Note: Descriptions are shown in the official language in which they were submitted.
63
Improved heat resistance is constantly in demand with respect to
plastic articles used in the automotive, appliance, electrical and aero-
space industries. Phenolic resins are typical polymers used in high
temperature applications in these industries. Phenolic parts for high
temperature applications have short-term heat resistance of about 300 to
500Fahrenheit, and long-term heat resistance of about 250 to 425Fahren-
heit. Heat resistance improvements of up to about 100Fahrenheit would
greatly enhance the utility of these materials.
Canadian Patents 1,187,424 issued May 21, 1985, and 1,198,379 issued
10 December 24, 1985, both John E. Emmett, are directed to improved plastic
pistons used in automotive disc brake assemblies. The improved pistons
have a metallic cap that is attached by various anchoring means to the
open end of the piston which contacts the backing plate of the brake shoe
and functions to drive the brake shoe against the rotor when stopping a
moving vehicle. It was found in working with the improved pistons
that the presence of the metallic caps greated reduced the thermal
degradation of the surface of the piston which contacts the brake shoe,
compared to use of the piston without the metal cap. It is believed that
the metal cap serves to shield the surface of the plastic piston from
the effects of oxygen at elevated temperatures caused by the braking
action of the brake shoes during braking of a vehicle.
The object of this invention is to maximize the oxidative shielding
of plastic molded articles or parts that are subjected to constant or
intermittent high temperatures. The just described plastic pistons are
just one example of a plastic part that can be improved by this
invention. Many other embodiments of the invention will be described
in this specification.
With respect to the plastic pistons, the present invention has a
further advantage that the metallic cap does not require a means for
securing the metallic cap to the plastic piston, such as the beads,
threads and other anchoring means disclosed in the aforementioned
Canadian patents. Moreover, metallic caps are less likely to become
accidentally detached from the plastic parts such as a plastic piston
while it is in service.
~:2896
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Summary of the Invention
In accordance with this invention, there are provided molded plastic
articles with improved heat resistance comprising a molded resin body
having a metallic heat shield molded in place on the surface of the
molded body that is exposed to elevated temperatures. The articles of
the invention are produced from plastic materials, preferably from
thermosetting plastics, and more preferably from phenol-aldehyde resin
molding materials.
A specific embodiment of the invention comprises a composite
vehicular brake piston for activating a vehicu1ar brake shoe during
braking oF a vehicle comprising a substantially cylindrical plastic body
having an open end and a closed end and a metallic cap extending over the
end wall of the open end and secured to the plastic body by molding of
the resin body against at least one surface of the metallic cap. The
metallic cap may have one or both of (1) means for attaching a vehicular
brake shoe or brake shoe assembly so that the brake shoe moves in unison
with the piston during braking and debraking of the vehicle, and (2) a
means for receiving and holding a dust boot that is conventionally used
in connection with disc brake pistons to prevent dust from accumulating
between the outside wall of the piston and the caliper.
Other embodiments of the invention in the automot;ve and
transportation industry include intake manifolds, automotive engine
pistons engine heads and the like.
The invention also finds use in the appliance industry, such as in
broilers, hot plates, toasters, and various other heated appliances that
have points where the plastic part is in contact or close to heating
elements and the like.
The invention also finds use in the electrical industry for articles
and parts that come in contact with hot environments, such as in
electrical light bulb sockets, light reflectors and shields and the
like.
~=Z~3963
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Detailed Embodiments of the lnvention
_utomotive and Transportation Applications
Although the invention will be described in terms of disc brakes
particularly intended for motor vehicles, it will be understood that the
present improved piston is equally adaptable to piston brakes utilized on
aircraft, railroad vehicles and in industrial applications such as
engines.
One type of brake assembly presently in use in motor vehicle disc
brakes is the opposed piston type. In such type, a piston i5 positioned
adjacent each opposite side of a brake disc and forces its respective
brake shoe or lining against the disc to impact a braking action. Other
types of brake assemblies to which the present invention is equally
useful are those in which a single piston is utilized to rnove the brake
shoe or lining into contact with both sides of the brake disc by
utilizing a caliper slide to impart a braking action.
