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Cross-linking density carbon black electrical resistance heating rubber hybrid materials vulcanisation

Rubber compounds contain different components, including crosslinking chemicals. The homogeneous and ener-gy-efficient vulcanisation of thick-walled rubber components is a chal-lenge. Only a technically extensive and energy-intensive combination of differ-ent available vulcanisation methods al-lows a homogeneous vulcanisation. By functionalising rubber compounds with electrically conductive fillers, such as carbon black, a new and energy-effi-cient vulcanisation process was devel-oped. This method uses the principle of resistance heating. By applying an elec-trical voltage, dissipative heating of the material and thus cross-linking takes place. Even with thick-walled compo-nents, a homogenous temperature dis-tribution can be achieved over the en-tire cross-section of the component.

Erwärmen und Vulkanisieren von Elastomer-Hybridmateria-lien durch elektrische Wider-standserwärmungElastomer-Hybridmaterialien elekt-risch leitfähiger Ruß elektrische Wi-derstandserwärmung Vernetzungs-dichte Vulkanisation

Kautschukmischungen enthalten unter-schiedliche Bestandteile, unter anderem Vernetzungssysteme. Die homogene und energieeffiziente Vulkanisation von dick-wandigen Elastomerbauteilen stellt eine Herausforderung dar. Nur eine anlagen-technisch aufwendige und energieinten-sive Kombination vorhandener Vulkani-sationsverfahren erlaubt eine homogene Vulkanisation. Durch eine Funktionalisie-rung von Kautschukmischungen mit elektrisch leitfähigen Füllstoffen wurde ein neuartiges Vulkanisationsverfahren entwickelt. Dieses nutzt das Prinzip der Widerstandserwärmung. Durch das An-legen einer elektrischen Spannung folgt die dissipative Materialerwärmung und somit die Vernetzung. Auch bei dickwan-digen Bauteilen kann über den gesamten Bauteilquerschnitt eine homogene Tem-peraturverteilung erzielt werden.

Figures and Tables: By a kind approval of the authors.

IntroductionThe vulcanisation of rubber materials is one of the most energy-intensive pro-duction steps of the production of rub-ber components. Additionally, most of the vulcanisation processes only cause a heating of the material followed by inte-rior heat transport. The low thermal-con-ductivity of rubbers leads to an inhomo-geneous heat distribution and vulcanisa-tion of thick-walled components. The only technical solution to realise a limit-ed homogeneous vulcanisation is to combine various available vulcanisation methods, e. g. hot air, infrared radiation or microwave [1, 2].

In order to vulcanise thick-walled rub-ber components a novel vulcanisation process was developed. This method is based on the principle of electrical resist-ance heating. Rubbers are electrical insu-lators. To functionalise rubbers, electri-cally conductive fillers are added to the compound. So-called elastomer hybrid materials are developed. By applying an electric voltage, heat is dissipated through the electrical power being ab-sorbed by the electrical resistance [3]. The advantage by vulcanising rubber through electrical resistance heating is, that the energy consumption can be re-duced due to the direct heating of the component without heating the entire tool. In addition to that, a homogeneous vulcanisation of thick-walled rubber components can be realised. This leads to an enormous quality increase of these components. Additionally, electrically conductive rubber can be used to pro-duce heatable rubber pipes. Convention-al heated rubber pipes are produced in a multitude of time and cost several pro-cess steps. Amongst others, the rubber pipe needs to be extruded, vulcanised, braided with heating wires and thermal-ly isolated [4, 5]. By using electrically conductive rubber compounds and the electrical resistance heating it is possible to reduce the number of production steps.

The difficulty of heating rubber mate-rials through electrical resistance heat-ing is that a determined electrical con-

ductivity is necessary. Low electrical con-ductivities lead to the problem, that the electrical resistance is not able to absorb enough energy, which can be dissipated into heat. If the electrical conductivity of the rubber is too high, the applied elec-trical energy input cannot be dissipated into heat. Besides, the determined elec-trical conductivity, which needs to be adjusted, the necessity of a high amount of electrically conductive fillers affects the mixing process and causes higher loads of the internal mixer.

At the Institute for Plastics Processing (IKV) in Industry and Craft at RWTH Aachen University the electrical conduc-tivity and the temperature development in the component after application of an electrical voltage are examined. Besides, the quality of the electrical vulcanisation is investigated and will be compared to the vulcaniation by using a heating press. To analyse the influence of the compo-nent geometry in correlation to the elec-trical resistance of the rubber hybrid materials, different component geome-tries are investigated. Concluding, the degree of cross-linking of a vulcanisation trough electrical resistance heating will be compared to the degree of cross-link-ing when a component is vulcanised in a hot press.

