Demand for face masks has been persistently high recently, however, the small, melt-blown machines are inefficient, the large melt-blown production line has not been put into production, and there are many problems after production. It takes a long time to stop the machine once. In the case of the high price of meltblown fabrics, the loss is very large. Today, I will first organize an article on the shutdown and operation sequence of meltblown nonwoven fabrics for your reference.
(1) Warming up
For a new meltblown system, when the system is first started from a cold state, equipment including screw extruders, melt filters, melt pipes, spinning pumps, spinning boxes, and drafting air heaters must be Synchronized heating, and all equipment must be in a normal state. During the heating period, the spinning system should be placed outside the off-line position.
After the new spinning box has passed the 65℃low temperature heating test, after confirming that the technical state of the system is normal, it can be sequentially changed from room temperature, 65℃, 160℃, 265℃(or the temperature required by the process) at a rate of 15-20℃/hour. The temperature is increased in four stages, and the temperature is maintained for about 1 hour each time. After the temperature is stable, the temperature is increased. 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 drafting fan should be started at the same time to send hot air to the spinning box. Some models can arrive at the factory
After the temperature is adjusted, the drafting fan is started to send hot air to the spinning box, but no matter what type of model it is, it is forbidden to send cold air to the spinning box during the heating period. Tighten various bolts 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 drafting airflow should be between +130℃(according to process requirements).
Management during the warming period
The management work during the heating and heating period of the spinning box can refer to as the spunbond system. When the temperature reaches the set value, a 0.5-1h equilibrium holding time must be required to ensure that the melt in the system can be completely melted and normal. flow. Depending on the ambient temperature and the configured heating power, the spinning box will warm up to the point where it can be turned on, and the required time is 3-4 hours.
During the heating and heating of the spinning box, the oil stains on the spinning box, the melt pipeline, the hot air pipeline, and the moisture in the insulation layer will vaporize or evaporate, and some white smoke mold will appear in these parts. At the same time, there is also a scorching smell. After about 30 minutes, the smoke production will gradually decrease, and the smell will fade and disappear, which is a normal process.
However, if the amount of smoke is still increasing, the color changes to yellow or black, and the smell becomes more intense, this indicates that there is overheating, smoldering, or open fire in the system, which is a dangerous signal, if not If handled in time, it will easily evolve into a fire accident;
Therefore, there must be personnel monitoring at the test site, a careful inspection must be carried out when an abnormality occurs, and the test can only be continued after troubleshooting. A certain number of dry powder fire extinguishers should be prepared on-site in case of emergency.
In normal production operation, the heating process can be accelerated without heat preservation. Depending on the temperature at the beginning of heating, when the temperature reaches the set value, it must take 0.5-1 hour of equilibrium heat preservation time to ensure that the melt in the system has been fully melted and is able to flow normally. This is especially important for lines using jacketed melt filters, as this type of filter requires a heating time of 6-8 hours.
In order to avoid the phenomenon of "overshoot" in which the temperature greatly exceeds the set value during the heating process, a step-by-step approach can be adopted.
That is to say, the temperature rise is set in stages, rather than the one-time setting method of "one step", which can alleviate the "overshoot" phenomenon. And shorten the transition spinning time after start-up.
(2) Install components
When the system reaches the working temperature, the preheated quick-load spinning assembly can be installed, depending on the ambient temperature and installation skills.
The preset temperature can be 30-50℃ higher than the cabinet temperature or working temperature. When the preset process is adopted, the quick-loading warp spinning assembly can be put into operation in about 1 hour.
For systems using on-site assembled components, the components can be installed when the temperature of the spinning box reaches 160℃, and preliminary adjustments can be made. After all the spinning components are installed, the spinning box After the temperature is set, the air gap size of the spinning assembly should also be checked during the heating period and before spinning.
Depending on the width of the production line and the level of technical proficiency, the installation, and heating process of a meltblown system using on-site assembly components generally takes 4-6 hours.
Before the spinning assembly is installed and the temperature of the system reaches the set value, the drafting airflow system should also participate in the operation to coordinate the spinneret temperature rise. After reaching the set temperature, the spinning pump should be started to spin at a low speed in time.
At the same time, systems using field-assembled spinning packs also require thermal adjustment of the packs according to the spinning state. After starting the spinning pump, be sure to pay attention to and control the melt pressure in the spinneret or in the spinning box to avoid damage to the spinneret.
(3) Production operation
After a period of trial 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 increase the spinning pump speed, adjust various process parameters, and enter normal production.
When just entering the production state, due to the increase of the spinning pump speed and the increase of the melt flow, the original thermal equilibrium state of the system will change. In addition, other process parameters are also being adjusted.
Before reaching a new equilibrium state, there may be some situations that affect the smooth operation of the system (such as melt temperature drop, melt pressure fluctuation, uneven spinning from the spinneret, fiber The net is disturbed by airflow, etc.), and the length of this time depends on the performance of the control system and the skill of the operator
If everything is ready, pay attention to sampling at the same time, test filtration efficiency, etc., remember to prepare a filtration efficiency tester in advance, and now this equipment is also extremely scarce.
(4) Shutdown and cooling
When the system is scheduled to shut down, first reduce the speed of the spinning pump to a state where normal spinning can still be maintained, increase DCD, and turn the spinning box to move the body (or netting machine) to the "offline" position, and then perform the following corresponding operations according to actual needs.
If the system is temporarily shut down for a short time, the system should continue to maintain the low-speed spinning state, and it can also be considered to remain in the online position, but the web forming machine should keep running.
If the system needs to be shut down for a short time (such as several hours or longer), first close the manhole valve of the screw extruder, and the system will continue to spin at a low pump speed. After all, the melt in the system is completely discharged, stop the operation of the spinning pump of the screw extruder, and the drafting fan and the hot air system have to keep running at low speed until the spinneret basically has no fibers ejected, then the temperature is lowered to 160-170℃to protect tears, and then stop operation of other equipment.
This method is often used to stop the spinning assembly when disassembling, but the temperature is generally above 200℃. Before the spinning pump stops running, The drafting airflow must be kept working.
This method can reduce the number of degraded polymers remaining in the system during the short-term shutdown, and it is easier to heat up when restarting so that the spinning assembly can be put into operation again in a relatively normal technical state. If the downtime is not too long, the spinning pump can be stopped directly.
If the system wants to stop the production operation, the valve of the feed inlet of the screw extruder should be closed and operated manually. After all the melt in the system is completely discharged, the operation of the spinning pump of the screw extruder should be terminated, and the heating will be cut off. System power, cooling, shutdown.
When this method is used to stop the machine, the melt remaining in the system will degrade (yellow) or carbonize, which will easily block the spinneret holes. Therefore, when production is resumed, the spinning components are generally replaced.
The above describes the shutdown and startup process and precautions of the meltblown nonwoven machine. If you have any questions during the operation or want to buy a meltblown nonwoven machine, please contact us
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