Molding and preloading of MDF
1.1 Forming and preloading
In the production of medium density fiberboard, the slab paving is a very important process, and only qualified slabs can be paved to obtain high quality medium density fiberboard products. To this end, the medium density fiberboard forming process has the following requirements:
1. When the fiber is molded, it does not agglomerate, gathers, distributes evenly, and is naturally intertwined.
2. The slab has a certain strength and does not loosen during transportation.
3. The density of each point of the whole slab should be uniform and uniform, and the weight error per unit area should not exceed ± 3%.
4, the slab should be as dense as possible to reduce the opening of the hot press.
Typically, the thickness of the formed slab is 15 to 28 times the thickness of the finished product.
Medium-density fiberboard molding pre-pressing process generally includes: fiber silo, fiber sorting, wind conveying, forming, slab weighing, pre-pressing, trimming, belt transport, density testing, metal detection, waste slab recycling System, etc. Continuous press production, slab does not need to be cut off, and reduce slab transportation.
1.1.1 Fiber silo
The dried fiber is sent to the fiber silo for storage by a fan, and the moisture content is continuously measured automatically. The role of fiber storage:
1. Ensure continuity of production, fiber balance between drying and molding.
2. The dried fiber is mixed and stayed in the silo, which is more favorable for the quality of the board.
3. Storage of recycled fibers such as flattened, flushed, and waste slabs of slabs.
The bulk density of dry fiber is very light. The storage of 1t fiber requires a volume of more than 40m3. If stored in a large amount, it will easily cause fiber agglomeration and “bridgeâ€, making it difficult and uneven to discharge, and seriously affecting the quality of slab forming. Therefore, the silo should not be too large, and it can be used for 10~20min of fiber. And the storage time should not be too long, summer should not exceed 1h, winter should not exceed 8h.
There are two types of silo types, vertical and horizontal. Vertical silos are easy to produce “bridge†and difficult to discharge. The structure is very complicated, so it is generally not used. Horizontal silos are more suitable for the storage of dry fibers. A uniform discharge mechanism is installed in the silo.
1.1.2 fiber sorting
When using a continuous hot press, in order to ensure the protection of the press, prevent hard materials from entering the press and damaging the steel strip, not only the metal should be removed, but also hard objects such as rubber blocks and fiber stalks must be removed. Therefore, the fiber entering the paving machine must be sorted again. The general fiber sorter is divided into two stages. The first stage of sorting is to sort and discharge heavy objects such as metal, stone, rubber block and fiber mass. The second-stage sorting is mainly to sort out the coarse fiber stalk and the secondary weight that has not been separated in the first stage.
1.1.3 slab forming
There are many methods for slab paving and forming. In the domestic introduction of medium-density fiberboard forming equipment of different scales, the forming machines are roughly classified into three types: mechanical forming, air flow vacuum forming and mechanical vacuum forming.
1. Mechanical forming machine forming is based on the mechanical throwing roll forming machine of the German “Shenke†company, mainly consisting of a swing belt conveyor, an intermediate storage bin, a bottom discharge belt conveyor, a throwing roller, a pre-distributing roller, and a forming head. , the flattening roller and the slab are called.
2. The main structure of the airflow vacuum type consists of four parts: the feeding swing head, the box body, the vacuum box and the bracket.
The fiber conveyed from the silo by the airflow is circulated and sprayed in the forming box through the rectangular pipe enlarged at the top of the molding machine, and the fiber is spread on the continuously moving mesh belt due to the suction force of the bottom vacuum box. A slab is formed.
The swinging of the feed oscillating head is achieved by sliding the hydraulic cylinder to the piston rod, pushing the slider to move linearly, and sliding the swing rod in the swinging block of the slider. The speed and travel of the slider are adjustable.
After the slab is formed, the fiber exceeding the required angle is swept by the sweeping roller, and is sent back to the fiber bin by the fan. A vacuum box is provided at the bottom of the sweeping roller. The molding machine is equipped with a fan for conveying fibers and vacuuming, as well as hydraulic, electrical, and conveying devices.
