U.S. patent application number 09/754986 was filed with the patent office on 2002-08-22 for mold assembly for making an expanded polystyrene article.
This patent application is currently assigned to Future Foam Technology, LLC. Invention is credited to Cutler, Philip William.
Application Number | 20020114859 09/754986 |
Document ID | / |
Family ID | 23187234 |
Filed Date | 2002-08-22 |
United States Patent
Application |
20020114859 |
Kind Code |
A1 |
Cutler, Philip William |
August 22, 2002 |
Mold assembly for making an expanded polystyrene article
Abstract
A mold assembly and method for molding a substantially
hemispherical construct from pre-expanded polystyrene beads. The
mold assembly includes a female half mold; a mating male half mold;
a first male mold insert mountable on the male half mold and having
a continuous, peripheral, beveled edge; and a second male mold
insert mountable on the first male mold insert. For forming a
construct having an impact-resistant exterior layer and an
energy-absorbing interior layer, such as a motorcyclist safety
helmet, the beads are initially molded under heat and compression
between the female half mold and the first insert to form a first
intermediate product of a first volume having a continuous,
peripheral, beveled edge; said product is thereafter molded under
heat and compression between the female half mold and the second
insert to a second, reduced volume to form a compressed, second
intermediate product, the beveled edge of the first intermediate
product serving to uniformly distribute the force applied thereto.
The second intermediate product is then remolded to the same volume
to improve volume stability, and thereafter backfilled between the
male half mold and the female half mold with additional
pre-expanded polystyrene beads to form an energy-absorbing inner
layer.
Inventors: |
Cutler, Philip William;
(Olympia, WA) |
Correspondence
Address: |
Brian J. Coyne
Suite B-3
905 24th Way, S.W.
Olympia
WA
98502
US
|
Assignee: |
Future Foam Technology, LLC
|
Family ID: |
23187234 |
Appl. No.: |
09/754986 |
Filed: |
March 27, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09754986 |
Mar 27, 2002 |
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09306870 |
May 7, 1999 |
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6241926 |
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Current U.S.
Class: |
425/192R ;
249/102; 425/4R; 425/412 |
Current CPC
Class: |
B29C 44/086 20130101;
A42C 2/002 20130101; Y10T 428/31855 20150401; B29C 67/205
20130101 |
Class at
Publication: |
425/192.00R ;
425/4.00R; 249/102; 425/412 |
International
Class: |
B29C 043/20; B29C
044/58 |
Goverment Interests
[0002] Not applicable.
Claims
I claim:
1. A process for molding an expanded polystyrene bead construct
within a mold assembly, said mold assembly including a female half
mold having a first, continuous, peripheral edge surface and an
interior surface configured to impart a desired exterior surface to
the construct, a male half mold having a second, peripheral edge
surface in mating alignment with the first peripheral edge surface
when the female half mold and the male half mold are aligned on an
alignment axis, a first male mold insert mountable on the male half
mold and having a third, beveled, continuous peripheral edge
surface, the female half mold and the first male mold defining a
first volume therebetween when the first male mold is inserted into
the female half mold, and a second male mold insert mountable on
the first male mold insert, the female half mold and the second
male mold insert defining a second, reduced volume therebetween
when the second male mold insert is inserted into the female half
mold, the process comprising: (a) filling the female half mold with
pre-expanded polystyrene beads of a predetermined density; (b)
mounting the first male mold insert on the male half mold; (c)
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral edge
surface of the female half mold; (d) rapidly cooling the fused
first intermediate product to within a subplasticizing temperature
range to cause lower than atmospheric pressure within the beads of
the first intermediate product; (e) mounting the second male mold
insert on the first male mold insert; and (f) compressing the
cooled first intermediate product between the second male mold
insert and the female half mold to a second, reduced volume before
the low pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads.
