How to solve the problem of sand mark on the surface of MDF board

Medium-density fiberboard (MDF, MDF) has high surface quality requirements when used. Especially when surface decoration is required, the surface of the board is required to be flat, fine and have high bonding strength. The characteristics of the MDF are: uniform internal structure, good bending strength, high bond strength between fibers, and high impact strength; smooth and smooth surface, easy to paste thin wood, no processing defects (away from seaming, lamination) and thrift , cracks, etc.; mechanical processing and assembly performance is good, sawing, grooving, slotting, sanding and other properties similar to wood; other materials have strong bonding strength, high strength with wood screws and nails; easy to engrave and mill Because the slab is evenly organized, the center part and the surface are basically the same, and its density is similar to wood, so it can be engraved; the edge of the MDF can be processed according to any property; the edge density is strong, and it can be directly painted without using the edge sealing material.

The sanding machine is used for finishing various artificial boards, wood products and wooden parts, improving the dimensional accuracy, surface flatness and smoothness of the processed parts, and secondary processing of the paint or sheet of wooden parts. (Wood grain printing, stickers and stickers, etc.) get a good base. However, through the sanding production process, the quality defects of the MDF itself and the quality defects caused by the sanding process will be reflected. Now we mainly talk about the line-like raised sand marks and the line-shaped sag sand of the MDF board. Trace problem.

1 line-like raised sand marks and line-shaped sunken sand marks

1.1 Line-like raised sand marks (that is, there are raised line-like marks in the longitudinal direction of the surface of the MDF board), which are generally easy to find when drawing on the board with chalk, etc., when it is serious, it can be seen with the naked eye. The raised line-like traces are found on the board surface, which can be felt by severe hands. It can be seen by scratching with a slight hand.

1.2 Line-shaped sag sand marks (that is, the longitudinal direction of the surface of the MDF board has a concave line-like trace, which is like a strip-like trace on the surface of the board). It is usually easy to find when using the chalk or the like. When it is very serious, you can see a line-like scratch on the surface of the board with the naked eye. Generally, you can feel it when you use your fingernail to make a slight stroke on the board surface. It can be used for a slight touch. come out.

2 Causes of line-like raised sand marks and line-shaped sag sand marks

2.1 Reasons for the generation of line-like raised sand marks

The so-called raised sand mark refers to the sanding of the sand belt or the partial abrasive belt failure, which causes the sand surface of the board surface to be sanded at the position where the surface of the board is not sanded, and the sand belt is de-grained. The situation is as follows:

2.1.1 Due to the presence of hard objects in the MDF, the sanding of the belt is caused by the raised sand marks. There are foreign objects in the MDF, and the foreign matter is divided into accidental foreign objects, such as equipment and screws, randomly generated foreign objects. There are also foreign materials in the wood raw materials, such as sandstone entrained in the transportation process when harvesting wood raw materials or sandstone caught in the purchased wood chips; the above two situations make the sand belt easy to appear after hitting these hard things. The sand is removed, which causes the MDF surface to have a line of raised sand marks.

2.1.3 The cleaners on the production line are free to use the old fiber bundle air conveying system on the ground to return to the inside of the MDF. The fibers dropped on the ground are easily mixed with sand, equipment bolts or iron items. Hard objects, the use of these old fibers containing impurities will cause the sand to have sand lines on the surface of the fiberboard after the sand is removed.

2.1.3 Since many manufacturers now use dust as fuel, dust is produced by polishing the surface pre-cured layer of MDF by sanding machine. After the belt is used for a long time, there will be de-graining or the quality problem of the belt itself. The problem of sand particles, so that the sand after the sanding is mixed with sand particles, and now the dust is used in the combustion process to carry out dust combustion, so that the sand particles trapped in the dust are not easily melted at the high temperature of the boiler. (General sand belt sand is made of silicon carbide or gold corundum, its melting point exceeds 2000 ° C, and the boiler temperature is generally about 1000 ° C). At this time, if the fiber is dried using flue gas drying, the boiler dust collector is not effective. The sand is easy to enter the fiber conveying system through the flue gas conveying system, which causes the sand grain hard material in the fiberboard during the production process to cause the sand fiber board to be easily sanded during the sanding process, thereby generating a line-like convex sand mark. The quality of the board surface is defective.

