Note: Descriptions are shown in the official language in which they were submitted.
2-~9~CA
COMPOSITE ~OTA~Y DRIVE MEMBER AND
METIIOD OF ITS FORM~TION
The present invention relates to a rotary drive member
such as a wheel, pulley, gear or the like that has a circumferen-
tially extending driv~ formation with features of desired shape
and size that are formed by the injection molding of thermoplas-
tics material, but without a need for conventional measures to
compensate for shrinkage of the thermoplastics material. More
particularly, the present invention relates to a composite rotary
drive member that has a circumferentially extending drive forma-
tion, wherein peripheral portions of the drive member are formed
by dual stage molding of thermoplastics material to first form a
composite metal and plastic preform member that is permitted to
undergo normal shrinkage before a relatively thin, band-like ring
of thermoplas~ics material is molded in place about the periphery
of the composite preform to define the drive formation with drive
surface features of desired shape and size, with the band-like
ring being so thin that it encurs a negligible amount of shrink-
age.
Rotary drive members such as wheels, pulleys, gears and
the like that are mountable on a shaft or other struc~ure for ro-
tation typically have been formed either from metal or from in-
jection molded thermoplastics material. Forming a rotary drive
member from metal has the advantage of providing a strong, riyid
structure that can be configured to transfer relatively large
tor~ue, for example between a shaft on which the drive member ls
mounted and another drive member such as a gear or an endless
belt that engages the rotary drive member. ~orming a rotary
drive member from injection molded thermoplastics material has
the advantage of providing a relatively lightweight structure
that often can be formed at a cost that is relatively low, com
pared to the price of machining the drive member from metal.
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I~ also is known to form one or more parts of a rot~ry
drive member such as a pulley from injection mol~ed plastics ma-
terial, and to use the molded part or parts in combina~ion ~ith
one or more separately fabricated metal parts to provide a rotary
drive member that is formed as an assembly of plastic and metal
components.
The invention of the present appllcation represents the
wor~ product of a continuing program of development that also
~ave rise to an invention that is the subject of United States
Patent No. 4,722,722 which issued February 2, 1988, entitled
ROTATABLE DRIVE MEMBER FORMED FROM INJECTION MOLDED PLASTICS
M~TERIAL ~ITH PREFORM INSERT, referred to hereinafter as the
"~lolded Pulley Patent."
The invention of the referenced Molded Pulley Patent
provides a rotary drive member, such as a wheel, gear, pulley or
the like, that is formed by injection molding thermoplastics ma-
terial to envelop selected portions of at least one preform in~
sert. The injection molding of the thermoplastics material is a
one-step process, and mold components are used that are sized to
allow for shrinkage of the molded thermoplastics material.
In the preferred practice of the invention of the ~old-
ed Pulley Patent, two preform inserts made of metal such as steel
are inserted into an injection mold to form a rotatable drive
member t~at is a composite plastic and metal structure. One of
the metal preform inserts is a tubular sleeve that defines por-
tions of a hub of the rotatable drive member. The other of the
metal preform inserts is an annular disc that defines portions of
a radially extending web that serves to rigidly connect hub and
rim portions of the rotatable drive member. The injection molded
plastics material envelopes peripheral portions of the tubular
sleeve as well as inner and outer edge portions of the annular
disc, and defines a drive formation on the rim of the drive
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2-~9OCA
member for engaging ano~her drive member such as a gear or an
endless belt.
A problem not addressed by the referenced Molded Pulley
Patent is that of providing a system for molding composite metal
and plastic wheels, gears, pulleys and the like without having to
take conventional steps (such as the o~er-sizing of mold compo-
nents) to compensate for shrinkage of the molded thermoplastics
material. Because shrinkage is encurred in the injection molding
of thermoplastics materials, with the extent o~ the shrinkage
typically being within the range of about 0.001 to about 0.015
inches per inch, and with shrinkage tending to be greater as the
thickness of the molded part is increased, the presence of
shrinkage on a pulley of 8 inches in diameter that is molded from
thermoplastics material can cause the pulley to diminish in size
from its original molded configuration by typi.cally about 0.150
inch unless care is taken to properly oversize the mold adequate-
ly -to compensate for shrinkage. Moreover, in determining the ex-
tent to which mold portions must be oversized in order to proper-
ly allow for shrinkage, a mold designer must take into account a
host of factors that influence the way in which a molded part of
particular cross section will cool. For e~ample, the presence of
hot spots in molded thermoplastics material that require prolong-
ed cooling time will significantly increase the shrinkage that
will occur.
