DE19858125A1 - Continuous press for wood or plastics board materials has a structured press stretch divided into part-sections for heating and cooling with controlled conditions according to the materials - Google Patents

Abstract

The continuous press assembly, for the production of wood chip- and fiberboards, and plastics boards, has a press stretch (L) which is divided into a heated press stretch of 50-75% of the length, a heated/cooled press stretch of 15-25% of the length, and a press cooling stretch of 10-25% of the length. Each section has its press plate system with a recirculating low friction unit (21,22). The press heated/cooled stretch of the continuous press assembly has a single or multiple structure, where the segments (S1,S2...) can be heated and/or cooled. A low friction support is at each wedge-shaped path (TB) section between part press sections. The low friction units are rolling rods (22) across the press width, carried by chains (21), or they are roller bearing rolling carpets. The low friction supports between the press part-sections (I-IV) are rotating roller bodies or roller carpets, static support rollers, sliding shoes, hydrostatic press cushions or air/steam cushions. The low friction units between the press plates (17,18) and the steel belts (13) are hydrostatic cushions or air/steam cushions, at one or more cooling press part-sections (I-IV), are sliding claddings, an air/steam cushion or a hydrostatic cushion at the press plates (17,18). The press cooling stretch is switched on by the control, within the press heated/cooled stretch, when 85-95% of the bonding agent reaction temperature has been achieved at the center of the board material. An Independent claim is included for the operation of the continuous board press assembly, where the heat from the steel belts during the cooling action is returned through a heater. Preferred Features: The temperatures for the steel belts and the low friction units are set according to the bonding agent setting temperature at <= 120 deg C for wood boards and <= 100 deg C for plastics boards. The final moisture content in the finished pressed board material is set by the cooling stretch at 0-3% below the initial moisture content level.

Description

The invention relates to a continuously operating press Manufacture of wood-based panels and plastic panels after Preamble of claim 1 and on methods for the production of Wood-based panels and plastic panels according to claims 6 to 8.

Such a continuously operating press, from which the invention is based, is known from DE-OS 29 22 151.

In the conventional production of wood-based materials, for example with resin binders based on phenol-formaldehyde or urethane-formaldehyde, the H ₂ O moisture introduced into the chip or fiber mat is preferred as the heat transfer medium into the core through the transition of this moisture into the vaporous state of matter the mat (plate) is used, the reaction start temperature of the binder (glue) depending on the plate thickness along the pressing section being reached sooner or later in the middle of the plate. This steam pressure, which still acts in the finished plate at the end of the continuous pressing process, is in equilibrium or imbalance with the transverse tensile strength generated in the plate by the curing process. For example, if the production speed in the continuously operating press is too high, the plate will be destroyed by steam bursts when leaving the continuously operating press due to the imbalance of a plate that has not yet been completely glue-set and the increased steam pressure.

General disadvantages of the conventional continuously operating pressing process without an additional cooling zone is therefore the risk of bursting due to excessive steam pressure acting in the hot plate. An evaporation effect within such a continuously operating press is achieved by a press steam or press pressure relief section. A disadvantage of such a process control is necessary to state that escapes through the input pressure gradient to the atmosphere outside the continuously operating press steam, that is, the disk is moisture (H ₂ O) withdrawn in the range of 2% to 3%, which is unfavorable in view of the swelling behavior and thus the utility value of the wood-based panel, especially in climatic zones with a high percentage of air humidity.

On the other hand, to generate a heat flow there is always a temperature gradient necessary. At the end of the heating section, this gradient is positive, that is, that Pressed material is lower in temperature potential than the steel belt, roller bars and the heating plates, whereby heat is supplied to the pressed material. When entering the direction of the temperature gradient must first be reversed in the cooling zone be done before cooling the pressed material in the case of a negative gradient can. This inevitably leads to a delayed and therefore pathetic offset insertion of the cooling of the material to be pressed and moreover only to one slow cooling effect.

