Patent Publication Number: US-2010126630-A1

Title: Method of producing flat chips out of wood

Description:
The invention relates to a method of producing flat chips out of wood, also designated as “OS chips” (“oriented strand”). 
     Structurally-oriented wood materials involve special lignocellulose-containing boards or molded articles that have oriented mechanical and hygric properties. Included among these wood material are LSL, PSL, and especially OSB. OSB is the structurally-oriented wood material of greatest economic significance. Due to the shape and size of the strands, the corresponding wood materials provide strong mechanical properties. As a result, they can be applied in particular as construction components in the construction industry. 
     U.S. Pat. No. 2,874,909A discloses a method for generating chips for fabricating boards and comprising the following method steps: an intermediate product is generated from fresh wood or recycled wood; the intermediate product is essentially bar-shaped; the intermediate product is fed to a chipper comprising a plurality of knives that are disposed on a knife ring, the blades of which run at least approximately parallel to the ring axis and which enclose a working space; the intermediate product is caused to revolve about the axis of the knife ring and thereby aligned such that it is oriented essentially parallel to the ring axis and is pressed against the blades of the knives by centrifugal force; the intermediate product measures several centimeters in length. 
     DE 11 71 143 B illustrates and describes the effect of heat, moisture, and pressure during the production of chips for the purpose of improving their quality. 
     A successful method for producing OS chips is described in EP 1 335 818 B1. Here the shape of the intermediate product is defined more precisely. 
     The method is capable of being improved, however. This mainly relates to the quality of the individual flat chip. The flat chip should if possible be of even higher quality in terms of its shape and its surface. In addition, the chipping process should produce the maximum in terms of high-quality flat chips but the minimum in terms of the fraction of fine material. Finally, the energy requirement should be minimized. 
     The fundamental problem to be solved by the invention is to provide a method by which a strand material composed of small-piece-type wood components (intermediate products such as Maxichips and flat chips) can be produced, which contains large fractions of distinctly laminar strands and small fractions of fine material. In addition, the energy for chipping should be minimized. 
     This problem is solved by the features of claim  1 . 
     The fundamental ideas of the invention relate to the shape of the intermediate product and to providing an additional treatment step: Specifically, the intermediate product undergoes an intermediate treatment comprising the action of heat and moisture before it is further treated mechanically. 
     The referenced treatment with moisture and heat is applied to the intermediate product (Maxichip) after shredding. The treatment can be combined with the application of hyperbaric pressure. 
     Any heat sources can be used to effect the treatment with heat, such as, for example, microwave or infrared devices. A hot-water treatment or steam treatment can also be considered. 
     The entire method can be implemented batchwise or continuously. In the continuous process, use of worm conveyors is conceivable. This worm conveyor can be charged with a woodchip-water mixture. Pressure can be generated by a shut-off valve opening a restricted discharge slit at the end of the feed screw, thereby building up pressure within the feed screw. A steam treatment can also take place within the feed screw. Low pressure or excess pressure can also be applied. 
     The results are amazing. Specifically, the process according to the invention has the following advantages:
         the chipping process yields a high fraction of flat chips and a minimum fraction of unwanted fine material:   the quality of the flat chips is better than those generated previously: the chips have a flawless surface suitable for generating OS board; the chips furthermore exhibit a higher strength than previously;   due to the hydrothermal treatment and less-damaging chipping, the strands furthermore exhibit fewer cracks; the risk of secondary shredding by subsequent processes during fabrication of the OSB is thus reduced;   the specific energy cost in kWh relative to quantity unity of generated OS chips is significantly lower than with known methods;   in terms of primary material, any lignocellulose-containing materials can be considered—thus, wood, waste wood, shredded wood, recycled wood, but also exotic materials such as bamboo, palms.       

    
    
     
       The following discussion describes the invention in more detail based on the drawing. In the drawing specifically: 
         FIG. 1  shows a block diagram to illustrate the operational process of a method for fabricating OS board. 
         FIG. 2  shows a front view of a chipper, that is, a view towards the side on which the housing cover with insert for the intermediate product is located. 
         FIG. 3  illustrates an axial section through the chipper of  FIG. 2  on an enlarged scale. 
         FIG. 4  shows an enlarged diagram illustrating a section from  FIG. 3 , specifically, a knife assembly. 
     