Heating and Vulcanisation of Rubber Hybrid Materials through electrical Resistance Heating

AuthorsCh. Hopmann, M. Kostka, M. Facklam, R. Sujatta, Aachen, Germany Corresponding Author:Melanie Kostka, M.Sc Institute for Plastics Processing (IKV) in Industry and Craft at RWTH Aachen University,D-52074 AachenE-Mail: [email protected].: +49 241 80-28353


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Electrical properties of plastics with different filler materialsThe electrical conductivity (σ) describes the ability of a material to transport elec-trical charges. The electrical conductivity needs to be adjusted exactly for the elec-trical resistance heating [6]. These con-ductive networks occur when the dis-tance between the filler materials is be-low 10 nm. The more developed the con-ductive network is, the higher is the electrical conductivity of the compounds. Depending on the filler material a critical amount of filler exists, the so-called per-colation threshold (Figure 1). There the electrical conductivity significantly rises. In the range below and above this thresh-

old, the electrical conductivity is just slightly affected by the variation of the amount of filler materials. Above the threshold the electrically conductive net-work is already fully developed and an increase of the amount of filler material is not increasing the electrical conductiv-ity. In contrast to that, below the thresh-old the punctual contacts between each filler particle outweight [7, 8].

The percolation behavior of electrical-ly conductive filler materials is contin-gent on a multitude of factors. These in-clude the amount of filler materials, the type, geometry as well as the polymer and the morphology of the conductive network resulting from the processing.

Fig. 1: Percolation behaviour of electrically conductive rubber materials depending on the amount and type of the electrically conductive filler material [9, 10].

1 With an increasing aspect ratio or specif-ic surface of the filler material, the perco-lation threshold is moved to lower amounts of conductive filler materials, because of the better ability to develop electrical paths. The structuring of the electrically conductive network of filler materials can be improved through prop-er processing parameters and pushes the percolation threshold to lower amounts of fillers as well [11].

Electrically conductive filler materials can be divided into microscale and nano-scale filler materials. For example, mi-croscale materials being used for electri-cal applications include carbon or steel fibers as well as flakes or powder made of graphite. The most common nanos-cale filler materials in the plastics pro-cessing are carbon blacks and carbon nanotubes [11]. The carbon blacks have primary particle sizes of 10 to 100 nm and offer the advantage that they are relatively low priced. Special electrically conductive carbon blacks exhibit a signif-icantly higher specific surface up to 2000 m2/g. Even though carbon blacks show a spherical shape because of their low aspect ratio. Due to the dimensions of carbon blacks, in components with carbon blacks a much lower develop-ment of non-conductive outer layers is observed, which benefits a homogene-ous electrical conductivity of the compo-nent. To realise an energy-efficient and homogeneous vulcanisation of thick-walled components through electrical resistance heating of rubber hybrid ma-terials, this homogeneous electrical con-ductivity is indispensable [11, 12].

ExperimentalTwo nitrile butadiene rubbers (NBR) are used. They differ in their viscosity from each other. In order to achieve a suffi-cient electrical conductivity, an electri-cally conductive carbon black is used in different amounts. Subsequently, the electrical conductivity, the temperature in the sample after applying an electrical voltage of 40 V is investigated. Further-more, the vulcanisation quality will be compared. The vulcanisation is carried out by means of current and using a heating press.

MaterialsThe polymer Krynac 3330 F with a moon-ey viscosity of 30 MU [(1+4) 100 °C] and the polymer Krynac 3370 F with a moon-ey viscosity of 70 MU [(1+4) 100 °C] were supplied by the Arlanxeo Deutschland

1 Material properties of the given carbon blacks [13,14]carbon black

specific surface [m2/g] OAN [cm3/g]trade name typeCabot N330 standard 76 102

Ketjenblack EC-600JD electrical conductive 1270 495

2 Complete formulation for the investigated NBR compounds

trade name component manufacturer mass fraction [phr]

