DE102020005511B4 - Process for manufacturing a chipboard, plant for manufacturing chipboard and chipboard - Google Patents

Abstract

The invention relates to a method for producing chipboard from chips with a length of 1 to 60 mm, comprising the following steps: a) comminution of wood into fines, usable material and coarse material, the usable material containing at least the majority of the chips, b) fractionation of fines , usable material and coarse material according to sizec) drying at least the usable material,d) gluing at least part of the usable material,e) scattering at least the usable material to form a grit mat andf) pressing the mat to form chipboard. In order to make the manufacturing process for chipboard of the same or even higher quality more resource-efficient and cheaper, it is planned that the wood used should also include small wood with a diameter of less than 0.08 m and that at least one knife shaft chipper should be used for shredding and the fractionation should already be carried out in the wet area at a wood moisture content of around 60 to 180%.

Description

1. a) Zerkleinerung von Holz zu Feingut, Nutzgut und Grobgut, wobei das Nutzgut zumindest den größten Teil der Späne aufweist,
2. b) Fraktionierung von Feingut, Nutzgut und Grobgut nach Größe
3. c) Trocknung wenigstens des Nutzgutes,
4. d) Beleimung wenigstens eines Teils des Nutzgutes,
5. e) Streuung wenigstens des Nutzgutes zu einer Matte und
6. f) Verpressen der Matte zu einer Spanplatte.

The invention relates to a method for producing a chipboard from chips with a length of 1 to 60 mm, comprising the following steps,

1. a) Crushing of wood into fines, usable material and coarse material, whereby the usable material contains at least the largest part of the chips,
2. b) Fractionation of fines, usable material and coarse material according to size
3. c) drying at least the useful material,
4. d) gluing of at least part of the useful goods,
5. e) scattering at least the useful material to form a mat and
6. f) pressing the mat to form chipboard.

Furthermore, the invention relates to a plant for the production of chipboard for carrying out the method according to the invention.

Furthermore, the invention relates to a chipboard produced by the method according to the invention.

There are numerous publications and patent applications on the production of chipboard. The features a) to f) for the production of chipboard are provided in almost all production processes and can sometimes be used in different ways. The specified order a) to f) can also differ. In particular, the fractionation can also take place after drying or before and after.

In some cases, the wood is debarked before shredding. After that, the wood intended for use is usually chopped up into chips in a two-stage manner in that first wood chips are produced, which in a subsequent work step are broken down into chips of the desired size using knife ring flakers or mills. A disadvantage of this method is the high outlay on machinery, which leads to high investment and energy costs (space requirements, foundations, buildings, electricity consumption). In addition, the service life of the knives in a knife ring flaker is often only a few hours, which leads to frequent maintenance failures. In some cases, other chip assortments are mixed in that were produced differently and further increase the cost of shredding machines.

It should be noted that according to DE 21 35 930 A It is taught how to press the small pieces of wood into blocks in hydraulic presses before feeding them to a knife shaft flaker.

The chips obtained are usually fractionated after drying, for example in a drum dryer. For this purpose, screens with a selected mesh size are used, depending on the system output, several screens connected in parallel or in series, which ensure the different chip fractions. Dust and coarse material are sorted out, which can be shredded again if necessary. The different chip sizes are assigned to the subsequent board layers and scattered accordingly. It can be provided, for example, to provide larger chips on the inside, the so-called middle layer, and smaller chip sizes on the outside, ie the cover layers. This makes the surface of the chipboard smoother for further use (painting or coating). Thus, numerous screens, for example vibrating screens, are required to produce different chip sizes, which in turn increases the mechanical complexity. On the other hand, for example, the inside of the plate can be formed by coarse chips in order to reduce the consumption of material during manufacture and to make the plate lighter overall.

From the DE 10 2008 047 168 A1 is already the fractionation of grit by sieving known and in the field of chipboard production, it is particularly, for example, from the WO 2018/215401 A1 known to fractionate chip sizes and to use the fraction with the larger grain sizes for the production of the middle layer of a chipboard.

It is therefore the object of the invention to design the manufacturing process for chipboard of the same or even higher quality in a way that saves resources and is cheaper. The value is primarily based on the mechanical properties, in particular flexural strength, screw pull-out strength and modulus of elasticity.

With regard to the production method, the object is achieved with the features of claim 1 and in particular in that the wood used also includes small wood with diameters of less than 0.08 m and at least one knife shaft chipper is used for shredding and fractionation is already carried out in the wet area at a wood moisture content of about 60 to 180% is made.

The inventors have recognized that small wood can also be used for high-quality chipboard if a knife shaft flaker is used for shredding instead of chippers and knife ring flakers. The space requirement and the maintenance effort at knife shaft shredders Spanern are significantly lower. The new embodiment makes the tremendous difference of using only about half the energy required with choppers and knife ring flakers, and in fact only a tenth of the space required.

