What Makes N95? The First Machine, The Second Master, The Third Process And The Fourth Melt Spray Material.

- May 14, 2020-

What makes N95? The first machine, the second master, the third process and the fourth melt spray material.

However, at present, the market model is quite chaotic, the earth gun machine flies all over the world, many friends consult, with the earth gun function can not improve the quality of melt blown cloth, 90 or 95 standard melt blown cloth?

In fact, whether we can produce 95 standard, not in the size of the machine scale, mainly depends on whether we can resist the temptation of huge profits, whether we can strictly use materials and strictly not rigorous production process.

In addition to different raw materials, the difference is in the machine, the die head, melting temperature, air volume and wind speed, electrostatic electret and other parameters are different.

 

 

1、 How do small machines make N95

1. Small machines are generally defined by screw diameter, while large machines are defined by the door width of cloth, that is, the effective door width of spinneret.

2. There is no pressure sensor and screen changing without stopping the machine. When the material pressure is too high, the screw friction heats up. The actual melt material temperature far exceeds the set temperature, and the cloth will be brittle.

3. The heating system of the small machine is controlled by the AC contactor, the heating plates are all full power output and stop, the temperature of the heating plates is actually very high, the barrel wall of the screw is thin, and the material near the barrel wall has actually overheated. But the temperature of the material inside is not enough.  Therefore, it will appear that the setting temperature is not high, but the cloth is relatively brittle.

4. The sorrow of small machine, material is too good, liquidity is too good. When the hot air is large, the melt is not drawn into silk, but directly blown off, forming small liquid beads and hitting the cloth surface.

5. The reason why the small turbine uses the material with lower melting point is that when the small turbine uses the material with higher melting point, because the material flow rate is too fast, the thermal compensation, wind compensation and air pressure compensation of the small turbine cannot keep up with each other.

5. The technology of the earth gun machine is not stable, the machine is not stable, and the accessories can also be used as soon as possible, which is uneven.

 

2、 How to adjust the temperature of melter

1. If the rubber stays at high temperature and high pressure for a long time, it is easy to sinter and carbonize.

2. When adjusting the machine, the temperature should be determined first, not the displayed temperature on the machine, but the actual temperature of the barrel and mold. Many small devices, sensors have not been calibrated, the display temperature and the actual temperature will be very different.

3. Melt finger 1500 material, the temperature is set to above 270 ℃, a little high.

 

3、 How to make the melt blown cloth brittle and hard

1. Uneven wire spraying and insufficient air volume of cooling fan cause uneven heat dissipation and internal stress, resulting in embrittlement. It can be improved by adjusting the melt volume of the extruder, adjusting the temperature of the hot air blower and increasing the air volume of the cold air blower.

2. From the aspect of raw materials, it may be that the low melting fat spinneret is used, and the wire is relatively thick. After 24 hours to 48 hours of complete crystallization, the melt blown cloth will become brittle and hard. The melt blown fabric with 1500 melt blown material has fine, soft and even distribution, so the softness of melt blown fabric is better.

3. It is related to the high temperature of raw materials and processing.  After the fiber is produced, there is a process of secondary crystallization rearrangement in PP. in fact, it is heated seriously in the screw, which has led to serious thermal degradation. If the initiator of peroxide process is not well controlled, such problems are easy to occur.

The most important thing of peroxide process is how to finish the chain break before the screw extrusion in time to prevent the secondary residue from entering the non-woven screw to continue the reaction, which is a test of screw equipment combination and formula control.

4. There is still temperature for the melt blown cloth just produced, especially for the cloth spraying machine with big drum for material collection. Maybe there is no fan, and the temperature of melt blown cloth is high after coiling. The greater the flexibility and toughness of plastics under high temperature, the more brittle they will become after cooling.

5. Add appropriate amount of toughener (2%)

 

4、 How to deal with the poor filtering effect of melt blown cloth

1. Increase the flow rate or temperature of hot air (increase the fineness of fiber, decrease the porosity, improve the capture ability, but increase the resistance);

2. Increase the electrostatic voltage (current) (polarization fiber, increase the electrostatic field energy of fiber, improve its adsorption capacity);

3. Adding powder or other electret into the raw material (improving the receiving capacity and storage time of the fiber, making the fiber carry more charge and charge time);

4. Increase the suction of the net bottom (increase the density of the fiber, improve the catching ability of the fiber. Large gram weight is obvious, not commonly used);

