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Matters needing attention in the production of foamed products

Time:2019-07-24

The key points of foaming process control in XPS foamed sheet production line, controlling the physical and chemical properties of the raw liquid, the chemical properties of polyisocyanate, polyether, foaming agent, catalyst and foam stabilizer in black and white materials, directly determine the chemical reaction and foam physical properties of polyurethane. It is the basic condition for producing qualified polyurethane foam. Black and white monomers should be clear viscous liquid without flocculent insoluble impurities. If there are insoluble impurities, the filter screen of foaming machine will be blocked, resulting in unstable flow of raw materials, the proportion of black and white materials does not meet the requirements of uneven mixing. Even blocked the pipe of the foaming machine.


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Polyurethane foaming is a complex physical and chemical reaction process by controlling process temperature and aging time. The fluctuation of raw material, mould, preheating temperature and ripening time will directly affect the foaming quality. Black material is a kind of more active chemical substance. It is easy to react with water. During storage, the container should be kept dry and sealed and protected by dry nitrogen. During use, it should not be in direct contact with water. Crystallization occurs when the storage temperature is below 5 C, so we must pay attention to the anti-freezing. Once crystallization occurs, it should be heated and melted at 70 ~80 ~C before use, and fully stirred uniformly. Storage temperature higher than 50 C will produce an insoluble solid, the viscosity increases, and the chemical properties change. White materials have the same properties. Therefore, black and white materials should be stored in ventilated, cool and dry places at room temperature to avoid sunshine and rain.


In order to control the ratio of raw liquor and injection volume, the ratio of black material, composite polyether and cyclopentane must be strictly controlled. When the total injection volume remains unchanged, vacuoles will appear when the proportion of black material is too large, soft bubbles will appear when the proportion of white material is too large, bubbles will appear when the proportion of cyclopentane is too large, and vacuoles will appear when the proportion of cyclopentane is too small. The proportion of black and white materials will be uneven, and uneven mixing will occur. The amount of injection should be based on the technological requirements. When the injection volume is lower than the process requirement, the foam will have low density, low strength, and even the phenomenon of filling not compact vacuoles. Bubbles and leaks will occur when the injection volume is higher than the process requirement, and the box will be deformed.

Black and white materials should be treated at constant temperature before foaming, and the foaming temperature should be controlled at 18 ~25 C. When the temperature is too low, the viscosity of the black-and-white material is large, the flow rate is unstable, the fluidity is poor, and the mixture is not uniform. When the temperature is too low, the reaction rate of foams is slow, and the curing time is long. When the ripening time is insufficient, the box body and door body will still foam after demoulding, and the appearance will be deformed. When the temperature is too high, the reaction is intense and difficult to control. It is easy to appear that the performance of the bubbles injected into larger boxes is not uniform. The bubbles injected at the beginning have undergone chemical reactions, and the viscosity increases rapidly. The bubbles injected after that have not yet reacted. As a result, the injected bubbles can not push the first injected bubbles to the front of the box foaming process, resulting in local bubbles in the box.


When using the extruder, it is necessary to check the purity and quality of the raw materials frequently, and no foreign matter such as sand or metal powder is allowed to mix into the raw materials or even enter the barrel; check the lubricating oil parts of the extruder, add lubricating oil, and the temperature rise of the bearing parts should not exceed 50 C; the barrel of the extruder should have enough constant temperature heating time, not to enter the barrel. It is allowed to start production under the condition that the raw material is below the technological temperature; when the screw is working, it should start at a low speed and work for a period of time, and then increase the screw speed after all is normal; if there is no raw material in the barrel, the screw is not allowed to run empty for a long time; the oscillation change of the ammeter pointer of the screw-driven motor is often observed, resulting in a longer period of electricity. When the motor is overloaded, stop immediately, find out the cause of the fault, and continue production after troubleshooting; after the first heating of the barrel to the process temperature, tighten the connecting fixed bolt between the barrel and the base once more; when installing the mould and the screw, the contact surface of the parts should be clean and free of any foreign matter, and the tightening bolt should be coated with silicone oil. In order to facilitate the disassembly of parts; when disassembling the extruder, it is not allowed to hit the surface of parts with a heavy hammer, pad the hardwood if necessary, and disassemble parts with a hammer. When removing the residue on the barrel, screw and die of extruder, only bamboo or copper knife can be used to brush and shovel the material. No steel knife can be used to scrape the adhesives, and barbecue is not allowed to clean the residue on the screw.