Regloplas’ new control mode of the eMold S series improves the possibilities for saving energy during temperature control in injection molding processes.

The new eMold S series can also be controlled via the temperature difference between the flow and return temperatures.

16:9

Spritzgießen

Kunststoffverarbeitung: Verfahren

Temperiergeräte

Kunststoffverarbeitung: Maschinen und Komponenten

Gießanlagen

Temperiertechnik

Energieeffizienz

Control Technology as an  Efficiency Booster

Fakuma: The European IM machine manufacturers are working on solutions for the future – apparently under increasing competitive pressure from the Far East.

Yizumi used a 6-station mold to produce thick-walled optical lenses from PMMA. Engel had introduced this type of multilayer injection molding over ten years ago.

Doriat, Clemens, Dr.

Schaumspritzgießen

Mehrkomponenten-Spritzgießen

Folientechnik (IMD, IML, FIM, u.a.)

Spritzgießwerkzeuge

Werkzeuge für die Kunststoffverarbeitung

Messe Fakuma

kunststoffe-international.com

Spritzgussteile, allgemein

Halbzeuge und Zwischenprodukte

Kunststoff-Halbzeuge

kunststoffe.de

Handling, Handhabungstechnik

Automatisierungstechnik

Headwind from the East

The choice of temperature control unit has a major impact on costs and sustainability. With the Series 6, HB-Therm relies on durable technology, energy efficiency and digital innovations.

HB-Therm temperature control technology of the last three generations (in each case next to the machines).

Digitaler Zwilling

Software

Simulation

Temperature Control Units that Pay Off

Single Temperiertechnik GmbH, Hochdorf, Germany, and Sauer Product, Dieburg, Germany, are now marketing a variotherm mold temperature control system under the brand name Alternating Temperature Technology (ATT). ATT which was presented for the first time at K2007 is a complete system for the variotherm fluid temperature control of injection and compression molds using cooling channels arranged near the mold surface. It contains an alternating temperature control unit as well as a specific arrangement of mold inserts and elements. 

Alternating Temperature Technology (ATT) 

System Solution for High Mold Quality 

If the cooling time in injection molding is overly long, it is often because difficult to reach hot zones, so called hot spots, cannot be efficiently cooled with a conventional mold cooling system. A new system from Stemke Kunststofftechnik GmbH, Döbeln, Germany, that is based on the same function principle as a fridge addresses exactly this area. A coolant circulates in a closed circuit between the injection mold and the refrigerating unit. The circulation of the coolant and therefore the mold cooling is controlled via a thermocouple. 

Closed Circuit Hot Spot Cooling 

Miniaturized high performance cooling 

Mold temperature is one of the most important injection molding parameters since it decisively influences the cycle time as well as the dimensional tolerance. The new cooling elements with their novel connecting mechanism from Wema GmbH, Lüdenscheid, Germany, are a cost effective solution for constructing a high performance cooling system. These make conventional thread cutting a thing of the past. The holes for the temperature control connections are simple and quick to prepare using standardized tooling. Regardless of whether it is a quick coupling, elements for core cooling, diverter and closure plugs, all the connections are made using the same technique. Unlike all the previous systems on the market the new one does not require connecting nipples. Particularly advantageous for the plastics processor is the fact that the protruding nipples cannot be damaged or broken off during transport and storage. Cost benefits result from the elimination of these components and the operations required to install them. 

Easy Connection 

Temperature Control Technology 

By using variotherm mold temperature control, processors are able to meet today’s demanding requirements for surface quality and injection molded part accuracy. Temperature control circuits operating in parallel, increase not only product quality, but also process efficiency. Implementation of such a concept requires accurate control technology and short response times. 

Steuern, Regeln

Control Technology: Retrofitting Molded Part Quality 

Injection molding with controlled variation of the mold temperature has been promoted as a solution to surface quality and structuring problems in recent years. The article gives an overview of the various techniques and application fields for variable mold temperature control, and, drawing on a non-representative survey of thirty plastics processing companies, shows how far the different processes have made inroads into industrial practice. 

