Wood flour, a general statement of the manufacture and use of wood flour and the status of the industry


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Wood flour, a general statement of the manufacture and use of wood flour and the status of the industry
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Forest Products Laboratory (U.S.)
U.S. Dept. of Agriculture, Forest Service Forest Products Laboratory ( Madison, Wis )
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Full Text


A C n( rdl Stalmilo nl f 4| 4 tII- a 4 iii tfdi turc ii(I Usic
of Wood Flour and 1th Status of the InduIstry

cR,'iscd, 1941

)~ 1

POPE" -t.

Madison, Wisconsin
In Cooperation with the University of Wisconsin

Digitized by the Internet Archive
in 2013


,; :D FLO0H

A -eneral statement of the manufacture and use of wood flour
and the status of the industry

Wfoo' flour is siem ly finely ground wood. As it comes from the mill
it resembles ordinary wheat flour in appearance, hence the name. ::e m-
terial is designated by "mesh" or number of bars oer lineal inch of ;:c--eS -
thro-:.-, which the product is sift, ly used are 40, 6, and 0nsh. .e finest grade of wood flour ma.-reted
is about 140 mesh. heree a fine flour is required, "J>-mesh stock w,;ill
usually be satisfactory, and the bulk of the pro luct is mC mesh and finer.

Prod.iction and Value

The manufacture of wood flour is centered in the -t at plants
located advantageously with reference to sources of raw material and the
more important consuming industries. Statistics covering the output of
wood flour in this country are not available, but fi-7ures from various
sources indicate that in 1937 about 32,j00 tons were roeduc-d. In addi-
tion probably ,00'0 tons were inT=.rted in that year. Current domestic
production of wood flour is probably considerably greaterr than in 1937
due largely to inability to rrocure foreign stocks.

Prices of wood flour at points of consumption in 1937 ranged from
about ^1 to $20 per ton for the coarser -ra--s to 2) :per ton for the
finer grades used in Tlastics. Scandanavian wood flour when last Ivail-
able sold at prices "r.-i:.- from $20 to $?S26 per ton in e.w York. Present
prices of woo-i flour in all grades have probably incr as.: somewnht over
1937 f.- 'es.


The use to which wood flouT is rut largely determine': the proper-
ties required of that material. Iyen in the same industry several kinis
of wood flour may be necessary in the production of the various co modi-
ties. Three or four properties, however, seem to be very commonly re-
quired of th-ft product in most industries Tood flour for practically
all present uses must be light in color, light in e,.,- -ht, fluffy, an
absorptive. It seems quite likely, however, th:t for some uses wood
flour of almost any sort would be satisfacto, -.


Species Suitable

Color and weight considerations limit to a large extent the species
that may be used for making wood flour. The woods chiefly employed are the
light-colored nonresinous softwoods, principally soft pines and spruces.
Probably upwards of 80 percent of the product is of these species. Various
kinds of poplar, fir, maple, birch, oak, and probably some hemlock make up
the greater part of the balance.

There are no mechanical reasons why wood flour cannot be made from
many other woods. There are, however, inherent qualities in some woods,
both softwoods and hardwoods, that preclude their use for that product.
Woods having excessive pitch, gum, oil, or resin are not satisfactory for
wood flour.

Unless there is some specific use for wood flour of hardwood species,
there is not much point in making hardwood flour, except possibly light-
colored, light weight woods, such as aspen, basswood, and similar species.
The preferred raw materials, the soft pines and spruces, are still plenti-
ful and cheap and the finished product is low priced. Wood flour of the
harder species of hardwoods has no stable markets and currently is of
little importance in the wood flour trade.


Wood flour is employed in the manufacture of a wide variety of
products. To accommodate the various uses more exactly three general
types of wood flour are made: nontechnical, technical, and granularmetric.

Nontechnical wood flour is a common grade in which the requirements
are not very exacting. It may consist of one species, or of a mixture of
closely related woods, and may be of various sizes. Nontechnical grades
are used in making certain plastics and the bulk of linoleum. The bulk
of wood flour consumption is of the nontechnical grades.