2.1.4 If the cooling time of the MDF is insufficient, the sanding will cause the MDF to produce a line-like raised sand mark defect. Since the adhesive of the MDF is not completely cured, it is easy to stick to the part of the belt. The surface of the belt is partially blocked and the heat is not good, which causes the belt to be broken to cause a line-like raised sand mark on the surface of the MDF board.

2.1.5 The choice of abrasive belt adhesive also has an effect on the sanding of the abrasive belt. The sand is adhered to the belt base by the adhesive. If the quality of the adhesive is not good, the high temperature of the abrasive belt will produce high temperature. The aging of the adhesive or the decrease of the bonding force can not hold the sand, resulting in sand loss, thereby producing a line-like raised sand mark on the surface of the MDF.

2.1.6 The transportation process of the abrasive belt also has an impact on the quality of the abrasive belt. The rough loading and unloading during the transportation of the abrasive belt can also cause the sanding of the abrasive belt to fall off, and the line-like raised sand marks on the surface of the MDF board bring certain quality defects. .

2.1.7 Insufficient ventilation of the sanding machine also affects the sand. When the MDF is sanded, the sand is broken from the sanding belt to the surface of the board due to the abrasion of the abrasive belt in the previous process. The exhaust is not enough to be removed in the medium fiber. The sand on the upper surface of the board, along with the sanding process from the middle of the MDF to the sanding process, will hit the sand on the surface of the MDF board, causing the sand in the back belt to fall off the sand, thus causing the surface of the MDF board to appear. There is a quality defect of the line-like raised sand marks. This is usually the case on the upper surface of the MDF sanding, because the sand of the lower surface of the MDF sanding directly falls off and is pumped away or directly Dropped to the ground, so there is no impact on the board surface.

2.1.8 The storage of the abrasive belt has a certain influence on the sand. The abrasive belt should be stored under a certain temperature and humidity. If the storage environment is not used, the aging of the abrasive belt adhesive will also cause the abrasive belt to fall off the sand. As a result, the surface of the MDF board has a quality defect of a line-like raised sand mark.

2.2 Reasons for the generation of lined sand marks

2.2.1 Because manufacturers now evaluate the quality of abrasive belts as measured by their longevity, some abrasive belt manufacturers have larger grit sizes than standard sand grits when selecting grit sands, such as 60 mesh grits with coarser than 60 mesh grit, or Doping some coarse sand, the life of the belt is better, but these coarse sand will leave some sunken line scratches on the board surface, which is called the line sand marks.

2.2.2 Due to the scratch on the surface of the sander of the sander, a bump is generated on the surface of the sanding roller, so that the sanding belt is raised at the position during the sanding process, and the sandstone is convex at the position due to the sanding of the MDF. The cutting amount of the MDF plate at this position is relatively large, so that a large amount of cuts will result in a concave line-like scratch, which can be seen by the naked eye in severe cases.

2.2.3 When the surface of the auxiliary transport equipment of the sander has a hard object, it is also the cause of the line-like sag of the MDF board. This is mainly caused by the near-plate roll on the MDF board. When the plate is near the plate, the MDF workpiece is clamped forward. If there is a protrusion on the plate roller, it will leave a scratch on the plate surface. Although some scratches can be eliminated after sanding, there are also Some scratches can not be eliminated, mainly causing the line surface of the MDF board to have depressions.

