Note: Descriptions are shown in the official language in which they were submitted.
1 1 63~7g
'l~his invention pertains to improYemerlts in
vi},ration isolator technology and more particularly
to a neh~ form of vibration isolators and a new
metl~od of manufacturing such device.
A number c-f different types of vibration
isolators are ~nown. This invention is concerned
primarily with plate-type and tukular-type isolators,
so called because the former -type has a small
len~th to cliameter ratio and thus is relatively
flat wllile tlle latter type has a relatively large
len~th to diarlleter ratio. Prior to this invention
such isolators have usually consisted of inner and
outer metal parts and a molded elastomeric part
extending between and bonded to the two meta
parts. While this well-known form of construction
has permitted the manufacture of isolators in
different sizes and load ranges, the manufacturiny
process en-tails a number of steps which add to the
cos-t of the product and must be carefully carried
out for the sa~e of product reliability. Among
these steps are the ~nportant one~ ~f cle~niny the
metal components, applying a bond conditioner or
adhesive to the metal parts so that they will bond
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to the ~lastomeric part, and then loading the
components into the mold for fabrication of the
elastomeric part. The molded product also mu$t be
heated to effect and complete vulcanization of the
elastomer. Thirdly a shear bond strength of about
400 to 500 psi is desirable in o~der to prevent
separation of the elastomer from the metal parts
and permit the isolator to satisfy commercial
requirements and withstand prolonged use. This
level of shear bond strength can only be achieved
by proper design and strict compliance with manu-
facturing requirements, including proper control of
molding temperatures and pressures.
The primary object of this invention is to
provide a new and improved method of manufacturin~
plate-type and tubular-type vibration/shock isolators
and new and improved forms of such isolators.
~ second important object is to make possible
the manufacture of isolators of the type described
in a manner which avoids or substantially reduces
the problems and limitations of the prior manufac-
turing m~thod.
Still another object is to provide a method of
manufacturing vibration and shock isolation isolators
which is substantially faster and cheaper than
methods of like purpose already employed in the
art.
These objects are achieved by makiny the
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vibration and shock isolators of two different
synthetic plastics using a co-injection molding
process. One plastic is a rigid thermoplastic
material; the other is a thermoplastic elastomer.
The latter is injected after the rigid thermo-
plastic material. This order of injection is
initiated in order to achieve proper bonding of the
two materials. There is provided particularly in
accordance with the present invention, a device
comprising:
a first part made of a stiff thermoplastic
polymer material; and
a second part made of thermoplastic elastomer
material secured to said first part by direct bonding
wherein the bond is a consequence of fusion of said
materials.
There is also provided in accordance with the
present invention, a method of molding a device
having a first part of substantially rigid thermoplastic
material and a second part of a thermoplastic elastomer
material, said method comprising:
(1) injection molding said first part; and
(2) injection molding said second part adjacent
to and contacting said first part so that said
thermoplastic elastomer material of said second part
will directly fusion bond to the thermoplastic
material of said first part.
The invention is illustrated by way of example
in the accompanying drawings wherein:
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Fig. 1 is a sectional view in side elevation
of a plate-type vibration isolator constituting a
preferred embodiment of the invention;
Figs. 2~-2C are sectional views illustrating
different positions of an injection mold assembly
for use in making the isolator of Fig. l; and
Figs. 3 and 4 are similar views of two other
embodiments of the invention.
Referring now to Fig. 1, the article which is
illustrated is a plate-type vibration isolator
which consists of inner and outer parts 2 and 4 and
an intermediate part 6. Both of the inner and
outer parts are made of a substantially rigid
thermoplastic material, while the intermediate part
is made of a thermoplastic elastomer. As used
herein the term "substantially rigid thermoplastic
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material" means a solid substantially rigid material
which has the propert~ of fusing (softening to the
point of becoming a liquid~ when heated to a
suitable temperature and of hardening and becoming
a solid and substantially ri~id again when cooled
to room temperature, i.e., 70~r and the term
"thermoplastic elastomer~' means a solid material
which has the property of fusin~ when heated to a
suitable temperature and o~ hardening and becoming
a solid which is resilient and behaves as an
elastomer when cooled to room temperature. These
thermoplastic materials may consist of a single
thermoplastic polymer subs-tance or a mixture of
such substances, with or without additives such as
colorants, plasticizers, anti-oxidants, stabilizers,
and other functional inyredients that suitably
modify one or more of the physical properties of
the thermoplastic substance(sl.
