Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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RUBBER MOLDING APPARATUS
FIELD OF THE INVENTION
This invention relates to an apparatus which is particularly
adapted for molding small quantities of experimental, prototype and
replacement parts from rubber materials.
BACKGROUND OF THE INVENTION
Rubber parts are commonly made by compressing, injecting or
extruding rubber materials in metal molds and dies. One aspect of the
prior art is that experimental, prototype and replacement rubber parts
with deep undercuts, re-entrant curves and convolutions require
precision metal molds and split or collapsing cores.
Another aspect of the prior art is that long lead times and high
costs are incurred in procuring complex experimental, prototype and
replacement parts made from rubber materials. Another aspect of the
prior art is that tests are often delayed until production molds are
available because of the high costs and long lead times for procuring
prototype parts with temporary molds.
Delays in testing prototype parts increase the risk of expensive
changes to production molds.
Another aspect of the prior art is that equipment is sometime
obsoleted because replacement parts are not available or too expensive.
SUMMARY OF THE INVENTION
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The present invention is an apparatus for molding experimental,
prototype, and replacement parts. The apparatus may also be used for
molding small quantities of production rubber parts. The invention
resides in a novel construction of a mold and core and a frangible
cellular core coated with a hard quick set resin which is broken into
small pieces and removed from the part after the part is removed from
the mold.
One benefit of the invention is reduced cost. Another benefit is
that the time for procuring rubber parts is reduced. An additional
benefit of the invention is that parts which are produced with the
invention closely simulate parts made in expensive production steel
molds and split or collapsing cores in accuracy, appearance and physical
properties.
Another benefit of the invention is that collapsing cores are not
required for molding rubber parts with deep undercuts, re-entrant curves
or convolutions.
The apparatus is comprised of a mold made from layers of fiberglass
cloth and laminating resin reinforced with a mixture of quartz sand and
laminating resin and a frangible cellular core coated with a thin hard
resin.
The steps in forming the frangible core comprise the steps of
applying a wax coating to the surfaces of a core forming cavity of a
core box to fill in irregularities; buffing the wax coating to provide
a smooth finish; applying a release agent over the wax; coating the
release agent with a thin hard resin; and filling the core forming
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cavity with a two component system polyurethane foam.
Further benefits and features of the invention will be apparent
from the ensuing description and accompanying drawings which describe
the invention in detail. A preferred embodiment is disclosed in
accordance with the best mode which is contemplated for practicing the
invention and the specific features in which exclusive property rights
are claimed are set forth in each of the numbered claims which are
appended to the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a plan view of a rubber air duct for an automobile.
Fig. 2 is a plan view of a mold for making the air duct which
embodies the present invention.
Fig. 3 is a right side view of the mold.
Fig. 4 is a front view of the mold.
Fig. 5 is a cross-sectional view through the mold taken on the line
5-5 of Fig. 4.
Fig. 6 is a cross-sectional view through the mold taken on the line
6-6 of Fig. 4.
- Fig. 7 is a view of a core for making the air duct which embodies
the present invention.
Fig. 8 is a cross-sectional view through the core taken on the line
8-8 of Fig. 7.
Fig. 9 is a plan view of a core box for making the core.
Fig. 10 is a right side view of the core box.
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Fig. 11 is a front view of the core box.
Fig. 12 is a cross-sectional view through the core box taken on the
line 12-12 of Fig. 11.
Fig. 13 is a cross-sectional view through the core box taken on the
line 13-13 of Fig. 11.
Fig. 14 is a front view of the mold and core drawn to an enlarged
scale in a tilted position for injecting a polymer for forming the
rubber air duct.
Fig. 15 is a cross-sectional view through the mold and core taken
on the line 15-15 of Fig. 14.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings wherein like numerals designate like
and corresponding parts throughout the several views, an automobile
rubber air duct 20 with convolutions and re-entrant angles is shown in
Fig. 1. The air duct 20 is exemplary of the complex parts which can be
molded with the present invention. Heretofore, procurements of complex
experimental and prototype parts made from rubber materials required
long lead times and expensive tooling.
