In recent years, the technological progress in the production of fiberboard by dry process has been witnessed by the world. For many years, continuous press technology, in addition to the production of medium density fiberboard, has also been widely used in the production of lightweight (LDF) or high density (HDF) fiberboard. By changing the shape of the inlet of the press and the precise control of the pressure throughout the length of the press, the range of density variations of the available panels is greatly widened.
Increase the range of density changes and broaden the application area
Due to the emergence of 3D finishing technology, the demand for medium density fiberboard has increased significantly. Today, kitchen and bathroom furniture is no longer a substrate for particleboard, but the world of paint is used, but a 3D veneer made of a very high-grade thermoplastic film attached to a MDF substrate. The 3D pressing process is currently available in both useful and non-film processes. It seems to be inevitable to replace the particleboard in the furniture manufacturing fiberboard.
High-density fiberboard has great market potential as a flooring material, and it can be used as a substrate for decorative laminated materials or multi-layer direct facing materials. At present, the short-cycle press is mainly used to press the veneer, and the double-belt press is used to press the veneer. The former has high flexibility and is inexpensive and embossed. The advantage of the double belt press is that there is a regenerative system under working pressure, which reduces the cost of temperature control and the workpiece runs smoothly. The use of thin fiberboard will become more widespread in the near future, especially in the field of glued sheets today. Here, a medium density fiberboard having a thickness of 1 mm or more may replace cardboard in the future.
Lightweight fiberboards do not currently have a large field of use, so other production is limited. Particleboard users, or furniture manufacturers, may become one of their main users. On the other hand, the weight and price of the fiberboard are limited, which limits its scope of use. However, lightweight fiberboard also has advantages in processing, especially its dense side. The density of lightweight fiberboard is only 650kg/m3. From this point of view, it is cheaper than the medium density fiberboard in the use of raw materials. In addition, it can be processed like a particle board. If the price is right, it is natural to open the market. Lowering the price of the product can create conditions for the MDF exhibition.
Production face is in a downward trend
By grinding the disc with a specially constructed hot mill, more waste types can be included in the raw material formulation of the medium fiberboard. It has been reported that all of the medium density fiberboard made of sawdust has been successful. In Germany, there is a mill with an annual production capacity of nearly 1 million cubic meters. If the medium density fiberboard production plant is built near this material factory, it is economically attractive. There are precedents for particleboard plants. Due to the low cost and price of the logs themselves, medium density fiberboard made from waste paper fibers has so far only been carried out in mechanical laboratory laboratories. The adhesive used in the production of medium density fiberboard is PMDI, which has been proven. Due to the increasing demand for waste paper in the paper industry, the process of making medium density fiberboard from waste paper fibers is not attractive from a long-term perspective. In addition, waste paper can also be used in the production of paste fiberboard.
The production of medium density fiberboard is much higher than the production of particleboard, so electricity prices play an important role in the selection of hot pressing systems. At present, the press system supported by the rolling elements requires a large energy consumption compared with the Hydro-Dyn process in which the oil circulation operates as a lubricant, so that some improvements can be made in the hot pressing process. To this end, by using high-value silicone oil to extend its service life, it can reduce its cost by a third. The above points, together with other factors, provide the possibility to further reduce the operating cost of the hot pressing system.
Slab preheating increases production
Not long ago, attention was focused on the use of high frequency or microwave heat transfer to the center of the plate but to the slab preheating. This method was too costly to be practical. At the Ligna Woodworking Exhibition in 1999, Kvaerner introduced a new system with a "core heater". With this heater, heat energy can be uniformly transferred from the center of the slab to the entire slab in the form of steam. The center of the fiber slab is horizontally separated by a band saw at the entrance of the continuous press. Immediately after the band saw blade is a sword-shaped nozzle, it allows the steam to be uniformly distributed throughout the slab width. The heat produced by steam condensation can increase the yield by about 20%, but if you want to increase the density of the core, the newly formed tidal pressure may be too small. But even such a small improvement has demonstrated its superiority in practical applications. It is necessary to take special measures when painting the side and profile of the deep-milled medium-density fiberboard for painting and secondary painting (with intermediate drying process). The patented "preheater" also has the advantage that the curing agent can be applied in the vapor phase at the water vapor portion, thereby shortening the heating time. But the specific amount may not be too high.