~ further requirement of this invention is
that the parts 2, 4 and 6 be formed by injection
molding. Hence the substantially rigid thermo-
plastic material and the thermoplastic elastomer
must be made from molding materials which are
capable of being injection molded. The molding
materials may consist of or be made up in the
majority of one or more polymers and/or one or more
copolymers. ~dditionally the matexial used to
manufacture the parts 2 and 4 ana ~he material used
to form the part 6 should be compatible in the
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sense that they are capable of bonding to one
another by fusion, i.e., by contactin~ the materials
when at least one is in a fluid state and then
cooling the fluid state material until it has
solidified and formed a bond with the other material.
While the PartS 2 and 4 could be made of different
mutually compatible materials which melt and
solidify at the same or nearly the same temperatures,
it is preferred that they be made of the same
1~ material. Preferably the parts 2 and 4 have a
flexural modulus i.n excess of 400,000 psi while the
part 6 is a soft low modulus thermoplastic elastomer
having a Shore A scale durometer value of between
35 and 85. By way of example but not limitation,
the parts 2 and 4 are made of polystYrene having a
flexural modulus of about 465,000 psi and the
part 6 is made of a butadiene styrene compound
having a Shore A scale durometer value of 55.
The parts 2, 4 and 6 are sh~wn in the drawings
as having sharply defined boundaries since, as
explained below in greater detail, the interfaces
between those parts are substantially free of any
intermixing or interdiffusing of the thermoplastic
materials.
Still referring to Fig 1, the inner part 2
has flat annular top and bottom surfaces 8 and 10,
a cylindrical inner surface 12 defining an axial
bore 17 and an outer boundary represented as a
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surface of revolution comprising cylindrical end
sections 16 and 18 and a double-cu~yed intermediate
section 20. The outer part 4 serves as a flange
for the isolator unit and has a cylindrical outer
surface 22 and an inner boundary 2~ represented as
a cylindrical surface, and mutually parallel top
and bottom surfaces 26 and 28 which are parallel to
the corresponding surfaces of inner part 2 and
extend at riqht angles to the axis of the inner
part. Outer part 4 also has a plurality of mountinq
holes 5. The intermediate part 6 has inner and
outer sect~ons 30 and 32 that are bonded respec-
tively to inner part 2 at its boundary section 18
and the part 4 at its inner boundary 24, plus a
convoluted intermediate section 34 that extends
~etween inner Part 2 and outer part 4. Inter-
mediate section 34 is bonded to the inner part 2 at
the boundary section 20. Intermediate section 34
acts as a spring to resiliently locate inner part 2
with respect to outer part 4.
When the device of Fig. 1 is made by the
molding method hereinafter de~cribed, substantially
no diffusion or mixing of one material into or with
the other material will occur. Additionally no or
only minor distortions of one material by the other
~ill occur along the boundary regions. It has been
determined, by inspecting cxoss-sections of isolators
l;ke those of Fig. 1 made according to this inven-
tion with a scanning electron microscope to a
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magnification of 20,000, that the boundaries
between the butadiene styrene thermoplastic elas-
tomer and the polystyrene parts have an interface
re~ion (the region of diffusion or intermixing of
one material into or with the other) with a thick-
ness in the order of only 1.0 x 10 6 inch. NeYer-
theless the bond between the elastomer and non-
elastomer parts is sufficiently strong for the
device to perform satisfactorily as an isolator.
Referring now to Figs. 2~-2C, the device of
Fig. 1 is produced in accordance with a preferred
mode of practic.ing the invention by means of a co-
inject-on mold that essentially comprises three
relatively movable mold members 36, 38 and 40 and a
center part or core 42 attached to mold member 36.