A mold for making the automobile air duct which embodies the
present invention is illustrated in Figs. 2 through 8, inclusive. The
mold 21 is a rectangular shaped assembly comprised of upper 22 and lower
23 portion lay-ups of fiber glass cloth and laminating resin. In the
mold 21, which is depicted in the drawings, the upper 22 and lower 23
portions contact each other along a horizontal plane 24 resulting in
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what is commonly designated as a parting line. It should be noted that
a horizontal parting line is not a requirement of our invention and that
for some parts an irregular parting line may be required. Except as
otherwise specified herein, a model of the air duct and conventional
shop practices are used for making the upper 22 and lower 23 mold
portions.
The outside shape of the air duct 20 is formed in a cavity, one
portion of which is in the upper mold portion bottom wall 32 and the
other of which is in the lower mold portion top wall 33.
In the upper mold portion 22 there is a tubular port 34 for
injecting a rubber polymer to form the rubber air duct 20. The port 34
extends from the top wall 35 of the upper portion 22 to the cavity 31
which forms the outside of the air duct 20. At the perimeter of the
mold cavity 31 are depressions 36 commonly referred to as core prints
for supporting a core 37 which forms the inside of the air duct 20. The
core prints 36 engage core supports 38 which will be later described.
Extending outwardly from the right side of the mold cavity 31 along
the bottom wall 32 of the upper mold portion 22 and along the top wall
35 of the lower mold portion 23 are small narrow grooves 39 which form
apertures 40 for exhausting air from the cavity 31 when a rubber
material is injected under pressure through the tubular port 34 into the
mold 21. One feature of the mold 21 which is believed to be novel is
that the interiors of the upper 22 and lower 23 mold portions are filled
with a mixture 41 of quartz sand and laminating resin. The quartz sand
and epoxy resin mixture 41 results in a massive and rigid mold 21, an
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important factor for producing accurate parts.
The upper 22 and lower 23 mold portions are aligned with corner
guides 42 at each corner of the mold 21. The corner guides 42 consist
of rectangular male portions 43 which extend downwardly from the upper
mold portion 22 and rectangular female portions 44 in the corners of the
lower mold portion 23. The corner guides 42 accurately align the upper
22 and lower 23 mold portions.
The frangible core 37, an essential element of the present
invention, is illustrated in Fig. 7 and 8. At the ends of the core 37
are core supports 45 which engage the core prints 36 and support the
core 37 in the mold 21.
The core 37 is a rigid cellular member with a thin hard outer
coating 46. Except as otherwise specified herein, conventional shop
practices are used for constructing the core 37. With reference to
Figs. 9 through 13, inclusive, the core box 47 is comprised of an upper
portion 48 and a lower portion 49. The upper 48 and lower 49 portions
of the core box 47 are lay ups of the same type of fiber glass cloth and
laminating resin as the mold 21.
At the corners of the core box 47 are corner guides 50 of similar
construction as the mold 21. In the interiors of the core box 47 are
ribs 51 which increase the rigidity of the core box 47. The upper 48
and lower 49 core box portions contact along a horizontal plane 52. One
portion of a core forming cavity 53 is in the lower wall 54 of the upper
core box portion 48 and the other portion of the cavity 53 is in the top
wall 55 of the lower core box portion 49.
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In the upper portion 48 of the core box 47 there is a tapered port
56 for filling the core 37. The tapered port 56 is sealed with a
removable closely fitting tapered wooden wedge 57. For larger and/or
more complex parts, more than one tapered port 56 may be required.
The method for molding the air duct 20 consists of preparing the
mold 21, making the frangible core 37 and molding the rubber part.
The mold 21 is prepared in the following manner. A thin coating
of paste wax 58 is applied by hand to the surfaces of the cavity 31 in
the upper 22 and lower 23 portions of the mold 21 which form the outside
of the air duct 20. One suitable wax is the "SC JOHNSON PASTE WAX" of
SC Johnson & Son, Inc. of Racine Wisconsin 53403. The paste wax 58 is
allowed to dry and then hand buffed with a soft tern cloth. The purpose
of the paste wax is to fill in irregularities and provide a smooth
production like outside surface on the air duct 20.
After the hand rubbing of the paste wax, a mold release agent 59
is sprayed over the entire surface of the paste wax 58. The mold
release agent 59 which has been used in practicing the invention is the
"CHEM-TREND" CT-88 release agent, of Chem-Trend Incorporated, Howell,
Michigan 48843.