Shorten hot pressing time and reduce cost
Due to the high density of the fiber slab and the poor thermal conductivity of the fiber, the hot pressing time of the medium density fiberboard is significantly longer than that of the particleboard. The hot press time of a medium-density fiberboard continuous press of the same production capacity is almost doubled. The press system for rolling supports is currently used primarily on the market. Another hot pressing system is the Hydro-Dyn system, which works by using oil as a lubricant. The process is currently under continuous development and optimization. Bison, and in particular Kvaerner, has done a lot of development work for this. However, it is still difficult to discuss the advantages and disadvantages of this hot pressing system in practical applications.
Recently, the return of cold under pressure has become the focus of attention. It affects the process parameters of the gluing process as well as the pressurization time. From the perspective of the necessary cooling zone length, the process is of interest for the production of thin fiberboard, especially as the demand for such panels increases due to the rapid growth of the flooring market. The cooling efficiency is related to the pressurization system used. Continuous column drive systems are not suitable for use due to the large amount of heat transfer in the cooling zone. The non-driven roller chain is divided into two adjacent presses, and the crucible has a common press belt. It is not uncommon for such a system to be able to separate high pressure portions when it is only necessary to cool the outlet end. The no-pressure zone, that is, the width from the press belt to the transition intermediate zone is about 130 mm. Since the pressure at the exit is almost zero, such a width is acceptable. The pressure belt acts as a hot body, and the heat energy is continuously sent to the cooling zone, so the thermal efficiency thereof is limited. In the Hydro-Dyn system, the hot press belt also enters the cooling zone. But it is rapidly cooled in a separate oil circulation system through a large number of oil cycles. In addition, such equipment operates at a lower temperature, on the one hand, the service life is reduced due to the high operating temperature, and on the other hand, the low-temperature curing of the adhesive is achieved by effective heat exchange.
On the Hydro-Dyn press, tests were performed on the effect of cooling on the hot press time. Under the premise of ensuring the mechanical performance of the press system, the production efficiency is significantly improved. For a fiberboard having a density of 900 kg/m3, the hot pressing time is shortened by about 25% at a sheet thickness of 5.5 mm, and the sheet thickness is shortened by about 15% when the sheet thickness is 8.0 mm.
This production efficiency has been significantly improved, and corresponding requirements have been placed on the mechanical properties of the equipment. The advancement speed of the rolling unit must meet a certain value because the sheet requires a very high speed even without re-cooling. When using the lubricating oil system, there is no mechanical limitation. The feed rate of 60m/min has proved to be feasible. The feed speed of 70min or even 80m/min is also being tested. When producing a thin plate with a thickness of 1.0mm or more, It is also obvious which kind of press system has a more promising future.
Recooling improves board performance
According to the process requirements, sensitive control of temperature and back-cooling process can greatly improve the adjustability of the press. Cooling can be performed below 100 degrees Celsius when using a lubricating oil system to ensure steam condensation. Even when the condensation point is 100 degrees Celsius or more, there is a remarkable effect.
Compared with the thin medium density fiberboard manufactured by the non-refrigerating process, the medium density fiberboard manufactured by the reflowing process can greatly improve the transverse tensile strength without affecting the static bending strength, thereby opening up new market applications. Especially for thin plates with a thickness of 1mm or more, if the performance requirement is not very high, the amount of glue used can be reduced.
The use of the re-cooling process can reduce the steam overflow at the hot-pressing outlet, making the surface of the shaped surface more dense, which is very advantageous for the subsequent processing of various finishes. Of course, smooth surfaces have some difficulty in gluing or painting. To do this, adjust the glue and paint used, or perform fine sand polishing on the surface.
Products that are re-cooled under pressure are also very flat when they are very thin. Whether this process can save expensive air temperature and humidity regulation investment (which is critical for the production of floorboards) remains to be further verified. Because the heat transfer during this subsequent finish also plays a role. The product can be covered before the inlet, that is, before the slab enters the press, 2 or 3 films are placed on top of the slab, and a balancing film is placed on the back side, and then hot pressed together. Recooling cools the temperature to below 100 degrees Celsius, which avoids exhaust problems and produces a highly wear resistant surface comparable to the short cycle hot pressing process. Embossing can be produced with release paper that is used multiple times. Such corresponding interference factors will inevitably increase, and the authentic rate will be lower than 98%.