~s seen in Fig. 2A, mold member 36 has a contoured
inner end surface which comprises four distinct
portions 44, 46, 48 and 50, while mold memher 38
has a flat inner end surface 52 and a cylindrical
inner surface 54. Mold member 40 has a contoured
inner end surface comprising sections 56 and 58 and
a cylindrical outer surface 60 that makes a close
sliding fit with surface 54. The mold members are
arranged so that when the mold members are in
closed position, surfaces 50 and 52 will mate with
one another while surfaces 44 and 58 and post 42
will form a first cayity 62 and surfaces 48, 52
and the upper portion of surface 60 will form a
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second cavity 64. Mold mem~er 40 has a center
hole 66 in which center post 42 makes a close
sliding fit. A plurality of pins 68 secured in
mold member 36 make close slidin~ fits in holes 70
in mold member 38. Pins 68 serve as cores for
forming the mounting holes 5. ~old members 36, 38
and 40 are adapted (by conyentional means not shown
but known to persons skilled in the art of in-
jection molding) to move relative to one another
along the axis of post 42, so that as described
hereinafter mold members 38 and 40 are movable
separately and selectively to different positions
along that axis relative to mold member 36.
The vibration isolator shown in Fig. 1 is
manufactured using the mold assembly of Figs. 2A-2C
according to the following method. First the mold
members 36, 38 a~d 40 are placed in the totally
closed position shown in Fig. 2A (the first in-
jection position) and a suitable liquid thermo-
plastic injection molding material capable of
solidifying into a rigid or near rigid solid (e.g.,
polystyrene~ is injected into mold cavities 62
and 64 via injection ports 74 and 76 so as to form
the isolator parts 2 and 4. Then mold member 40 is
retracted until the outer edge of its surface 56 is
flush ~ith surface 52, so as to form a third
cayity 78 as shown in ~ig. 2B (the second injection
positionl. Next a suitable liquid thermoplastic
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injection molding material capable of solidifying
into a solid material wit~ the properties of an
elastomer (e.g., butadlene styxene) is injected
into cavity 78 via one or more injection ports 80
so as to form the isolator part 6~ This injection
step is conducted after the material injected into
the cavities 62 and 64 h~s solidified or become
viscous enou~h so that it will not be displaced or
distended by the material injected via port 80, yet
is soft enough to bond to the elastomer material.
Thus the second injection step is carried out while
the material in cavities 62 and 64 is still hot but
after it sets up as a solid. By appropriate choice
of matexials, it is possible for the cavity 78 to
be filled withi~ as short a time as one to three
seconds after the cavities 62 and 64 have been
~illed and still achieve a satisfactory bond
between the elastomer and non-elastomer parts.
Finally, after the part 6 has set up as a solid in
cavity 78, the mold members 38 and 40 are separated
from mold member 36 as shown in Fig. 2C, whereupon
the finished isolator may be remoyed from the mold
and set aside to cool. Thereafter the mold members
are returned to the position shown in Fig. 2~ for
the next molding cycle.
In the preferred mode of pxacticing the
inyention, the isolator parts 2 and 4 are molded of
polystyrene which solidifies so as to have a
flexural modulus of about 465,000 psi and the
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isolator part 6 is made of a butadiene styrene co-
polymer which solidifies so as to have a durometer
measured on the Shore A scale of between 35 and 85
(depending upon the spring rate desired for the
isolator), with the polystyrene preferably being
the material sold by Shell under Shell DP-203 T.M.
and the butadiene styrene being the material sold by
Shell under Kraton T.M. 3000 Series thermoplastic rubber.
Adequate temperatures and pressures are determined by
the characteristics of the materials used; i.e., the
foregoing polystyrene molding material is injected
with a pressure of approximately 5,000 psi and a
temperature of about 390F; the foregoing butadiene
styrene molding material is injected into cavity 78
at a pressure of approximately 6,000 psi and a
temperature o~ about 390F. The latter injection
step should occur about one to three seconds after
terminating injection of the polystyrene molding
compound into cavities 62 and 64. The injection
materials are maintained at a temperature of about
390F during the two injection steps, but the mold
is maintained at a temperature of about 100F to
about 150F during the molding process. The mold
is opened and the finished part is removed about
one minute after the second injection step is
completed. The mold part is then set aside and
allowed to cool to room temperature before being
labelled, tested and packaged. The finished
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products exhibit a shear bond strength between the
part 6 and parts 2 and 4 of at least 400-500 psi
and usually between about 600-800 psi, in com-
parison with the typical bond strength of about
500 psi between the metal and elastomer parts of
conventional metal/elastomer isolators.