Swing head travel, fiber flow and swing frequency are three main factors:
If the trip does not change. The larger the flow rate, the higher the swing frequency; the smaller the flow rate, the lower the swing frequency.
If the flow rate does not change. The larger the stroke, the lower the swing frequency; the smaller the stroke, the higher the swing frequency.
The swing frequency is generally 25 to 48 times/min. When two forming heads are used, the first forming head can be slightly lower.
The density distribution of the slab cross section is closely related to the vacuum of the vacuum box. The degree of vacuum is large, the fiber density is large, and the amount of dropped fiber is also large. It is necessary to strictly avoid that the air does not pass through the slab, but enters the vacuum box from the edge of the slab, resulting in a decrease in density on both sides of the slab.
In addition, when the vacuum degree on both sides of the flattening roller vacuum box and the vacuum box is equal to 1.35 times of the middle, the cross-sectional density distribution of the formed slab is relatively uniform.
3, mechanical airflow vacuum forming
The fiber enters the fiber metering silo through the feed port, and then is sent to the rear of the silo by the material hopper. Since the direction of rotation of the material 与 is opposite to the advancing direction of the metering belt, the fiber is evenly distributed to the entire silo. The ground is distributed. The fiber moves forward under the drag of the metering belt and is sent to the discharge comb roller. Through the discharge comb roller, the fibers are fed to the throwing roller, spread evenly to the paving chamber, and the air stream generated by the vacuum box at the lower portion of the paving chamber is adsorbed on the paving mesh belt. With the adjustable vacuum box, the fiber weight distribution required by the process can be achieved, so that the fiber slab is uniformly formed on the paving mesh belt. The slab continues to move forward under the drag of the mesh belt, and the upper portion of the fiber slab is leveled by an adjustable height sweeping roller. The height of the sweeping roller is automatically positioned using an isotope density controller. The excess fibers that were swept away are sent back to the fiber silo for further use through the pneumatic conveying system. After the leveling, the slab is dragged under the mesh belt and continues to move forward, and is sent to the continuous belt pre-press.
1.1.4 slab preload
The continuous slab after molding is relatively bulky, the strength is small and easy to break, and the large thickness is not suitable for transportation and hot pressing. Therefore, the slab must be further compacted after molding, which is the purpose of slab pre-compression.
1 Exclude the air in the slab to prevent a large amount of air from rushing out of the slab during hot pressing and destroying the fiber layer.
2 The slab has a certain supporting strength to prevent collapse or breakage due to bump vibration during transportation.
3 Reduce the thickness of the slab to reduce the opening of the hot press plate of the hot press, reduce the structural height of the press and the loader, and save the cost, which is especially important for the multi-layer laminator.
4 As the density of the slab increases, the heat transfer, the closing speed and the pressure increase during the hot pressing are accelerated, thereby improving the production efficiency.
1. Pre-press pre-pressing machine has intermittent flat pre-pressing machine and continuous belt pre-pressing machine, the latter being the most widely used. Generally, the small and medium-sized continuous belt pre-pressing machine is composed of a fixed lower part of the machine, a floating upper part of the machine, a transmission machine and a hydraulic system. The equipment for the drive and hydraulic sections can be placed near the mainframe according to the overall layout requirements.
2, slab transport cutting and detection
The pre-pressed fiber slabs are conveyed to the next process through the synchronous conveyor belt, and the longitudinal sawing is first performed to remove the slabs which are rolled and collapsed by the pre-pressing machine. When multi-layer hot pressing is adopted, the slab is also cut by the cross-sectional saw, so that the length and width of the slab are in accordance with the requirements of the hot pressing equipment and the process. After the slab is cut off, the slab is pulled away by a rapid transporter and sent to the loading conveyor. Prepare to load the loader. When continuous hot pressing is used, the slabs are transported directly into the hot press without cross-section direct synchronous transport.
