Prevention and treatment of carbonization of the h

Prevention and treatment of carbonization of plastic products

carbonization of plastic products will have a serious adverse impact on the quality and production cost of products. For plastic products manufacturers, it is of great significance to effectively prevent and solve the carbonization of plastic products

causes and process of carbonization

in the actual production of plastic products, it is generally necessary to isolate the feed inlet before shutdown, eliminate the plastic melt in the extruder and head, turn off the temperature of each zone, and then turn off the power supply. Due to the strong adhesion of plastic melt to metal, it is impossible to completely eliminate it during each shutdown. Finally, a thin layer of plastic melt will firmly adhere to the inner wall of the extruder barrel and head and the screw. After shutdown, the equipment will naturally cool down and stay at high temperature for a long time during the next heating process. Obvious thermal degradation will occur, and gradually turn yellow and coke into carbides. According to the conventional shutdown method, effective sealing measures were not taken at both ends of the die opening and feed inlet of the machine head, which led to the oxidation of air entering the machine, which often aggravated the thermal degradation of residual plastics in the machine during calculation, providing favorable conditions for carbonization. Because the equipment is of metal structure, its thermal expansion rate is quite different from that of plastic, and the adhesion of carbonized plastic to metal is reduced, which is easy to fall off from the inner wall of the barrel, the inner wall of the machine head and the screw of the equipment, and mix into the plastic melt, resulting in many black spots on the inner and outer walls of the products, which is easy to show holes or leaks and many other quality problems

carbonization diagram of plastic raw materials

because ultra-high molecular weight plastic has good hardness, and when the temperature is high, the cleaning object will be softened, so it becomes easy to fall off, which is conducive to the carbide being brought out by the plastic melt. During the cleaning process, the speed of the extruder is repeatedly switched between low speed and high speed for many times. If there is still margin in the motor load, the extruder can be stopped and restarted repeatedly during the operation, so as to further improve the cleaning effect

carbonization solution

in machine cleaning

after a long time of shutdown, heating and restart, many large and small black spots are easy to appear on plastic products, which cannot meet the quality requirements of products. These black spots are the carbides after thermal degradation of residual plastic in the machine. Usually, the washing machine method of continuous extrusion of plastic and elimination of plastic melt with black spots is adopted to clean the machine, and the washing time is up to hours. If the original ultra-high molecular weight plastic is carbonized and the primary color products are produced, the difficulty of washing the machine will be greatly increased, and the washing time will be longer and the washing cost will be higher

in order to quickly clean the carbides in the machine, it is necessary to use plastic with relatively hard material properties or its recycled material plus white mineral oil for cleaning, and the temperature should be appropriately increased by 10 ~ 15 ℃. At this time, the plasticizing ability of the small extruder to the plastic should be considered. For large and medium-sized extruders that can plasticize ultra-high molecular weight plastics, they can be cleaned with ultra-high molecular weight plastics or their recycled materials plus white mineral oil. Because the hardness of UHMWP is good, and when the temperature is high, the cleaning object will be softened and become easy to fall off, which is conducive to the carbide being brought out by the plastic melt. During the cleaning process, the speed of the extruder is repeatedly switched between low speed and high speed for many times. If there is still margin in the motor load, the extruder can be stopped and restarted repeatedly during the operation, so as to further improve the cleaning effect. When the carbides (black spots) in the melt are significantly reduced, replace the usual plastic and clean it until it is clean, and gradually adjust it to the appropriate temperature, then normal production can be achieved

disassembly and cleaning

using the internal cleaning method, it is easier to clean the carbides in the extruder, and it is difficult to clean the carbides in the storage head of hollow blow molding equipment. Because the internal structure of the extruder is simpler, the internal structure of the storage head of the hollow blow molding equipment is complex, and the equipment is used for too long, it will be more difficult to clean. In this case, disassembly and cleaning is imperative. Turn off the power supply and disassemble all the assembly parts of the machine head after the machine head is heated to enough temperature. Clean the plastic melt in the machine head with copper, remove the charred carbide with a metal brush, and then polish all the assembly parts with sandpaper or flower impeller before assembly. Although the disassembly and cleaning effect is very good, it takes a long time and is laborious. Generally, this disassembly and cleaning method is not easy to use

