Note: Descriptions are shown in the official language in which they were submitted.
~43Z6
'.
;~
, ARTICLES MOLDED FROM PAPERMILL SLUDGE
FIELD OF THE INVENTION
This invention relates to articles made from
papermill sludge. In one aspect, the invention relates
.~ to one-piece material handling pallets molded from
~i' 5 papermill sludge.
In the manufacture of paper, various materials
are added to the paper pulp prior to and during the
sheet-forming operation for the purpose of producing
desired properties in the finished paper, such as proper
surface, opacity, strength and feel. For example,
finely ground inorganic fillers, such as talc, certain
clays, calcium carbonate, blanc fixe and titanium
dioxide, are added to all papers, except absorbent types
(tissue or blotting paper), to improve surEace smoothness,
whiteness, printability and opacity. Sizing agents,
such as soaps, gelatins and rosins (with alum), wax
emulsions and starches, are added to most papers for
improving resistance to penetration by liquids. Also,
coloring agents, such as acid, basic, direct and sulfur
dyes and natural and synthetic pigments are added to
most papers.
. _ . . . . , . _ . . _ . __
Substantial quantities of water are recovered
during the sheet forming operation and recycled to the
process after filtering. The solid residue or so-called
papermill sludge separated from the recovered water primarily
contains wood fibers and additive materials, particularly
filler such as clay Uses for this sludge.are ~uite limited
and, consequently, it is often disposed of as waste. Thus,
some effort has been made to develop new uses for this waste
product.
SUMMARY OF THE INVENTION
.. . ... ...
According to an aspect of the invention there is
provided a method for molding an article comprising the steps
of: (a) admixing a resinous particle board binder with a
dried comminuted papermill sludge and a fibrous reinforcement
material; (b) depositing a loosely-felted mat formed from
the mixture on one open part of a mold including two separable
parts defining a mold.chamber having the shape of the artlcle;
and tc) closing the mold and applying sufficient heat and
pressure on the mat to compress it to the substantially desired
shape and size of the article and to bond the particles together.
According to a further aspect of the invention
there is provided an article having a major plane and integral
non-planar portions displaced from the major plane compression
molded from a mixture including about 25 to about 75 weight %
of a comminuted papermill sludge containing about 20 weight
or less moisture, about 25 to about 75 weight % of a fibrous,
cellulosic, reinforcing material and a resinous particle
board binder, the weight percentages being based on the total
dry weight of the papermill sludge and the cellulosic
material.
- 2 -
! ~ p C / ," ~
~1~41.~26
Even though papermill sludges contain substantial
amounts of wood fibers, articles formed from a papermill
sludge and a binder do not have adequate
- 2a ~
~. pc/~' .
a~
--3--
structural strength for many purposes. In accordance
with the invention, the structural strength is increased
by admixing a fibrous reinforcing material, preferably a
fibrous cellulosic material such as bark particles and a
resinous particle board binder, such as a thermosetting
resin or an organic polyisocyanate, with the papermill
sludge in dried, comminuted form and compression molding
the resulting mixture or furnish into the desired shape
~: of t~e article.
In a preferred method, the comminuted papermill
sludge is admixed with the fibrous reinforcing material
and resinous particle board binder, the resulting
~ mixture or furnish is deposited as a loosely-felted mat
: on one part of an open mold or press including two
separate parts defining a mold chamber having the shape
~ of a pallet, the mold is closed, and sufficient heat and
-~ pressure is applied to the mat to compress it into
: substantially the desired shape and size of the pallet.
In one embodiment, a mat of substantially uniform
thickness is formed outside the mold and this mat is
placed between the male and female dies of the mold.
In another embodiment, a mat is formed outside
the mold as described in the previous paragraph and
mounds of furnish is added on top of the mat at locations
corresponding to the leg-forming cavities of the female
die.
In a further embodiment, the leg-forming cavities
of the female die are first substantially filled with
furnish and the mat is then placed between the male and
female dies.
