76/ ft 5~G S WOOD fLCLR 4 General Statement of the Manufacture and Use of Weed Flour and the Status of the Industry Revised- 1941 fs-tt L I UNITED STATES DEPARTMENT OF AGRICULTURE FOREST SERVICE FOREST PRODUCTS LABORATORY Madison, Wisconsin In Cooperation with the University of Wisconsin Digitized by the Internet Archive in 2013 http://archive.org/details/flourglOOfore ./OOP FLOUS A general statement of the ■ manufacture and use of wood flour and the status of the industry Wood flour is simply finely ground wood. As it comes from the mill it resembles ordinary wheat flour in appearance, hence the name. The ma- terial is designated "by "mesh" or number of bars per lineal inch of screen through which the product is sifted. The sizes of wood flour most common- ly used are Uo, 60, and 80 nesh. The finest grade of wood flour marketed is about lUo mesh. .7here a fine flour is required, 80-mesh stock will usually be satisfactory, and the bulk of the product is 80 mesh and finer. Production and Value The manufacture of wood flour is centered in the Sast at plants located advantageously with reference to sources of raw material and the more important consuming industries. Statistics covering the output of wood flour in this country are not available, but figures from various sources indicate that in 1937 about 3^,000 tons were produced. In addi- tion probably 8,000 tons were imported in that year. Current domestic production of wood flour is probably considerably greater than in 1937 due largely to inability to procure foreign stocks. Prices of wood flour at points of consumption in 1937 ranged from about $18 to $20 per ton for the coarser grades to $50 per ton for the finer grades used in plastics. Scandanavian wood flour when last avail- able sold at prices ranging from $20 to $28 per ton in New York. Present prices of wood flour in all grades have probably increased somewhat over 1937 figures. Properties The use to which wood flour is put largely determines the proper- ties required of that material. Even in the same industry several kinds of wood flour may be necessary in the production of the various commodi- ties. Three or four properties, however, seem to be very commonly re- quired of that product in most industries. Wood flour for practically all present uses must be light in color, light in weight, fluffy, and absorptive. It seems quite likely, however, that for some uses wood flour of almost any sort would be satisfactory. R565 Species Suitable Color and weight considerations limit to a large extent the species that may be used for making wood flour. The woods chiefly employed are the light-colored nonresinous softwoods, principally soft pines and spruces. Probably upwards of 80 percent of the product is of these species. Various kinds of poplar, fir, maple, birch, oak, and probably some hemlock make up the greater part of the balance. There are no mechanical reasons why wood flour cannot be made from many other woods. There are, however, inherent qualities in some woods, both softwoods and hardwoods, that preclude their use for that product. Woods having excessive pitch, gum, oil, or resin are not satisfactory for wood flour. Unless there is some specific use for wood flour of hardwood species, there is not much point in making hardwood flour, except possibly light- colored, light weight woods, such as aspen, basswood, and similar species. The preferred raw materials, the soft pines and spruces, are still plenti- ful and cheap and the finished product is low priced. Wood flour of the harder species of hardwoods has no stable markets and currently is of little importance in the wood flour trade. Types Wood flour is employed in the manufacture of a wide variety of products. To accommodate the various uses more exactly three general types of wood flour are made: nontechnical, technical, and granularmetric. Nontechnical wood flour is a common grade in which the requirements are not very exacting. It may consist of one species, or of a mixture of closely related woods, and may be of various sizes. Nontechnical grades are used in making certain plastics and the bulk of linoleum. The bulk of wood flour consumption is of the nontechnical grades. Technical wood flour is made to specified standards. The require- ments may relate to size or mesh, species, color, weight, resin content, character of fiber, absorptive properties, or some other property, or a combination including any of the above. Granularmetric wood flour is really a special type of technical wood flour in which for any mesh the particles are uniform in size and character. Ma nufac t uring Frocesses Wood flour produced in this country is made chiefly from sawdust and shavings resulting from planing mill and other re manufacturing opera- tions using white pine. Round wood, slabs, edgings, and trimmings are R565 -2- the principal other raw materials used in the wood flour industry and comprise about kO percent of the total volume consumed. Raw material for wood flour use must be of good quality and free from bark and other foreign matter to yield first-class stock. The wood used should be well seasoned, so that the particles of stock will be fluffy and not have any tendency to pack when lightly compressed. For best results in manufacture and in use the moisture content of the wood should not exceed 8 to 10 percent. ',7ood flour is produced by many types of equipment, chiefly, however, stone mills, steel burr roller mills, attrition mills, and several types of hammer and beater mills. In Europe, particularly Scandinavia, where a great deal of wood flour is made, the stone mills seem to be used exclu- sively and most of the early plants in this country were equipped with that type of mill. The stones are from UO to 60 inches in diameter and only the lower stone is driven, the upper one being stationary. Power for operating the mills is derived from water turbines, since flour produced with power developed in other ways cannot compete with Norwegian flour ground by water power. Frobably the most common metal wood pulverizers are attrition mills of the double attrition and single attrition types. The grindi:. ; elements of the first named type consist of two revolving plates operat- ing in opposite directions, between which the raw material is ground. Single attrition