Melt pumps for blown film extrusion

Melt pumps for blown film extrusion are positive displacement devices, producing a consistent flow regardless of discharge pressure. These melt pumps benefit in blown film extrusion line.

Melt pumps for blown film extrusion function and application:
Melt pumps for blown film extrusion are positive displacement devices, producing a consistent flow regardless of discharge pressure. Installed between the extruder and blown film die, the melt pump takes on the job of generating pressure and does so at efficiencies approaching 98% versus approximately 40% for an extruder. This leaves the extruder responsible for only feeding, melting, and mixing. The gear pump’s tight clearances also greatly dampen the pressure pulsations generated by the extruder. This provides a much more consistent die pressure, enabling closer tolerances, which in turn permits higher yields. The gear pump will also cause a lower net product temperature by lowering the extruder head pressure. This temperature drop will more than offset any temperature rise through the gear pump.

Melt pumps benefit review in blown film extrusion:
The three key benefits of adding a gear pump to an extrusion line are:
1. Reduction of Extruder head pressure fluctuations - isolation of downstream equipment from the extruder - increased level of regrind usage possible - less scrap due to off spec at start up - raw material savings
2. Increased Throughput - for every 1,000 psi reduction in head pressure a 1-4% increase in throughput can be achieved - rate increases of up to 25% have been seen
3. Reduction of melt temperature to the die (less residence time = lower temperature = higher rates) - potential increase in throughput can be found for situations where output is limited due to melt temperature
Additional Benefits: - reduced extruder barrel and screw wear, resulting in lower maintenance costs - faster start up, requiring less manpower - reduced energy requirements, typically appx. 20%

Melt pumps for blown film extrusion challenges:
1. Increases in throughput can vary, depending on head pressure required to produce a good homogeneous melt
2. Downstream limitations: on a retrofit can the equipment be moved?
3. Gauge variations may already be at an optimum level with the use of the right combination of cooling, screw design and take off equipment
4. Added floor space
5. Initial cost of pumps and auxiliaries

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