U.S. patent application number 10/447071 was filed with the patent office on 2003-11-06 for load-carrying structures comprising bamboo fibers and polymers.
Invention is credited to Ryan, Dale Bradley.
Application Number | 20030207098 10/447071 |
Document ID | / |
Family ID | 27105803 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030207098 |
Kind Code |
A1 |
Ryan, Dale Bradley |
November 6, 2003 |
Load-carrying structures comprising bamboo fibers and polymers
Abstract
Shaped load-carrying structures are fabricated using bamboo
linear fibers with a compatible bonding material and synthetic
polymers such as polyesters, epoxies, and polyolefins. The
structures are manufactured by coating at least one of bamboo
culms, split bamboo culms, bamboo fiber tape, or prepared bamboo
fibers with a bonding material to produce a core. The core is then
combined with a polymer matrix and extruded or molded to form a
structure having the desired shape. The structures compare
favorably with wood, steel, and concrete regarding strength,
longevity, price and ability to withstand earthquakes. The
structures may be used as beams, columns, telephone poles, marine
piles and pallets.
Inventors: |
Ryan, Dale Bradley;
(Mitchell, SD) |
Correspondence
Address: |
Kevin A. Buford, Esq.
Holland & Knight LLP
1600 Tysons Boulevard, Suite 700
McLean
VA
22102-4868
US
|
Family ID: |
27105803 |
Appl. No.: |
10/447071 |
Filed: |
May 28, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10447071 |
May 28, 2003 |
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09260904 |
Mar 2, 1999 |
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6576331 |
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09260904 |
Mar 2, 1999 |
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08908589 |
Aug 8, 1997 |
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5876649 |
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08908589 |
Aug 8, 1997 |
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08696484 |
Aug 14, 1996 |
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Current U.S.
Class: |
428/297.4 ;
264/136; 264/171.13; 264/265 |
Current CPC
Class: |
B29C 70/48 20130101;
B29C 48/10 20190201; Y10T 428/249948 20150401; Y10T 428/24994
20150401; B29K 2711/14 20130101; B29C 48/156 20190201; B27N 5/00
20130101 |
Class at
Publication: |
428/297.4 ;
264/136; 264/171.13; 264/265 |
International
Class: |
B32B 027/04 |
Claims
1. A shaped load-carrying structure comprising a plurality of
linear bamboo fibers covered with at least one binder and
surrounded by a synthetic polymer plastic material.
2. The structure of claim 1, wherein binder is at least one member
selected from the group consisting of maleated polypropylene,
maleated polyethylene, maleic anyhdride, hydroxyl methacrylate,
silane compounds, N-vinyl pyridine, N-vinyl caprolactam, N-vinyl
carbazole, methacrylic acid, ethyl methacrylate, isobutyl
methacrylate, sodium styrene sulfonate, bis-vinyl phosphate,
divinyl ether-ethylene glycol, vinyl acetate, vinyl toluene,
vinylidene chloride, chloroprene, isoprene, dimethylaminoethyl
methacrylate, isocetylvinyl ether, acrylonitrile, glycidyl
methacrylate, N-vinyl pyrrolidone, acrylic acid, ethyl acrylate,
itaconic acid, methyl acrylate, sodium vinyl sulfonate, cetyl vinyl
ether, divinyl ether-butanediol, and octadecyl vinyl acetate.
3. The structure of claim 1 wherein the synthetic polymer is
selected from the group comprising a thermoplastic resin and a
thermosetting resin.
4. The structure of claim 1 wherein the bamboo is selected from the
group comprising Gradua and Tonkin cane.
5. The structure of claim 1 wherein the bonding material is acrylic
acid.
6. The structure of claim 1 wherein the synthetic polymer is
polyethylene.
7. The structure of claim 1 wherein the bamboo fibers are in the
form of split bamboo culms.
8. The structure of claim 1 wherein the bamboo fibers are in the
form of a tape.
9. The structure of claim 1 wherein the structure is a beam.
10. The structure of claim 1 wherein the structure is a column.
11. The structure of claim 1 wherein the structure is a telephone
pole.
