This table lift has two step and is very popular for height adjustable desks, tables, and can be used as a Tv Lift. The set includes 2 lifting columns, 1 control box to control both lifting columns and 1 remote.
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In the case of quality problems such as sand leakage and rough surface, it is often necessary to increase the thickness of the board to ensure the minimum amount of sanding, which not only increases the production cost of the product, but also causes uneven density and warpage of the board. Such as quality defects, while bringing great difficulties to the adjustment of the sander.
According to the actual face in the actual production, the author expounds some reasons for the thickness deviation for the reference of the colleagues:
1 Hydraulic system position control is not accurate
Generally, many laminating machines use multiple cylinders to work at the same time. In some cylinders, the respective cylinders can be individually adjusted according to their respective positions, but all the cylinders of the press are directly connected to the same pressure pipe. The pressure is equal at all times and cannot be adjusted individually. Thus, it is impossible to overcome the thickness deviation caused by the unevenness of the pavement, the asymmetry of the slab in the middle of the press plate, and the like. In addition, the accuracy of the position sensor also has a large effect on the thickness deviation.
2 Slabs are asymmetrical in the hot platen
When the position of the slab in the hot platen is asymmetrical, the hot platen will not always maintain a horizontal state during the pressurization process, thereby causing thickness deviation, especially in a hot press in which the pressure of each cylinder cannot be separately adjusted. . The author tried in the middle of production. If the deviation is 15mm in the width direction, the average thickness of each slab is about 0.1-0.2mm.
2.1 Phenomenon of slab asymmetry
1 The slabs coming out of the post-processing section are inclined, especially when producing thin sheets.
2 On the display, there is a large deviation between the detection values ​​of the two press position sensors.
3 When the slab is tested, even if the weight per unit area of ​​each point is the same, the density varies greatly due to the inconsistent thickness.
2.2 The main reason for the left and right offset of the slab
1 Each conveyor belt on the paving line runs off during operation or its center deviates from the center line of the hot press.
2 The adjustment position of the slab width edge saw on the paving line is not suitable.
2.3 The main reason for the deviation before and after slab generation
1 The final position setting of the loading process of the loading plate is not suitable, or the position of the slab in the tray is not allowed.
2 Because the speed of the loading of the loading trolley is inconsistent with the speed of the pallet belt, the slab is moved forward or behind in the hot plate.
3 The clutch of each layer of the tray mesh belt does not work well.
4 There is no corresponding change in the position of the slab after the slab length adjustment.
3 hot plate deformation
3.1 Causes of deformation of hot plate
At present, the reason for the large deviation of the thickness of the MDF board in many manufacturers in China is mainly caused by the deformation of the hot plate. The deformation of the hot plate has lateral deformation and longitudinal deformation, and the main reasons are as follows:
1 When the preheating is not uniform, the temperature rises too fast, especially when it is preheated after the cold machine. If it is heated by Yanqi, it will not be smooth due to the limitation of its own heating characteristics and the condensed water discharge during preheating. It is easy to control the temperature, which is more likely to cause deformation.
2 In the production process, there are leakage slabs, short slabs, light slabs, etc., so that the pressure is concentrated on the thickness gauge and the hot plate is deformed.
After the deformation of the hot plate, the plate is prone to the following problems: a. warp deformation is large; b. the plate thickness and size distribution of each plate is regular, and one of the upper and lower adjacent plates is thin and thin on both sides. One side is thick and thin in the middle; c. The density of each point of the board differs greatly during the detection.
4 uneven installation
Paving uniformity is also an important factor affecting the thickness deviation of the board. Compared with a single laminator or a continuous press, the multi-layer laminator has a more serious influence on the thickness deviation of the board. If a slab is unqualified in a slab (such as heavy or light weight, uneven slab left and right, etc.), it will cause thickness deviation of other slabs. In the production process, "wedge plates" and ultra-thick, ultra-thin plates will appear.
The paving uniformity can be analyzed in detail by detecting the weight per unit area of ​​the horizontal and vertical points of the wool sheet (kg/crn2), which makes it easier to analyze whether the thickness deviation is caused by the uniformity of the pavement than the measured density (kg/crn3).
The uniformity of slab paving depends mainly on the advancement of the equipment and control system and the level of worker operation. The uniformity of the pavement is ensured by controlling the weight of the slab and the distribution of the fibers in the paving chamber.
4.1 Causes of longitudinal thickness deviation of slab
The thickness deviation is mainly caused by fluctuations in the weight of the slab during paving. The main reasons for the weight fluctuation are as follows:
1Because the fiber in the fiber silo is insufficient or uneven, the material level of the paving chamber is unstable, which causes the fluctuation of the weight of the slab. Although the height of the material level of the paving chamber can be automatically controlled by the speed of the belt of the fiber silo, The height of the material level is guaranteed to be stable, but the change of the fiber conveying quantity is not allowed to be too sensitive, otherwise the production accident of the blocking material will often occur. In operation, try to match the amount of abrasive with the amount of press production.