1.1 Forming and preloading
In the production of medium density fiberboard, the slab paving is a very important process, and only qualified slabs can be paved to obtain high quality medium density fiberboard products. To this end, the medium density fiberboard forming process has the following requirements:
1. When the fiber is molded, it does not agglomerate, gathers, distributes evenly, and is naturally intertwined.
2. The slab has a certain strength and does not loosen during transportation.
3. The density of each point of the whole slab should be uniform and uniform, and the weight error per unit area should not exceed ± 3%.
4, the slab should be as dense as possible to reduce the opening of the hot press.
Typically, the thickness of the formed slab is 15 to 28 times the thickness of the finished product.
Medium-density fiberboard molding pre-pressing process generally includes: fiber silo, fiber sorting, wind conveying, forming, slab weighing, pre-pressing, trimming, belt transport, density testing, metal detection, waste slab recycling System, etc. Continuous press production, slab does not need to be cut off, and reduce slab transportation.
1.1.1 Fiber silo
The dried fiber is sent to the fiber silo for storage by a fan, and the moisture content is continuously measured automatically. The role of fiber storage:
1. Ensure continuity of production, fiber balance between drying and molding.
2. The dried fiber is mixed and stayed in the silo, which is more favorable for the quality of the board.
3. Storage of recycled fibers such as flattened, flushed, and waste slabs of slabs.
The bulk density of dry fiber is very light. The storage of 1t fiber requires a volume of more than 40m3. If stored in a large amount, it will easily cause fiber agglomeration and “bridgeâ€, making it difficult and uneven to discharge, and seriously affecting the quality of slab forming. Therefore, the silo should not be too large, and it can be used for 10~20min of fiber. And the storage time should not be too long, summer should not exceed 1h, winter should not exceed 8h.
There are two types of silo types, vertical and horizontal. Vertical silos are easy to produce “bridge†and difficult to discharge. The structure is very complicated, so it is generally not used. Horizontal silos are more suitable for the storage of dry fibers. A uniform discharge mechanism is installed in the silo.
1.1.2 fiber sorting
When using a continuous hot press, in order to ensure the protection of the press, prevent hard materials from entering the press and damaging the steel strip, not only the metal should be removed, but also hard objects such as rubber blocks and fiber stalks must be removed. Therefore, the fiber entering the paving machine must be sorted again. The general fiber sorter is divided into two stages. The first stage of sorting is to sort and discharge heavy objects such as metal, stone, rubber block and fiber mass. The second-stage sorting is mainly to sort out the coarse fiber stalk and the secondary weight that has not been separated in the first stage.
1.1.3 slab forming
There are many methods for slab paving and forming. In the domestic introduction of medium-density fiberboard forming equipment of different scales, the forming machines are roughly classified into three types: mechanical forming, air flow vacuum forming and mechanical vacuum forming.
1. Mechanical forming machine forming is based on the mechanical throwing roll forming machine of the German “Shenke†company, mainly consisting of a swing belt conveyor, an intermediate storage bin, a bottom discharge belt conveyor, a throwing roller, a pre-distributing roller, and a forming head. , the flattening roller and the slab are called.
2. The main structure of the airflow vacuum type consists of four parts: the feeding swing head, the box body, the vacuum box and the bracket.
The fiber conveyed from the silo by the airflow is circulated and sprayed in the forming box through the rectangular pipe enlarged at the top of the molding machine, and the fiber is spread on the continuously moving mesh belt due to the suction force of the bottom vacuum box. A slab is formed.
The swinging of the feed oscillating head is achieved by sliding the hydraulic cylinder to the piston rod, pushing the slider to move linearly, and sliding the swing rod in the swinging block of the slider. The speed and travel of the slider are adjustable.
After the slab is formed, the fiber exceeding the required angle is swept by the sweeping roller, and is sent back to the fiber bin by the fan. A vacuum box is provided at the bottom of the sweeping roller. The molding machine is equipped with a fan for conveying fibers and vacuuming, as well as hydraulic, electrical, and conveying devices.
