The screw is the most critical component inside a Mono Layer blown film machine. It determines melting capacity, mixing quality, and output stability. Choosing the wrong screw design leads to surging, gels, poor thickness uniformity, and reduced output. This article guides you through selecting the optimal screw for your specific resin and application on a Mono Layer Blown Film Machine.

First, understand the three zones of a blown film screw: feed zone, compression zone, and metering zone. In a Mono Layer Blown Film Machine, the feed zone receives resin from the hopper. Deep flights provide high conveying capacity. The compression zone gradually reduces flight depth to compress and melt the polymer. The metering zone has shallow flights to pump molten material uniformly. For LDPE, which has low melting temperature and low viscosity, a standard general-purpose screw with compression ratio 3:1 works well. For LLDPE, which is more shear-sensitive, you need a longer compression zone and a compression ratio of 2.5:1 to 2.8:1. For HDPE, with higher crystallinity and melting point, a high-compression screw (4:1) with a barrier design is recommended.

Barrier screws are increasingly common in modern Mono Layer Blown Film Machines. They separate solid pellets from melted polymer inside the screw channel, improving melting efficiency and reducing temperature variation. A barrier screw can increase output by 20% compared to a conventional screw of the same diameter. For example, a 65mm barrier screw on a Mono Layer Blown Film Machine can produce up to 180 kg/h of LLDPE film, whereas a conventional screw might manage only 140 kg/h.

Mixing sections at the end of the screw further improve film quality. Dispersion mixers break down unmelted particles, while distributive mixers homogenize additives and colorants. If you use recycled resin or calcium carbonate fillers in your Mono Layer Blown Film Machine, a mixing section is essential to avoid specks and poor mechanical properties. Some suppliers offer Maddock mixers or pin-type mixers that can be retrofitted to existing screws.

Screw material and coating also matter. For processing abrasive materials like TiO2 white masterbatch or glass-filled resins, a bimetallic screw with tungsten carbide coating will extend screw life from 12 months to 5 years. A Mono Layer Blown Film Machine running mainly natural LDPE can use a nitrided screw, which is less expensive but still durable. If you plan to process corrosive resins like EVA or flame-retardant compounds, consider a screw made of stainless steel or with a chromium coating.

Diameter selection depends on required output and film width. A 45mm Mono Layer Blown Film Machine is suitable for layflat widths up to 500mm and outputs of 40-70 kg/h. A 65mm machine handles 800mm layflat and 100-150 kg/h. A 90mm machine goes up to 1200mm layflat and 200-300 kg/h. Larger screws are not always better; oversized screws run inefficiently at low outputs because the residence time becomes too long, causing degradation. Match the screw size to your typical production volume.

Finally, consider a screw with variable pitch or grooved feed section. Grooved feed extruders provide higher output pressure stability, which is beneficial for producing very thin films (below 20 microns) on a Mono Layer Blown Film Machine. However, they require more torque and generate higher melt temperatures. For thick films above 100 microns, a smooth bore extruder is usually sufficient.

In conclusion, the screw design of your Mono Layer Blown Film Machine should be tailored to your resin type, desired output, film thickness range, and additive usage. Consult with the machine manufacturer and provide them with your material data sheet. A well-matched screw can increase throughput by 25%, reduce energy consumption by 10%, and improve film uniformity significantly. Do not settle for a one-size-fits-all screw; invest in a customized design for your mono layer line.