DIE DEVELOPMENTS | MACHIINERY


but raised the inlet and outlet pressures and the pressure drop at each stage. This study concluded that uniform velocity distribution, lower pressure and reduced energy consumption were crucial for high-quality film production. Optimal parameter values were: an inlet flow rate of 0.03 m/s; buffer groove length of 40mm; shaping section length of 20 mm; and non-Newtonian index of 0.36. “These findings provide a theoretical foundation for optimising die head design and improving thin film quality in practical applications,” said the researchers, in a paper published in the journal Processes.


Clean parts Schwing Technologies has helped a customer to clean a series of its blown film dies using thermal vacuum pyrolysis. The customer, Polycine, makes PP-based flexible


packaging for the medical and pharmaceutical sectors. These include three-layer APP films and tubes, which are used as primary packaging in medical technology. They directly surround pharmaceutical and medical products – so must be produced in a high-class cleanroom environment. “We monitor and control the entire production


process online to ensure the highest product quality,” said Gert Klemann, technical manager at Polycine. To ensure high quality, it uses Schwing’s vacuum


pyrolysis system (Vacuclean) to clean its film and tubing die heads. This removes any adhering polyolefins without leaving a residue. The result is clean channels that show consistent flow behaviour of the melt and avoid cross-contamination by foreign material. “The blown film die head can be cleaned when assembled – then dismantled with minimal effort and without damage,” said Klemann. The company regularly uses six blown film dies and two tubing die heads. Cleaning frequency depends on the individual production orders. There is no specific cleaning interval, which makes Schwing’s flexible cleaning service more attractive. Parts can be returned to production within two or three days, which reduces costs due to mainte- nance, plant downtime and production losses. “When it’s time for cleaning, the blown film die


head is disassembled in our plant, prepared for shipment and picked up by Schwing,” he added. “After cleaning it is reassembled and transported back.” The Vacuclean system cleans multi-layer blown film die heads with a diameter of up to 1.7m and a


www.filmandsheet.com June 2025 | FILM & SHEET EXTRUSION 41


weight of up to 12 tonnes. First, any remaining plastic inside the die head is gently melted off under vacuum. Then, any remnants of plastic still adhering are heated up to around 450°C. This decomposes and oxidises the plastic, with the addition of oxygen. Inorganic residues can be removed in a post-treatment step, such as by using compressed air.


Cleaning tips In a blog post, Nordson EDI has laid out a set of tips and techniques for extrusion die cleaning. It says that a flat extrusion die – for film, sheet, or


coating – must be disassembled at least once a year for standard maintenance – a procedure called a ‘split and clean’. The need for this is usually indicated by a reduction in production quality. The purpose is to remove polymer buildup from the flow surface inside the die, lubricate moving parts of the adjustment system and inspect the die for possible problems. It breaks down into three processes: disassem-


bly; cleaning; and reassembly. Disassembly: once the die is placed on the working surface, remove the end plate and seal plate assemblies. Use Allen wrenches to remove the die body bolts. Bolts and washers should be placed on a heat-proof surface and cleaned separately. Before separating the die bodies, attach the


lifting device to the eye bolts and ensure that the lifting chain is drawn tight in a vertical position – so the upper die body is lifted straight up. Afterwards, remove protective cover from the front of the die and insert brass, aluminium or high-temperature plastic shim stock (slightly smaller than the lip opening) between the lips, to protect them. Cleaning: as the die body is raised, molten polymer strands between the die bodies can be cut away. Move the upper die body away from the other half, remove jack bolts lay the upper body


Below: After cleaning a die with Schwing’s Vacuclean, individual layers are disassembled


IMAGE: SCHWING


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