Patent Publication Number: US-6986425-B2

Title: Apparatus and method to separate elements or materials of different sizes

Description:
FIELD OF THE INVENTION 
   The invention refers to an apparatus and a method to separate elements or materials of different sizes, such as for example wood chips or shavings, commonly known as strands or wafers, used in the production of OSB panels (Oriented Structural Boards or Oriented Strands Boards), pieces of paper or plastic material. In particular, the apparatus and method allow to screen or sort a mass of materials of different sizes, in order to separate the smaller pieces (the so-called fine or super-fine) from the bigger ones, without putting too much stress on the latter which, as they are so fragile, could easily be damaged or break. 
   BACKGROUND OF THE INVENTION 
   In order to screen elements or materials of different sizes, especially those of vegetable origin, such as wood or similar, it is known that the device described in the international patent application WO-A-98/40173, belonging to the same Applicant. This known device comprises a plurality of rolls, all rotating in the same direction, facing each other so that the cusps of each roll are inserted into the corresponding V-shaped grooves of the adjacent rolls, thus defining a zig-zag discharge profile. The rolls are also distanced laterally to define adjustable gaps between them, through which only those pieces which are equal to or smaller than the gaps can pass. Moreover, the connection surfaces between cusps and grooves are worked with protuberances, protrusions, hollows or faceted parts which allow to separate the pieces to be screened better. 
   Although this known device is very efficient for separating and sub-dividing relatively small pieces, that is to say, of a few millimetres, it is not suitable for separating materials which have large surfaces in proportion to their volume, as is the case with strands or wafers, which although they are relatively thin (about from 0.4 to 1.0 mm), have relatively large other dimensions: a length varying from about 60 mm to about 180 mm and a width varying from about 20 mm to about 80 mm. In fact, they tend to fall prevalently in horizontal layers, incorporating between them both smaller pieces (also called as micro-strands) and also very small pieces, such as slivers (called fine pieces) and also tiny pieces, such as saw dust (called super-fine pieces). 
   The state of the art also comprises other types of screening devices, such as those with a rotary drum, plane, oscillating or vibrating screens. 
   Rotary drum screens are not only very bulky, but also they have the problem of low specific efficiency since: only the lower surface is involved in the screening; the holes of the sieves are easily blocked; many long pieces, having however limited width, are erroneously discarded together with the fine pieces because they pass through the holes lying coaxial therewith. Rotary drum screens, moreover, do not allow to modify, simply and quickly, the value of the granulometry to be obtained, since this operation requires the sieves on the periphery of the drum to be completely replaced, and this takes a notoriously long time. The long time during which the strands remain inside the drum and their continuous mixing also generates further fine pieces. 
   Plane screens, whether oscillating or vibrating, are not able to separate the different layers of strands, which lie one on top of another in a sandwich, and which incorporate the fine materials inside them or retain them above. 
   DE-C-589557 discloses a screening device wherein a plurality of discs, having circular or elliptical form, are mounted on shafts disposed parallel therebetween and axially staggered, in order to define substantially constant discharge apertures between the opposed discs of two adjacent shafts. 
   U.S. Pat. No. 6,149,018 discloses an apparatus for sorting recycled material, which comprises a plurality of co-rotating spaced parallel shafts, each of which has a longitudinal series of screen discs. On each shaft the axial distance between the discs is rather high. Moreover each disc is shaped in order to have a constant discharge aperture with respect to the opposed disc during rotation of the shafts. 
   The present Applicant has devised the method and embodied the apparatus according to the invention to overcome the shortcomings of the state of the art, and to obtain further advantages which will be described hereafter. 
   SUMMARY OF THE INVENTION 
   The invention is set forth and characterized in the main claims, while the dependent claims describe other characteristics of the invention. 
   The purpose of the invention is to perfect a method and achieve an apparatus to separate and sort elements or materials of different sizes, particularly but not exclusively, pieces of wood such as strands or wafers, that is to say, substantially flat, so as to ensure on the one hand that the small size materials, the so-called fine or super-fine pieces, are separated from those of larger or regular size, before the whole mass to be sorted leaves the screening bed, and on the other hand that the larger size materials are not discarded together with the fine ones. 