3 Solutions for line-like bulges and dents

3.1 Method for solving the line-like raised sand marks

3.1.1 The wood chip washing system is used in the production process. The main purpose of the wood chip washing system is to remove the hard impurities such as sand, stone and iron contained in the wood chips, and replace the water used in the washing system regularly, and replace it. The water is reused after being treated by precipitation, which effectively ensures the quality of the water and eliminates the quality problems caused by the excessive content of fine sand after long-term use of the water in the wood washing system.

3.1.2 Strengthen the management of the production line cleaners, eliminate the use of unqualified fibers, and prevent the inclusion of hard materials such as sand, stone and iron into the fibers, which will help to solve the line-like raised sand marks.

3.1.3 For drying systems that use flue gas for fiber drying, the flue gas deduster of the thermal energy plant should be cleaned regularly, so that the abrasive belt particles that cannot be burned in the dust can not enter the middle fiberboard through the fiber air conveying system to cause a line shape. Quality defects in raised sand marks.

3.1.4 The MDF must be cooled and placed in a well ventilated place for 48 hours before sanding, so that the glue in the plate has sufficient time for complete curing, so that the sanding work will not occur because of the sanding belt. The local sand particles are affected by the quality of the sand belt, which solves the problem of the line-like raised sand marks on the board surface due to insufficient placement time of the MDF.

3.1.5 Strictly challenge the manufacturer of the abrasive belt, especially to understand the production process and control the stability of the belt production process, so that there will be no sand due to the problem of the abrasive belt sand adhesive. The quality problem of falling off and causing line-like raised sand marks.

3.1.6 For the belt transportation process, it is necessary to use the cardboard to wrap the tape. When placing the belt, it should be handled gently. It cannot be thrown by force or other rough handling methods. The transportation process should be as stable as possible. Do not let the belt be in the belt. The car is violently oscillated to avoid the problem of the quality of the line-like raised sand marks caused by the sanding of the abrasive belt sand due to external forces.

3.1.7 Measure and calculate the air volume of the sanding machine dust removal fan to ensure the effect of the sanding machine dust removal fan, not to let the abrasive belt sand particles fall on the middle fiber board surface, to solve the quality problem of the strip-shaped convex sand marks .

3.1.8 For the storage of abrasive belts, special sand belts should be placed to place the belts, keep the temperature of the belt room at around 20 °C, and the relative humidity is about 60%, so that the sand can be well preserved and the sand can be guaranteed. The quality of the belt is not affected, and the quality defects of the strip-shaped raised sand marks caused by the sand drop problem caused by the sand belt are reduced.

3.2 Method for solving linear sag sand marks

3.2.1 Resolve the stable and reliable manufacturer of the belt production quality, and ensure the quality of the belt, because the manufacturer of the fiberboard will generally not test the flatness of the belt, especially the detection of the belt sand. The sand belt is tested and re-purchased, and the used belt manufacturer is judged from the effect of use. Therefore, this requires the Chinese fiber manufacturer to select the manufacturer of the abrasive belt to ensure the quality of the abrasive belt, and solve the problem of the quality defect of the line-shaped concave sand mark on the surface of the MDF due to the quality problem of the abrasive belt sand.

3.2.2 Regularly inspect the sanding roller of the sanding machine, remove it if necessary, and re-polish and polish to ensure the smooth and smooth working surface of the sanding roller, and solve the problem that the surface of the MDF board has a line-shaped concave sand caused by the uneven working of the sanding roller. Trace quality defects.

3.2.3 Check the auxiliary transport roller of the sanding machine, clean the impurities on the surface of the transport roller, ensure the smooth and smooth working surface of the transport roller, and solve the problem that the surface of the MDF board has a line-shaped concave sand mark due to the uneven working of the transport roller. Quality defects.

4 Conclusion

Through the above method, the problem of the line-like bulge sand marks and the dents of the line state can be effectively solved, and the secondary processing (ie, veneering) of the MDF board surface is provided with a good quality guarantee, so that the MDF board The processing sector has been further expanded to increase the added value of the product.

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