As is known from DE-OS 29 22 151, separate arrangements for the heating and cooling zone area have been used to date in industrial practice. Each of these heating and cooling zones has autonomous circulation systems for the rolling support elements between the heating and cooling plates and the steel belts with the advantage of efficient energy use for each of these separate process areas. The disadvantage of this continuously operating press is the short-term pressure reduction to zero N / mm ² in the transition area of the return of the hot roller support elements at the end of the heating section and the inflow of the cold roller support elements (roller bars or chain carpet) at the beginning of the cooling section. This can be particularly critical at slow transport speeds in the production of thick boards because, for example, in wood-based boards, the steam pressure in the core of the board does not cause adhesive bonds that have not yet hardened to burst, meaning that the physical properties of the product are restricted. Another major disadvantage is the fixation on only one optimal parameter setting, for example the production speed for a certain plate thickness. The disadvantage of this continuously operating press is that there is still a fixed assignment within the pressing section between the heating and cooling areas. This means that the system with fixed heating and cooling zones is generally uneconomical when used for a wider range in the production of thin (2.5 mm) plates to thick (38 mm) plates.

This system with separate roller body circulation results in one abrupt reversal from heating to cooling. However, this has the disadvantage a too high initial cooling, causing a high in the pressed material Temperature gradient arises, which in turn leads to harmful shear stresses can lead, which can destroy already set glue bridges. The high initial cooling is system-related and is due to the fact that the Roll body removed from the system at the end of the cooling section, cooled to a great extent and then fed back at the beginning of the cooling section. There they are initially significantly colder than the steel strip and the product and cause a shock-like initial cooling.

The invention has for its object a continuously operating press to create with the cooling within the press section optimally to the Adapted to the needs of the respective production or product can be and with the further along the pressing section of the heating and Cooling process on and within the mat can be controlled so that the overall efficiency of the continuously operating press increased and the physical utility value of the plates produced the desired Requirements can be adapted exactly as well as production security against bursting by monitoring control / regulation of the steam pressure improve.

The solution to this problem is that the division of the pressing section L into a press heating section L _H with a share of 50% to 75%, a press heating cooling section L _{H, K} with a share of 15-25% and a press cooling section L _K with a share from 10% to 25%, each section L _H , L _{H, K} , L _K each having its own press plate area with circumferential friction-reducing elements, the press heating and cooling section L _{H / K is} single or multiple and the segments of which can be heated and / or cooled are executed and a friction-reducing support device is arranged in each wedge-shaped section T _B between two sections.

With this structure of the continuously operating press according to the invention, the press heating section L _H or the press cooling section L _K can be targeted and exactly according to the thickness of the material to be pressed or the thickness of the finished plate, according to the reaction temperature of the binder and in alignment with the consistency of the straight Spreading material coming from the press heating cooling section L _{H, K can be} extended or shortened.

In order to achieve this, both the starting point of the cooling must be variable be designed, as well as the required technological cooling rate can be controlled specifically and over the length of the cooling section.

The cooling can thus be variable depending on the material to be pressed, the chip / fiber glue culture or the plastic used and the permeability behavior of the chip, fiber or granule geometry and the production speed set according to the invention, either from the pressed part II or the pressed part III and can be set from the individual segments S ₁ , S ₂ , S ₃ or S ₄ . As a result, the continuously operating press and the method according to the invention achieve a greater overall efficiency and the physical utility value of the plate produced can be adapted to the desired requirements, since the mechanical-technological properties of the individual cross-sectional areas can be influenced better than before.

The controlled cooling process also causes a vapor pressure drop, which in comparison to the conventional continuous press Activation of a steam pressure relief section with approximately 10% of the total Press section at the end of the press section is no longer necessary, that is approx 10% of the press section is used to increase production output to disposal. Since there is still a risk of space in the finished plate is excluded, due to the lower vapor pressure at the end of the Press cooling section the process speed of the continuously working Press can be increased by approximately 10% to 15%. So far this has not been the case possible, because in the continuous process of the continuously working press, in Regarding the risk of bursting with an additional safety value production had to be driven safely. Overall, this results in one Production output increase of approximately 20% to 25%.