12. The structure of claim 1 wherein the structure comprises a
pallet.
13. The structure of claim 12 wherein the pallet comprises a top
panel, a bottom panel and a plurality of spacers connecting the top
panel to the bottom panel and defining an opening therebetween for
receiving forks of a transport apparatus.
14. The structure of claim 13 wherein the top panel comprises a
solid plate having an exposed load bearing surface, the top panel
being formed of a plurality of elongate bamboo fibers arranged in
overlapping, transverse layers adhesively bonded together within a
molded plastic encapsulation.
15. The structure of claim 14 wherein the load bearing surface is
formed with a plurality of raised ribs to minimize load
slippage.
16. The structure of claim 13 wherein the spacers each comprise a
molded plastic block filled with bamboo fibers.
17. The structure of claim 16 wherein the bamboo fibers comprise
pellets of bamboo fibers cut into relatively short lengths compared
to the extent of the spacers and with each pellet having a
polymeric plastic coating.
18. The structure of claim 16 wherein the spacers each comprise a
cut-off segment of an extruded column of linear bamboo fibers
encased in an outer polymeric plastic coating.
19. The structure of claim 13 wherein the bottom panel comprises a
peripheral support and a cross-shaped central support, each of said
supports comprising a plurality of linear bamboo fibers encased in
an outer polymeric plastic coating.
20. The structure of claim 13 wherein the top panel comprises a
plurality of stacked woven mats of-bamboo fiber adhesively bonded
together and encased in a polymeric plastic coating.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of application Ser. No.
08/908,589 filed Aug. 8, 1997 which is a continuation-in-part of
application Ser. No. 08/696,484 filed Aug. 14, 1996.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to poles, pilings, railroad
cross-ties, and load-carrying structures, such as beams, columns
and pallets made up of linear bamboo fibers bonded to, and
surrounded by, synthetic polymers and to processes of preparing
these structures.
[0004] 2. Description of the Related Art
[0005] Presently, wood timber beams, columns and lumber depend on
specie and dimensional size as the only engineering variables.
Paint and other chemical treatments are used to lengthen the life
of wood products that are exposed to the elements. However, there
has been a growing concern over these toxic chemical treatments.
Creosote, which has been used for years, is now considered to be a
carcinogen, and has been banned from marine timber applications
where immersion allows seepage into surrounding waters. Railroads
are similarly concerned about creosote treated cross-ties. Utility
companies are aware of the danger these preservatives present to
their linemen and material handling people. Managed forests are
producing faster growth but lower grade timber than was available a
few years ago. This new timber sometimes does not pass the ANSI
standards for timber pole structures.
[0006] Concrete with reinforcing steel has a greater ability to be
custom engineered for various specific applications. However, the
resulting products are extremely heavy, and in the case of
load-carrying structures, such as bridges, the greatest portion of
the structure is involved in holding itself up. This extreme weight
forces many concrete structures to be fabricated on-site as opposed
to being built in the factory. This adds greatly to the cost of
these products. Also, concrete is very sensitive to motion, such as
caused by earthquakes. Thermal expansion and freeze-thaw cycles
wreak havoc on concrete components. A lightweight load-carrying
beam, column or cross-tie that would not be sensitive to seismic or
temperature changes would be a very desirable replacement for
concrete.
[0007] Structural steel is extensively used for beam and column
applications due to its strength, workability, and other factors.
Steel has an on-going maintenance problem due to rust and corrosion
that shortens its life span. Also, energy costs to produce steel
and to fabricate and maintain steel components are quite expensive,
keeping the price of the raw materials and finished products
high.
[0008] Fiberglass is being researched and new products are being
developed regularly, but the high cost of glass fibers and the
resin matrices has proven to be a formidable barrier to
overcome.
