Coating processes – With cutting – holding – severing – or abrading the base – Prior to coating
Patent
1984-01-04
1986-11-04
Smith, John D.
Coating processes
With cutting, holding, severing, or abrading the base
Prior to coating
427325, 427440, B05D 312
Patent
active
046209905
DESCRIPTION:
BRIEF SUMMARY
The present invention refers to a method of impregnating wooden structures which consist of long wooden objects, such as for example window-frames, window-casements, window-posts, door-frames, joists, cappings, sills etc., with a wood preservative, depots or reservoirs of the wood preservative being placed within the wood in a way known per se.
The purpose of the wood preservative is to protect the wood against biological destruction. Diffusion impregnation (also called osmotic impregnation) implies that the wood preservative diffuses into the moist wood. Diffusion impregnation is generally carried out by applying a water soluble wood preservative in the form of a paste or concentrated solution to be surface of raw, undried timber. The preservative then diffuses into the moist wood. By raw, undried timber is meant wood the moisture ratio of which exceeds about 25%. The moisture ratio is defined as the ratio of the mass of water in moist wood to the mass of the dried wood.
The British patent specification No. 912 381 describes diffusion impregnation of the type mentioned in the introduction. However, the method is suitable only for wood which is subjected to very moist conditions, for example wood in boats, quays, wooden structures buried in earth etc.
The Swedish patent specification No. 7810771-1 also describes a method of diffusion impregnation of the type described in the introduction. The wood preservative is in the form of a fused body of boron oxide. This prior method is suitable for impregnating wood the moist ratio of which is greater than about 25%. In wood the moisture ratio of which is less than about 25% the wood preservative spreads only to a very small extent. Thus it is not possible, with a reasonable number of depots per unit of length, to impregnate a piece of wood the moisture ratio of which is less than about 25%. The Swedish patent application No. 7803250 describes a method of impregnation of the type described in the introduction. The wood preservative is dissolved in a water-expellent liquid, usually an organic solvent. The water-expellent liquid expels free water and water bound in the wood so that the moisture ratio of the wood becomes a minimum of 21% (or more), which is a value that prevents the growth of fungi. The method is suitable for use in wood the moisture ratio of which is less than about 25%. In wood the moisture ratio of which exceeds about 25% this prior method does not work. Nor can the method be used for impregnating long pieces of wood in which the moisture ratio varies along the length of the wood piece. In a zone in which the moisture ratio of such a wood piece exceeds about 25% the water is not expelled and the remaining water further prevents the spreading of the wood preservative used along the length of the wood piece.
In the case of constructions of the type mentioned in the introduction the moisture ratio varies heavily along the long wooden object. The moisture ratio in the area of an end surface of the wooden object exceeds 30% while further away from the end surface it may be less than 20% and again further away possess moisture ratios which provide optimum moisture conditions of establishing fungus or insect attack. Accordingly, none of the methods described above is suitable for the impregnation of a wood piece of such a nature. Either the impregnation is not able to penetrate into the relatively dry wood which will thus remain untreated or the relatively dry wood may be treated while the relatively moist wood remains untreated. In the method according to the said Swedish patent application also the relatively dry sections of the wood piece may theoretically be impregnated if one assumes that the depots of the wood preservative are placed closely adjacent each other. In practice this would mean that the depots would have to be placed at a distance of the magnitude of 1 to 2 cm from each other so that the whole of the dry volume of wood can be impregnated. However, this is non-realistic since the wood piece will be perforated by bores. If the distance bet
REFERENCES:
patent: 29363 (1860-07-01), Dain
patent: 1018624 (1912-02-01), Klossvary et al.
patent: 1936439 (1933-11-01), Siever
patent: 2062081 (1936-11-01), Zwingauger
patent: 2208361 (1940-07-01), Eckert
International Research Group for Wood Preservation Report, Document No. WP/3225 by Swedish State Institute for Wood Technology.
Bell Janyce A.
Eslinger Lewis H.
Smith John D.
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