Knife shaft flakers also allow smaller log diameters or industrial waste wood, such as slabs, to be chipped. This is only possible to an unsatisfactory extent with knife ring flakers with trunk diameters of often well over 0.08 m with debarked wood. The diameter is defined as the circumference divided by the number Pi (π= 3.14). So-called splintering often occurs when using knife wound flakers. These are woodcut remnants that are very difficult to sort out using conventional screening technology. Some of the splinters can get into the press and cause damage, especially in continuous presses. Splinters also reduce the quality and appearance of the particleboard produced.

However, the improved possibility of using so-called weak wood with a diameter of less than 0.08 m is also significantly more cost-effective, since these types of wood are cheaper to procure. Even logs with a diameter of 0.04 m and more were tested with positive results.

It is preferred that the proportion of chips made from small wood in the chipboard is at least 30%, preferably at least 50%.

Above this size, the manufacturing process becomes particularly economical. The total proportion of the chips used from the knife shaft flaker for the chipboard should be 30 to 100%. Of course, several knife shaft flakers can also be used. For example, in many cases it makes sense to use two differently adjusted knife shaft flakers, whereby one produces chips for the middle layer and the other chips for the top layers.

It is provided with particular advantage that wood which has not been stripped of bark is also used as the wood.

Here, too, the profitable use of the knife shaft chipper can be seen, which is able to chip wood that has not been debarked into high-quality chips much better, in such a way that the bark parts are either incorporated into the chipboard or easily sorted out in a way explained later can become.

The knife shaft flaker preferably produces chips with a thickness of 0.1 to 0.8 mm.

The shape of the chips is very important for the subsequent quality of the chipboard. It influences the glue consumption, the specific weight and the mechanical properties. While knife ring flakers tend to produce matchstick-shaped shavings, knife shaft flakers tend to cut very flat, thin plates. These have a higher degree of slenderness (chip length to chip thickness), are easier to wet with glue and create a strong bond.

This is also considered to be the reason why the method is preferably used in such a way that the thin chips in the chipboard ensure a screw pull-out strength of over 1300 N in the area according to EN 320.

However, it is the case that with the conventionally most frequently used screening technology, for example with vibrating screens or roller screens, the chips of a knife shaft flaker can be fractionated more poorly than that of a knife ring flaker.

Therefore, the inventors propose, as an option but in a very advantageous manner, that the fractionation takes place at least partially with a drum screen or a star screen.

A drum screen can be found, for example, in DE3836608A1 and a star screen in the DE4415815A1 . However, the screening device downstream of the comminution device is preferably designed as a drum screen fed from the inside, which has been tested in tests and should be cleaned in particular with a rotating brush. This can be 30 to 70% of the drum length, for example. The drum through which the chipped material is sent is preferably slightly inclined in the direction of passage. It has an inner wall of the drum that is designed as a sieve. Such a drum screen with a possibly downstream hammer mill saves over €200,000 in investment costs for the board manufacturer in a chipboard production plant compared to the vibrating screens of the prior art combined with double stream mills and requires at least 30% less electrical power consumption.

With particular advantage, the mesh size of the sieve is getting larger and larger in the direction of travel, so first the fine material is discharged from the drum, at a point following in the direction of travel the usable material and at the rear end in the direction of passage the coarse material exits and can preferably be removed before gluing .

In the embodiment according to the invention, the fractionation (that is to say preferably with a drum screen or a star screen) is already carried out before drying.

Experts distinguish between the “wet area”, in which the ratio of the water mass contained in the wood to the dry mass of the wood, referred to as wood moisture content, is around 60 to 180%, and the “dry area” after drying, in which the value is around 60 to 180% usually 1.5 to 10%. In the known plants of the prior art, the fractionation always takes place in the dry area. However, the inventors have recognized the advantages that result from fractionation in the wet area, because the energy consumption is significantly reduced.

Preferably, the usable material and possibly also the fine material are separated again for different chipboard layers and fed to different bunkers. From these bunkers, the chips are passed on to the individual scattering heads assigned to the top and middle layers. Of course, the chips must be glued before spreading, which is where the use of the knife shaft flakers again proves to be an advantage. The shape of the shavings produced by the knife shaft flaker is more suitable for easy-to-design gluing via glue atomizer nozzles in a rotating mixer than the significantly narrower shavings from a knife ring flaker. These break much faster at the high rotation speeds and thus generate unwanted wood dust or fines that are too small for the spreading process. Due to their morphology, they are also finer and lead to material deposits in the mixer, which increase the cleaning effort.

In addition, a plant for the production of chipboard that works according to the method described is to be protected.

Furthermore, the chipboard is to be placed under protection, which can be produced by the method described according to claims 1 to 11.

