Note: Descriptions are shown in the official language in which they were submitted.
~z~
BACKGROUND OF THE INVENTION
This invention relates to articles molded from
flake-like wood particles and, more particularly, to
such articles having non-planar portions, such as
material handling pallets and the like.
Considerable effort has been devoted to develop-
ing techniques f~r molding articles including non-planar
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portions from inexpensive residue and surplus t~oods.
One area of particular interest for utilizing such
woods is in the production of material handling pallets
having a~ least the same strength and durability and
other desirable characteristics of standard pallets
constructed from lumber.
It is well known to manufacture flat or substan-
tially flat structural boards or so-called particle
board from comtninuted wood by mixing the wood particles
with a suitable resinous binder, such as a synthetic
thermosetting resin, forming the mixture into a multi-
layered mat and then compressing the mat between heated
platens to set the binder and bond the wood particles
together. This type process is exemplified in U.S.
Patents 3,164,511, 3,391,233 and 3,940,230.
~ 101ding of pallets and other articles including
non-planàr portions presents problems of little or no
concern in the manufacture of flat or substantially
flat particle board. For instance, one difficulty
involved in molding pallets is the necessity to pull or
draw a plurality of hollow legs having acceptable
crushing strengths from a substantially flat mat of
wood particles without adversely affecting the strength
of the deck member or the legs.- Conse~uently, the
above type process for manufacturing particle board
heretofore has not been employed to manufacture pallets
or other similar articles from wood particles.
In one prior art method for molding pallets from
wood particles, exemplified by U.S. Patents 3,104,085,
3,359,929 and 3,611,952, wood fibers are made into a
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pul~ slurry which typically also contains a resinous or
other suitable binder. The slurry is introduced ineo a
mold wherein most of the water is removed by compress-
ing, application of a vacuum or positive pressure, etc.
The wet, molded pallet is transferred to a heated mold
and dried under elevated pressure and temperature
conditions to expedite removal of water, and to cure
the binder if one is included in the slurry. If a
binder is not included in the slurry, the dried pallet
usually is dipped into a resin containing soluticn for
; strengthening and water proofing. This prior art
method involves several expensive processing steps and
the pallets produced thereby do not have acceptable
strength characteristics or durability for many
applications. ,~
`~ In another prior art/for molding pallets from wood
; particles, promoted in the United States under the
trademark "WERZALIT" ànd e~emplified by U.S. Patents
~, ~ .
~,146,285 and 3,354,2~8, a mixture of finely comminuted
wood particles and a heat curable, resinous binder is
introduced into a cold press to form a preform having
nearly the final size and shape of the pallet, with
partial or no curing of the binder. The preform is
transferred to a heated press or mold whe~ein it is
compressed to the final size and shape at an elevated
temperature to completely cure the binder. This method
is relatively expensive because of the degree to which
the starting material must be comminuted, the amount of
binder required to bond the relatively small wood
particles together, the capital investment for the
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dlfferent presses, and the opera-ting cos-ts associa-ted
wi-th the numerous processing steps.
A principal object of -the inven-tion is to provide
an article, such as a material hand]ing pallet, having a
main body and non-planar portions displaced from the major
plane of the body, the main body and non-planar portions
being molded as a one~piece unit from low cost woods.
Another object of the invention is to provide a
pallet molded from low cost woods and having strength and
handling characteristics at least comparable to standard
pallets made- from s-tick lumber.
A further object of the invention is to provide
a simpliEied method for molding such pallets and other
articles having non-planar portions from low cost wood
particles.
A still further object of the invention is to
provide such a method which does not require :Eormation of
a preform prior to molding to final dimensions and does
not require finely comminuted wood particles.
2~ Other objects, aspec-ts and advantages of the
invention will become apparent to those skilled in the art
upon reviewing the following detailed descriptlon, the
drawings and the appended claims.
