FI57228B - FOERFARANDE OCH ANORDNING FOER BEHANDLING AV SAOGSPAON FOER TILLVERKNING AV SPAONSKIVOR - Google Patents

Description

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Patent »och reglsterstyrelsen AmökM utitgd och uti.ikrHtm publicand 31.03.80 (32) (33) (31) Pyydetty atuolkau * -tagiH prtorlttt 2i +. OU. 70

Sweden-Sweden (SE) 57 ^ 0/70 (71) AB Karlstadplattan, Kungsgatan 12, Karlstad, Sweden-Sweden (SE) (72) Erik Gustav Lennart Eriksson, Karlstad, Sweden-Sweden (SE) (7L) Berggren Oy Ab (5M Method and apparatus for treating sawdust for the manufacture of particle board - Förfarande och anordning för behandling av sägspän för tillverkning av spänskivor

The invention relates to a method and an apparatus for treating sawdust for the production of particle boards according to the definition of species according to claim 1 and 5, respectively.

Sawdust is mainly obtained as a waste product from frame, band, circular and cutting saws, etc. Sawdust here means wood particles with a length equal to or less than 15 times the thickness, but less than about 10 mm.

Substantial amounts of such sawdust are generated, and the wood processing industry and wood research have for many years been engaged in the problem of recovering this waste product. The amount of sawdust that has so far been put into technical use is quite small and is probably about 10% of the total amount. Most of the sawdust generated is still used today mainly as fuel. Because of the poor efficiency obtained when burning sawdust, the value in use of sawdust and thus its price is relatively low. If a valuable processing opportunity could be obtained for this waste product, a large amount of cheap raw material would be available for this purpose and at the same time a national economic advantage could be achieved.

Thus, to date, several studies and experiments have been carried out to determine whether sawdust is suitable for the manufacture of particle board. For the first time, the production of sawdust was started industrially using sawdust as a raw material as early as 19 * 11, when using boards with phenolic formaldehyde resins, boards with a bulk density of between 0.8 and 1.1 g / cm 2 were prepared. However, these sheets proved uncompetitive under normal conditions and production ceased. Scientific studies on the use of sawdust in the manufacture of particle board have shown that these 8-10Ϊ binders are not technically feasible when added to the binder because the technological properties of the products are not satisfactory. Thus W.

Klauditz has shown in laboratory experiments that the flexural strength of chipboards with a bulk density of 0.8 g / cm 2 is only n.

110 kg / cm when six-frame sawdust is used, while the corresponding value when using 0.1-0.3 mm thick cutting chips is of the order of 500 kg / cm. The corresponding values with a bulk density of 0.6 are 30 and resp. 300, and at a bulk density of 1.1 g / cnr * about 400 and approx. 700. From this it can be concluded that sawdust may be useful in heavy chipboards, but not in lightweight ones.

In W. Klaudiz, H.J., on the properties of light particle boards. Further studies by Ulbricht and W. Kratz found that sawdust was likely to be used in the production of lightweight particle board. However, it was also found that the low slenderness of sawdust particles means that their technological suitability for the production of particle board is relatively low and that sawdust is only to a limited extent suitable for the production of strong, valuable particle board from it alone.

In further studies, W. Klauditz and A. Buro found that when sawdust was glued using 8 g of solid resin per 100 g of abs. dry sawdust, the binder content in the coarser fractions was only 3 - ** ί while the binder content in the finer fraction was about 15Ϊ. From this it was concluded that the material should be homogenized by separating the finest component (about 5-10¾) to obtain a more even gluing. When studying the strength properties, it was found that compared to conventional cutting boards, it is expected that sawdust boards will give much lower values for bending, tensile and compressive strengths as well as the elastic modulus of bending. Laboratory tests performed showed that the flexural strength is only approximately 1 / * 4 - 1/3 of the corresponding values of the chipboard, while the transverse tensile strength is 10-30¾ higher. These studies, as well as previous experience, confirmed that medium-heavy boards cannot be made from sawdust if they have to meet practical requirements, for example in the furniture industry.

