Many people might confuse kiln drying with heat treatment since both kiln processes have to do with heat. A kiln is an oven or furnace used for burning, baking, and drying materials such as wood or ceramics. Various products can be produced from kilns, mainly clay and porcelain objects or lumber used for home building. Here's a closer look at the differences between kiln drying and heat treatment.
How Kiln Drying And Heat Treatment Differ
The main point to remember about kiln drying vs. heat treatment is that the former is a process to reduce moisture levels while the latter sterilize wood. Kiln drying is a much longer process and could require several days because of the detailed steps and lower heating temperature. Ideally, the moisture should decrease by up to 19% without the wood warping or bending.
Lumber and wood pallets are placed in kilns to dry them out at a core temperature much lower than the more common heat-treatment process. Heat treatment also involves placing items in a kiln but at a higher temperature. Kiln-dried wood becomes more durable and weather-resistant than untreated timber. Another significant advantage is that it reduces flaws in the wood.
It's important to note that the heat treatment process, as per ISPM 15 specifications, requires all wood packaging materials must be sanitized before being approved for commercial use in shipping imports or exports. Heat treatment is a wood sterilization process that kills insects and pathogens but doesn't affect wood packaging as much as kiln drying does. The ISPM 15 standard is supported by 182 nations and serves as an effective proactive measure for preventing cross-contamination among countries.
Reducing Moisture In Wood
Even though moisture is a crucial key to a tree's growth, it's an undesirable ingredient when timber is used for building materials. The wood used for decking can crack, shrink, warp and degrade in other ways the more it retains moisture over time. However, pressure-treated lumber, which adds chemical preservatives to the wood, allows outdoor decking to resist environmental elements.
Wood changes as a material when you remove a certain amount of moisture from it. The weight of lumber decreases while mold resistance increases due to less water content. Kiln-dried lumber is also generally resistant to pests and insects because of the wood's higher density once it's dry. The amount of water found in trees depends on the species and the season. Trees store water within cellular walls and cavities of the wood.
There are various other reasons beyond drying and sanitizing to reduce moisture from freshly cut timber. Manufacturers generally demand wood products containing a 22% moisture level. When timber starts to dry below 28% moisture content, its mechanical properties strengthen. Dry wood is a much stronger and more durable material than moist wood. Lumber specialists pay attention to the percentage of moisture content loss as a meaningful metric in kiln-dried wood.
A significant consequence of bypassing moisture removal is that at some point, the wood may become degraded. It might shrink, warp, crumble or even twist. Water causes movement within the wood, whereas dryness provides greater stability. Although the kiln drying process creates stresses within the wood, kiln operators use a method called "conditioning," in which live steam is injected into the heating area. Stream relieves stresses in timber as it condenses on the surface.
Why Lumber Needs Heat Treatment
Heat treatment itself does not thoroughly dry wood but helps prevent bugs from crossing borders. Lumber used for making wood pallets must undergo heating as the internal core temperature must hit 133F for a half-hour for the process to be considered heat treatment. Sometimes lumber may appear darker after getting heat treatment. Unlike kiln drying, heat treatment only takes a few hours since the temperature is much higher. During that process, all living organisms within the wood are wiped out. An added benefit of heat treatment is that it removes enough moisture to reduce the wood's weight, making it easier and cheaper to ship.
Heat treatment is a necessary step to meet government compliance if you plan to sell pallets commercially on the global market. All wood pallet products sold as imports or exports must be stamped with the appropriate heat treatment code specified by the HT ISPM 15 standard. Without this stamp, an item can be rejected in the shipping process since it raises the possibility of transporting microorganisms that grow in untreated timber. If a pallet delivery is accepted, and it is later discovered that they do not contain the proper heat code, then the process of handling returns becomes counterproductive.
Kilns And Sustainability
In the 2020s, sustainability is becoming a growing concern among businesses and consumers. A kiln offers sustainable solutions by making timber more durable and useful for outdoor purposes. Modern kilns are typically powered by natural gas, making them cleaner than the kilns that ran on refined fuel in the industrial age. Kilns make wood safe from spreading bacteria, which promotes a cleaner and safer environment.
Understanding the differences between kiln drying vs. heat treatment is essential if you buy crates or custom pallets in Fontana, CA. While the drying process lowers the moisture content, the heat treatment process cleans the wood to meet regulations for selling on the global market. Both approaches contribute to more sustainable wood products.