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Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency

Oliver Rashid, Kenny Low, John Pittman

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...

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Published in: Journal of Cleaner Production
ISSN: 0959-6526
Published: Elsevier BV 2020
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URI: https://cronfa.swan.ac.uk/Record/cronfa54514
first_indexed 2020-06-19T03:09:39Z
last_indexed 2020-08-17T03:16:04Z
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spelling 2020-08-16T10:55:02.6324946 v2 54514 2020-06-18 Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency 23f6b0583661629da3c12fc0e314776b Oliver Rashid Oliver Rashid true false 1262a79bdd473e4a8805c6fdefb2c5b1 Kenny Low Kenny Low true false 9e89bf430b648088d29a705d182849b4 John Pittman John Pittman true false 2020-06-18 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. Journal Article Journal of Cleaner Production 264 121375 Elsevier BV 0959-6526 Thermoplastics injection molding; Energy efficiency; Mold cooling; Cycle time reduction; Cooling time prediction 10 8 2020 2020-08-10 10.1016/j.jclepro.2020.121375 COLLEGE NANME COLLEGE CODE Swansea University 2020-08-16T10:55:02.6324946 2020-06-18T19:44:12.2521766 Oliver Rashid 1 Kenny Low 2 John Pittman 3
title Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
spellingShingle Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
Oliver Rashid
Kenny Low
John Pittman
title_short Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
title_full Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
title_fullStr Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
title_full_unstemmed Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
title_sort Mold cooling in thermoplastics injection molding: Effectiveness and energy efficiency
author_id_str_mv 23f6b0583661629da3c12fc0e314776b
1262a79bdd473e4a8805c6fdefb2c5b1
9e89bf430b648088d29a705d182849b4
author_id_fullname_str_mv 23f6b0583661629da3c12fc0e314776b_***_Oliver Rashid
1262a79bdd473e4a8805c6fdefb2c5b1_***_Kenny Low
9e89bf430b648088d29a705d182849b4_***_John Pittman
author Oliver Rashid
Kenny Low
John Pittman
author2 Oliver Rashid
Kenny Low
John Pittman
format Journal article
container_title Journal of Cleaner Production
container_volume 264
container_start_page 121375
publishDate 2020
institution Swansea University
issn 0959-6526
doi_str_mv 10.1016/j.jclepro.2020.121375
publisher Elsevier BV
document_store_str 0
active_str 0
description 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.
published_date 2020-08-10T14:02:30Z
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