NZ505841A

NZ505841A - Double strap press for continuously producing materials in the form of plates

Info

Publication number: NZ505841A
Application number: NZ505841A
Authority: NZ
Inventors: Peter Beck; Heinz-Peter Wolff; Bernd Heimes
Original assignee: Valmet Panelboard Gmbh
Priority date: 1998-03-10
Filing date: 1999-03-09
Publication date: 2002-03-28
Also published as: WO1999046111A1; DE59902560D1; AR014689A1; EP1062087B1; CA2322418A1; EP1062087A1; AU3032599A; CA2322418C; ATE223304T1

Abstract

A double strap press (100) having a pressing section (3), in the rear portion (3") whereof is driven a heat transferring medium through channels extending transversely relative to the belt (4), of the support plates (26", 27") of the moulding straps (1, 2). The heat transferring medium is not heated but partially releases its heat into a heat exchanger (50) to be used in another unit (53), thereby improving the heat balance of the installation comprising the double strap press (100). The moulding straps (1, 2) rest on roller chains (30', 30"). The roller chains (30', 30") are subdivided in the belt (4) forward motion direction (16), such that the heat transfer from the pressing section (3) front portion (3') to its rear portion (3") is reduced.

Description

' ; 11 y Revised Specification Pages 1 - 7a PROCESS AND DOUBLE-BELT PRESS FOR THE CONTINUOUS PRODUCTION OF BOARD MATERIALS The invention relates to a process according to the 10 preamble of Claim 1 and a double-belt press according to the preambles of Claims 4 and 8, respectively.

Such a process and such a double-belt press are known, for example, from DE 21 57 746 C3 or DE 39 04 982 Cl. 15 Provided in the press line are supporting plates, on which the forming belts are supported via co-running roller chains. The supporting plates are braced by strong bearers which are arranged transversely to the track above and below the respective supporting plates and are 2 0 held together by spindles outside the width of the track.

Provided in the supporting plates, extending transversely to the track, are bores which form channels for carrying a heat-transfer medium, generally a thermal oil. The 25 channels follow one another frequently in the direction of travel of the track. Successive channels are interconnected by U-shaped pipe elbows mounted at the edges of the supporting plates, so that the heat-transfer medium follows a zig-zag course transverse to the track, 3 0 thus improving the uniformity of the heat transfer. A plurality of successive transverse bores in the direction of travel of the track form a group fed in common with heat-transfer medium.

In producing board materials, particularly particle boards and similar materials, a substantial amount of REVISED PAGE intellectual property office of n.z. 0 5 DEC 2001 received heat must be introduced into the feed material in the first zone of the press line, in order to carry out the curing reaction of the binder. In this context, the moisture contained in the feed material serves to 5 transfer the heat into the material and plastify it. In a downstream, i.e. subsequent, section situated toward the \ end of the press line, the heat input no longer needs to be so great, but rather, the primary concern here is the maintenance of the spacing between the forming belts 10 perpendicular to the track for a given time during which the material is cured, so that a calibrated board panel emerges from the press line. By maintaining the thickness in the downstream section, bonds which have been introduced within the board material are not torn apart 15 again by premature relief of pressure before curing is complete, which would weaken or even destroy the board material.

In the installation known from DE 39 04 982 CI, the 2 0 forming belts between which the board material is formed are supported, rolling via roller chains, on the flat supporting surface of a supporting structure located in the press line above the upper forming belt and below the lower forming belt. Even if the supporting structure is 25 no longer to be positively heated in the downstream region of the press line, a substantial amount of heat is transferred into the downstream section of the press line by the advancing forming belts with the roller chains and the web of board material.

Thus, a large part of the quantity of heat introduced into the board panel in the first zone of the press line is transported by the board panel, the forming belts and, in particular, the roller chains into the downstream REVISED PAGE ^ ^OWCE'o/'N!'^ 0 5 DEC 2001 section of the press line, and is radiated there into the surroundings, unused. Often no heat input is required any longer for the board panel itself in the downstream zone of the press line. On the contrary, it is sometimes even 5 desirable to already cool the board panel in the press to a certain extent.