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~ 3'~
.j
In a still further embodiment, the mat is formed
directly on the female die or a remote caul which has a
shape conforming with the female die and is subsequently
placed over the female die. This technique and those
described in the t~o preceding paragraphs are particular-
ly advantageous for molding longer or deeper leg members.
The pallet provided by the invention includes a
deck member having a major plane and a plurality of
hollow leg members projecting integrally from the deck
member, each leg member having a bottom wall spaced from
the deck member and side walls inclining outwardly from
the bottom wall toward the deck member. The deck and
` leg members are molded as a one-piece unit from a
mixture of dried, comminuted papermill sludge, a fibrous
reinforcing material and a resinous particle board
binder. The side walls of the leg members can extend at
an angle of about 60 or less relative to the major
- plane of the deck member and can have an average thick-
ness which is about 70-110% of the average thickness of
the deck member.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a pallet incor-
-- porating various features of the invention.
Fig. 2 is a sectional view taken generally
along line 2-2 in Fig. 1.
Fig. 3 is a schematic flow diagram illustrating
various steps of preferred process for molding pallets
of the invention from papermill sludge and bark.
~ Z 6
Figs. 4-7 are simplified, schematic side views
of a mold or press illustrating various techniques Eor
depositing a mat of the papermill sludge and bark
particles on the female die prior to closin~ the mold.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention relates to articles molded from a
papermill sludge, such as support members including a
main body having a major plane and non-planar portions
displaced from that major plane molded as a one-piece
unit. The invention is particularly adaptable to
material handling pallets and will be described in
connection therewith.
Illustrated in Figs. 1 and 2 is a palle[ 10
-~ including a generally flat, rectangular deck member 12
having a substantial 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 pads for the pallet. In the specific
construction illustrated, each of the leg members 16
(Fig. 2) includes a bottom wall 18 having a flat bottom
surface 20 and two opposed pairs of sidewalls 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 entry of the tines of a
fork lift beneath the deck member.
The deck member 12 and the leg members 16 are
molded as a one-piece unit from a mixture of a papermill
sludge, a fibrous reinforcing material and a suitable
-
,L~4~,32q~G
resinous particle board binder as described below The
sidewalls 22 and 24 of the leg members 1~ are inclined
or tapered to facilitate molding and also to 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 sidewalls
22 and 24 are substantially flat and the leg members 16
have a general form of an inverted, truncated hollow
pyramid. If desired, leg member 16 can be formed in
other suitable cross-sectional shapes, e.g., in the form
of an inverted, truncated hollow cone.
As used herein, the term "papermill sludge" means
the solid residue separated from water recovered from
various commercial paper making processes. While the
v~ 15composition of the papermill sludge varies considerably
_ ~ depending upon the particular pap~r making process, the
A major ingredients are relatively ~ . wood fibers,
~ usually about 40 to 70 weight %, and inorganic fillers,
- particularly clay. The papermill sludge may also
contain one or more of the additive materials mentioned
above.
The fibrous reinforcing material includes natural
and synthetic materials in fiber or ~ -like form. To
minimize cost, the fibrous reinforcing material prefer-
ably is a waste or scrap material, particularly wastewood products ~rom lumber manufacture and wood pulping
operations, such as bark, shavings, veneer and pulp
chips, wood pulp, flakes, and the like. Other suitable
fibrous reinforcing materials include other tree compo-
nents, such as leaves, evergreen needles, etc. and othercellulosic materials such as scrap paper and paperboard,
432~;
rags, straw, corn stalks, hemp, flax, jute and the like.
Cenerally, natural or processed cellulosic materials are
preferred. Bark is particularly suitable and the
process will be described with bark being used as a
fibrous reinforcing material. The composition of the
furnish and general process parameters discussed below
are applicable to other reinforcing materials.