[0009] One particular application that has been traditionally
filled by wood products is the construction of pallets. A typical
wood pallet is approximately 40 inches by 48 inches by 5 inches and
comprises a plurality of top slats and bottom slats supported on
edge oriented 2.times.4" timbers. The market for such pallets is
several million each year. While this market is a substantial drain
on the timber industry, such wood pallets are not a preferred
pallet for the food industry. In the food industry, contamination
is a problem and efforts have been made to create a sanitizable
pallet for re-use. Various efforts have been made to create a
plastic pallet but such efforts have been largely unsuccessful for
at least two reasons. A first reason is that plastic, as its name
implies, will deform in response to load and therefore creates a
failure condition when loaded pallets are mounted on edge racks in
warehouse storage. A second problem is that plastic is
substantially more expensive than wood raising pallet costs by
several multiples. Accordingly, it would be advantageous to provide
a structural substitute for wood and plastic in the pallet
industry.
[0010] Bamboo has been considered for use in weight-bearing
structures. Thus, Chemical Abstracts 107:135345q (1987) discloses
composite materials containing 0.3-1 mm long bamboo strips,
powdered bamboo, powdered wood, and resin in a molded piece.
Chemical Abstracts 122:107321v (1995) discloses bamboo fibers as a
reinforcing material for resinous composite structural panels.
Chemical Abstracts 122:241192g (1995) discloses bamboo fibers and
strips as reinforcing materials for thermosetting resin structural
materials. Chemical Abstracts 118:148517z(1993) discloses strands
of bamboo fibers as reinforcing materials for resinous laminates.
Chemical Abstracts 117:173557z (1992) discloses bamboo fiber
reinforced plastic structural materials. This reference also
teaches a perfect bonding between the bamboo and the resin.
Chemical Abstracts 116:199922u(1992) discloses bamboo fibers
treated with a binding agent used in concrete structural materials.
U.S. Pat. No. 4,774,121 to Vollenweider, II discloses blocks
comprising stalks of bamboo surrounded by plastic foam cut into
thin sections and coated with fiber reinforced plastic to be used
in boat construction. The inventor has found that, contrary to the
teachings of Chemical Abstracts 117:173557z, the use of untreated
bamboo fibers as reinforcing agents for resinous structural
materials results in slippage between the bamboo fibers and the
resin matrix.
[0011] The present invention seeks to eliminate the above-noted
disadvantages by providing a low-cost, high-strength composite
formed from linear bamboo fibers bonded to synthetic polymers with
binding agents which have been found to provide exceptional binding
between the bamboo fibers and the polymer matrix. these composites
can replace wood, concrete, steel, or fiberglass reinforced
polymers in poles, pilings, and load-carrying structural
applications such as pallets.
SUMMARY OF THE INVENTION
[0012] This invention seeks to provide an improved composite that
has the ability to overcome the disadvantages of the presently
available structural materials. In accordance with this invention,
a composite structural piece is provided which comprises linear
bamboo fibers bonded to and surrounded by synthetic polymers such
as thermoplastic and thermosetting resins. In one form, the fibers
are formed in elongated strips with an outer polymer coating and
compression cut into short stubs which can be used in place of
conventional plastic nodules in an injection molding machine
Products formed by injection molding using this form are lighter in
weight and stronger than items molded of plastic alone.
[0013] In preparing the products of this invention, bamboo fibers
of dimensionally equal sizes are treated or primed with a bonding
material to be described below so as to accept a synthetic polymer.
The fibers may take the form of split culms or tape. The products
may be prepared by extruding a mixture of primed linear bamboo
fibers and synthetic polymers or the product may be prepared by
molding the mixture. The products may desirably take the form of
beams, columns, poles, dimensional lumber or other structural
products.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] For a better understanding of the present invention,
reference may be had to the following detailed description taken in
conjunction with the accompanying drawings in which:
[0015] FIG. 1 is an elevational view of a split bamboo culm and
gives a pictorial explanation of the making of bamboo fibers and
tapes useful in this invention;
[0016] FIG. 2 is an elevational view showing a utility pole
prepared according the extruding method of this invention;
[0017] FIG. 3 is an elevational view of a primed split bamboo
culm;
[0018] FIG. 4 is an elevational view of a beam containing a
synthetic polymer circumference and an interior comprising bamboo
fiber and wood prepared according to the molding method of this
invention;
[0019] FIG. 5 is an elevational view of a supporting column made
according to this invention;
[0020] FIG. 6a is a graphical representation of the extrusion
machine having a circular die used according to this invention;
[0021] FIG. 6b is an elevational view of a rectangular die used
according to this invention as a replacement for the circular die
in the extrusion machine of FIG. 6a;
[0022] FIG. 7 is a graphical representation of a cooling bath and a
molding apparatus used according to this invention;
[0023] FIG. 8 is a side elevational view of a bridge made using
supporting columns prepared according to this invention;
[0024] FIG. 9 is an exploded view of one form of structural pallet
using at least some of the teachings of the present invention;
and
[0025] FIG. 10 illustrates a mold for producing the pallet of FIG.