Because the problems that are encurred in providing
molds that will properly and reliably allow for shrinkage can add
quite significantly to the cost of producing molded thermoplastic
components, those who are skilled in the art long have sought a
molding technique that will permit parts such as wheels, gears,
pulleys and the like to be molded without a need to take shrink-
age factors into account, while still providing a capability to
accurately form drive surface features of desired size and shape~
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~9~Lr3al
~ he present lnvention addresses the problem of provid-
ing a composite rotary drive member formed of metal and plastic,
such as a wheel, pulley, gear, or the like, by providing a system
that utili~es a dual-stage injection molding process to form
peripheral portions of a composite drive member, with a circum-
ferentially extending drive formation being defined solely by a
band-like outer ring of plastics material that is so thin that
the extent to which it experiences shrinkage is negligible.
In accordance with the process of the present inven-
tion, a rotary drive member is formed in a two-step molding pro-
cess, beginning with the formation of a composite pxeform of
metal and plastic, and concluding with the formation of a band-
like ring of plastic that extends about and joins with the plas-
tics material of the preform. By forming hub, web and inner
peripheral portions of the drive member during a first injection
molding step that creates a composite preform, and by forming
outer peripheral portions including drive surface features during
a separate second injection molding step (wherein thermoplastics
material is molded about the peripheral portions of the preform),
features of the drive surface can be accurately formed at a time
after the bulk of the thermoplastics material that comprises
the drive member has undergone shrinkage. By this method, the
shrinkage that is encurred as the result of the molding of the
thin outer layer of material (the plastics material that defines
features of a circumferentially extending drive formation) is so
small as to be negligible.
Stated in another way, what the system of the present
invention advantageously provides is 1) an inexpensive production
method by which gears, pulleys and the like can be formed, and 2)
products such as gears, pulleys and the like that are inexpen-
sively formed by using the method. Two guiding concepts are of
importance to the practice of the invention. One is that by
forming composite metal and plastics structures, the cost of
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90CA
~ 3
providing the overall structure is minimlz~d while giving the
resulting products the needed strenyth. The other is the use of
a dual-sta~e molding process with intermediate shrinkaye and with
the last of the two stages being used to mold a thin, ring~like
layer that encurs minimal shrinkaye, whereby conventional steps
to deal with shrinkage of molded thermoplastics material (and the
attendant cost of these steps) can be avoided.
The dual-stage molding process that is employed in the
preferred practice of the present invention forms radially inward
an~ ~a~ially outward portions of a thermoplastics component of a
composite metal and plastics rotary drive member such that the
locus of the juncture between the radially inward and the radial-
ly outward portions of the thermoplastics component are carefully
selected to maximize the amount of plastics material that is
molded with the first of the two molding stages so that the re-
maining band-like ring of plastics material that is molded with
the second of the two molding stages has the features of 1) being
molded about the plastics material of the first molding stage at
a time after the plastics material of the first molding stage has
undergone its shrinkage, 2) being uninterrupted in character as
it e~tends continuously and contiguously about peripheral por-
tions of the plastics material of the first molding stage, and 3)
having a minimal thickness, measured radially, that is held with-
in the range of about 0.040 inch to about 0.090 inch. By closely
holding the minimum radial thickness of the ring-like band to
within a range of about 0.040 inch to about 0.090 inch, it has
been determined that a proper unifying juncture is made between
the plastics materials of the first and second stages while keep-
ing the radial thickness of the band-like ring of material as
thin as possible so as to minimize the shrinkage that it experi-
ences.
Another concept that is believed to aid in assuring
that the thermoplastics materials of the first and second molding
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stages properly unifies in the region of their juncture (so as to
assure that the resulting ro~ary drive member has the streng-th
that is provided by a single plastics component rather than the
weakness that is characteristic of a pair of concentrically bond-
ed plastics components) involves using thermoplastics materials
for both stages of molding that are of very nearly the same or
identical composition. While using materlals of identical com-
position is not essential, by keeping the compositions of the two
thermoplastics materials as close to identical as possible, it is
assured that, when these two materials are joined during the
second molding stage, there is no line of demarcation in material
composition in the resulting structure that extends along the
location of juncture of the plastics materials of the first and
second moldings stages. A preferred material is glass fiber
reinforced Nylon of about 33 percent fiber content that has a
characteristic shrinkage within the range of about 0.006 to about
0.009 inches per inch. Such a material is sold by E.I. DuPont de
Nemours ~ Company, Wilmington, Delaware, under a product designa-
tion that is well known to those s~illed in the art, namely
"Nylon 612."
In preferred practice, the system of the present inven-
tion is implemented as an improvement on the method of forming a
composite metal and plastic rotary drive member that is described
in the referenced Molded Pulley Patent. Stated in another way,
the best mode known to the inventor for carrying out the prefer-
red practice of the present invention is in the formation of com~
posite metal and plastic gears, pulleys and the like that each
are formed using a pair of metal inserts. However, the system of
the invention is not limited in its application to the formation
of rotary drive members that include a pair of metal inserts;
rather, it can be used to form composite rotary drive members
that include a single metal insert or a plurality of metal in-
serts, as will be described.