2. A process for molding an expanded polystyrene bead construct
within a mold assembly, said mold assembly including a female half
mold having a first, continuous, peripheral edge surface and an
interior surface configured to impart a desired exterior surface to
the construct, a male half mold having a second, peripheral edge
surface in mating alignment with the first peripheral edge surface
when the female half mold and the male half mold are aligned on an
alignment axis, a first male mold insert mountable on the male half
mold and having a third, beveled, continuous peripheral edge
surface, the female half mold and the first male mold defining a
first volume therebetween when the first male mold is inserted into
the female half mold, and a second male mold insert mountable on
the first male mold insert, the female half mold and the second
male mold insert defining a second, reduced volume therebetween
when the second male mold insert is inserted into the female half
mold, the process comprising: (a) filling the female half mold with
pre-expanded polystyrene beads of a predetermined density; (b)
mounting the first male mold insert on the male half mold; (c)
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral surface of
the female half mold; (d) rapidly cooling the fused first
intermediate product to within a subplasticizing temperature range
to cause lower than atmospheric conditions within the beads of the
first intermediate product; (e) mounting the second male mold
insert on the first male mold insert; (f) compressing the cooled
first intermediate product between the second male mold insert and
the female half mold to a second, reduced volume before the low
pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads; and (g) remolding the cooled intermediate
product under heat and compression between the second male mold
insert and the female half mold to a second, reduced volume before
the low pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads.
3. A process for molding a layered, expanded polystyrene bead
construct within a mold assembly, said mold assembly including a
female half mold having a first, continuous, peripheral edge
surface and an interior surface configured to impart a desired
exterior surface to the construct, a male half mold having a
second, peripheral edge surface in mating alignment with the first
peripheral edge surface when the female half mold and the male half
mold are aligned on an alignment axis, the male half mold having an
exterior surface configured to impart a desired interior surface to
the construct, a first male mold insert mountable on the male half
mold and having a third, beveled, continuous peripheral edge
surface, the female half mold and the first male mold defining a
first volume therebetween when the first male mold is inserted into
the female half mold, and a second male mold insert mountable on
the male half mold, the female half mold and the second male mold
insert defining a second, reduced volume therebetween when the
second male mold insert is inserted into the female half mold, the
process comprising: (a) filling the female half mold with
pre-expanded polystyrene beads of a predetermined density; (b)
mounting the first male mold insert on the male half mold; (c)
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral surface of
the female half mold; (d) rapidly cooling the fused first
intermediate product to within a subplastizigin temperature range
to cause lower than atmospheric conditions within the beads of the
first intermediate product; (e) mounting the second male mold
insert on the first male mold insert; (f) compressing the cooled
first intermediate product between the second male mold insert and
the female half mold to a second, reduced volume before the low
pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads; (g) removing the second male mold insert and
the first male mold insert from the male half mold; and (h) adding
pre-expanded polystyrene beads to the mold assembly and remolding
the added beads between the female half mold and the male half mold
under heat and compression to cause fusion of the added beads at an
interface to the expanded bead body to form a layered construct
comprising at least two layers of beads wherein the layers have
different densities.
4. A process for molding a layered expanded polystyrene bead
construct within a mold assembly, said mold assembly including a
female half mold having a first, continuous, peripheral edge
surface and an interior surface configured to impart a desired
exterior surface to the construct, a male half mold having a
second, peripheral edge surface in mating alignment with the first
peripheral edge surface when the female half mold and the male half
mold are aligned on an alignment axis, the male half mold having an
exterior surface configured to impart a desired interior surface to
the construct, a first male mold insert mountable on the male half
mold and having a third, beveled, continuous peripheral edge
surface, the female half mold and the first male mold defining a
first volume therebetween when the first male mold is inserted into
the female half mold, and a second male mold insert mountable on
the male half mold, the female half mold and the second male mold
insert defining a second, reduced volume therebetween when the
second male mold insert is inserted into the female half mold, the
process comprising: (a) filling the female half mold with
pre-expanded polystyrene beads of a predetermined density; (b)
mounting the first male mold insert on the male half mold; (c)
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral surface of
the female half mold; (d) rapidly cooling the fused first
intermediate product to within a subplasticizing temperature range
to cause lower than atmospheric conditions within the beads of the
first intermediate product; (e) mounting the second male mold
insert on the first male mold insert; (f) compressing the cooled
first intermediate product between the second male mold insert and
the female half mold to a second, reduced volume before the low
pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads; (g) remolding the cooled intermediate product
under heat and compression between the second male mold insert and
the female half mold to a second, reduced volume before the low
pressure conditions within the beads equilibrate to ambient
conditions to produce a fused expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads; (h) removing the second male mold insert from
the first male mold insert; and (i) adding pre-expanded polystyrene
beads to the mold assembly and remolding the added beads between
the female half mold and the male half mold under heat and
compression to cause fusion of the added beads at an interface to
the expanded bead body to form a layered construct comprising at
least two layers of beads wherein the layers have different
densities.