preventive measures for carbonization

temperature and time control

the processing temperature of plastic products is determined according to the plasticization requirements of raw materials and products, and cannot be too high or too low. Too low temperature will lead to excessive load, as well as defects such as water marks and weld lines on the product appearance. If the temperature is too low, the fluidity of the melt will be poor, which will also have a great impact on the gloss of the product surface and the fullness of edges and corners; If the temperature is too high, and sometimes temporarily shut down for two hours, or even several hours, it is easy to produce melt carbonization in the machine. In this case, the constant temperature is between 100 ~ 120 ℃, and it needs to be heated to the required temperature before starting up, so as to prevent carbonization caused by sudden temperature rise or long shutdown and insulation time

heating and start-up operation control

usually adopts one-step heating method, that is, after setting the temperature, continuously heat it to the set temperature, according to the size of the equipment, and then keep the constant temperature for 1 ~ 3 hours before starting up. This method is easy to carbonize the residual plastic in the machine. If the step heating method is adopted, the effect is much better if the temperature is increased in time. For example, set the temperature to 100 ℃ at the beginning, adjust the setting temperature to 130 ℃ after constant temperature, and then adjust the setting temperature to 170 ℃ after constant temperature, and gradually raise the temperature according to the time period until it reaches the required temperature. Small and medium-sized equipment can be started up when it reaches the required temperature. Of course, relevant supporting preparations need to be made in advance. After the large equipment reaches the required temperature, it is better to start the machine with constant temperature for 1 ~ 2 hours

when starting up, you must pay attention to the speed of the extruder slowly accelerating from 1 ~ 5 rpm, the feeding port slowly opening, and pay attention to the current value displayed on the extrusion ammeter at any time. If the load is too large, the constant temperature time should be appropriately extended to achieve step-by-step temperature rise, and the machine should be started as soon as possible when it can be started, so as to prevent the residual plastic in the machine from carbonizing in case of high temperature and too long waiting time for startup

when starting up, you must pay attention to the speed of the extruder slowly accelerating from 1 ~ 5 rpm, the feeding port slowly opening, and pay attention to the current value displayed on the extrusion ammeter at any time. If the load is too large, the constant temperature time should be appropriately extended to achieve step-by-step temperature rise, and the machine should be started as soon as possible when it can be started, so as to prevent the residual plastic in the machine from carbonizing in case of high temperature and too long waiting time for startup

shutdown and temperature shutdown operation control

usually, the shutdown operation is to close the feed inlet of the extruder before shutdown to remove the plastic melt in the extruder. As the current of the extruder decreases, the plastic melt in the extruder is gradually eliminated, and then shutdown and temperature shutdown. In this conventional method, due to the high temperature in the machine and the unclosed die opening, a small amount of plastic adhered to the inner wall of the machine is most likely to be thermally degraded during shutdown, cooling and heating. In addition, oxygen entering the air from the die opening intensifies its thermal degradation and becomes carbide. If the new method of cooling and sealing is adopted for shutdown, the effect is very good. Since the oxygen resistance of recycled materials and color masterbatch carrier plastic is lower than that of new pure plastic, whether recycled materials or ingredients containing color masterbatch are used before shutdown, the new pure plastic low speed washing machine should be added after all plastic melts in the machine are removed. While washing the machine, the temperature is reduced by 25 ~ 35 ℃. As the temperature decreases, the extruded plastic melt gradually eliminates the potential heat stored in the machine. However, special attention should be paid to observe the current value of the extruder to avoid accidents caused by overload of the driving motor. When the actual temperature is about 25 ℃ lower than the normal use temperature, according to the actual situation of melt flow, close the feeding port, close the die port after the plastic melt in the machine is removed to prevent air from entering, and then shut down the machine to turn off the temperature. In the above process, the washing machine can also be stopped when the actual temperature is 25 ~ 40 ℃ lower than the normal use temperature, so that the semi flowing plastic melt can fill the space in the machine and seal it. In this case, special attention should be paid to the appropriate extension of the next heating and holding time, otherwise the operation of the fixture may exceed the limit of travel and cause damage to the equipment. After ensuring that the melt in the machine is warm enough, the content is characterized by covering graphene and 2D material items before starting up

inspection and selection of plastic raw materials

in the production process of plastic granulation manufacturers, there will also be plastic carbonization. Sometimes when in use, it is found that there are many black spots in the particles of the plastic large load friction and wear tester (1000KN), which has the greatest impact on the quality of primary color products. This requires strengthening the incoming inspection of plastic raw materials. If necessary, select the plastic particles with black spots and try not to reuse them, To avoid affecting the quality of the whole batch of products

to avoid the harm of carbonization to plastic products, we should not only deeply understand the essence of carbonization, but also be good at using effective solutions. The key is to effectively prevent and minimize the loss. We need to strictly control every link in solving and preventing the carbonization of plastic products. (end)