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~2~
By ~he arrangement described above, a lightweight
rotary drive member is formed qui~e inexpensively as a combina-
tion of molded plastics material and a preform me-tal insert or
inserts, with the molded plastics material enveloping selected
portions of the preform insert or inserts, and with the molded
plastics material defining a periphery that has a ~rive formation
thereon ~or engaging one or more other drive members.
~ significan~ feature of the invention lies in the
provision of a simple and inexpensive method for forming rotary
drive members that are capable of transmitting relatively high
torques, for example between shafts on which the rotary drive
members are mounted and drive elements that engage the drive
formations which are provided on the rims of the rotary drive
members.
A further feature of the present invention is its par
ticularly advantageous use in the formation of toothed pulleys
for use with what are referred to as "timing belts." A "timing
belt" has an inner surface that is provided with a regularly
spaced array of tooth formations which extend into grooves de-
~ined by similarly configured toothed outer surfaces that are
provided on timing belt pulleys. The advantages found in timing
belt drives (as compared with gear drives, V-belt drives, roller
chain and sprocket drives, etc.) are relatively low cost, light
weight construction, low noise, zero backlash, and no requirement
for lubrication. Timing belt drives provide a positive drive
without a need for high belt tension, and these drives have a
long life as compared with V-belt drives. Because timing belt
drives feature these and other advantages, they are being uti-
li2ed to an increasing degree to replace other kinds o~ drives.
The system of the present invention has particular value because
it provides a means for forming timing belt pulleys of almost any
useful size (extending from a fraction of an inch in diameter to
a diameter of several feet), and because it can be utilized to
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~Z~
rorm timing belt pulleys that are capable of trans~itting as much
as 15 to 20 horsepower and more.
These and other Eeatures, and a fuller understanding of
the invention may be had by referring to the following descrip-
tion and claims, taken in conjunction wi~h the accompanying draw-
ings, wherein:
FIGURE l is a perspective view showing one side of a
first form of a rotary drive member that embodies the preferred
practice of the present invention, with the rotary drive member
having a hub portion that is mounted on a shaft, and having a rim
portion that defines a toothed drive formation which is shown in
driving engagement portions of a toothed endless timing belt;
FIGURE 2 is a perspective view of the components of
FIGURE 1 showing opposite side portions of the rotary drive
member;
FIGURES 3 and 4 are sectional view as seen from planes
indicated by lines 3-3 and 4-4 in FIGURES 1 and 2;
FIGURES 5, 6, 7, 8 and 9 are sectional views as seen
Erom planes indicated by lines 5-5, 6-6, 7 7, 8-8 and 9-9 in
FIGU~E 3;
FIGURE 10 is a perspective view similar to FIGURE 1 but
with portions of the rotary drive member and the timing belt
being broken away;
FIGURE 11 is a side elevational view of a preform
sleeve-like insert that is utilized in the rotary drive member of
FIGURES 1-10;
FIGURES 12, 13, 14 and 15 are sectional views as seen
from planes indicated by lines 12-12, 13-13, 14-~14 and 15-15 in
FIGURE 11;
FIGURE 16 is a sectional view similar to FIGURE 3 but
showing how other adjacent rotary mechanisms can be fastened to
exposed metal web portions of the rotary drive member for rota-
tion therewith;
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FIGURE 17 is a side elevational view of a blank of
metal from which a preform disc-like insert of the type utilized
in the rotary drive member of FIGURES 1-10 can be formed;
FIGURE 18 is an end elevational view thereof;
FIGURE 19 is a side elevational view of a disc-like
preform metal insert oE the type utilized in the rotary drive
member of FIGURES 1-10;
FIGURE 20 is an end elevational view thereof;
FIGURE 21 is a sectional view as seen from a plane in-
dicated by a line 21-21 in FIGURE 19;
FIGURE 22 is a side elevational view of an al~ernate
embodiment of a preform disc-like metal insert;
FIGURE 23 is an end elevational view thereof;
FIGURE 2~ is a sectional view as seen from a plane in-
dicated by a line 21-21 in FIGURE 22;
FIGURE 25 is a side elevational view of still another
alternate embodiment of a preform disc-like metal insert;
FIGURE 26 is an end elevational view thereof;
FIGURE 27 is a sectional view as seen from a plane in-
dicated by a line 27-27 in FIGURE 25;
FIGURE 28 is a side elevational view of still another
alternate embodiment o~ a preform disc-like metal insert;
FIGURE 29 is an end elevational view thereof;
FIGURE 30 is a sectional view as seen from a plane in-
dicated by a line 30-30 in FIGURE 28;
FIGURE 31 is a perspective view of a composite preform
that is injection molded during the preferred method of forming
the rotary drive member of FIGURE l;
FIGURE 32 is a sectional view, on an enlarged scale, as
seen from a plane indicated by a line 32-32 in FIGURE 31;
FI~URE 33 is a perspective view of the rotary drive
member of FIGURE 1 that is formed by injection molding rim
2 - 4 9 0 CA
portions that deflne a rotary drive formation about the periphery
of the composite preform of FIGURE 31;
FIGURE 34 is a sectional view, on an enlarged scale, as
seen from a plane indicated by a line 34-34 in FIGU~E 33;
FIGURE 35 i5 a perspective view of a metal preform that
is used in an alternate form of rotary drive member that embodies
features of the invention;
FIGURE 36 is a sectional view as seen from a plane in-
dicated by a line 36~36 in FIGURE 35;
FIGURE 37 is a perspective view of a composite preform
that is injection molded during the preferred method of forming
the alternate form of rotary drive member;
FIGURE 38 is a sectional view as seen from a plane in-
dicated by a line 38-38 in FIGURE 37;
FIGURE 39 is a perspective view of a rotary drive mem-
ber that is formed by injection molding rim portions that define
a rotary drive formation about the periphery of the composite
preform of FIGURE 37; and,
FIGURE 40 is a sectional view as seen from a plane in-
dicated by a line 40-40 in FIGURE 39.