5. The process of claim 1, 2, 3, or 4, wherein the beveled edge
surface of the first male mold insert is deviated at least 45
degrees, but not more than 60 degrees, from a mold parting line
normal to the alignment axis.
6. A mold assembly for molding an expanded polystyrene bead
construct, comprising: (a) a female half mold having a first,
continuous, peripheral edge surface and an interior surface
configured to impart a desired exterior surface to the construct;
(b) a male half mold having a second, peripheral edge surface in
mating alignment with the first peripheral edge surface when the
female half mold and the male half mold are aligned on an alignment
axis; (c) a first male mold insert mountable on the male half mold
and having a third, beveled, continuous peripheral edge surface,
the female half mold and the first male mold defining a first
volume therebetween when the first male mold is inserted into the
female half mold; and (d) a second male mold insert mountable on
the first male mold insert, the female half mold and the second
male mold insert defining a second, reduced volume therebetween
when the second male mold insert is inserted into the female half
mold.
7. The mold assembly of claim 5, wherein the first male mold insert
has a plurality of upstanding alignment pins and the female half
mold has a plurality of first apertures in mating alignment with
said pins, whereby said first apertures receive said pins when the
first male mold insert is mounted on the male half mold and is
inserted into the female half mold.
8. The mold assembly of claim 6, wherein the second male mold
insert has a plurality of second apertures in mating alignment with
said pins, whereby said second apertures receive said pins when the
second male mold insert is mounted on the first male mold
insert.
9. The mold assembly of claim 7, wherein an exterior surface of the
male half mold is configured to impart a desired interior surface
to a construct molded within said mold assembly.
10. A layered volume-stable expanded polystyrene bead construct,
the construct produced by a molding process within a mold assembly,
said mold assembly including a female half mold having a first,
continuous, peripheral edge surface and an interior surface
configured to impart a desired exterior surface to the construct, a
male half mold having a second, peripheral edge surface in mating
alignment with the first peripheral edge surface when the female
half mold and the male half mold are aligned on an alignment axis,
the male half mold having an exterior surface configured to impart
a desired interior surface to the construct, a first male mold
insert mountable on the male half mold and having a third, beveled,
continuous peripheral edge surface, the female half mold and the
first male mold defining a first volume therebetween when the first
male mold is inserted into the female half mold, and a second male
mold insert mountable on the male half mold, the female half mold
and the second male mold insert defining a second, reduced volume
therebetween when the second male mold insert is inserted into the
female half mold, and said process comprising: (a) filling the
female half mold with pre-expanded polystyrene beads of a
predetermined density; (b) mounting the first male mold insert on
the male half mold; (c) molding the beads under applied heat and
pressure by forcing the first male mold insert against the beads to
fuse the beads together to form a first intermediate product of a
first volume having a continuous, beveled edge surface formed
between the beveled edge surface of the first male mold insert and
the peripheral surface of the female half mold; (d) rapidly cooling
the fused first intermediate product to within a subplasticizing
temperature range to cause lower than atmospheric conditions within
the beads of the first intermediate product; (e) mounting the
second male mold insert on the first male mold insert; (f)
compressing the cooled first intermediate product between the
second male mold insert and the female half mold to a second,
reduced volume before the low pressure conditions within the beads
equilibrate to ambient conditions to produce a fused expanded bead
body of at least 200 percent higher density than the predetermined
density of the pre-expanded beads; (g) removing the second male
mold insert from the first male mold insert; and (h) adding
pre-expanded polystyrene beads to the mold assembly and remolding
the added beads between the female half mold and the male half mold
under heat and compression to cause fusion of the added beads at an
interface to the expanded bead body to form a layered construct
comprising at least two layers of beads wherein the layers have
different densities.
11. The construct of claim 10, wherein the construct is a safety
helmet.
12. The construct of claim 10, wherein the construct is an edge
protector.
13. The construct of claim 10, wherein the construct is a corner
protector.
14. The construct of claim 10, wherein the construct is a packing
crate.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] None, however, Applicant filed Disclosure Document Number
445113 on Oct. 7, 1998, which document concerns this application;
therefore, by separate paper it is respectfully requested that the
document be retained and acknowledgement thereof made by the
Examiner (MPEP 706).
