WO2006000625A1 - Apparatus for processing by, e.g., screening or scattering, particulate matter such as flakes and chips - Google Patents

Abstract

An apparatus is disclosed for processing by way of, e.g., screening or scattering, particulate matter such as flakes or chips, the apparatus comprising at least one roll set formed by two or more parallel rotating screen rolls (1), onto which set of screen rolls the material to be processed is fed, the screen rolls of the set having a hollow core. The goal of the invention is attained by making the outer periphery of the screen rolls (1) mesh-like and by adjusting the speed of rotation of the rolls such that the flow of flakes fed onto the rolls is thrown away from the roll surfaces in a fashion that causes the separation of the flakes from each other.

Description

Apparatus for processing by, e.g., screening or scattering, particulate matter such as flakes and chips

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 screen rolls, onto which set of screen rolls the material to be processed is fed, the screen rolls of the set having a hollow core.

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 wood 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. The sorting of moist OSB flakes is a demanding process inasmuch as the fines fraction to be screened away is concealed amongst the large flakes and, wetted by the moisture, even adheres to the large flakes of good quality. While conventional mechanical or roller screens have been designed to shatter and agitate the flow of flakes, this action is not by far sufficient to separate the finer chips from the large flakes.

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 outer periphery of the screen rolls is made mesh-like and that the speed of rotation of the screen rolls is adjusted such that the flow of flakes fed onto the rolls is thrown away from the roll surfaces in a fashion that causes the separation of the flakes from each other.

A preferred embodiment of the apparatus according to the invention is char¬ acterized in that, with the diameter of the rolls (1 ) being approx. 300 mm, the rolls are operated at a speed of rotation of 50-200 r/min, advantageously of 80-170 r/min.

Another preferred embodiment of the invention is characterized in that the number of roll sets is two in a substantially superimposed position, whereby the upper roll set is mounted into an upward-inclined position in the travel direction of the material flow, while the lower roll set is mounted into a downward-inclined position in the travel direction of the material flow.

A still another preferred embodiment of the invention is characterized in that the upward-ramping inclination angle of the upper roll set relative to the horizontal plane is 0.5° - 15°, most advantageously 5° - 10°, while the downward-ramping inclination angle of the lower roll set relative to the horizontal plane is 0.5° - 25°, most advantageously 5° - 15°.

Accordingly, the goal of the invention is attained by virtue of using large- diameter, highly frictional rolls (mesh-shell rolls) rotated at a high speed to throw the flakes into free air, whereby the thus separated large flakes are readily separated from fines resting thereon or adhering to the surface thereof.

The benefits of the invention include 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 a preferred embodiment of apparatus according to the invention implemented using two superimposed roll sets;

F)G. 2 shows a side elevation view of a mesh-shell roll used in the roll set of an apparatus according to the invention;

FIG. 3 shows an axonometric view of a mesh-shell roll used in a roll set according to the invention; and

FIG. 4 shows an end view of the roll illustrated in the other diagrams.

Referring to FIG. 1 , there is shown an apparatus according to the invention incorporating an upper roll set A and a lower roll set B. Above either one of the roll sets is drawn an arrow indicating the flow travel direction of the mate¬ rial being treated. The upper roll set A is inclined upward-ramping in regard to the flow travel direction of the flaked material fed thereon, while the lower roll set B is respectively inclined downward-ramping in regard to the flake mate¬ rial flow travel direction. The inclination angle of the upper roll set relative to the horizontal plane is 0.5° - 15°, most advantageously 5° - 10°. Respective¬ ly, the inclination angle of the lower roll set relative to the horizontal plane is 0.5° - 25°, most advantageously 5° - 15°.

Both the upper and the lower roll sets are comprised of parallel-aligned, hollow, rotatable mesh-shell rolls 1 having a structure shown in greater detail in FIGS. 2-4. Advantageously, the rolls of both set are arranged to rotate mutually in the same direction, whereby the rolls during screening also trans¬ port the material forward on the roll set toward the exit end of the screen.

As mentioned earlier in the text, screening of moist OSB flakes is a demand¬ ing process inasmuch as the fines fraction to be screened away is concealed amongst the large flakes and, wetted by the moisture, even adheres to the large flakes of good quality. Mere shattering or agitation of the flake flow, such as takes place in conventional mechanical or roller screen apparatuses, is generally insufficient to the fines from the large flakes. In contrast, the invention utilizes large-diameter mesh-shell rolls 1 rotated at a high speed that frictionally throw the flakes into free air thus aiding the separation of flakes from each other. The flight path of the flakes to a given height above the rolls can be controlled by adjusting the rotational speed of the rolls. For rolls of, e.g., 300 mm diameter, a suitable speed of rotation is about 50- 200 r/min, advantageously 80-170 r/min.