Because the best mode known for carrying out the prac-
tice of the present invention relates to an improved method for
forming a rotary drive member o~ the type that is described in
the referenced Molded Pulley Patent, what is depicted in FIGURES
1-30 has close correspondence to what is depicted in FIGURES 1-30
of the referenced Molded Pulley Patent. Likewise, the descrip-
tion below that refers to FIGURES 1~30 bears close resemblance to
the description that is presented in the referenced Molded Pulley
Patent in conjunction with FIGURES 1-30 thereof.
Referring to FIGURES 1-4, a rotary drive member in the
form of a timing belt pulley 100 is shown that embodies features
of the pre~erred practice of the present invention. The timing
belt pulley 100 is depicted as being mounted on a shaft 102. The
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shaft 102 has an outer surface 104 of essentially constan-t diame-
ter that extends through a hole 106 that is formed centrally
through the pulley 100. Portions of an en~less timing belt 110
are shown reeved around peripheral portions of the pulley 100.
In overview, the pull.ey 100 includes a generally tubu-
lar hub 1 0 that defines the through-hole 106 that receives the
shaft 102. Set screws 80 are threaded through holes 108 that are
formed in the hub 120, with inner end regions of the set screws
80 being tightened into engagement ~7ith the outer surface 104 of
the shaft 102 for connecting the pulley 100 securely to the shaft
102. The pulley 100 additionally includes an annular web 150
that is of relatively thin cross section and that extends radial-
ly outwardly from the hub 120. A ring-like rim 190 connects with
and surrounds the periphery of the web 150. The rim 190 defines
a drive formation 200 that is shown as taking the form of a
toothed outer circumference that is configured to mate with and
drivingly engage another drive member such as a gear (not shown)
or the endless timing belt 110.
Selected structural portions of the pulley 100 are de-
fined by a pair of preform metal inserts 130, 160. Specifically,
a tubular, sleeve-like inner insert 130 is loosely surrounded by
an annular, disc-like outer insert 160. The inner insert 130 is
preferably formed as a cut- off length of tubular steel stock
which is preformed to provide the central mounting hole 106 and a
generally hexagonal outer surface 132. The outer insert 160 is
preferably formed by stamping a flat blank of sheet metal stock
(designated by the numeral 260 in FIGURES 17 and 18) to give the
outer insert 160 the desired annular configuration (shown in
FIG~RES 19-21), and to cause radial.ly inner and outer edge por-
tions 162, 164 of the insert 160 to be bent out of the plane of
the majority of the material of the insert 160 which forms a
central web 166.
2-49QCA
Referring to FIGURÆ 3, portions of -the inserts 130, 160
are enveloped ~y plastics material which is designated generally
by the numeral 210. Specifically, the outer surface 132 of the
sleeve-like inner insert 130 i~ surrounded and enveloped by plas-
tics material that is designated by the numeral ~12, while the
radially inner and outer edge portions 162, 164 of the insert 160
are surrounded and enveloped by plastics material that is desig-
na~ed ~y the numerals 212, 214 respectively. Additionally, three
spokes of plastics material 216 (see FIGURE 2) extend along one
side of the outer insert 160 to interconnect the plastics ma-
terial 212, 214 that surrounds the inner and outer edge portions
of the insert 160.
The method by which the combination metal and plastic
pulley 100 is formed in accordance with the system of the present
invention will be discussed after features of the components
described above are discussed in greater detail.