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] This invention relates generally to expanded polystyrene
constructs having a high-impact resistance and strength without an
unacceptable increase in brittleness, and a method for making the
same. More particularly, this invention relates to such constructs
that are created by a molding process that includes, as an
intermediary step, the imparting of a cam or beveled edge surface
to the construct preparatory to compressing the construct to high
density. The beveled edge surface imparted to the construct serves
to uniformly distribute the forces applied during the compression
step even over relatively large angular deviations from the mold
parting line, thereby permitting the molding of a single large
construct that formerly, prior to this invention, would have
required the molding and combining of several smaller, partial
constructs. Thus, the disclosed method is particularly useful in
the molding of polystyrene motorcyclist and bicyclist safety
helmets and polystyrene shipping boxes such as those commonly used
for shipping iced fish. This invention also provides molding
apparatus adapted for molding constructs of the type described.
[0005] 2. Background Art.
[0006] A method for molding an expanded, highly impact-resistant,
polystyrene construct from polystyrene beads was disclosed in U.S.
Pat. No. 5,718,968 to P. W. Cutler et al., which by this reference
is incorporated herein. The polystyrene beads include a thin outer
shell of polystyrene and a hollow interior that includes a blowing
agent, such as pentane, for example. According to the method, the
beads were first pre-expanded by application of heat through hot
air or steam, which caused the blowing agent to vaporize and expand
the beads. The beads were then cooled, which caused the beads to
have reduced internal pressure. The pre-expanded beads were next
placed into a mold assembly where they were subjected to heat and
pressure for molding to a first volume. The molded article was then
rapidly cooled in the mold assembly, thereby causing the vaporized
blowing agent within the beads to condense and create a pressure
less than atmospheric inside the beads. Thereafter, the molded
product with beads having low internal pressure-was immediately
subjected to compression within the mold assembly to a second
volume, less than the first volume. This resulted in a single layer
construct that had memory shape and was particularly suited for
acoustic and thermal insulation. Alternatively, additional layers
were molded within the mold assembly by adding beads to the first
molding step and then molding together the originally-molded layer
with the additional beads. This yielded a layered construct wherein
each layer had a different density than the other layers and each
layer had a density higher than the density of the beads from which
it was molded, except when a last layer was a backfill layer of
density equal to that of the beads from which it was molded. The
layered construct was volume stable, high density, high strength,
and highly impact resistant.
[0007] When this method was used to mold a safety helmet for a
motorcyclist or bicyclist, the outermost layer had the highest
density, while inner layers had lower densities to absorb impact
forces to minimize transmission of these forces through the
construct. Such a helmet, being substantially hemispherical and
having a 360 degree circumference, was thought to require molding
in at least five parts--crown, front, back, and two sides--which
thereafter were assembled together in a single mold and finally
molded together. This was because it had been found that the
compression process was less effective when the pressure is applied
at angles between 46 degrees and 89 degrees to the parting line of
the mold. It was theorized that compression pressure was diffused
so that the compression ratio rapidly diminished with pressure
applied at angles more than 45 degrees with respect to the parting
line of the mold.
[0008] There remains a need, therefore, for a method and mold
assembly for molding pre-expanded polystyrene beads that permits
molding a substantially hemispherical polystyrene construct as a
whole, in a single, integrated molding process, thereby eliminating
the need for first molding two or more individual component parts
thereof and the combining of the parts through an additional
molding step. There also remains a need for expanded polystyrene
constructs that are produced by the method and mold assembly
described herein, which feature high impact resistance and strength
without an unacceptable increase in brittleness, and which can be
molded in substantially hemispherical shapes in a single,
integrated molding process. These needs are fulfilled by the
present invention.