5. In the same process, the extrusion volume is smaller, the fiber is thinner and the resistance is higher;

6. Increase the working temperature of die head (die tip) and other areas (better melt fluidity, thinner fiber);

7. When the room temperature is higher, the resistance increases obviously and other physical indexes decrease;

8. Increase the amount of powder properly.

 

5、 How to improve the strength of melt blown cloth

1. Increase the flow rate of hot air (the fiber is thin, there are many winding nodes, the stress of the fiber is even, the strength increases, but when it increases to a certain extent, it will decrease);

2. Increase the temperature of hot air (as above);

3. Properly increase the weight of the product (within the scope of internal control);

4. Increase the temperature of die head (die tip) and other areas (the same as 1);

5. Reduce production properly;

6. Properly reduce the receiving distance of the melt blown cloth (not too small, but the brittleness and strength of the cloth will be reduced, which can be used together with other parameters);

7. Increase the net bottom suction (the weight of big gram is more obvious);

8. Use melt to refer to lower material.

 

6、 How to improve the elongation of melt blown cloth

1. Reduce the hot air flow or temperature properly (the node slip path becomes larger, and the handle becomes hard);

2. Reduce the working temperature of die head (die tip) (as above);

3. Reduce production properly;

4. Increase the receiving distance of the melt blown cloth (more obvious when used with 1 or 2);

5. Reduce the ambient temperature (spinning ambient temperature);

6. Increase the net bottom suction (the effect is not obvious, the weight of big gram is better);

7. Change the fiber angle by 6 degrees (change the structure of fiber mesh laying, not commonly used)

8. Increase the output properly (this method will reduce other physical indexes and is not commonly used).

 

7、 How to reduce resistance

1. Reduce the flow rate or temperature of hot air (fiber coarsens, porosity is large, resistance is small, efficiency is poor);

2. Increase the receiving distance of the melt blown cloth (increase the fluffy property of the fiber, increase the porosity and decrease the efficiency);

3. Reduce the spinning environment temperature (fiber cooling fully, structure fluffy, porosity increase, with hot air can achieve the purpose of reducing resistance and improving efficiency);

4. Reduce the suction of the net bottom (the density of the fiber becomes fluffy, the porosity becomes large, and the weight of the big gram is obvious);

5. Reduce the working temperature of heating zone such as die head (die tip) (fiber coarsens, porosity increases);

6. Increase the metering pump (the extrusion volume becomes larger, the fiber becomes thicker, and the porosity increases, which is generally used in the rapid conversion);

7. Reduce the weight properly (within the scope of internal control).

 

8、 How to reduce resistance and improve efficiency

1. At the same time of increasing the receiving distance of the melt blown cloth, increasing the hot air flow or temperature properly, reducing the suction of the mesh bottom (increasing the fineness and fluffness of the fiber);

2. Increase fiber fineness and reduce spinning environment temperature (such as adding cooling air device);

3. At the same time, increase the electrostatic voltage (current) and the amount of powder;

4. Increase the fineness of the fiber and reduce the weight of the fiber (not commonly used).

 

9、 How to improve both strength and elongation

1. Properly reduce the hot air flow or temperature, reduce the receiving distance of the melt blown cloth, and properly increase the air suction at the bottom of the mesh (for the physical indexes caused by the high ambient temperature and the high melting finger of the raw material are unqualified);

2. Properly increase the hot air flow or temperature, increase the receiving distance of the melt blown cloth, and properly reduce the air suction at the bottom of the mesh (used for the physical indexes caused by the low ambient temperature and the low melting index of the raw material);

3. Reduce production;

4. Increase the fiber fineness and decrease the spinning temperature.

 

10、 How to reduce the CV value of melt blown cloth

1. Correspondingly, the working temperature of each area of die head should be changed (the weight of gram should be increased at a low temperature, otherwise the temperature should be decreased);

2. When the local efficiency, resistance and CV value are inconsistent, the baffle can be added at its position (to improve the local spinning ambient temperature);

3. The CV value of the longitudinal weight is mainly related to the stability of the velocity of the meshing system.

 

11、 Cause of "shot" agglomerated polymer

1. Improper setting of working temperature (too high or too low, generally too high and easy to occur);

2. Raw materials or masterbatch are too dirty (generally the whole cloth surface or large area appears);

3. At the later stage of die head use, the die tip is dirty (sometimes the local wire out is bad or large area appears, can be solved by scraping the die tip with a scraper);