Process Options: The Possibilities and Limitations of Variable Mold Temperature Control 

30 years of trailblazing technologies was the motto adopted by Remak, manufacturer of robots and temperature control units, to celebrate its jubilee. In the last few years the company, previously known as a manufacturer of standardized linear robots, has turned itself into an automation specialist supplying complete solutions. The company substantiated its claim by means of an open day held in the middle of March. 

In-house Exhibition: Switch to System Integrator 

Energy saving has meanwhile become an issue that is considered also in regard to the peripherals of production machines. Increasingly, plastics processors call for holistic approaches that comprise the entire range of process technology and plant engineering. 

Temperieren

Energy Consumption: Efficient Tempering and Economic Cooling 

The thermal design of movable cores in injection molds is hampered by the restricted available space and the additional parting lines. Therefore, the IKV has compared different cooling concepts for sliding cores and made recommendations for their design. The thermal boundary conditions of the movable installation position are supported with measurement data for use in injection molding simulation. 

Design of Sliding Cores: Temperature Control Systems in Motion 

Producing high-quality injection moldings not only reproducibly but also on a cost-efficient basis requires precise knowledge of the processes involved. Of particular importance here are the thermal processes that take place in the mold. Anyone who does not bear this in mind will have to pay a high price for ignoring it. 

Heating/Cooling: Cost Factor Corrosion 

The search for a pragmatic approach to cyclic heating and cooling of injection molds has yielded a ready-to-install mold insert that incorporates both high-performance heating and effective cooling. This newly developed heating and cooling element thus integrates two existing partial solutions and has already demonstrated its effectiveness in a trial mold. 

Temperature Control: Hot and Cold Molds 

A new variothermal process for the temperature control of injection molds makes use of laser radiation. Heating in the mold is performed using transparent mold inserts. The laser variothermal technique allows heating rates of up to 300 K/s. 

Functional Surfaces: Variothermal Temperature Control with Laser Radiation 

Raytek GmbH, Berlin, Germany, has launched a new generation of pyrometers. The infrared (IR) sensors of the Raytek MI3 Series consist of a miniature measuring head and separate communication electronics with the sensor head also functioning as an independent pyrometer. With a length of 28 mm and a diameter of 14 mm, the sensor is – according to the manufacturer – the world’s smallest fully functional infrared pyrometer. 

Infrared (IR) sensors of the Raytek MI3 Series 

The World’s Smallest Infrared Pyrometer 

Goodbye Hot Spots – with No Extra Energy Expenditure

Molds with integrated heat pipe technology can be cooled with less energy input and thus significantly more efficiently than previous systems. The superiority of structurally integrated heat pipe molds has been successfully demonstrated in practical tests: The cavity temperature in the area of a hot spot can be reduced by 50 °C compared to conventional cooling systems – without additional system peripherals. A win-win situation in injection molding.

A study demonstrates the superiority of heat pipes integrated into the mold core – lower temperatures were achieved in the injection mold.

In order to achieve a high article quality with an economic cycle time, an exact and uniform cavity temperature is necessary, which is usually set by an oversized water temperature control [1, 2]. This sub-process is very energy-intensive. Temperature control, with 37 %, makes up the largest share of the total energy consumption in the injection molding of engineering plastics and thus also of CO2 emissions [3]. This has consequences, because energy costs are the key problem today: the industrial electricity price in Germany has risen from 17.8 cents/kWh (2020) to 54.4  cents/kWh (2022) [4]. The margin and thus the competitiveness of many companies is falling or tending towards zero.

Local heat accumulations (hot spots) are particularly cycle-critical. Due to the engineering realities of moldmaking, uniform cooling is often not possible. This can have various reasons:

<ul><li> In long, narrow areas, water has a predominantly laminar flow with less heat dissipation.</li><li>Water-carrying standard elements only run in straight lines and thus offer limited design freedom. The water is guided to hot spots and led away within the same space. This further narrows the already thermally critical areas.</li><li> Expensive additively manufactured molded elements are increasingly being used [5]. However, small cooling cross-sections and branches lead to a high pressure loss. Furthermore, insulating impurities can form in the cooling channels.</li><li>The position and number of ejectors are often specified by the customer, which restricts the contour of the temperature control channels.</li></ul>

The simple but costly solution in each case outlined here is a higher flow rate – which increases energy consumption as well as CO2 emissions all the more.