Accordingly, the upper roll set A is inclined upward-ramping in the travel di¬ rection of the flakes, whereby the travel speed of flakes is retarded thereby enhancing the screening effect inasmuch as the flakes under the centrifugally flinging effect of the rolls 1 are thus thrown more upward and less forward. Thus, the flakes are subjected to a longer period of screening, as a result of which action less fines are transported along with the large flakes over the roll set.

The fraction falling from the upper roll set A through its mesh-shell rolls 1 accumulates onto a conveyor 7 placed thereunder that transports this fraction further to the entry end of the lower roll set B (to the left side as indicated by the arrow drawn above the conveyor in the diagram) for a second screening. In contrast to the function of the upper roll set A, the screening performed by the lower roll set B is advantageously set to admit as accurately as possible the passage of flakes of the accept size while simultaneously preventing the passage of all particles of larger size than accepts through the interroll nips 2. Inasmuch as due to the normal manufacturing tolerances of the rolls, an interroll gap of at least a millimeter or so must be left between the rolls and the thickness of the flakes of the same order, it is possible that a small por¬ tion of good-quality large flakes escape through the interroll gaps 2 with the provision that the inclination angle of the lower roll set is adjusted upward- ramping or horizontal. However, having the lower roll set adjusted to a downward-ramping inclination angle, flakes admitted during screening through the gap 2 fall the more readily onto the next roll the greater the downward-ramping inclination angle of the roll set. The ramping angle of the roll set is determined by the diameter of the rolls and the desired interroll gap. E.g., a roll diameter of 300 mm in combination with a maximum interroll gap of 3 mm results in a theoretical minimum downward-ramping inclination angle of about 8° for the roll set. Having the roll set adjusted to this inclination prevents a downward-falling flake from "seeing" the interroll gap and, instead, forces the flake to land onto the next roll of the set.

FIGS. 2-4 show a feasible mesh-shell roll construction. Herein the roll comprises a shaft 4 having end flanges 5 mounted thereon and, when necessary, also intermediate supportive flanges (not shown) similar to the roll end flanges interspacedly mounted therebetween. To the end flanges 5 and the optional intermediate supportive flanges is attached a mesh-like peripheral shell 3 of the roll. The size of mesh openings is selected according to the maximum size of particles in the fraction to be removed from the particle flow. This kind of screen is particularly effective in the sorting of long flakes inasmuch as the penetration of long flakes through the mesh-like roll periphery is possible practically only in a perpendicular position, while smaller particles of less desired smaller size pass freely through the rolls.

In the prior art, this kind of wire-mesh screen rolls are known as being used in other applications. 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, particularly 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 mesh-shell rolls have not been used in the art as a set of screen rolls for sorting or scattering particles.

In this exemplary embodiment, 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 directions laterally 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 lateral direction and, respectively, the next two rolls in succession are inclined in a different lateral 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 lateral inclination eventually leaving the roll interior space via the roll end.

On the other hand, it has been found that the rolls do not become plugged even if the openings of end flanges are omitted. The reason behind this is therein that, in the arrangement according to the invention, the OSB flakes hit first the convex upper periphery of the mesh-sheil roll, whereby the flakes either are impacted by the meshed surface thereby being flung up- and forward on the roll set or, having a sufficiently short length and/or thin cross section, pass through the mesh openings into the interior space of the roll. In the interior of the roll, the particle is subjected to an equivalent action: the particle either is projected tangentially along the inner periphery of the roll shell or coincides with a mesh opening, whereby it is ejected out of the roll interior via the meshed roll shell. These alternative situations, however, are different from each other in the apparatus according to the invention therein that when the flake meets the convex upper periphery of the mesh-shell roll, it impinges the roll shell in regard to ingress through the roll shell at an unfavorable angle that for a roll of, e.g., 300 mm diameter, varies in the range of about 0° - -40°. With the same flake and roll dimensions, the flake meets the concave inner periphery of the roll shell at a positive angle that varies in the range of about 0° - +40° thus favoring the egress of the flake out from the roll interior space. Another difference in these two ingress/egress processes of the flake through the mesh shell is related to the direction of the inertial (centrifugal) force. Namely, at the possible ingress of the flake through the roll shell, there is no inertial force prior to the instant the flake touches the surface of the roll shell. The force thus imposed and the resultant motion of the flake is directed outwardly from the roll shell, whereby the probability of the flake ingress into the roll interior is diminished. However, if a suitable situ¬ ation has allowed a flake to enter the roll interior, a new contact of the inner periphery of the roll shell with the flake imposes thereon an inertial force di¬ rected outwardly from roll interior. In both cases there is present an auxiliary force that promotes the egress of the flake from the roll interior space. Run¬ ning tests performed at full speed have shown that the roll interior spaces re¬ main almost void of flakes and all particles capable of entering the roll interior fall almost without any delay through the roll to the underside of the roll set. Accordingly, the application of the apparatus in screening aims to allow fines comprising reject-size flakes to pass through the mesh-shell rolls and to pass the accept-size flakes over the roll set to further processing. In turn, the reject fraction falling through the upper roll set is taken to the lower roll set for a second screening in order to obtain improved screening efficiency.

