The present invention relates to an apparatus for processing by way of, e.g., screening or scattering, particulate matter such as flakes or chips, the appa¬ ratus comprising at least one roll set formed by two or more parallel rotating rolls, onto which set of rolls the material to be processed is fed, the rolls of the set being at least partially hollow.

Installations in the mechanical woodworking industry, such as saw mills and manufacturing processes of wood-based boards, have need for equipment capable of sorting wood particles, particularly those of an elongated shape, by their length. Such particulate matter includes, e.g., different waste of saw mills, chipped peeling waste of veneer industry, as well as the relatively large Oriented Strand Board (OSB) and waferboard flakes, chiefly employed in the North-American particleboard industry.

As to the properties of OSB and waferboard products, e.g., in regard to their flexural strength, it is advantageous to screen very short flakes coming from the flaking machine entirely away from the process. Today, length sorting takes place with the help of screening apparatuses including, La., screen beds, drum screens and disc screens. These screens types of different designs, however, are hampered either by a low capacity or inferior selectivity of screening. Moreover, some types of screens tend to break the flakes which obviously is undesirable particularly in OSB manufacture.

Fl Pat. No. 98,276 discloses an apparatus for length screening of elongated particles such as wood chips, the apparatus comprising at least two substan- tially horizontally mounted, mutually substantially parallel-oriented rolls. According to this publication, the screening operation is carried out using a roll screen of parallel rolls, wherein the rolls are so-called cage bar rolls. The cage bar rolls are comprised of a number of cage bars aligned parallel to the longitudinal axis of the roll and are substantially equidistantly spaced from each other along the periphery of the roll, the bar ends being attached to disc- or ring-type flanges aligned perpendicular to the longitudinal axis of the roll. The flanges themselves are mounted on the rotary shaft of the roll. Typically, the roll set comprises 8 to 12 parallel-mounted cage bar rolls. According to this Fl Pat. No. 98,276, the construction is characterized in that the number of longitudinally aligned cage bars in the intake-end rolls of the roll set is larger than in the exit-end rolls of the set. Hence, the rotary rolls elevate elongated particles at the intake end of the roll set thus preventing them from falling excessively early through the interroll gaps of the roll set. However, the roll set according to cited patent publication is not particularly suited for screening particles, especially those of the finest size, away from the bulk of particles. To this end, the interbar gaps of cage bar rolls are excessively large.

Analogously, also patent publication WO 02/062493 discloses one type of disc screen. Herein, the rolls are disc rolls or the like members adapted to partially intermesh with each other, lntermeshing may also be accomplished by way of contouring the roll surfaces with different protuberances and recesses. This apparatus is aimed for sorting particles of different sizes apart from each other, with a particular object to screen apart the finest particles. In practice, this roller-type disc screen does not offer sufficient precision of screening.

A similar type of screening and/or scattering apparatus is also disclosed in EP patent publication 1 ,010,508 teaching sorting by means of a roll screen. Also according to this publication, the roll surfaces are contoured with protuberances and recesses. The roll surfaces, however, are not adapted to intermesh with each other, but rather, are spaced apart from each other by a narrow gap. Yet, this apparatus suffers from the same drawbacks as that disclosed in patent publication WO 02/062493. It is an object of the present invention to provide an entirely novel type of apparatus for processing, particularly by screening, wood particles, such as flakes, chips and the like. The apparatus according to the invention is charac- terized in that the periphery of the rolls is substantially along the entire axial length and substantially over the entire circumference of the roll shell provided with openings allowing a desired size fraction of the bulk material being processed to fall through the roll peripheries.

A preferred embodiment of the apparatus according to the invention is char¬ acterized in that the periphery of the rolls is substantially similar to a wire- mesh screen.

Another preferred embodiment of the invention is characterized in that the rolls are mounted in an inclined position having their one end adapted at a lower level than the other end and that the roll ends serving as the roll shell support members have at least one opening made thereto with a size sub¬ stantially larger than the size of particles in the bulk material being processed thus facilitating continuous run-time emptying of the roll interior space.

A still another preferred embodiment of the invention is characterized in that the adjacent rolls are inclined in different directions relative to each other such that every second roll is mutually inclined in the same direction at an inclination angle of about 0.1° - 5°.

The benefits of the invention include a extremely precise screening with a screening throughput capacity greater than that of conventional screening apparatuses. Furthermore, screening takes place in a "gentle" fashion without causing disintegration of the particles.

In the following, the invention is described in more detail with reference to the appended drawings in which FIG. 1 shows an axonometric view of a preferred embodiment of apparatus according to the invention implemented using one set of rolls;

FIG. 2 shows an axonometric view of a preferred embodiment of apparatus according to the invention implemented using two sets of rolls;

FIG. 3 shows a side view of the roll to be used in the apparatus according to the invention;

FIG. 4 shows a side view of the roll perpendicular to the roll axis;

FIG. 5 shows an end view of the roll; and

FIG. 6 shows a dual set of rolls in a preferred embodiment of the invention.

The apparatus according to the invention incorporates a roll set comprised of parallel-aligned, hollow, rotatable rolls 1 , whose periphery is substantially along the entire axial length of the roll shell and substantially over the entire circumference of the roll shell provided with openings of a desired size and shape. Screening is preferably carried out using a so-called wire mesh screen roll shown in more detail in FIGS. 3 and 4. Advantageously, the rolls of the set are arranged to rotate mutually in the same direction, whereby the rolls during screening also transport the material forward on the roll set toward the exit end of the screen.

