Frequently asked questions about glue for panel and blockboard
Guide: Plywood and blockboard is an important process in the production of solid wood furniture. In the process of wood panel and blockboard, the glue line of the second thickened panel and blockboard is easy to crack, and what is the reason for the end glue line cracking?
Here is a detailed explanation for you. Problem 1: Analysis of the main reasons for cracking at the glue line of the secondary thickened panel and blockboard: 1. The thickness of each board is relatively large and slightly poor, which causes the pressure on the thin parts or the pressure is not in place when thickening the panel and blockboard. 2. The uneven processing of the splicing surface has the phenomenon of knife jumping or head and tail gnawing, which causes the splicing surface not to be pressed tightly. 3. The simple pressurizing equipment and fixture cannot guarantee the required pressure (hard wood 12-15kg/cm2), and the simple pressurizing of the fixture cannot guarantee the uniform pressure on all surfaces. 4. The pressurization time is too short. Because the secondary splicing and blockboard are basically raw materials superimposed, the stress rebound of the splicing itself is large, and the adhesive curing degree is not enough, it will slowly rebound and crack after pressure relief. Solution: 1. For the jointed boards and blockboard materials that need to be thickened for the second time, the thickness must be determined by double-sided planing or sanding to ensure that the thickness difference of each board is less than 0.2mm and the splicing surface is smooth and flat. 2. It is better to use a special hydraulic panel and blockboard machine to make secondary thickened panels and blockboards to ensure sufficient pressure and uniformity of pressure application. When using manual clamps, the upper and lower clamps must be balanced to ensure uniformity of pressure application and sufficient pressure. 3. The pressing time of the secondary thickened panel and blockboard shall be sufficient. The medium and soft materials shall be guaranteed for more than 2 hours (25 ℃), and the medium and hard materials shall be guaranteed for more than 3 hours (25 ℃). 4. Second thickening of the assembled plate. Problem 2: The main reasons for the end glue line cracking of the assembled boards after being placed for a period of time or shipped to different areas are as follows: 1. The relationship between water content. The water content of panel and blockboard is relatively high during processing, 14-16%. After being placed for a period of time or in a relatively dry area, large internal stress changes with the change of water content, resulting in wood cracks or glue line cracks. 2. The surface of the panel and blockboard is not smooth enough with saw marks or knife jumping, and the best bonding strength of the panel and blockboard surface cannot be achieved after the panel and blockboard are pressurized. The change of internal stress of solid wood leads to insufficient bonding strength and cracking. 3. The proportion of curing agent (bridging agent) in the glue of the panel and blockboard is too small and insufficient, resulting in insufficient bonding strength of the splicing surface. The strength of the splicing surface is less than the internal stress strength of the solid wood itself, so that the glue line cracks. 4. The adhesive strength matching the wood material is not enough, and the adhesive with corresponding strength requirements is not selected. Solution: 1. Control the moisture content of solid wood splicing at 10-12%. It is better to control it at 8-10% to avoid cracking caused by large stress change in the later period. The assembled plates shall be sealed and wrapped with film before the next process to avoid moisture absorption and moisture regain. 2. When splicing boards and blockboards, ensure that the splicing surface is smooth and flat without any saw marks or knife jumping, and ensure that the splicing surface is clean and flat. 3. Regularly check the proportion of glue main agent and curing agent for panel and blockboard every day, and use precision measuring tools to mix. 4. Before the glue of different wood species is applied, the strength test shall be done first, and the glue shall be applied in large quantities after reaching the required strength of the wood species. The use of glue for plywood and blockboard will have different application methods in different environments, generally in terms of temperature, wood moisture content, wood processing accuracy, glue mixing, glue mixing, glue coating, pressure and follow-up, some application skills should be paid attention to. Key points for the use of plywood and blockboard glue 1. In terms of temperature, the working environment temperature and wood surface temperature should be measured in time in different seasons. The temperature, to some extent, determines the speed of cross-linking reaction of plywood and blockboard glue. 2. Wood moisture content 8-12% is the best; The critical moisture content difference of wood should be controlled within 3%. 3. Wood processing precision The wood processing precision shall be within 0.15mm. The wood bonding surface shall be free of processing defects such as “gnawing head, sweeping tail”, and the wood bonding surface shall be free of “planing marks, sawing marks, carbonization”, etc. Keep the splicing surface flat and free of wavy surface or curved or twisted surface. For the wood that is easy to deform (such as oak, ash, etc.), the wood that is planed on the same day must be spliced on the same day, and the wood that is planed overnight must be planed again; 4. It is forbidden to mix wood chips, dust and other impurities or add water when mixing glue. Proportions: glue for jointed boards and blockboards: curing agent=10:0.8~1 (weight ratio), and the standard glue amount is 250-300g/m2. 5. In glue mixing, add the curing agent into the glue and stir it evenly. Once the amount of curing agent is confirmed, it cannot be changed at will, otherwise it will seriously affect the bonding strength, water resistance and other key functions. It is best to use it within 1-2 hours. It is normal to find bubbles in use. If there are too many bubbles, you need to stir them several times until the bubbles settle naturally before use. 6. In terms of gluing, users should determine the amount of gluing according to the space temperature and humidity at that time of the day. When the space temperature is low, the humidity is high (below 80%), and the wood is hard, the amount of glue should be less; When the space temperature is high, the humidity is low (below 60%), and the wood is soft, more glue should be applied. 7. In terms of pressure, according to different tree species and bonding areas, the corresponding pressure of jointed boards and blockboards should be adjusted constantly. Pressure removal: It needs to be pressurized for a long time. Small area plates can be removed 1.5 hours after pressurization, but must be removed 3 hours before moving to the next process. 8. During pressurization, check and pressurize to prevent the wooden strip from being drawn out (uneven and small ends are most likely to occur). If it is drawn out, loosen and reset it, and do not forcibly reset it under pressure; Check whether there is glue overflow in the abutted joint. If there is no glue overflow, it means that the amount of glue is not enough or the pressing time is too long after the glue is applied. Correct this phenomenon immediately. The pressurization inspection process cannot be ignored. 9. The curing period after pressure relief is in the process of solid wood panel, blockboard or tooth joint. In order to prevent glue opening, the spliced workpieces shall be stacked for curing after pressure relief. According to the different climate conditions of different woods, a curing time period should be set to ensure the normal use of the next process. We suggest that the best time for yard curing should be 3-5 days when the temperature is low, the humidity is high, and the wood is hard. The best time for stacking curing should be 1-2 days when the temperature is high, the humidity is low, and the wood is soft. 10. If the glue for the plywood and blockboard with curing agent can not be used up at the moment, it must be sealed and stored temporarily until it is reused next time (it cannot be exposed to the air for a long time to prevent dry skin), so as not to affect the splicing quality.