Contrary to the previous and prevailing opinion, the teaching of the invention is not to start the cooling process for reducing the vapor pressure inside the pressed material mat only after the binder has completely hardened over the plate cross-section, but with cooling on the surfaces of the pressed material mat as soon as 85 % to 95% of the reaction temperature T _R required for the hardening of the binder used to begin in the center of the material to be pressed T _M. That means, as knowledge of the invention and solution of the problem, the following must be stated:
Due to the steadily increasing heat content inside the material to be pressed, the heating for the partial pressing section is switched off and the press cooling is switched on before the curing temperature of the binder used in the material to be pressed T _{M is} reached.

The technical application of the invention brings about a drastic reduction the steel strip temperature and thus the surface temperature of the Pressed goods. As a result, the binder (glue) is in the top layers exposed to extremely high temperature loads far less in time. So far, this had the degradation (decay) of the binder and thus the Reduction of the bending strength in the finished plate and is in the Usually compensated with the excessive addition of binder. As a result So can higher bending strengths or with less glue same bending and transverse tensile strengths can be achieved for the finished product.

The controlled cooling of the steel strips at the end of the press cooling section to 120 ° Celsius to a minimum of 100 ° Celsius has the further advantages that the inlet temperature of the steel strip in the press circulation is also greatly reduced and that from the inlet to the pressing process under high pressure of approximately 3 to 5 N. / mm ² and a high temperature of 220 ° Celsius no uncontrolled pre-hardening of the pressed material top layers can take place. This results in another advantage of reducing the grinding allowance by ≧ 20%.

The friction reducing elements can be made in a known manner Width of the roller bars, rolling elements or pipes reaching the press plates consist.

Another useful arrangement is that in the outgoing part the continuously operating press, in which there are no longer large pressures are required, the friction-reducing elements between the press plates and the steel strips of one or more cooling section sub-presses II, III, IV ff as a sliding surface or as an air or steam cushion or Liquid sliding surface are formed on the press plates. This can especially in overdetermined applications with low pressure be associated with cost advantages in the calibration area.

The cooling according to the invention is also in chipboard / fiberboard Combination with thermoplastic as a binder with advantages applicable. Such combined materials as wood and thermoplastic Plastic in the quantity distribution of, for example, wood chips from 75% to 50% or thermoplastics from 25% to 50% preferably come in Recycling process used. The basic advantage is here  also in the use of a cooling and adjustable to the pressing section in that for thermoplastic plastic panels or wood-based panels in Combination with, for example, thermoplastic binders according to the Thermal plasticization process of the thermoplastic and the press molding the molded mat under pressure, the shaped plate then through adaptable cooling effect solidified, that is, the state change point from plastic-liquid to solid state thermally below and thus the plate is demoldable, that is, in the final plate thickness state after Cooling section the finished plate leave the continuously working press can and wood-based panels in combination with plastics can with the application advantage of an extremely low moisture absorption, getting produced.

Further advantages of the continuously operating press according to the invention are:

• - Depending on the quantity distribution, a variable connection of the heating and coolable press plates possible to the plasticizing area or Adjust the hardening range and depending on the plate thickness Production speed economically adjustable.
• - With the use of the continuously operating press according to the invention can be connected to downstream, apparatus-technically very complex thermal  Post-conditioning, that is cooling through the use of z. example Star turners can be partially or completely dispensed with.
• - This goes hand in hand with the reduction in fixed investment costs and less space required for a corresponding system.

The following process operations are necessary for the continuously operating press according to the invention:

• - The steel belts will go through to the end of the press section Cooling withdrawn heat in the return flow by appropriate Heating fed again.
• - By cooling the friction-reducing elements and the steel strips to 120 ° Celsius to 100 ° Celsius and the material temperature T _M 100 ° Celsius, a higher final moisture content of the finished plate can be produced in the range of 8 percent by weight.
• - This means that the panels with a higher final moisture content up to 8 Weight percent can be made if desired. With this higher Final moisture is also possible that the initial moisture of the finished plate over the press cooling section from 0% to approx. 3% below the input moisture can be adjusted to the continuously operating press.
• - The plate thickness can be moved more precisely because of the Post-shrink effect is reduced by more than 50%, and further the Reduced grinding thickness is controlled by less pre-hardening  cooled steel belts and retention of the glue structure without decay due to temporal overheating.