9.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] The invention will now be described with reference to the
above drawing. In all Figures, like numerals represent like
features. In accordance with this invention, a load-carrying
structure 1 is provided which comprises linear bamboo fibers 6
bonded to, and surrounded by, synthetic polymers 8. The bamboo
fibers 6 may be in the form of split culms 17 or tapes. The
structures 1 are made from bamboo culms 17 which are split into
dimensionally equal sizes and treated with a bonding material
7.
[0027] It has been found that the following binding agents give
surprisingly good bonding between the bamboo and the polymer
matrix: maleated polypropylene, maleated polyethylene, maleic
anhydride, hydroxyl methacrylate, silane compounds, N-vinyl
pyridine, N-vinyl caprolactam, N-vinyl carbazole, methacrylic acid,
ethyl methacrylate, isobutyl methacrylate, sodium styrene
sulfonate, bisvinyl phosphate, divinyl ether-ethylene glycol, vinyl
acetate, vinyl toluene, vinylidene chloride, chloroprene, isoprene,
dimethylaminoethyl methacrylate, isocetylvinyl ether,
acrylonitrile, glycidyl methacrylate, N-vinyl pyrrolidone, acrylic
acid, ethyl acrylate, itaconic acid, methyl acrylate, sodium vinyl
sulfonate, cetyl vinyl ether, divinyl ether-butanediol, and
octadecyl vinyl acetate.
[0028] According to one aspect of this invention, a plastics
extruding machine 10 (FIG. 6a) is connected to a die 9 that allows
the bamboo fibers 6 (FIG. 1) primed with at least one of the above
binders to fill the outside circumference of a die 9. The primed
bamboo fibers 6 enter the die 9 as heated plastic 8 is injected
under high pressure and caused to flow through the interior of the
die 9. The mixture of primed bamboo fibers 6 and plastic 8 is
extruded as a column and enters powered pullers 12 that are capable
of extracting the column to form any practical length. A power saw
13 travels beside the extruded piece, sawing it to a desired length
without slowing the extruding process. The traveling saw 13 returns
to its starting point to select the next length. The thus-prepared
composite structure 1 is transferred to a water-cooled bath 14
where it is cooled to ambient temperatures and the sawed ends are
capped.
[0029] In an alternate method of preparing bamboo fiber 6/plastic 8
composite structures 1 according to this invention, the bamboo
fibers 6 are primed by coating alt least one of the above binders
by immersing the bamboo fiber in a bath of the primer, spraying the
binder onto the bamboo fiber, or brushing the primer onto the
bamboo fiber. The primed bamboo fiber is secured to a carrying core
2 of-wood or metal to form a core assembly and this core assembly
is inserted into a mold 18 and positioned so as to allow clearance
for the plastic 8 matrix to flow around all exposed surfaces in
desired thicknesses. The mold 18 is heated and connected to an
extruder 10 or large injection molding machine. Some molds nay
require a vacuum to be pulled by a vacuum system 19 on the interior
of the mold 18 prior to injection. The synthetic polymer 8 is then
injected, the mold 18 is chilled, and the resulting composite
structure 1 is removed from the mold 18.
