 in FIGS. 8-10. The various rim (belt~
constructions are illustrated schematically in FIGS.
11-17 and the following table compares belt construction
to test results:
22.
!
llS~OS4
ABLE III
GLASS DISC FATIGUE RIM FATIGUE
BELT DWG. LENGTH (cm) (cycles) (cycles)
CONSTRUCTION FIG. D/R _ @ 2263 N-m _ @ 12,910 N
None * None/2.5 428,000 ** 169,000
A (R-503 11 None/2.5 1,090,000 5,382,390
Bl (D-30/R-20) 12 20/2.5 376,592 ** 289,830
B2 (D-20/R-30) 12 20/5 159,390
B3 (D-30/R-20) 12 20/5 1,100,000 3,599,000
B4 (DL10/R-40) 12 20/2.5 _ _ 288,400
C (D-30/R-20) 13 20/5 up to 8.7M***
D (R-65, ~ DR 16 (None/2.5) 865,000 *** up to 21M
63 to 65~ (DR = 2.5)
E (D-30/R-20, 14 20/2.5 avg. 2M to 4M
R-50) None/2.5
F (R-65, 17 None/2.5 from 4.6M
~ DR 63 to 65) (DR = 2.5)
G (R-50, 15 None/2.5 _ up to 6.5M
D-30/R-20) 20/2.5
* Disc and rim compression molded from one mold charge
consisting of a rosette stack-up of SMC-R50 arranged
in a manner to sections of FIG. 3.
** Wheel construction an early version of FIGS. 5-]0
with radial ribs 142 spanning cavities 144 as shown
in FIG. 19.
*** Only wheel tested had disc constructed of SMC-R65.
**** M ~ mega or million cycles.
23.
1154054
FIGS. 11-17 schematically illustrate lay-ups
of sheet molding compounds in various belt constructions
in accordance with the invention. In each of FIGS. 11-17,
the stock is viewed from the tire-side or radially outer
side of the rim charge. The bead-to-bead direction is
vertical as shown in FIG. 11, the horizontal dimension
being broken to facilitate illustration. FIG. 11
illustrates construction A in Table III wherein the
kelt is comprised of three spiral plies of sheet molding
compound with 50% by weight random glass rovings (i.e. SMC-R50~J
manufactured in accordance with the previous discussion
relative to FIG. 1. Although the test results for con-
struction A are good, it was found that this selection
of belt material gave less than desired uniformity wheel-
to-wheel,
FIG~ 12 illustrates the construction previously
described in detail and for which test results for
different glass compositions and lengths are shown in
exemplary constructions Bl, B2, B3 and B4 in Table III.
In the various types of sheet molding compound constructed
in accordance with FIG. 1, the rando~ and directional
-~ fibers are deposited at separate stages as previously
described in essentially separate layers. FIG. 12
illustrates the preferred orientation wherein the random
fibers in each ply are disposed radially outwardly of the
directional fibers in the same ply with reference to the
rim charge axis. Three to six plies are required depending
upon material thickness and density. The directional fibers
are oriented circumferentially of the wheel rim. As will
be appreciated from Table III, construction B3 gave good
test results.
24 .
' ~ '~.. ' , '
llS4054
~ IG. 13 illustrates belt construction C con-
sisting of a continuous spirally wound sheet with cir-
cumferential directional fibers as previously described
and with a second spiral pattern of individual charge
pieces located between the continuous spiral plies and
having axially oriented directional fibers, i.e. trans-
versely of the final wheel rim. This charge was con-
structed by cutting the individual pieces from a first
continuous strip of sheet molding compound and then
laying the pieces side-to-side on a second strip before
the latter was spirally wound. The directional fibers
in the continuous spiral ply were oriented lengthwise
of the strip and therefore essentially circumferentially
of the charge axis. The directional fibers in the
individual pieces or segmented charge ply, however, were
oriented axially of the charge - i.e. at an angle of 90
with respect to those in the continuous ply - so that the
directional fibers in the composite lay-up formed an
essentially grid pattern directed circumferentially
and axially of the rim and wheel. Wheels molded fro~ a
rim charge so constructed and tested under load conditions
ran for up to 8.7M tmillion) cycles prior to rim failure
; (construction C in Table III). It should be noted at
`~ ; this point that all wheels actually tested and exemplified
in constructions A and B2-G in Table III were that pre-
viously discussed in connection with FIGS. 5-10 and
incluaed (with the exception of one construction D wheel)
discs molded from SMC-R50 rosette stack-ups (FIG. 3)~
It was therefore believed that disc performance would
be consistent throughout with the performance of constructions
A and B3 and was not tested (with the exception of one
~S
115~05~
eonstruction D wheel).