The improved disc brake plastic piston of the present invention has
a metallic cap or face which provides a means of attaching a brake shoe
or a brake shoe assembly, or provides a dust boot groove, or, in the most
preferred mode, the metallic cap component provides both a brake shoe
retaininy means and a dust boot groove.
The improved piston of this invention is comprised of a cylindrical
resin body having an open end and a closed end. The "closed end" can be
cored out for structural or other purposes and is deemed to be within the
foregoing description. A metallic cap extends over the end wall of the
open end of the cylindrical body and is secured to the body by the
process of molding of the resin body against at least one surface of the
metallic cap as will be described in greater detail hereinafter. The
metallic cap is adapted to receive and hold a brake shoe clip, also
referred to in the trade as a retainer clip, and also to provide a dust
boDt groove. In the most preferred embodiments of the invention, the
metallic cap prov;des both a brake shoe retain;ng means and a dust boot
groove.
Thus the metallic caps of the invention have means for attaching a
vehicular brake shoe assembly so that the brake shoe moves in unison with
the piston during braking and debraking of the vehicle. The above described
attachment is not a permanent bond such as created by welding or soldering.
Rather the brake shoe clip engages the cap as a result of the shaped sur-
face thereof, and~is readily removable when it is desired to disassemble
the piston from the braking mechanism.
3.~Z~3~36~
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The improved plastic pistons of the invention are generally
manufactured by placing the metallic cap, suitably shaped to accomplish
the requirements of the application, in a mold shaped in the form of a
piston. The meta11ic cap or heat shield can be a pre-shaped or
pre-formed metal cap or a metallic foil or film that becomes shaped or
formed to the contour of the mold during the subsequent molding steps.
The metal cap or foil can have a thickness from about 0.0005 to about
0.25 inch, preferably from about 0.001 to about 0.05 inch. Thereafter,
plastic molding material, such as a phenolic resin molding material
comprising resin and fillers, is placed in the body of the mold, the
temperature is elevated and pressure is applied to the resinous material
to fill out the mold and form the plastic piston against at least one of
the surfaces of the metallic cap. The plastic molding material can be
introduced into the mold in any of the conventional forms such as various
particulate forms such as powders, nodules and the like, or in "pre-form"
slugs, and the like. The resinous material is heated and pressed by
compression molding or other suitable processes and is composite molded
to the inner surface of the metallic cap. When the molded article is
removed from the mold, the plastic piston and metallic cap are integrally
bonded together. The result is that the metallic cap is embedably molded
to the plastic piston. These methods of manufacture have been described
with respect to the plastic piston, but are also applicable for
manufacturing the other embodiments of the invention described
hereinafter.
In the various embodiments of the invention, the metallic caps or
heat shields can be any suitable metal such as steel, aluminum, copper
and alloy.
Other embodiments of the invention in the automotive and
transportation industries includes automotive engine pistons made from
phenolic resins and having a metal skin or cap (such as aluminum) on the
piston head as a replacement for the present steel and aluminum engine
pistons. Internal combustion engine heads and intake manifolds can be
made with a thin metal inner skin and a molded phenolic resin outer shell
to provide the required dimensional stability and to,que retention.
Automobile mufflers can be produced with a metal inner skin and an outer
phenolic resin casing that will last the lifetime of the automobile.
~2139~i3
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Appliance Applications
Most hand-held, countertop and other heated appliances are limited
by the fact that the materials of construction must stand up to UL and
other industry standards at the operating temperatures. Phenolic resin
molding compounds are often used for enclosures or current-carrying func-
tional parts because of the good thermal properties of this thermosetting
plastic. Such properties include short term heat resistance of about 300
to 500Fahrenheit and long term heat resistance of about 250 to 425Fah
renheit, as well as high heat distortion temperatures of about 325 to
500F and low creep and retention of strength at elevated temperatures.