As a remedy, it was recommended to mix about 30% of conventional cutting chips with the surface layer material, which was thought to improve the flexural strength and modulus of elasticity compared to sawdust-only particleboard approximately three times, i.e. only about 2055 worse than with finished chipboard alone. This, of course, leads to the downside that the transverse tensile strength is significantly reduced.

O. Liiri has also stated that the flexural strength of sawdust boards is lower than that of conventional chipboards. Transverse tensile strength is relatively better than flexural strength, but is also reported to be inferior to particleboard. In this connection, Liiri also states that fine sawdust on circular saws is not as good a raw material as coarse sawdust. In the experiments described for the production of sawdust boards, Liiri separated on the one hand too large particles and on the other hand dust. As dust, Liiri counts the one that passes through a sieve with 0.296 mm holes (48 mesh). Liiri has also presented the typical properties of pine sawdust boards. They clearly show that bulk density is also crucial for the strength properties of sawdust boards. Thus, the bulk density greatly affects the flexural strength. Plates made from sawdust obtained from cutting saws, which is more finely divided, have lower bending strength than those made from frame sawdust. The difference decreases as the bulk density increases. No significant difference in flexural strength has been found by Liiri in boards made of different sawdust fractions and unscreened sawdust. Instead, he noted larger differences in transverse tensile strength on plates made from different sawdust fractions. Consistent with other studies in the field of Liirik, Liirik mentions that the sawdust board is smaller, more precisely almost half of the corresponding value of a "normal" chipboard, but Liiri reports that Liri considers that this is due to the fact that very fine sawdust is not advantageous, and finally, in line with Klauditz et al. leikkuulastuja.

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In combination, it can thus be said that the prior art for producing chipboard from sawdust, which, with the exception of heavy boards, is almost generally not yet beyond the laboratory stage, in no case includes the finest fraction or usually the coarsest fraction of the resulting sawdust. These are instead separated and then glued in the laboratory to this chip and pressed into sheets having the flexural strength values of Figure 1 and the transverse tensile strength values of Figure 2. Also shown in these figures are the results of studies of sawdust boards according to the present invention, which are manufactured on a half and full scale according to the method developed by the inventor.

In addition, it can be stated that in the laboratory experiments of Liir and Klauditz, even for those sawdust boards in which "normal" cutting chips have been used as a surface material, it has not been possible to obtain full-strength bending strength. These sawdust boards are thus inferior in quality to conventional chipboards.

It should be further emphasized that the flexural strength and the transverse tensile strength are usually inversely related to each other, i. that a plate with a particularly high bending strength normally has poorer transverse tensile strength and vice versa.

In addition to the studies mentioned above, there are some other publications in this field that deal with laboratory studies using sawdust as a raw material. However, in all the examples described, it has been a matter of separating the material, which is too large and too fine, and the raw material has not been otherwise mechanically treated. However, the aforementioned Liiri, Klauditz and others are probably very representative of development, as they are considered to be the most significant researchers in the field.

It is an object of the present invention, on the basis of the prior art, to provide a method for producing particle board from a raw material containing up to 100 lbs but at least 50% sawdust, and to provide particle board with conventional bulk weights but nevertheless strength values compared to conventional particle board. preserved or even improved, especially flexural strength, transverse tensile strength, and swelling when absorbing moisture. The consumption of the binder when gluing must then remain within the normal limits. In addition, the opposite relationship between bending strength and transverse tensile strength that has occurred so far must be considerably impaired. In addition, sawdust boards must be competitively priced.

According to the invention, this is achieved by the fact that after separating the wreckage from the sawdust, a fine part of the sawdust, i. small thin chips, small cubic granules, dust, any wood flour, etc. are separated by sieving from the coarser parts, i.e. coarser chips, cubic granules, etc., which are relatively thick in the transverse direction of the fibers, that the coarser part is at least partially cut or split, reducing the thickness and / or width of the particles but changing the fiber length only negligibly, and deriving the pre-treated chip material through sorting as coarser and finer chips into one or more gluing devices with a binder in a manner known per se for further processing.