It is also contemplated that continuous directional
fibers may be used in the rim charge. Ho~tever, directional
discontinuous fibers are preferred over continuous
fibers eircumferentially of the rim charge for reasons
of superior moldability in the disclosed process, i.e.
to allow separation of the reinforcing fibers circum-
ferentially of the hoop blank 60 auring the molding
operation. Such separation must oecur since in the
preferred process the rim eharge is made smaller than
the ultimate rim diameter and must be capable of eir-
cumferential stretching, with attendant increasea
fiber separation, as the hoop blank is expanaed in
mold 62-66 and in mold 74.
As another modification, it is eontemplated
that ~he spiral three-layer wrap for rim charge hoop 60
(FIG. 2) may be replaced by three separate concentrie
hoops with eircumferentially staggered lap joints.
Alternatively, the rim charge may comprise one coil of
thiek (sheet) molding eompound (TMC) of the type described
in "Best of SMC and BMC - And Then Some", la_t cs World,
July 1977. See also U. S. Patent No. 3~932,980. Similarly,
rosette disc eharge pattern 80 (FIG. 3) may be replaced
by one sheet section of TMC whieh is a trademark of U. S.
Steel. Such a modification has the potential aavantage
when using TMC-R of providing random (R) fibers oriented
in all airections, i.e. not just primarily in planes
perpendicular to the wheel axis. Thus, although SMC is
preferred for molding the wheel of the instant invention
_.
in the embodiments thus far described, TMC may be utilized
26
054
and is contemplated in accordance with the invention
in its broadest aspects.
~IGS. 14 and 15 respectively illustrate com-
plementary belt constructions E and G (Table III). In
construction E (FIG. 14) three inner layers of SMC-D/R
with directional fibers oriented transversely of the
wheel rim are surrounded by a ply of SMC-R50. In con-
struction G (FIG. 15) the SMC-R50 is the inner ply. In
each belt construction E and G, three plies of D30/R20
compound weighing 2.0 kilograms (kg.) and one ply of R50
compound weighing 1.3 kgO gave a total weight of 3.3 kg.
Fiber content was 50%, 31.8% random ~R) and 18.2 directional
(D). The preferred range for both random and directional
fibers is 18% to 32%, with the total of both being about
50%, all by weight. Test results are shown in Table III.
FIG. 16 illustrates a belt construction D
comprising one ply of SMC-R65 and two plies of sheet
molding compound marketed by PPG Industries, Inc. of
Pittsburgh, PA under the trademark XMC. This sheet
molding compouna is constructed in accordance with the
process schematically illustrated in FIG. 18 by drawing
a plurality of continuous fibers 200 from corresponding
individual creels (not shown) through a resin bath 202
and a number of eyelets 204 onto a rotating mandrel 206.
Eyelets 204 are mounted on a carriage 208 which oscillates
in a direction parallel to the axis of mandrel 206, such
that the fibers 200 are deposited in multiple helical
layers in either direction to form essentially a double-
helical pattern.
.
5~054
A chopper/gun 210 is mounted on carriage 208
and receives one or more fiber threads 212.
These fibers are chopped to preselected lengths and
blown onto the wrap or lay-up 214 on mandrel 206.
Because of the motion of carriage 208 and chopper/gun
210 with respect to the mandrel axis, the choppe~ fikers
are deposited in a "rando~" pattern essentially or sub-
stantially in a direction parallel to the mandrel axis.
