How to eliminate wrinkles on blown film

How to eliminate wrinkles on blown film

the biggest reason for wrinkles in blown film processing is the instability of the film bubble between the wind ring and the maximum diameter. In this range, if it is slightly offset from the normal circle position, the points on the bubble circumference at the herringbone plate and the corresponding points at the traction roller will have a great difference in length. These different length differences cause tight bands and loose bands during the flattening process of membrane bubbles, in which the loose bands will wrinkle

the harder the resin is and the higher the crystallinity is, the easier it is to form wrinkles, and because the tight band cannot be extended, the wrinkles formed are difficult to eliminate. Therefore, films made of HDPE, nylon, polyester, polystyrene and polycarbonate are more likely to wrinkle than films made of soft resins such as LDPE, LLDPE and EVA

control the melting temperature

the movement of the bubble is caused by the random change of the melting temperature; The higher the crystallinity of the polymer, the more sensitive the melting coefficient to temperature. The control failure of blower and internal cooling system may also cause bubble movement, but it is relatively easy to diagnose and correct

stable and uniform melt extrusion temperature can prevent film bubble movement. Check and adjust the temperature setpoint distribution on the barrel to transfer the heat of the barrel to the material particles as soon as possible. And does not affect the material transportation. Usually from the screw feeding section to the transmission section. Use heat transfer to speed up solid feeding, soften particles and reduce the generation of friction heat

the friction shear heat generated by the screw will generally cause local overheating, resulting in discrete areas of high-temperature melting. When these areas come out of the die. It will affect the cooling of the air ring and cause the movement of the membrane bubble. Using heat conduction as early as possible can reduce the viscosity of the screw transmission compression section and reduce the melting caused by shear force

the temperature distribution of temperature hot cold temperature is conducive to stable extrusion. The temperature setting should start from the melting temperature of the feeding section recommended by the resin manufacturer. The temperature of most of the transmission section increases by 10-37.7 ℃, and the temperature at the end of the transmission section and the front section of the metering section is 10-37.7 ℃ lower than the recommended temperature. The temperature at the discharge port rises to the recommended melting temperature. If the problem cannot be solved by adjusting the temperature, sometimes changing the design of the screw or repairing the surface of the screw thread can reduce the shear and improve the temperature stability

random temperature changes expose more hot film bubbles to cold air. It may also cause the problem of increasing the expansion ratio. Reducing the area of unsupported membrane bubbles exposed to cold air can reduce the sensitivity of membrane bubbles to small changes in melting temperature. This can reduce the expansion ratio. But it also reduces the bending diameter

given the die and the required folding diameter, and the production of hard resins, such as nylon, acrylonitrile copolymer or PC, these can only be produced continuously on the clamping fixture under a very small inflation ratio. You can increase the diameter of the membrane bubble at the separation air ring. Reduce the cooling area without reducing the bending diameter

there are also the following methods: use a wind ring with a conical extension of the upper lip "The development of PU material is to create a wide range of properties. When the membrane bubble separates from the main cold air flow, increase the diameter of the membrane bubble, and the conical wind in the middle. 2. Press the reset key to reset. The longer the ring lip is, the larger the upper lip is, and the more obvious the effect is; with a pair of air rings, the one placed on the top is larger than the one placed on the side of the die, or use an air ring whose size is much larger than that of the die.

keep the membrane bubble stable

if the extrusion melting temperature is stable and uniform, reduce The cooling area of small bubbles can not eliminate the wrinkles caused by bubble movement. You can only stabilize the membrane bubble mechanically. The most common stabilizing device is the bubble guide roller. (soft membrane materials such as LDPE will not wrinkle, and fixed wood plates can be used.)

the foam stabilizing frame provided by the internal cooling system is also an effective way to maintain the stability of membrane bubbles. Moreover, the rigid resin needs a more solid round stable foam frame to prevent it from shaking left and right. The stable bubble frame of the membrane bubble starts from above the condensation line

some advanced foam stabilizing devices with two or four side mold frames can also be used in the foam. One is to start from the die and use the support arm to prevent the membrane bubble from forming wrinkles before the membrane bubble is completely flattened. The other is a water-cooled inner bubble rotating cylinder, on which the melt will not adhere. It is necessary to control the inner bubble pressure at the upper and lower parts of the rotating cylinder respectively

if there are wrinkles. The last way is to change the herringbone board. Because the herringbone plates on both sides are asymmetric, part of the membrane bubble will be clamped faster than other parts. The solution is to increase the herringbone plate, which makes the membrane bubble more uniform on the circumference, but more frictional resistance needs to be overcome. Guide rollers with low friction or lubricated surfaces can reduce resistance, but this requires maintenance and regular cleaning. Otherwise, wrinkles will also occur

the membrane clamping system with four sides can make the cross section of the membrane bubble square, even if PP and nylon are used, the year-on-year increase is 43.65% Dragon or PC gaging is a very hard film, which can also be evenly clamped to avoid wrinkles, but the friction on the surface must be very small