Method For Dividing A Main Stream Of Particles Into Part Streams And Apparatus For Carrying Out The Method

Abstract

A method and apparatus for transforming a constant main stream of particles into a particle web having a uniform mass particle distribution which varies in a desired manner transversely of the web by directing the main stream into an annular chamber against a rotating member concentric within the chamber. The rotating member distributes the main stream about the chamber and the particles pass out through a plurality of outlets opening along a plane in the chamber which is normal to the longitudinal axis of the chamber.

Description

There are many instances in industry in which it is found necessary to divide a main stream of solid particles into part streams in a manner whereby the flow per unit of time of each part stream constitutes a specific portion of the flow per unit of time of the main stream, and that the particle composition of the part streams is the same as that of the main stream.

If the particles are identical and have a specific degree of consolidation, for example as with lead shot of uniform size, the problem of distribution can be solved exactly by volumetric division. Volumetric division, which is relatively simple and inexpensive method, provides in the majority of cases good division of material comprising particles of relatively concentrated and stable form sufficient for practical purposes, even though the shape and size of the particles may vary, e.g. such as with sand and like material, if it can only be effected so that a screening effect is avoided.

However, in the case of a material comprising particles of a flat or elongated configuration and particularly when the particles are easily deformed, such as with wood chips and wood fiber used in the manufacture of particle and fiber board, the method of volumetric division provides relatively unsatisfactory results. When dividing the main stream into a number of part streams it is usual to lead the main stream to a bunker, from which the desired part streams are proportioned individually. When a large number of part streams is required, however, this method becomes expensive and requires the use of much too complicated apparatus. As a result, volumetric division is also applied in the case of materials for which it is not suited, with the result that the accuracy of division is not as good as would be desired.

It is known from the calculation of probability, however, that if a large --actually an enormously large --number of particles are spread purely randomly over a surface of limited size or along a path of limited length a completely uniform distribution of the particles over the surface or along the path is obtained.

It is also known that the time taken for identical particles to pass through a space filled with a fluid, e.g. with air, under the influence of, for example, gravity, varies randomly around an average value, depending upon such circumstances as variations in the resistance of the fluid with regard to the orientation of the particles in relation to the force direction, turbulence in the fluid, collisions with other particles or with the walls of the confined space in which they fall etc.

The time taken for the particles to pass through the fluid filled space varies greatly about the average value with the properties of the fluid and the particles. In the case of particles having a relatively large average falling speed through the fluid, the aforesaid variation is substantially caused by variations in the resistance thereof. This resistance is high for rod shaped or flat particles and decreases successively with increased compactness of the particles. In the case of truly spherical particles, e.g. the aforementioned lead shot, the fluid resistance does not vary at all with the orientation of the particle, and the aforesaid variation about the average value is small. There will, however, always be a certain degree of variation about the said average value, as result of turbulence of the fluid, and this range of variation will increase in the case of a stream of particles owing to shadowing effects between the particles, collisions etc. The lower the mean speed of the particles falling through the fluid the greater the part of turbulence in the fluid plays with regard to the variation about said average values.

The present invention is based on these known conditions and its prime object is to provide for the division of a constant main stream of particles into part streams in accordance with arbitrary wishes and in such a manner that the composition of particles in the part streams is practically the same as in the main stream, and that the flow per unit of time of each part stream comprises a practically constant portion of the flow of the main stream, irrespective of the magnitude of said main stream. The object of a further development of the invention is to form a web of particles from the particle stream, in which the lateral distribution thereof substantially coincides with a certain desired degree of distribution. These objects are realized by means of the present invention, which is mainly characterized in that the main stream is first transformed into a tubular flow of particles being passed axially through a chamber which is substantially in the form of a rotation body and is filled with a fluid, and in which the fluid is maintained in rotation around the axis of the chamber, and in that the tubular stream of particles is then divided circumferentially by being passed into an outlet arranged concentrical with the chamber and which at the periphery thereof is divided peripherally into part outlets.

The invention will now be described with reference to the accompanying drawings, where for the purpose of explaining the principle of the invention,

FIGS. 1 and 2 schematically illustrate an apparatus by which the method of the invention can be carried out. FIG. 1 shows a vertical section through the apparatus and FIG. 2 a horizontal section taken through the line 2--2 in FIG. 1 seen in plan.