• 1 ein Ablaufschema des erfindungsgemäßen Verfahrens,

The invention is explained in more detail below with reference to drawings showing an exemplary embodiment. It shows

• 1 a flow chart of the method according to the invention,

In the 1 an embodiment of the invention is represented by an exemplary flowchart of the manufacturing method for chipboard according to the invention. The system components essential for the process are shown in seven boxes. Also, for most cases, the order presented is the procedure followed when using the units. However, slight changes in the sequence or the addition of further units are possible and should not restrict the idea of the invention.

The knife shaft flaker 1 is an important part of the system, which, in contrast to the choppers and several knife ring flakers otherwise used, ensures a significantly cheaper manufacturing process. Such a knife shaft chipper can definitely provide a proportion of 30 to 100% of the chopped wood for the chipboard. In addition, the manufacturing process is cheaper because the knife shaft flaker can use small pieces of wood with a diameter of less than 0.08 m that have been stripped or not stripped of bark. The proportion of small wood in the new chipboard can be at least 30%, preferably at least 50%.

A drum screen 2 is provided as another important unit in the chipboard manufacturing process. This is much more energy-efficient to use than vibrating screens, for example. The drum screen is able to fractionate the chips produced directly into fines 12, usable material 11 and coarse material 13 to be sorted out. The usable material includes the chips that are used for chipboard production. These can be separated again into the chips for the middle layer of a chipboard and the chips for the top layers. Under certain circumstances, for example, fines can also be added to the top layer in order to make the surface particularly smooth.

Thus, part of the usable material 11 and the fine material 12 is preferably processed in a hammer mill 3 . In general, it applies to the flow chart that further system parts can be arranged between the individual stations that are important for the invention. For example, bunkers or reservoirs, air treatment or similar aggregates are not shown.

The chips are then dried in one or more commercially available dryers 4, for example one each for a specific size or scatter layer. The grit can then be fed from bunkers or stores to a gluing device 5, which is also known. As usual, the chips are sprayed with binding agents in a chute or a mixer drum or a blow line so that they can be firmly bonded in the later pressing process.

The chips are separated for the individual layers in different sizes, fed to a scattering station 6 individual scattering heads that use the Scatter well evenly distributed on a scatter belt and thus form a grit mat 9. This grit mat is then placed in the continuous press 7 and pressed there under pressure and at a higher temperature. Such a continuous press is marketed by the applicant under the name ContiRoll.

Due to the fact that the knife shaft flaker produces very thin (thickness from 0.1 to 0.8 mm) and not as narrow chips as a knife ring flaker, the screw pull-out strength according to EN 320 can be significantly increased and values of more than reach 1300N.

Reference List

1

knife shaft flaker

2

drum screen

3

hammer mill

4

dryer

5

gluing device

6

Spreading station with spreading heads

7

Continuous press

8th

weakwood

9

grit mat

10

chipboard

11

utility

12

fines

13

coarse material

Claims (11)

Method for producing a chipboard from chips with a length of 1 to 60 mm, comprising the following steps, a) comminution of wood into fines (12), useful material (11) and coarse material (13), the useful material having at least the majority of the chips, b) Fractionation of fines, usable material and coarse material according to size c) drying at least the useful material, d) gluing of at least part of the useful goods, e) scattering at least the useful material to form a grit mat (9) and f) Pressing the mat of grit into a chipboard (10), whereby the wood used also includes small wood (8) with diameters of less than 0.08 m and at least one knife shaft chipper (1) is used for shredding and the fractionation even before drying in the wet area is carried out at a wood moisture content of about 60 to 180%. procedure after claim 1 , characterized in that the proportion of chips made from small wood (8) in the chipboard (10) is at least 30%, preferably at least 50%. procedure after claim 1 or 2 , characterized in that not debarked wood is used as wood. Procedure according to one of Claims 1 until 3 , characterized in that the knife shaft chipper (1) produces chips with a thickness of 0.1 to 0.8 mm. Procedure according to one of Claims 1 until 4 , characterized in that the fractionation takes place at least partially with a drum screen (2) or a star screen. Procedure according to one of Claims 1 until 5 , characterized in that the fractionation with a drum screen (2) or a star screen includes the disposal of coarse material (13). Procedure according to one of Claims 1 until 6 , characterized in that coarse material (13) is sorted out before gluing. Procedure according to one of Claims 1 until 7 , characterized in that at least part of the fines (12) is used as a top layer additive. Procedure according to one of Claims 1 until 8th , characterized in that the chips for a top layer and a middle layer of the chipboard (10) are supplied to separate bunkers and then separately provided with glue. Plant for the production of chipboard according to the method according to one of Claims 1 until 9 , comprising at least one knife shaft chipper (1), a drum screen (2), a dryer (4) for chips, a gluing device (5) for chips, a scattering station (6) and a continuous press (7). Particle board manufactured according to any one of Claims 1 until 9 .

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