From an ecological point of view, the wet preparation process of hardboard is very meaningful, but now in Europe and around the world, more and more companies have abandoned this production method. Because they believe that the use of this wet process requires the use of fresh water, while also requiring a corresponding wastewater treatment process. Wet-made boards are ecologically top-notch because they reduce the amount of adhesive and reduce costs. The variety of products currently produced by the wet process is very limited. Only rigid fiberboard and extremely light insulation panels. Because these two products are the two extreme conditions in which the multi-step press is used, in the production of hardboard, the press has to squeeze excess water under high pressure to achieve an acceptable hot pressing time. When producing extremely light insulation panels, no excess water is squeezed, only corrections are made, and then dried in a specific area.
Wet continuous production
All continuous presses are suitable for fiberboard production processes including wet processes. There should be no difficulty in running the lower circulating mesh belt with the slab. However, the large amount of water that is discharged at the beginning of the run must be managed to be eliminated. It is important to emphasize that the oil and water are not compatible, so it is not compatible with the lubrication of the rolling system and the oil of the Hydro-Dyn press system. The hot oil flow overflowing from the upper side of the upper belt of the press and the lower side of the lower belt can be discharged almost without leakage, and is discharged from the upper portion of the lower pressing belt.
The problem is the practical application of this process. It is conceivable that a large amount of excess cold water at the inlet is discharged from a cold or near high pressure zone of approximately 100 degrees Celsius and then operated at a high hot pressure temperature to take advantage of the intense cooling at the outlet. The adhesive in the wet process does not have much effect, so it is only necessary to optimize the physical process such as main drainage-evaporation-solidification. When the water cycle is carried out in a cold high pressure zone, the possibility of mixing cold water with hot oil can be ruled out.
The choice of medium density fiberboard development
Dry production of fiberboard, such as medium density fiberboard, high-density hardboard and low-density lightweight fiberboard, is still alive. Various situations indicate that this production process has the potential to further reduce costs. The Hydro-Dyn press system offers another possibility for fiberboard development, making fiberboard more competitive with particleboard.
Increase the range of density changes and broaden the application area
Due to the emergence of 3D finishing technology, the demand for medium density fiberboard has increased significantly. Today, kitchen and bathroom furniture is no longer a substrate for particleboard, but the world of paint is used, but a 3D veneer made of a very high-grade thermoplastic film attached to a MDF substrate. The 3D pressing process is currently available in both useful and non-film processes. It seems to be inevitable to replace the particleboard in the furniture manufacturing fiberboard.
High-density fiberboard has great market potential as a flooring material, and it can be used as a substrate for decorative laminated materials or multi-layer direct facing materials. At present, the short-cycle press is mainly used to press the veneer, and the double-belt press is used to press the veneer. The former has high flexibility and is inexpensive and embossed. The advantage of the double belt press is that there is a regenerative system under working pressure, which reduces the cost of temperature control and the workpiece runs smoothly. The use of thin fiberboard will become more widespread in the near future, especially in the field of glued sheets today. Here, a medium density fiberboard having a thickness of 1 mm or more may replace cardboard in the future.
Lightweight fiberboards do not currently have a large field of use, so other production is limited. Particleboard users, or furniture manufacturers, may become one of their main users. On the other hand, the weight and price of the fiberboard are limited, which limits its scope of use. However, lightweight fiberboard also has advantages in processing, especially its dense side. The density of lightweight fiberboard is only 650kg/m3. From this point of view, it is cheaper than the medium density fiberboard in the use of raw materials. In addition, it can be processed like a particle board. If the price is right, it is natural to open the market. Lowering the price of the product can create conditions for the MDF exhibition.