In order to have sufficient heat available in the first zone of the press line, it is necessary to operate there 10 to an extent with an excess of heat which can no longer be used in the downstream part of the press line, and increases the energy costs.

The object of the invention is to reduce the energy costs 15 of an installation including the double-belt press.

This objective is achieved from the aspect of process by the invention described in Claim 1. 2 0 Using the invention, the heat transported into the downstream section from the upstream section by the board material being formed, the two forming belts and the chains can at least partially be kept from getting lost, thus improving the heat balance in the overall 25 installation. In this context, there is also an additional effect which improves the environmental compatibility of the operation of the double-belt press: the extraction of heat from the heat-transfer medium of the downstream section is synonymous with cooling it. 3 0 Thanks to the reduced temperature in the downstream zone of the press line resulting from the withdrawal of heat, the evaporation of formaldehyde originating from the binder and the escape of other organic vapors which can be inflammable, e.g. from waxes, are reduced.

REVISED PAGE intellectual property office of N.z. 0 5 DEC 2001 received In many cases, it is possible to dispense with a greater input, or even any input of heat in the downstream section, since the forming belts with their higher temperature continue to transport heat into the interior 5 of the board.

In the process according to Claim 2, the heat extracted in the downstream section of the press line is used at another point in the process for manufacturing the board 10 materials themselves, for example, for pre-heating or drying the particles from which the panel of board material is formed, or for heating water and/or thermal oil.

In another embodiment of the process according to Claim 3, the heat obtained in the downstream region of the press line can be used, for example, for heating the factory installation in which the double-belt press is installed, or even the associated offices, that is to 20 say, outside of the actual board material manufacturing process.

In its apparatus aspect, the invention is embodied in an installation according to Claim 4.

In this connection, the "other aggregate" in which the recovered heat is employed can be the already mentioned aggregate, upstream of the double-belt press, for forming and pre-treating the feed material, or the heat exchanger 3 0 for warming water and/or thermal oil or a similar device.

In this context, the downstream section of the press line is provided with completely unheated heat-transfer medium.

REVISED PAGE intellectual property office of n.z. 0 5 DEC 2001 received Claims 5 and 6 focus on the possibilities for utilizing the heat obtained in the downstream section of the press line.

In another aspect for achieving the objective of reducing the energy costs, the transfer of heat into the downstream section of the press line is reduced in that, in each case, a continuous roller chain or a group of such roller chains side-by-side is not used for the 10 entire press line and for each forming belt, but rather, according to Claim 7, a chain separation is carried out at a suitable location in the press line, so that the first section of the press line has its own roller chains and the downstream section of the press line has further 15 roller chains separate from them. The portion of heat otherwise transported into the downstream section of the press line by continuous roller chains thereby remains largely in the first section of the press line and does not become lost through the downstream transport. A 20 temperature drop of 20°C or more in the downstream section of the press line can be achieved solely by the separation of the roller chains. Meanwhile, the first section of the press line can be kept at the necessary temperature with a reduced application of heat.

The chain separation in double-belt presses is implied by itself from U.S. 4,334,468, however, in that case, it is only from the aspect of being able to supply or extract different amounts of heat to and from successive sections 30 of the press line in the direction of travel, but not from the aspect of heat utilization.

In a double-belt press of another type, which is used for drying fiber webs and is known from WO 97/39187, one belt intellectual property REVISED PAGE office of N.Z. 0 5 DEC 2001 received is heated with vapor and the other is cooled with water. Running between the fiber web and the cooled belt is a felt web into which the water condensed on the cooled belt passes. The heat from the cool water is transferred 5 in a heat exchanger to another water which, with its then increased temperature, can be used as process water in a paper or cardboard machine.

The separation of the roller chain into a front section 10 and at least one following section also has significance, independently of the question of the other use of the heat recovered in the last section of the press line.

