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#1 Sept. 18, 2017 09:58:47

Registered: 2017-09-18
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The relatively large amounts of ether-soluble components

Pressure Bar is secreted by vertical and horizontal resin canals in such softwood groups as pine, spruce, Douglas-fir, and tamarack. In hemlock, fir, and redwood, resin canals are normally absent but may be produced by injury to the tree. In veneer cutting, resin is a handicap. It may collect on the pressure bar and encourage chips to jam between the pressure bar and the wood bolt, causing depressions in the veneer. Frozen or solidified resin in knots is very hard and will quickly blunt a sharp knife. Ether-soluble resin occurs in small amounts in many U.S. hardwoods, but generally has little effect on their use for veneer.

The relatively large amounts of ether-soluble components found in basswood may explain why this species is more difficult to glue than would be expected from its specific gravity. Resin in core and crossply veneers, such as may occur in the heartwood of cativo and southern pine, is objectionable because it may bleed through the face veneer.

Similarly resin in face veneer species like white pine can interfere with furniture finishes. This is particularly true if the end pi'oduct is a TV cabinet, which becomes warm during use. Among the imported hardwoods, vertical and horizontal resin canals are found only in certain species of Dipterocarpaceae. The contents of these canals usually appear white or yellow.

M 136 441 Figure 4.—Gum in a sheet of rotary-cut Brazil nut veneer. These extractives may be part of the problem in gluing kapur and keruing. Polyphenols Polyphenols can be broadly grouped into tannins and nontannins. Most tannins are of a molecular size generally soluble in water. Polyphenols that are not soluble in water can be removed from wood with polar organic solvents like alcohol or alcohol-benzene.


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