Possibilities of reducing the heating time and influencing the properties of a thick-walled component during the injection molding of rubber compounds using an EFE injection unit

The above-mentioned research project was carried out between 2010 and 2012 and was financially supported by the German Rubber Society DKG. Three theses were written as part of the project.

Problem

Rising raw material and energy costs combined with ever increasing demands on the quality and reliability of products characterize technical developments in the market today. Developments in rubber injection molding units can also be seen from this perspective. The vulcanization process in the mould is a major cost factor in the injection moulding of moulded rubber articles, as unlike the injection moulding of thermoplastics or thermoplastic elastomers, the chemical network must be built up. A significant contribution to energy savings in the injection molding of rubber compounds is made by the EFE system of the Fa. LWB-Steinl . According to LWB-Steinl, dissipative shear heating by means of a throttle during the injection process and the associated higher inlet temperatures of the compound in the cavity can achieve heating time reductions of up to over 50% for different articles in practice. The reduction in heating time ultimately achieved in reality depends not only on the process parameters of the injection molding process but also essentially on the component geometry and the composition of the rubber compound. Due to the generally poor thermal conductivity of rubber compounds, the effect of the higher mold entry temperature on the reduction in heating time is all the more pronounced, particularly in the case of thick-walled components. Figure 1 shows a rubber cylinder (left) and a thermographic image of the cut-open cross-sectional area of the cylinder immediately after the vulcanization process.

Figure 1: Thick-walled rubber cylinder (left) and thermographic image of the cut-open cylinder cross-sectional area.
Figure 1: Thick-walled rubber cylinder (left) and thermographic image of the cut-open cylinder cross-sectional area.

Objective

A study carried out at the THWS aimed to experimentally and quantitatively record the reduction in heating time that is possible using the EFE system on a specific thick-walled component. In addition to this, selected properties of the sprayed bodies were to be recorded, in particular over the sample cross-section. The aim of this was also to assess the influence of the use of the choke on component properties.

Figure 2: Rubber injection press from LWB Steinl (vertical machine with C-frame, 50 t, 115 ccm) in the processing technology center of the Applied Polymer Engineering degree programme (left) with EFE injection unit (right) [after Gogolin].
Figure 2: Rubber injection press from LWB Steinl (vertical machine with C-frame, 50 t, 115 ccm) in the processing technology center of the Applied Polymer Engineering degree programme (left) with EFE injection unit (right) [after Gogolin].

Results

By means of shear input, which is possible with the EFE injection unit, temperature increases of over 15 K could be achieved with the rubber compounds tested in the project. The heating time reductions that can be achieved in this way depend significantly on the determination method and the process settings (throttle position, mold temperature, injection speed). Realistic values are up to a maximum reduction in heating time of around 40 %. The profile of the crosslinking density over the sample cross-section is not independent of the vulcanization time. For different settings, local crosslinking densities were measured at RWTH Aachen University (Prof. Dr. B. Blümich) using NMR imaging methods. Figure 3 shows selected results of these measurements.

Figure 3: NMR images and Shore A curve over the sample cross-section for 4 min (top) and 8 min (bottom) heating time without (left) and with (right) 85 % throttling; the scale for Shore A is shown on the left-hand side of the image; red = "weakly cross-linked", blue = "strongly cross-linked".

Completed diploma thesis

  • Naß, F., "Possibilities of reducing the heating time and influencing the properties of a thick-walled component during the injection molding of rubber compounds using an EFE injection unit", Diploma thesis, University of Applied Sciences Würzburg-Schweinfurt, 2011

  • Lemmich, S., "Investigations into the influence of process parameters on heating time reduction and component properties during injection molding using an EFE injection unit", Diploma thesis, University of Applied Sciences Würzburg-Schweinfurt, 2012

  • Wachter, F., "Investigations into the influence of mixture components on heating time reduction and component properties during injection molding using an EFE injection unit", Diploma thesis, University of Applied Sciences Würzburg-Schweinfurt, 2012

Award ceremony for an outstanding diploma thesis

Sebastian Lemmich (Photo: Dr. Stefan Wüsten)
Sebastian Lemmich (Photo: Dr. Stefan Wüsten)

Mr. Sebastian Lemmich was honoured with the 1st DKG Sponsorship Award at the German Rubber Conference 2012 in Nürnberg for his outstanding thesis and his work within the research project. In addition to the certificate, the award included prize money of €2,500.

