Patent Publication Number: US-7210511-B2

Title: Intermediate product, method and device for producing wood chips

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   The present application is claiming priority of German Patent Application No. 100 58 626.0 filed on Nov. 25, 2000 and PCT Patent Application No. PCT/EP01/12460 filed on Oct. 27, 2001. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   2. Description of the Prior Art 
   The invention relates to a method as well as a device for producing wood chips. For this, there are basically two systems, which differ fundamentally from each other and which, accordingly, also produce different products. 
   The first system relates to so-called direct chippers. In it, uncut round timber is fed into a chute. Arranged parallel to the axis along which the wood is fed is a knife ring, which is equipped along its circumference with a large number of knives. The cutting edges of the knives run parallel to the knife ring. The knife ring can move in such a way that it plunges into the body of the round timber and is able to chip it. See, for example, 
   DE 2,947,199 C1. 
   Another design of direct chippers, which belongs to the first system mentioned, has a disk that is mounted so that it can pivot. The disk carries chipping knives on one of its side faces. The round timber or tree stumps are fed to this working face in a direction parallel to the fibers. Because the circumferential speeds of the individual face elements of the working face differ in magnitude, depending on whether the face element lies radially inward or radially outward, the chipping result also differs and this is detrimental to the quality. 
   The machines mentioned, which belong to the first system, serve, above all, to produce so-called oriented strand (OS) chips. The fibers of these chips are oriented along the lengthwise direction of the chip. The chip is extremely thin. It serves to produce boards of the same name, so-called oriented strand boards (OSB). These are regarded as being of high quality. They have great strength, so that they can be used as construction elements for the construction of prefabricated houses, for example. 
   The second system mentioned uses so-called knife ring chippers. These consist of a ring or collar that is made up of knives, whose cutting edges run, at least largely, parallel to the ring axis. The knife ring encloses a working chamber in which the chippings are introduced into a radially inner region through a filling shaft. A rotor spins the chippings radially outward against the inner face of the knife ring and thus against the cutting edges of the knives, where chipping takes place. 
   The intermediate product that is fed to the chipper consists of appreciably smaller particles, namely, chippings, that were produced beforehand in a chopping process. In quite generalized terms, they have, at least to an approximation, the size of a match box. 
   The chips that can be produced by a knife ring chipper differ quite fundamentally from the OS chips produced by the first-mentioned category of machines, which operate according to the first-mentioned system. They are essentially pin-shaped and are reminiscent of thin matches. These chips can be processed only into chipboards or particle boards. However, particle boards are of only limited strength and, in particular, they have no special flexural strength. Thus, they cannot be used as construction elements, but instead find application in the furniture industry. 
   The advantages and drawbacks of machines of the first-mentioned system—direct chippers for producing OS chips—and of the second-mentioned system with the preceding stage for producing chippings and the final result of chips for particle boards can be summarized as follows: 
   Direct chippers require, in general, fresh wood, that is, tree trunks of, for example, one meter. Although they are capable of producing high-quality OS chips, they have comparatively large dimensions on account of the large dimensions of the intermediate product. Accordingly, it is extremely expensive to purchase them. The investment costs lie between one and three million DM. Accordingly, they also have relatively little flexibility in use. 
   Chippers, by contrast, are smaller, more flexible, and more advantageous in cost to purchase. However, they are not capable of producing OSB chips, but only the lower-quality matchlike chips for particle boards. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to present a method or a device that allows so-called fresh wood as well as recycled wood to be used as intermediate product, has appreciably less construction volume than the known direct chippers, therefore requires lower investment costs, and is flexible in use and that is also fundamentally suitable for producing OSB chips. 
   This object is solved by the independent claims. 
   The inventor has thus freed himself of a widely held prejudice. He has resorted to the basic features of the knife ring chipper, but has fundamentally changed the conditions surrounding it. This relates, in particular, to the choice of the dimensions of the intermediate product. The latter has a greater first dimension than the dimension perpendicular to it, so that the intermediate product could be referred to as rod-shaped. 
   With a method in accordance with the invention and a corresponding device, it is now possible to use highly differing intermediate products, namely, both fresh wood of excellent quality and fresh wood of less good quality, such as dwarf timber and branches, as well as recycled wood. Coming into consideration here as recycled wood is, for example, wood packaging, which is very common. 
   The method and device in accordance with the invention can—as mentioned—produce high-quality OSB chips, but, at the same time, also chips of lesser quality. If different categories of chips are produced, these can be classified by a subsequent classification step. 

