Common quality problems and solutions in the process of MDF router board!
Guide: Compared with ordinary medium density fiberboard, high-end medium density fiberboard has higher density (the density is above 790 kg/m3), more symmetrical structure, and more delicate fiber. After carving or milling, the surface is flat, free of burrs and curls, which can effectively reduce the maintenance and processing of users in the later period (such as no need to polish or reduce the number of polishing, reduce the use of paint or coating, etc.), and save production costs.
High end MDF router board refers to a new type of MDF decoration material that can be made from MDF that can be deeply processed for the second time by carving various lattice shapes through a large woodworking computer processing center, and then by polishing, spraying, baking and other processes on the side surface. Compared with ordinary medium density fiberboard, high-end medium density fiberboard has higher density (the density is above 790 kg/m3), more symmetrical structure, and more delicate fiber. After carving or milling, the surface is flat, free of burrs and curls, which can effectively reduce the maintenance and processing of users in the later period (such as no need to polish or reduce the number of polishing, reduce the use of paint or coating, etc.), and save production costs. High end MDF router boards are mainly used for high-end customized furniture, cabinets, wardrobe doors, bathroom cabinets, children’s furniture, decorative wallboards, process parts and handicrafts that need to be milled and carved, skirting lines, buckles and decorative lines, door and window lines, etc. Although the production process of high-end MDF router board is relatively advanced and the product quality is relatively good, there are still many quality problems in the actual router processing of customers, such as roughening, curling, unevenness, roughness, plate bending deformation, etc. Based on years of production experience, the author introduces the common quality problems and their solutions as follows. 01 Roughing of the milling surface High end medium density fiberboard The milling surface is not smooth during the milling process, which affects the use. The reasons for the fuzzing of the MDF router board are: the density distribution of the board section is unreasonable, the density difference of the surface core layer is too large, and the core layer density is low; The raw materials used have been stored for a long time, rotten and deteriorated; The fiber is coarse during hot grinding; The plates that are not produced normally in the production process are not stored and degraded differently; Low amount of adhesive leads to low internal bonding strength; The processing tools are not sharp, and they were not replaced in time.
Solution: In the production process, the quality of each process must be well controlled, and comprehensive control must be carried out from the selection of raw materials, chipping, wood chip screening, washing, cooking and softening, hot grinding, sizing, drying, paving and molding, pre pressing, continuous hot pressing, wool curing to the selection of cutting tools, cutting depth and feeding speed. 1) Selection of raw materials: the age of the tree is 3-5 years, the storage time is 30-60 days after cutting, and the mass ratio of miscellaneous wood and eucalyptus is 2 ∶ 8. 2) The quality of wood chips is the precondition to determine the quality of fiber. The chipping process ensures that the wood chips are 16~30 mm long, 15~25 mm wide and 3~5 mm thick, and that the size of wood chips is uniform. 3) Cooking softening: the cooking temperature is 160~170 ℃, the steam pressure in the cooking tank is 7.5~9.0 bar, the cooking time is 2.5~4.0 min, and the pressure difference in the cooking tank is kept at 0.6~1.0 bar. 4) The amount of fine fiber in hot grinding is less than or equal to 45%, and the screening value of coarse fiber is less than or equal to 0.1%; The moisture content of the dried fiber is 7.5% ～ 8.5%. 5) During the process of sizing, ensure that the sizing amount is about 18.0% to ensure that the bonding strength in the plate is ≥ 1.5MPa. 6) The amount of mold release agent sprayed on the surface of the paved belt is increased from 18 g/m2 to 20 g/m2 to reduce the adhesion of fibers to the belt and ensure the smooth and flat surface after sanding. 7) The starting point pressure of continuous hot pressing slab is 0.40 MPa to 0.50 MPa, and gradually reduces the pressure to 0.12 MPa to 0.18 MPa, so as to prevent slab damage due to improper pressure setting, and ensure that the upper and lower density peaks of the slab are symmetrical and uniform. 8) Adjust the density curve of hot pressing process to ensure that the peak density is 1080-1100 kg/m3, and the density of core layer accounts for more than 92% of the average density, so as to ensure that the plate surface is smooth and the core layer is dense. 9) In order to ensure that high-end medium density fiberboard engraving and milling boards meet user requirements, the process requires that the curing time of rough boards should be ≥ 72 h. 10) Sharp cutters shall be used and replaced regularly during the engraving, and the appropriate engraving depth and feeding speed shall be selected to ensure the smooth surface without fuzzing. 02 Edge curling of the routing surface The reason for the edge curling of the routing surface is that the density of the MDF routing board is low or the routing cutter is not sharp, which causes the edge curling of the routing edge after the routing is not smooth. The solution is to increase the peak density of high-end medium density fiberboard, ensure that the peak density is 1 080 ～ 1 100 kg/m3, and regularly replace the milling cutter or select the diamond cutter for milling, so as to ensure the quality of the plate milling. 03 The main reasons for uneven milling surface and pits of high-end MDF milling board are low bonding strength, and the feeling is not smooth and flat when touching. The solution is to use raw materials. Eucalyptus and miscellaneous wood can be stored for about 30~60 days and mixed evenly according to a certain quality ratio; During hot grinding, ensure that the proportion of coarse fiber in hot grinding process is controlled at ≤ 0.1%; Keep the fiber moisture content stable during drying, and control the moisture content at 7.5%~8.5%; The amount of glue shall be about 18% to ensure that the bonding strength in the plate is ≥ 1.5 MPa. Only in this way can the plate milling surface be fine, smooth and free of sticking. The adhesive was modified to improve the internal bonding strength of the board. 04 It is very important to ensure that the high-end MDF router board is flat and not warped during the routing process due to the bending deformation of the MDF router board. However, it is not easy to completely avoid the warping deformation. It is necessary to carefully analyze the causes of the warping deformation of the board and solve them. 1) The raw materials used in the production process are various. The deformation degree of plates produced by different tree species is different.