Kryanc 3330 F polymer Lanxess Deutschland GmbH, Cologne, Germany

100

Krynac 3370 F Lanxess Deutschland GmbH, Cologne, Germany

100

N330 standard carbon black Cabot Corporation, Boston, USA 50Ketjenblack EC-600JD

electrical conductive carbon black

AkzoNobel Polymer Chemistry N.V., Arnhem, Netherlands

5, 10, 12.5, 15, 17.5, 20, 22.5

Rhenofit F moisture trap Lanxess Deutschland GmbH, Cologne, Germany

10

Vulkanol OT softening agent Lanxess Deutschland GmbH, Cologne, Germany

20

Sulphur 90/95 cross linking-agent Solvay S.A., Brüssel, Belgium 2Zinkoxid aktiv curing activator Lanxess Deutschland GmbH,

Cologne, Germany5

Vulkacit CZ/C Vulcanisation accelerators

Lanxess Deutschland GmbH, Cologne, Germany

1.5



GmbH, Cologne, Germany. Due to the higher polarity of the NBR, compared to other conventional polymers, it is more suitable for the electrical resistance heating. Various NBR compounds are produced and investigated. They differ from each other with regard to the add-ed amount of carbon black. To guarantee a high electrical conductivity, an exalted specific surface as well as a tall oil ab-sorbtion number (OAN) is necessary. This allows to create a conductive network. The standard carbon black N330 by the Cabot Corporation, Boston, USA, is used. To reach a sufficient electrical conductiv-ity of the rubber compounds, the electri-cally conductive carbon black Ketjen-black EC 600 JD by AkzoNobel Polymer Chemistry N.V., Amsterdam, Netherlands is used. The relevant material constants are shown in Table 1.

Table 2 shows the entire formulation for the investigated compounds.

EquipmentThe compounds are mixed in a laborato-ry internal mixer of the type PlastiCorder 350 E provided by the Brabender GmbH & Co. KG, Duisburg, Germany. All the process parameters are kept constant for all compounds to minimise the process impact on the electrical properties. The internal mixer temperature is set to 50 °C and the rotation speed to 50 rpm. During the first step of the compound-ing, polymer, carbon blacks and additives are mixed together for three minutes before adding the vulcanisation agents. Then all components are mixed together for a further minute.

Afterwards, the materials are milled in a rolling mill of the type KV247.01 by Rucks Maschinenbau GmbH, Halle, Ger-many, and pressed for 90 min by a tem-perature of 35 °C and a pressure of 220 bar (3142.85 psi) to different samples. To investigate the impact of the component geometry on the electrical resistance heating of the compounds, two different geometries are examined (Figure 2). On the one hand samples with a constant thickness of 2 mm (A) and on the other hand with a varying thickness from 2 to 4 mm at the middle of the sample (B). Investigation of the electrical conductivityThe electrical conductivity of the com-pounds is investigated with a ring elec-trode and a resistance meter of the type 3451 Resistance Hitester HIOKI E.E. Cor-poration, Nagano-ken, Japan. The meas-

urement is performed according to DIN EN 62631-3 [15]. To determine the elec-trical conductivity, the pressed samples of type A with a thickness of 2 mm, are placed between the two electrodes. By applying an additional defined weight of 3380 g (8.616 kPa) on top of the upper electrode, the contact resistance is re-duced. Due to the slow orientation of the polymer molecules by applying an elec-trical voltage, the electrical resistance decreases at the beginning of the meas-urement. This process is also known as electrification [16]. As a consequence, the results are read off after an incuba-tion period of 1 min. All measurements are performed at a temperature of 23 ± 2 °C [15]. With the measured electrical resistance and the exact thickness of

each sample, the electrical conductivity for each compound can be calculated with equation 1 [17]:

𝜎𝜎 =4 ∙ 𝑠𝑠

𝑅𝑅𝑑𝑑 ∙ 𝜋𝜋 ∙ 𝐷𝐷2 (eq. 1)

σ is the electrical conductivity, s is the thickness of the sample, Rd is the meas-ured electrical resistance and D is the di-ameter of the electrodes (70 mm).

Investigation of the thermal properties and vulcanisation through electrical re-sistance heatingFor the investigation of the thermal properties and vulcanisation behaviour through electrical resistance heating, a at the IKV developed testing device is used (Figure 3). The samples are clamped

Fig. 3: Testing equipment for the investigation of the thermial properties and vulcanisati-on through electrical resistance heating.

3

Fig. 2: Sample geometries

2



between two metallic terminal strips on each side to apply the voltage during the investigations. The terminal tapes are pushed together through spiral springs to guarantee the same pressure on the samples during all measurements as well as a good reproducibility. All compo-nents, except of the terminal strips and the spiral springs, are made of plastics to prevent an unintentional power line through the testing device. The used power supply unit is of the type Voltcraft TNG 245 by Conrad Electronics AG, Wollerau, Switzerland, with a maximum voltage of 40 V and a current up to 2.5 A.