FIGS. 3 and 4 show in vertical section two apparatus embodying the concept of the invention and suited for practical use in dividing a stream of particles into part streams intended for two different types of particles.

FIG. 5 shows in side view and partly cut away an apparatus according to the invention for forming a web of particles from the particle stream.

FIG. 1 shows a housing 11 in the form of a cylinder having a vertical axis and the two ends of which are closed. In the upper end wall 12 of the cylinder, close to its periphery, is arranged an inlet 13, through which a main stream 14 of particles is passed to a cylindrical chamber 15 enclosed by the housing 11. The lower portion of the housing is formed as an outlet portion 16. The inner portion of the housing is divided into sectors by means of a number of radial walls 17 (see FIG. 2) all of which terminate at the top thereof in one and the same plane 18 extending at right angles to the cylinder axis. The bottom of the walls 17 are connected to the lower cylinder end wall 19. In this way, there are formed under the surface 18 a number of part outlets 20, which receive the particle stream when it leaves the chamber 15. Each part outlet is provided with an exit 21 and the lower end wall 19 is designed (in a manner not specifically shown) so that the particles cannot collect in the part outlet 20, but that the particles which arrive in a part outlet 20 pass continuously out through its exit 21 in the form of a part stream 22 of particles.

The chamber 15 is filled with a suitable fluid, which is held in constant rotation around the axis of the chamber by appropriate means (not shown in the drawing). When the particles in the main flow 14 enter the chamber 15 they are imparted a rotary movement by the fluid rotating in the chamber about the axis of said chamber simultaneously as they fall down through the chamber axially thereof as a result of gravity. They are held at the outer diameter of the chamber by the influence of centrifugal force. The particles will therefore pass through the chamber 15 along essentially helical paths which, for natural reasons, obtain on average different pitch angles for particles of different types, but which for identical particles obtain individually different, haphazardly varying pitch angles. As previously mentioned, identical particles will pass through a certain distance axially downwardly in the cylinder in a haphazardly varying time. At the same time the particles move tangentially, on average at a speed which is equal to or -- as a result of friction on the cylinder wall -- somewhat lower than the tangential velocity of the fluid adjacent the cylinder wall.

The tangential velocity of the particles will also vary haphazardly around an average value, as a result of turbulence in the fluid, collisions and frictions etc., although this variance at fairly high tangential velocities of the fluid should be relatively much lower for the tangential velocity of the particles than for their axial velocity. There is no specific relationship between the extent to which a specific particle will deviate from the average velocity in a tangential and axial direction, even though, for example, friction against the cylinder wall tends to cause a reduction in velocity in both directions. The two velocity vectors therefore vary haphazardly each per se, and the pitch angles of the particle paths vary purely haphazardly.

Particles which arrive in the chamber 15 at one and the same position, at the inlet 13, and follow paths having different pitch angles, defined purely by chance, will adopt peripheral positions determined by these haphazardly determined angles when they pass one and the same section of the chamber. An example is given in FIGS. 1 and 2 of how a particle which follows a gentle path 23 has reached the peripheral position 24 as it passes section 18, while another particle, which follows a steeper path 25, has reached the periphal position 26 as it passes the same section.

Consequently, identical particles which are introduced at the same position 13 will be distributed randomly around the periphery of chamber 15, which means that the particles will be relatively uniformly distributed along the periphery at a section 18 sufficiently far down in the chamber where the variation in pitch angle includes a plurality of turns. Particles which arrive at the same time through the inlet 13 will therefore reach the section 18 at different points of time, also determined haphazardly, although if the main stream 14 is constant this plays no great part, since the main flow 14 at section 18 is then transformed to a tubular constant particle stream with all different types of particles distributed relatively uniformly in the peripheral direction and the longitudinal direction of the stream.

In practice the separate particles will not, of course, follow paths having even an approximately constant path angle, but that the path angle for a specific particle will vary as the particle moves downwards through the chamber 15. This variation, however, is also determined by chance and consequently does not affect the uniform distribution of the particles to any extent other than reducing the speed at which the distribution is effected.

The constant tubular flow of particles is divided into desired part flows 22 at the outlet 16 beginning at section 18, the outlet 16 being divided into part outlets 20 in some suitable manner.