    
    
     The block diagram of  FIG. 1  shows the following stations of the method for producing OS board: 
     The material to be processed is first stored in station  100 . In terms of this example, these can be used wood pallets. Obviously, all possible other lignocelluose-containing materials can be considered, as was mentioned above. 
     Rough pre-shredding occurs in station  101 —for example, in a shredder. 
     Shredding occurs in station  102 . The intermediate product is generated here. This is at least approximately bar-shaped. 
     A treatment with moisture and heat occurs in station  103 . Treatment can consist of immersion in hot water. The water is at a temperature of more than 50° C.—for example, 60, 70, 80, 90, 100° C. The residence time ranges between 3 and 30 minutes. Even longer time periods can be considered—for example, one hour, two hours, etc. 
     Scalding with superheated steam can also be considered in place of immersion in hot water. 
     The wet-hot treatment can also take place under hyperbaric pressure or subatmospheric pressure, thus in a closed vessel. Here the intermediate product—and thus the wood chips—are completely penetrated by moisture. A certain level of plastification takes place, in some cases a solubilization of the lignin. 
     The intermediate product is pre-screened at station  104 . 
     Chipping takes place at station  105 . The result is OS chips having a chip thickness ranging between 0.2 and 0.8 mm, at best 0.2 to 0.6 mm. 
     After chipping, post-screening takes place at station  106 . 
     This is followed by subsequent processing into OS board at station  107 . 
     As seen in  FIGS. 2 and 3  in detail, the chipper comprises a rotor  1  that is driven by a shaft  2 . Rotor  1  contains a ring of axially-parallel vanes  3 . A knife box also with knives  4  disposed in axially-parallel fashion surrounds rotor  1 . Rotor  1  and knife box are in turn disposed in a housing  5  and together enclosed by this housing. Housing  5  has an inlet  6  for the wood chips to be supplied and an outlet for the finished chips. 
       FIG. 3  illustrates a bar-shaped intermediate product  20  at two positions. In the present case, this has been prepared in the form of regular rectangular blocks. This intermediate product could also have a different shape instead, however—for example, have irregular peripheral surfaces. The only critical aspect is that this intermediate product  20  is more or less bar-shaped, that is, it has a longitudinal section that is greater than the transverse section in planes running perpendicular thereto. 
     The intermediate product  20  is fed into shaft-like inlet  6 —see arrow. It then moves into the interior space surrounded by rotor  1 . Here, intermediate product  20  comes to be oriented—either automatically or by an appropriate orientation device—such that it runs predominantly parallel to the longitudinal axis of rotor shaft  2 , and thus more or less parallel to knives  4 . The intermediate product is of considerable size, in particular, of considerable length when compared with wood pieces of this type that have previously been fed to knife-ring chippers. 
       FIG. 4  illustrates an axially-perpendicular section through a knife assembly. Each knife assembly is a component of the knife ring of the machine. 
     Each knife assembly is constructed as follows: A support block  10  supports a cutting knife  11  that is affixed to support block  10  by a clamping plate  12  and a screw  13 . 
     Each support block  10  has a wear surface  10 . 1 . The critical aspect is that this wear surface  10 . 1  facing the machine axis is approximately flat and thus not concentric as in the prior art. 
     Here wear surface  10 . 1  is composed, as in  FIG. 4 , of a wear plate  10 . 2  that is in turn affixed on the rest of support block  10 . The wear surface can also be composed of a wear layer that has been generated by applying a wear layer, preferably by build-up welding or spraying on, followed by grinding. 
     In the embodiment of  FIG. 4 , a bed knife  14  is provided, which is attached on the side of support block  10  opposite cutting knife  11  and that works together with the cutting knife of the adjacent knife assembly. A wear plate is also conceivable in which the bed knife is integrated and assumes the function thereof. 
     LIST OF REFERENCE NUMBERS 
     
         
           1  rotor 
           2  shaft 
           3  vane 
           4  knife 
           5  housing 
           6  inlet 
           10  support block 
           10 . 1  wear surface 
           10 . 2  wear plate 
           11  cutting knife 
           12  clamping plate 
           13  screw 
           14  bed knife 
           20  intermediate product 
           100  storage station for waste wood 
           101  rough shredding station 
           102  shredding station 
           103  hot water station 
           104  pre-screening station 
           105  chipping station 
           106  post-screening station 
           107  subsequent processing