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burr2, buhr, bur
(also called flash), a projection on the surface of a product that is being worked; it forms as a result of the extrusion of material into the gap along the joint of a tool (a die or a pair of rollers) or because of imperfect cutting of the billet. When metal is worked using other methods, burrs are formed only if the production process has not been adjusted properly or if a worn tool is used.
in woody trees, a thickening or growth on the trunks, branches, or roots. Burrs result from the local thickening of tissues, apparently in response to irritation or damage to cambium cells and dormant buds by fungi, frost, fire, or mechanical injuries (blows, slashes). According to the external appearance and to the structure of the fibers, two types of burrs are distinguished: those with smooth surfaces and slightly wavy wood and those with uneven surfaces and knotty wood (burls). The former type develops on the trunks of all varieties of trees; on pines and firs such burrs have wavy and relatively broad annual rings and consist of short thick-walled tracheids with curved or separated ends and of numerous large heartwood rays. The wood of burrs is much denser and harder than the ordinary trunk wood. Depending on dimensions and texture, burr wood may be used for producing structural ornament or for small household and artistic objects.