Reference is made to Fig. 3 which diagrammatic-
ally illustrates the steps of a representative process
for manufacturing a pallet from papermill sludge and
bark. The illustrated process broadly includes the
steps of blending dried, comminuted papermill sludge
with predetermined quantities of dried fibrous bark
particles and a suitable resinous particle board binder,
- 15 forming the resultant mixture or furnish into a loosely-
felted mat, placing the mat in an open mold or press
_ including separable male and female dies defining a mold
chamber having the desired shape of the pallet, closing
the mold and applying sufficient heat and pressure in
the mat to compress it into substantially the desired
shape of the pallet, removing the molded pallet from the
press and trimming the peripheral edges of the pallet
with a power saw or the like to the desired final
dimensions.
The papermill sludge usually is in the form of
relatively large lumps having a moisture content substan-
tially above that acceptable for molding as discussed
below. Accordingly, the papermill sludge is dried to a
moisture content in the order of about 20 weight % or
less, preEerably about 4 to about 10 weight %, based on
the dry weight of the solids, and comminuted in a
43~6
suitable device, such as a hammer mill, prior to the
blending step. The moisture content to which the
papermill sludge is dried depends primarily upon the
particular type of resin being used as discussed
below. During the comminuting step, the papermill
sludge preferably is broken down into a size not
substantially larger than the individual wood fibers
therein. If the moisture content of the papermill
sludge is less than about 15 %, the drying and
comminuting steps can be reversed if desired and the
drying step can be eliminated for papermill sludges
having a moisture content less than about 10%.
Ilhile the particle size of the comminuted
papermill sludge is not particularly critical, the
average size generally should be about 32 to about
200 screen mesh.
,~
.,~
Any of the fibrous reinforcing materials
mentioned above can be used; however, bark presently
is preferred because of its low cost, availability
and ease of preparation for use in the process. Logs
~~ 20 are usually mechanically debarked prior to being
chipped or flaced for use in a pulping operation.
Consequently, the manufacturing acilities producing
papermill sludge usually have a readily available
supply of bark.
l~ile bark from a wide variety of hardwood
and soEtwood species can be used, bark from species
co~monly used in the manufacture of paper products
generally are preferred. Representative examples of
suitable barks include those rom aspen, maple, oak,
balsam fir, pine, cedar, spruce, locust, beech and
birch.
32~
.
_9_
- The bark from green trees has a relatively
high moisture content up and usually is not in the
desired ~ibrous or strand-like form. The bark is
dried to a moisture content of about 20 weight % or
less, prefer~bly about 4 to about 10 weight %, and
comminuted into a suitable device, such as a hammer
mill. As with the papermill sludge, the moisture
content to which the bark for any particular batch is
~-. dried depends primarily on the type of resin being
used. If the moisture content of the bark is less
than about 15 weight %, the drying and comminuting
steps can be reversed if desired and the drying step
can be eliminated for barks having a moisture content
-- less than about lO weight %.
-~ 15 During the comminuting step most barks are
broken down into a fibrous fraction and a cubical-
like, "corky" fraction. The portion of the bark from
` which each fraction is obtained varies from species
to species. The "corky" particles do not significant-
ly increase strength and preferably are separated
from the more desirable fibrous fraction. This
separation can be performed in a conventional air
classifier. The desirable long, thin strands or
fibrous bark particles tend to float, even though
they may be heavier than the undesirable heavier
cubical, "corky" particles, and are collected from
the overhead. Mechanically removed bark usually
contains some wood fibers, splinters, etc., which are
collected along with the fibrous bark particles and,
thus, are encompassed within the term bark particles.
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The size of the fibrous bark particles is not
particularly critical. They preferably have an
average length of about 1/16 inch to about 3/4
inches, an average width of about .020" to about
.060" and an average thickness of about .010" to
about .030".
~3
Known amounts of dried papermill sludge and
~ fibrous bark particles are introduced into a conven-
tional blender, such as a paddle-type like blender,
wherein a predetermined amount of a resinous particle
binder and, optionally, additives such as water
proofing agents, dimensional stabilizin~ agents and
the like, is applied to the particles as they are
: tumbled or agitated in the blender. The amount of
papermill sludge in the blended mixture, based on the
~ total dry weight of the sludge and bark solids
-~ therein, preferably is about 25 to about 75 weight %,
most preferably about 40 to about 60 weight %, and
-; the amount of bark preferably is about 25 to about 75
weight %, most preferably about 40 to about 60 weight
%.