The monitoring of the surface tem-perature of the samples is carried out with the thermographic camera A320 by FLIR Systems Inc., Wilsonville, USA. The camera is mounted 0.4 m above the sam-ple and is controlled by the software Re-searchIR by FLIR Systems. To control the component internal temperature, fiber optical temperature sensors of the type

TS3 by Optocon GmbH, Dresden, Germa-ny, with a diameter of 1.7 mm are used. The sensors are made of glass fibers. As a result, they provide the advantage of a lower heat conduction compared to con-ventional thermoelements and they do not divert the current being applied to the samples.

Investigation of the degree of cross- linking by use of the Temperature- Scanning-Stress-Relaxation-IndexThe Temperature-Scanning-Stress-Relax-ation (TSSR) is a non-isothermal stress relaxation to characterise material prop-erties of rubbers. In this case the TSSR-Me-ter produced by the Brabender Messtech-nik GmbH & CO. KG, Duisburg, Germany, is used to characterise the degree of cross-linking. The measurement consists of two steps. First, the isotherm stress relaxation takes place. The test tempera-ture is set to 0°C and the elongation to 30%. During the duration of 60 min short-

term relaxation processes can subside. Secondly, the non-isothermal stress re-laxation occurs. The test chamber heats up with a heating rate of 2 K/min to the maximum temperature of 120 °C. Over this temperature the force standardised on the initial force of the non-isothermal relaxation (F/F0) is plotted. By setting the area under the curve in relation to the area of an idealised elastomeric material, where the force remains constant (Figure 4), the TSSR-Index is determined and can be calculated with equation 2 [18].

𝑇𝑇𝑇𝑇𝑇𝑇𝑅𝑅 − 𝐼𝐼𝐼𝐼𝑑𝑑𝐼𝐼𝐼𝐼 =∫ 𝐹𝐹(𝑇𝑇)

𝐹𝐹0𝑑𝑑𝑇𝑇𝑇𝑇𝑚𝑚𝑚𝑚𝐼𝐼

𝑇𝑇0

𝑇𝑇𝑚𝑚𝑚𝑚𝐼𝐼 − 𝑇𝑇0 (eq. 2)

Tmax is the maximum temperature (120°C), T0 is the minimum temperature (0°C), F(T) is the force depending on the temperature in N and F0 is the force at the beginning of the non-isothermal stress relaxation in N. The higher the TSSR-Index of a material is, the higher is the degree of cross-linking.

Results

Investigation of the electrical conductivityMixtures with the high viscous NBR (Krynac 3370 F) and different mass ratios of electrically conductive carbon black from 5 phr to 15 phr are investigat-ed. The electrical conductivity amounts 1.23 10-3 S/m for a compound with a carbon black content of 5 phr and 1,65 102 S/m with 15 phr Ketjenblack EC 600JD (Figure 5).

The heatability of rubber parts with different carbon black contents at a vol-tage of 40 V is investigated. To heat rub-ber components the electrical conducti-vity must amount values betweeen 4 103 S/m and 5.4 10-8 S/m. Lower va-lues describes the electrical conductivity of a device that canoot bei heated. The upper value is the electrical conductivity of a rubber element that can be heated.

Starting from a mass ratio of 12.5 phr of Ketjenblack EC 600JD, the compounds show a sufficient electrical conductivity to be heated through electrical resist-ance heating. A higher amount of Ketjen-black EC 600JD above 15 phr cannot be incorporated into the polymer matrix of the polymer Krynac 3370 F due to a sur-passing of the maximum torque (400 Nm) of the used internal mixer. Another reason is the heat development during the mixing process. The temperature of the compound rises up to 160 °C and an

Fig. 4: Schematic measurement of the TSSR-index.

4

Fig. 5: Electrical conductivity depending on the amount of Ketjenblack EC-600JD and the base polymer.