Advantageously, the number of mesh-shell rolls 1 in a set is 8 to 35, mounted in a plane. The rolls are aligned substantially parallel to each other with minimal interroll gaps 2. The size of mesh openings in the screen rolls is selected such that small reject particles below a given size pass through the mesh openings and thus fall onto an underlying conveyor 7 (adapted to operate under the upper roll set A) or, alternatively, onto some like apparatus performing further processing. The other portion of the particle flow, called the accepts, travels over the entire roll set and exits at the other end of the apparatus opposite to its entry end.

Although OSB flakes are long and wide, their thickness is generally substan¬ tially smaller than 1 mm. Hence, they tend to adhere to the surface of the rolls on which they are propelled forward and, with the provision that a sub- stantially large gap is offered between the rolls, the interroll gaps may allow the passage of a substantial portion of large flakes that in fact should be includeed in the reject portion of flakes intended to pass over the roll set. Hence, it is an object of the invention to prevent any passage of ftakes through the interroll gaps 2 of the rolls 1 , by virtue of, i.a., manufacturing and mounting the rolls sufficiently precisely to make the interroll gaps smaller than the minimum size of accept flakes, whereby the large flakes are passed from roll to roll without the risk of allowing the flakes from escaping through the interroll gaps.

To a person skilled in the art it is obvious that the invention is not limited by the above-described exemplary embodiments, but rather may be varied within the inventive spirit and scope of the appended claims. Accordingly, the roll set comprised of mesh-shell screen rolls implemented in accordance with the invention can also be used for scattering of chips, e.g., in the manufac¬ ture of chipboard products. If size sorting of chips is necessary prior to scattering, the successive mesh-shell screen rolls can be provided with differently sized or shaped openings. Furthermore, the rotational direction of the rolls of a roll set may be individually 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 essential feature herein is that the number of rolls in a set is at least two, advantageously, however, 8 to 35. 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.

Claims

What is claimed is:

1. An apparatus for processing by way of, e.g., screening or scattering, par- ticulate matter such as flakes or chips, the apparatus comprising at least one roll set formed by two or more parallel rotating screen rolls (1), onto which set of screen rolls the material to be processed is fed, the screen rolls of the set having a hollow core, characterized in that the outer periphery of the screen rolls (1) is mesh-like and that the speed of rotation of the rolls is adjusted such that the flow of flakes fed onto the rolls is thrown away from the roll surfaces in a fashion that causes the separation of the flakes from each other.

2. The apparatus of claim 1 , characterized in that, with the diameter of the rolls (1 ) being approx.300 mm, the rolls are operated at a speed of rotation of 50-200 r/min, advantageously of 80-170 r/min.

3. The apparatus of claim 1 or2, characterized in that the number of roll sets is two in a substantially superimposed position, whereby the upper roll set (A) is mounted into an upward-inclined ramping position in the travel direction of the material flow while the lower roll set (B) is mounted into a downward-inclined position in the travel direction of the material flow, and the material fraction falling through the upper roll set is passed with the help of a conveyor (7) to the lower roll set.

4. The apparatus of claim 3, characterized in that the upward- ramping inclination angle of the upper roll set (A) relative to the horizontal plane is 0.5° - 15°, most advantageously 5° - 10°, while the downward- ramping inclination angle of the lower roll set (B) relative to the horizontal plane is 0.5° - 25°, most advantageously 5° - 15°.

5. The apparatus of any one of claims 1-4, characterized in that the interroll gap (2) of any two adjacent rolls (1) in each of the rolls sets is narrower than the minimum thickness of the accept-size flakes, whereby large flakes travel from roll to roll without falling down via the interroll gaps.