[0030] Some plastics have an almost unlimited life span when
exposed to the elements. This explains the ability of fiberglass to
dominate the marine market where wood and steel require too much
maintenance. However, plastics by themselves lack sufficient
tension and compression strength to stand alone as load-carrying
structures. The marine industry solved this problem with the
addition of glass fibers to the plastic matrix resulting in
fiberglass. This engineered composite has three times the
load-carrying capability of steel of an equal weight. The cost of
glass fiber reinforced plastics has limited this material to
special products and niche markets. Asian and some South American
bamboo species such as Gradua and Tonkin cane have tension strength
close to steel and compressional strength exceeding concrete. At
{fraction (1/100)} the cost of glass fiber, linear bamboo fiber can
be more competitive with traditional materials. By utilizing fiber
in a plastic matrix, the resulting composite is very strong and has
the nearly unlimited life span of the plastic exterior.
[0031] In order to produce load carrying structures from the
composite of this invention, the bamboo linear fiber 6 must bond to
the plastic matrix 8. The elongation of the plastic glue allows the
load to be evenly distributed along all of the unidirectional
bamboo fibers 6. This is the key to the exceptional strength of the
composite structures 1 of this invention. A bonding material 7 of
at least one of the materials named above is used, allowing
difficult matrices, such as polyethylene, to bond to the bamboo
fibers 6.
[0032] In making the structures 1 of this invention, a bamboo culm
17 is split to its desired size. The fibers 6 may take the form of
a full width split bamboo culm, smaller slices, or a tape. In all
figures of this description, linear bamboo fiber refers to all
three of these possibilities.
[0033] The linear bamboo fiber 6 is treated with at least one
bonding agent 7 as described above, most preferably acrylic acid or
maleic anhydride or salt or ester derivatives thereof, to promote
the adhesion of the fibers 6 to the synthetic polymer matrix 8. The
synthetic polymer 8 may be a thermosetting resin or a thermoplastic
resin.
[0034] With reference to FIG. 6a, in preparing poles or pilings,
dried and split bamboo culms 17 of a length equal to the pole or
piling being produced are treated with a bonding material 7 as
described above and inserted into the die 9 and a synthetic polymer
8 such as recycled polyethylene pellets is loaded into the hopper
11 of the extruder 10. The extruder 10 is heated to melt the
polymer 8. The extruder 10 is turned on and the pushers or pullers
12 start to insert the bamboo fiber 6 reinforcement into the
proximal end of the heated die 9 while the extruder 10 begins to
inject molten plastic 8 into the die 9. The molten plastic 8
completely envelops the bamboo fiber 6 and the mixture of bamboo
fiber 6 and synthetic polymer 8 starts to emerge from the distal
end of the heated die 9. At a proper time, the puller 12 engages
the cooled composite extrudate as it emerges from the die 9. This
process continues until the desired length of extrudate is
obtained. The traveling saw 13 starts sawing off the desired length
of extrudate and automatically returns to the starting position to
begin sawing the next section. The newly extruded pole or piling is
chilled in a circulating water bath 14 ad when sufficiently cooled
is placed into storage.
[0035] Because utility companies presently prefer tapered poles, it
is anticipated that utility poles may be produced as a thick-walled
pipe in a molding process. For example, a thin wall tube is first
extruded from pelletized material such as the below described
bamboo pellets. The tube is then wrapped with bamboo fibers using
the tape form building up different thicknesses to create a desired
taper. The wrapped pole is placed in a mold and the plastic polymer
injected to coat the pole. Alternately, the inner tube could be
molded with a tapered shape and then uniformly wrapped with bamboo
tape to create a tapered product which is again placed in the final
tapered mold and injection coated with polymer.
[0036] A cross-arm for a utility pole may be similarly constructed.
Bamboo linear fiber 6 in the form of a tape is treated with at
least one bonding material 7 as described above and is bonded to a
central carrier core 2. This assembly is forced through a die 9 to
produce a rectangular beam cross-section, as shown in FIG. 4. The
die 9 operation, the extracting, and cooling are identical to the
operation described for producing poles or pilings.
[0037] Other structures incorporating bamboo as a filler can also
be injection molded by preparing bamboo in small, plastic
encapsulated beads or pellets that can be fed into the machine 10
through hopper 11 in the same manner as conventional plastic beads.