According to one aspect of the invention there
is provided a pallet which includes a generally flat,
rectangular deck having a major plane and a flat upper
surface. A plurality of parallel rows of spaced, hollow
leg members project integrally from the deck member from
the leg members in each of the rows being laterally aligned
with a leg member in the adjacent row. Each of the leg
members has a bottom wall spaced from -the deck member a
sufficient distance to permit entry of fork lift tines
beneath the deck member and opposed pairs of side walls
pc/ ~
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intec~rally connectincJ the bo-ttom walI with -the deck member
ancl inc]ining outwardly from the bot-tom wall toward the
deck member.
The decks and legs are molded as a one-piece unit
from a layered mix-ture of resinous particle board binder
and flake-like wood particles having an average length of
about 1-1/4 to about 6 inches, an average thickness of about
0.005 to about 0.075 inch, and an average wid-th of about 3
inches or less and no greater than -the average length, each
layer of the wood particles forming at least the deck member
lying substantially flat in a plane generally parallel to
the major plane with the wood particles therein being randomly
oriented.
According to another aspect of the present
invention there is provided a method for molding an article
having a major plane and at least one non-planar portion
displaced from the major plane, the rnethod including the
steps of providlng flake-like wood particles having an
average length of about 1-1/4 inch to about 6 inches, an
average thickness of about 0.005 to about 0.075 inch and
an average width o~ about 3 inches or le~s and no greater
than the length. A resinous particle board binder is
admixed with the wood particles, and a ~oosely-felted,
layered mat formed from the mixture is deposited on one
open part of a mold including two separate parts de-fining
a mold chamber having the shape of the ar-ticle, the wood
particles in each layer of the mat lying substan-tially flat
in a plane generally parallel to the major plane and being
pC/ ~Ij 1,
` ~4~364
randomly oriented. The mold is closed and sufficient
hea-t and pressure is applied on the mat to compress it
into substantially the desired shape and size of the
article and to bond the wood particles together to form
a unitary structure.
BRIEF DESCRIPTION OF T~IE DRAWINGS
Fig. 1 is a perspective view of a pallet incorpo-
; rating various features of the invention.
Fig. 2 is a sectional view taken generally along
lLne,2-2 in Fig. 1.',
Fig. 3, which appears on the same sheet of
drawings as Figure 1, is a schematic flow diagram illustrating
.
the various steps of a preferred process for molding,pallets
of the invention from residue and surplus woods.
Figs. ~-7 are simplified, schematic side views of
the mold or press, illustrating various techniques for
depositing a mat of the wood flakes on the female die prior
to closing the mold.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates broadly to articles,
particularly support members, including a main body having
a major plane and non-planar portions displaced from that-
major plane, both molded as a one-piece unit ~rom wood flakes. '
The invention is particularly adaptable to material handling
pallets and will be described in connection'therewith.
Illustrated-in Figs. 1 and 2 is pallet 10 includ-
ing a generally flat, rectangular deck member 12 havin~ a
substantially uniform wall thickness and a flat upper
surface 14 which serves as a supporting plane. Projecting
downwardly from the deck member 12 is a plurality (e.g. 9
of hollow leg members 16 adapted to serve as supporting
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pads for the palle-t. In the speciEic construction
illustrated, each of the leg members 16 (Fig. 2~ includes
a bottom wall 1.8 having a flat bottom surface 20 and two
opposed pairs of flat side walls 22 and 24. The bottom
surface 20 of the bottom wall 18 is spaced from the
underneath surface of the deck member 12 a sufficient
distance to permit entxy of the tines of a fork lift
beneath the deck member.
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sb/ ~ ~
The deck member 12 and leg members 15 are molded
as a one-piece Ullit ~rom a mixture of a suitable
resinous particle board binder and flake-like wood
particles as described below~ The side walls 22 and 2
of the leg members 16 are inclined or tapered to
facilitate molding and to also permit nesting of
several pallets into a compact stack so as to minimize
the space required for shipment and storage. In the
specific construction illustrated, the side walls 22
and 24 are substantially flat and the leg members 16
have the general form of an inverted, truncated hollow
pyramid. If desired 9 the leg members 16 can be formed
with other suitable cross-sectional shapes~ e.g., in
the ~orm of an inverted, truncated hollow cone.