It is obvious that the described method and apparatus may also be used for dividing a certain restricted total quantity of particles into part quantities in a manner whereby the mass of each part quantity constitutes a specific portion of the mass of the total quantity and whereby the particle composition of each part quantity is the same as in the original total quantity, providing that the total particle number is sufficiently high. It is not necessary -- and not possible as a matter of fact -- to maintain constant the main stream 14, which is formed when the restricted total quantity of particles is emptied into the apparatus, and the part streams 22 will not therefore momentarily have either the correct mass or the correct particle composition, although when all the particles have passed through the apparatus the desired division has in any event been obtained.

It is also obvious that in several respects it is principally unimportant to the function of the apparatus whether it is constructed in the manner described and illustrated in FIGS. 1 and 2.

The housing 11 need not be cylindrical, although it is essential that its inner surface is constructed as a rotary body on that portion of the surface which is contacted by the particles to prevent heaping. Of course, the cylindrical surface of the rotary body should not at any part thereof form too large an angle to its axis and thereby causing the particles to tend to remain on said cylinder surface.

Neither need the main stream 14 be introduced to the chamber 15 in the proximity of its periphery or in an axial direction, as shown in FIG. 1. The main stream may be introduced at any radial distance from the axis of the chamber 15 and in any direction whatsoever, more or less axially, radially or tangentially. Neither need the main stream 14 be introduced at one single position 13, as described and illustrated in explaining the principle of the invention. To the contrary, it is appropriate that the stream is introduced to the chamber 15 as uniformly distributed around its perphery as possible, e.g. through an annular inlet arranged concentrically with the chamber and as uniformly distributed as possible beforehand around the periphery of the inlet.

Furthermore, the chamber 15 need not be completely free adjacent the axis of the chamber. The particles, after all, pass in a thin layer around the cylindrical surface of the chamber and the central portion thereof can thus be filled to a large extent with packing material, e.g. with one or more rotors placed therein, which maintain the fluid in rotation, as will be described below with reference to FIG. 3. The fluid, however, can also be held in rotation in another manner, e.g. by continuously introducing the fluid and passing it away from the chamber 15, the fluid being introduced at a suitable velocity in a tangential direction. In this instance, the packing material should also be in the form of a rotary body having the same axis as the inner surface of the housing 11, so that the chamber 15 obtains a cross section having the shape of a true circle. On the other hand, a rotor adapted to maintain rotation of the fluid need not be constructed as a rotary body. However, it is most convenient to design such a rotor as a rotary body which fills the larger portion of the housing 11 radially, so that it forms an annular chamber 15 with relatively small radial extension between the housing 11 and the rotor. The rotor may suitably be provided with low, preferably axial vanes, strips or other projecting members, thereby facilitating entrainment of the fluid.

The type of fluid used is in principle of no importance, although if the particles float in the fluid the apparatus shown in FIG. 1 must of course be turned upside down. In practice air is thought to be the fluid most suitable in the majority of cases, although special instances are conceivable, e.g. in the case of compact particles of very high density, when it may be to advantage to use some other appropriate liquid.

If the housing 11 is surrounded by the same fluid with which the chamber 15 is filled, which is the case when the fluid is air, the housing 11 need not be closed at the ends thereof, but that the said chamber 15 can be made to communicate with the surrounding fluid in a suitable manner.

The outlet portion 16 may also be filled out in the centre thereof in a manner whereby said outlet obtains an annular cross section. Neither need the outlet begin at a plane perpendicular to the axis of the chamber, but that the inlet surface 18 of the outlet may have some other suitable configuration, such as conical, for example. The essential feature is that the outlet is concentrical with the chamber 15. The walls 17 which divide the outlet into part outlets need not be radial, but may extend in another direction, and the part outlets may be provided with suitably arranged partitions, in order to stop rotary movement of the particles.

The outlet, however, is a sensitive portion of the apparatus. Small errors in design can, if no other measures are taken, lead to considerable error in the division of the main stream into part streams. It is obvious, for example, that if one wall projects up a little higher than the others and that if the particles at the same time meet the outlet in a very gentle path the said wall is liable to impede the part outlet 20 lying there beyond, causing it to receive too small a portion of the main stream 14. It is therefore suitable to brake the rotary movement of the particles as much as possible before said particles reach the inlet surface 18 of the outlet. Obviously the particles must be braked in a manner in which the haphazard distribution of the particles is not affected, i.e. in a manner whereby heaping and similar phenomenon are avoided. In the case of certain types of particles which show smaller tendency to agglomerate, braking can be effected essentially mechanically, e.g. by providing the housing 11 above the outlet with a number of rows of preferably cylindrical studs or pins directed inwardly and uniformly distributed relatively sparsely around the circumference. The pins will, of course, also brake to a certain extent the rotation of the fluid and thereby, via the rotation of the fluid, also rotation of the particles which do not strike the pins. Particularly with regard to particles which tend to agglomerate or filter together readily it is better, however, to brake the rotation of the fluid in a portion of the chamber 15 nearest the outlet, so that rotation of the particles is mainly braked by the fluid. It may, on occasions, also be suitable to impart rotation to the fluid nearest the outlet in an opposed direction of rotation to the space 15 in general and at an adapted velocity, so that the particles meet the outlet in directions which are fairly uniformly distributed in both directions around the true axial direction.

