SIFTER

Abstract

A sifter for separating coarse particles from a particle-carrying stream during the manufacture of wood fiber panels has a housing forming a chamber. The housing also has a material inlet for admitting the particle-carrying stream to the chamber, a front wall formed with an upper air inlet below the material inlet for admitting a respective upper air stream to the chamber and a lower air inlet below the upper inlet for admitting a respective lower air stream to the chamber, an exhaust-air outlet for conveying air and fine particles from the chamber, and a coarse-particle outlet for conveying coarse particles out of the chamber. The front wall of the housing has between the upper air inlet and the lower air inlet a portion with an inwardly concavely curved shape that forms a support vortex that supports the upper air stream entering through the upper feed air inlet in the chamber of the housing between the upper air inlet and the lower air inlet.

Claims

1. A sifter for separating coarse particles from a particle-carrying stream during the manufacture of wood fiber panels, the sifter comprising a housing forming a chamber and having a material inlet for admitting the particle-carrying stream to the chamber, a front wall formed with an upper air inlet below the material inlet for admitting a respective upper air stream to the chamber and a lower air inlet below the upper inlet for admitting a respective lower air stream to the chamber, an exhaust-air outlet for conveying air and fine particles from the chamber, and a coarse-particle outlet for conveying coarse particles out of the chamber, the front wall of the housing having between the upper air inlet and the lower air inlet a portion with an inwardly concavely curved shape that forms a support vortex that supports the upper air stream entering through the upper feed air inlet in the chamber of the housing between the upper air inlet and the lower air inlet.

2. The sifter defined in claim 1, wherein the upper front wall of the classifier housing above the upper air inlet is oriented at least partially at an angle to the vertical.

3. The sifter defined in claim 1, further comprising: an air connector connected to the upper air inlet, rising at an angle with respect to the horizontal, and generating the upper air stream that enters the interior with an upwardly inclined orientation to the horizontal.

4. The sifter defined in claim 1, further comprising: a lower air connector connected to the lower air inlet, rising at an angle with respect to the horizontal, and generating a lower air stream that enters the interior with an upwardly inclined orientation with respect to the horizontal.

5. The sifter defined in claim 1, wherein the portion of the front wall extends at an angle of less than 20 to the vertical.

6. The sifter defined in claim 1, wherein the curved portion of the front wall adjoins an upper edge of the upper air inlet.

7. The sifter defined in claim 1, wherein an upper edge of the upper air inlet in side view is vertically aligned above a lower edge of the upper air inlet or projects by an amount into the chamber beyond the lower edge.

8. The sifter defined in claim 1, wherein an upper edge of the lower air inlet in side view is vertically aligned above the lower edge of the lower air inlet or projects by an amount into the chamber beyond the lower edge.

9. The sifter defined in claim 1, wherein the upper air inlet and the lower air inlet have a free and unobstructed inflow cross section into the chamber of the housing.

10. The sifter defined in claim 1, wherein the upper air inlet and the lower air inlet extend continuously over essentially an entire width of the housing.

11. The sifter defined in claim 1, wherein the front wall is convex toward the exterior between the upper and lower air inlets.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0026] The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

[0027] FIG. 1 is a largely schematic perspective view of a sifter according to the invention;

[0028] FIG. 2 is a simplified vertical section of the sifter of this invention;

[0029] FIG. 3 is a schematic diagram showing particle flow (broken lines) and fiber flow (solid lines) in the inventive sifter; and

[0030] FIG. 4 is a view like FIG. 3 but showing air flow in the sifter according to the invention.

SPECIFIC DESCRIPTION OF THE INVENTION

[0031] As seen in the drawing, the sifter of this invention serves for separating coarse particles from a particle-carrying air stream, in particular a fiber stream, during the manufacture of wood material panels, in particular wood fiber panels. Such a sifter is preferably integrated into a facility for manufacturing wood material panels, in particular to remove undesirable components (for example, bits of metal, clumps of adhesive, coarse fibers, rust flecks, or the like) from a material stream (of glued fibers, for example), in particular primarily to prevent damage of downstream facilities or facility parts, for example, steel belts of a continuously operating wood material panel press.

[0032] The sifter has a sifter housing 1 that in its basic design has an upright front wall 2, an upright rear wall 3 spaced from but generally parallel thereto, and two side walls 4 defining a generally closed treatment chamber 7. The terms front wall 2 and rear wall 3 refer to the main flow direction of the inflowing classifying air from front to rear. The housing 1 on its upper side has an upwardly open material inlet port 5 through which an air stream G carrying glued fibers F, for example, is introduced from a dryer, for example, after gluing. Particle-separating elements, for example rollers 6 as in above-cited EP 0 795 395 that are indicated schematically in the figures, may be in the area of the material inlet 5 or also above or below the material inlet. The fibers F pass into the chamber 7 of the housing 1 via the material inlet 5.

[0033] The housing 1 has a upper, upper air inlet port 8 in the front wall 2 below the material inlet 5 to which is fed an air stream carrying fine particles, mainly fibers F, and coarse particles G. In the illustrated embodiment, a lower, lower air inlet port 9 is below the upper air inlet port 8. This upper air inlet 8 is formed by a process air connector 8a to which a process air line 8b is connected. The lower air inlet 9 is formed by a process air connector 9a to which a lower process air line 9b is connected. A coarse-particle outlet 10 is provided on the housing 1 below the air inlets 8 and 9, i.e. at the lower end of the housing 1.