These fibers are referenced herein as "directional-rando~"
fibers, or DR in Table III. The rate of oscillation of
carriage 208 with respect to the angular velocity of
mandrel 206 may be varied to control the helix angle of
fibers 200. Reference may be had to U. S. Patent No.
4,167,429 for a general discussion of the process here- -
inabove described in connection with FIG. 18.
When wrap 214 ]s completed, it may be cut axially
and removed from mandrel 206. For construction of wheel
rim charges in accordance with the invention, the sheet
is further cut in the direction of the mandrel axis as at
216 to preselected widths generally corresponding to rim
width. The result is a plurality of lengths of strip
stock, preferably eight inches wide, o~ which one is
partially illustrated in FIG. 18~ Each strip includes
directional fibers 22~ in essentially an X-pattern at
acute angles transversely of the strip and with the
directional-random 220 fibers oriented essentially length-
wise of the strip. Following is a material specification
of XMc sheet molding compound utilized in constructing
wheels in accordance with the invention and to be discussed:
28.
llS~(~5~ - .
TABLE IV
Type Designation XMC
Weight 5,5 k~/~2 (18 oz./sq. ft.)
I Glass Content:
Total: .
Range 55% to 80%
Preferred 60% to 65%
Directional-Ranaom:
Range 15% to 20% of total
Preferred ~ 20% of total
Directional . Remainder
'~ Glass length (airectional-random):
Range 1.25 cm to 5.0 cm (0.5 in.
to 2.0 in.)
! 15 Pr~eferred 2.5 cm (1.0 in.)
Glass type:
Directional - PPG K15 E glass
Directional-Random PPG K37 E glass
Helix angle:
Range 79 to 82 (with reference
~ (to the mandrel axis)
Preferred 80-16 (with reference to
the man~rel axis)
Paste Formulation tsources sa~ as in Table I):
Resin DERA~E 790 80%
'~ Filler Calcium Carbonate 20%
! ~old Release . Zinc Stearate 3% BOR
`. Catalyst T-Butyl Perbenzoate 1% BOR
Thic~ener r~agnesium Oxide 2/~ BOR
; 30 Formulation for SMC-R65 same as ab~ve except containing 65~
ranaom 2.5 cm (1 in.) fibers.
1~ S4(~
Above 80% total glass cOntent, the sheet molding compound
is thick and difficult to handle. Below 55% glass, the
resulting wheel rims are weak. Below a helix angle of
79, the fiber ends in the rim flanges are too spread
to yield desired strength. Above 82, the wheel rim
~xhibits diminished circumferential strength. The angle
of 80.16 is one available in this range without modificatio~
in the existing wrap-winding machine at PPG, and is presently
preferred for this reason. The degree of criticality of
the helix angle within the range of 79 to 82 is unknown.
The number of layers of directional fibers, i.e. the
number of passes of carriage 208 (FIG. 18) across mandrel
206, must be sufficient to "fill" all diamond-shaped
openings between the directional strands.
FIG. 16 illustrates a belt construction D com-
prising an inner layer of SMC-R65 and two outer layers
of X-pattern/directional-random sheet material (X/DR
in Table III). Total weight of each belt was 3.2 kg.,
consisting of 2.48 kg. XMC compound(total for two
plies) and 0~72 kg. R65 compound. Total glass was on
the order of 65% by weight, comprising 14.7% random (~),
10% directional-random tDR) and 40.3% directional or
X-fibers.
As will be appreciated from Table III, belt
construction D gave surprisingly excellent results,
particularly when it is recalled that steel wheels are
normally expected to run only 800,000 cycles without a
rim fatigue failure. It is believed that the improved
test results of construction D are due at least in part
-
to the orientation of directional fibers transversely of
30.
- .
~15~054
the wheel rim, i.e. axially of the wheel. Due to the
improved molding process previously described, these
transverse dlrectional fibers extend into the rlm flange
and thereby strengthen the flange-bead seat radius where
fatigue failures often occur in steel wheels. Indeed,
it was found that the most common mode of eventual
failure of construction D wheels consisted of small
cracks at the front rim well radius. Since this failure
mode results in a slow air leak, it would be a preferred
mode offailure during actual highway use.