Referring principally to FIGURES 10 and 11, the sleeve-
like inner in~ert 130 preferably is of substantially uniform
cross section along its length except at two axially spaced loca-
tions where ring-like arrays of short groove segments 134, 136
are formed in the outer surface. Referring to FIGURES 13 and 15
in conjunction with FIGURES 10 and 11, it will be seen that the
groove segments 134 and 136 extend to su~stantiallv uniform
depths. However, as is best seen by referring to FIGURES 4 and
16, the groove segments 134 are of generally V-shaped configura-
tion, while the groove segments 136 are of generally V- shaped
configuration, with opposed s.ide walls 138 of the groove segments
136 e~tending in parallel, spaced planes that orthogonally inter-
sect the central axis of the elongate tubular sleeve-like inner
insert 130.
Referring to FIGURES 4, 6 and 9, the groove segments
134, 136 that are provided in the outer surface of the .inner
insert 130 are matingly engaged by correspondingly configured
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projections 212a, 212b that are formed by the plastics material
~12 that envelops ~he outer wall of the inner insert 130. The
mating engagemen-t of the plastics material 212 that envelops the
hexagonal-shaped outer surface of the tubular inner insert 130
~stablishes a rigid driving connection be-tween the inner insert
130 and the surrounding plastics material 212. Moreover, the
projections 212a, 212b of plastics material that e~tend into the
groove segments 134, 136 enhance the rigid character of this
driving connection and assure that the sleeve-like inner insert
130 will not move axially with respect to the surrounding plas-
tics material 212. Other types of formations on the circumfer-
ence of metal inserts can be used to establish rigid driving
connections with surrounding plastics material, as will be under-
stood by those skilled in the art. An example of another type of
formation used on a metal insert is a knurled surface portion,
which is illustrated in FIGURE 35.
The outer~ disc-like metal insert 160 is an annular
structure that defines a radially-extending central web 166 which
interconnects the inner and outer edge portions 162, 164 that
have been bent as by stamping to extend out of the plane of the
central web 166. The inner and outer edge portions 162, 164 of
the stamped disc~like outer insert 160 preferably define a
plurality of circumferentially spaced anchor formations that
serve to enhance the rigidity and secure nature of the driving
connection that is established between the inner and outer edge
portions 162, 164 and the enveloping plastics material 212, 214.
Referring to FIGURES 17 and 18, a flat blank of sheet
metal 260 is shown from which the disc-like outer insert 160 is
formed. The blank 260 can be formed from substantially any
selected gage thickness of commercially available sheet metal,
with galvanized steel of about 12 or 14 gage being appropriate
for use in forming most pulleys having an outer diameter of about
2 inches to about 6 inches. Thicker sheet stock is preferred for
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use with larger diameter pulleys, with 10 gage being su~ficiently
thick ~or use wi~h most large diameter pulleys. Thinner sheet
stock is preferred for use with pulleys of very small diameter,
with the thickness of the sheet stock being scaled down in accor-
dance with the diameter of the pulley, whereby 20 or 22 gage
sheet stock is usually appropriate in forming pulleys of less
than an inch in diameter.
Anchoring formations for securing inner and outer end
re~3ions of the disc-like outer insert 160 to the enveloping plas-
tics material are preferably formed either in stamping the blank
260 to define its preliminary configuration as ls depicted in
FIGURES 17 and 18, or in stamping the blank 260 to form its final
configuration as is depicted in FIGURES 19~21. In FIGURES 17-18,
it will be seen that inner and outer rings of holes 282, 284 are
formed through the material of the blank 260 in de~ining the
blank's preliminary configuration. I'he holes 282, 284 are de-
formed during the final stamping of the blank 260 to define
trough-like notches 292, 294 that straddle lines of juncture
between the planar central portion 166 of the disc-like outer
insert 160 and the inner and outer edge portions 162, 164. These
anchoring formations 292, 294 are caused to be filled by plastics
material 212, 214 when the inner and outer edge portions 162, 164
are enveloped by injection molded plastics material, as will be
explained shortly, whereby very secure driving connections are
established between the inner and outer edge portions 162, 164
and the enveloping plastics material 212, 214.
Referring to FIGURE 17, additional holes 290 may be
formed in a symmetrical array about the center o~ the blank 260,
with the symmetrical arrangement of these holes being desirable
iII order to preserve the balance o~ the resulting pulley 100. As
is typically illustrated in FIGURE 16, a threaded fastener such
as a cap screw 302 can be inserted through each of the holes 290
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to secure the pulley 100 to adjacent rotary elements, as designa-
ted by the numeral 3Q4.