~,
- 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". Repre-
sentative examples of suitable binders include
thermosetting resins such as phenolformaldehyde,
resorcinaol-ormaldehyde, melamine-formaldehyde,
urea-formaldehyde, urea-furural and condensed
furfuryl alcohol resins, and organic polyisocyanates,
either alone or combined with urea- or melamine-
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2,6
formaldehyde resins. Particularly suitable polyiso-
cyanates are those containing at least t~o active
isocyanate groups per molecule, including diphenyl-
methane diisocyanates, m- and p-phenylene diisocya-
nates, chlorophenylene diisocyanates, toluene di- and
triisocyanates, triphenylmethene triisocyanates,
diphenylether-2,4~4'-trisicocyanate and polypheyl-
polyisocyantes, particularly diphenylmethane-4,4'-
diisocyanate.
The particular type binder used depends
primarily upon the intended use for the pallet. For
instance, pallets employing urea-formaldehyde resins
have sufficient moisture durability for many uses
which involve minimal exposure to moisture, but
: 15 generally cannot withstand extended outdoor exposure
_ and reusability is quite limited. Phenol-formaldehyde
and melamine-formaldehyde resins provide good moisture
-~ resistance but require substantially longer cure
times. Polyisocyanates, even in lesser amounts,
provide greater strengths and moisture resistance
than the urea- or phenol-formaldehyde 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.
2~i
~ binder system including both a urea-
formaldehyde resin and a polyisocyanate, at a solids
weight ratio of about 4:1 to about 1:1, is advantag-
eous for many applications because, although less
costly than polyisocyanate aline, it provides strength
characteristics and moisture resistance which is
superior to those obtainable from either urea- or
phenol-formaldehyde resins along and the pallets are
reusable.
-
The amount of binder added during the blend-
ing step depends primarily upon the specific binder,
used, the amount and type of fibrous reinforcing
material used, and the desired characteristics of the
pallet. Generally, the amount of binder added is
_ 15 about 2 to about 15 weight %, preferably about 4 to
about 10 weight %, as solids based on the total dry
weight of the papermill sludge and bark particles.
_ When 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 added in either dry or
liquid form. To maximize coverage of the papermill
sludge and bark particles, the bir,der preferably is
applied by spraying droplets of the binder in liquid
form onto the particles as they are being tumbled or
agitated in the blender. To improve water resistance
oE the pallet, a conventional liquid wax or phenol
emulsion preferably is also sprayed onto the particles
during the blending step. The amount of wax or
phenol added generally is about 0.5 to about 2 weight
%, as solids based on the total dry weight of the
. .
` ? ~3L~43~6
papermill sludge and bark particles. Other additives
such as coloring a~ents, fire retardants, insecti-
cides, fungicides and resins for enhancing dimensional
stability (e.g., polyethylene, polyvinylchloride,
etc.) may also be added during the blending step.
The binder and other additives, can be added separate-
- ly in any sequence or in combined form.
_ The moistened mixture of papermill sludge and
- bark particles and binder or furnish from the blending
step is formed into a loosely-felted, single or
multi-layered mat which i5 compressed into a pallet
or other molded articles. The moisture content of
the papermill sludge and bark particles should be
-
controlled with certain limits so as to obtain
~~ 15 adequate coating by the binder during the blending
~ step to enhance binder curing and prevent generation
~ of excessive internal pressure during molding.
. ~,
The presence of some moisture in the paper-
mill sludge and the bark particles 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, particularly urea-Eormaldehyde resins, and
generates steam which can cause blisters and build up
of internal pressure. At high moisture contents, the
clay usually present in papermill sludge tends to
form an impervious mat which inhibits release of
water vapor and can cause "blow-outs". On the other
hand, if the wood fibers in the papermill sludge and
the bark ~articles are too dry, they tend to absorb
excessive amounts of the binder, leaving an insuffi-
. _ . . .. . . .. .. . . . ...