SUMMARY OF THE INVENTION
[0009] A method and apparatus are provided for molding an expanded
polystyrene bead construct within a mold assembly. The mold
assembly includes a female half mold having a first, continuous,
peripheral edge surface and an interior surface configured to
impart a desired exterior surface to the construct. The mold
assembly further includes a male half mold having a second,
peripheral edge surface in mating alignment with the first
peripheral edge surface when the female half mold and the male half
mold are aligned on an alignment axis. The mold assembly also
includes a first male mold insert that is mountable on the male
half mold. When the male half mold, with the first male mold insert
mounted thereon, is inserted into the female half mold, the space
between the female half mold and the first male insert defines a
first volume. The mold assembly also includes a second male mold
insert, mountable on the first male mold insert, such that when the
male half mold, with the first and second male mold inserts mounted
thereon, is inserted into the female half mold, the space between
the female half mold and the second male mold insert defines a
second volume, which is less than the first volume. The first male
mold insert has a third, beveled, continuous edge surface for
engaging an outer, peripheral portion of the preexpanded
polystyrene beads that are to be molded within the mold assembly,
and to which portion it imparts a beveled edge. Preferably the
beveled edge surface of the first male mold insert is deviated at
least 45 degrees, but not more than 60 degrees, from a mold parting
line normal to the alignment axis. In a preferred embodiment, for
mounting the second male mold insert over the first male mold
insert, the first male mold insert has a plurality of upstanding
alignment pins and the second male mold insert has a plurality of
second apertures in mating alignment with said alignment pins, and
the female half mold similarly has a plurality of third apertures
in mating alignment with said alignment pins.
[0010] In a first embodiment, the method includes filling the
female half mold with pre-expanded polystyrene beads of a
predetermined density; mounting the first male mold insert on the
male half mold; molding the beads under applied heat and pressure
by forcing the first male mold insert against the beads to fuse the
beads together to form a first intermediate product of a first
volume having a continuous, beveled edge surface formed between the
beveled edge surface of the first male mold insert and the
peripheral edge surface of the female half mold; rapidly cooling
the fused first intermediate product to within a subplasticizing
temperature temperature (usually between 160 and 180 degrees F.) to
cause lower than atmospheric pressure within the beads of the first
intermediate product; mounting the second male mold insert on the
first male mold insert; and compressing the cooled first
intermediate product between the second male mold insert and the
female half mold to a second, reduced volume, before the low
pressure conditions within the beads equilibrate to ambient
conditions, to produce a single-layer, fused, expanded bead body of
at least 200 percent higher density than the predetermined density
of the pre-expanded beads. The reason for rapidly cooling the first
intermediate product to wthin a plasticizing temperature range is
so that the temperature of the intermediate product will be low
enough to escape the post expansion that would follow if the
termperature is too high and, at the same time, avoid the cell wall
damage that would occur during the subsequent compression if the
temperature is too low.
[0011] In a second embodiment, for molding a more
volume-stabilized, single-layer, polystyrene bead construct, the
method includes the preceding series of acts followed by the
additional act of remolding the cooled intermediate product under
heat and compression between the second male mold insert and the
female half mold to a second, reduced volume, before the low
pressure conditions within the beads equilibrate to ambient
conditions, to produce a fused, expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads.
[0012] In a third embodiment, for molding a layered, expanded
polystyrene bead construct, the method includes filling the female
half mold with pre-expanded polystyrene beads of a predetermined
density; mounting the first male mold insert on the male half mold;
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral edge
surface of the female half mold; rapidly cooling the fused first
intermediate product to within a subplasticizing temperature range
to cause lower than atmospheric pressure within the beads of the
first intermediate product; mounting the second male mold insert on
the first male mold insert; and compressing the cooled first
intermediate product between the second male mold insert and the
female half mold to a second, reduced volume, before the low
pressure conditions within the beads equilibrate to ambient
conditions, to produce a single-layer, fused, expanded bead body of
at least 200 percent higher density than the predetermined density
of the pre-expanded beads; removing the second male mold insert
from the first male mold insert; and adding pre-expanded
polystyrene beads to the mold assembly and remolding the added
beads between the female half mold and the male half mold under
heat and compression to cause fusion of the added beads at an
interface to the expanded bead body to form a layered construct
comprising at least two layers of beads wherein the beads have
different densities. In a fourth embodiment, a backfilled, layered
construct is molded by a method that includes filling the female
half mold with pre-expanded polystyrene beads of a predetermined
density; mounting the first male mold insert on the male half mold;
molding the beads under applied heat and pressure by forcing the
first male mold insert against the beads to fuse the beads together
to form a first intermediate product of a first volume having a