It is to be noted that injecting the elastomer
material after the rigid material has been injected
is critical. It has been determined that if the
elastomer is injected at the same time as or before
the rigid material, a satisfactory isolator product
cannot be achieved since the elastomer is incapable
of withstanding deformation in cavity 78 under the
pressures required to be used in injecting the
rigid plastic material into cavities 62 and 64.
his is true evcn if the elastomer has fully cured
before the non-elastomer material is injected.
Only if the elastomer injection is delayed until
after the rigid plastic material has set up suf-
ficiently to withstand deformation under the
pressures required to inject the elastomeric
material is it possible to achieve a strong enough
bond between the elastomer and non-elastomer parts
and also have the isolator parts conform exactly to
the shape of the three mold cavities.
A further disti~ct advantage of the invention
is that the spring rate of the isolator may be
changed by modifying the composition and hence the
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durometer of the matexial used to form the inter-
mediate part 6. Thus~ for ex~mple, the Kxaton
molding material is available f:rom Shell as K~aton
3226 for 35 durometer A scale, Kraton 3202 for
55 durometer A scale, and Kraton 3204 for 85 duro-
meter A scale. Other durometer yalues can be
achieved by suita~ly blending any two or all three
of the foregoing Kraton materials or by the addition
or substitution of other thermoplastic elastomers.
The stifflless of the parts 2 and 4 may be modified
by mixiny some of the elastome~ molding material
with the polystyrene molding material. In this
connection it is to be appreciated that the parts 2
and 4 need not be absolutely rigid; for some
isolator applications it may suffice or be de-
sirable t~lat those parts be merely stiff, i.e.,
semi-riyid .
~ further advantageous feature of the fo~e-
going pre~erred method of practicin~ the invention
is that the molding materials are injected co-
axially rather than by the biaxial method disclosed
by I~ Martln Spier in his U.S. Patent NQ. 3,950~483.
It has been found that molding by coaxial injection
is simpler to execute and thus leads to a mQre
reliable product.
~nother ad~antage of the inYention is that
isolators of various shapes, sizes and Yibration-
isolating characteristics may be ~ormed. Thus~ for
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example, the shape and/or size of the intermediate
part 6 may be altered merely by modifying the
several mold parts. Further by way o~ example, by
appropriately molding the mold assembly it is
possi~le to form a flat isolatox 90 (Fig. 3~
consisting of a cylindrical inner part 2A, a
cylindrical outer part 4A with a flat circular
flange 92, and a cylindrical intermediate part 6A
having flat end surfaces. Also by way of example,
the invention is adaptable to providing an axially-
elongate isolator 96 (Fi~. 4I where the three
parts 2B, 4B and 6B are all cylindrical and the
length of part 6B substantially exceeds its inner
radius as well as its outer radius. The two
alternative forms of isolators have different
vibration isolation characteristics than the unit
of Fig. 1 even where made of the same materials as
the latter.
Still another advantage of the invention is
that it may be practiced with a variety of thermo
plastic injection molding materials. Thus, the
injection molding thermoplastic elastomer material
constituting the part 6 could comprise or consist
of a material other than butadiene styrene known to
persons skilled in the art. In this connection it
is to be noted that the term "thermoplastic elastomer"
is a term already known to persons skilled in the
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art, as evidenced by Tobolsky et al, Polymer Science
and Materials, page 277, Wiley-Interscience (1971);
and that a variety of such materials exist as
disclosed by A. A. Walker, Handboo] of Thermo-
plastic Elastomers (1979~.
Further, by way of example but not limitation,
the stiff thermoplastic parts 2 and 4 may be made
of acrylonitrile-butadiene styrene (ABS~, Poly
Methyl Methacrylate (Plexi~lasl, a polypropylene
polymer and other materials obvious to persons
skilled in the art, as taught for examplet by u.S.
Patents 3,941,859; 3,962,154 and 4,006,116. The
exact choice of materials used will depend upon the
characteristlcs desired and the compatibility of
the elastomer and non elastomer materials with
respect to bonding to one another.
Other modifications and advantages of the
invention will be obvious to persons skilled in the
art.
