METHOD OF GLUE-COATING PLANT PARTICLES

Abstract

Fiberboard or chipboard is made by first comminuting vegetable starting material in a first comminutor into a stream of loose plant particles with silicate particles. Then, in a first classifier silicate particles of a diameter of less than 50 μm are separated from the plant particles of the stream. The plant particles remaining in the stream are then glue-coated, and the stream is pressed into fiberboard or chipboard.

Claims

1. A method of making fiberboard or chipboard, the method comprising the steps of: comminuting vegetable starting material in a first comminutor into loose plant particles and silicate particles; in a first classifier air separating silicate particles of a diameter of less than 50 μm from the plant particles; glue-coating the remaining plant particles; and compressing the glue-coated plant particles into fiberboard or chipboard.

2. The method according to claim 1, further comprising the steps of: applying an air stream in the first classifier to the stream such that the plant particles fall by gravity and the silicate particles are entrained by the air stream; discharging the entrained silicate particles via an air outlet of the first classifier; and discharging the fallen plant particles from the classifier below the air outlet.

3. The method according to claim 2, wherein the air stream is formed by drawing air out of the air outlet.

4. The method according to claim 1, further comprising the steps of: further comminuting the plant particles downstream of the first comminuter in a second comminutor; and in a second classifier downstream of the second comminuter separating any remaining silicate particles from the plant particles.

5. The method according to claim 4, wherein the first comminutor reduces the plant particles to coarse particles and the second comminutor reduces the plant particles to fine particles.

6. The method according to claim 4, wherein the first comminutor is a hammer mill.

7. The method according to claim 4, wherein the second comminutor fiberizes the plant particles into plant fibers.

8. The method according to claim 1, wherein the first classifier has a material inlet for the receiving the plant and silicate particles, an air inlet for the air stream below the material inlet, an air outlet, and at least one particle trap that is below the air outlet.

9. The method according to claim 1, further comprising the step of: trapping and removing coarse foreign bodies from the vegetable starting material upstream of the first classifier.

10. The method according to claim 1, further comprising the step of; crushing the particles of the stream upstream of the first comminuter.

11. The method according to claim 1, wherein the glue coating is effected by a drum mixer.

12. The method according to claim 1, further comprising the step after glue-coating and before pressing the particles of spreading the particles into a loose-particle mat.

13. The method according to claim 2, wherein the air stream is formed by drawing air out of the air outlet

Description

BRIEF DESCRIPTION OF THE DRAWING

[0026] The invention will be explained in greater detail in the following with reference to the drawing, which merely illustrates embodiments. In the drawing,

[0027] FIG. 1 is a highly simplified schematic view of an apparatus (and a method) for making boards from glue-coated plant particles,

[0028] FIG. 2 is a side view of a classifier of the apparatus according to FIG. 1,

[0029] FIG. 3 is a front view of the classifier of FIG. 2,

[0030] FIG. 4 is a top view of the classifier of to FIG. 2, and

[0031] FIG. 5 is a section taken at A in FIG. 3 showing flow conditions.

SPECIFIC DESCRIPTION OF THE INVENTION

[0032] In FIG. 1 a system is shown with the glue-coated plant particles, for example glue-coated fibers from annual plants, for example made of straw and particularly preferably rice straw and pressed into boards.

[0033] After for example precomminution in a straw chopper 1, straw that is provided as a starting material M is comminuted in a first comminuter 2, a hammer mill 2 in this embodiment. The material produced in this first comminuter 2 is fed to a first classifier 3 forming a first classifying stage for separating silicate particles from the straw particles. This first classifier 3, which will be discussed in greater detail below, is shown in an enlarged view in FIGS. 2 to 5.

[0034] In such a classifier 3, which is an air classifier, the straw particles are introduced into the classifier housing 5 via an upper material inlet 4 and an air stream (supply air Z) is injected into the classifier housing. For this purpose, the classifier 3 has a front, upper air inlet 6 and a rear, upper air outlet 7. A particle trap 8 is provided for the straw particles P that are freed of silicate S is provided beneath the air outlet 7. A coarse-material trap 9 for receiving foreign bodies, for example stones or similar coarse material G, is upstream from the particle trap 8 in the direction of flow. In this classifier, the silicate particles S are entrained by the air stream due to their very small and uniform size and discharged via the air outlet 7, while the plant particles that are intended for further processing, for example straw particles P, drop into the particle trap 8 and are discharged thence. In principle, it is possible to feed the straw particles that are freed of silicate to a glue coater and then to press the glue-coated particles into a board after forming a loose-particle mat in a press. In this embodiment shown, however, the straw particles that are freed of silicate in the first classifying stage are optionally fed to a second comminuter 10 in an additional step after being temporarily stored in a bunker 13. In this embodiment, this second comminuter is a fiberizing device in which straw fibers are produced from the straw particles for making fiberboard. This fiberizing device 10 can, in an inherently known manner, have a digester 11 (merely suggested) in which the particles are softened for example with high-pressure steam. This is followed in an inherently known manner by a refiner 12, in which the softened particles are ground into fibers. In the embodiment shown, the fibers ground in this manner do not, after appropriate drying, travel directly into a glue coater via a blow line, for example (not shown); instead, further separation of silicate particles from the straw particles or the straw fibers now produced is performed before glue-coating.