Swing head travel, fiber flow and swing frequency are three main factors:
If the trip does not change. The larger the flow rate, the higher the swing frequency; the smaller the flow rate, the lower the swing frequency.
If the flow rate does not change. The larger the stroke, the lower the swing frequency; the smaller the stroke, the higher the swing frequency.
The swing frequency is generally 25 to 48 times/min. When two forming heads are used, the first forming head can be slightly lower.
The density distribution of the slab cross section is closely related to the vacuum of the vacuum box. The degree of vacuum is large, the fiber density is large, and the amount of dropped fiber is also large. It is necessary to strictly avoid that the air does not pass through the slab, but enters the vacuum box from the edge of the slab, resulting in a decrease in density on both sides of the slab.
In addition, when the vacuum degree on both sides of the flattening roller vacuum box and the vacuum box is equal to 1.35 times of the middle, the cross-sectional density distribution of the formed slab is relatively uniform.
3, mechanical airflow vacuum forming
The fiber enters the fiber metering silo through the feed port, and then is sent to the rear of the silo by the material hopper. Since the direction of rotation of the material 与 is opposite to the advancing direction of the metering belt, the fiber is evenly distributed to the entire silo. The ground is distributed. The fiber moves forward under the drag of the metering belt and is sent to the discharge comb roller. Through the discharge comb roller, the fibers are fed to the throwing roller, spread evenly to the paving chamber, and the air stream generated by the vacuum box at the lower portion of the paving chamber is adsorbed on the paving mesh belt. With the adjustable vacuum box, the fiber weight distribution required by the process can be achieved, so that the fiber slab is uniformly formed on the paving mesh belt. The slab continues to move forward under the drag of the mesh belt, and the upper portion of the fiber slab is leveled by an adjustable height sweeping roller. The height of the sweeping roller is automatically positioned using an isotope density controller. The excess fibers that were swept away are sent back to the fiber silo for further use through the pneumatic conveying system. After the leveling, the slab is dragged under the mesh belt and continues to move forward, and is sent to the continuous belt pre-press.
1.1.4 slab preload
The continuous slab after molding is relatively bulky, the strength is small and easy to break, and the large thickness is not suitable for transportation and hot pressing. Therefore, the slab must be further compacted after molding, which is the purpose of slab pre-compression.
1 Exclude the air in the slab to prevent a large amount of air from rushing out of the slab during hot pressing and destroying the fiber layer.
2 The slab has a certain supporting strength to prevent collapse or breakage due to bump vibration during transportation.
3 Reduce the thickness of the slab to reduce the opening of the hot press plate of the hot press, reduce the structural height of the press and the loader, and save the cost, which is especially important for the multi-layer laminator.
4 As the density of the slab increases, the heat transfer, the closing speed and the pressure increase during the hot pressing are accelerated, thereby improving the production efficiency.
1. Pre-press pre-pressing machine has intermittent flat pre-pressing machine and continuous belt pre-pressing machine, the latter being the most widely used. Generally, the small and medium-sized continuous belt pre-pressing machine is composed of a fixed lower part of the machine, a floating upper part of the machine, a transmission machine and a hydraulic system. The equipment for the drive and hydraulic sections can be placed near the mainframe according to the overall layout requirements.
2, slab transport cutting and detection
The pre-pressed fiber slabs are conveyed to the next process through the synchronous conveyor belt, and the longitudinal sawing is first performed to remove the slabs which are rolled and collapsed by the pre-pressing machine. When multi-layer hot pressing is adopted, the slab is also cut by the cross-sectional saw, so that the length and width of the slab are in accordance with the requirements of the hot pressing equipment and the process. After the slab is cut off, the slab is pulled away by a rapid transporter and sent to the loading conveyor. Prepare to load the loader. When continuous hot pressing is used, the slabs are transported directly into the hot press without cross-section direct synchronous transport.
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