FIGURES 22-24, 25-27 and 28-30 illustrate three other
typical embodiments 160', 160'', and 160''' that can be utilized
in place of the previously described embodiment 160 of the outer
insert. The embodiment 160' of FIGURES 22~2~ has inner ~nd outer
edge portions that define wave-like anchoring formations 310 that
project into the enveloping plastics materials 212, 214 at vary-
il~g an~les to establish secure driv-ng connections. The embodi-
ment 160'' of FIGURES 25- 7 has :inner and outer edge portions
that define notched anchor formations 312 that are engaged by the
enveloping plastics materials 212, 214 to establish secure driv-
ing connections. The embodiment 160''' of FIGURES 28-30 has
arrays of holes 314 that are formed through the inner and outer
ed~e portions, into which the enveloping plastics materials 212,
214 enter to establish secure drivin~ connections. As will be
apparent to those skilled in the art, other types, kinds and com-
binations of formations can be used to provide suitable means to
anchor the inner and outer edge portions of the disc-like outer
insert to the enveloping plastics material.
The prefexred method by which a rotary drive member
that emkodies the preferred practice of the present invention is
formed employs a two-stage injection molding process. In FIGURES
31-34, features of the method are illustrated in conjunction with
the formation of the rotary drive member lO0 of FIGURE 1. In
FIGURES 35-40, features of the method are illustrated in conjunc-
tion with the formation of another rotary drive member embodiment
500 that is shown in FIGURE 39.
Referring to FIGURES 31-34, the preferred method of
forming the rotary drive member 100 begins with a first injection
molding stage wherein a composite preform member is molded, as i5
designated in FIGURES 31 and 32 by the numeral 400. After the
thermoplastics material of the composite preform 400 has
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4~
undergone the shxinkage -that follows its being molded, it has an
outer peripher~l surface 420 of a diameter that is less than the
diameter of any part of the drive formation 200. A second
injection molding stage is utilized to provide a band-like rin~
of plastics material, as is designated in FIGURE 34 by the
numeral 41d.
While the band-like ring 410 is depicted in FIGURE 34
by section lines ~11 that are inclined relative to section li.nes
401 that designate the plastics material of the composite preform
400, it will be understood that the band-like ring of thermoplas-
tics material 410 is molded about the periphery of the thermo-
plastics material of the composite preform 400 so as to intimate-
ly, continuously and contiguously engage the outer surface 420 of
the preform 400, and so that the thermoplastics material of the
ring 410 unifies with the thermoplastics material of the com-
posite pre~orm 400 to form the single molded body of thermoplas-
tics material that has been described in con~unction with the
foregoing discussion that is associated with FIGURES 1-30.
Stated in another way, although section lines 401, 411
that are oriented at differing angles are employed in FIGURE 34
(to enable the material of the ring 410 to be distinguished from
the material of the composite preform 400), it will be understood
that the section lines 401, 411 are intended quite simply to
designate nothing more than portions of the same one-piece uni-
fied body of plastics material. The same applies to the section
lines 501, 511 that are employed in FIGURE 40 to illustrate por-
tions of a single unified body of plastics material that forms a
component of the rotary dri~e member 500.
~ he majority of the shrinkage in diameter that is en-
curred in the molding of all of the plastics material that is
incorporated in the rotary drive member 100 takes place when the
composite preform 400 is molded -- the significance of which is
that, when the band-like ring 410 is molded about the preform
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400, a mold (not shown) that is configured to define sur~ace
features of substantially the actual desired size that are to be
~olded in forming the drive formation 200 can be used (without a
need to take into account the effects of shrinkage of the plas-
tics material of the band-like ring 410). The reason that
shrinkage can be ignored in the molding of the band-like ring 410
is because the thickness of the plastics material that defines
the features that are of most critical dimension is so thin that
the extent of the shrinkage that results in the vicinity of the
formation of the features that are of most critical dimension is
of negligible magnitude.
Referring to FIGURES 31 and 32, the composite preform
400 is formed by inserting such metal preform inserts as are to
be enveloped by plastics material (namely the inserts 130, 160)
into a mold (not shown) that has a cavity which defines an outer
~urface diameter 420 that is smaller in diameter than is the
smallest diameter portion of the drive formation 200, whereby the
formation of the composite preform 400 leaves the circumferen-
tially extending drive formation 200 to be molded by a subsequent
molding process or stage. Because the mold cavity that is used
to provide the composite preform 400 need not provide the preform
400 with a peripherally extending surface 420 that is of any
aspecially critical size or shape, there is no need in the mold-
ing of the preform 400 to compensate for radially inward plastics
material shrinkage. ~owever, in sizing the mold that forms the
surface 420, care should be taken to assure that, after the plas-
tics material of the composite preform member 400 undergoes the
shrinkage that occurs following its molding, the minimum radially
measured thickness of the band-like ring of material 410 that
needs to be molded to define the minimum diameter of the drive
formation 200 lies within the range of about 0.040 inch to about
0.0~0 inch, as is described elsewhere herein.