In one form, the bamboo beads can be made by extrusion molding a
continuous strip as described above for a bamboo fiber 6/plastic 8
composite structure such as is shown in FIG. 5. However, the
cross-sectional dimension is substantially reduced to about 0.25
inches. The elongated strip is then cut into about 0.25 inch
lengths. Preferably the cutting process is implemented by a
chopping type cutter having opposing cutting blades that are
somewhat dull so as to effectively compress the outer plastic layer
over the ends of the bamboo fibers during the cutting process so
that all surfaces of the fiber are generally encompassed within the
plastic. The resulting product is a pellet that may be generally
oval shaped by the cutting process and includes a bamboo fiber core
within an outer plastic layer. When the pellets are fed through
hopper 11 into extruder 10, various shaped objects, depending upon
the form of the mold coupled to the extruder, may be made from this
lightweight, filled bamboo plastic composite. The bamboo provides
structural support to enable formation of objects having thickened
supports or walls. While the 0.25 inch dimension is believed to be
a best mode, it will be recognized that other dimensions may be
more appropriate for some applications.
[0038] For making columns having maximum compressional
load-carrying capacity, the bamboo culms 17 are treated with at
least one of the bonding materials 7 named above and are inserted
into a mold 18. The synthetic polymer is then introduced into the
mold 18 to bond to, and surround, the bamboo culms 17. In this way,
support columns of exceptional load-carrying ability and the
ability to withstand seismic events and other horizontal pressures
are produced.
[0039] While various structural devices can be made using the
inventive bamboo/plastic composite of the present invention, one
application that is adaptable to such composite is the structural
pallet. As previously mentioned, pallets are used worldwide for
supporting various products for shipment or storage. The use of
pallets is so pervasive that standards have been established to
define sizes of pallets. In the United States, one standard is the
Grocery Manufacturers Association or GMA standard defining a pallet
of 40 inches by 48 inches with a bottom structure having a
cross-shaped form, i.e., having 4 large openings and a perimeter
base. Europe has a different standard in which the bottom structure
for the Euro-pallet uses three lengthwise extending boards or
braces and the overall dimension is 1000.times.1200 cm. In general,
the standards require that the pallet be able of edge mounting in
warehouse racks with a 2000 lb. load and exhibit less than one inch
deflection. These standards have created a problem for plastic
pallets since plastic flows under load, is substantially weaker
than an equivalent volume of wood and costs about 3 times the price
of wood. However, plastic does have the advantage of being
cleanable or sterizable.
[0040] Referring now to FIG. 9, there is shown an exploded view of
a pallet 20 having a solid top panel 22, a bottom panel 24
conforming to GMA standards and a plurality of support blocks or
spacers 26 which support and position top panel 22 with respect to
bottom panel 24. The top panel 22 is formed of a plurality of
bamboo strips of the type described above which may be laid in
layers with each layer being oriented at 90 degrees to adjacent
layers or, in a preferred form, with the strips woven into mats
that can be laid atop one another to a desired number of layers.
For weight reduction, the top panel 22 may be cored somewhat like
bottom panel 24. The spacers 26 may be injection molded blocks
using the aforementioned bamboo/plastic pellets or may be sections
of an extruded elongate composite such as shown in FIG. 5. Bottom
panel 24 is formed by multiple overlapping layers of bamboo fibers
bonded using the above described methods. All the exposed surfaces
of the top and bottom panels and spacers are protected and covered
by an outer plastic shell.
[0041] FIG. 10 illustrates a simplified form or mold 28 for
producing the GMA pallet 20 of FIG. 9. The mold 28 includes a base
30 having a bottom member 32 to which are attached outer periphery
defining side members 34. The pallet 20 is actually formed in an
inverted orientation and the inner surface 36 of member 32 may
desirably be embossed with selected patterns so as to form mating
patterns on an upper surface of the pallet to minimize sliding of a
load on the pallet's plastic surface. The embossing on the surface
36 is preferably formed as continuous connected grooves such as in
a spider web configuration (radial lines intersecting concentric
circles) so as to create flow paths for injection of plastic into
the mold for covering the bamboo mats. In the use of the
illustrated mold, the bamboo fibers, preferably in the form of
woven mats, are laid into the mold base 30. It may be desirable to
create a pre-form of bamboo fibers, either woven or transversely
overlaid, that are glued together similar to the process described
above for producing columns or timbers, so that the pre-formed base
of bamboo can be easily positioned in mold base 30. As will be
apparent, plastic molding generally requires that the mold be
pre-heated and, while heating apparatus is not shown, those skilled
in the molding art will understand various methods and apparatus
for pre-heating the mold components to temperatures suitable for
molding, e.g., about 400.degree. F.