When a rotor provided with vanes or the like is used to maintain the fluid in rotation, a free annular space with sufficiently large radial extension should be left in the majority of cases so that the tubular particle stream is able to pass without the particles coming into direct contact with the rotor to any considerable extent and being subjected to blows thereby.

Finally, it is obvious that some force other than gravity can be employed to lead the particle stream axially through the chamber 15. In the case of material suited thereto the particles can be subjected, for example, to magnetic forces, in which case it is not necessary for the axis of the chamber 15 to be vertical. While the influence of gravity is important to the transport of the particles, however, the axis should be vertical since otherwise the particle tend to collect at the lowest side of the outlet.

The fluid may also be used to increase or decrease the average velocity at which the particles pass axially through the chamber 15, by imparting to the fluid an axial velocity opposed or concurrent the direction in which the particles are transported. A reduction in the average axial velocity of the particles may be suitable to provide the necessary spreading circumferentially in the case of contact particles of high density, without the axial length of the apparatus being too great. An increase in the average axial velocity may be necessary in order to increase the capacity of the apparatus in the case of particles whose falling velocity in the fluid is low, preferably with regard to their falling velocity in air. In the case of such particles it is often convenient to convey the particles to and from the apparatus by means of the fluid. It should be seen, however, that the flow in the fluid is arranged so that it affects the particle distribution to the part outlet 20 as little as possible, i.e. so that the axial flow velocity through the inlet surface 18 of the outlet is either practically the same at all part outlets 20 or is sufficiently low to prevent particle distribution from being impaired to any great extent by varying velocities at the different part outlets.

FIG. 3 shows by way of an example, and greatly simplified, an apparatus according to the invention designed for use when there is need to convey the particles by means of the fluid. Like parts in FIG. 3 are identified by the same reference numerals as those used in FIGS. 1 and 2. The Figure illustrate a cylindrical housing 11 having a vertical axis and an outlet portion 16 arranged concentrically with and connected to the housing. The outlet portion includes an annular outlet which is divided up in a desired manner into a number of part outlets 20 by means of partition walls 17 which begin at one and the same horizontal plane 18, said part outlet 20 each having its respective exit 21, and a center portion 28 concentric with the housing 11 and supporting two rotors 29 and 30 arranged within the housing concentrical therewith. The lower rotor 29 is provided with a hollow shaft 31, which is journalled in a suitable manner direct to the frame 28 at 32 and 33, and the lower end of which is provided with a belt plate 34 or the like for driving the rotor 29 from a drive means (not shown) which is arranged in a foundation 35 (only a fragment being illustrated) on which the outlet portion 16 is erected. The upper rotor 30 is provided with a shaft 36 which in turn is journalled in a suitable manner in the bore of the hollow shaft 31 at 37 and 38 and which at the bottom is provided with a belt plate 39 or the like for driving the rotor 30 from a drive means not illustrated in the drawing.

The rotors 30 and 29 and the center portion 28 of the outlet portion form together an essentially cylindrical filling structure in the center of the housing 11, so that an annular chamber 15 of circle ring shaped horizontal section is formed therebetween and the housing.

The upper rotor 30 rotates at a relatively high peripheral velocity and its purpose is to maintain rotation of the air in the upper portion of the annular chamber 15 above the axis of the chamber. In order to entrain the air in a more effective manner the rotor may suitably be provided with strips or vanes 40 extending substantially axially over the larger portion of the length of the rotor. In order to increase the turbulence of the air vertically, it may also be suitable to use instead of long vanes 40 short projections or vanes 41, separated by relatively large axial spaces, as shown to the right of the Figure. These short vanes may suitably be placed obliquely in relation to each other, alternate vanes having a right hand pitch and a left hand pitch respectively.

