An Improved Process for Increasing the Density of Wood.
Year: 1897

page_text: Date of Application, 26th Jan., 1897-Accepted, 3rd Apr., 1897
COMPLETE SPECIFICATION.
An Improved Process for Increasing the Density of Wood.
I, CHARLES ARTHUR ALLISON, of 52 Chancery Lane, London, in the County
of Middlesex, Patent Agent, do hereby declare the nature of this invention, (which
has been communicated to me from abroad by Frank P. Stone, of Chicago, in the
County of Cooke, in the State of Illinois, United States of America,) and in what
mauder the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
;.
The object of this invention is to produce an article of compressed wood, which
shall be so hard, solid and firm as not to be readily penetrated, divided or abraded
which shall be proof against natural decay and moisture, and which may be also
made proof against destruction by vermin and by fire. The qualities imparted to
the wood by my invention are such as to fit it to be used as a substitute in many
places for metal. The improvement calls not only for such a compression of the
wood as will greatly reduce its bulk and solidify its fibres, and thus produce the
degree of hardness required, but it may also include a peculiar treatment adapted
to give it the other qualities mentioned.
In the preferred manner of practising my invention I take natural wood, either
hard or soft, and first subject it to the cooking action of a hot fluid either in a
liquid or gaseous form, as by water-boiling or steaming it sufficiently to expand it.
and open its pores, soften the fibers and dissolve the saps and juices and bring it
into favorable condition for the next step in the treatment. Instead of this,
however, the wood may be either air or kiln dried so as to dry up the juices and
saps and leave the material in gcod condition to take up the oil freely and be
thoroughly permeated and impregnated therewith. When well seasoned it can be
well impregnated with the oil, though perhaps not so easily, or perfectly as when
it is boiled or steamed.
The cured wood which has been deprived of its sap or cured by boiling,
steaming or seasoning is next immersed in oil, using by preference for this
purpose an oil of a penetrating quality which will harden when it becomes cold.
The oil penetrates the wood and as it does this most efficiently when hot,
I immerse the wood in oil which is already hot or is heated at some time during
the immersion. My preference is to submerge the wood while still hot from the
water or steam treatment in cold oil, and then to heat the latter until it boils
gently.
By this treatment the albuminous matter in the wood is either dissolved,
removed or so softened as to ensure its being squeezed out when the compressing
power is applied, and at the same time the fibers are so softened that they readily
flatten out under the compression and come into very close and intimate contact with
each other, each fiber conforming to its neighbor fibers, and forming a very close
textured product.
I have found cotton seed oil to be peculiarly well adapted to this use, particularly
for its penetrating quality.
After the wood has been sufficiently saturated with oil I subject it while hot to
powerful pressure applied to the sides of the fibers, the pressure being sufficient to
reduce the thickness or width of the wood from one half to two thirds. The press
employed for this purpose being previously heated or heat being applied to it so
that it will remain hot during the entire operation and prevent any chill being

page_text: imparted to the wood before the compression has reached the desired stage. The
degree of compression and the length of time during which the pressure is applied
vary according to the nature of the wood, its size, the use to which it is put etc.
When the product is intended as a substitute for metal, it is compressed to a
considerable degree and until it becomes very dense. When it is not to be so used,
less compression may be employed. In the case of the softer or less dense woods,
the reduction in bulk may be carried to a greater extent than in the case of
the harder or more dense kinds. The compression squeezes out not only the
softened albumen, but also any surplus oil which may have been taken up by the
wood.
The wood after the compression has brought it to the proper degree of solidity,
is now cooled without any release of the pressure. This may be done quickly by
immersing the press and wood in water. I find it quite important that all the heat
be extracted before the pressure is taken off. As soon as the heat has been
extracted the pressure may be released, and the product will then remain in its
compacted and reduced state with the fibers set together as if by natural growth
and without any tendency by them to expand or resume their original size.
The limited quantity of oil which remains in the wood after the compression
adds hardness and toughness to the wood and renders it moisture proof. It also
tends to deprive the fibers of their natural tendency to expand upon the releasing
of the pressure. The product can be used wherever hard, durable moisture proof
wood is required. It is capable of taking a fine polish and of being painted,
varnished, carved or otherwise finished or ornamented. But it may in some cases
be desirable to subject it to heat to drive out any possible excess of oil which may
remain in it before finishing the surface. If it is desired to render the product
either vermin or fire proof, it may be done by aiding well known ingredients to
the water, in which the wood is boiled or by otherwise forcing such ingredients
into the wood.
In treating the wood with oil it may be desirable to force the latter into the wood
by pressure in any of the known ways of treating wood with preservatives.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. The art of compressing cured wood which consists in saturating it with a
fluid, then subjecting it in a hot state to powerful direct mechanical pressure
exerted in a direction transversely only of its fibers until its bulk in that direction
is greatly reduced, then locking it in its so compressed condition and subjecting it
while so locked to a cooling operation whereby its fibers become set and fixed in
the highly compressed state.
2. The art of compressing cured wood which consists in saturating it with an
oleagenous liquid under heat, then subjecting it in a hot state to powerful direct
mechanical pressure exerted in a direction transversely only of its fibers until its
bulk in that direction is greatly reduced, then locking it in its so compresse.l
condition and subjecting it while so locked to a cooling operation whereby its fibers
become set and fixed in the highly compressed state.
3. The art of compressing wood which consists in depriving the wood of its sap
by subjecting it to the action of a hot fluid, then saturating it with an oleagenous
liquid under heat, then subjecting it in a hot state to powerful direct mechanical
pressure, exerted in a direction transversely only of its fibers until its bulk in that
direction is greatly reduced, then locking it in its so compressed condition aud
subjecting it while so locked to a cooling operation whereby its fibers become set
and fixed in the highly compressed state.
4. The process herein described of treating wood, consisting in depriving the
wood of its sap, then saturating it with cotton seed oil, then subjecting it to
pressure and dry heat simultaneously, and finally cooling it while still under
pressure.

page_text: 5. A hard, compressed, waterproof, wooden block consisting of an integral
structure composed of solidified cotton seed oil, and the naturally united fibers of
the wood transversely flattened and compacted and having their natural length an 1
direction, the flattened fibers and their intermixed cotton seed oil being set,.
substantially as set forth.
Dated thin aeth
ALLISON BROS.,
Agents for the Applicant..