FIG. 17 illustrates a belt construction F
comprising an X/DR ply sandwiched between plies of SMC-R65.
In wheels possessing belt construction F constructed and
testea, total belt weight was 3.2 kg., comprising 1.92
kg. R65 compound (total for two plies) and 1.28 kg. XMC
compound. As with construction D, total glass content
,~ .
was 65% by weight. In c`onstruction F, this total was
divided as 39% random (R), 20.8% directional and 5.2%
directional random (DR). Presently preferred ranges
for belts of construction as in D and F are about 15%
to 39% random, about 4% to li% directional random and
about 19% to 40% directional, all by weight. Total
glass COntent is preferably in the range o~ about 60%
to 65%, with 65% being particularly preferred.
As will be appreciated from construction F
in Table III, test results for this belt configuration
were not as good as those for construction D (FIG. 16).
This is believed to be due to a loss of lateral strength
resulting from replacement of the out~r-most X/DR ply in
FIG. 16 with an all-random (R) ply in FIG. 17. Con-
31.
' ` l~S4V5~
struction D of FIG. 16 is presently preferred. In
production, it is contemplated that the separate X/DR
plies will be replaced by one continuous length of strip
stock (of a length not commercially available at this
time). It is anticipated that wheel rims so constructed
will be stronger than those heretofore tested due to
elimination of potential weak spots where the separate
plies are now joined end-to-end. Disc constructions of
stacked SMC-R50 (test results at A and B3 in Table III)
~0 are presently preferred.
FIGS. 20-21 illustrate an alternative embodi-
ment of a wheel constructed in accordance with the invention
as molaed, and FIGS. 22-23 illustrate the same wheel as
finished. The wheel of FIGS. 20-23 is specifically
designed from front-wheel arive vehicles and is characterized
by a substantially increased disc offset as compared with
':
the wheel of FIGS. 5-10. Elements in FIGS. 20-23 similar
to elements in FIGS. 5-10 previously described in detail
are indicated by corresponding reference numerals followed
by the suffix "a". Pocket-connection bridgin~ sections
106a in FIG. 21 are substantially thinner than are those
at 106 in FIG. 6 which will permit pockets 102 to be
broken off of the wheel disc without requiring a separate
finishing operation.
In accordance with another important feature
of the invention, a method of providing a quality control
for inspecting directional fiber patterns in molded wheels
is envisioned. This feature is accomplished by winding
into the raw sheet stock and molaing into the wheel
directional fibers of X-ray opaque material such as barium-
glass or leaded glass. Thus, in the ~mbodiments of FIGS.
32.
~ 4()5~
16 and 17, the quality control feature of the invention
may be carried out by utiliæing X-ray opaque fibers
as one or more of the fibers 200 in FIG. 18. Similar
modifications may be readily incorporated in the SMC
process of FIG. 1. Wheels as molded and/or finished
may then be sampled and examined by X-ray for inspection
of the directional fiber layout.
In the following claims, the term "directional
fibers" refers to fibers of controlled orientation in
the raw sheet molding stock and, thus, essentially
controllable orientation in the molded wheel. Fibers
30 and 52 (FIG. 1~ and 222 (FIG. 18) are examples of
directional fibers as previously discussed in detail.
The term "random fibers" refers to fibers oriented
substantially randomly in at least one plane, as at 24
in FIG. 1. "Directional-random fibers" refers to random
fibers controlled during the process of fabricating the
sheet molding compound so as to be oriented substantially
in a given direction, as at 220 in FIG. 18. All
directional terms are with reference to the axis of
a finished wheel unless otherwise indicated.
115~054
The specific belt constructions illustrated
in FIGS. 14-17 and discussed hereinabove are the subject
of the copending application of James A. Woelfel Serial
No. 346,072 filed concurrently herewith and assigned
to the assignee hereof.
The invention claimed is:
~
.
~ 3~.
