FEATURE
air-seasoning . Prolonged air-seasoning of wooden poles can result in poles with sharply reduced bending properties ( MOE ).
KILN DRYING
Kiln drying usually involves exposing wood to elevated temperatures while controlling both the air flow and relative humidity . Heating at lower humidity will tend to dry poles more rapidly .
While this reduces drying times , it also increases the risk of developing extreme checking . Therefore , it is important that the customer specification stipulates poles are not dried at temperatures or humidities that can result in extreme checking .
The primary drawback to kiln drying is the costs associated with the equipment , but the benefits of kiln drying include the ability to rapidly process poles , thereby reducing pole holding costs as well as the risk of fungal damage associated with air-seasoning . The heating also eliminates any fungi that might have been present at the time of drying .
RETENTION AND TREATMENT REQUIREMENTS
• Effect of moisture retention The amount of preservative that can be contained in treated wood is in a large part , dependent upon the available amount of void space in the wood cell cavities . Under pressure treatment , preservative solution being forced into timber seeks cell cavities and pit membrane orifices as primary avenues of penetration .
Available void space for solution penetration is reduced progressively by increased moisture content until cell cavities are water-filled and flow of solution into otherwise permeable wood becomes impossible .
Opinions of operators in pressure-treating plants vary regarding what is optimum moisture content at which wood should be treated . Moisture content values near the fibre-saturation point ( 28 %) are usually satisfactory . Wood becomes easier to treat as its moisture content is reduced .
• Treating plant facility requirements All treating plants need strict guidelines on the whole treatment cycle .
• Quality Control The treating plant needs to appoint an employee , trained in quality control procedures , who shall be designated as plant quality control supervisor and who will be responsible for conformance of treated products to the standards and specifications and for the accuracy of equipment used to monitor the treating processes .
• Wood Moisture Content Products before treatment must meet moisture content requirements . ͦ Record Keeping : Records must be kept for each processed lot or charge showing the material description , volume , and moisture before treatment . Records shall also be kept to show compliance with requirement for penetration , and for retention as measured by either gauge or assay in accordance with the applicable customer specification .
20 AUGUST / SEPTEMBER 2021 // www . timberiq . co . za