Technical wood flour is made to specified standards. The require-
ments may relate to size or mesh, species, color, weight, resin content,
character of fiber, absorptive properties, or some other property, or a
combination including any of the above. Granularmetric wood flour is
really a special type of technical wood flour in which for any mesh the
particles are uniform in size and character.

Manufacturing Processes

WIood flour produced in this country is made chiefly from sawdust
and shavings resulting from planing mill and other remanufacturing opera-
tions using white pine. Round wood, slabs, edginrs, and trimmings are

R5 5


the principal other raw' materials used in the v.'ood flour industry ard
co rise about 4.) percent of the total volume consumed.

Raw material for w'ood flour use must be of .-ooid quality and free
from bark ani other fore. -i. matter to yieli first-class stock. The od
used should be well seasoned, so that the particles of 'tock ,','ill be
-'iuffy and not have any tendency to rack when lightly comrressed. or
best results in manufacture and in use the moistxu' content of the ',oo
should not exceed & to 10 percent.

iood flour is produced by ,ny types of equiIment, chiefly, ho. v.'r,
stone mills, steel burr roller mills, attrition mills, aind sevrai ty "t
of hammer and beater mills. In .-rope, particularly Scandinavia, ;:h :>
^reat deal of wo,- flour is made, the stone mills seem to be used excla-
sively and most of the early plants in this country were equirred with
that ty of mill. The stones are from 40 to 60 inches in diameter and
only the lower stone is driven, the upper one being stationary. Power
for or,-ratine the mills is derived from water turbines, since flour
produced with power developed in other wai":. cannot compete -,ith 7ior'e>ian
flour ground by water power.

Probably the most common metal wood rulverisers are attrition
mills of the double attrition and sin-le attrition types. The 2rindin-
elements of the first named ty -e consist of two revolving plates orerat-
i" in orrooite directions, between whichh the raw%: material is Sin -le attrition mills have one revolvin? plate operation' a,-ainst the
side of the machine housin-, which accomplishes the same result. Most
attrition mills are equipped with air separators for screenin/ the rroduct.

The "beater" mill is of &.irly recent origin. It is an uxri.-ht
steel affair, the distinctive feature of which is a shaft to which are
attached star--red beaters about 6 or S inches Ions', which attack the ra'.'
material and beat it to the required fineness.

There are two ty- s of "beater" mills based on method of screening s
the flour. Then stock O6 mesh or finer is desired air serarator equi -
ment is attached. Screen separators are used when material coarser thn
tO mesh is made. From 7 to 13 pounds of wood flour rer horse power ;r
hour are produced by ":-ter" mills. A -- horse rower machine -;ill yie li
" Dut 2-1/2 tons of -.-mesh flour, 9' percent fine, in 24 hours. The
reductionn of flour by "beater" types of equipment is in almost direct
r..- portion to the fineness of the stock. ,aterial of lc-r-m sh i roaiced
about one-third as fast as 40 mesh; '0 mesh only a.out one-half s f.t
as 40 mesh, etc.

The -r;-ii:.p of stock C mesh and finr is accom- listed by an ir
separator. Adjustments of the fan control the spetd at which h ,ir i -
drawn through the beating c:.'i'-:.r. Slow .peed of th, fan. carries out
only the finest dust. Faster speed carries out thu lar-er .articY.
L.. flour is collected in an improved y'lone du;:t collector, vhic-h s.'ve
practically the entire yield of the machine.

ITames and addresses of firms making wood flour machinery can be
had from trade directories or from this Laboratory.

Uses for Wood Flour


Over half of the wood flour used in the United States annually
is consumed in the linoleum industry. In 1937 that industry accounted
for about 20,000 tons. Wood flour .is used exclusively in the production
of goodsbelonging to the inlaid class, either "granulated inlaid" or
"straightline." Cork linoleum is usually dark, either the natural brown,
or dark red or green. Patterns are printed on cork linoleum, but the
pattern soon wears off, leaving the dark base. For the production of in-
laid goods in which the pattern goes clear through the piece to the burlap
backing, a white base is necessary, not only to furnish a white background
where desired, but also to permit of dyeing to any color. For this
reason a flour as white as possible is desirable, and the material must
be uniform and should be all of one species.