2 The production process often fails, and the equipment stops when it is opened. This will not only ensure sufficient fiber volume, but also recycle the discharge material on the paving line into the fiber silo, causing the material level to be unstable. When the slab weight is loaded, there is a large fluctuation, and the thickness of the board is likely to be uneven.
3 The fiber bulk density changes due to fluctuations in the airflow of the paving machine.
4 The weight fluctuation caused by changing the paving speed too much during operation.
5PID process control parameter setting is not suitable or other electrical faults cause control actions to be inaccurate.
4.2 Causes of lateral thickness deviation of slab
The uneven distribution of fibers in the pavement chamber can cause lateral thickness deviation of the slab. The main reasons are as follows:
1 The fiber is too thick and of poor quality.
2 The height sensor of the pavement chamber is dusty, resulting in a false material level.
3 The level setting is not enough, and the sweeping amount of the sweeping roller is too small.
4 The pulse airflow is insufficient or its control valve is out of order.
5 Insufficient air flow or improper adjustment.
5The rebound of the slab is too large after hot pressing
There is a settable final position value of the press in the hot pressing parameter. For example, the slab of 15mm size can be set to the final position of L4=16.8mm. Due to the plasticity of the fiber, the slab will produce a small amount after being heated and pressurized. The amount of rebound. In the production process, the set value of the hot pressing parameters does not change much after the process is mature, and the reasons for the excessive rebound of the slab are mainly:
1 Changes in raw materials. Due to the different nature of the various tree species, the shape and plasticity of the produced fibers are different. The rebound amount of the slab after heating and pressurization is also inconsistent. For example, our factory uses the tree and acacia wood respectively. It was found that the slab rebound produced by Acacia wood was much smaller when other process parameters were unchanged.
2 The moisture content of the fiber also has a great influence on the rebound of the slab. The water content is high and the rebound amount is small; if the water content is low, the rebound amount is large.
3 If the slab weight setting value is too large, the rebound amount will be large.
4 Fiber morphology also has a certain impact on the rebound of the slab.
5 When the amount of glue is insufficient, the rebound amount is large due to insufficient fiber bonding force.
6 hot press simultaneous closing mechanism adjustment is not accurate
At the same time, the closing mechanism not only plays the role of synchronous lifting, opening the laminates, and reducing the closing time, but also plays the role of balancing the weight of each laminate and slab. Theoretically, the adjustment mechanism can be adjusted as much as possible. To overcome the influence of the weight of each laminate and slab on the thickness deviation of each layer of slab. Since the weight of the pressure plate and the slab is much smaller than the pressure of the hydraulic system, plus the compensation device on the tie rod of the simultaneous closing mechanism, in practice The effect on thickness deviation during production is not very obvious.
7 summary and experience
In summary, the author believes that in order to minimize the thickness deviation of the multi-layer laminating machine, the following problems should be noted.
1 When selecting the hot press, consider whether it can meet the thickness deviation requirements, such as whether there is advanced and reasonable
Pressure and position control system, whether the material and thickness of the hot plate meet the requirements, as well as its heating medium and heating uniformity.
2 In the choice of paving machine, it is necessary to consider whether the paving uniformity and stability can be guaranteed.
3 In the operation, we must pay attention to control the quality of the fiber, water content and the weight of the slab; when preheating the press, it must be slowly heated according to the operating procedures to prevent the compressor air pressure and slab leakage.
4 Do a good job of maintenance and repair of equipment to ensure continuous and stable production.
5 Mechanical thickness gauges can be used in the press (especially when the hot platen has been somewhat deformed), which can reduce the deviation, but the following points should be done:
a. The thickness gauge should be processed with high precision, and the thickness gauge and the fiber block on the hot platen should be removed frequently.
b. It is necessary to prevent the unsatisfactory slab from being sent to the press for pressure to prevent leakage of the slab. When using the double-layer production process to produce thick plates, it is necessary to prevent the single-layer slab from being sent to the press. Pressurize.
c. If the potential thickness gauge is used to control the pressure of the hydraulic system, it should be noted that the final position set should not be less than the thickness of the mechanical thickness gauge to protect the hot plate from deformation. When operating, pay attention to the hydraulic curve.
d. When the thickness gauge is deformed, it should be replaced in time.
In short, the reason for the thickness deviation of the medium density fiberboard produced by the multi-layer laminator is multi-faceted. In the production process, it is necessary to use scientific statistical methods, analyze the main causes, and make targeted improvements and adjustments. It is possible to reduce deviations, improve product quality, and reduce production costs.
Welcome customers from all over the world to purchase the Height Adjustable Desk and Lifting Column.
Causes and solutions for thickness deviation of MDF produced by multi-lamination machine
The medium density fiberboard produced by the multi-layer laminating machine generally has a large deviation of the thickness of the board. In order to reduce the product in the sanding process