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As the composite preform 400 is molded, opposite ends
of the sleeve-like inner insert 130 are closed off by opposite
side portions of the mold cavity; likewise, such side surface
areas of the annular disc-like outer inser~ 160 as are to be
e~posed (i.e., not covered by overlying plastics material) are
directly engaged by portions of the s~ructure that define the
mold cavity, whereby no plastics material is caused to flow along
these side surface areas. The gates that feed molten plastics
material into the mold during the injection molding process
preferably communicate with such mold cavity portions as define
the radially extending spokes 216 that interconnect the plastics
material that surrounds the inner and outer edge regions 162, 164
of the disc-like outer insert member 160.
In injection molding the band of plastics material 410
that defines the drive formation 200 about the composite insert
member 400, dimensions of the mold cavity need not be adjusted to
accommodate for shrinkage of the plastics material as it cools.
The reason for the absence of a need to allow for shrinkage is
that, as the thin band-like formation of plastics material 410
that extends about the periphery of the composite insert member
400 is molded and cools, the shrinkage that ensues (at least in
the vicinity of the formation of the features that are of most
critical dimension) is so small in comparison to the overall
diameter of the structure that is being molded that it is truly
negligible, whereby the resulting part has dimensions that are
well within the range of tolerances that are acceptable for the
rotary drive member lOO.
In preferred practice, the diameter of the outer sur-
face 420 of the composite insert member 400 is selected so that
the band of plastics material 410 that is molded about the pre-
form 400 to provide the needed drive surface features has a
minimum thickness, measured radially, of at least about 0.040
inch (so that the band of material 410 has a thickness that is
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sufficient to assure proper uniflcation of the plas-~ics materi~1
of the composite preform 400 and the band-like ring 410), ~.nd so
that the minimum thickness, measured radially, is not greater
than about 0.090 inch (so that the minimum thickness is kept as
small as possible consistent with good molding results to mini-
mize the shrinkage that is experienced by the ring of material
410 -- and to especially minimize the shrinkage that occurs
within the vicinities of the drive surface features that are of
most critical dimension, namely the features that define the
teeth of the drive formation 200).
Stated in another way, a restriction to be observed in
carrying out the preferred method of forming the rotary drive
member 100 is to make certain that the band of material 410 has a
minimum thickness that assures integrity and longevity of service
of the resulting molded part as by effecting proper unification
~ith the plastics material that is injection molded to form the
composite preform 400. The minimum thickness of the band 410, as
measured at its thinnest point (e.g., as measured at the base of
a groove that separates two adjacent teeth of the drive forma-
tion, and as is designated by the dimension 413 in FIGURE 34), is
within the range of about forty thousandths of an inch to about
ninety thousandths of an inch. Experiments have shown that, by
closely holding the minimum thickness of the ring-like band 410
to within a range of about 0.040 inch to about 0.090 inch, a
proper unifying juncture is made between the plastics materials
of the first and second molding stages (i.e., -the stages wherein
the composite preform 400 and the bandlike ring 410 are formed,
respectively); and, by closely holding the minimum thickness of
the band 410 to within the stated range, the band-like ring of
material 410 is kept as thin as it can be kept while permitting
the proper type of plastics material unification to take place
along the juncture of the molded entities 400, 410, whereby the
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2-490CA
~9~
shrinkage that is encurred hy the band-like ring of material 410
is minimized.
Referxing to FIGURES 35-~0, the manner in which an al-
ternate type of rotary drive member 500 (see FIGURE 39) is formed
is illustrated. The principal dif~erence between the rotary
drive member lQ0 of FIGURE 1, and the rotary drive mernber 500 of
FIGURE 39 is that, whereas the rotary drive member 100 includes a
pair of coaxially positioned metal inserts, the rotar~ drive rnem-
ber 500 includes only one metal insert 530. Stated in another
~ay, what is illustrated in FIGURES 35-40 is that the dual stage
molding technique of the present invention can be used to form a
circumferentially extending rotary drive formation about a com-
posite preform that includes only a single metal insert.
Referring to FIGURES 35 and 36, the single metal insert
530 that is employed in forming the rotary drive member 500 is a
tubular, sleeve-like member that preferably is formed as a ma-
chined part that has an enlar~ed diameter portion 532 with an
outer surface 53~, a portion of which is knurled, as is indicated
by the numeral 536. The knurled formation 536 helps to enhance
the integrity of the driving connection that is established be-
tween the insert 530 and such plastics material 540 as envelops
the enlarged diameter portion 532 of the insert 530.
Referring to FIGURES 37 and 38, a composite preform
member 550 is formed by injection molding plastics material 540
about the enlarged diameter portion 532 of the metal insert 530
using a mold (not shown) that has a cavity that will provide the
resulting composite preform 550 with an outer surface 560 that
has a diameter which extends into close proximity to the base of
such toothed drive features of a drive formation 570 that is to
be formed as a part of the rotary drive member 500, but which
leaves a suitably thick band-like ring 580 (see FIGURE 40~ of
plastics material to be molded about the composite preform 550.