The housing 11 is provided at the top with an end wall 12 in the centre of which is provided a cylindrical inlet 42 through which a main stream 14 of particles is introduced from a feed means 43 (only graphically illustrated in the drawing). Arranged in the inlet 42 is an impeller 44, which is supported from the rotor 30 by means of a shaft 45. The impeller 44 is struck by the main stream 14 and distributes the same towards the periphery of the inlet 42, as shown by dotted lines 46, which illustrates approximately how the stream of particles is distributed throughout the apparatus. The main stream 14 roughly formed in the inlet 42 into a tubular shape then falls somewhat concentrically on the upper, slightly conically shaped end wall of the rotor 30, and is then passed under the influence of frictional forces, centrifugal forces, air forces and gravity, along force lines created along said end wall towards the periphery thereof. The forces, with the exception of the gravity force line, acting on the separate particles are determined more or less by chance, which means that the distribution of the particle stream circumferentially is improved during the passage over the end wall of the rotor 30, so that the stream of particles when it reaches the annular inlet 13 to the chamber 15 is relatively uniformly distributed circumferentially. The end wall of the rotor 30 may be provided with projections in the form of pins, radial or spiral vanes or the like, thereby more rapidly to impart to the particles a rotary velocity and thereby prevent large collections of particles on the central portions of the end wall.

The particles then pass from the inlet 13 in helical paths down through the annular chamber 15, essentially through the outer portion thereof, whereupon the distribution of particles circumferentially becomes more and more uniform in the tubular particle stream 46 the farther the stream extends into the annular chamber, as described with reference to FIGS. 1 and 2.

The purpose of the lower rotor 29 is to brake the rotation of air in the lower portion of the annular chamber 15, and thereby brake the tangential velocity of the particles before they reach the outlet 16. The rotor 29 therefore rotates in the opposite direction to rotor 30. The rotor 29 may also be provided with substantially axially extending strips or vanes 47. The dimensions and the speed of rotation thereof is adapted so that the air in the angular chamber 15 below the same rotates with a suitable low velocity in the same direction as the rotor, so that the paths of the particles are on average approximately vertical before they meet the outlet 16, in which the tubular particle stream 46 is divided in the desired manner in the part flows 22.

Since the tangential velocity of the particles is reduced the centrifugal force, which endeavours to hold the particles adjacent the wall of the chamber 15 is of course also reduced and the particles obtain a tendency to spread inwardly in the chamber 15 in the lowermost portion thereof when the rotation velocity is low or zero, as indicated by the double dotted lines 46. The radial spread of the particle stream is, in itself, unimportant but may vary with the size of the particle stream and should be taken into account when designing the part outlets 20. The partition walls 17 between said outlets should be arranged so that a variation in the radial thickness of the tubular particle stream 46 at the inlet surface of the outlet does not affect the division of said main stream into part streams.

The space between the end wall of the rotor 30 and the end wall 12 of the housing 11 is formed so that a fan effect is avoided to the highest possible extent, which would otherwise cause axial flow through the chamber 15 and through the part outlets and, via different flow resistances in the part outlets 20 and the conduits connected thereto, affect division of the main stream 14. The axial space between the two end walls is ample and the end wall 12 is provided on the inside thereof with radial walls or guide vanes 48, to brake any possible rotation of air therein which could give rise to radially acting pressure differences. Finally, there is provided a circular opening 49 between the end wall 12 and the housing 11 to create, via the outer atmosphere, pressure equilization between the upper end of the chamber 15 and the outlet 21 of the part outlets, thereby preventing axial air flow into chamber 15.

FIG. 4 is another embodiment of an arrangement according to the invention which can be used in the case of particles whose falling velocity in air is low enough to render it suitable to transport the particles by means thereof. The apparatus of FIG. 4 is very similar to the apparatus of FIG. 3, and like parts have been identified with like reference numerals in the two figures. FIG. 4 illustrates a housing 11 having a vertical axis and an outlet portion 16 connected to the housing and which comprises an annular outlet divided into part outlets 20 and arranged concentrically with the housing and a central portion 28 which supports two rotors 29 and 30 arranged concentrically with said housing. The rotors form together with the centre portion 28 of the outlet portion a filling structure occupying the centre portion thereof concentrically with the housing so as to form therebetween and the housing an annular chamber 15 of circle-ring horizontal section.