The cutting or splitting is suitable to be performed with cutting or splitting tools. This can be done with knife-like devices or also by centrifuging the material against a perforated sieve plate or the like where the edges of the holes are sharp.

The sawdust boards produced according to the invention are completely comparable to conventional chipboards in terms of flexural strength, even in the lower volume weight range, i.e. between 0.40 and 0.75 g / cm 2. The bending strength values are then much higher than those reported by Liir and Klau-ditz, see in particular Figure 1. In addition, thanks to the present invention, both good bending strength and good transverse tensile strength, i.e. the previous inverse relationship does not occur to the former extent. Figure 2 shows the transverse tensile strength of particleboards made according to the invention as a function of bulk density, and the curve obtained by Liiri when studying a large number of chipboard products on the market is also drawn. The reference values for the sawdust boards according to the invention have been obtained in experiments in which the invention has been applied on a half and full scale.

The relatively high flexural strength and transverse tensile strength obtained when examining sawdust boards made according to the invention is mainly due to the method of processing the chip according to the invention. In contrast to what has been previously proposed, according to the invention, the finest fraction is not removed, but on the contrary the proportion of small chips, etc. is increased by cutting, splitting and / or grinding the coarser fraction to increase the fine fraction.

The invention also relates to an apparatus for carrying out the above-mentioned method. Such a device is known from a screening device 6 57228 for separating scrap from sawdust, a screening device for separating a fine part of sawdust from coarser parts, a cutting or splitting machine for reducing coarse material, a size sorting device a bonding agent.

The plant can be simplified to some extent by combining the first and second size sorters into a single size sorter, the coarsest fraction of which is adapted to be fed to the grinding device and then returned to the size sorter.

The invention is explained in more detail below in connection with the accompanying drawing. In the drawing: Fig. 1 shows the flexural strength of different sawdust boards as a function of bulk density, Fig. 2 shows the transverse tensile strength of sawdust boards according to the invention and conventional chipboards as a function of volume weight, Fig. 3 shows a plant for performing the method according to the invention,

The process according to the invention starts from a raw material containing at least 50% sawdust. In this case, it is also possible to use only sawdust. Sawdust is obtained e.g. frame saws, circular saws, band saws, cutting saws, etc. in sawmills and planing mills, etc. In general, this sawdust is quite clean from bark or bark waste. It should be noted, however, that this method is not particularly disturbing by the shell. Sawdust also usually contains coarser pieces, such as cutting residues, etc., which are called scrap material.

The raw material first passes through a coarse sieve SI, where the pieces of board, large sticks and other waste material are separated off. These can be used, for example, as fuel or also fed to a chipper and then returned to the coarse screen.

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After the coarse sieve S1, in the plant according to Fig. 3, a fine sieve SII follows, in which the material is divided into fine pulp f1 and coarse pulp gl. By coarse chewing is meant larger chips, cubes and other wood particles too large for the application of the method, and fine chewing is meant by smaller cubes, chips, small bundles of fiber and wood flour and dust, respectively. The coarse chew gl is fed to the device MI for cutting or splitting with cutting tools, the cutting and splitting being characterized in that the length of the chewing particles changes only insignificantly while their thickness and / or width decreases. After cutting, the length of the chips can be said to be equal to or less than 30 times the thickness, i. the so-called slenderness number of the wood particles is less than 30. After cutting, the material obtained from the coarse chips, like the fine chips fl, is suitably fed first into the tank and then out of it in a steady, adjustable stream to a dryer T, where it is dried in a known manner and then stored in a tank. This is suitably provided with an outlet device which discharges a uniform, adjustable particle stream to the first size sorter F1. In this size sorting device F1, in the embodiment according to Fig. 3, three fractions are separated, namely a fine fraction f2 comprising dust, wood flour, small chips and very small cubes. This fine fraction f2 is fed - possibly via a tank - directly to the gluing station L. The second fraction g2a is separated into larger cubes and chips, which are fed to a second size sorter FII, which divides this fraction into six further fractions f3-f8, which are fed to the above-mentioned gluing seam L. the coarsest fraction g3, which together with the third coarsest fraction g2b separated in the first size sorter F1b is fed to the grinding device MII, where these two fractions g2b and g3 are ground to a smaller particle size and returned to the first size sorter F1.