Fig. 3 diagrammatically illustrates the various
steps of the process of the invention for manufacturing
the pallet 10 from inexpensive residue and surplus
woods. The process broadly includes the steps of
comminuting small logs, branches or rough pulpwood into
flake-like particles, drying the wood flakes to a
predetermined moisture content, classifying the dried
flakes to obtain wood particles having a predetermined
size, blending predetermined quantities of a suitable
resinous particle board binder, and optionally a liquid
wax composition, with the dried and sized fla~es,
forming the resultant mixture of binder, wax and wood
- flakes or furnish into a loosely-felted, layered
mat (single or multi-layers), placing the mat in an
open mold or press including separable male and female
dies definin~ a mold chamber having the desired shape
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of the pal]et, closing the mold and applying sufficient
pressure to mat to compress it into substantially the
desired shape and size of the pallet7 removing the
molded pallet ~rom the press, and trimming the peripheral
edges of the pallet with a power saw or the like to the
desired final dimensions.
The wood flakes used can be prepared from various
species of suitable hardwoods and softwoods used in the
manufacture of particle board. Representative examples
of suitable woods include aspen, maple, oak, elm,
balsam fir, pine, cedar, spruce, locust, beech, birch
and mixtures thereof.
Suitable wood flakes can be prepared by various
conventional techniques. In the specific process
illustrated, the wood flakes are prepared by one of two
different techniques. In the technique illustrated in
the upper left hand portion of Figure 3, pulpwood grade
- logs, or so-called roundwood, are converted into flakes
in one operation with a conventional roundwood flaker.
In the technique illustrated in the upper right hand
portion of Figure 3, logs, logging residue or the total
tree are first cut into fingerlings in the order of 2-6
inches long with a conventional device, such as the
helical comminuting shear disclosed in U.S. Patent
4,053,004, and the fingerlings are flaked in a conven-
tional ring-type flaker.
Roundwood flakes generally are higher quality and
p~oduce stconger pallets because the lengths and
thickness can be more accurately controlled. Also,
roundwood flakes tend to be somewhat flatter which
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L42~4
f~cilitates more efficient blending and the logs
can be debarked prior to fLaking which reduces the
amount of less desirable fines produced during flaking
and handling. Acceptable flakes can be prepared by
rin~, flaking fingerlings and this technique is more
readily adaptable to accept wood in poorer form,
thereby permitting more complete utilization of certain
types of residue and surplus woods.
Irrespective of the particular technique employed
for preparing the flakes9 the size distribution of the
flakes is quite important, particularly the length and
thickness. The wood flakes should have an average
length of about 1~1/4 inch to about 6 inches and an
average thickness of about 0.005 to about 0.075. In
any given batch, some of the flakes can be shorter than
1-1/4 inch and some can be longer than 6 inches so long
as the overall average length is within the above
range. The, same is true for the thickness.
The presence of major quantities of flakes having
a length shorter than about 1-1/4 inch tends to cause
the mat to pull apart as the leg members are being
drawn therefrom during the molding step. This undesir-
able condition is particularly prevalent at the corner
junctures of the leg members and the deck member as
described in more detail below. The presence of some
fines in the mat produces a smoother surface and ? thus,
may be desirable for some applications so long as the
majority of the wood flakes, preferably at least 75%,
is longer than l-1/8 inch and the overall avera~e
length is at least 1-1/4 inch.
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Substantial quanLities of Elakes longer than about
6 inches tend to cause interleaving or felting of the
flakes during handling prior to formation oE the mat
and can complicate drawing of the leg members. For
example, such interleaving can prevent adequate coating
of the flakes with the binder during the blending step
with a resultant inadequate bonding of the flakes
during molding. The average length of the wood flakes
preferably is about 2 to about 3 inches.