Wood flour is one of the principal absorbents for nitro-glycerine
in the manufacture of dynamite. The total quantity used in the manufac-
ture of that product is probably upwards of 10,000 tons annually or more
than 25 percent of the total volume of wood flour consumed. The use of
wood flour in dynamite manufacture is probably increasing. A white flour
is essential in dynamite, since the bulk of users judge the age of that
product by its color. Light-colored dynamite is considered as fresh stock,
of high strength.

Other Uses for Wood Flour

Probably the greatest single use for wood flour other than for
linoleum and dynamite is as a filler in the manufacture of phenol resin
and similar products. Among the more common phenol resins are bakelite,
redmanol, condensite, and durez. These products mixed with wood flour
and coloring materials are molded under heavy pressure and heat into
various commodities, such as radio dials and knobs, telephone parts,
ignition blocks, radiator caps, handles, kitchen ware novelties, etc.
The amount of wood flour in these articles, by weight, comprises from
30 to 50 percent or more of the total weight of the finished product.
Here high luster is required of an article only a small amount of wood
flour is used. When luster is secondary to stren-th the amount of wood
flour is increased.

Starch, sodium silicate, resin, glue, and other materials are
used to bind pressed wood flour into a number of other products, such


as doll heads, novelties, picturee Irame ', ten ins, bowling tall-, rhono-
:ra:h records, brus. backs, insultin;brick, etc. ompo i tion flooring
is made with wood flour, and" tr:A -v
is made with wood flour, sa.....-t, and caustic mag:nnesia cement. The wood
elements are used to provide the bulk and to produce resiliency. ',ood
flour is also used in the manufacture of "oatmeal" wv'all rarer.

Status of the 'Wood Flour industry

;lhile there is an ai'.bunidance of raw material for ,';.ood flour p roduc-
tion, the relatively small cons martion of that .malriai and a rather slow
market are factor that limit new enterprises in 'o flour field.
rrlein<: voiflour hfield
:.-- rincipal rrocucers c wo flour have been :r the .uine' a lon
time and have succeeded I:. because of theii k.i im: e knowledge of
the industry an:a he exact."-- quirements of ccr 'me Cth-r factors
important to suc:s:ful wc:. flour production arc a lar.-e and continuous
supply of suitable raw ma:, .ial, nearness to market, 'nd, of course, a
.-3od demand for r'ood flour at fair rice.

The uses of wood flour may be expected to increase and absorb
lar-.:r nu'...tities of stock in the future. They can hardly be expected,
however, to develop sufficiently to afford a profi.table. outlet for more
than a fraction of the :'-cod fllour that could be producedd from wood 'vaste.
n-r potential supply of wood fLour is much greater than the potential
demand, and the dancers of excessive overproduction must be considered
by those who .i-ht contemplate its manufacture.

The Forest Products Labor!tory has made no extended investigation
of either the technic or status of the wood flour industry. This mimeo-
graph is prepared for the purpose of brin-ing together information of
,general interest only, ,nd no attempt is made to cover the sur'ct in a
thorough way.

Information relative to the wood flour industry is also contained
in a bulletin entitled "Sa'.vdust, '7ood Flour, Shavi:. -, and xce-lior,"
issued 1'I the vision of Forest Products, Bureau of Forei."n and Dome'tic
commercee U. S. Department of Com mere, ashinton, D. Other :ources
of information are: "Wood Flour: Its Manufacture and Industrial U'es,"
Lumber "'orld Review, Chica-.o, 11l, Jan. 1C, 1925: ".'ood Flour Industry,"
The Timberman, Portland, Ore., Jan. 1930; "!An Ens:'bl of Flour or a
rusty Gesture," Hardwood Record, Chicago, Ill., Ha i0 192

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