These seven fractions f2 and f3 ~ f8 are each fed separately to a gluing device, where they are treated with glue in a manner known per se. The coarser particles then stay longer in the labeling device and the finer particles stay in it for a shorter time. After gluing, the material is fed into the forming slurry and further processed into chipboard in a known manner. In this case, it is important that the formation is carried out in such a way that the finest particles are closest to the surface layers and the coarser particles are in the middle layer. When using so-called blow spraying, this can be performed as one of the '8 57228 formation steps.

The application example according to Fig. B differs from that according to Fig. 3 in that the chip material after the coarse screen S1 is fed directly to the drying device T, from there to the tank and then to the fine screen SII. The coarser partial stream gl is returned after cutting to the fine sieve SII. The size sorting device FI divides the finer material stream f1 into two fractions: a finer fraction f2, which is fed to the tank and from there to the gluing station LII, which in turn feeds the two forming stations FOII and FOIII to form the base and cover layer of the chipboard. The coarser fraction g2 is divided into two parts g2a and g2b, of which the former is fed through the tank to the second size sorting device FII and the latter part g2b is fed to the grinding device MII and then returned to the first size sorting device FI. The grinding device MII is also fed with the coarsest fraction g3 from the second size sorting device FII. The other fractions f3-f8 of the second size sorting apparatus FII are fed to a separate gluing station L1 and then to a forming station FOI to form a middle layer of chipboard.

Also in the plant according to Fig. 5, the raw material containing 50-100% sawdust is first fed to a coarse screen SI, where the oversized material is removed, fed to a chipper and returned to the coarse screen SI. The raw material is then dried in a dryer T and fed to a fine sieve SII, which divides the material into three fractions f1, gl1 and g2, namely a very fine fraction f1 comprising dust, wood flour and very small chips and fiber bundles fed to tank B, which in turn the crumb is fed to the gluing device LII. The coarsest fraction gl of the fine screen is fed to a cutting device MI, where the particles are cut vast, split in the direction of the fibers and returned to the fine screen SII. The third fraction g2 from the fine screen SII is fed to the hopper and from there to the size sorter F. The coarsest fraction g3 of the sorter is fed to the grinder MII, reduced and returned to the hopper or alternatively directly to the sorter F. The other fractions f3 to f8 of the sorter are fed as mentioned above. to the gluing station Li. The gluing stations L1 and LII can, of course, be combined into a single gluing station, from which the chip is fed to the forming station. After forming, the material is treated in the usual manner by pressing, edging, cutting, etc. into chipboard. The waste generated in edging and cutting can be returned to the grinding device MII or to the coarse screen SI.

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The devices used to carry out the process according to the invention can be arbitrarily modified within the scope of the claims, however, it is important that the plant includes a device for separating oversized ingredients (waste material) if the raw material contains waste material, and a device for separating sawdust with particle sizes according to the invention. for processing, a cutting device for the too coarse end of the sawdust, in which the thickness and / or width of the individual wood particles is reduced, but their length is only negligibly affected. In addition, the plant should include a size sorting device in which the first separated sawdust is further divided into at least one finer and one coarser fraction, whereby in order to ensure a sufficient amount of finer particles it is suitable to separate part of the coarse material stream and grind it to a smaller size. The forming device must be such that the particle size in the finished chipboard decreases as it goes outwards. The rest of the plant could be made normal.