Further advantageous measures and refinements of the subject of Invention emerge from the subclaims and the following description with the drawing.

Show it:

Fig. 1 in side view, the invention continuously working press according to the invention,

Fig. 2 shows the 1 part of the region between the part pressing in a first embodiment according to FIG. As a support device for the steel strips,

Fig. 3 shows the portion between the partial pressing in a second embodiment according to Fig. 1 as a support device for the steel strips,

Fig. 4 to 1 part of the region between the part pressing in a third embodiment according to FIG. As a support device for the steel strips,

Fig. 5 shows the partial region between the partial pressing in a fourth embodiment according to FIG. 1 as a support device for the steel strips,

Fig. 6, 7 and 8 diagrams of the heating and cooling over the course of the pressing zone within the prior art in comparison to that of the invention.

The continuously operating press 1 according to the invention consists of the partial presses I, II, III and IV with the stationary lower press bars 2 , 3 , 4 , 5 and the movable upper press bars 6 , 7 , 8 and 9 . To adjust the press nip 11 , the upper press bars 6 , 7 , 8 and 9 of hydraulic piston-cylinder arrangements (not shown) are moved up and down and locked in the selected position. The steel belts 12 and 13 are each guided over a drive drum 14 and a deflection drum 15 around all lower and upper press bars and pull the mat 10 through the continuously operating press 1 . In order to reduce friction between the press plates attached to the press bars 2 to 9, press heat plates 16 , press heat cooling plates 17 and press cooling plates 18 being provided, and the circumferential steel strips 12 and 13 , a carpet formed from friction-reducing elements is also circumferentially formed, in the exemplary embodiment designed as roller bars 22 , intended. Longitudinal and transverse bores 19 are made in the pressure plates 16 , 17 and 18 for the passage of heating or cooling media. The roller bars 22 , the axes of which extend transversely to the direction of belt travel, are connected on both longitudinal sides of the presses I, II, III and IV in guide chains 21 with a predetermined pitch and roll on the pressure plates 16 , 17 and 18 on the one hand and on the steel belts 12 and 13 guided by the steel belts 12 and 13 through the continuously operating press 1 , the pressed material mat 10 being carried along being pressed to the finished plate 20 . The introduction wheels 27 and the deflection wheels 28 serve for the roller bars 22 and the guide chains 21 as circulation devices.