The housing 11 is provided with a completely closed end wall 12 and the main stream 14 of particles is introduced through a supply line 50 connected to the centre of the end wall by means of a stream of air of relatively high velocity, 20 to 40 m/s. At least certain types of particles which are normally transported pneumatically, e.g. wood fiber in the manufacture of fibre board, have a high tendency to adhere to the walls of the conduits and form coatings thereon. It requires a relatively high air speed in order to prevent this occurrence.

The end wall 12 of the housing and the end wall of the rotor 30 are also constructed so that a relatively high air speed is maintained radially therebetween. Since particles are transported to the apparatus substantially by means of air flow it is not necessary to avoid the aforementioned fan effect, nor is it possible to avoid this effect. On the contrary, it may be to advantage to provide the end wall of the rotor with projections or vanes 51 to improve spreading of the particles by an increase in turbulence, an increase in the fan effect being, of course, obtained at the same time. The impeller 44 illustrated in FIG. 3 at the inlet 42 on the end wall of the housing has been omitted in the apparatus of FIG. 4, since it has no function to fullfil.

The upper portion of the annular chamber 15 between the housing 11 and the upper rotor 30 has a much wider area than the inlet conduit 50, whereby the axial velocity of the air and therewith the average axial velocity of the particles is low at this point, e.g. 1 m/s or less, thereby allowing the particles time to be uniformly distributed around the circumference of the chamber as they pass the upper rotor 30. To facilitate spreading, which in the case of particles having a low falling speed is substantially caused by turbulence of the air, the rotor 30 is provided with short vanes 41, as previously mentioned with reference to FIG. 3.

There is no great difficulty in retaining the particles during their passage through the upper portion of the chamber 15 substantially in the outer portion of said chamber, even though their average falling speed in air is low. It is relatively simple by suitable construction of the apparatus to provide a centrifugal force which is at least two powers of ten greater than gravity. When the rotation of the air has been braked in the lower portion of the chamber 15, the particles will, on the other hand, also be spread widely in a radial direction as a result of air turbulence.

The low axial velocity in the upper portion of the annular chamber 15 ensures that no particles will be deposited in this region since the air has a high tangential velocity, which keeps the wall of the housing 11 clean, and the particles are to a large extent retained at the wall of the housing and away from the rotor 30. It is, of course, possible that the finest of the particles reach the rotor, and since the rotor is provided with vanes 41 the difference in tangential velocity between the air and the rotor is much less than the tangential velocity of the air relative to the wall of the housing. Consequently, particles which reach the rotor may be liable to form deposits thereon. On the other hand, the vanes 40 create a very strong turbulence adjacent the rotor, which contributes towards keeping it clean of particles. Possible deposits on the rotor are not able to build up to any large extent, but are torn loose by the centrifugal force and, in the form of separated lumps, are thrown out towards the outer wall of the chamber 15, where they are rapidly broken up into separate particles friction and air eddy currents.

On the other hand, particles are liable to be deposited in the lower portion of the annular chamber 15, where the tangential velocity of the air is braked, if the low axial velocity is maintained there. The lower rotor 29 is therefore constructed so that the axial velocity of the air is increased at the same time as its tangential velocity is decreased and a sufficiently high air velocity is maintained to prevent particles from being deposited. As a result of the strong turbulence created by the rotors 30 and 29 it is not necessary to rise to the same high velocity of air as in the annular chamber 15 as that in the inlet conduit 50. The high axial velocity of the air is maintained or increased further in the part outlet 20, depending on whether the particle streams 20 issuing from the part outlets are to be used immediately or are to be conveyed further through long discharge conduits. Further, it is suitable always to provide for a small continuous increase in the axial velocity of the air throughout the whole distance from the lower end of the rotor 29 to the outlet 21 of the part outlet, to prevent stagnation of the boundary layers which may cause particles to be deposited on the wall.

FIG. 5 finally illustrates an example of a further development of the invention for converting a continuous, constant stream of particles to a continuous web of particles, in which the distribution of flow is very uniform in both the longitudinal and lateral direction or varies in a desired manner laterally of the longitudinal direction of the web. It is a normal procedure in the particle board and fibre board industry to first arrange particles or fibres into a longitudinally extending continuously growing web, from which appropriate lengths are taken and then under the influence of heat and pressure, normally by pressing in a hot press, are converted to particle and fibre boards. The Figure illustrates schematically an apparatus for forming a particle web.