Substantial quantities of flakes having a thick-
ness of less than about 0.005 should be avoided because
excessive amounts of binder are required to obtain
adequate bonding. On the other hand, flakes having a
thickness greater than about 0.075 inch are relatively
stiff and tend to overlie each other at some incline
when formed into the mat. Consequently, excessively
high mold pressures are required to compress the flakes'
into the desired intimate contact with each other~ For
flakes having a thickness falling within the abov'e
range, thinner ones produce a smoother surface while
thicker ones require less binder. These two factors
are balanced against each othe~ for selecting the best
average thickness for any particular application. The
average thickness of the flakes preferably is about
0.015 to about 0.25 inch, most preferably about 0.020
lnch.
The width of the flakes is less important. The
flakes should be wide enough to insure that they lie
substantially Elat when Eelted during mat formation.
The average width generally should be about 3 inches or
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~ ~ 421 36~
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less and no greater than the average length. For best
results, the majority oE the Elakes should have a width
o~ about 1/16 inch to about 3 inches.
The thickness of the flakes can be controlled pri-
S marily by the blade setting on the flakerO The lengthand width of the flakes are also controlled to a large
degree by the flaking operation. For example, when the
flakes are being prepared by ring flaking fingerlings,
the maximum lengths are generally set by the length of
the fingerlings. Other factors, such as the moisture
content of the wood and the amount of bark on the wood
affect the amount of fines produced during flaking.
Dry wood is more brittle and tends to produce more
fines. Bark has a tendency to more readily break down
into fines during flàking and subsequent handling than
wood.
` While the flake size can be controlled to a large
degree during the flaking operation as described above,
it usually is necessary to use some sort of classifica-
tion in order to remove undesired particles, both
~ ~ undersized and oversized, and thereby ensure the
; ~ average length, thickness and width of the flakes arewithin the desired ranges. I~en roundwood flaking is
used, both screen and air classification~usually is
required to adequately remove both the undersize and
oversize particles, whereas fingerling flakes usually
can be properly sized with only screen classification.
Flakes from some green woods can contain up to 90%
moisture. The moisture content of the mat must be
substantially less for molding as discussed below.
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142~ 4
Also, wet Elakes tend to stick together and complicate
classiEication and handling prior to blending. Accord-
ingly, the flakes are preferably dried prior to classi-
fication in a conventional type drier, such as an
tunnel drier, to the moisture con~ent desired for the
blending step. The moisture content to which the
flakes are dried usually is in the order of about 6
weight % or less, preferably abou~ 2 to about 5 weight
%, baséd on the dry weight of the flakes. If desired,
the flakes can be dried to a moisture content in'the
order of 10 to 25 weight % prior to classification and
then dried to the desired moisture content for blending
after classification. This two-step drying may reduce
the overall energy requirements for drying flakes
prepared from green woods in a manner producing substan- -
tial quantities of particles which must be removed
during classification and, thus, need not be as thoroughly
dried.
~ known amount of the dried, classified flakes is
introduced into a conventional blender, such as a
paddle-type batch blender, wherein predetermined
amounts of a resinous particle binder, and optionally a
wax and other additives, is applied to the flakes as
they are tumbled or agitated in the blender. Suitable
binders include those used in the manufacture of
particle board and similar pressed fibrous products
and, thus, are broadly referred to herein as "resinous
particle board binders". Representative examples of
suitable binders include thermosetting resins such as
phenol-formaldehyde, resorcinol-formaldehyde, melamine-
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2g~4
formaldehyde, urea-formaldehyde, urea-furfural and
condensecl ~ur~uryl alcohol resins, and organic polyiso-
cyanates, either alone or combined with urea- or
melamine-formaldehyde resins. Particularly suitable
polyisocyanates are those containing at least two
active isocyanate groups per molecule, including
diphenylmethane diisocyanates, m- and p-phenylene
diisocyanates, chlorophenylene diisocyantes, toluene
di- and triisocyantes, triphenylmethene triisocyanates,
diphenylether-2,4,4'-triisocyanate and polyphenylpolyi-
socyanates, particularly diphenylmethane-4,4'-diisocya-
nate.