continuous, beveled edge surface formed between the beveled edge
surface of the first male mold insert and the peripheral edge
surface of the female half mold; rapidly cooling the fused first
intermediate product to within a subplasticizing temperature range
to cause lower than atmospheric pressure within the beads of the
first intermediate product; mounting the second male mold insert on
the first male mold insert; and compressing the cooled first
intermediate product between the second male mold insert and the
female half mold to a second, reduced volume, before the low
pressure conditions within the beads equilibrate to ambient
conditions, to produce a single layer, fused, expanded bead body of
at least 200 percent higher density than the predetermined density
of the pre-expanded beads; remolding the cooled intermediate
product under heat and compression between the second male mold
insert and the female half mold to a second, reduced volume, before
the low pressure conditions within the beads equilibrate to ambient
conditions, to produce a fused, expanded bead body of at least 200
percent higher density than the predetermined density of the
pre-expanded beads; removing the second male mold insert from the
first male mold insert;-and adding pre-expanded polystyrene beads
to the mold assembly and remolding the added beads between the
female half mold and the male half mold under heat and compression
to cause fusion of the added beads at an interface to the expanded
bead body to form a layered construct comprising at least two
layers of beads wherein the layers have different densities. The
latter embodiment of the method is particularly suited for molding
substantially hemispherical constructs having a 360 degree
circumferential edge, such as bicyclist and motorcyclist safety
helmets, and packing crates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an exploded, perspective view of a mold assembly
of an illustrative embodiment of the invention for molding a
motorcyclist safety helmet, showing the male half mold, female half
mold, and the first male mold insert thereof aligned on an
alignment axis A-A;
[0014] FIG. 2 is a perspective view of the male half mold
thereof;
[0015] FIG. 3 is a top plan view of the first male mold insert
thereof;
[0016] FIG. 4 is a perspective view of the first male mold insert
mounted on the male half mold thereof;
[0017] FIG. 5 is a perspective view of the second male mold insert
thereof;
[0018] FIG. 6 is a perspective view of the second male mold insert
mounted on the first male mold insert and male half mold thereof;
and
[0019] FIG. 7 is a fragmentary, cross-sectional view of a crown
portion of said mold assembly in the configuration depicted in FIG.
6, taken along line 6-6 thereof, and of the hemispherical portion
of the female half mold when the mold assembly is in a closed
position.
[0020] FIG. 8 is a bottom plan view of a first intermediate product
molded between the female half mold and the first male mold insert
of FIG. 1.
[0021] FIG. 9 is a bottom plan view of a second intermediate
product molded from the first intermediate product by compression
between the female half mold and the second male mold inserts of
FIGS. 1-6.
[0022] FIG. 10 is a bottom plan view of a backfilled construct
formed from the second intermediate product between the female half
mold and the male half mold of FIGS. 1-6 after removal of the first
and second male mold insert from the male half mold.
[0023] FIG. 11 is a cross-sectional view of the first intermediate
product of FIG. 8 taken along line 11-11.
[0024] FIG. 12 is a cross-sectional view of the second intermediate
product of FIG. 9 taken along line 12-12.
[0025] FIG. 13 is a cross-sectional view of the backfilled, layered
construct of FIG. 10 taken along line 13-13.
[0026] FIG. 14 is an enlarged, schematic view of a section S taken
from FIG. 13, showing the three, fused, expanded polystyrene layers
thereof (P1--highest density layer; P2--intermediate density layer;
P3--back filled, energy absorbing layer).
[0027] FIG. 15 is a perspective view of a motorcyclist safety
helmet (visor removed) that incorporates a multilayer polystyrene
construct molded on the mold assembly depicted in FIGS. 1-5.
[0028] FIG. 16 is a perspective view of an expanded polystyrene
packing crate molded by the process described herein.
[0029] FIG. 17 is a perspective view of an expanded polystyrene
edge protector molded by the process described herein.
[0030] FIG. 18 is a perspective view of an expanded polystyrene
corner protector molded by the process described herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0031] Referring to FIG. 1, an illustrative embodiment of four
component parts of a mold assembly, denoted generally by the
numeral 10, for molding a motorcyclist safety helmet 12, are shown
in exploded, perspective view--namely, a female half mold 14, a
male half mold 16, a first male mold insert 18 placed over the male
half mold 16; a second male mold insert 20, which is also part of
the mold assembly 10, is insertable over the first male mold insert
18, as described below. All four components are aligned on an axis
A-A. The female half mold 14 includes a flat plate portion 14P
normal to axis A-A and a centrally disposed, substantially
hemispherical portion 14H that extends axially away from the male
half mold 16. The hemispherical portion 14H has an interior surface
that is configured to impart a desired exterior surface to a mold
construct for a motorcyclist safety helmet 12. The male half mold
16 has a flat plate portion 16P normal to axis A-A and a centrally
disposed, substantially hemispherical portion 16H that extends
axially towards the female half mold 14. A mold parting line P-P'
is defined as any straight line normal to axis A-A and lying in a
plane that contains apposed, engaged surfaces of plate portions
14P, 16P when the mold assembly 10 is in a closed position with the
substantially hemispherical portion 16H of the male half mold 16
inserted inside of the substantially hemispherical portion 14H of
the female half mold 14.
