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Sven Wenigmann described in this article how to optimize plastics with improved flow properties

Faster flow and energy saving

Sven Wenigmann, Department of technology of processing, Engineering Plastics Europe of BASF SE15/09/2011

September 15, 2011

Increasingly more manufacturers offer polymeric degrees of freer flow for molding by injection. The improved reproduction of the surfaces and the increase in the miniaturization of the pieces are just two of the reasons that drive the development of these polymers. But can these materials save energy and thus contribute to the production of sustainable pieces? Everything depends on the application.

Plastics with improved flow properties can beat their traditional counterparts when it is necessary to overcome relationship between the length of the flow and the thickness of the wall. One of the typical applications is the production of plugs for the [1,2] electronics industry. Shells of the plugs are every day more complex due to the increase of the miniaturization of the plugs, constituting simultaneously becoming more functional elements. It is characteristic of such applications as sections with large wall thicknesses, as well as sections with wall thicknesses very fine come together in the same piece.

When these pieces with good quality and appropriate configurations could not occur, the specialists in the injection molding only had two options: increase either the melting temperature or the temperature of molding, or both, in the worst cases. As a result, there is an increase of the cycle time and production becomes more expensive. Here is where the advantage that provide improved flow materials becomes immediately apparent.

Likewise, this raises the question of what is the advantage of a freer flow polymer, if a piece with the configuration of existing production have already can easily occur: i.e.: what are the advantages in detail of the production to lower melting temperatures? To quantify the savings, Basf SE installed new tools in a molding machine by injection, to collect data on all materials and incoming and outgoing energy flows. This allows to obtain a total energy balance of the process of moulding by injection, as well as to identify the nature and magnitude of energy saving.

The experimental conditions are based on the circumstances that occur in the electricity industry. The piece is a simple plaque (2 cavity mould) with a volume of injection of approximately 64 cm3 (Fig.1). The material used is a PBT with a content of 30% of glass fibre (type: Ultradur B4300G6 manufacturer: Basf). It is also available in a variant of high speed, which is a version with flow especially improved, but with the same properties. A fully electric injection molding machine (type: IntElect100 manufacturer: Sumitomo (SHI) Demag Plastics Machinery GmbH, Wiehe, Germany) works with a screw of 30 mm in diameter, depending on the molded part.

Fig. 1. The piece injection moulded is a simple plaque (two cavity mould). The total volume of injection is about 64 cm 3.

Energy consumption in a cyclical process

In order to receive reliable information on energy consumption it is necessary to prepare an assessment of energy and material to the process complete and measure all energy flows, both incoming and outgoing. The scope of the balance sheet includes the unit and the mould of plasticizing. All the parameters that are introduced in the system are marked with red arrows, while outgoing flows of materials and energy sources are identified in blue (Fig.2).

Fig. 2. Thermodynamic consideration of the injection molding process. For the energy balance, flows of material and energy that apply to the system are shown on one side (red) and outgoing flows are indicated in blue.

While the injection moulding is cyclical, can be considered a nearly steady state process and obtained a balance according to the first law of Thermodynamics [3]. The association formula (Equation 1, see the table) illustrates the relevant parameters for flows of materials and energy inbound and outbound, which can normally register easily using temperature sensors, or with sensors that comes already equipped the machine.

Fig. 3. Power supply of the gauge extensiométrica: the pair can be directly determined in the screw. The power supply is performed through the Induction coil and the transmission of data by the telemetry system. The axial movement of the screw is possible.

Primärspule = primary coil
Sekundärspule = secondary coil
Führungsschiene = rail guide
Mitnehmer = carrier

Heat energy is determined by the electricity fed to the heater, based on the assumption that all energy turns into heat. Heat losses due to convection and radiation are very difficult to measure and it is necessary to make an estimate, according to the principles of heat transfer. For example: heat transfer caused by convection can be estimated from the temperatures of the surface and assuming that a cylinder with Convection is used free [4].

Fig. 4 Curves of couple from frequency converter and the gauge extensiométrica for two plasticizing speed: the strong differences between the two methods of measurement are especially high pairs patent.

Drehmoment = Par in squeeze
Frequenzwandler n = 270 = n frequency converter = 270
DMS n = 270 = gauge extensiométrica n = 270
Zeit = time

Greater savings through the reduction of the cycle time

Testing aims to draw a comparison between a standard PBT (Ultradur B4300G6) and the alternative of fast flow. To achieve this, the two degrees are processed with the same viscosity. The fact that high speed material hit the viscosity of standard grades to a lower melting temperature because its flow is best, is reflected in processing (from 255 to 285 ° C) temperatures.

