An Improved Process for Preserving, Colouring, and Hardening Wood.
Year: 1898

page_text: Date of Application, 16th Feb., 1898-Accepted, 2nd Apr., 1898
COMPLETE SPECIFICATION.
An Improved Process for Preserving, Colouring, and Hardening
Wood.
I, FRIEDRICH GRUMBACHER, of 6, Kirchstrasse, Berlin, in the Empire of Germany,
Works Manager, do hereby declare the nature of this invention and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement :-
One of the best means for preserving wood consists in treating it with tar oil. The
wood tar obtained by the dry distillation of wood is particularly rich in phenol and
other decay-arresting substances. In impregnating wood with wood tar for the purpose
of preserving it, a material is thus artificially introduced into the wood which is
obtained by distillation from other wood. Attempts have been made by the use of
heat to form in the wood itself these antiseptic substances which are contained in
wood tar, and to condense and retain them in the wood itself by the use of high
pressure.
In course of time it has however been found that woods of the same kind cannot
all be treated alike, and experiments have shown that the varying degree of moisture
of the wood is the cause of the unequal results. By scientific examinations, it has
also been ascertained that the cellulose of the wood decomposes under the action of
heat in case moisture is present in the same.
The methods of treatment heretofore employed provided for only a partial
desiccation or removal of the moisture as only the free moisture was removed and
not that which was hygroscopically combined. By the present invention the
hygroscopically combined water is also removed either by heating to over 100° C. or.
by treatment in vacuo at a suitable heat for instance 40-60° C. By this removal
of the hygroscopically combined water from the wood there takes place also an actual
conversion of the inter-cellular substance more rapidly than was previously possible
and this conversion can be undertaken at a temperature which is considerably lower
than that at which the inter-cellular substance was formerly converted for the purpose
of forming antiseptic substances. The conversion of the inter-cellular substance may
in this manner be effected at temperatures of 130-165° C., whilst when free moisture
or rather hygroscopic moisture is present, the temperatures must occasionally be raised
to above 200° C. The actual conversion into antiseptic substances may in this manner
take place even at temperatures of 130-140° C.
If new or green wood is to be given the appearance of old wood such as, in the
case of oak, walnut and mahogany, is only obtained by natural ageing, an intense
colouring may be imparted to the wood simultaneously with the formation of the
heavier distillation products by heating up to 200° C., so that for instance yellowish
mahogany obtains a deep red colour which it could otherwise obtain only through
years of storage.
In order to prevent the wood cracking after treatment, and to impart to it also a
higher degree of hardness, it is preferably cooled under pressure and in order to
obtain a special hardness it is exposed for some time to pressure at a low temperature
if desired at under 0° C. For this object either special cooling coils may be

page_text: employed or cooling liquids, cooling gases or cold air may be caused to pass through
the heating coils.
If wood treated according to the method herein before described is also to be
rendered incombustible, it will be found particularly adapted for the retention of the
salts employed for rendering the wood incombustible.
The salts and chemicals usually employed for this object by the ordinary process
were as little permanently retained as those employed in the ordinary method of
impregnation for preserving wood from decay. In wood so treated, there was always
the danger of the means employed being again washed out of the wood by rain,
moisture or the like. If however in the wood to be treated the substances for
rendering the wood incombustible be suitably introduced therein before the vulcanising,
that is to say, the conversion and preservation of the inter-cellular substance, and if
the de-hydration or desiccation characterising the vulcanising process herein before
described be then undertaken, only those substances which have been introduced into
the wood to render the same incombustible, will exist in proximity to the inter-
cellular substance. On the conversion of the latter and a portion of the cellulose by
the action of heat and compressed air, the substances for rendering the wood incom-
bustible form partly chemical and partly mechanical combinations. with the ordinary
antiseptic substances formed in the dry distillation, in such a way that a washing out
is only with difficulty possible or is even no longer possible.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is :-
,
1. A process for preserving wood, characterised by the wood being treated at low
temperatures (40-60° C.) in vacuo until not only the free moisture but the major
part of the hygroscopic moisture is removed, and by the formation of preservative
substances being then produced in the wood itself under pressure at a higher
temperature (about 130-170° C.) by the inter-cellular substance being converted into
preservative substances, substantially as hereinbefore set forth.
2. A modification of the hereindescribed process for preserving wood, characterised
by the temperature being increased, during the heating, to 200° C. with the object
of intensifying the colour of the wood, according to the kind of wood and degree of
colour required, substantially as herein before described.
3. A modification of the hereindescribed process for preserving wood characterised
by the wood being cooled under pressure for the purpose of hardening it after the
treatment at a high temperature, the limit of temperature in such cooling process
being if desired below 0° C. according to the degree of hardness required, substantially
as hereinbefore described.
4. A modification of the herein described process for preserving wood characterised
by substances adapted to render the wood incombustible being introduced therein
previous to the treatment herein before described, in case the wood is not only to be
preserved, coloured and hardened but also rendered incombustible, substantially as
hereinbefore described.