Shutdown process and precautions for meltblown non-woven fabric equipment


1. Heating up


For the new melt blowing system, when the system is first started from a cold state, equipment such as screw extruder, melt filter, melt pipeline, spinning pump, spinning box, and draft air heater must all be heated up synchronously, and all equipment must be in a normal state. During the heating period, the spinning system should be in an offline position.


Heating method


After passing the 65 ℃ low-temperature heating test and confirming the normal technical status of the system, the new spinning box can be heated in four stages at a rate of 15-20 ℃/hour from room temperature, 65 ℃, 160 ℃, and 265 ℃ (or the temperature required by the process), with each insulation for about 1 hour. After the temperature stabilizes, the temperature can be raised again. During the heating stage, all heaters should be put into operation, and the temperature of the spinning box should be evenly distributed.


When the temperature reaches 65 ℃, the draft fan should be started at the same time to supply hot air to the spinning box. Some models can arrive at work


Start the draft fan to supply hot air to the spinning box only after the temperature is set, but regardless of the model, it is prohibited to supply cold air to the spinning box during the heating period. After the spinning box reaches the highest temperature and stabilizes, tighten various bolts again according to the specified torque. The temperature control accuracy is required to be no less than ± 1 ℃, and the temperature difference between the spinning box and the draft airflow should be between ± 130 ℃ (according to process requirements).


Management work during the heating up period


The management work during the heating and heating period of the spinning box can refer to the spunbond system. When the temperature reaches the set value, it must be 0 A balance insulation time of 5-1 hours to ensure that the melt in the system can completely melt and flow normally. Depending on the ambient temperature and the configured heating power, the spinning box needs 3-4 hours to warm up from a cold state until it can be turned on for operation.


During the heating and warming process of the spinning box, residual oil stains on the spinning box, melt pipeline, and hot air flow pipeline, as well as moisture in the insulation layer, will vaporize or evaporate. While emitting some white smoke in these areas, a smell of burnt butterfly will also be generated. After about 30 minutes, the amount of smoke produced will gradually decrease, and the odor will fade and disappear. This is a normal process.


But if the amount of smoke still increases, the color changes to yellow or black, and the odor becomes more intense, it indicates that overheating, smoldering, or open flame combustion has occurred in the system. This is a dangerous signal, and if not handled in a timely manner, it will easily evolve into a fire accident;


Therefore, it is necessary to maintain personnel monitoring at the test site, and to carefully inspect any abnormalities that occur. Only after troubleshooting can the test continue. A certain number of dry powder fire extinguishers should be prepared on site for urgent needs.


During normal production and operation, the heating process can be accelerated without the need for insulation. Depending on the temperature at the beginning of the heating process, a balance insulation time of 0.5 to 1 hour is necessary when the temperature reaches the set value to ensure that the melt in the system has completely melted and can flow normally. This is particularly important for production lines using sleeve type melt filters, as the heating time required for this type of filter can reach 6-8 hours.


In order to avoid the phenomenon of "overshoot" when the temperature significantly exceeds the set value during the heating process, a gradual approach can be adopted, which is to set the temperature in stages instead of a one-time setting method of "one step in place". This can alleviate the "overshoot" phenomenon and shorten the transition spinning time after startup.



2. Install components


After the system reaches operating temperature, pre heated fast spinning components can be installed. Depending on the ambient temperature and installation skills, the preheating temperature can be 30-50 ℃ higher than the box temperature or working temperature. When using the preheating process, the fast spinning component can generally be put into operation within about 1 hour.


For systems using on-site assembled components, assembly can begin when the temperature of the spinning box reaches 160 ℃, and preliminary adjustments can be made. After all the spinning components are installed, the temperature of the spinning box can be set according to the process requirements. During the heating period and before formal spinning, the air gap size of the spinning component should also be checked.


Depending on the width of the production line and the level of technical proficiency, the installation and heating process of a melt blown system using on-site assembled components usually takes 4-6 hours.


Before the spinning components are installed and the temperature of the system reaches the set value, the draft airflow system should also participate in the operation and coordinate the temperature rise of the spinneret. After reaching the set temperature, start the spinning pump in a timely manner for low-speed spinning. At the same time, for systems using on-site assembled spinning components, thermal adjustments must be made to the components based on their spinning status. After starting the spinning pump, be sure to pay attention to and control the melt pressure in the spinneret or spinning box to avoid damaging the spinneret.



3. Production operation


After a period of experimental spinning and confirming that the entire system has entered the working state, the spinning box (or web forming machine) can be moved from the "offline" position to the "online" state with a larger DCD, and then the spinning pump speed can be increased to adjust various process parameters, entering normal production.


At the beginning of production, as the spinning pump speeds up and the melt flow increases, the original heat balance state of the system will change. In addition, other process parameters are also being adjusted. Before reaching the new balance state, there may be some conditions that affect the smooth operation of the system (such as melt temperature drop, melt pressure fluctuation, uneven spinning of spinneret, interference of air flow on the fiber mesh), The length of this period is determined by the performance of the control system and the level of operator skills.


If everything is ready, pay attention to sampling and testing filtration efficiency at the same time. Remember to prepare a filtration efficiency tester in advance, as this equipment is currently extremely scarce;


Filtering efficiency testing equipment, welcome to inquire and contact. For more information, please refer to the video



4. Shutdown and cooling


When the system plans to shut down, first reduce the spinning pump speed to a state where normal spinning can still be maintained, increase the DCD, move the spinning box (or web forming machine) to the "offline" position, and then perform the following corresponding operations according to actual needs.


If the system is temporarily shut down, the system should continue to maintain a low-speed spinning state, or it can be considered to remain in the online position, but the web forming machine should remain in operation.


If the system needs to be shut down for a short time (such as several hours or longer), first close the screw extruder's inlet valve, and the system will continue to spin at a low pump speed. After the melt in the system is completely discharged, the screw extruder's spinning pump will stop running, while the drafting fan and hot air system will keep running at a low speed until there is basically no fiber ejected from the spinneret. Afterwards, reduce the temperature to 160-170 ℃ for insulation, and then stop the operation of other equipment.


This method is often used to shut down spinning components during disassembly, but the temperature is generally above 200 ℃. Before the spinning pump stops running, the draft airflow must be kept in working condition. When the machine is shut down for a short time, using this method can reduce the amount of polymer remaining in the system that undergoes degradation. When restarted, it is easier to heat up and can keep the spinning components in a normal technical state before being put into operation again. If the downtime is not too long, the spinning pump can be stopped directly.


If the system wants to terminate production operation, it is necessary to close the material inlet valve of the screw extruder, operate manually, discharge all the melt in the system, terminate the operation of the screw extruder spinning pump, cut off the power supply of the heating system, cool down, and shut down. When using this method to shut down, the remaining melt in the system will undergo degradation (yellowing) or carbonization, which can easily block the spinneret hole. Therefore, when resuming production, it is generally necessary to replace the spinning component.