5



unintentional vulcanisation takes place in the mixing chamber. If compounds with a higher softener content are pro-duced, the torque of the internal mixer decreases about 20 Nm. However, it has to be taken into account that the soften-er agent works electrically isolating. This halves the electrical conductivity by an increase of the softener agent from 20 phr to 30 phr. Accordingly, the softener agent needs to be kept as low as possible to reach a high electrical conductivity and is maintained to 20 phr in the given investigations. To reach a higher amount of electrically conductive carbon black the low viscous NBR (Krynac 3330 F) with different amounts of the electrically con-ductive carbon black is examined. Due to the lower viscosity a maximum mass ra-tio of 22,5 phr of Ketjenblack EC 600JD can be incorporated. All compounds have a sufficient electrical conductivity be-tween 9.03 103 S/m at 12.5 phr and 5.66 10-2 S/m at 22.5 phr Ketjenblack EC 600JD. Worth mentioning is that the con-ductivity above 17.5 phr only exhibits a slight increase. This points out that the percolations threshold is already exceed-ed. Furthermore, the comparsion of the compounds with the different NBRs shows that the compounds with the low viscous NBR have a up to 65 % higher electrical conductivity with equal amounts of both carbon blacks. Both compounds (high and low viscosity NBR) contain 12,5 phr Ketjenblack EC-600JD. This can be explained by the more homo-geneous incorporation of the carbon black due to the lower viscosity of the used polymer Krynac 3330 F [2, 19]. As a consequence the carbon black can devel-op a more homogeneous and electrically conductive network.

Investigation of the electrical resistance heating of rubbersBecause of the high electrical conductivity being reached with the compounds with the low viscous NBR (Krynac 3330 F), these compounds are further investigat-ed. Figure 6 shows the temperature as a function of the test time and the amount of electrically conductive carbon black of the samples with a thickness of 2 mm.

The investigations show that the compound with an amount of 17.5 phr electrically conductive carbon black reaches the highest temperature of 154.9 °C, that proves a feasible vulcanis-ation through electrical resistance heat-ing. A similar temperature (151.2 °C) is reached with the compound including an

amount of 15 phr conductive carbon black. It should be noted that the com-pounds with the lowest and highest mass ratios of carbon blacks show a low-er heating rate than the compounds with an average amount of carbon black. Be-cause of the lower electrical conductivity of the compound with 12.5 phr carbon black, the electrical resistance is too high and not able to absorb and dissipate enough energy into heat. Apart from that, the compounds with the highest amount of carbon black show a lower heating rate because of the extremely high electrical conductivity. Due to the low electrical resistance, the electrical energy cannot be dissipated. The sample is just passed through by the electrical power. Therefore, it is essential to adjust the exact electrical conductivity of the

compounds. Additionally, the ideal elec-trical conductivity for an electrical resist-ance heating is depending on the given voltage. The higher the voltage, the lower the electrical conductivity needs to be [3, 20].

Based on the temperature profile it can be seen, that the temperature is not rising linear with time. This can be ex-plained with the changing electrical re-sistance during the test. All carbonated conductors are part of the thermistors with a negative temperature coefficient. With rising temperature, the electrical resistance decreases [20]. Figure 7 shows the electrical resistance of the com-pounds (being displayed by the power supply unit) depending on the tempera-ture during the heating tests through electrical resistance heating.

Fig. 7: Electrical resistance depending on the mass temperature of the samples and the amount of electrically conductive carbon black.

7

Fig. 6: Mean temperature depending on the test time and amount of electrically conduc-tive carbon black (Test voltage = 40 V)

6



It becomes clear that the electrical re-sistance of all compounds is decreasing when the mass temperature is reaching at least 35 °C. Due to the rising tempera-ture more and more charge carriers are activated, which leads to the given de-crease of the electrical resistance. At a temperature over approximately 120 °C, the investigated electrical resistance of all compounds amount a resistance between 10 and 15 Ω. At this temperature, the charge carriers being available in each compound, are already activated and a further temperature increase is not reduc-ing the electrical resistance. While heat-ing the samples through electrical resist-ance heating the temperature rises and therefore the electrical resistance drops down to a value with which the heating is not that effective anymore. Consequen-tial, the heating rates are decreasing for higher temperatures (see Figure 6).

Influence of the component geometry on the electrical resistance heating of rubbersIn the following, the influence of the component geometry on the electrical resistance heating is further analysed by means of the samples of type B with the varying thickness from 2 to 4 mm (Figure 2). The compound with the low viscous NBR (Krynac 3330 F) and an amount of 15 phr of the electrically conductive car-bon black Ketjenblack EC 600JD is exam-ined, which showed the highest temper-ature in preliminary tests of the compo-nents with a varying thickness. The volt-age is set to 40 V and the test time to 240 s. Figure 8 shows the thermographic im-ages (left: 2 mm segment, right: 4 mm segment) for different test times as well as the mean and maximum temperature of the 2 mm and the 4 mm segment of the samples dependent on the test time. The voltage is applicated on the left and on the right of the depicted samples in the thermographic images.

