PDF Publication Title:
Text from PDF Page: 015
Sometimes during the early stage of drying, water is removed too quickly from a cell and the cell is sucked inward (like sucking on a straw that has one end closed). The cell collapses. Shrinkage, where many cells collapse, appears much greater than normal or expected. After drying, when collapsed cells are exposed to liquid water or wet steam, they will usually return to their expected size as if they hadn't collapsed (i.e., the collapse is recovered). Also important in shrinkage is the amount that occurs after drying when the MC is incorrect. Considering that glue lines can have gaps no larger than 0.006 inches, a small change in MC can result in poor gluing. For example, see the size changes in a 3 inch wide piece of wood when the MC changes (Table 4). Fiber Saturation Point Water is held in wood in two locations. One is in the hollow center region (the lumen) of the cell. This water is held due to the physical size of the cell. Theoretically, this water could be blown out of the cell just like blowing the soda out of a soda straw. This water is called "free water." Water is also held in the cell wall, but this water is chemically held in the wall. It is called bound water. When a cell is dried, the free water is removed first. When all the free water is removed, but the cell wall is still saturated, the cell is at the fiber saturation point (fsp). The approximate MC of the fsp is 28%, but this varies with species. When drying up to this point (i.e., from "tree green" to the fsp), the wood cell has not shrunk (unless it has collapsed, which is rare). As the cell begins to dry below the fsp, bound water is removed from the cell wall and the cell begins to shrink. Shrinkage continues until 0% MC. Note that the discussion above has referenced the wood cell. In a piece of drying lumber, cells on the outside will dry below the fsp and begin shrinking quite quickly. Cells in the center of the piece may require weeks, in some cases, before they reach the fsp and begin shrinking. Therefore, it is incorrect to say that a piece of wood is "at the fsp" when it is at 28% average MC. In fact, at 28% MC, some of the cells are well below the fsp and have shrunk, or tried to shrink quite a bit, while other cells are still well above the fsp and haven't begun to think about shrinking. 15PDF Image | Principles and Practices of Drying Lumber
PDF Search Title:
Principles and Practices of Drying LumberOriginal File Name Searched:
DryingLumber.pdfDIY PDF Search: Google It | Yahoo | Bing
5,000 BF Shipping Container Lumber Dry Kiln For Quality Lumber The 5,000 BF container kiln consists of one 40 foot high-cube aluminum shipping container... More Info
Shipping Container Lumber Dry Kilns by Global Energy Global Energy designed and developed the container kiln back in 1991. The purpose is to give access to portable sawmill owners, furniture makers, and small business the value added profit of dry kiln lumber and quality hardwoods... More Info
Vacuum Kiln Conversion Kit for Lumber and Wood Dry Kilns Convert your existing conventional dry kiln into a fast drying vacuum kiln. Similar to vacuum bagging in the boat building and aircraft industry, we have come up with a proprietary process which allows you to build a very simple vacuum kiln at a fraction of the price, and without the intensive conventional metal chamber structure... More Info
Vacuum Pump Cart System for Bagging Clamping Wood Drying and more Vacuum Cart with 2HP Pump and Dual Pistons with multiple multiplex vacuum ports and liquid reservoir... More Info
Vacuum Bagging Basics Vacuum bagging is a method of clamping, which has traditionally been used in the composites industry, but can also be used for vacuum drying materials, including wood products... More Info
| CONTACT TEL: 608-238-6001 Email: greg@globalmicroturbine.com | RSS | AMP |