[0042] After the pre-form of fiber mats are laid in the mold base
30, a male insert section 40, also pre-heated, is positioned in
base 30 overlaying the fiber mats. The section 40 includes four
open-top box members 42 coupled together by intermediate closed
connectors 44. The members 42 are shell structures in order to
reduce weight and to enable placement of hydraulic/pneumatic
actuators (not shown) in the members 42. The actuators are attached
to extendible blocks 46 protruding outward from the members 42. The
illustrated mold 30 is designed to produce the GMA pallet of FIG. 9
in the inverted position and the members 42 define the four
openings 27 in the bottom panel 24. The extendible blocks 46
establish the position of the spacers 26. The blocks 46 are
preferably extendible from members 42 and can be retracted to
facilitate removal of the section 40 from the base 30 and molded
pallet. However, it will be recognized that retracting all the
blocks 46 into members 42 will create an interference problem. Mold
designers will understand that one process to resolve interference
is to associate some of the blocks with the base mold 30 rather
than with the removable section 40.
[0043] With the section 40 positioned in base 30 over the bamboo
mats, the openings 48 between blocks 46 define positions for
spacers 26 and such spacers are inserted into the mold. Bamboo
fiber reinforced tape or fiber reinforced extruded bamboo/plastic
composite strips are next laid over the blocks 463 and spacers 26
forming the bottom panel or skid 24 of the pallet. A die (not
shown) having the same configuration and size as the panel 24 is
then brought into position and compresses the mold assembly to
about 75% of maximum pressure. Plastic is then injected into the
mold at relatively low pressure so as not to disturb the bamboo
fiber mats. (Once the mold cavities have been filled with the
molten plastic, plastic injection is shut-off and the die is closed
to 100% volume to consolidate the pallet. During the consolidation
stage, the spacers 26 bond to the upper and lower panels through
the plastic matrix. Mold temperature can be reduced at this stage
to cool the plastic sufficiently to) allow the completed pallet to
be removed from the mold. During this process, the die is retracted
and the section 40 lifted from the base 30, carrying the finished
pallet supported on at least some of the extended blocks 46. The
pallet is removed from section 40 by retracting blocks 46 into
members 42. The mold is then ready to be used for another pallet
manufacture.
[0044] The mold assembly of FIG. 10 is provided only by way of
example of a method for manufacturing a bamboo/plastic composite
pallet. For production of large volumes of pallets, it is
anticipated that the mold assembly will be substantially modified
and will have other moving elements to speed-up and simplify the
molding process. Accordingly, it is not intended that the invention
be limited by the illustrated mold assembly or process. For
example, it may be desirable to form the pallet in multiple steps
such as by molding top panel 22 in one operation, molding bottom
panel 24 in another operation and then attaching the top and bottom
panels together by adhesively bonding spacers 26 to facing surfaces
using a plastic solvent type adhesive or heat to raise the plastic
temperature to a bonding state.
[0045] While the invention is primarily directed to and has been
tested using bamboo, it is possible that other fibrous plant
material may be found suitable as a replacement for bamboo. For
example, Indian hemp, agave sisalana, rattan palm and papyrus palm
also produce fibrous material that is often used in manufacture of
cord and rope for handling tensile loads.
[0046] While the invention has been described in what is presently
considered to be a preferred embodiment, many variations and
modifications will become apparent to those skilled in the art.
Accordingly, it is intended that the invention not be limited to
the specific illustrative embodiment but be interpreted within the
full spirit and scope of the appended claims.
* * * * *