Production face is in a downward trend
By grinding the disc with a specially constructed hot mill, more waste types can be included in the raw material formulation of the medium fiberboard. It has been reported that all of the medium density fiberboard made of sawdust has been successful. In Germany, there is a mill with an annual production capacity of nearly 1 million cubic meters. If the medium density fiberboard production plant is built near this material factory, it is economically attractive. There are precedents for particleboard plants. Due to the low cost and price of the logs themselves, medium density fiberboard made from waste paper fibers has so far only been carried out in mechanical laboratory laboratories. The adhesive used in the production of medium density fiberboard is PMDI, which has been proven. Due to the increasing demand for waste paper in the paper industry, the process of making medium density fiberboard from waste paper fibers is not attractive from a long-term perspective. In addition, waste paper can also be used in the production of paste fiberboard.
The production of medium density fiberboard is much higher than the production of particleboard, so electricity prices play an important role in the selection of hot pressing systems. At present, the press system supported by the rolling elements requires a large energy consumption compared with the Hydro-Dyn process in which the oil circulation operates as a lubricant, so that some improvements can be made in the hot pressing process. To this end, by using high-value silicone oil to extend its service life, it can reduce its cost by a third. The above points, together with other factors, provide the possibility to further reduce the operating cost of the hot pressing system.
Slab preheating increases production
Not long ago, attention was focused on the use of high frequency or microwave heat transfer to the center of the plate but to the slab preheating. This method was too costly to be practical. At the Ligna Woodworking Exhibition in 1999, Kvaerner introduced a new system with a "core heater". With this heater, heat energy can be uniformly transferred from the center of the slab to the entire slab in the form of steam. The center of the fiber slab is horizontally separated by a band saw at the entrance of the continuous press. Immediately after the band saw blade is a sword-shaped nozzle, it allows the steam to be uniformly distributed throughout the slab width. The heat produced by steam condensation can increase the yield by about 20%, but if you want to increase the density of the core, the newly formed tidal pressure may be too small. But even such a small improvement has demonstrated its superiority in practical applications. It is necessary to take special measures when painting the side and profile of the deep-milled medium-density fiberboard for painting and secondary painting (with intermediate drying process). The patented "preheater" also has the advantage that the curing agent can be applied in the vapor phase at the water vapor portion, thereby shortening the heating time. But the specific amount may not be too high.
Shorten hot pressing time and reduce cost
Due to the high density of the fiber slab and the poor thermal conductivity of the fiber, the hot pressing time of the medium density fiberboard is significantly longer than that of the particleboard. The hot press time of a medium-density fiberboard continuous press of the same production capacity is almost doubled. The press system for rolling supports is currently used primarily on the market. Another hot pressing system is the Hydro-Dyn system, which works by using oil as a lubricant. The process is currently under continuous development and optimization. Bison, and in particular Kvaerner, has done a lot of development work for this. However, it is still difficult to discuss the advantages and disadvantages of this hot pressing system in practical applications.
Recently, the return of cold under pressure has become the focus of attention. It affects the process parameters of the gluing process as well as the pressurization time. From the perspective of the necessary cooling zone length, the process is of interest for the production of thin fiberboard, especially as the demand for such panels increases due to the rapid growth of the flooring market. The cooling efficiency is related to the pressurization system used. Continuous column drive systems are not suitable for use due to the large amount of heat transfer in the cooling zone. The non-driven roller chain is divided into two adjacent presses, and the crucible has a common press belt. It is not uncommon for such a system to be able to separate high pressure portions when it is only necessary to cool the outlet end. The no-pressure zone, that is, the width from the press belt to the transition intermediate zone is about 130 mm. Since the pressure at the exit is almost zero, such a width is acceptable. The pressure belt acts as a hot body, and the heat energy is continuously sent to the cooling zone, so the thermal efficiency thereof is limited. In the Hydro-Dyn system, the hot press belt also enters the cooling zone. But it is rapidly cooled in a separate oil circulation system through a large number of oil cycles. In addition, such equipment operates at a lower temperature, on the one hand, the service life is reduced due to the high operating temperature, and on the other hand, the low-temperature curing of the adhesive is achieved by effective heat exchange.
On the Hydro-Dyn press, tests were performed on the effect of cooling on the hot press time. Under the premise of ensuring the mechanical performance of the press system, the production efficiency is significantly improved. For a fiberboard having a density of 900 kg/m3, the hot pressing time is shortened by about 25% at a sheet thickness of 5.5 mm, and the sheet thickness is shortened by about 15% when the sheet thickness is 8.0 mm.