   In accordance with this purpose, the apparatus according to the invention comprises a separation chamber into which the mass of material to be separated is able to be inserted, a plurality of riddling rolls mounted inside said separation chamber, rotating on axes of rotation parallel to each other and lying substantially on a same plane. According to one characteristic of the invention, each riddling roll comprises a plurality of riddling elements, each of which is substantially square in shape when shown on a plane perpendicular to the rotational axis of the corresponding riddling roll, so as to have four substantially rectilinear sides and to form four cusps at 90° with respect to each other, in correspondence with the respective tips. The riddling elements, adjacent to and suitably spaced from each other, define a plurality of grooves. Each riddling roll, moreover, is staggered axially with respect to the adjacent rolls, so that the cusps of the riddling elements of each roll are constantly inserted, more or less deeply, into the corresponding grooves of the adjacent riddling roll, so as to define discharge apertures with an alternated profile of peacks and valleys. 
   The lateral surfaces of the riddling elements can be coverging from the center to the periphery, whereby the resulting grooves have a zig-zag profile, or parallel therebetween, whereby the resulting grooves have a profile with right angles. In the first case, the gap between the riddling elements, that is, the distance between the lateral surfaces of the riddling elements of two adjacent rolls, has variable sizes between about 0.5 and 20 mm according to the interaxis between the riddling rolls, while in the second case the gap between the riddling elements has variable sizes between 1 and 10 mm. In any case, the gap can be selectively varied both within the plane of the riddling rolls, progressively increasing or decreasing, and for groups of rolls. 
   The cusps can be pointed with a sharp edge or can have the tips and crests joined or bevelled. 
   The riddling elements of each roll are mounted on a central shaft so that the riddling elements of one roll are staggered angularly with respect to the riddling elements of the adjacent roll. 
   The lateral surfaces can be advantageously provided with a plurality of irregular elements such as dips, hollows, protuberances, protrusions or faceted parts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other characteristics of the invention will be clear from the following description of a preferential form of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: 
       FIG. 1  is a plane view, partly sectioned, of an apparatus according to the invention; 
       FIG. 2  is a side view, partly sectioned, of the apparatus shown in  FIG. 1 ; 
       FIG. 3  is a side view, partly sectioned, of a first variant of the apparatus shown in  FIG. 1 ; 
       FIG. 4  is a cross section from A to A of  FIG. 1 ; 
       FIG. 5  is an enlarged detail of  FIG. 4 ; 
       FIG. 6  is an enlarged detail of  FIG. 1 ; 
       FIG. 6   a  is a plane view of an enlarged detail of a second variant of the apparatus shown in  FIG. 1 ; 
       FIG. 7  is an enlarged detail of  FIG. 2 ; 
       FIG. 7   a  is an enlarged detail of the first variant of  FIG. 3 ; 
       FIG. 8  is an enlarged detail of  FIG. 6  which shows a first form of embodiment of the irregular elements  27 ; 
       FIG. 9  is a side view of the detail in  FIG. 8 ; 
       FIG. 10  is an enlarged detail of  FIG. 6  which shows a second form of embodiment of the irregular elements  27 ; 
       FIG. 11  is a side view of the detail in  FIG. 10 ; 
       FIG. 12  is an enlarged detail of  FIG. 6  which shows a third form of embodiment of the irregular elements  27 ; 
       FIG. 13  is a side view of the detail in  FIG. 12 ; 
       FIG. 14  is a side view of the apparatus shown in  FIG. 1  in combination with a first separation apparatus of a conventional type; 
       FIG. 15  is a side view of the apparatus shown in  FIG. 1  in combination with a second separation apparatus of a conventional type. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
   With reference to  FIGS. 1 and 2 , an apparatus  10  to separate elements or materials  11  of different sizes according to the invention comprises a metal bearing structure  12 , substantially parallelepiped in shape, able to define a separation chamber  13 , on one side of which, through a hopper-type mouth  15  a loose mass of material  11  is able to be introduced. This mass can advantageously consist of pieces of woody material, in the form of sheets or strands, mixed with micro-strands, and other fine and super-fine materials. The chamber  13  is closed at the top by a metal covering sheet  14  and is open at the bottom. 
   Inside the chamber  13  a plurality of riddling rolls  16  is arranged, mounted rotating on lateral walls  18  and  19  of the structure  12 . The rolls  16  have the axes of rotation parallel to each other and lying substantially on a same plane X, so as to form a so-called riddling bed. 