The particular type binder used depends primarily
upon the intended use for the pallet. For instance,
lS pallets employing urea-formaldehyde resins have suffi-
cient moisture durability for many uses which involve
; minimal exposure to moisture, but generally cannot
withstand extended outdoor exposure and reusability is
quite limited. Phenol-formaldehyde and melamine-formal-
dehyde resins provide good moisture resistance but
require substantially longer cure times. Polyisocya-
nates, even in lesser amounts, provide greater strengths
and moisture resistance than the urea- or phenol-formal-
dehyde resins and the resultant pallets can be reused
for an extended number of cycles. Polyisocyanates cure
in about the same time as urea-formaldehyde resins.
However, polyisocyanates are more expensive and require
the use of a mold release agent because of their
tendency to stick to metal parts. These factors are
balanced against each other when selecting the specific
binder to be used.
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L4~'~6~
A binder system includiny bot'~ a urea-forrnaldehyde
resin and a polyisocyanate, at a solids weight ratio o
about 4:1 to ahout l:l, is advantageous for many
applications because, although less costly than polyiso-
cyanate alone, it provides strength characteristics andmoisture resistance which is superior to those obtain-
able from either urea- or phenol-formaldehyde resins
alone and the pallets are reusable.
The amount of binder added to the flakes during
the blending step depends primarily upon the specific
binder used, size, moisture content and type of the
flakes, and the desired characteristics of the pallet.
Generally, the amount of binder added to the flakes is
about 2 to about 15 weight %, preferably about 4 to
about lO weight %, as solids based on the dry weight of
the flakes. ~hen a polyisocyanate is used alone or in
combination with a urea-formaldehyde resin, the amounts
can be more toward the lower ends of these ranges.
The binder can be admixed with the flakes in either
dry or liquid form~ To maximize coverage of the
; flakes, the binder preferably is applied by spraying
droplets of the binder in liquid form onto the flakes
` as they are being tumbled or agitated in the blender.
When polyisocyanates are used, a conventional mold
release agent preferably is applied to the die or to
the surfaces of the formed mat prior to pressing. To
improve water resistance of the pallet, a conventional
liquid wax emuision preferably is also sprayed onto the
flakes during the blending step. The amount of wax
added generally is about 0.5 to about 2 weight %, as
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~ L3.42~S4
solicls based on the dry ~eight of the flakes. Other
additives, such as a coloring agent fire retardant,
insec~icide, fungic;de and the like may also be added
to the flakes during the blending step. The binder,
wax and other additives, can be added separately in any
sequence or in combined form.
The moistened mixture of binder, wax and flakes
or furnish from the blending step is formed into a
loosely-felted, single or multi-layered mat which is
compressed into a pallet. The moisture content oE the
flakes should be controlled within certain limits so as
to obtain adequate coating by the binder during the
blending step and to enhance binder curing and deforma-
tion of the flakes during molding.
The presence of moisture in the flakes facilitates
their bending to make intimate contract with each other
and to form the leg members and enhances uniform heat
transfer throughout the mat during the molding step,
thereby ensuring uniform curing. However, excessive
amounts of water tends to degrade some binders, partic-
ularly urea-formaldehyde resins, and generates steam
which can cause blisters. On the other hand, if the
flakes are too dry, Lhey tend to absorb excessive
amounts of the binder, leaving an insufficient amount
on the surface to obtain good bonding and the surfaces
tend to case harden which inhibits the desired chemical
reaction between the binder and cellulose in the wood.
This latter condition is particularly true for
polyisocyanate binders.
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Generally, Lhe moisture content of the furnish
a~ter completion of blending, including the original
moisture content of the flakes and the moisture added
during blending with the binder, wax and other addi-
tives, should be about 5 to about 25 weight %, prefer-
ably about 8 to about 12 weight %. Generally, higher
moisture contents within these ranges can be used for
polyisocyanate binders because they do not produce
condensation products upon reacting with cellulose in
the wood.