In order to reduce the temperatures in the hot spot area, several temperature control units for different circuits and temperatures are often used to keep the mold at production temperature. Due to the different temperatures, the channels thermally influence each other, which results in a high energy loss.

This effect is particularly noticeable when using copper for hot spot cooling. Thus, copper inserts are cooled with cold water for a high temperature difference and thus good heat dissipation. Although copper conducts heat very well, this solution is not optimal. Heat is conducted most effectively in the case of large cross-sections and short lengths – which is in conflict with the design challenges of moldmaking.

Heat Pipes Offer Superior Heat Transfer Performance

Heat pipes have a much higher heat transfer performance than copper or water with the same contours. To illustrate this fact, a heat pipe and a copper rod of the same size were placed in boiling water (Fig. 1). After approx. one minute, the heat pipe had reached its steady state of approx. 75 °C. The temperature difference with respect to the heat pipe was lower than the temperature difference with respect to water. A lower temperature difference with respect to the heat source was not achievable due to heat losses. The copper rod only showed a slight color change after about one minute and had reached a steady state of approx. 50 °C after just under eight minutes.

A heat pipe is a closed hollow body that contains some water under a slight negative pressure (Fig. 2). At a hot side (heat source: cavity), the transition from water to steam takes place. In the process, a large amount of heat is absorbed and extracted from the mold. The steam flows to a remote location and condenses (heat sink). The water flows back to the heat source [6, 7]. Gravity-assisted condensate return flow is recommended and leads to significantly higher outputs.

The high heat transport rates, even over long distances, make it possible to mitigate hot spots and thus save energy and CO2. However, instead of assembling commercially available standard elements, Bielefeld University of Applied Sciences and Arts, Germany, builds entire cores or slide systems directly as a structurally integrated heat pipe – so the mold itself functions directly as a heat pipe. The great potential of heat pipes has already been demonstrated [8 – 11]. Since then, the performance has again been significantly increased compared to the previous experiments.

A test article in the form of a sleeve (length 85 mm, outer diameter 14 mm, wall thickness 1.1 mm) is made of ABS (type: Sitralac 8E-IM / C94150; manufacturer: Sitraplas GmbH; melt temperature: 220 °C). The sleeve is formed by two exchangeable cores. This allows different cooling methods to be compared directly with each other (Fig. 3).

The investigations focus on different mold cores:

<ul><li>heat pipe cores with natural roughness on the interior (smooth),</li><li> heat pipe cores with groove structure on the interior,</li><li>core with copper center,</li><li>conventional core with water flow.</li></ul>

The core interior has a diameter of 7 mm in each case. In the heat pipe variants, an air gap between the phase transition areas (adiabatic zone) forms the thermal separation [12 – 14].

The tests were carried out on an Allrounder 370 E injection molding machine (manufacturer: Arburg). The mold is cooled to approx. 16 °C with a temperature control unit (Thermo-5, HB-Therm). The cycle time is 8.3 s, with a cooling time of 2 s and a holding pressure time of 1.4 s. The cycle time results from a visual quality assessment of the part produced with conventional water cooling and is intended to represent the benchmark in the system comparison.

A thermography system is used to determine the article temperature (type: PIR uc 180, software Irbis 3; manufacturer: InfraTec). The mold cores are not measured directly because reflection influences from the environment are to be expected due to the cylindrical core contour. Therefore, the temperature was determined via the inner surface of the plastic part directly after demolding. The camera looks into the article from above (Fig. 3). The recordings were started after 20 cycles in a quasi-steady state.

