Pressure processes Wood preservation

1 pressure processes

1.1 full-cell process
1.2 fluctuation pressure process
1.3 boucherie process
1.4 high-pressure sap displacement system

pressure processes

late 19th century pressure treatment

pressure processes permanent method around today in preserving timber life. pressure processes in treatment carried out in closed cylinders applied pressure or vacuum. these processes have number of advantages on non-pressure methods. in cases, deeper , more uniform penetration , higher absorption of preservative achieved. advantage treating conditions can controlled retention , penetration can varied. these pressure processes can adapted large-scale production. high initial costs equipment , energy costs biggest disadvantages. these treatment methods used protect ties, poles , structural timbers , find use throughout world today. various pressure processes used today differ in details, general method in cases same. treatment carried out in cylinders. timbers loaded onto special tram cars, called buggies or bogies, , cylinder. these cylinders set under pressure addition of higher temperature. final treatment, vacuum used extract excess preservatives. these cycles can repeated achieve better penetration.

losp treatments use vacuum impregnation process. possible because of lower viscosity of white-spirit carrier used.

full-cell process

in full-cell process, intent keep of liquid absorbed wood during pressure period possible, leaving maximum concentration of preservatives in treated area. usually, water solutions of preservative salts employed process, possible impregnate wood oil. desired retention achieved changing strength of solution. william burnett patented development in 1838 of full-cell impregnation water solutions. patent covered use of zinc chloride on water basis, known burnettizing. full-cell process oil patented in 1838 john bethell. patent described injection of tar , oils wood applying pressure in closed cylinders. process still used today improvements.

fluctuation pressure process

contrary static full-cell , empty-cell processes, fluctuation process dynamic process. process pressure inside impregnation cylinder changes between pressure , vacuum within few seconds. there have been inconsistent claims through process possible reverse pit closure spruce. however, best results have been achieved process spruce not exceed penetration deeper 10 mm (0.39 in). specialized equipment necessary , therefore higher investment costs incurred.

boucherie process

developed dr. boucherie of france in 1838, approach consisted of attaching bag or container of preservative solution standing or freshly cut tree bark, branches, , leaves still attached, thereby injecting liquid sap stream. through transpiration of moisture leaves preservative drawn upward through sapwood of tree trunk.

the modified boucherie process consists of placing freshly cut, unpeeled timbers onto declining skids, stump elevated, fastening watertight covering caps or boring number of holes ends, , inserting solution of copper sulfate or other waterborne preservative caps or holes elevated container. preservative oils tend not penetrate satisfactorily method. hydrostatic pressure of liquid forces preservative lengthwise , through sapwood, pushing sap out of other end of timber. after few days, sapwood impregnated; unfortunately little or no penetration takes place in heartwood. green wood can treated in manner. process has found considerable usage impregnate poles , larger trees in europe , north america, , has experienced revival of usage impregnate bamboo in countries such costa rica, bangladesh, india , state of hawaii.

high-pressure sap displacement system

developed in philippines, method (abbreviated hpsd) consists of cylinder pressure cap made 3 mm thick mild steel plate secured 8 sets of bolts, 2-hp diesel engine, , pressure regulator 1.4–14 kg/m capacity. cap placed on stump of pole, tree or bamboo , preservative forced wood pressure engine.