The furnish is formed into a generally flat,
loosely-felted, mat, preferably as multiple layers,
having a rectangular shape generally corresponding to
the outer dimensions of the pallet. ~ conventional
dispensing system, similar to those dîsclosed in U.S.
Patents 3,391,223 and 3,824,058, can be used to form
the mat. Generally, such a dispensing system includes
a plate-like carriage carried on an endless belt or
conveyor and one or more (e.g., 3) hoppers spaced along
the belt in the direction of travel for receiving the
furnish. When a multi-layered mat is ~ormed in
accordance with a preferred embodiment, a plurality of
hoppers usually are used with each having a dispensing
or forming head extending across the width of the
carriage Eor successively depositing a separate layer
of the furnish as the carriage is moved beneath the
forming heads.
In order to produce pallets having the desired
strength characteristics, the mat should have a substan-
tially uniforM thickness and the flakes should lie
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28~4
subst;3n~ ially ~lat in a horizontal plane parallel to
the surface of the carriage and be randomly oriented
relative to each other in that plane. The uniformity
of the mat thickness can be controlled by depositing
two or more layers of the furnish on the carriage and
metering the flow of furnish from the forming heads.
The desired random orientation of the flakes can
be enhanced by spacing the forming heads above the
carriage so the flakes must drop about 1 to about 3
feet en route to the carria~e. As the flat flakes fall
from that height, they tend to spiral downwardly and
land generally flat in a random pattern. Wider flakes
within the range discussed above enhances this action.
A scalper or similar device spaced above the carriage
can be used to ensure uniform thickness or depth of the
mat; however, such means usually tends to align the top
layer of flakes, i.e., elirninate the desired random
orientation. Accordingly, the thickness of the mat
preferably is controlled by closely metering the flow
of Çurnish from the Eorming heads.
The mat thickness used will vary depending upon
such factors as the size and shape oE the wood fIakes,
the particular technlque used Eor forming the mat, the
desired thickness and density of the pallet deck and
leg members, the configuration of the pallet ~particu-
larly the size and shape of the leg members), and the
molding pressure to be used. For example, if the
pallet is to have a l/2-inch thick deck member and a
density oi 45 pounds per cubic Eoot, the mat usually
will be about 3 inches thick when roundwood flakes are
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used and about 4 inches thick when Elakes prepared by
ring ~lakiny, fingerlings are used. Of all these
variables, the final density oE the pallet is the
primary Çactor for determining the mat thickness.
Referring to Fig. 4, the mat 30 is compressed in
a heated press or mold 32 including a moyable male die
34 and a stationary female die 36 which cooperate to
define a mold chamber having the shape of the pallet.
The female die 36 includes a plurality of cavities 40
(one shown), each defining the exterior of a leg-member
16, and the male die 34 includes a plurality of corre-
sponding protruberances 42 (one shown), each defining
the interior of a leg member 16.
The mat 30 is removed from the forming carriage
and deposited on the female die 36 as illustrated.
~hen the male die 34 is closed, portions of the mat 30
are drawn or pulled down into the female die cavities
40 to form the leg members 16 as contrasted to the
material flowing into the mold cavities as is the case
with plastic materials and finely comminuted fibrous
molding compositions. Thus, the corner junctures
between the leg member 16 and the deck member 12 are
particularly vùlneraùle to structural weakening result-
ing from a tendency for the flakes to be pulled apart
during the molding operation.
The process of the invention minim-izes this ten-
dency, in a large part, by using wood flakes having
dimensions within the ranges noted ahove and forming
the mat 30 so that the layers oÇ wood flakes lie
substantially flat and are randomly oriented. Instead
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4~ ;4
of pulling al?art at the corner junctures, a number of
the flakes more or less are bent or deformed around the
corners and thereby provide joints having substantial
structural integrity.