Namely, in this manner, gaseous components of the board 15 material can already be partially evaporated prior to reaching the actual end of the press line. This applies not only to water vapor, formaldehyde and the like, but also to the combustible vapors mentioned, for example, from waxes and the like used in the board material which, 20 if they are only able to emerge altogether in large quantity at the actual end of the press line, have already ignited there and led to fire accidents. In addition, the mere reduction of the vapor pressure at the separating point by partial discharge to the side, which 25 is possible due to the short-term "breathing out" of the board panel as a consequence of the temporary absence of the support of the forming belts at the separating points and therewith accompanying reduction in the resistance to flow for the vapor, has great practical significance, 30 just like the temperature reduction achieved in the final section of the press line.

However, according to the present invention, the separating points of the roller chains on at least one REVISED PAGE intellectual property office of n 7. 0 5 DEC 2001 received V;'' o side of the panel are not disposed on a straight line running at 90° with respect to the direction of travel, transversely to the panel (Claim 8).

It may be that, according to Claim 9, the separating points on at least one side of the panel can be disposed on a straight line which, however, runs at an angle other than 90° with respect to the direction of travel; according to Claim 10, the angle can be different on both 10 sides, as well.

However, according to the embodiment as recited in Claim 11, the separating points do not need to lie on a straight line, but rather - viewed in the direction of 15 travel - can be in different positions, so that the roller chain field is jagged or lacerated, so to speak, at its boundaries situated in the longitudinal direction. In this way, abrupt alterations in pressure are avoided at one point - viewed in the direction of travel -20 simultaneously over the entire width of the panel.

This can be achieved in particular in the design according to Claim 12, in which the successive roller chain fields are, as it were, interlocked like a zipper.

Viewed in the direction of travel, the separating point at the final section of the press line can lie at the same point for the respective upper forming belts and for the respective lower forming belts. However, then the 30 upper forming belt and the lower forming belt bulge simultaneously outwards and there is a momentary "breathing out" of the panel on both sides, which is unacceptable for the formation and maintenance of the bonds developing in the panel.

REVISED PAGE intellectual property office of n.z. 0 5 DEC 2001 received 1 -7a- An important refinement of the invention, both with and without recovery of heat, is that, according to Claim 13, the interruptions in the roller chains both sides of the panel are staggered in the direction of travel of the panel.

This makes it possible to prevent the formation of an outward bulge of the panel on both sides between the forming belts, and the partial discharge of, for instance, trapped gases can take place to an extent by increments, first upwards and the other time downwards.

It is of no significance whether the separating point in the roller chains of the upper forming belt is situated ahead of or behind the separating point of the lower forming belt in the direction of travel of the panel.

Experiments have shown that particle boards produced according to the invention exhibit significantly better technological values than particle boards produced according to known methods. intellectual property office of n.z.

REVISED PAGE 0 5 DEC 2001 received

Claims

What is claimed is: -8-

1. A process for the continuous production of particle boards from board materials composed of particles held together by a binder cured under heat and pressure in a double-belt press (100) , in which process the particles provided with the binder are sprinkled on a horizontal run of a conveyor belt to form a feed material (4') and are cured under heat and pressure in a press line (3) between upper run (2') of a metallic, continuously circulating, lower forming belt (2) and lower run (1'), moving in synchronism in the direction of advance travel (16) of the double-belt press (100) , of a metallic upper forming belt (1) to form a panel (4) yielding the board material, the operating pressure and the heat needed for forming being transferred in the press line (3) from supporting structure (26, 27) to the forming belts (1, 2) and from them to the feed material (4'), and the heat being introduced into the supporting structure (26, 27) by a heat-transfer medium conducted through channels therein, characterized in that the heat-transfer medium for a downstream section (3") of the press line (3) is not heated, and that in this section (3"), heat transferred to the heat-transfer medium in the upstream region of the press line (3) is extracted from the heat-transfer medium and employed outside of the press line (3) .

2. The process as recited in Claim 1, characterized in that the heat extracted in the downstream section (3") of the press line (3) is employed at another point in the process.

3. The process as recited in Claim 1, . NTEUKTUAL pl'°5EKr' REVISED PAGE I OFFICE OF N.Z. I 3 JAN 2002 received -9- characterized in that the heat extracted in the downstream section (3") is employed outside of the process.

