EXTRUDER DEVELOPMENTS | MACHINERY
Boosting energy efficiency in pipe extrusion
Identifying exactly where energy is used in pipe and profile production – and introducing measures that reduce consumption – can help extruders to raise production efficiency, writes Massimiliano Fenili
Energy costs, it seems, are always “somebody else’s problem” – and the plastics processing industry generally regards energy as an overhead and a fixed cost. However, energy is both a variable and a controllable cost. Most processors could reduce energy costs – without large investment – and increase profits through simple energy management. There are now many energy-efficient technolo- gies to help pipe and profile extruders increase their productivity. Energy accounts for 3-5% of the total cost of a product, so it is of great interest to understand where, when, and how it can be reduced in order to obtain maximum profitability.
Extruder efficiency Extrusion is an energy-intensive process. Optimising the use of process energy while maintaining melt stability – remembering that product quality depends on the level of melt homogeneity achieved by the extruder screw – is necessary in order to produce good quality product at low unit cost.
www.pipeandprofile.com The main requirement is the heat necessary to
raise the plastic from the temperature at the inlet to the temperature at the outlet. This corresponds with the enthalpy differences ∆h (H2 – H1) of the processed polymers. If the plastic is fed at room temperature, the specific energy to raise the temperature of the plastic is typically 0.16 kWh/kg for semi-crystalline plastics like PE or PP, and 0.10 kWh/kg for amor- phous plastics such as PVC and PS. The energy used for useful work (E_req) from an extruder – that is, the energy used for material melting and forming through the die – can be given as:
_* = _( ) - _
where E_in is the total energy supplied to the extruder, and E_losses the total energy wasted without doing useful work.
* The energy required is calculated by the formula: _ = _ - _ = m × ∆ = m x ∆ x ∆ [] where m is the mass flow rate (kg/s) and ∆ the specific enthalpy difference.
July/August 2018 | PIPE & PROFILE EXTRUSION 31
Main image: By identifying exact energy consumptions, extrusion
companies can boost efficiency
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