The 2 mm segment shows the highest temperatures during the entire test peri-od. This phenomenon of the inhomoge-neous heating can easily be explained with the correlations of the Joule Heat-ing (eq. 3) [21].

𝑃𝑃 = 𝜌𝜌 ∙ 𝐼𝐼𝐴𝐴

2

∙ 𝑉𝑉 (eq. 3)

P is the current heat loss which leads to the heating of the components, ρ is the specific electrical resistance of the com-pound, I is the applied current, A is the cross-section area of the component and

V is the material volume. In the given case, the cross-section area as well as the material volume of the 4 mm segment are twice as big as those of the 2 mm segment. The current and density of both segments are the same, so that the heat-ing of the 2 mm segment is also physical-ly expected to be the segment with the higher temperatures. According to equa-tion 3, the current heat loss of the 2 mm segment is expected to be twice as high as those of the 4 mm segment.

By analysing the temperature profiles, it can be seen that the highest tempera-ture differences of the two segments exists at a test time of 120 s (Table 3).

When considering a test duration of 240 s, it becomes clear that the tempera-ture difference between the maximum and the mean temperature is decreasing (Table 4).

This decrease of the temperature dif-ferences of the two segments is due to

the heat transfer at higher temperature and can also be seen in the thermo-graphic images (Figure 8). Additionally, it has to be mentioned that the maximum temperature of the 2 mm segment ex-ceeds the critical temperature of 215 °C while the mean temperature of the 4 mm segment has reached the mini-mum vulcanisation temperature of 160 °C. At this temperature, the first de-tectable material degradations occur. This critical temperature of the 2 mm segment could possibly prevent the vul-canisation of components with strongly differing wall thicknesses by using the given experimental test set up.

Vulcanisation of rubbers through elec-trical resistance heating and compari-son of the vulcanisation quality to a vulcanisation by using a heat pressTo characterise the quality of the com-plete vulcanisation through electrical re-

Fig. 8: Thermographic images and temperatures (mean and maxiumum) of the samples with varying thickness depending on the test time.

8

3 Mean and maximum temperature as a function of the sample thickness (test time = 120 s)

2 mm sample thickness 4 mm sample thicknessMean temperature [°C] 152 125Maximum temperature [°C] 193 167

4 Mean and maximum temperature as a function of the sample thickness (test time = 240 s)

2 mm sample thickness 4 mm sample thicknessMean temperature [°C] 175 163Maximum temperature [°C] 220 199



Fig. 9: Temperature profile of the vulcanisation through electrical resistance heating.

9

Fig. 10: TSSR-index of the samples vulcanised through a heat press and electrical resistance heating.

10

sistance heating, a comparison to a con-ventional heat press is performed. For this investigation the components with a thickness of 2 mm and the compound with the low viscous NBR (Krynac 3330 F), standard carbon black N330 (50 phr) and electrically conductive carbon black Ketjenblack EC 600JD (17.5 phr) are se-lected. The vulcanisation time was deter-mined with a rubber process analyser to be 3 minutes at a temperature of 170 °C. Firstly, samples were completely vulcani-sed in the heat press with a pressure of 220 bar. Secondly, the same compounds are vulcanised through electrical resis-tance heating (Figure 9).

At the beginning of the vulcanisation through electrical resistance heating, a heating phase is necessary to heat up the components to the required temperature of 170 °C. In the given investigations the heating phase lasts for approximately 160 s. To minimise this phase as well as the cycle time, a higher voltage can be used. After reaching the vulcanisation temperature, the voltage needs to be regulated to prevent an overheating of the material. Because of that, the tem-perature does not remain the same dur-ing the vulcanisation phase being start-ed right after reaching the vulcanisation temperature. After the same time like in the heat press (3 min), the voltage is switched of and the vulcanisation pro-cess is completed. It is important to men-tion that the vulcanisation already starts at higher temperatures during the heat-ing phase. As a consequence the time of the energy input as well as the amount of energy input of both vulcanisation methods is not exactly the same. To char-acterise the quality of the vulcanisation through electrical resistance heating, the TSSR-indices for the heat press and the electrical resistance heating are shown in Figure 10.

The TSSR-index of the samples vulcan-ised in the heat press is with 0.75 higher than that of the electrical resistance heating with a value of 0.70. This differ-ence indicates that the degree of cross-linking is slightly higher by the vulcanisation with the heat press. It must be said, that the vulcanisation through electrical resistance heating is not taking place under pressure with the current test set up like in the heat press. Because of that, the cross-linking of the polymer chains is not able to be as tight as in the heat press. This makes an im-pact on the TSSR-index and reduces the measured values.