When forming fiber boards, a stream of particles is created with practically a constant flow per unit of time, by proportioning the particles from a bunker by means of a conveyor scale or the like. The stream of chips or particles is then spread by means of one or more so-called chip spreading machines onto support surface which is capable of moving therebeneath in one direction, e.g. a conveyor belt. When employing known chips spreading machines, the stream of chips is spread onto the support surface in the cross direction of the formed web by volumetric methods, while distribution of the chips longitudinally is essentially caused by moving the support surface in relation to the chip spreading machine. The chip spreading machines are, of course, practically always constructed so as to spread the stream of chips also over a specific longitudinal section of the support surface, but spreading in the longitudinal direction is for the purpose of screening different chips in the web so that the center layer substantially comprises larger chips and the two outer layers finer chips, and it does not affect the distribution per unit of time longitudinally to any great extent. The total mass or weight of chip web per unit of length is thereby determined by the constant flow per unit of time, obtained by proportioning, and by the speed at which the support surface moves, and can without difficulty be maintained practically constant. But distribution of the chips laterally across the web when applying volumetric methods leads to unintentional and often considerable variations in mass distribution transversely of the longitudinal direction of the web, since the bulk density of the loosely packed chips varies appreciably already at small variations in packing pressure. Consequently even when using the best of the known chip spreading machines and with constant supervision unintentional variations in weight per unit or surface area in the chip web of the order of .+-.5 percent must be expected. Since the lightest portion of the chip web determines the minimum strength of the pressed fibre board this means an extra consumption of raw materials of approximately 5 percent. Variations in the weight of the fiber web per unit area can also cause uneven thickness of the pressed fiber boards and extra costs in adjusting said variations to produce a board of uniform thickness. The chip spreading machine illustrated in FIG. 5, however, provides a practically uniform mass distribution in the fiber web or mass distribution laterally, which varies in a desired manner without appreciable deviations from the desired distribution.

The Figure illustrates a device 52 of the aforedescribed type, suitably a device such as that illustrated in FIG. 3. The outlet of the device 52 is divided into a relatively large number of part outlets of equal size, which are extended through outlet lines 53, which are inclined to such an extent that chips are not able to collect at any portion thereof. The exits 21 from the outlet lines 53 for each half of the device 52 are connected in adjacent rows to the upper end wall of their respective distribution box 54 having a planar, relatively steeply declining bottom 55, which terminates short of the lower end wall of the distribution box, so that an opening 56 is formed adjacent the end wall and extending across the entire box. The distribution boxes are shown partly cut away for the sake of clarity.

The device 52 together with the distribution boxes 54 are placed over a conveyor belt 57 on which the particle web 58 is formed. Arranged above the conveyor belt 57 and beneath the opening 56 in the distribution boxes are two ejection rollers 59 which are provided with outwardly projecting pegs or the like. The two rollers rotate in opposite directions, so that chips which fall thereon are thrown inwardly of the space between said rollers.

A constant stream of chips 14 created in a conventional manner, is passed to the device 52 and enters the distribution boxes 54 divided into a number of constant part streams 22 of equal magnitude, which are arranged in rows in side-by-side relationship in the transverse direction of the web 58. If a uniform mass distribution transversely of the longitudinal direction of the web 58 is required, the outlet lines 53 are connected with uniform spacing to the distribution boxes 54. It is often desired, however, to provide a somewhat larger quantity of chips along the edges of the web 58, in order to compensate for the increasing width of the web which arises during the pressing operation. This is best provided for by connecting the outlet line 53 to the distribution boxes 54 at a narrower spacing for the outermost outlet lines. Alternatively uniform spacing can, of course, be employed and a larger stream of chips passed to the outermost outlet lines.

The chips slide down along the bottom 55 of the distribution boxes, as indicated in the Figures by the dotted lines. In this way the regular, local uneveness in chip distribution transversely of the web caused by the chips being divided into part streams, is equalized at least to a great extent. The chips leave the distribution boxes through the opening 56 and fall down onto the thrower rollers 59, which spread the chips substantially longitudinally along the web 58, to provide in a known manner distribution of different chip sizes vertically of the web with finer chips 60 at the outer surfaces and the coarser chips 61 in the middle. The thrower rollers, however, also spread the particles to a certain extent transversely of the web and thereby create a final equalization of the aforementioned local irregularities in chips distribution in this direction. It is possible that a satisfactory levelling of the local irregularities transversely of the web can be effected solely with suitably constructed thrower rollers, so that the distribution boxes 54 can be omitted.