4. A double-belt press for the continuous production of particle boards from board materials composed of particles held together by a binder cured under heat and pressure, having two metallic forming belts (1, 2) circulating continuously in a vertical plane, of which the upper run (21) of the lower forming belt (2) and the lower run (1') of the upper forming belt (1) overlie one another in a press line (3), are supported against a supporting structure (26, 27) and press together the feed material (41) in the press line under the action of heat and pressure, and having channels provided in the supporting structure (26, 27), through which the heat-transfer medium can be conducted, characterized in that the channels of a downstream section (3") of the press line can be supplied with unheated heat-exchange medium and are connected to a heat exchanger (50), and in it, heat extracted from the heat-transfer medium of the downstream section (3") is transferrable to another aggregate (53) not belonging to the press line (3).

5. The double-belt press as recited in Claim 4, characterized in that the other aggregate (53) is an aggregate connected upstream of the double-belt press (100).

6. The double-belt press as recited in Claim 4, characterized in that the other aggregate is an aggregate REVISED PAGE intellectual property office of n.z. 2 3 JAN 2002 received -10- independent of or separate from the process for continuous production of particle boards and the like from board materials composed of particles held together by a binder cured under heat and pressure.

7. The double-belt press as recited in any one of Claims 4 through 6, characterized in that provision is made between the forming belts (1,2) and the supporting plates (26, 27) in the press line (3) for co-advancing, continuous roller chains (30) which transfer the pressure and heat from the supporting plates (26, 27) to the forming belts (1,2), and that roller chains (30") of the downstream section (3") are separate from the roller chains (30) of the previous section (3') of the press line (3) which are disposed on the same line in the direction of travel.

8. A double-belt press for the continuous production of particle boards from board materials composed of particles held together by a binder cured under heat and pressure having two metallic forming belts (1, 2) circulating continuously in a vertical plane, of which the upper run (21) of the lower forming belt (2) and the lower run (l1) of the upper forming belt (1) overlie one another in a press line (3), are supported against a supporting structure (26, 27) and press together the feed material (4') in the press line under the action of heat and pressure, having channels provided in the supporting structure (26, 27), through which the heat-transfer medium can be conducted, and having continuous roller chains co-advancing between the forming belts (1, 2) and the supporting REVISED PAGE intellectual property office of n.z. 2 3 JAN 2002 received -11- 41 plates (26, 27) in the press line (3) and transferring the pressure and heat from the supporting plates (26, 27) to the forming belts (1, 2), and of which, roller chains (30") of the downstream section (3") are separate from the roller chains (30') of the previous section (3') of the press line (3) which are disposed on the same line in the direction of travel (16) characterized in that the separating points of the roller chains (301, 30") on at least one side of the panel (4) are not disposed on a straight line running at 90° with respect to the direction of travel (16).

9. The double-belt press as recited in any one of Claims 4 through 8, characterized in that the separating points of the roller chains (30', 30") on at least one side of the panel (4) are disposed on a straight line (31) running at an angle other than 90° with respect to the direction of travel, and running transversely to the panel (4).

10. The double-belt press as recited in Claim 9, characterized in that the angles on the two sides of the panel are different.

11. The double-belt press as recited in any one of Claims 4 through 8, characterized in that the separating points of roller chains (30', 30") adjacent to one another in the transverse direction of the panel (4) are disposed on at least one side of the panel (4) at different heights -viewed in the direction of travel (16).

12. The double-belt press as recited in Claim 11, characterized in that the separating points of at least REVISED PAGE intellectual property office of n.z. 2 3 JAN 2002 received -12- one roller chain (30', 30") - viewed in the direction of travel (16) - are set back with respect to the roller chains (30', 30") adjacent in transverse direction, and the roller chain (30', 30") of the other section disposed on the same line in the direction of travel (16) engages in the gap.

13. The double-belt press as recited in any one of Claims 4 through 12, characterized in that the separating points (28*, 29') of the roller chains (301, 30") on the two sides of the panel (4) are staggered in the direction of travel (16) of the panel. 303732 intellectual property office of n.z. 2 3 JAN 2002 received