Because of this drawing or pulling action on the
mat during molding, there are some practical limitations
for the pallet configuration. Referring to Fig. 2, the
slope of the side walls 22 and 24 with respect to the
major horizontal plane oE the deck tnember 16, designated
by angle A, should not exceed about 78. If relatively
tight corners are desired between the bottom of the
deck member 12 and the leg member 16,-the outer radii,
designated as Rl, should be substantially larger than
the inner radii, designated as R2. Larger leg
members (e.g., 7 inches X 9 inches) generally are
easier to mold than smaller leg members (e.g., 5 inch
diameter) when the side walls have the same slope. As
a general rule, the slope and depth is less for smaller
leg members. The leg member side walls 22 and 24
generally are provided with a thickness which is 70 to
110%, preferably about 80-85%, of the deck member
thickness. The bottom wall thickness can be about
60-100% the deck member thickness.
The leg members should not be closer than about 6
inches from each other. Even at this distance, an
additional quantity of the flakes may be required to
compensate or those pulled or drawn down into the
female die cavities during the molding operation,
particularly when deeper or longer leg members are
formed. Eor example, when a mat formed outside the
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mold anci placed between the male and Eemale dies as
illustrated in Fig. 4 is used in the production of a 40
inch X 48 inch pallet having 9 legs, leg mernbers having
a depth (designated by dimension D in Fig. 2) up to
about 1-3/4 inches can be conveniently drawn from such
a mat.
Figs. 5-7 illustrate alternate techniques for
deposit-ing the flakes in the mold so as to permit
drawing of longer or deeper leg members. In the
technique illustrated in Fig. 5, the cavities 40 of the
female die 36 are first substantially ~illed with
furnish 44 and a loosely-felted mat 46, having a
substantially uniform thickness and formed outside the
mold similar to mat 30 in Fig. 4, is deposited on the
female die 36 over the filled cavities prior to closing
the mold.
In the technique Illustrated in ~ig. 6, a loosely-
felted mat 48 of substantially uniform thickness is
formed outside the mold, similar to the mat 30 in Fig.
4, and mounds 50 of additional furnish required for a
deep draw are deposited on top of the mat 48 at loca-
tions corresponding to the locations of the female die
cavities 40 prior to placing the mat 48 in the mold.
The techn;que illustrated in Figs. 5 and 6 have been
successfully employed to form pallets having leg
members of depths up to 5 inches or more and sidewall
slopes between 56 and 77.
In the technique illustrated in Fig. 7, the mat
52 is loosely fel~ed directly onto the female die 36 by
passing the female d~e 36 beneath the forming heads.(not
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shown) ~Ite~rllately, the mat can be deposited on a
remote CflUl 0~ or pan which conforms to ~he female die
ancl is subsequently placed over the female die. The
additional furnish re~uired for a deep draw is provided
by the tendency for the cavities 40 of the female die
36 or the caul to absorb extra furnish during the
felting operation.
~ olding temperatures, pressures and times vary
widely depending upon the thickness and desired density
; 10 of the pallet, size and type oE wood flakes, moisture
content of the Elakes, and the type oE binder used.
The molding temperature used is sufficient to at least
partially cure the binder and expel water from the mat
within a reasonable time period and without charring
the wood. Generally, a molding temperature ranging
Erom ambient up to about 450F can be used. Temperatures
above about 450F can cause charring of the wood. I~nen
a binder system including a urea-formaldehyde resin and
a polyisocyanate is used, a molding temperature oE
about 250 to about 375F is preEerred while a molding
temperature of about 300~ to about 425F is prefer~ed
for phenol-formaldehyde resin binders.
The molding pressure used should be sufficient to
press the wood flakes into intimate contact with each
other without crushing them to the point where lignin
starts to exude, causing a breakdown in the fibers with
a resultant degradation in structural integrity. The
molding pressure on the net die area typically is about
300 to about 700 psi.
.
~22-
~ 4 2~ ~
The time of the mol(iing or press cycle is suf f i -
cient to at leas~ partialLy cure the binder to a point
where the pallet has adequate structural integrity for
handling,. ~he press cycle typically is about 2 to
about 10 minutes; hot~ever, shorter or longer times can
be used when pressure-curing binders are employed to
when more complete curing of certain thermosetting
binders is desired.