4326
-14-
cient 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 fibers and the bark particles.
This latter condition is particularly true for
polyisocyanate binders.
Generally, the moisture content of the fur-
-~ nish after completion of blending, including the
original moisture content of the papermill sludge and
bark particles and the moisture added during blending
along with the binder, wax and other additives,
should be about 5 to about 15 weight %, preferably
about 8 to about 12 weight %. Generally, higher
` moisture contents within these ranges can be used for
~ 15 polyisocyanate binders because they do not produce
- condensation products upon reacting with cellulose in
the wood fibers and the bark particles. Lower
moisture contents are used for higher density pallets
` because oE the above-discussed tendency for t~e clay
to form an impervious mat is compounded at higher
mold pressures.
In some cases the papermill sludge tends to
ball up during the blending step. This can cause
inadequate intermixing of the wood fibers in the
sludge with the bark particles and the binder to
provide the desired structural strength in the final
` product. In the specific process illustrated, the
- blended mixture or furnish is further processed in a
hammermill or similar milling device to insure
homogeneous mixing of the wood fibers, bark particles
and binder. This additional step may not be required
4~326
for blenders which also provide a milling action,
such as disc-type refiners commonly used in the
manufacture of fiberboard.
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. A conventional
~~dispensing system, similar to those disclosed in U.S.
Patents 3,391,223 and 3,~24,058, can be used to form
the mat. Generally, such a dispensing system includes
a plate-like carriage carried on an endles belt or
conveyor and one or more hoppers spaced along the
belt in the direction of travel for receiving the
furnish. When a multi-layered mat is formed in
accordance with a preferred embodimen., a plurality
of hoppers usually are used and each hopper has a
dispensing or forming head extending across the width
-~_of the carriage for 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
substantially uniform thickness. Uniformity of the
mat thickness can be controlled primarily by deposit-
ing two or more layers of the furnish on the carriage
and metering the flow of furnish from the forming
heads. A doctor blade, scalper or similar device
spaced above the carriage can be used to further
control the thickness or depth of the mat.
4 ~ 2
-16-
The mat thickness varies depending on such
factors as the particular technique used for forming
the mat, the desired thickness and density of the
molded article, the configuration of the molded
article (particularly the size and shape of the leg
members when the article is a pallet) and the molding
pressure to be used. As a guide, the mat is usually
about 3 to 15 inches thick and is quite fluffy or
almost cotton-like, i.e., a density in the order of
1-5 pounds per cubic foot. When thicker mats are
used, some pre-compression usually is required before
the fi~al molding step. Otherwise, the large amount
of air which must be displaced, particularly for
pallets having a high final density, can cause mold
"blow-out". This pre-compression can be performed at
relatively low pressures. For example, the mat,
carried on a conveyor belt or the like, can be moved
under rollers, in a manner similar to that commonly
- used in the manufacture of fiber board, prior to
being placed in the mold.
Referring to Fig. 4 which diagrammatically
illustrates the dies of a pallet mold, a mat 30
(either pre-compressed or as formed) is compressed in
a mold 32 including a movable male die 34 and a
stationary female 36 which cooperates to define a
mold chamber having the shape of the pallet and
heating means. 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 corresponding protruberances 42 (one
shown), each defining the interior of a leg member
16. When a polyisocyanate binder is used, a conven-
3Z6
-17-
;
- tional mold release agent preferably is applied to
the sur~aces of the dies 34 and 36 or to the surfaces
of the mat 30 prior to pressing.
The mat 30 is removed from the forming car-
riage and deposited in the female die as illustrated.When the male die is closed, portions oE the mat 30
are drawn into the female die cavities 40 to form the
~` leg members 16. Because of this drawing action on
the mat during molding, there are some practical
limitations for the pallet configuration. Referring
to Fig. 2, the slope of the sidewalls 22 and 24 with
respect to the major horizontal plane of the deck
: member 16, designated by angle A, should not exceed
- about 60. If relatively tight corners are desired
between the bottom of the deck member 12 and the leg
members 16, and 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 about 70-110%,
preferably about 80-85%, of the deck member thickness.