   Each roll  16  ( FIGS. 6 and 7 ) comprises a substantially cylindrical central shaft  17  on which a plurality of riddling elements  20 , adjacent to each other, is mounted and keyed; advantageously, they are made of metal, rubber or synthetic material. 
   According to a characteristic feature of the invention, each element  20  is substantially square in shape, so as to have four rectilinear sides and to form cusps  22 , disposed at 90° with respect to each other, in correspondence with the respective tips of the square. 
   The lateral surfaces  21   a ,  21   b  or each riddling element can be either converging from the center towards the periphery as shown in  FIGS. 1 ,  4 ,  5  and  6 , or parallel therebetween, as shown in  FIG. 6   a.    
   The cusps  22  can either have a sharp edge, as shown in the drawings, or, according to a variant shown by a line of dashes in  FIG. 7 , at least partly joined or rounded. 
   The transverse size D of each element  20  is advantageously between 130 and 250 mm. 
   The angle of inclination α, formed by the lateral surfaces  21   a  and  21   b , is comprised between 25° and 50°, advantageously between 35° and 40°. 
   The elements  20 , adjacent to each other and possibly with spacer rings  23  between them, define a plurality of grooves  24 , alternating with the cusps  22 . The grooves  24  have a substantially V-shape when the lateral surfaces  21   a ,  21   b  are converging from the center towards the periphery, while have a substantially U-shape when the lateral surfaces  21   a ,  21   b  are parallel therebetween. The riddling elements  20  with lateral surfaces  21   a  and  21   b  parallel therebetween have a width comprised between about 2 and 6 mm. 
   Each riddling roll  16  is mounted so that the cusps  22  of the elements  20  of each roll  16  is constantly inserted, more or less deeply, into the corresponding grooves  24  of the adjacent roll  16 , so as to define discharge apertures  25  having an alternated profile, i.e. a zig-zag profile ( FIG. 6 ) or a right-angles profile ( FIG. 6   a ). The discharge apertures  25 , in particular, comprise gap  26  between the facing lateral surfaces  21   a ,  21   b.    
   The minimum sizes of the discharge apertures  25  and the gaps  26  are variable according to the granulometry of the material which is to be discarded, that is, passed through the rolls  16 . 
   The apparatus  10  according to the invention also allows to vary the discharge apertures  25  and the gaps  26 , and to have them of different values even within the context of the same riddling bed, in a very simple manner, as will be explained hereafter. The value of the gap  26  is advantageously variable between 0.5 and 20 mm in the case shown in  FIG. 6  and between 1 and 10 mm in the case shown in  FIG. 6   a.    
   Instead of being smooth, the lateral surfaces  21   a  and  21   b  of each element  20  are advantageously provided with a plurality of irregular elements  27 , consisting of dips, hollows, protuberances, protrusions or faceted parts, as shown as an example in  FIGS. from 8 to 13 . 
   The rolls  16  are also mounted on the shafts  17  in such a manner that the elements  20  of each roll  16  are angularly staggered with respect to the elements  20  of the adjacent roll  16  ( FIG. 7 ), so that the cusps  22  of the elements  20  of each roll  16  are in correspondence with one of the sides of the square of the facing element  20 . 
   According to a variant shown in  FIGS. 3 and 7   a , the elements  20  of two adjacent rolls  16  are not angularly staggered, as mentioned above, so that the cusps  22  of the elements  20  of each roll  16  are always in correspondence with the cusps of the adjacent rolls  16 . 
   The ends of the shafts  17  ( FIGS. 2 ,  4  and  5 ) are mounted rotating on bearings or bushings  28 , arranged sliding in guide slits  29  of the lateral walls  18  and  19 . 
   At one end of each shaft  17 , outside the chamber  13 , a toothed wheel  30  is keyed. In particular, the toothed wheels  30  are arranged, alternately staggered, either on the side of the lateral wall  18  or on that of the lateral wall  19 , so that two adjacent rolls  16  have the respective toothed wheels  30  arranged on opposite sides with respect to the structure  12 . 
   Each row of toothed wheels  30  is constantly engaged with a distribution chain  31 , made to rotate by a corresponding pinion  32  of a single electric motor  33  with the relative reduction unit. 
   The distribution chains  31  are both able to rotate in the same direction (anti-clockwise in  FIG. 2 ), to make all the rolls  16  rotate in the same direction too. 
   Two pairs of elastic elements  34  (of which only one is shown in the drawings) are arranged inside the distribution chains  31  to keep them tense. 