This production efficiency has been significantly improved, and corresponding requirements have been placed on the mechanical properties of the equipment. The advancement speed of the rolling unit must meet a certain value because the sheet requires a very high speed even without re-cooling. When using the lubricating oil system, there is no mechanical limitation. The feed rate of 60m/min has proved to be feasible. The feed speed of 70min or even 80m/min is also being tested. When producing a thin plate with a thickness of 1.0mm or more, It is also obvious which kind of press system has a more promising future.
Recooling improves board performance
According to the process requirements, sensitive control of temperature and back-cooling process can greatly improve the adjustability of the press. Cooling can be performed below 100 degrees Celsius when using a lubricating oil system to ensure steam condensation. Even when the condensation point is 100 degrees Celsius or more, there is a remarkable effect.
Compared with the thin medium density fiberboard manufactured by the non-refrigerating process, the medium density fiberboard manufactured by the reflowing process can greatly improve the transverse tensile strength without affecting the static bending strength, thereby opening up new market applications. Especially for thin plates with a thickness of 1mm or more, if the performance requirement is not very high, the amount of glue used can be reduced.
The use of the re-cooling process can reduce the steam overflow at the hot-pressing outlet, making the surface of the shaped surface more dense, which is very advantageous for the subsequent processing of various finishes. Of course, smooth surfaces have some difficulty in gluing or painting. To do this, adjust the glue and paint used, or perform fine sand polishing on the surface.
Products that are re-cooled under pressure are also very flat when they are very thin. Whether this process can save expensive air temperature and humidity regulation investment (which is critical for the production of floorboards) remains to be further verified. Because the heat transfer during this subsequent finish also plays a role. The product can be covered before the inlet, that is, before the slab enters the press, 2 or 3 films are placed on top of the slab, and a balancing film is placed on the back side, and then hot pressed together. Recooling cools the temperature to below 100 degrees Celsius, which avoids exhaust problems and produces a highly wear resistant surface comparable to the short cycle hot pressing process. Embossing can be produced with release paper that is used multiple times. Such corresponding interference factors will inevitably increase, and the authentic rate will be lower than 98%.
From an ecological point of view, the wet preparation process of hardboard is very meaningful, but now in Europe and around the world, more and more companies have abandoned this production method. Because they believe that the use of this wet process requires the use of fresh water, while also requiring a corresponding wastewater treatment process. Wet-made boards are ecologically top-notch because they reduce the amount of adhesive and reduce costs. The variety of products currently produced by the wet process is very limited. Only rigid fiberboard and extremely light insulation panels. Because these two products are the two extreme conditions in which the multi-step press is used, in the production of hardboard, the press has to squeeze excess water under high pressure to achieve an acceptable hot pressing time. When producing extremely light insulation panels, no excess water is squeezed, only corrections are made, and then dried in a specific area.
Wet continuous production
All continuous presses are suitable for fiberboard production processes including wet processes. There should be no difficulty in running the lower circulating mesh belt with the slab. However, the large amount of water that is discharged at the beginning of the run must be managed to be eliminated. It is important to emphasize that the oil and water are not compatible, so it is not compatible with the lubrication of the rolling system and the oil of the Hydro-Dyn press system. The hot oil flow overflowing from the upper side of the upper belt of the press and the lower side of the lower belt can be discharged almost without leakage, and is discharged from the upper portion of the lower pressing belt.
The problem is the practical application of this process. It is conceivable that a large amount of excess cold water at the inlet is discharged from a cold or near high pressure zone of approximately 100 degrees Celsius and then operated at a high hot pressure temperature to take advantage of the intense cooling at the outlet. The adhesive in the wet process does not have much effect, so it is only necessary to optimize the physical process such as main drainage-evaporation-solidification. When the water cycle is carried out in a cold high pressure zone, the possibility of mixing cold water with hot oil can be ruled out.
The choice of medium density fiberboard development
Dry production of fiberboard, such as medium density fiberboard, high-density hardboard and low-density lightweight fiberboard, is still alive. Various situations indicate that this production process has the potential to further reduce costs. The Hydro-Dyn press system offers another possibility for fiberboard development, making fiberboard more competitive with particleboard.
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