   
     DESCRIPTION OF THE FIGURES 
     The invention is explained in more detail on the basis of the drawing. Represented therein individually are the following: 
       FIG. 1  shows a chipper in a front view, that is, in a view on that side on which the casing cover together with the spout for the intermediate product is situated. 
       FIG. 2  shows, on an enlarged scale, an axial section of the chipper in accordance with  FIG. 1 . 
       FIG. 3  shows, in an enlarged representation, a section taken from  FIG. 2 , namely, a knife set. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   As seen from  FIGS. 1 and 2  individually, the chipper consists of a rotor, which is driven by a shaft  2 . The rotor  1  contains a collar of blades  3 , which are parallel to the axis. A knife box with knives  4 , which are likewise arranged parallel to the axis, surrounds the rotor  1 . Rotor  1  and the knife box are, in turn, arranged in a casing  5  and jointly enclosed by it. Casing  5  has a inlet  6  for the chippings that are to be fed in as well as a discharge for the finished chips. 
     FIG. 2  illustrates a rod-shaped intermediate product  20  at two sites. In the present case, this is delivered as a block in the shape of a regular rectangle. Instead, however, this intermediate product could be of a different shape—for example, it could have irregular peripheral surfaces. It is essential only that this intermediate product  20  be more or less rod-shaped; that is, it has a lengthwise dimension that is greater than the crosswise dimensions in planes running perpendicular to it. 
   The intermediate product  20  is fed into the shaft-shaped inlet  6 —see arrow. It then arrives at the inner chamber that is enclosed by the rotor  1 . In doing so, the intermediate product  20  comes to lie—either automatically or by means of a corresponding orienting device—in such a way that it is oriented mainly along the lengthwise axis of the rotor shaft  2  and thus more or less parallel to the knives  4 . The intermediate product is of substantial size and particularly of substantial length in comparison with the chippings that are fed to the knife ring chippers that have been commonly used up to now. The intermediate product may be characterized by a length of 80 to 150 mm. The intermediate product may be characterized by a width with a magnitude of at least 20 mm. 
   In  FIG. 3 , two knife sets are represented in a section perpendicular to the axis. These two knife sets are each a component of the knife ring of the machine. 
   Each knife set is constructed as follows: A supporting bedplate  10  bears a cutting knife  11 , which is attached to the supporting bedplate  10  by means of a clamping plate  12  and a screw  13 . 
   The operating parameters, such as the shape of the knife and the knife angle. may be chosen in such a way that they afford a chip thickness of 0.2 to 0.6 mm. preferably 0.2 to 0.4 mm. 
   Each supporting bedplate  10  has a wear surface  10 . 1 . It is crucial that these wear surfaces  10 . 1 , which face the machine axis, are nearly flat and thus not concentric, as in the prior art. 
   In the case of the figure here, the wear surface  10 . 1  is made up of a wear plate  10 . 2 , which, in turn, is attached to the remaining supporting bed plate  10 . The wear surface  10 . 1  is made up of a wear layer that is produced by application of a wear layer, preferably by build-up welding or spraying and subsequent smooth grinding. 
   In the embodiment in accordance with  FIG. 3 , a knife with M teeth,  14 , is provided, which is attached to the side of the supporting bed plate  10  lying opposite to the cutting knife  11  and which works together with the cutting knife of the neighboring knife set. The embodiment is an embodiment without knives with M teeth. 
   A classification step may follow the chipping in order to determine whether the chips are to be classified according to criteria of their shape or their dimensions or their weight.