This kind of wire-mesh screen rolls are known as being used in other applica¬ tions. E.g., from patent application Fl 93,807 is known a wire-mesh screen roll intended for use in the flow control of chip travel and scattering, partic- ularly at the exit of the chip flow from a scattering chamber, prior to the screening and scattering of the chips into a particle mat to be pressed into a chipboard. Yet, these wire-mesh rolls have not been used in the art as a set of screen rolls for sorting or scattering particles.

Advantageously, 8 to 12 wire-mesh screen rolls 1 are assembled to operate in parallel. The roll axes are aligned substantially parallel and the rolls are mutually displaced so that the interroll gaps 2 therebetween are adjusted to an absolute minimum. The mesh opening size of the screen rolls is selected such that particles of a given size smaller than a limit pass through the mesh openings thus falling onto a conveyor below or other apparatus performing further processing. The remaining fraction of the particle flow, known as accepts, is transported over the entire set of rolls thus exiting from the opposite end of the roll in regard to the intake end of the roll set.

In FIG. 2 is shown an alternative embodiment implemented using two super¬ imposed, substantially identical roll sets. This layout achieves improved screening selectivity over that of the first embodiment. In a still further alternative layout, the particle flow having first passed over the upper set of rolls is routed onto the lower set of rolls for a second screening passage.

For a selective screening result, it is essential to locate adjacent rolls 1 maximally close to each other so that the interroll gap (nip) 2 is minimized. This arrangement avoids the risk of allowing elongated particles that are fundamental particularly in the manufacture of OSB products to be lost into the fines fraction being removed. In practice, the interroll gap can be set as narrow as below one millimeter. On the other hand, already the rotary motion of the rolls prevents very long particles from falling into the interroll nip 2.

FIGS. 3-5 illustrate one feasible embodiment of a wire-mesh screen roll set. The roll itself is comprised of a shaft 4 with end flanges 5 mounted thereon and, if necessary, of intermediate supportive flanges (not shown) that are similar to the end flanges and are adapted therebetween along the shaft. The wire-mesh-like shell 3 of the roll is attached to the roll ends 5 and possible supportive flanges. The size of mesh openings is selected according to the maximum size of particles in the fraction to be removed from the particle flow. The present type of screen is particularly effective in the screening of elongated chips inasmuch as long pins can in practice pass through the mesh only in a perpendicular position while smaller particles of less desired size pass through the rolls.

The ends of roll 1 are provided with openings 6, e.g., three openings at each end flange (and the internal supportive flanges). The function of the openings is to facilitate the outflow of material fallen into the interior space of the roll away therefrom. This discharging function is further enhanced by tilting the rolls such that one end of the roll is adapted to rotate at a lower level than the other end. Advantageously, the rolls are mutually inclined in different direc¬ tions such that, e.g., every second of two adjacent rolls is mutually inclined in the same direction or that, e.g., every two adjacent rolls are mutually inclined in the same direction and, respectively, the two rolls in the succession are inclined in a different direction, and so on. Thus, the material fallen into the interior space of the rolls during their rotation (i.e., the material portion not naturally escaping out from the roll via the openings thereof) anyhow gradually becomes transported in the direction of roll inclination eventually leaving the roll interior space via the roll end.

In FIG. 6 is shown an embodiment implemented using two superimposed roll sets, both of them being inclined downward in the travel direction of the ma¬ terial flow, whereby the escape of elongated chips through the interroll gaps can be reduced in an improved fashion inasmuch as the interroll gaps in this arrangement remain "hidden"". The downward inclination of the roll set may be adjusted to, e.g., about 30 - 60°, advantageously to about 45°. Obviously, a similar downward-inclined assembly can be used also irrespective whether the number of roll sets is only one or there are two or more superimposed roll sets in the assembly.

It is further possible that the capacity of the apparatus is increased by way of mounting the roll set or the superimposed roll sets into an upward-inclined position in the travel direction of the material flow, whereby the screening throughput of the roll set is further improved. The upward inclination of the roll set or superimposed assembly of roll sets is adjusted to about 0 - 45°, advantageously to about 10°.

To a person skilled in the art it is obvious that the invention is not limited by the above-described exemplary embodiment, but rather may be varied within the inventive spirit and scope of the appended claims. Accordingly, the roll set comprising wire-mesh screen rolls can also be used for screening and scattering of chips, e.g., in the manufacture of chipboard products. If size sorting of chips is necessary prior to scattering, the successive wire-mesh screen rolls can be provided with differently sized or shaped openings. Furthermore, the rotational direction of the rolls may be varied, whereby the rolls can be arranged to rotate in different directions as required. Obviously, also the speed of rotation of the rolls can be freely selected. It is further evident that the number of rolls in a set can be varied as desired. An essen¬ tial feature herein is that the number of rolls in a set is at least two, advanta¬ geously, however, 8 to 12. The diagrams illustrate the rolls mutually aligned substantially in the same plane. Nevertheless, the rolls can be arranged alternatively, e.g., by having some of the rolls mounted above the others or in some other fashion.