ConclusionThe investigations show that a sufficient electrical conductivity of 4 10-3 S/m to 5.4 10-8 S/m can be reached with electri-cally conductive carbon blacks to realise a general heating or the vulcanisation through electrical resistance heating up to 240 °C. It must be observed, that the burden of the internal mixer during the mixing process tremendously increases due to the high amount of filler materi-als needed. In addition to that, the anal-ysis of the heating through electrical re-sistance heating shows that the electri-cally conductivity of a compound needs to be in a small range to ensure the ab-sorption of a sufficient amount of electri-cal energy which can be dissipated into heat. At the same time, it has to be con-sidered, that the electrical conductivity depends on the mass temperature of the compound and drops during the heating

with increasing temperature. A homoge-neous heating of the compounds with constant thickness can be observed. In contrast to that, the samples with a var-ying thickness show an inhomogeneous heating with the currently available sys-tems. The degree of cross-linking of the vulcanisation through electrical resist-ance heating compared to a heat press is slightly lower. This can be mainly justi-fied with the missing cavity pressure during the vulcanisation through electri-cal resistance heating. This leads to a more wide-meshed cross-linking of the polymer chains and lower TSSR-indices.

Following, the conception and pro-duction of a pressing tool for the vulcan-isation through electrical resistance heating needs to be carried out. Thereby, the electrical voltage of different tool el-ements should be separately controllable to compensate potential differences in



the thickness. Beyond that, the possible realisation of a heating pipe made of rubber hybrid materials needs to be checked.

Acknowledgement The research project 7 EWN of the Forschungsvereinigung Kunststoffverar-beitung was sponsered as part of the „industrielle Gemeinschaftsforschung und -entwicklung (IGF)“ by the German Bundesministerium für Wirtschaft und Energie (BMWi) due to an enactment of the German Bundestag through the AiF. We would like to extend our thanks to all organisations mentioned.

Literature[1] Jobes, M.: Experimentelle und simulative An-

alyse der Energieeffizienz bei der kontinuier-lichen Vulkanisation. Institute for Plastics Processing (IKV) in Industry and Craft at RWTH Aachen University, Germany, Master-thesis, 2016.

[2] Röthemeyer, F.; Sommer, F.: Kautschuk Tech-nologie. Munich: Carl Hanser Publications, 2013.

[3] Kramer, C.; Mühlbauer, A.: Praxishandbuch Thermoprozess-Technik. Essen: Vulkan-Verlag GmbH, 2002.

[4] Baumgart, M., Verfahrenstechnik (2015) 9, S. 20.

[5] N.N.: templine – elektrisch beheizte Schläuche mit System. Data Sheet, Master-flex SE, Gelsenkirchen, Germany, 2013.

[6] Grote, K.-H.; Engelmann, F.; Beitz, W.; Syrbe, M.; Beyerer, J.; Spur, G.: Das Ingenieurwissen: Entwicklung, Konstruktion und Produktion. Heidelberg: Springer Publications, 2012.

[7] Knothe, J.M.: Elektrische Eigenschaften von spritzgegossenen Kunststoffformteilen aus leitfähigen Compounds. RWTH Aachen Uni-versity, Germany, Dissertation, 1996 – ISBN: 3-86073-563-2.

[8] Pfeiffer, B.: Überblick leitfähige Kunststoffe. OTTI-Symposium: Elektrisch leitfähige Kunststoffe. Regensburg, Germany, 2012

[9] Kim, G.-M.: Verstärkungsmechanismen auf Makro-, Mikro-, und Nano-Längenskalen in heterogenen Polymerwerkstoffen. Mar-tin-Luther-University Halle-Wittenberg, Ger-many, Habilitation Treatise, 2007.

[10] Möbius, K.-H.: Elektromagnetische Abschir-mung mit füllstoffhaltigen elektrisch leit-fähigen Kunststoffen. Kunststoffe 78 (1988) 4, S. 345.

[11] Fragner, J.F.: Elektrisch leitfähige Kunststoff-compounds auf Basis von Füllstoffkombina-tionen. RWTH Aachen University, Germany, Dissertation, 2014 – ISBN: 978-3-95886-010.

[12] Pfefferkorn, T.G.: Analyse der Verarbeitungs- und Materialeigenschaften elektrisch leit-fähiger Kunststoffe auf Basis niedrig schm-

elzender Metalllegierungen. RWTH Aachen University, Germany, Dissertation, 2009 – ISBN: 3-86130-864-9.