4. There is carbonized material or dirty plug around the die tip, resulting in poor wire out (usually caused by abnormal shutdown). Generally, a small number of parts appear, which can be solved by scraping the die tip with a scraper);

5. Local dirty air knife or physical damage of air knife (affecting the uniformity of normal spinning air flow, local appearance with longitudinal thin groove);

6. The output is too high or too low (generally large area, reduce or increase the output to solve);

7. Too high or too low melting point of raw material (usually too high and easy to appear);

8. There is water in the raw material.

 

12、 The cause of "flying flowers and flying catkins"

1. Too much hot air flow or too high temperature (too much fiber breakage);

2. The working temperature of each zone is too high (too many fibers are broken);

3. The receiving distance of the melt blown cloth is too small (the cloth is too dense, which affects the air absorption efficiency);

4. Spinning environment temperature is too high (same as 1);

5. When the recycled material is added, the quantity of recycled material is too large, and the melting point of recycled material is uncertain;

6、 The output is too low;

7. The wire is difficult to attach to the curtain, and the receiving distance of the melt blown cloth is too small (the cloth is too dense, which affects the air absorption efficiency)

8. The suction parameters of the net bottom are not set properly or the net curtain is too dirty (the suction is small, the fiber cannot be fully absorbed on the net curtain, and the net curtain is separated);

9. There is lack of fusion between the wires, the holes of the spinneret are filled, and the crystallization temperature is too high.

10. The melting finger of raw material is too high.

 

13、 What to do if the spinneret is broken in and blocked

1. The new machine must be installed with die head spinneret after a while. It's like running in a new car.

2. Many spinneret die materials on the market are not standard materials. Some low-end die steels are used instead. During the use process, there will be some small cracks that can not be seen by the eyes. The hole diameter processing is rough and the accuracy is poor. It is directly used without polishing. It causes uneven spinneret, poor toughness, different spinneret thickness and easy to produce crystallization.

3. The material has large ash and impurities

4. The spinneret hole is not smooth enough

5. Material instability

6. No filter

7. The bucket is not cleaned

 

14、 Screw speed problem

1. The faster the screw speed is, the larger the extrusion per unit time is. Under the same hot air draft condition, the fiber forming is coarser, the fiber content in the products with the same weight is reduced, and the strength of the fiber mesh is reduced.

 

15、 Receiving distance and drum speed

1. The receiving distance is an important parameter that affects the performance of the fiber net. Generally, with the change of receiving distance, the longitudinal and transverse strength, bending stiffness, fiber diameter and so on of the melt blown cloth will change. The longer the receiving distance is, the longer the cooling time of the draft fiber is, the less the bonding point between the fibers is, the more fluffy and soft the product is, and the less the breaking strength is.

2. The rotation speed of the drum determines the orientation of the fibers in the cloth. The faster the rotation speed is, the more the orientation of the fibers along the rotation direction of the receiving device is, and the greater the vertical and horizontal difference of the cloth is.

 

16 How to choose the melt spray material? Powder or granule?

1. The granular material has long storage time and fast degradation, especially in hot weather;

2. The mixture of powder and degradation agent is more uniform, the contact surface is large and has more advantages;

3. Base material melting point is small, adding more degradation agent, melting point is large, adding less;

4. Selection of melt blown polypropylene with concentrated molecular weight distribution

5. The key technology is to find a way to eliminate the influence of the instability of the base material.

 

17 How to deal with electret and how to buy equipment?

1. Electret time, electret voltage and electret distance are three important process parameters that affect the effect of electret. With the increase of electret time, the equivalent surface charge density and the potential of electret surface increase, which enhance the adsorption and polarization of electret. However, with the increase of electret time, when the surface potential of filter material is high enough, the charge under the tip of needle will be rejected He moves where the charge density is low. At the end of the electret, the charge surface density reaches saturation state, so when the electret time increases again, the filtration efficiency of the filter material has no obvious change.

2. The electret equipment should be positive, not negative. Because of the positive charge on the cloth, it can absorb the negative charge in the air. When the melt blown cloth contacts the skin, the negative charge will be consumed more easily. If the positive charge is carried, the loss will be slower.

3. Dust, bacteria and viruses in the air are attached to the particles, which are mainly negatively charged, and the melt blown cloth is positively charged, so it is easy to absorb these negatively charged particles.

4. The ability of electret masterbatch to increase static electricity is not great, mainly to store electric charge and slow down the attenuation.