[0032] Referring now to FIG. 2, the male half mold 16 is shown in
enlarged, perspective view, removed from the remainder of the mold
assembly 10. It may be seen that the male half mold 16 includes a
convex, crown portion 16C integral with, and surrounded by, a
peripheral, relatively narrow, upturned flange portion 16F, the
narrow space between the flange portion 16F and the crown portion
16C defining a peripheral well 16W. The flange portion 16F is
somewhat raised at the front relative to the sides and rear of the
flange portion 16F, corresponding to the brow portion 12B of a
motorcyclist safety helmet 12, depicted in FIG. 15, as molded on
the illustrated mold assembly 10.
[0033] Referring to FIG. 3, the first male mold insert 18 has a
convex, crown portion 18C integral with, and surrounded by, a
beveled, continuous peripheral edge 18E. Four alignment pins 18P,
extend axially from the crown portion 18C and are configured for
insertion into mating apertures 20A, 14A in the second male insert
20 and in the female half mold 14, respectively. The crown portion
18C and the edge 18E are sized and configured such that the insert
18 mounts snugly on the male half mold 16 with the edge 18E
overlying the well 16W of the male half mold 16. As shown in FIG.
4, when the first male mold insert 18 is so mounted on the male
half mold 16, the beveled edge 18E extends radially inward from the
flange 16, and axially away from the mold parting line P-P' by
angle R defined by a line OX tangent to the beveled edge 18E and
the parting line P-P', where O is a peripherally-disposed point of
intersection of said tangent line with the parting line P-P'.
Preferably, R is between 45 and 60 degrees.
[0034] FIG. 5 shows that the second mold insert 20 is substantially
hemispherical and, unlike the male half mold 16 and the first male
insert 16, has no peripheral flange or beveled edge. As shown in
FIG. 6, the second mold insert 20 is sized and configured for
mounting atop the first male mold insert 18 (shown in phantom).
Thus, as shown in FIG. 7, when the mold assembly 10 is closed, the
distance D.sub.1, and hence the volume, between the substantially
hemispherical portion 14H of the female half mold 14 and the second
male mold insert is least; when the second mold insert 20 is
removed and only the first male mold insert is mounted on the male
half mold, the distance D.sub.2, and hence the volume between
portion 14H and the first male mold insert 18 is somewhat larger;
and when both inserts 18, 20 are removed, the distance D.sub.3, and
hence the volume, between portion 14H and the male half mold 16 is
the largest.
[0035] In use, for molding a motorcyclist safety helmet 12, the
substantially hemispherical portion 14H of the female half mold 14
is filled with pre-expanded polystyrene beads (not shown) of a
predetermined density. The first male mold insert 18 is mounted on
the male half mold 16. Once filled, the mold is clamped shut. The
beads are molded under applied heat and pressure by forcing the
male mold insert against the beads to fuse the beads together to
form a first intermediate product 32 of a first volume, depicted in
FIGS. 8 and 11. Preferably, the molding is carried out at a
pressure from about 9 to about 12 psi, and the product being molded
is allowed to dwell at a temperature of from about 100 degrees C.
to about 110 degrees C. for from about 15 to about 30 seconds. The
first intermediate product 30 is then rapidly cooled by the
introduction of water into the mold assembly. The first
intermediate product 30 is allowed to dwell with the cooling water
for a sufficient time to enable the blowing agent within the beads
to once again liquefy, typically, less than 2 minutes, depending on
the thickness of the molded part. The pressure is then
relieved.
[0036] With the first intermediate product 30 still within the
female half mold 14, the second male mold insert 20 is mounted over
the first male insert 18 with the alignment pins 18P inserted
through the alignment apertures 20A, and the mold assembly 10 is
closed. The first intermediate product 30 is substantially
hemispherical, but has a continuous, beveled edge 30B, as may best
be seen in FIG. 11. When the mold assembly 10 is in closed
position, the peripheral edge 20E of the second mold insert 20
engages the beveled edge 30B of the first intermediate product 30.