The bottom wall thickness can be about 60-100% the
deck member th;ckness.
The leg members should not be closer than
about 6 inches from each other. Even at this distance,
an additional quantity of the furnish may be required
to compensation for that drawn down into the female
A3~>J6~
-18-
die cavities during the molding operation, particular-
ly when deeper or longer leg members are formed. For
example, when a mat formed outside the mold and
placed between the male and female dies as illustrated
in Fig. 4 is used in the production of a 40 inch X 48
inch pallet having 9 legs, leg members having a depth
(designated by dimension D in Fig. 2) up to about 3
inches can be conveniently drawn from such a mat.
Figs. 5-7 illustrate alternate techniques for
depositing the furnish 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 filled with
furnish 44 and a loosely-felted mat 46, having a
- 15 substantially uniform thickness and formed outside
. 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 Fig. 6, a
loosely-felted mat 48 of substantially uniform
' thickness is formed outside the mold, similar to the
mat 30 in Fig. 4, the mounds 50 oE additional furnish
required for a deep draw are deposited on top of the
mat 48, at locations corresponding to the locations
of the female die cavities 40, prior to placing the
mat 48 in the mold.
In the technique illustrated in Fig. 7, the
mat 52 is loosely felted directly onto the female die
36 by passing the female die 36 beneath the forming
heads (not shown). Alternately, the mat can be
`
-19-
deposited on a remote caul or a pan which conEorms to
the female die and is subsequently placed over the
female die. The additional furnish required 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.
Molding temperatures, pressures and times
vary widely depending upon the thickness and desired
density of the molded article, composition and
moisture content of the furnish, and the type of
binder used. The molding temperature used is suffi-
cient to at least partially cure the binder and expel
water from the mat within a reasonable time period
and without charring the wood and bark fibers.
Generally, a molding temperature ran~ing from ambient
up to about 450F can be used. When a binder system
_ including a urea-formaldehyde resin and a polyiso-
cyanate is used, a molding temperature of about 250
to about 375F is preferred while a molding tempera-
ture of about 300 to about 425F is preferred for
phenol-formaldehyde resin binders.
,.~
The molding pressure used should be sufficient
to press the papermill sludge and bark particles into
intimate contact with each other without crushing the
wood fibers or the fibrous bark particles. The
molding pressure on the net die area typically is
about 25 to about 700 psi, preferably about 100 to
500 psi. For example, a mold pressure of about 300
psi on a 10 inch thick mat ~ormed from a furnish
containing about 44 weight % papermill sludge, about
44 weight % bark particles, about 4 weight % moisture
and about 8~io resin binder, produces a molded article
having a density of about 63 pounds per cubic foot.
43;~6
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-20-
The time of the molding or press cycle is
sufficient to at least partially cure the binder to a
point t~here the pallet has adequate structural
integrity for handling. The press cycle typically is
about 2 to about 10 minutes; however, shorter or
longer times can be used when pressure curing binders
. are employed or when more complete curing of thermo-
setting binders is desired.
After the pallet is removed from the mold,
the peripheral edges are trimmed to the desired final
dimensions, e.g., 40 inches X 4~ inches. The mold
can be provided with means which automatically trims
the edges during pressing.
From comparative testing, it has been found
-. 15 that the addition of fibrous bark particles to
~ papermill sludge produces surprising increases in the
--; structural strength. For example, pallet leg sections
molded from 100% sludge had an average crushing
strength of 1503 pounds, wherease pallet leg sections
of the same configuration molded from a 50/50 mixture
of sludge and bark particles had an average crushing
strength of 4941 pounds, a more than threefold
increase.
From the foregoing description, one skilled
in the art can easily ascertain the essential charac-
teristics of the invention and, without departing
from the spirit and scope thereof, can make various
changes and modifications to adapt the invention to
various usages and conditions.