The use of the present invention to provide oxidative shielding of
phenolic resin molding compound appliance parts at the "hot spot" or
plastic surface that sees the highest temperature permit use of operating
temperatures of up to 100 higher than those stated above. Thus the
present invention finds use in heated appliances such as broilers, hot
plates, toasters, heating ovens, frying pans, hamburger cookers, popcorn
poppers, coffee makers, egg cookers and similiar appliances having hot
spots or points where the plastic part is in contact with or close to
heating elements or metallic heating surfaces. Use of this invention
permits improved, smaller and lower cost appliances. When hot spot tem-
peratures exceed the allowable limit of the plastic used in appliances,
industry has been resorting to air-gapping, and using metallic or ceramic
insulators or shields or combinations of the above, which requires large
plastic housings. The plastic housings can be considerably reduced in
size to accommodate the heat shielded plastic components of this inven-
tion.
Other applications in the appliance industry include electric irons
that use heated sole plates. Traditional "electric iron" designs use
heated sole plates and metal housings with handles made with phenol
resin molding materials, or a combination phenolic housing and phenolic
handle. Newer designs use a metal sole plate, an air gap, a heat shield
molded from a glass filled or other high heat resistant phenolic molding
compound and a thermoplastic handle. The use of oxidative shielding for
electric irons consists of a phenolic resin molding compound molded
directly to the sole plate, then attached to a thermoplastic or thermoset
handle. The use of the invention offers safer, more compact and economi-
cal appliances.
~Z~8~363
6 -
In the cookware field, "stick handles", the presently employed
phenolic resin molding compound handles used on metal cookware, such as
frying pans and sauce pans present two inherent problems. First, the
handles are subject to thermal degredation on long term useage, and
loosen at the point of attachment. Second, since this type of cookware
is used on gas burners or ranges, they can be in contact with a gas flame
and temperatures exceeding the normal, exposure limit for phenolic
resins. The cookware industry uses flameguards to reduce the potential
premature handle Failure from a high gas flame. Flameguards are of two
designs. One is a metal spacer that fits between the handle and the
metal cookware. The second is a metal shield that covers all or the
bottom half of the handle for the first inch or so from the point of
attachment. These shields are usually not molded on or tight fitting.
The use of the present invention in the form of a molded in metal
cap on the end of the phenolic resin handle provides an oxidative shield
around the handle. This is an improved flameguard that greatly reduces
the possiblility of thermal degradation at the point of assembly and the
resulting loose, unsafe handle. For the knobs used on pot and pan covers
or lids or in side handles for oven cookware, oxidative shielding
increases the liFe of the handle or knob, which are the parts that often
fail first in these appliances. In present appliances, knobs and side-
handles are bolted through to the cookware. Long term exposure to normal
oven temperatures cause the handles to shrink, providing exposure to air
and oxidation in the threaded part section. Handles and knobs on contin-
ued high temperature exposure fail by thermal degradation and the result-
ing cracking from the attachment hole. Molded in attachment bolts and/or
metal caps or shields in accordance with the present invention, prevent
surface oxidation in the critical points and substantially increase the
life ox the handle and knobs. The invention can also be used for handles
and knobs for gas, charcoal, propane and electrical heated grills, broil-
ers, smokers and the like.
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Electrical Applications
Electrical applications, especially phenolic resin molding compoundlighting fixtures used in enclosed or poorly vented areas can benefit
significantly by the use of the oxidative shielding provided by the
present invention. At present, phenolic resin, ceramic and metal are
used for electrical light bulb sockets, light reflectors and shields.
The problem with metal is that it is an electrical conductor, resulting
in a potential safety hazard if the insulating system fails. Ceramic is
heavy, difficult to manufacture to tolerance and subject to breakage.
Phenolic resins, even the highest heat resistant grades, are better
thermal insulators but unacceptable for some designs due to thermal
degradation. All systems present a potential fire or electrical hazard
if a light bulb with a higher than recommended wattage is used. These
problems can be eliminated or seduced by the use or a phenolic resin
molding compound with the oxidative metallic cap or shield of the present
invention in light bulb sockets and/or light reflectors. These provide
improved heat resistance plus the desired thermal conductivity to control
heat buildup. The oxidative shield can be achieved by a molded in inter-
nal metal skin. The same method can be used for reflectors for halogen
lights used for automotive and other uses.
