The Oscillating Pressure Method of Wood Impregnation

A brief explanation is given of the “aspirated torus” theory of impenetrability in wood cells. When a liquid is forced through a section of wood at a given pressure, the amount passing through in a given time interval decreases the longer the flow continues. Experimental data applying the oscillating pressure method proves that the previous theory can be altered. This method involves the use of pressure oscillating between 115 psi and 28 inch vacuum with the period between cycles gradually lengthening. The article discusses physical principles involved in this process. It also describes the equipment used in the experimental work and that required in a full scale production plant. The start of the treatment involves a complete cycle from pressure to vacuum and back to pressure again of about 1 minute. Pressure is higher than atmospheric about 30 percent of the time and the cycles are repeated. The cycles are gradually lengthened until at the end of the run the duration is 6-1/2 minutes with the pressure being 85 percent above atmospheric. The laboratory work reported involved a series of tests impregnating green round posts of spruce (Picea excelsa) and scotch pine (Pinus silvestris). The treating solutions used were modifications of Boliden salt. The oscillating pressure method was compared with the conventional full-cell method. The significant results of these experiments were as follows with the comparisons based on an analysis of the sapwood for percent arsenic oxide (As205): 1) Spruce: a. Oscillating pressure 1.16 percent; b. Full cell 0.31 percent. 2) Scotch pine: a. Oscillating pressure 1.30 percent; b. Full cell 0.44 percent. The test further indicated significant differences in treating time depending upon the degree of seasoning in the wood: 1) For both treating methods only 2 to 4 hours was required for dry wood. 2) Partially seasoned wood required more than 8 hours for both methods. 3) Fourteen hours was required for treating green wood by OP and was insufficient time for treating by the FC method. It is estimated that it would cost less than $5,000 to purchase the additional equipment required for converting a conventional treating plant to a process able to use OP. The overall cost of treating green wood would be $25 per thousand board feet.

You must be logged in to download any documents. Please login (login accounts are free) or learn how to Become a Member