Thus, when next pressure is applied to the mold assembly 10 to
compress the cooled first intermediate product 30 from a first
volume to a second, lesser volume, the beveled edge 30B serves to
uniformly distribute the force applied by the peripheral edge 20E.
The mold assembly 10 is clamped shut during this step for at least
3 seconds. This operation produces a relatively thin, second
intermediate product 32, depicted in FIGS. 9 and 12, which is a
fused expanded bead body of at least 200 percent higher density
than the predetermined density of the pre-expanded beads.
[0037] Next, the cooled, second intermediate product 32 is remolded
under heat and compression between the second male insert 20 and
the female half mold 14 to a second, reduced volume before the low
pressure conditions within the beads equilibrate to ambient
conditions; the remolded product is then cooled as before. This
operation significantly increases the volume stability of the
molded construct and results in a construct consisting of two
layers.
[0038] The second male mold insert 20 and the first male mold
insert 18 are then removed from the male half mold 16. The female
half mold 14 is again filled with pre-expanded polystyrene beads
for remolding the added beads between the female half mold 14 and
the male half mold 16 under heat and compression to cause fusion of
the added beads at an interface to the expanded bead body to form a
backfilled, layered construct 34, here comprising two layers,
l.sub.1 (high density) and l.sub.2 (back fill, low density), as
shown in FIG. 14. The backfilled, layered construct 34 is cooled as
before and removed from the mold assembly 10. A suitable exterior
finish is thereafter applied to the backfilled, layered construct
34 in making the helmet 12. In this manner, a substantially
hemispherical construct 34 can be molded without the necessity for
first molding individual components thereof (crown, front, back and
two sides) and the concomitant necessity thereafter for combining
them in an additional molding operation.
[0039] It will be understood that the above-described process for
molding a multilayer polystyrene construct for use in a
motorcyclist safety helmet can be adapted to the making of a
variety of other objects by appropriate adjustments to the shapes
and sizes of the component parts of the mold assembly. Such other
objects include, for example, bicyclist safety helmets, packing
crates, corner protectors, motor vehicle dashboard components, and,
in general, any object in which a sturdy, impact-resistant,
expanded polystyrene exterior layer is to be combined with a
relatively soft, energy absorbing, interior layer. For example, a a
packing crate 100, including a chest 100C and a lid 100L, depicted
in FIG. 16, an edge protector 110 (three-layered), useful for
shipping furniture, for instance, and depicted in FIG. 17, and a
corner protector 112 (two-layered), for protecting a window during
shipping and installation, depicted in FIG. 18, were each made
according to the above-described process. In the case of the
packing crate chest 100C, a high density layer 100K surrounds a low
density, back-filled layer 100J.
[0040] Moreover, variations on the above-described molding process
yield expanded polystyrene constructs having differing
characteristics and a wide variety of uses. That is, instead of
following all of the foregoing steps of the illustrated embodiment,
one can terminate the molding process upon producing the first
intermediate product, which is high density, unfixed (i.e., it
spontaneously and partially expands somewhat to its original
volume), with high memory (i.e., high resistance to being crushed
under compression). Such constructs are suitable for molded shape
parts for supporting weight, such as as a base under a uni-molded
shower stall or a motor vehicle dashboard. The first intermediate
product is also useful as acoustical and thermal insulation,
wherein high impact resistance is ordinarily not required, but the
ability to mold a substantially hemispherical shape by a single,
integrated molding process may nevertheless be highly desirable.
Alternatively, one can go on to remold the first intermediate
product, which yields a high density, fixed construct with low
memory. Such a construct is suitable for molded shape parts that
778 require great structural strength; examples include surf board
cores and industrial in-line assembly trays. One can proceed
further to back fill the contruct, yielding a combination high
density layer and back-filled low density layer; such constructs
are suitable for energy-absorbing molded shape parts, such as
motorcyle safety helmet liners and corner pads. One can proceed
still farther to produce a combination high density, fixed layer
with a back-filled, low density layer; such constructs are
suitable, for example, for bicycle safety helmets, box-less
clamshell packaging, and for the energy-absorbing component of a
DRIVET.RTM. system for stucco-covered wall construction. Thus,
while the preferred embodiment of the invention has been
illustrated and described, it is accordingly intended that the
disclosure be taken as illustrative only and not limiting in scope,
and that the scope following claims.
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