A S:AIPLIE DEVICE FOP DETECTING COMPRESSION WCC1D

Transcription

1 A S:AIPLIE DEVICE FOP DETECTING COMPRESSION WCC1D Revised June 1953 Reprinted December 1962 LOAN COPY No sogio i!num Please return to: Wood Engineering Research Forest Products Laboratory Madison, Wisconsin 53705, MINIMMININ n M IIMI101111= = UNITED STATESPRODUCTS LABORATORY n Cooperation with the University of Wisconsin

2 A SIMPLE DEVICE FOR DETECTING COMPRESSION WOOD! 2 Forest Service Forest Products Laboratory, _ U. S. Department of Agriculture A simple device that facilitates the detection of compression wood in lumber from Sitka spruce and other coniferous species has recently been developed by the Forest Products Laboratory. Consisting of a simple box containing an electric light arranged to cast its rays through an aperture, the apparatus discloses the presence of compression wood, which is relatively opaque compared with translucent normal wood. When a thin specimen containing compression wood is placed in the aperture, the compression wood blocks the passage of light much more than does normal wood (fig. 1). Compression wood is responsible for much crook and bow in lumber and has mechanical properties inferior to those of normal wood.. For these reasons it is particularly objectionable in lumber to be used for aircraft. The new apparatus (fig. 2) reveals the presence of gradational forms of compression wood which hitherto have been discernible only under microscopical examination. It permits rapid examination of thin cross sections from lumber..1 The extreme forms of compression wood, which are particularly objectionable, ordinarily can be detected on large transverse surfaces by the comparatively wide and eccentric annual rings containing a high percentage of summerwood not so hard as normal summerwood nor, when dry, so dark. Compression wood consequently lacks the customary marked 1 This report was one of a series of progress reports originally issued by the Forest Products Laboratory to aid the Nation' s war program. 2 Maintained at Madison, Wis., in cooperation with the University of Wisconsin. 3 Pillow, M. Y. and Luxford, R. F. Structure, Occurrence, and Properties of Compression Wood. U.S.D.A. Tech. Bul. 546, illus Pillow, M. Y. A New Method for Detecting Compression Wood. Jour. Forestry 39 (4): , April Report No (Revised)

3 contrast between normal summerwood and springwood, and thus has a "lifeless" appearance. It is in revealing the borderline and intermediate forms of compression wood, difficult to detect without a microscope, that the new apparatus is particularly helpful. The summerwood of compression wood evidently is more opaque than normal summerwood because the microscopically discontinuous structure of the secondary cell wall of the summerwood tracheids dissipates the light. Normal summerwood does not have the microscopic checks and striations in the secondary cell wall which characterize compression wood. Variations in moisture content of wood appear to have little effect on this method of detecting compression wood. Pitch-soaked wood, on the other hand, is highly translucent regardless of whether it contains compression wood. It is therefore not well adapted for this test. Some pitch is found in Douglas-fir, but Sitka spruce is little affected by it. Surfaces of samples cut with a circular cut-off saw or ordinary hand saw, provided it is reasonably sharp, are suitable for this test provided the end grain surfaces are parallel. Sanded surfaces are unsatisfactory because in sanding the cell cavities become filled with particles of wood and sand which destroy the translucence of normal wood, and, hence, its contrast to compression wood when examined. Thin specimens should be cut, before fabrication, from each piece of lumber suspected of containing compression wood and examined in the light box. Cross sections 5/32 inch thick provided the most satisfactory specimens in Laboratory tests. Making the Apparatus While direct sunlight or a powerful flashlight sometimes gives useful results for thin specimens, for accurate inspections the Laboratory apparatus is needed. Working drawings show its construction features (fig. 3). A 75-watt electric light is strong enough to give good penetration. This box should be used in a dimly lighted area or at least not in bright light. Its exterior and the grooves for the specimen slides are painted black to reduce reflection of extraneous light. If it is necessary to use the light box in ordinary room light, a simple fiberboard viewing device can be made as indicated in figure 4, and held together with gummed paper. A wood viewing device, fitted with specimen slides at one end and used with an ordinary flashlight, electric light bulb, or direct sunlight, has also been designed. Working drawings for it are shown in figure 5. The Laboratory model takes only specimens up to 2 inches wide, but dimensions of the slide can be varied for larger specimens. Report No (Revised)

4 Fig. 1. Cross sections of wood which were photographed by transmitted light. Above, normal wood showing translucence, and below, compression wood interspersed with normal wood showing location of compression wood by its opaque summerwood. ZM F

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9 SUBJECT LISTS OF PUBLICATIONS ISSUED BY THE FOREST PRODUCTS LABORATORY The following are obtainable free on request from the Director, Forest Products Laboratory, Madison 5, Wisconsin. Box and Crate Construction and Packaging Data Chemistry of Wood and Derived Products Fungus Defects in Forest Products and Decay in Trees Glue, Glued Products, and Veneer Growth, Structure, and Identification of Wood Mechanical Properties and Structural Uses of Wood and Wood Products Partial list of publications for Architects, Builders, Engineers, and Retail Lumbermen Fire Protection Logging, Milling, and Utilization of Timber Products Pulp and Paper Seasoning of Wood Structural Sandwich, Plastic Laminates, and Wood-Base Aircraft Components Wood Finishing Wood Preservation Partial list of publications for Furniture Manufacturers, Woodworkers and Teachers of Woodshop Practice Note: Since Forest Products Laboratory publications are so varied in subject, no single list is issued. Instead a list is made up for each Laboratory division. Twice a year, December 31 and June 30, a list is made up showing new reports for the previous 6 months. This is the only item sent regularly to the Laboratory's mailing list. Anyone who has asked for and received the proper subject lists and who has had his name placed on the mailing list can keep up to date on Forest Products Laboratory publications. Each subject list carries descriptions of all other subject lists.

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