The boards obtained by the method according to the invention are characterized in that they contain cubic granules of different sizes, chips of different sizes, different thicknesses and degrees of thinness, as well as bundles of fibers with a high degree of thinness, and possibly wood flour and dust. In conventional particle boards, there is an obvious orientation of the chips parallel to the plane of the board, so that only a very small part of the fiber bundles, chips, etc. is at an angle to said plane, due to the fact that the chips are usually 10-25 mm or even longer. that their largest dimension becomes parallel to the plane of the plate. In the sawdust boards according to the invention, on the other hand, the maximum particle length is mostly well below 10 mm. As a result, it is possible that the number of particles transverse to the plane of the longitudinal axis may become large. In addition, the chip contains a considerable number of smaller and larger cubes, chips, and bundles of fibers oriented at an angle to the fiber plane between the long and thin chips. This is due to e.g. the fact that the plate, when formed as a whole, is compressed less. This results in the smaller particles in the surface layers being compressed harder than in conventional plates, as a result of which the bulk density 57228 10 becomes larger near the surface and smaller in the middle. This in turn causes the flexural strength to be higher in the sawdust boards of the present invention than in conventional particle boards when the bulk density and adhesive content are of the order of magnitude.

Considering where well-known scientists in the field have come to a unanimous conclusion, this result is completely surprising, as it has been argued and confirmed that elongated flat chips provide better flexural strength than short and thick chips, especially if the latter also contain very fine Granules. Good bending strength simultaneously with the transverse tensile strength is achieved by the fact that the surface layer has e.g. chips with a high degree of slenderness and adhesive content and that the surface layers are strongly compressed during the manufacturing process and therefore have better tensile and compressive strength than conventional chipboards, see Figure 1.

Since quite a part of the chips and fibers are not parallel to the plane of the board, good transverse tensile strength is also achieved - even almost double compared to conventional chipboards with the same bulk density and adhesive content, see Figure 2. Due to said orientation of chips and fibers, the thickness of the board swells suction remains considerably smaller because the swelling of the individual fibers does not occur in their longitudinal direction but in the transverse direction.

Instead of generally believing that sawdust alone, even at a relatively high binder content, provides poor strength and that wood flour, dust and chips have previously been considered downright unsuitable, the present invention uses precisely sawdust, including wood flour, dust and chips, and achieves the binder content is not changed, higher strength values than have been achieved so far in conventional particle boards, see Figures 1 and 2,

Furthermore, it should be surprising that according to the invention, by enriching small particles in particular on the surface, better strength values, in particular better bending strength, are achieved, although conventional test results have been suggested by those skilled in the art based on practical test results, i. longer chips, use in the middle layer.

Claims (5)

1. A method for treating waste material resulting from the signing of wood, containing at least 50% and up to 100% sawdust, for the production of spin discs, wherein the sawdust prior to gluing is at least partially transferred to less average particle size, dried and after gluing at least one forming device, characterized in that, after separating (SI) from waste from the sieve clamp the fin (s) of the sieve pin, ie. small thin spins, forge cube-like grains, dust, possibly wood flour, etc. by screening (SII) are separated from coarser parts (gl in Figs. 3 and 4; gl and g2 in Fig. 5), ie. coarser spin, cube-like particles, etc., which are relatively thick across the fiber direction, that the coarser portion (gl) is at least partially cut or cleaved (MI), reducing the thickness and / or width of the particles, but their length in the fiber direction only insignificantly degree, and that the thus-pretreated clamping material (fl and gl in Fig. 3; fl in Fig. 4; fl and g2 in Fig. 5) is fed via a sorting (F, FI, FII) into coarser and finer clamp fractions (f2 -f8 in Figures 3 and 4, f1 and f3 ~ f8 in Fig. 5) for one or more sizing devices (L in Fig. 3; LI, LII in Figs. 4 and 5) for further treatment with adhesives on their own. known way. 2. A method according to claim 1, characterized in that the cutting or splitting (MI) is performed with cutting or cutting. felted tool. 3. A method according to claim 1, characterized in that the cutting or splitting (MI) takes place in a device where the saw buckle is thrown against a perforated screen plate or the like with sharp perforating edges. An apparatus for carrying out the process according to any of the preceding claims, wherein as raw material a waste material originating from the signing of wood containing at least 50% and up to 300% sieve spin is used, wherein the cutting span before the sizing is at least partially transferred to a smaller average particle size. and after the size reduction is sorted in sorted condition