Conveyor Belt Pressure Impregnation of Wood

Abstract

The Unitreat or Conveyor belt treatment process utilizes residual vacuum trapped in the wood to improve preservative distribution, once the treated commodity has been removed from the treatment plant (Vinden 2003). Unlike traditional industrial wood treatment technologies, (Bethel, Lowry and Rueping processes) limited quantities of preservative are metered into the wood rather than using traditional methods of treating to refusal or low final rates of flow. This paper explores a range of treatment options that benefit from this technology. Highlights of the technology include: (a) very short and low pressure treatment periods, whilst maintaining full sapwood penetration (b) absence of any final vacuum with no preservative dripping or wood sugar contamination of preservative. (c) hot treatments with very rapid preservative fixation and no sludge formation (i.e. reaction between CCA preservatives and wood sugars in the parent solution). Industrial applications of the Unitreat technology include: (a) treatment of pressure steamed green pine round-wood with copper-chrome-arsenic preservatives, (b) conveyor belt processing using microwave technology, (c) treatment of framing timber with water-based boron preservatives, (d) vapour phase treatment with boron preservatives, (e) chemical modification, (f) antisapstain chemical impregnation. Large-scale microwave conditioning substitutes high-pressure steaming and provides conveyor belt treatment processes whereby trees are converted into poles or railway sleepers that are ready for use within minutes rather than days or weeks. Most importantly, treatment with microwave technology extends the number of wood species that can be preservative treated by rendering the wood more permeable. This is achieved by micro-incising the wood during microwave processing.