[0034] An upper clean-air stream L.sub.1 is fed in via the upper air inlet 8 so that the fibers F entering via the material inlet 5 are entrained by this air stream L.sub.1 and transported upward into the area of the exhaust-air outlet 11 that is formed by an upwardly open exhaust air connector 11a to which an exhaust air line 11b is connected. The coarse particles G, for example metal or rubber particles, are not entrained by the air stream L.sub.1 into the area of the exhaust-air outlet 11, and instead fall downward into the area of the coarse-particle outlet 10 where they are transported away through a gate formed by a pair of meshing rollers, for example (not illustrated).

[0035] A lower clean-air stream L.sub.2 enters through the lower inlet port 9 to optimize classifying efficiency in the manner described in above-cited EP 0 798 359.

[0036] In the illustrated embodiment, an upper front wall 12 that is above the upper air inlet 8 and that therefore extends up to the area of the material inlet 5, is oriented at an angle to the vertical over at least its lower portion. The drawing shows one embodiment in which the upper front wall 12 has a vertically oriented upper wall portion 12a, and therebelow, a lower wall portion 12b that is inclined at a small acute angle to the vertical and forming a slightly acute angle with the horizontal flow direction of the air stream L.sub.1. Here, this (middle) wall portion 12b merges into a (convexly) curved (lower) guide wall portion 12c that extends down to the upper air inlet 8. In a side view, an upper edge 13 of the air inlet port 8 projects by an amount M horizontally inward beyond a lower edge 14 of the air inlet port 8. In the side view of FIG. 2, the upper edge 13 is consequently further to the right by the distance M, and thus, further inward into the chamber 7 of the sifter housing 1. The illustrated design prevents particles, and in particular material to be removed, from passing through the air inlet 8 into the process air line 8b or the process air connector 8a. This has the advantage that fittings, protective grills, or the like may be dispensed with in the area of the air inlet 8 or the inlet connector 8a or the air line 8b, so that the air inlet 8 has a completely clear cross section without fittings.

[0037] The design of the upper air inlet 8 is similarly implemented for the lower air inlet 9. There as well, the upper edge of the air inlet 9 projects with respect to the lower edge by an distance inward toward the chamber 7. Fittings or the like are also dispensed with in the air inlet 9 and its adjacent conduits 9a-c.

[0038] Moreover, it is apparent in the drawing that the upper front wall 12 or its inclined wall portion 12b is at a relatively acute angle of less than 20 to the vertical. The classifying chamber 7 may thus be bigger than in the prior art. A horizontal dimension or length X of the classification zone along the longitudinal and horizontal overall flow direction L of the sifter extends (essentially) from the upper edge 13 of the air inlet 8 to the lower end of a partition 15, illustrated in particular in FIG. 2 in the housing 1. This partition 15, starting from the upper end of the sifter housing 1 in an essentially vertical orientation, is approximately in the center of the chamber 7 of the housing 1, in particular between the two side walls 4. Such a baffle or partition 15, known in principle, guides the fibers to the air outlet 11. This partition 15 may be adjusted longitudinally parallel to the direction L of the sifter in a basically known manner, in that it is pivotable about a horizontal axis 16, for example. Alternatively or additionally, there is an option for the partition 15 to be adjustable or changeable with respect to height in a transverse vertical direction H. As a result, the amount Y by which the partition projects downward into the chamber 7 of the housing 1 may be adjusted, and the effectiveness of the separation at different tonnages may be adapted and increased in this way.

[0039] In addition, a lower front wall 17 is between the upper air inlet 8 and the lower air inlet 9. Here, the lower front wall is curved, preferably concave inward toward the chamber 7. Thus a support vortex 18 forms in the chamber 7 between the upper air inlet 8 and the lower air inlet 9, and supports the upper air stream L.sub.1 entering through the upper air inlet 8. The flow conditions are schematically indicated in FIG. 4, while FIG. 3 shows in simplified form the path of the fibers F on the one hand, and of the coarse material on the other hand. In this regard, it is preferably provided that (at least) the lower process air connector 9a rises at an angle with respect to the horizontal, so that the lower process air stream L.sub.2 enters the chamber 7 of the housing 1 in an upwardly inclined orientation with respect to the horizontal. In the illustrated embodiment, the upper process air connector 8a is also oriented slightly upward at an angle with respect to the horizontal, so that the upper process air stream L.sub.1 also enters the inner space in an upwardly inclined orientation with respect to the horizontal.

[0040] Moreover, FIG. 1 shows that the air inlet 8 as well as the air inlet 9, and therefore also the corresponding process air connectors 8a and 9a, extend (essentially) over the entire horizontal width B of the housing 1. Thus, in contrast to the prior art, operations are not carried out using multiple separate process air lines over the width, but instead, in each case a process air line or supply conduit 8b or 9b extends over the entire width B of the housing 1.

[0041] The air inlet 8 and also the air inlet 9 preferably are of rectangular cross section. The same applies for the process air connectors 8a and 9a connected to the housing 1. The process air lines 8b and 9b may have a circular cross section, and may be connected to the process air connectors 8a and 9a via corresponding transition pieces or adapters 8c and 9c.

[0042] It is also apparent in FIG. 2 that the exhaust air line 11b connected to the exhaust-air outlet 11, has a deflecting curve U or is designed as a deflecting curve, in particular having a deflection angle of approximately 180 through which the air stream and fibers exiting the housing 1 pass. Connected to this deflecting curve is a material sorting gate 19 that divides the fiber-air stream exiting from the air outlet 11 into a fiber-air stream and an air-only stream.

[0043] Finally, the drawing shows that additional baffles 20 may be in the chamber 7 of the housing 1. However, such fittings in the sifter may be reduced compared to the prior art, so that the tendency toward fouling is decreased, and the overall effectiveness of the sifter (with regard to separation quality and energy efficiency) may be optimized