[13] N.N.: Vulcan 3 Carbon Black. Data Sheet, Cabot Corporation, Boston, USA, 2014

[14] N.N.: Ketjenblack EC-600JD. Data Sheet, AkzoNobel Polymer Chemistry N.V., Arn-hem, Netherlands, 2016.

[15] N.N.: DIN EN 62631-3-1: Dielektrische und resistive Eigenschaften fester Isolierstoffe - Durchgangswiderstand und spezifischer Durchgangswiderstand. Berlin, Germany: Beuth Verlag GmbH, 2016.

[16] Brown, R.: Physical Testing of Rubber. New York, USA: Springer Science and Business Media, 2006.

[17] Hellerich, W.; Harsch, G.: Baur, E.: Werkst-offührer Kunststoffe. Munich: Carl Hanser Publications, 2010.

[18] N.N.: TSSR-Meter. Data Sheet, Brabender Messtechnik GmbH & Ck. KG., Duisburg, Germany, 2012.

[19] Schnetger, J.: Kautschukverarbeitung. Würzburg, Germany: Vogel Communication Group GmbH & Co. KG., 1998.

[20] Napierala, A.: Kontaktieren von stromfähi-gen Silikon-Bauelementen. Brandenburg University of Technology (BTU) Cottbus, Germany, Dissertation, 2010.

[21] Meschede, D.: Gerthsen Physik. Berlin, Ger-many: Springer Publications, 2004.

Horizontalmaschine für die Großserienproduktion

RAPID 700 DUALE/300, ERGO 6000/400 Im Fokus der Messe-präsentation des Gummi-Spritzgießmaschinenbauers Maplan, Kottingbrunn, Öster-reich, stand neben dem neu strukturierten Neumaschinen-Programm das Upgrade beste-hender Anlagen. Eines der bei-den Maschinenexponate steht repräsentativ für die neu über-arbeiteten Horizontalmaschi-nen-Baureihe, die unter der Baureihenbezeichnung Ra-pid+ im Schließkraftbereich von 2.000 bis 4.000 kN verfüg-bar sein wird. Es ist die Rapid+ 700 Duale / 300 mit 3.000 kN Schließkraft und dem Energie-sparenden Servoantrieb MAP-Cooldrive für das Hydraulik-Sys-tem. Spritzseitig verfügt die Maschine über ein 725 cm³ Fifo-Plastifizieraggregat mit einem

Spritzdruck bis zu 2.300 bar. Verarbeitet wird 50-Shore-A-HTV-Silikon. Für die Silikonzu-führung auf dem Plastifizierag-gregat ist eine Stopfvorrichtung mit hydraulischer Verriegelung vorgesehen. Produziert wurden

elastische Kronenkorken-Fla-schenverschlüsse mit einem 16-Kavitäten-Kaltkanalwerk-zeug. Die 16 Kaltkanaldüsen sind hydraulisch einzeln an-steuerbar und können somit bei Bedarf in ihrem Füllverhalten einzeln oder in Clustern ange-passt werden. Im konkreten Fall übernimmt die Entformfunkti-on im Werkzeug eine Abstreif-platte. Das zweite Maschinen-exponat ist eine hydraulische, von unten schließende Vertikal-

maschine aus der neuen Ergo+-Baureihe, die in vier

Schließkraftstufen bis 4.000 kN verfügbar ist. Von jeder Schließkraft-größe gibt es zusätzlich zur Standard-Platten-

größe auch eine Version mit ver-größerter Aufspannfläche. Kon-kret wird auf dem Messestand die Version 6000/400 mit 4.600 kN Schließkraft stehen. Sie ist mit einem 6.000 cm³ Fifo-Plasti-fizieraggregat mit 2.000 bar Spritzdruck ausgerüstet. In Kombination mit einem ABB-Industrieroboter, der die Kavitä-tenplatten-Manipulation zwi-schen der Maschine und einer Entform- und Nacharbeitsstati-on übernimmt, wird die Maschi-ne zur automatisierten Produk-tionszelle. n

KONTAKT Maplan, Kottingbrunn, Österreich www.maplan.at

Zelle auf Basis einer hydraulischen Vertikalmaschine mit automati-sierter Formteilentnahme und Weiterbearbeitungseinrichtungen.

Bildquelle: Maplan

heating and vulcanisation of hybrid materials vulcanisation ......maschinen und anlagen machinery...

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