[0035] It is always possible to divide the particle stream into multiple parallel substreams and thus to work with multiple parallel classifiers. In the figures, only one classifier is shown as an example. The second classifier 14, which is merely suggested in FIG. 1, is again an air classifier. It is basically constructed in the same manner and functions in the same manner as the first classifier 3 that was already described, it being optionally possible to dispense with the coarse-material trap or stone trap in the vicinity of the second classifier. In any case, silicate particles S are again discharged and disposed of via an air outlet 7 in this second classifying stage or used for other processes. The straw fibers P that are freed of silicate S are in turn discharged via the particle trap 8 and, optionally after temporary storage in a bunker 20, fed to a glue coater 15. Even though only one glue coater 15 is shown as an example in the drawing, multiple glue coaters can be provided for parallel operation here as well. In this embodiment, this glue coater 15 is a mixer that, in terms of its construction and functionality, corresponds to the mixer described in DE 10 2009 057 916. In this glue mixer, the straw fibers are glue-coated with an isocyanate or other glue.

[0036] The glue-coated straw fibers produced in this manner and freed of silicate are now usable for making fiberboard. For that purpose, they are fed to a spreader 22 via a fiber classifier 21, for example, in which lumps of glue or the like are separated. Using this spreader 22, the glue-coated straw fibers are strewed on a conveyor belt, for example, to form a loose-particle mat and, from there, optionally after another pretreatment in a prepress, for example, the mat travels to a hot press 25 where the loose-particle mat of glue-coated straw fibers is pressed into a fiberboard. The press 25 can be a continuously operating press 25, here a dual-belt press.

[0037] According to the invention, the classifier 3 or 14 is of particular importance for the separation of silicate particles from the particle stream of the straw particles or straw fibers. The classifier is shown in FIGS. 2 and 5.

[0038] The classifier 3 or 14 is an air classifier. In this embodiment, it has a box-shaped housing 5 with the material inlet 4, the air inlet 6, the air outlet 7, as well as the particle trap 8 and the coarse-material trap 9. An upper chute 16 holding crushing rollers 17 is connected to the material inlet 4. Moreover, feed screws 18 are shown that feed the material to the material inlet 4. The material inlet 4 extends substantially over the entire width of the classifier housing 5 and is integrated into the upper wall or ceiling of the classifier housing in this embodiment shown, so that the material falls into the classifier housing from above. The air inlet 6 is integrated into the upper region of the front wall of the classifier housing. This air inlet 6 can also extend over the entire width of the classifier housing 5. The air outlet 7, which also extends over the entire width of the classifier housing, is on the rear wall of the classifier housing and then merges into at least one outlet line 27 with a reduced diameter, the stripped-out silicate particles S being discharged with the air stream via this line or lines 27. In this embodiment, output augers 29 are provided in the lower particle trap 8 with which the straw particles P that are freed of silicate are discharged and fed to discharge lines. FIG. 5 shows the flow conditions in the classifier. It can be seen that, due to their small dimensions, the silicate particles S are discharged as an aerosol with the air stream via the upper air outlet 7, while the straw particles P fall down due to gravity and into the particle trap 8. Coarse material G, such as stones, for example, falls immediately after entering the housing 5 into the coarse-material trap 9, which is also referred to as a “stone trap.”

[0039] The flow within the classifier is achieved in this embodiment by a suction device, meaning that exhaust fans are connected to the air outlet, with the effect that the supply air Z is supplied passively via the air inlet 6. In this embodiment that is shown, fresh air is supplied in the first classifying stage, while the classifying air is conducted in a circuit (not shown) in the second classifying stage, so that the moisture level can be kept constant at this stage of the process after fiberization.

[0040] Moreover, it can be seen in FIGS. 2 to 4 that the classifier housing in the illustrated embodiment is produced in a very simple manner from multiple ISO freight containers, specifically from three standard containers 28 that are arranged one above the other, each with a length of 40 ft. Such a construction has the great advantage that the individual parts can be easily transported.

[0041] The air inlet 6 can be formed very simply by open container doors. A screen or the like can be integrated into the inlet in order to prevent the entry of foreign bodies. In addition, a rain cover 26 can be arranged above the inlet 6.