Solution: In the chipping process, tree species with similar properties and densities shall be selected as far as possible, and the raw materials shall be reasonably proportioned and mixed evenly. 2) The waterproof performance of the medium density fiberboard milled board is poor. High end medium density fiberboard engraving boards are required to have certain waterproof performance, otherwise they are easy to absorb moisture and deform. In general, the density curve of high-end MDF router board should be evenly distributed, the density of surface and core layers should be uniform and smooth, and the core layer density should account for more than 92% of the average density. Solution: increase the amount of waterproof materials to ensure that the thickness expansion rate of water absorption of the board is ≤ 5%. 3) The storage conditions of MDF milled boards are poor. High end medium density fiberboard planks, if placed in a damp environment, are prone to moisture absorption and deformation, or even mildew. Therefore, they should be stored in a dry and ventilated environment, and should be stacked flat. The wood under them should be flat and consistent in height, to prevent the planks from being stacked and deformed. 4) The lateral density deviation of the plate is large and the peak difference of the plate density is large. Large transverse density deviation, large difference between the upper and lower surface density peaks, or no symmetrical sanding as required, resulting in large difference between the sanded plate surface and the bottom peak value, causing the stress deviation of the plate and causing the deformation of the plate.
Solution: due to the poor interweaving capacity of fine fibers in the medium density fiberboard, the air is discharged to the edge during the prepressing process, which is easy to break the slab, and the edge collapses after the prepressing, resulting in low edge density. Therefore, the transverse density is adjusted by adjusting the self-made baffles on both sides of the prepressing during production; Adjust the water content of the upper and lower surface layers of the slab by adjusting the amount of mold release agent sprayed up and down, and adjust the peak density of the slab surface and bottom by adjusting the inlet pressure of the press; Ensure symmetrical sanding, and ensure that the peak density is consistent after sanding to prevent deformation. 5) After sanding, due to some reasons, the boards were not inspected and warehoused in time, leading to moisture absorption deformation of the boards. In the actual production process, the sanded products have not been inspected and warehoused in a timely manner due to some reasons, and the boards have been exposed to the air for a long time, leading to moisture absorption deformation. Therefore, the sanded boards should be inspected and warehoused in a timely manner. 6) Symmetrical processing technology is not adopted for the secondary processing of MDF router board. During the secondary processing of high-end medium density fiberboard, one side is pasted with melamine impregnated paper, and the other side is milled with blister. The bending deformation of one side of the paper pasted with melamine impregnated film after cutting and blistering is relatively large, and the deformation exceeds 5 mm. The reason is that the stress produced on both sides of the product during secondary processing is inconsistent, and the plate is prone to bending and deformation when subjected to external forces, which is caused by the low static bending strength and elastic modulus of the plate. Solution: By adjusting the press process, increase the peak density of the board and the thickness of the hard shell layer, so as to improve the static bending strength and elastic modulus, and slow down the bending deformation of high-end medium density fiberboard in use. 05 Conclusion With the rapid development of MDF production, its production enterprises are facing severe challenges. How to improve product quality, meet market demand and handle the relationship between product quality and cost has become an important topic for enterprises to study. At present, more and more customers use customized furniture, and high-end MDF router boards are increasingly favored by high-end customers. In the fierce market competition in the future, manufacturers should control every link in the production process, produce every board, and constantly improve product quality to ensure the use requirements of high-end users.