The measured article temperatures and the formula of the contact temperature are used to calculate the cavity temperature. The difference between the temperatures of the heat pipe cooling and of conventional methods such as water cooling or copper core is clearly visible (Fig. 4). The article temperatures of the heat pipe cores are between approx. 52 °C and 74 °C, which corresponds to calculated core temperatures of approx. 41 °C and 64 °C respectively. The articles with water- or copper-cooled cores show temperatures of approx. 100 °C and core temperatures of approx. 93 and 94 °C, respectively. This results in temperature differences between heat pipe and water cooling of about 30 to 53 K and an average of 41.5 K.

The heat pipe cores are below the recommended cavity temperature of 60 °C in three out of four cases. However, with the water and copper cooling systems, the required mold temperature of maximum 70 °C cannot be achieved. The quality is probably satisfactory due to the rotationally symmetrical contour. Flatter contours would require lower temperatures, otherwise there is a risk of warpage and deformation. The respective physical and material-specific effects for heat dissipation can be demonstrated as expected and shown in their respective effectiveness. This shows that the evaporation processes in the two-phase heat transfer of a heat pipe are significantly more effective than heat conduction or water cooling.

Application for Low-Energy  Hot Spot Reduction

The superiority of structurally integrated heat pipe cores has been proven – significantly lower temperatures could be achieved compared to conventional systems. Thus, a loss of power can be accepted. This results in opportunities:

<ul><li> The performance of the heat pipe core is higher than that of its counterparts with copper and water cooling. Thus, longer and narrower contours can be cooled and hot spots can be mitigated.</li><li> The performance of the heat pipe decreases with smaller temperature differences. Therefore, the heat sink can be cooled with an existing temperature control system. Initial tests on the presented mold with a heat sink temperature of approx. 50 °C were successful. Extra cooling circuits and temperature control peripherals are saved.</li><li> The heat sink can also be cooled in pulses and thus the temperature at the heat source can be adjusted.</li></ul>

The advantage of using heat pipes is that heat is dissipated by boiling processes. Therefore, contour-adapted cross-sections can be used. With water cooling, non-circular cross-sections create flow dead spots that have an insulating effect.

All in all, cooling time and machine downtime can be shortened, productivity increased, CO2 emissions reduced and energy and water saved. All these aspects help the processor to secure his margin and the mold maker to remain competitive through a high-performance cooling alternative.

[1] Jaroschek, C.: Hot or Cold, that Is the Question. Plastics Insights 102 (2012) 10, pp. 60–65

[2] Zöllner, O.: Optimierte Werkzeugtemperierung. Bayer, ATI 1104, November 1997

[3] Schläger, M.; Balka, C.; Giessauf, J.: Working with instead of against One Another. Plastics Insights 107 (2017) 1, pp. 17–20

[4] Statista: Industriestrompreise (inklusive Stromsteuer) in Deutschland in den Jahren 1998 bis 2023. URL: <a href="https://de.statista.com/statistik/daten/studie/252029/umfrage/industriestrompreise-inkl-stromsteuer-in-deutschland/" target="_blank">https://de.statista.com/statistik/daten/studie/252029/umfrage/industriestrompreise-inkl-stromsteuer-in-deutschland/</a> (Zugriff am 24 Februar 2023)

[5] Frank, E.; Kirchheim, A.: Hotspots gehören der Vergangenheit an. KunststoffXtra (2019) 1–2, pp. 2–3

[6] Stephan, P.: Wärmerohre. In: VDI-Wärmeatlas, 11. Auflage. Springer Verlag, Heidelberg 2013

[7] Faghri, A.: Heat pipe science and technology. Taylor & Francis, Washington DC 1995

[8] Kartelmeyer, S.; Hüttemann, V.; Moritzer, E.; Jaroschek, C.: Simulation and Testing of a Heat Pipe Tempered Injection-Mold-Tool vs. Conventional Water-Based Cooling. In: Tagungsband Antec, Detroit 2019