After the pallet is removed from tlle mold, the
L0 peripheral edges are trimmed to the desired final
dimensions, e.g., 40 inches X 48 inches. The molding
~pparatus can include means which provides built-in
trimming during pressing. A typical pallet will
contain about 9 weight % resin, about 1 weight % wax
and about 92 weight % wood when a thermosetting resin
type binder is used. The resin content typically is
about 5 weight /O when a po:Lyisocyanate resin is used
and about 7 weight % when the binder is a combination
of a urea-formaldehyde resin and a polyisocyanate.
Without furt~er elaboration, it is believed that
one skilled in the art can, using the preceding descrip-
tion, utilize the present invention to its fullest
extent. The following examples are presented to
illustrate the invention and are not to be construed as
limitations thereof.
EXA~IPLE I
Various stcength tests were run on sample pallets
made in accordance with the invention using aspen
coundwood Ela~es (avecaOe lengt'n of 1-3/4 inch and
average thickness of 0. 21 inch), 9 weight % urea-
6~ ~
formaldehyde resin and l weight % wax. The samplepallets had an avera~e density of 39 pounds per cubic
inch. A pressure of 300-3S0 psi a temperature of
300~3250F and a press time of 4.5 to 7 minutes were
used for molding.
Leg crushing tests were conducted on a Tinius Olson
testing machine using 16 leg sections in a dry condition
and 18 leg sections which had been soaked for 24 hours
and then dried to a constant weight at 15% relative
humidity and 70F. The average crushing strength ~o a
maximum load was 3548 pounds for the first group and
2727 pounds for the second group. On the basis of
these test results, a 9-leg pallet theoretically can
support a maximum of 24,543 pounds after being soaked
and redried.
Deck strength was determined by testing 3 inch X 14
inch specimens cut from the decks of sample pallets.
The average modulus of rupture was 2435 pounds per
square inch. Other samples soaked for 48 hours and
tested when wet had an average modulus of rupture of
1000 pounds per square inch.
EXAMPLE II
Pallets having different size and shape legs were
molded from a variety of wood flakes and binders. Leg
sections from these pallets were tested for crushing
strength. The pallet legs conditioned at 5U% relative
humidity and 70F, were loaded in compression perpendicuIar
to the pallet dec~ surface with a load rate of 0.10
inches per minute to a maximum of 1/2 inch deflection.
The results from these tests are summarized in Table
I.
-24-
2~r~
,, I o -
C ~ D5 n ~- cr
- ~ G ~ L'~
Y. '` I
I ~_ ~
J
~_
._.~
~ ~ C C O O O
O I r~ _ O O o
_~
. I_ i -
. ,. C V~ ,,
Vr~ C~U~O 3~ E i
,~.
~ Q' 1 ~-,, c c
.~ ~ U -- . ~ D ~ L'~
. ,~ x a2
_ Cl X `X X X X
Z cO 1~ `~
~r~ '~ . I
~ t'~ _! ~J I
~_i 1~/ ~ ~ .
C~~ ~
L_~ ~!) ^ L--l L'~ 1-- ~ L~
~ ~ O._ ~
l ~
.`
.: _'
lJ ~ I .
.~ l l l l l
_ ~ o~
O _~
^ 1.
C C C' C
_, ~ U " ~: J
-24a-
.
.. .. . .......... , .. . _ _ _ __ .. __ _ _, _ _ ___
From these test results, it can be seen that all
the leg sections Ear exceeded the minimum requirements
of the Static Load Capacit~ st of AST~ D-1185-73
i.e., a center leg of a 2000 pound capacity pallet must
support 15% oE a 9750 pound load or 1462 pounds.
From the Eoregoing description, one skilled in the
art~can easily ascertain the essential c'naracteristics
of the invention and~ ~7ithout departing from the spirit
and scope thereof, can make various changes and modifi-
cations to adapt the invention to various usages and
conditions.
.
~ ..