   The distance between the rolls  16 , and consequently the entity of the gaps  26 , is defined by a plurality of spacer elements  35  mounted in removable manner in the slits  29  of the lateral walls  18  and  19 . In order to vary a determined gap  26  between two adjacent rolls  16 , it is sufficient to change the spacer elements  35  between said two rolls  16 , without having to dismantle the same rolls  16  from the structure  12 . 
   The apparatus  10  is able to be arranged with the mouth  15  in correspondence with one end of a conveyor belt  36 , able to unload the material  11  to be sorted into the chamber  13 . 
   Below the bed of rolls  16  one or more deflector elements  38  are arranged; they can be positioned angularly and are able to divide the bed into two or more selection zones. Thus, for example, a first deflector element  38  can be arranged a short distance from the mouth  15 , to define a first selection zone A with the rolls  16  arranged relatively close together, to form gaps  26  of a few millimetres, advantageously from 0.5 to 5 mm, through which the so-called fine materials can pass. A second element  38  can be arranged in proximity with the last roll  16  (the one farthest to the left in  FIG. 2 ), to define a second selection zone B with the rolls  16  arranged farther from each other, to form gaps  26  of several millimetres, advantageously from 5 to 10–20 mm, through which the so-called micro-strands can pass. 
   Between the last roll  16  of the riddling bed and the end of the chamber  13  opposite the mouth  15 , a third selection zone C is defined, from which only the accepted pieces exit, that is to say, the pieces which have not passed through the discharge apertures  25 , as for example the regular strands. 
   The metal structure  12  ( FIG. 14 ) can also be inclined up to about 40° with respect to the horizontal plane, in order to orientate upwards the plane X on which the axes of rotation of the rolls  16  lie, and to define an upwards travel of the material  11  introduced into the chamber  13 . 
   The method to separate materials  11  of different sizes, by means of the apparatus  10  as described heretofore, comprises the following steps: the mass of materials  11  is introduced into the separation chamber  13 , advantageously in correspondence with the first of the riddling rolls  16  (the one farthest to the right in  FIG. 2 ); the material  11  introduced is made to advance towards the opposite side of the chamber  13 , by means of simultaneous rotation in the same direction of the plurality of rolls  16 , simultaneously causing the material  11  to jolt, in continuous and advantageously synchronous manner, in a direction orthogonal to the plane X on which the axes of rotation of the rolls  16  lie; the materials  11  discarded, that is, those with a size equal to or less than those defined by the discharge apertures  25 , are removed from said discharge apertures  25 , formed between the riddling elements  20 ; the materials of a greater size, that is, those separated from the others and accepted, are removed from a discharge zone C, located downstream of the bed of rolls  16 . 
   According to one characteristic of the invention, the square shape of the riddling elements  20 , combined with the constant mutual penetration of the cusps  22  into the grooves  24 , and with the continuous rotation of the same elements  20 , causes the jolting movement of the pieces which make up the material  11  to the point that they are detached from each other, even if they have a relatively large plane surface in proportion to their thickness, as in the case of strands. This makes the apparatus  10  extremely efficacious. 
   The apparatus  10  according to the invention is also able to be advantageously coupled with a conventional-type separation apparatus  40 , for example of the type described in the afore-mentioned international patent application WO-A-98/40173. 
   The combination of the two apparatuses  10  and  40 , with the first arranged above the second, allows to select the material  11  according to at least four granulometries: the whole of the material which passes between the gaps  26  of the rolls  16  of the apparatus  10  above, that is to say, the fine, super-fine and micro-strands, exiting from the zones A and B, goes to feed the apparatus  40  below, which provides to sub-divide them (super-fine in a zone F, fine in a zone G and micro-strands in a zone H). The regular strands continue to exit from the apparatus  10 , through the zone C. 
   According to a variant, shown in  FIG. 15 , the apparatus  10  can also advantageously be coupled with an underlying mechanical transporter  41 , able to feed the material collected towards a conventional-type screen  42 , either oscillating or vibrating. 
   It is clear that modifications or additions of parts or steps can be made to the apparatus  10  and the method to separate elements or materials  11  of different sizes, as described heretofore, without departing from the spirit and scope of the invention. 
   It is also clear that, although the invention has been described with reference to specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms, all of which shall come within the field and scope of the invention.