Fig. 6 after curve e shows the course of the mean temperature of the pressed material when passing through a press with heating section L _H and with cooling section L _K according to the prior art DE-OS 20 58 820 and continuous roller bar circulation. At the end of the heating section L _{H there} is a switch from heating to cooling. As can be seen, the mean temperature T _{M of} the material to be pressed initially continues to rise until the flow of heat reverses at point "A" and the actual cooling begins. In this case, cooling is initially carried out using only a small heat flow, which initially increases steadily and then runs asymptotically against a limit value. Fig. 6, curve f, on the other hand, shows the course of the mean pressed material temperature in a conventional system with separate roller bar circulation according to DE-OS 29 22 151. Here, the sudden reversal with the high initial cooling speeds is visible, which, however, entails the disadvantages described at the beginning. Industrial production plants are usually designed for a defined range of products. For the production of wood-based panels on continuously operating presses, the core spectrum is usually 6 mm according to Fig. 8, thin pressed material mat o, medium pressed material mat n and thick pressed material mat m, up to 38 mm, with the project-specific spectrum down to 2.5 mm and can be extended up to 40 mm. Depending on the product thickness, density, type of board (chip, OSB, MDF, LVL, plastic,...) Heating plate temperature, moisture content, type of binder and other measures influencing production, such as water spraying, preheating the pressed material, etc., the initial temperature T increases _A according to FIG. 8 to the reaction temperature T _{R of} the binder depending on the thickness m, n or o of the pressed material mat 10, however, differently in the continuously operating press 1 and thus also the onset of cooling, as in FIGS. 6, 7 and 8 curve g shown, at approximately 85% -95% of the reaction temperature T _{R1 / O} , T _{R2 / N} or T _{R3 / M} , that is to say earlier and at different points T _{K1 / O} , T _{K2 / N} or T _{K3 / M} respectively. Depending on the project, the range in which 85% -95% of the reaction temperature T _R in the middle of the plate can be reached or calculated by interpolation can be achieved by calculation and using empirical values from existing systems. Within this range, the cooling must be variable switched, that is, the continuously operating press 1 is to be fitted into the part presses II and III with one or more combination of segments S ₁ to S _4, wherein each of these segments S _1, S _2, S _3, and S ₄ can be activated as fields of action either for heating or cooling. In front of this area, that is to say the partial press I, the continuously operating press 1 can be designed without a cooling facility and behind this area, that is to say the partial press IV, without a heating facility. The entire technological press length L can thus be divided into 3 groups. On the inlet side, a pure heating section is first built up over a length L _H , in which the process heat required for the reaction of the binder is introduced into the pressed material. This length L _H will extend to 50% to 75% of the press length L of the partial press I. This is followed in the production direction by a combined heating / cooling section with the length LHIK of the partial presses II and III, within which it is possible to switch from heating to cooling at a variable point in accordance with the segmentation S ₁ to S ₄ . L _{H, K} is usually carried out in a length of 15% to 25% of the press length and divided into two to four heating / cooling segments S ₁ to S ₄ . This is followed by a pure cooling section with the remaining length L _K of 10% to 25% in proportion. A control system with ideal setting options with regard to the starting point of the cooling and controllability of the cooling rate can be generated by the individual heating / cooling segments S ₁ to S _{4 of} the heating / cooling section L _{H, K} , and the subsequent pure cooling section L _K , each with a separate roller bar circulation. With all possible variations, this prevents the energy stored in the roller bars 22 from being carried over from a heating zone into a cooling zone and the disadvantages already described thereby arise. The cooling rate can be regulated individually for each roll body circulation and can thus be adapted to the needs of the respective production. As shown in FIGS. 6 and 7, the steepness and course of the cooling curve can thus be controlled over a wide range. Due to the short roll bar revolutions, there are also lower temperature differences between the incoming roll bars 22 and the steel strips 12 and 13 at the beginning of a respective cooling segment S ₁ to S ₄ , whereby the initial cooling speeds can be reduced.

For the heating section L _H , the individual segments of the heating / cooling section L _{H, K} and the pure cooling section L _K , individual roller bar circulations are created. Each of these cycles has its own chain tensioning and drive system. To avoid pressure relief in the partial areas T _B between the individual revolutions, support devices 23 , 24 , 25 or 26 are provided which support the steel strips 12 and 13 . Such support variations can be designed as sliding shoes 23 , provided with a static or hydrodynamic lubricating film 25 , as a roller carpet 24 or with fixed support rollers 26 . For the pure cooling section L _K it will be necessary to provide a heating or tempering option so that the heating plate temperature is already set to the later steady state before the start of production. The cooling temperature set during production of, for example, 120 ° Celsius would otherwise be undershot when the production was stopped and would lead to rejects when production was resumed.

The continuously operating press 1 is shown in simplified form in FIG. 1 only for the movable upper press bars 6 , 7 , 8 and 9 with friction-reducing roller bars 22 fixed in guide chains 21 . Of course, the fixed lower press bars 2 , 3 , 4 and 5 of the continuously operating press 1 are designed with the same guide chains / roller bar systems 21 , 22 , the press plates 16 , 17 and 18 and the bores 19 made therein.

Reference list

1

continuously working press

2nd

lower press spar I

3rd

lower press spar II

4th

lower press spar III

5

lower press spar IV

6

upper press spar I

7

upper press spar II

8th

upper press spar III

9

upper press spar IV

10th

Pressed mat

11

Press nip

12th

Steel band below

13

Steel band at the top

14

Drive drum

15

Deflection drum

16

Press heating plates

17th

Press heat cooling plates

18th

Press cooling plates

19th

Holes in

16

,

17th

,

18th

20th

Finished plate

21

Leadership chain

22

Roller bars

23

Sliding shoe

24th

Roll carpet

25th

hydrodynamic press pad

26

Support rollers

27

Entry wheels

28

Deflection wheels
I, II, III, IV partial presses
L press line
L _H

Press heating section
L _{H, K}

Press heating and cooling section
L _K

Press cooling section
S (n) segments of the press heating and cooling section
T _A

