Blown Film Machine: What 65/75/65 Means

A datasheet for a blown film line usually opens with a model code, and most buyers read it as a name. ABC65/75/65-1800 is not a name. The three numbers are the screw diameters inside the three extruders, and the order tells you which layer each screw feeds.

THE MODEL NUMBER IS A SCREW LIST

A, B and C are the three extruders. A and C run 65 mm screws. B, the middle one, runs 75 mm. All three are 30:1 length over diameter. That is the layer architecture in six characters. A buyer who can read it knows the machine is three-layer, knows which screw carries the volume, and can ask the right question about layer ratio before a drawing or a site visit. Most competing offers will not put that in the model code at all.

WHY THE MIDDLE SCREW IS BIGGER

In an ABC structure the middle layer is usually the core, and the core is where most of the thickness sits. A 75 mm screw moves more melt per revolution than a 65, so the core can be produced at the same output with the screw turning slower. Slower means less shear heat in the resin that makes up most of the film. Run the same line with three 65s and something has to give. Either the middle screw turns faster than the outer two and pushes hotter melt into the die, or the whole line slows to hold the layer ratio. Neither is fatal. Both show up later, in gauge and in the look of the film.

L/D 30:1, AND THE METAL BEHIND IT

Length over diameter sets how long the resin spends being melted and mixed. 30:1 is a common figure for PE. Long enough to plasticise properly, short enough that the melt does not sit in the barrel collecting heat it does not need. The screws are 38CrMoAl with a PTA alloy coating and a nitrided surface. The coating is there for fillers, and fillers are more common than buyers expect: calcium carbonate in breathable film, titanium dioxide in white masterbatch, talc in cavitated grades. A standard nitrided screw runs them. It also wears, and wear does not announce itself. Output drifts down, melt temperature drifts up, and the gauge band that appears at three in the afternoon gets blamed on the air ring. For heavy filler loads, or a high proportion of regrind, the barrel can be supplied in a bimetallic version. It is an option on the sheet, and it is worth taking when the resin mix is abrasive rather than when it is not.

THE NUMBERS AROUND THE SCREWS

With those three screws, the published figures are 200 to 300 kg/h output, take-up speed 100 to 120 m/min, film thickness 0.013 to 0.20 mm, maximum folding diameter 1,600 mm, maximum winding diameter 1,000 mm. Thickness deviation is stated as plus or minus 4 percent for LDPE at 0.15 to 0.20 mm. Read that line as written. It is a tolerance for one resin at the thick end of the range, not a promise across every gauge. Power is 110 kW at 380 V, 50 Hz, three-phase, and the machine occupies 13 by 5.2 by 11 metres. The footprint matters more than it looks on paper, because the tower height decides which building the line can go into.

WHEN THE BUBBLE MISBEHAVES

Bubble faults get blamed on the die and the air ring first, and often that is right. Some of them start in the extruder. A worn screw surges, surging moves the frost line, and the frost line moves the gauge. The checklist in this set of seven practical steps for efficient blown film extrusion starts with the instruments rather than the die: air ring pressure gauges, IBC temperature, barrel cooling, motor amperage. A line that has lost its instruments cannot tell you whether the melt is steady.

WHAT THREE LAYERS BUY

Three extruders exist because one resin cannot do three jobs well. The skin carries print and gloss. The core carries mechanical strength, and often regrind. The sealant layer carries the seal, which is why it is usually the layer nobody wants to contaminate. Split the jobs and each layer can be optimised for one of them. The same split has a second effect, on the material that leaves the plant. Design choices made here decide whether the film can be recycled at all, and design for recycling has moved from an aspiration to a purchasing criterion in several markets.

WHERE THE FILM GOES

Where the film goes is set by the same split. The published scope for this range covers food and snack packaging, frozen food and cold-chain film, personal care and cosmetics, pharmaceutical packaging, and industrial consumables. Gauge decides which of those a given run serves. Thin gauges sit in snack and lamination work, where the film is measured in microns and the seal matters more than the strength. The top of the 0.013 to 0.20 mm range is where heavy-duty bags and cold-chain wraps live, and there the film is asked to hold a load rather than look good on a shelf. That spread is the reason a converter buys one line instead of five. Snack film in the morning and industrial bags at night is a change of resin and gauge, not a change of extruder.

RUNNING RECYCLED RESIN ON THE SAME SCREW

Regrind is not the same material twice. Melt flow varies between batches, contamination is normal, and the film that comes back may carry fillers from a different job. On the machine that shows up as pressure variation and faster screw wear. On the output side it shows up as gauge. Processors are getting better at taking film recycling to a new level, and demand for recycled film now has offtake deals behind it rather than intentions. Capacity is consolidating as well, as the Clysar acquisition shows. All of that puts more recycled resin through screws specified for virgin pellets, which is the practical argument for the bimetallic option above.

WHAT HAPPENS TO THE FILM AFTER USE

A three-layer film is hard to take apart, and that is the trade for the performance described two sections up. Collection pilots in California and commercial collection trials are testing how far flexible film can travel through existing streams. Brand owners are joining initiatives to replace structures that cannot be recycled. Where mechanical sorting cannot separate the layers, chemical recycling is being written into the PPWR framework, and even the question of when film becomes packaging is still being argued.

WHAT XIAOPAI SUPPLIES

XIAOPAI works with the manufacturer of the ABC65/75/65-1800 three-layer co-extrusion line, the machine this article is built around. It runs LDPE, LLDPE, MLLDPE and HDPE, uses IBC internal cooling, and is specified with the three screw diameters, the 30:1 L/D, the barrel treatment and the tolerance line listed above. The machine page carries the full specification. The resin page covers the pellet grades, and the finished film page covers what comes off the line. Wenzhou Xiaopai Electric Power Technology handles the specification conversation, the documentation and the export side. The building of the extruder stays with the manufacturer, which is where the screw geometry is actually decided. The decision in front of a buyer is rarely about one number. It is which of those applications the line has to serve in its first year, whether the gauge range covers the second and third product, and whether the screw and barrel spec still holds when the resin mix shifts toward regrind.

The Model Number Is a Screw List