Three secrets of blown film technology: how to coordinate temperature, air pressure and traction speed

In blown film production, the master often says: ``three points by equipment, seven points by operation." Where the blower is, how to adjust the parameters directly determines whether the quality of the coil is "high quality" or "wasteful." Of all the parameters, the three most critical and precise elements requiring precise coordination are temperature, air pressure and traction speed. They're like three parts of an orchestra-they look simple in themselves, but when they come together, they create a symphony of cinematic quality.
Temperature: Plastic 'tempering switch'
Temperature is the first threshold that determines whether plastic melts evenly. The heating cylinder of an extruder is usually divided into several temperature zones, with a step up in temperature from the feed section to the nose of the machine. The temperature of feed section is lower, which ensures the smooth transportation of material and does not melt prematurely. The temperature of middle section and head is higher, which makes the plastic fully plasticized and flow evenly.
If the temperature is too high, the polymer chains degrades and the film turns yellow and brittle, with "bubbles" or "fish eyes" on the surface. It is too low to the plasticization and cannot be opened. It is also highly pressure-resistant, with a rough surface, poor transparency and even "stiff blocks." The ideal temperature is for the melt to be viscous and smooth like honey-it should be able to flow without being too thin. In many cases, Fu extrapolated the temperature by observing the transparency, luster and texture of the film bubbles.
Atmospheric pressure: Determines the degree of distention of the membrane.
If the temperature tube doesnot melt, then the pressure tube is about how much to blow. The size of the inflatable pressure directly determines the diameter of the membrane bubble, also known as the "inflation ratio."
The larger the inflation ratio, the wider and thinner the film is, but the longitudinal strength is relatively weak. More importantly, the air pressure must remain stable. The air pressure fluctuates, making the film bubbles gain weight and lose weight. After rolling, the film shows a clear "thickness cycle" -the underlying reason why many packaging bags tend to crack when torn. Small smart production lines are usually equipped with pressure stabilizers, and experienced technicians adjust the air valve while checking the membrane bubble's the "breathing" stability.
Traction speed: determines the pull of the film.
The speed at which the film bubbles is stretched upwards by a traction roller determines the process of film ``blowing thin"to ``shaping ''. If the traction speed is fast, the film is drawn thin and long, lengthwise oriented. However, if the speed is too fast, it cannot be cooled in time to form, prone to adhesion and deformation. When the traction speed is slow, the film thickness is solid, but the yield decreases.
The speed and expansion of traction are a combination of "horizontal and vertical": horizontal traction is stretched by blowing air, and vertical traction is stretched by traction. The ratio of the two determines the final thickness and strength balance of the film. In order to ensure stability, modern blown film lines often uses frequency converter to precisely control the traction speed and link it with the extrusion volume, forming a steady rhythm of ``feed extrusion expansion traction ''.
Triple collaboration: A Exquisite Balancing Technique
The true master sees and adjusts all three as a whole. If the extrusion volume is large, the suction force should be fast, otherwise the film will thicken. If the temperature is too high and the melt becomes thin, the blowing pressure needs to be adjusted accordingly, otherwise the bubble will fluctuate. Each adjustment is ultimately aimed at "stable bubble thickness and uniform membrane thickness."
For example, if the film thickness fluctuation horizontally, it is necessary to look for the reason mainly from the stability of air pressure and the gap of the die. If the film thickness changes vertically and periodically, it is necessary to check the synchronization of traction speed and extrusion. Adjusting temperature, setting air pressure, calibrating speed-these three knobs are looped and layered together, which is the beauty of the blower. Mastering this' triangle balance"is the key to truly mastering the art of blown film.