The core 37 is made in the following manner. The tapered wedge 57
is removed from the upper core box portion 48. The cavity 53 in the
upper 48 and lower 49 portions of the core 37 are coated with the same
type of paste wax 58 as the mold 21 and polished with a soft tern cloth.
The same type of mold release agent 59 is sprayed over the paste wax 58.
After the release agent 59 has been appIied over the paste wax 58, a
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quick set resin 60 is applied by hand with a brush over the entire
surface of the mold release agent 59.
The quick set resin 60 which has been used is the "FR-30-A Quick
Set Adhesive" of the Fiber-Resin Corporation, Warren, Michigan.
"FR-30-A Quick Set Adhesive" is an epoxy resin system comprised of over
90 percent of Bisphenol A Diglycidyl Ether Resin (Cas No. 25068-38-6).
The resin 60 forms a thin hard non-porous layer in the core forming
cavity 53.
After the quick set resin 60 is applied over the mold release agent
59, the upper 48 and lower 49 portions of the core box 47 are tightly
clamped together with a "C" clamp (not shown) or by some other
conventional clamping means. A two component system polyurethane foam
61, such as, Ireson's polyurethane foam "Rigid-Resin 721" and
"Rigid-Catalyst #800", manufactured by Foamseal, Inc., Oxford, Michigan
48371 is prepared by mixing thé catalyst with the resin as per the
directions supplied with the product.
The mixture 61 of "Rigid-Resin 721" and "Rigid-Catalyst #800" is
stirred vigorously for about thirty seconds and an amount of mixture
equal to approximately one third the volume of the core 37 is poured
through the tapered port 56 and the port 56 is immediately sealed with
the wooden wedge 57 whereby the mixture 61 is allowed to foam and expand
inside of the core box 47.
As the mixture 61 expands, it contacts and adheres to the thin
layer of quick set resin 60 to provide a frangible and rigid cellular
core 37 with a thin hard non-porous outer coating. The density of cores
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37, which have been made in accordance with the described method, has
been determined to be within a range of approximately 2.5 to 3.5 pounds
per cubic foot. Higher densities are undesirable because they increase
the difficulty of removing the core 37 from the finished part 20.
However, it should be noted that for very thin sections it may be
necessary to increase the density regardless of the difficulty of core
removal.
After the core 37 has been removed from the core box 47, excess
cellular material at the port 56 is trimmed from the core 37 and the
exposed cellular portion of the core 37 is coated with the quick set
resin 60. The core 37 is placed in the mold 21 supported on the core
supports 38. The mold 21 is then closed and the upper 22 and lower 23
mold portions clamped together with conventional "C" clamps (not shown)
or some other clamping means. A two part synthetic polymer 62 is
injected under pressure through the tubular port 34 using the two-part
injection cartridge gun "TS530" (not shown) marketed by Techcon Systems,
Inc., Carson, California 90746.
The final steps consist of removal of the air duct 20 and core 37
from the mold 21 and removal of the core 37 from the air duct 20. The
air duct 20 and core 37 are removed by separating the upper 22 and lower
23 portions of the mold 21 and the core 37 is removed by breaking the
frangible urethane cellular core 37 into small pieces. Removal of cores
37 with densities within the 2.8 to 3.2 pounds per cubic foot range has
required only modest efforts.
The two component polymer, namely, the Enichem two part ECTR Resin
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of the EniChem Polyurethane Division, Conyers, Georgia has produced
rubber parts with appearance and physical properties which were very
close to production parts. Enchem ECF-65A is a two component hybrid
polyurea system which sets at room temperatures. The physical
properties of prototype parts made from this material were as follows.
Tensile Strength (psi)3,500
Flexural Modulus 30,000
% Elongation 500
Shore Hardness 65A
Notched Isod Impact Ft-lbs 9
Heat Sag - 259 ~F (in.)
6 In. Overhang 0.1
From the foregoing, it will be appreciated that the present
invention provides an efficient, economical and timely means for making
experimental, prototype, replacement and low volume production parts.
Although but a single embodiment of our method has been
illustrated and described, it is not our intention to limit our
invention to this embodiment, since other embodiments are possible by
changes in material, steps and sequence of steps which are known to
ordinary persons skilled in the art.
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