Sebastian Lemmich (left), Prof. Dr. V. Herrmann (right) (Photo: Dr. Stefan Wüsten)
Sebastian Lemmich (left), Prof. Dr. V. Herrmann (right) (Photo: Dr. Stefan Wüsten)
f.r.t.l.: J. Gunther (DKG), S. Lemmich (FHWS), B. Engelhardt (DKG) (Photo: Dr. Stefan Wüsten)
f.r.t.l.: J. Gunther (DKG), S. Lemmich (FHWS), B. Engelhardt (DKG) (Photo: Dr. Stefan Wüsten)

Award-winning science from the DKG

Here you can download further information on the DKG awards

 

Further information

Further detailed information can be found in the following references, in particular the trilogy in Gummi Fasern Kunststoffe (Dr. Gupta-Verlag).

 

Resulting publications

  • Herrmann, V., Naß, F., Lemmich, S., Wachter, F., "Influence of the EFE injection system on heating time reduction and properties of the injection-molded components", Rubber Fibers Plastics GAK 66 (2013); Part 1: "Consideration of heating time reduction via reaction kinetic calculation and accompanying investigations on component and crosslink density using NMR imaging", 37 - 42

  • Herrmann, V., Naß, F., Lemmich, S., Wachter, F., "Influence of the EFE injection system on heating time reduction and properties of the injection-molded components", Rubber Fibers Plastics GAK 66 (2013); Part 2: "Influence of the process parameters of the injection molding process on heating time reduction", 108 - 112

  • Herrmann, V., Naß, F., Lemmich, S., Wachter, F., "Influence of the EFE injection system on heating time reduction and properties of the injection-moulded components", Rubber Fibers Plastics GAK 66 (2013); Part 3: "Estimation of shear energy and influence of the choke on selected properties of the injection-moulded components", 180 - 184

  • Herrmann, V., Naß, F., Lemmich, S., Wachter, F., "Investigations into the reduction of heating time in the production of thick-walled rubber components", FHWS Journal 2014, Volume 2, Issue 1, pp. 84-97

 

Presentations at specialist events

  • Naß, F., Herrmann, V., "Possibilities of reducing the heating time and influencing the properties of a thick-walled component during the injection molding of rubber compounds using an EFE injection unit", DKG research project presentation, 23.02.2011, Fulda

  • Naß, F., Herrmann, V., "Studies on heating time reduction and cross-linking behaviour of thick-walled rubber components during injection moulding using EFE injection technology", 93rd Meeting of the District Group South and Southwest Germany of the German Rubber Society DKG in Würzburg, 7-8.4.2011

  • Herrmann, V., Naß, F., "Heating time reduction and optimization of the properties of a thick-walled component with the EFE injection system", Tech Days 2011, LWB Steinl, Landshut, 6-7.10.2011

  • Lemmich, S., Herrmann, V., "Reduction in heating time and component properties during injection moulding of an NR compound using an EFE unit: influence of the process parameters", 95th Meeting of the District Group South and Southwest Germany of the German Rubber Society DKG in Würzburg, 29-30.3.2012

  • Herrmann, V., Naß, F., Lemmich, S., Wachter, F., "The EFE injection system: heating time reductions and other effects", German Rubber Conference in Nuremberg, July 2-5, 2012

  • Lemmich, S., Herrmann, V., "Influence of process parameters on heating time reduction and component properties during injection molding using an EFE unit", German Rubber Conference in Nuremberg, 2-5 July 2012

  • Herrmann, V., "Evaluation of a Rubber Injection Molding Process by NMR Imaging", NMR Symposium, RWTH Aachen, 02.11.2012

  • Herrmann, V. Naß, F. Lemmich, S. Wachter, F., "Possibilities of reducing the heating time and influencing the properties of a thick-walled component during the injection molding of rubber compounds using an EFE unit", 1st Annual Conference of the German Rubber Society, Nuremberg, 5-6 June 2013