Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
  • B27N3/08—Moulding or pressing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
  • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
  • B27N3/00—Manufacture of substantially flat articles, e.g. boards, from particles or fibres
  • B27N3/08—Moulding or pressing
  • B27N3/24—Moulding or pressing characterised by using continuously acting presses having endless belts or chains moved within the compression zone

Definitions

• the present invention relates to a method of producing lignocellulosic boards according to the preamble of claim 1.
• Methods of producing boards of lignocellulosic material are well known and have significant practical applications.
• the manufacturing includes the following main steps: breaking up of the raw material to particles having a suitable size and/or fibers, drying to a predetermined moisture ratio and gluing of the material before or after the drying, forming of the glued material into a mat which may be constructed of several layers, possibly cold pre-compressing, pre-heating, water spraying of surfaces etc. and heat compressing under pressure and heat in a stroke compressor or a continuous compressor until the board is finished.
• the compressed material is heated mainly by using heat coils from adjacent heating plates or the steel bands. These have a temperature of 150-200° Celsius depending on the type of product that is being compressed, the type of glue used, desired capacity etc.
• the moisture in the material is evaporated closest to the heat sources so that a dry layer is developed in this area and the steam front gradually moves towards the center of the board from each side as the compression continues.
• the temperature in this layer is at least 100° Celsius which initiates the curing of conventional glues.
• the steam front has reached the center, the temperature at the center has reached at least 100° Celsius and the boards even starts to cure at its center so that the compression can be stopped within a couple of seconds.
• MDF Medium Density Fiberboard
• SE patent 469,270 regarding continuous compression
• SE patent application 93 00772-2 regarding a one step stroke compressor.
• the methods that have been developed for MDF are now also used, at least partially, for other board types.
• a compressor must apply a high surface pressure at a high temperature. This is not a problem for non-continuous compression in a so called stroke compressor but such compressors have other drawbacks such as worse thickness tolerances etc.
• stroke compressors When continuous compressors are used, the requirement for high surface pressures and high temperatures at the same time have led to expensive high precision solutions with regard to the roller felt between the steel band and the heating plate positioned below.
• the method of providing heat to the board via heat coils makes the heating relatively time consuming which results in long compression lengths (large compression surfaces).
• the compression time required has been substantially increased within the period due to high pressure and heat conduction requirements. All this leads to a substantially lower capacity, or in the alternative greater compression surface, of a steam compressor and requires greater compression forces compared to the forces required if an even density was desired.
• a soft surface layer having a lower strength, unacceptable paintability etc. are created by using all of the above mentioned manufacturing methods which means that this layer must be removed by grinding. Therefore, a material loss of 5-15% is obtained depending on the type of board, thickness etc. Even for the manufacturing of boards using a continuous process heating by introducing steam has been known for a long time. See for example EP 383 572, US 2 480 851, GB 999 696, DE 2 058 820, De 3 640 682, DE 4 009 883 and AU 57390/86.
• the steam can be injected into the material mat by using a steam box but this has certain drawbacks.
• an apparatus having perforated compression rolls have been developed which serves as a steam introduction member. Such an apparatus is described in SE 502 810.
• SE 502,272 describes a method that uses the advantages of steam heating for achieve the desired density profiles of the finished board.
• the compression is performed in two steps wherein the mat in the first step is compressed to a moderate density having a substantially even density profile across the thickness thereof.
• the mat is compressed to a higher density where the density profile is heterogeneous so that the surface layer has a higher density than the middle portion of the board.
• the board is either fully cured or partially cured.
• An object of the present invention is to remove the drawbacks that are associated with the prior art technology for manufacturing fibrous boards having a desired density profile and to take advantage of steam heating the fiber mat. According to the present invention, this has been achieved through a method described in the preamble of claim 1 and the steps included in the body of the claim.
• the fiber mat is provided with a heterogenous structure wherein the surface layer is made soft and cured by introducing steam while the middle layers are substantially un-affected.
• the conditions have been created so that the subsequent calibration compression makes a board having a certain density profile by permitting this to occur at a greater thickness compared to what is accomplished at pre-compression so that the un-affected middle layer is permitted to expand under the surface layer that substantially maintains its density.
• the density of the middle layer is thus lower than the density of the surface layer.
• the mat should be pre-compressed at the time of or immediately before the steam is injected.
• the method is particularly adapted to continuous production of boards wherein the steam is preferably introduced at the roller or at the rollers that are used for the pre-compression.
• the thickness of the surface layer having an increased density, can be brought about by regulating the amount of steam introduced so that the characteristics of the board with regard to, for example, bending strength and treatability can thus be adapted to the different applications.
• fig. 1 is a schematic cross sectional view along the length of the mat and board at the time of compression
• fig. 2 is an enlarged cross sectional view through a board produced according to the present invention
• fig. 3 is a diagram illustrating the density profile of the board shown in fig.2
• fig. 4 is a schematic cross sectional view of a roller through which the steam is introduced
• fig. 5 is a cross sectional view of a portion of the roller of fig.
• fig. 6 is an axial cross sectional view of the roller of fig. 5