The band like ring 580 has a minimum thickness 513 that lies
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2-490CA
within the range of about 0.0~0 inch to a~out 0.090 inch, as has
been described above.
Re,'errirlg to FIGURES 39 and 40, in carrying out the
final injection moldin~ step ~hat defines the circ~ferentially
extending drive formation 570 surface as a part of the band-like
ring 580 of plastics material that extends about the periphery of
the composite preform 550, a mold (not shown) is used that has a
cavity which is configured to substantially precisely form the
desired siæe and shape of the drive formation 570 -- which is to
say that shrinkage of the drive surface features can be ignored
a~ being negliyible.
As will be apparent from the foregoing description,
what the system of the present invention advantageously provides
is 1) an inexpensive production method by which gears, pulleys
and the like can be formed, and 2) products such as gears, pul-
leys and the like that are ine~pensively formed by using the
method. Two guiding concepts are of importance to the practice
of the invention. One is that by forming composite metal and
plastics structures, the cost of providing the overall structure
is minimized while giving the resulting products the needed
strength. The other is the use of a dual-stage molding process
with intermediate shrinkage and with the last of the two stages
being used to mold a thin, ring-like layer that encurs minimal
shrinkage, whereby conventional steps to deal with shrinkage of
molded thermoplastics material (and the attendant cost of these
steps) can be avoided.
The dual-stage molding process that is employed in the
preferred practice of the present invention ~orms radially inward
ar.d radially outward portions of a thermoplastics component of a
composite metal and plastics rotary drive member such that the
locus of the juncture between the radially inward and the radial-
ly outward portions of the thermoplastics component are carefully
selected to maximize the amount of plastics material that is
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2-490CA
~9~
molded with the first of the two molding stages so that the re-
maining band-like ring of plastics material that is molded with
the second of the two molding sta~es has the features of 1) being
molded about the plastics materia] of the first molding stage at
a time a~ter the plastics material of the first molding stage has
undergone its shrinkage, 2) being uninterrupted in character as
it extends continuously and contiguously about peripheral por-
tions of the plastics material of the first molding stage, and 3)
having a minimal thickness, measured radially, that is held with-
in the range of about 0.040 inch to about 0.090 inch regardless
of the fact that the thickness may vary along the circumference
of the ring-like band. By closely holding the minimum radial
thickness of the ring-like band to within a range of about 0.040
inch to about 0.090 inch, it has been determined that a proper
unifying juncture is made between the plastics materials of the
first and second stages while keeping the radial thickness of the
band-like ring of material as thin as possible so as to minimize
the shrinkage that it experiences.
While a preferred range of minimum thickness for the
ring-like band of material that is molded about the periphery of
a composite preform during the second stage of a two-stage mold-
ing process has been described herein as being about 0.040 inch
to about 0.090 inch, a more preferred range is between about
0.050 inch and 0.080 inch, for maintaining the minimum thickness
within this more preferred range aids in assuring that the re-
sulting molded products are consistently of good quality, with
proper unification of the plastics materials of the two molding
stages, and with minimal shrinkage taking place in the molding of
the ring-like band.
Another concept that is believed to aid in assuring
that the thermoplastics materials of ~he first and second molding
stages properly unifies in the region of their juncture (so as to
assure that the resulting rotary drive member has the strength
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2-~90C~
that is provided by a single plastics component rather than the
weakness that is characteristic of a pair of concentrically bond-
ed plastics components) involves using thermoplastics materials
for both stages of molding that are of very nearly the same or
identical composition. While using materials of identical compo-
sition is not essential, by keeping the compositions of the two
thermoplastics materials as close to identical as possible, it is
assured that, when these two materials are joined during the
second molding stage, there is no line of demarcation in material
composition in the resulting structure that extends along the
location of juncture of the plastics materials of the first and
second moldings stages. A preferred material is glass fiber
reinforced Nylon of about 33 percent fiber content that has a
characteristic shrinkage of about 0.006 to about 0.009 inches per
inch. Such a material is sold by E.I. DuPont de Nemours & Compa-
ny, Wilmington, Delaware, under a product designation that is
well known to those skilled in the art, namely "Nylon 612."
Although the invention has been described in its
preferred form with a certain degree of particularity, it is
understood that the present disclosure of the preferred form has
been made only by way of example, and that numerous changes in
the details of construction and the combination and arrangement
of parts may be resorted to without departing from the spirit and
scope of the invention as hereinafter claimed. It is intended
that the patent shall cover, by suitable expression in the ap-
pended claims, whatever features of patentable novelty exist in
the invention disclosed.
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