mills have one revolving plate operating against the side of the machine housing, which accomplishes the same result. Most attrition mills are equipped with air separators for screening the product. The "beater" mill is of Jairly recent origin. It is an upright steel affair, the distinctive feature of which is a shaft to which are attached staggered beaters about 6 or 8 inches long, which attack the raw material and beat it to the required fineness. There are two types of "beater" mills based on method of screening the flour. TChen stock 60 mesh or finer is desired air separator equi - ment is attached. Screen separators are used when material coarser than 60 mesh is made. From 7 to 13 pounds of wood flour per horse power per hour are produced by "beater" mills. A 20 horse pov/er machine will yield about 2-1/2 tons of 80-mesh flour, 95 percent fine, in 2h hours. The production of flour by "beater" types of equipment is in almost direct proportion to the fineness of the stock. Material of 120-mesh is produced about one-third as fast as Uo mesh; 80 mesh only about one-half as fast as ko mesh, etc. The grading of stock bO mesh and finer is accomplished by an air separator. Adjustments of the fan control the speed at which air is drawn through the beating chamber. Slow speed of the fan carries out only the finest dust. Faster speed carries out the larger particl The flour is collected in an improved cyclone dust collector, which saves practically the entire yield of the machine. H565 -3- Names and addresses of firms making wood flour machinery can lie had from trade directories or from this Laboratory. Uses for Wood Flour Linoleum Over half of the wood flour used in the United States annually is consumed in .the linoleum industry. In 1937 that industry accounted for about 20,000 tons. Wood flour .is used exclusively in the production of goods be longing to the inlaid class, either, "granulated inlaid" or "straight line." Cork linoleum is usually dark, either the natural brown, or dark red or green, Fatterns are printed on cork linoleum, but the pattern soon wears off, leaving the dark base. For the production of in- laid goods in which the pattern goes clear through the piece to the burlap backing, a white base is necessary, not only to furnish a white background where desired, but also to permit of dyeing to any color. For this reason a flour as white as possible is desirable, and the material must be uniform and should be all of one species. Dynamite Wood flour is one of the principal absorbents for nitro-glycerine in the manufacture of dynamite. The total quantity used in the manufac- ture of that product is probably upwards of 10,000 tons annually or more than 25 percent of the total volume of wood flour consumed. The use of wood flour in dynamite manufacture is probably increasing. A white flour is essential in dynamite, since the bulk of users judge the age of that product by its color. Light-colored dynamite is considered as fresh stock, of high strength. Other Uses for Wood Flour Probably the greatest single use for wood flour other than for linoleum and dynamite is as a filler in the manufacture of phenol resin and similar products. Among the more common phenol resins are bakelite, redmanol, condensite, and durez. These products mixed with wood flour and coloring materials are molded under heavy pressure and heat into various commodities, such as radio dials and knobs, telephone parts, ignition blocks, radiator caps, handles, kitchen ware novelties, etc. The amount of wood flour in these articles, by weight, comprises from 30 to 50 percent or more of the total weight of the finished product. "There high luster is required of an article only a small amount of wood flour is used. When luster is secondary to strength the amount of wood flour is increased. Starch, sodium silicate, resin, glue, and other materials are used to bind pressed wood flour into a number of other products, such R565 -k- as doll heads, novelties, picture frames, tenpins, bowling balls, phono- graph records, brusr. backs, insulating brick, etc. Composition flooring is made with wood flour, sawdust, and caustic magnesia cement. The wood elements are used to provide the bulk and to produce resiliency. 7food flour is also used in the manufacture of "oatmeal" wall paper. Status of the "wood Flour Industry While there is an abundance of raw material for wood flour produc- tion, the relatively small consumption of that material and a rather slow market are factors that limit new enterprises in the wood flour field. The principal producers of wooi flour have been in the business a long time and have succeeded chiefly because of their intimate knowledge of the industry and the exacting .requirements of consumers. Other factors important to successful wood flour production are a large and continuous supply of suitable raw material, nearness to markets, and, of course, a good demand for wood flour at fair prices. The uses of wood flour may be expected to increase and absorb larger quantities of stock in the future. They can hardly be expected, however, to develop sufficiently to afford a profitable outlet for more than a fraction of the wood flour that could be produced from wood waste. The potential supply of wood flour is much greater than the potential demand, and the dangers of excessive overproduction must be considered by those who might contemplate its manufacture. The Forest Products Laboratory has made no extended investigation of either the technic or status of the wood flour industry. This mimeo- graph is prepared for the purpose of bringing together information of general interest only, and no attempt is made to cover the subject in a thorough way. Information relative to the wood flour industry is also contained in a bulletin entitled "Sawdust, Wood Flour, Shavings, and Excelsior," issued by the Division of Forest Products, Bureau of Foreign and Domestic Commerce, U. S. Department of Commerce, Washington, D. C. Other sources of information are: "Wood Flour: Its Manufacture and Industrial Uses," Lumber World Review, Chicago, 111, Jan. 10, 1925; "Wood Flour Industry," The Timberman, Portland, Ore., Jan. 1930; "An Ensemble of Flour or a Dusty Gesture," Hardwood Record, Chicago, 111., Mar. 10, 1927. R565 UNIV ERSITV OF FLORID*. 3 1262 08926 5978