Fig. 5. The best part of the energy flows entering the process of molding injection corresponds to the work of global warming

Einspritzarbeit = injection work
Dissipationsenergie = energy dissipation
Heizarbeit = global warming work

They carried out eight trials for each degree (table 1). The proportion of the total energy supplied to the plastic that occurs because of the heat energy is very high, reaching 85 per cent (Fig.5). Energy dissipation introduced by the work of cutting and injection plays a more minor role. The different configurations of the machine practically no influence in the distribution. These results are applicable to a screw with a diameter of 30 mm, while a larger screw diameters them will be a distribution of different energy.

Table 1. The energy balance is generated in eight trials with different parameters of the machine

Versuch = test
Staudruck = back pressure
Plastifiziergeschwindigkeit = plasticizing speed
Einspritzgeschwindigkeit = speed of injection

The results of the comparison of materials demonstrate that simply using a degree of free flow can be an energy savings of up to 13% (table 2). For the experimental methodology, the cycle time has remained constant at 38 s for both materials. The comparison between test points showed in turn that energy savings is greater than high injection speeds. This is possible thanks to the better flow of material is made more apparent here. However, the differences between the individual trials are quite small, since most of the input power is supplied via the heater. A flow better becomes more evident in the work of injection, although it represents only a small proportion of total energy consumption.

Table 2. Energy savings of high-speed material determined as a function of the parameters of the machine (for the same cycle of 38s times) amounted to 13 %

Versuch = test
Energieeinsparung gegenüber Standard-Type = energy savings compared to standard grade

If now we also note that the use of a material of improved flow may shorten the cycle time, melting temperature is lower, the result is additional energy savings. Based on the temperature of 255 ° C is used and with the same temperature of anti-corrosion of standard grades and high speed, a reduction of the cycle time of 6s for the piece can be calculated through the formula of the cooling time. As the heating time is also reduced cycle times for shorter, the large proportion of heat energy is reflected particularly positively in the balance sheet (table 3). At best, it is possible to achieve a total energy savings of almost 30%.

Table 3. If you consider the cycle time less (32s) to use the material of high speed, the potential for energy savings increases to almost 30%

Versuch = test
Energieeinsparung kürzerer Zyklus, gegenüber Standard-Type = energy savings compared to standard grade, shorter cycle

Summary

The use of polymers of more free flow, as well as achieve a filling mold and a reproduction of the larger surface, allows to achieve important energy savings. One of the prerequisites of this achievement is that it should be also possible to fill the piece with a standard degree. With relatively small screw diameters, as they are used and are characteristic of the plugs and similar small parts of the electrical industry, there are large potential savings of up to 30%, as a result of the contribution of high heat energy. These pieces are usually manufactured with PBT, as for example Ultradur (High Speed) of Basf. The greater the diameter of the screw, the lower the influence of heat energy and lower the potential savings that increase the proportions of energy dissipation.

For large pieces, as the traditional components of the compartment of the motor (motor, sleeve of air inlet liners) which are not manufactured with PBT but with PA preferably PA6 (polyamide), degrees of enhanced flow provide other advantages. As the injection pressure and blockade force are lower, the processor can perform manufacturing with smaller machines. This also provides a significant added value, since the operating costs of an injection moulding machine grow disproportionately with the size. These arguments have convinced Basf to expand its range of enhanced flow [7.8] engineering plastics. After Ultradur High Speed (PBT) and Ultramid High Speed (PA66), Basf has just presented its first compound of PA6 improved flow, Ultramid B3WG6 High Speed, now at K2010 fair.

Awards

The studies were carried out with the collaboration of the University of applied sciences, Karlsruhe. We appreciate the work of Niko Weber and Professor Frank Pöhler by carrying out and supervising the work.

Quotes:

Stransky, R.; Bernnat, to.; Reinfrank, K-m.; Völkel, m.; Zeiher, V.: Ever More Electricity and Plastic. Kunststoffe international 99 (2009) 6, pp. 49-53, PE110133
Rosenau, B.; Fernández-Rodiles, r.: Polyamides (PA). Kunststoffe international 98 (2008) 10, pp. 82-85, PE104380
Baehr, H. D.; Kabelac, S.: Thermodynamik. 14 Auflage, Springer Dordrecht, Heidelberg, London, New York 2009
Baehr, H. D.; Stephan, k.: Wärme - und Stoffübertragung. 6. Auflage, Springer-Verlag, Berlin, Heidelberg, 2008
Fritzensmeier, T.: KEB-Antriebstechnik Karl E. Brinkmann GmbH, Schneeberg. Personal communication, 2009
Weber, N.: Untersuchung der Möglichkeiten zur Energieeinsparung durch den Einsatz leichter fließender Kunststofftypen im Spritzgießprozess. Diploma Thesis, Karlsruhe University of Applied Science, 2010
Bernnat, a.: Alles fließt. Press conference at BASF on K 2010, Frankenthal, 22. - 23. June 2010
Eipper, to.; Stransky, r.: Small Particles - Big Effect. Kunststoffe international 98 (2008) 1, pp. 65-67, PE104165