• fig. 7 is a schematic cross sectional view illustrating the different treatment steps according to a preferred embodiment of the present invention.
• Fig. 1 shows how a fiber mat 1 is conveyed in the direction of the arrow A and is compressed to a board 21.
• the mat is pre-compressed by a pair of rollers 2, 3 to a density that is close to the desired surface density.
• Steam is introduced through the rollers 2, 3 in a way that is explained in more detail below.
• the amount of steam that is introduced through the rollers 2, 3 is carefully adjusted so that the steam penetrates and only heats the surface layer of the mat.
• the thickness of this surface layer is proportional to the added amount of steam and can therefore be regulated by the amount of steam.
• the surface layers are softened and cured by the heating of the steam introduced.
• the layer disposed in the middle of the mat, to which the no steam has penetrated, is unaffected.
• the mat After the mat has passed through the pair of rollers 2, 3 the mat goes in to a calibration zone where the mat is calibrated to a desired finished thickness. This thickness is greater than the thickness of the board when it was passed through the rollers 2, 3 so that the unaffected middle layer is expanded. During the passage in this zone, heat is introduced to such an extent that the middle layer is cured.
• the roller compressors 22 can be a different apparatus, for example, a conventional roller felt or a hydraulic felt. The result is that the finished board obtains a surface layer having a higher density than the middle layers.
• heat is introduced and the board is compressed while the heat is added until the middle layer is cured to obtain such a strength that it can withstand the existing expansion force.
• Both the surface layers 21a and 21b have a density of about 800 kilogram/cubic meter while the density of the intermediate layers is about 600 kilogram/cubic meter. This is illustrated in the diagram of fig. 3. Both or either of the rollers 2, 3 can be designed as is described in SE 502,810 and as is illustrated in figs. 4, 5, and 6.
• the compression and injection roller 2 that is shown in fig. 5 is constructed with a perforated casing surface 6 for delivering steam to the mat 1.
• An axial channel system 7 is disposed inside the casing surface 6 around the roller 2.
• the channel system 7 is adapted to distribute the steam over the roller 2 and thus along the width of the mat 1.
• An adjustable sliding shoe (fig. 6) is arranged to sealing engage an end of the roller 2 to introduce steam into the channel system 7.
• the introduction of steam is thus performed to a limited section (fig. 4) of the roller 2 where the mat 1 is compressed.
• the limited sector 9 is surrounded at both sides, as seen in the periphery, by sealing zones 10 where the roller 2 is in contact with the mat 1.
• the channel system 7 can be closed at the opposite end of the roller 2.
• a sliding shoe 8 can be disposed at each of the ends.
• the sliding shoe 8 is held in place by an adjustable stand so that the sliding shoe is adjustable along the direction of the periphery. In the way, the position of the injection sector 9 can be varied.
• the sliding shoe 8 is preferably includes a replaceable wear part 14 made of a low friction material that bears against a treated surface on the end of the roller 2.
• the sliding shoe 8 is held and pushed against the end of the roller 2 by, for example, springs, compressed air or hydraulically, so that any leakage in the sealing surface is minimized.
• the sliding shoe 8 can be constructed with one or more channels 11, 12, 13 that can have different surface areas. Even replaceable wear parts 14 having different openings defined therein may be used such as a sliding plate having an opening that can be varied. Thus, the size of the injection sector 9 can be varied. What is more, different flows and pressures can be maintained in different parts of the injection sector
• the channels of the sliding shoe 8 can also be used for cleaning and suction.
• Fig. 6 schematically shows the contact surface of the sliding shoe 8 against the end of the roller 2.
• the sliding shoe 8 is equipped with injection channels 11 for steam, cleaning channel 12 and suction channel 13.
• the perforated casing surface 6 on the roller 2 can be a stamped or drilled sheet metal having the shape of rings that have been heat shrunk onto the roller.
• Axial support moldings 15 for the sheet metal can be shaped into the casing sheet metal 16 on the roller by milling or casting or the sheet metal may be constructed as separate moldings that are attached to recesses in the casing sheet metal 16. These moldings can at the same time limit the channel system 7 disposed inside the casing surface 6.
• the openings of the channel system 7 at the end of the roller that have not been covered by the sliding shoe 8 can be sealed by pressing an adjustable sliding ring made of a low friction material against the end.
• Fig. 7 shows a method according to the present invention including the different treatment steps that preferably precedes and follows the actual compression.
• the material mat 1 is brought to a predetermined temperature, moisture content and density.
• the finished compressed board 21 is passed through an after conditioning zone 20. Furthermore, gases are collected in this zone, for example, formalaldehyde that is emitted from the compressed board.
• gases are collected in this zone, for example, formalaldehyde that is emitted from the compressed board.
• the board is also permitted to cool down in the conditioning zone because the high temperature of the board generated from the compression makes it plastic to a certain extent which makes it difficult to handle.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Wood Science & Technology (AREA)
• Forests & Forestry (AREA)
• Dry Formation Of Fiberboard And The Like (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=20399083

Family Applications (1)

Country Status (11)

Cited By (7)

Families Citing this family (5)

Citations (3)

• 1995
  • 1995-07-27 SE SE9502714A patent/SE504637C2/sv not_active IP Right Cessation
• 1996
  • 1996-07-15 TW TW085108553A patent/TW396101B/zh active
  • 1996-07-22 MY MYPI96003004A patent/MY132237A/en unknown
  • 1996-07-24 AR ARP960103710A patent/AR003012A1/es unknown
  • 1996-07-25 EP EP96925239A patent/EP0842022A1/en not_active Withdrawn
  • 1996-07-25 CA CA002226749A patent/CA2226749A1/en not_active Abandoned
  • 1996-07-25 WO PCT/SE1996/000975 patent/WO1997004933A1/en not_active Application Discontinuation
  • 1996-07-25 JP JP9507526A patent/JPH11510115A/ja active Pending
  • 1996-07-25 AU AU65395/96A patent/AU6539596A/en not_active Abandoned
  • 1996-07-25 PL PL96324651A patent/PL324651A1/xx unknown
  • 1996-07-26 ZA ZA9606391A patent/ZA966391B/xx unknown

Patent Citations (3)

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