Experts outline the importance of kiln-drying American hardwoods at 'Dubai WoodShow 2012' conference.
The U.S. hardwood forest resource, lumber production and the importance of kiln-drying were key highlights of a presentation by Dr. Scott Bowe at the ‘Dubai WoodShow 2012’ conference, which was held on April 04, 2012 at the Dubai International Convention and Exhibition Centre (DICEC). The seminar by Dr. Bowe, Professor & Wood Products Specialist Department of Forest and Wildlife Ecology College of Agricultural and Life Sciences University of Wisconsin, USA also threw the spotlight on the environmental credentials of American hardwoods to an audience comprising of industry professionals and trade visitors at the ‘Dubai WoodShow 2012’. AHEC’s participation at the event is centered on the move to reinforce trade ties with the rapidly developing wood and wood processing industry whilst promoting the increased usage of American hardwoods across the many ongoing construction, interior design and furniture projects across the region.
Speaking at the sidelines of the conference, Rod Wiles, AHEC Director for Africa, Middle East, India and Oceania, said: “Of all the value-added processes undertaken by the American hardwood industry in preparing lumber for export, kiln drying is probably the most important. It is this process which allows for a naturally unstable product to remain stable throughout its journey to the end user overseas, as well as in processing and final application.”
Kiln drying involves regulating the temperature and humidity of the circulating air to suit the state of the lumber at any given time. This condition is achieved by applying kiln drying schedules and the desired objective of an appropriate schedule is to ensure drying timber at the fastest possible rate without causing too much degrade. Schedules are devised according to various important factors and these include the species, the thickness of the lumber, how the boards have been sawn (plain or quarter sawn), permissible degrade and the intended end use of the lumber. Considering each of the factors, no one schedule is necessarily appropriate, even for similar loads of the same species. This is why there is so much research and development in kiln drying and why the process is generally not easy or cost effective to carry out in export markets, where the prerequisite skills and technology may not be readily available.
“The U.S. hardwood industry has extensive experience of drying hardwood lumber. In fact much of the research over the last 35 years related to drying temperate hardwood has emanated from the United States. Satisfactory kiln drying can only be achieved through having the proper equipment, by employing the correct techniques and by having a full understanding of the material,” added Wiles.
Specifically for American hardwoods, drying times will vary enormously depending on thickness and species. For example, 4/4" (25.4mm) tulipwood can be dried from green in 7-10 days, whereas 12/4" (76.2mm) white oak may take up to 8 months to kiln following an extensive period of air drying. Economics dictate that in the majority of cases, domestic and export lumber is kiln dried together. Therefore, export lumber will usually be dried to the domestic standard moisture content (MC) of 6-8 percent. Whilst, thicker material in some species may be up to 10-12 percent moisture content.
"Wherever the final destination of sawn timber (lumber) in temperate species, it is always advisable that the wood is kiln-dried before shipment. The process is a fine art and those who produce the wood in North America or Europe, for example, have perfected it over many, many years. It is a genuine value-addition to the product and should ensure that what is delivered to the customer is higher yielding, pest and fungus free, ready to use and dimensionally stable. In effect, when you buy kiln-dried lumber, you have more chance of knowing what you are going to get and there will be much fewer unwanted surprises," concluded Wiles.