Aerospace and Missile Industry
Phenolic resin, ceramic and high temperature metal alloys are used
for rocket nozzles, such as thrust nozzles, and for ablative nose cones.
In accordance with the present invention, these applications are ful-
filled by a composite molded rocket nozzle with an inner skin of hightemperature metal and a shell made of phenolic resin molding material.
Another emobodiment uses several layers of high temperature metal with
layers of phenolic resin molding compound in between in a sandwich type
structure. The benefits include more controlled burning and accuracy,
thinner walls, lighter weight and improved reliability. other uses
include ablative reentry systems and nose cones.
~2~3
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_ief Description of the Drawings
Figures 1 through 4 are elevational views of composite pistons,
partly in section, which illustrates various preferred embodiments of the
invention.
Detailed Description of the Drawings
Referring to Figure 1, cylindrical piston 11 has a closed end 13 and
ar open end 15. The exterior surface 23 of closed end 13 is shown to be
concave, but the surface can be more nearly slush with the bottom line of
closed end 13 provided that there is a sufficient cavity to provide or a
fluid reservoir behind the piston. Metallic cap 19, preferably of steel
or aluminum, extends over and covers end wall 14 of opened end 15 of
piston 11 and is secured on piston 11 by virtue of the fact that piston
11 is formed by molding the resinous molding material that forms the body
of piston 11 against one surface of metallic cap 19. In the molding
operation, the metallic cap 19 is placed in the mold first, and then the
resinous molding material, preferably in some particulate form or as a
"pre-form" is placed in the mold adjacent to one surface of the metallic
cap 19. In the molding operation, the resinous molding material is
melted and compressed against the surface of the metallic cap 19 so as to
2n form a firm bond therewith. The bond between the resin body of piston 11
and the metallic cap 19 can be improved by forming the metallic cap with
one or more of its edges crimped such as shown in Figures 2 and 3 so that
these edges become embedded in the molded resin body. In this
embodiment, metallic cap 19 forms a heat shield to protect the end wall
l against oxidation as a result of the heat generated when the plastic
piston is in service. In this embodiment groove 17 has been machined to
provide a means for retaining a brake shoe clip. A groove 21 has been
machined in the outside wall of piston 11 to provide a means for
retaining a dust boot.
Figure 2 illustrates an embodiment of the invention wherein piston
11 is provided with a metallic cap 19 which has a groove 27 on the inside
wall of piston 11 which is adapted to receive and retain a brake shoe
clip. In this embodiment a groove 21 is machined in the outside wall of
piston 11 to provide means or retaining a dust boot.
3963
g
Figure 3 illustrates an embodiment of the invention wherein the
metallic cap 19 is formed to provide a groove 29 in the narrowed portion
of the outer wall of piston 11 as a means for retaining a dust boot. In
this embodiment a groove 17 has been machined in the inside wall of
5 piston 11 to provide a means for retaining a brake shoe clip.
Figure 4 illustrates an embodiment of the invention wherein metallic
cap 19 is formed to provide a groove 29 in the narrowed portion of the
outer wall of piston 11 which serves as a means for retaining a dust boot
41. The metallic cap 19 is also formed to provide a groove 27 on the
inside surface of the piston _. Groove 27 provides a means for
retaining brake shoe clip 37. Brake shoe clip 37 has two or more bent
prongs 39 which are joined to a base plate which is attached by bolts or
rivets 43 to a brake shoe backing plate 33 to which is attached brake
shoe 35. In operation, the face of the backing plate 33 touches the
portion of metallic cap 19 which covers end wall 14, but it is through
the prongs 39 that the brake shoe clip 37 is attached to piston 11 by
means of the groove 27 wormed in the metallic cap 19. The manner of
attachment of the brake shoe clip and dust boot shown in Figure 4
illustrates the manner of attachment contemplated with respect to
previously described Figures 2 and 3.
The foregoing description of embodiments is intended to illustrate
the invention without limiting it thereby. It will be understood that
various modifications can be made in the invention without departing from
the spirit or scope thereof.