[9] Kartelmeyer, S.; Hüttemann, V.; Moritzer, E.; Jaroschek, C.: Spritzgiesswerkzeuge mit Heatpipe-Temperierung. Tagungsband Technomer 2019, Chemnitz 2019

[10] Kartelmeyer, S.; Hüttemann, V.; Moritzer, E.; Jaroschek, C.: Injection Mold Cooled with Additive Manufactured Heat Pipe Core. In: Tagungsband Antec 2020, Accepted for Presentation at Society of Plastics Engineers’ Antec 2020 (Paper not presented because of Covid-19)

[11] Kartelmeyer, S.; Hüttemann, M. V.; Moritzer, E.; Jaroschek, C.: Cooling with Heat Pipes. Plastics Insights 121 (2021) 3, pp. 32–35

[12] Kartelmeyer, S.; Jaroschek, C.; Moritzer, E.: Temperieren ohne Wasser – Einsatz von Heatpipes in Spritzgiesswerkzeugen. VDWF im Dialog (2018) 04, pp. 20–25

[13] Kartelmeyer, S.; Hüttemann, V.; Moritzer, E.; Jaroschek, C.: Werkzeugkonstruktion mit Heatpipes. Plastverarbeiter (2019) 05, pp. 48–51

[14] Kartelmeyer, S.; Hüttemann, V.; Moritzer, E.; Jaroschek, C.: Additive Manufactured Heat Pipe Injection Mould Element. Conference Proceedings Fraunhofer DDMC Virtual Edition, 2020

Hochschule Bielefeld University of Applied Sciences and Arts (HSBI) 

https://www.hsbi.de

Ausgabenartikel

The performance of heat pipe cores is shown on the simple article.

Fig. 1. Comparison of a heat pipe (left) and a copper rod (right) in boiling water. The dimensions are identical with a diameter of 6 mm and a length of 300 mm. The upper 100 mm are marked with white paint for thermographic display.

Fig. 2. Closed cavity with negative pressure: The heat pipe extracts heat from the tool when the water evaporates on the warm side.

Fig. 3. Mold with thermographic camera for temperature measurement in the article (left), experimental set-up for the heat pipe core and the water-cooled core (right).

Fig. 4. Comparison of the measured article and calculated core temperatures with four different cooling systems.

Hauptartikel

Heatpipes for Reducing Mold Temperature in Areas with Hotspots 

<ul><li>Stephan Kartelmeyer, M.Sc., works as a research assistant at Bielefeld University of Applied Sciences and Arts, Germany, on heat pipe cooled molds; <a href="mailto:stephan.kartelmeyer@hsbi.de">stephan.kartelmeyer@hsbi.de</a></li><li>Dennis Kraemer, <a href="https://B.Eng" target="_blank">B.Eng</a>., is a research assistant at Bielefeld University of Applied Sciences and Arts.</li><li>Prof. Dr.-Ing. Elmar Moritzer has been Professor of Plastics Technology at the KTP of Paderborn University, Germany, since 2008.</li><li>Prof. Dr.-Ing. Christoph Jaroschek has been Professor of Plastics Processing at Bielefeld University of Applied Sciences and Arts since 1998.</li></ul>

Special thanks of the authors go to Grohedal Sanitärsysteme GmbH & Co. KG, Porta Westfalica, Germany, for providing the experimental mold, and to Krause DiMaTec GmbH, Bielefeld, Germany, for manufacturing the heat pipe cores.

The project “Additive Manufacturing of Heat Pipe Injection Molds – AMHeaP” (FKZ: KK5129707JO0) is funded by the German Federal Ministry of Economics and Climate Protection (BMWK) through the Central Innovation Program for SMEs (ZIM), represented by the German Federation of Industrial Research Associations (AiF). Furthermore, the research and development project “Implementation of Heatpipe Tempering in the Rheology Simulation of Plastic Injection Molded Parts – SimHeaP” is funded by the Federal Ministry of Education and Research (BMBF) in the funding measure “KMU-innovativ: Produktionsforschung” (FKZ: 02K21K012) and supervised by the Project Management Agency Karlsruhe (PTKA).