Although not shown in the Figure, conventional side walls are naturally arranged adjacent the conveyor belt 57, to provide for the exact width and clean side edges of the particle web.

The principal method for transforming a constant stream of particles to a particle web having a uniform mass distribution or a mass distribution which varies transversely of the web in a desired manner, as illustrated in FIG. 5 and the aforegoing, means that the flow of particles must first be divided into a suitable number of part flows at constant mass flow and unchanged particle composition, as described in the aforegoing, and that the part flows are then passed to the movable support surface 57 on which the particle web 58 is formed at one or more stations in the longitudinal direction of the web, arranged in side-by-side relationship and appropriately spaced in the transverse direction of said web. In order to level the regular local variations in mass distribution transversely of the web, which would otherwise be caused by division of the main stream into part streams if the numer of part streams were not sufficiently great, there are arranged means 54, 59 which, in a manner known per se, can be mounted between the outlet of the part flows 22 and the support surfaces 57 on which the particle web 58 is formed.

The method can be applied with all types of particles, although, of course, the device 52 for dividing the main stream 14, the arrangements 54, 59 for levelling the local variations of mass distribution transversely of the web and the support surface 57, on which the particle web 58 is formed, with associated arrangements and devices must be adapted to the type of particles used.

Claims

I claim:

1. A method for dividing a main stream of particles into a plurality of part streams comprising the steps of:

transforming a main stream of particles into a tubular stream of particles by passing said main stream axially through a chamber which has substantially the form of a rotation body and is filled with fluid;

imparting to said particles in said tubular stream a rotation movement about the axis of said chamber;

dividing said tubular stream of particles circumferentially by passing said tubular stream through an outlet concentric with the chamber and having a plurality of radial partition walls all of which extend from a plane concentric with the chamber and normal to the axis thereof; and

introducing a controlled rotation retarding component to brake the rotary movement of the particles around the axis of said chamber in said tubular stream to a desired rotary movement before said tubular stream reaches the plane of the outlet.

2. The method of claim 1, wherein the rotary movement of the particles is braked by said rotation retarding component in a portion of the chamber adjacent to the surface of the outlet by applying to the particles a second flow having an opposite direction of rotation as compared with the rotation of the particles in the chamber in general.

3. The method of claim 1, wherein the main stream is spread approximately uniformly along the whole of the periphery of an annular inlet arranged concentrically with the chamber and through which the stream is passed to said chamber.

4. An apparatus for dividing a main stream of particles into a plurality of part streams comprising:

a substantially vertical cylindrical housing having an inlet end and an outlet end;

a rotor rotatably mounted within the housing with its axis of rotation coincident with the longitudinal axis of the housing to define an annular chamber therebetween;

a plurality of projections fixed about the outer periphery of said rotor and extending radially thereof, said projections having a height substantially less than the width of said annular chamber;

a fluid filling said chamber and having a rotary motion imparted thereto by said rotor;

means for supplying a main stream of particles to said inlet end;

said outlet end including a plurality of partition walls extending radially through said chamber and depending from a single plane concentric with the chamber and substantially normal to the longitudinal axis thereof; and

controlled means to retard the rotation of the particles around the axis of said chamber in said tubular stream to a desired rotation before said tubular stream reaches the plane of the outlet.

5. The apparatus of claim 4, wherein said projections are short in relation to the length of the rotor and are substantially uniformly dispersed over the circumference of the rotor and along at least a portion of its length.

6. The apparatus of claim 4, wherein the distance between the outer diameter of the projections and the inner diameter of the housing is so great that the particles can pass through the chamber without coming into direct contact to any large extent with the rotor and the projections.

7. The apparatus of claim 4, further comprising a second rotor arranged within the housing between the rotor and the outlet, the axis of rotation of said second rotor being coincident with the axis of the housing, said second rotor being rotated in a direction opposite to the first rotor.

8. The apparatus of claim 4, wherein the partition walls in the outlet are placed at the outlet end facing the chamber in a radial plane through the axis of said chamber with such spacing that the outlet is divided into sectors with sector angles corresponding to the desired partitioning of the flow of the main stream.

9. The apparatus of claim 4, wherein the outlets from the part outlets are arranged in side-by-side relationship in at least one row.