Journal article 300 views
Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
Journal of Cleaner Production, Volume: 264, Start page: 121375
Swansea University Authors: Oliver Rashid, Kenny Low, John Pittman
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DOI (Published version): 10.1016/j.jclepro.2020.121375
Abstract
Energy use by thermoplastics injection molding machines is estimated to result in global CO2 emissionsin the order of 80 million metric tons annually. Shortening the molding cycle time is a key factor inimproving energy efficiency and since cooling occupies a major part of the cycle, effective desig...
| Published in: | Journal of Cleaner Production |
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| ISSN: | 0959-6526 |
| Published: |
Elsevier BV
2020
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| Online Access: |
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa54514 |
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| Abstract: |
Energy use by thermoplastics injection molding machines is estimated to result in global CO2 emissionsin the order of 80 million metric tons annually. Shortening the molding cycle time is a key factor inimproving energy efficiency and since cooling occupies a major part of the cycle, effective design andoperation of cooling systems is essential. While guidelines exist, there is a lack of quantitative genericinformation to complement these. To provide this, a parametric study of mold tool cooling is carried outusing numerical simulations, examining coolant channel layout, coolant flowrate and temperature, andtooling thermal properties. Briefly, some findings for representative cases include:Within recommended guidelines for coolant channel layout (channel diameter, pitch and distancefrom the cavity) cooling time for the worst case was found to be 70% longer than for the best.Reduction of coolant temperature by 5 C (35 C to 30 C) allows reduction of coolant flowrate by afactor of more than two while keeping the cooling time unchanged.Use of an aluminum tooling alloy reduces cooling time, as compared with tool steel, by about 30% (15 se10 s in an example) across a range of coolant flowrates and temperatures.If the maximum plastic temperature variation on ejection is to be no more than 5 C, coolant channelpitch should be less that 50 mm when the channels are 10 mm from the cavity, and 80 mm when at20 mm.A coolant heat transfer coefficient of 5,000 W/m2K is recommended. This corresponds to a Reynoldsnumber of 10,000 in a coolant channel of 10 mm diameter.The effectiveness of higher heat transfer coefficients is limited by the thermal resistance of the tool andrapidly increasing pumping costs.Cooling times can be collapsed onto a single line when plotted against an overall thermal resistancethat takes into account the coolant channel layout, tooling thermal conductivity, and coolant heattransfer coefficient.A widely promoted formula for cooling time is found to be inadequate and an improved formulaincorporating this overall thermal resistance provides better estimates.The need for careful balancing of opposing effects to optimize energy use in cooling is emphasized. Thepresent results will assist with this in the early-stage design, with the aim of shortening cycle time tobetter amortize base loads. Furthermore, insights gained will be valuable in providing better estimates ofcooling time for predictions of productivity, energy use and environmental impacts. |
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| Keywords: |
Thermoplastics injection molding; Energy efficiency; Mold cooling; Cycle time reduction; Cooling time prediction |
| Start Page: |
121375 |