Press mat temperature at the beginning of the pressing process
T _B

wedge-shaped section
T _K

Start of cooling
T _M

Temperature in the center of the material to be pressed
T _R

Reaction temperature of the binder
e Temperature curve in a continuously operating press with an L _N

and L _K

f temperature profile in a continuously operating press according to DE-OS 29 22 15
g temperature profile in a continuously operating press according to the invention
m thick finished plate / mat
n medium finished plate / mat
o thin finished plate / mat

Claims (8)

1.Continuously working press for the production of wood-based panels such as chipboard, fiberboard and chipboard as well as plastic panels from a combined proportion of wood and plastic as well as plastic with and without reinforcing inserts, with the pressure transferring and the material to be pressed through the press, flexible, endless steel strips that drive drums and deflection drums are guided around each of a lower and upper press spar of two partial presses and are supported first with friction-reducing elements against heated and subsequently cooled press plates of the press spars, the press spars of the partial presses arranged one behind the other in the press frame forming the press section, characterized by the division the press section (L) into a press heating section (L _H ) with a share of 50% to 75%, a press heating cooling section (L _{H, K} ) with a share of 15-25% and a press cooling section (L _K ) with a share of 10 to 25%, each section (L _H , L _{H, K} , L _K ) each having its own press plate area with circumferential friction-reducing elements ( 21 , 22 ), the press heating and cooling section (L _{H / K} ) is single or multiple and its segments (S ₁ , S _2,. . .) are both heatable and / or coolable and a friction-reducing support device ( 23 , 24 , 25 , 26 ) is arranged in each wedge-shaped section (T _B ) between two sections. 2. Continuously operating press according to claim 1, characterized in that the friction-reducing elements as over the press width (b) extending roller bars ( 22 ) with guide chains ( 21 ) or as a roller bearing carpet are executed. 3. Continuously operating press according to claim 1 and 2, characterized in that the friction-reducing support devices ( 23 , 24 , 25 , 26 ) in the wedge-shaped partial area (T _B ) between the partial presses (I, II, III, IV) from rotating rolling elements or are designed as a roller carpet ( 24 ) from stationary support rollers ( 26 ), as a sliding shoe ( 23 ) or consist of a hydrostatic press cushion ( 25 ) or air or steam cushion. 4. Continuously operating press according to claims 1 to 3, characterized in that the friction-reducing elements between the press plates ( 17 , 18 ) and the steel strips ( 12 and 13 ) of one or more cooling section sub-presses (II, III, IV) as sliding surface or as an air or steam cushion sliding surface or as a hydrostatic cushion on the press plates ( 17 , 18 ). 5. Continuously operating press for the production of wood-based panels such as chipboard, fibreboard and chipboard as well as plastic panels from a combined proportion of wood and plastic as well as plastic with and without reinforcing inserts, with the pressure transferring and the material to be pressed through the press, flexible endless steel strips that drive drums and deflection drums are guided around each of a lower and upper press spar of two partial presses and are supported with friction-reducing elements first against heated and subsequently cooled press plates of the press spars, the press spars of the partial presses arranged one behind the other in the press frame forming the press section, characterized by a control or control in which the press cooling section (L _K ) is switched on within the press heating cooling section (L _{H, K} ) when 85% to 95% of the reaction temperature (T _R ) of the binder is in the center of the pressing mat (T _M ) it is reached. 6. The method for the system according to claim 1, characterized records that the steel strips extracted from the cooling Amount of heat in the return through appropriate heating is fed again. 7. The method according to claim 6 and for the system according to claim 1, characterized in that the cooling of the friction-reducing elements and the steel strips accordingly the curing temperature of the binder to ≦ 120 ° Celsius Wood-based panels and for plastic composite panels at ≦ 100 ° Celsius is done. 8. The method according to claim 6 and for the system according to claim 1, characterized in that the initial moisture of the finished plate over the press cooling section from 0% to about 3% below the Input moisture is adjusted.