Conference on rubber mixing planned.

The Institute of Plastics Engineering of the University of Paderborn, Germany, is organizing its second international conference focusing on European research in the area of rubber processing. The results of three major research projects will be introduced to the public within the scope of this conference, which will take place in Paderborn from January 25-26.

Increasing cost pressure and simultaneously rising quality standards have caused the rubber industry to question traditional production processes in order to discover and utilize possibilities for cost-cutting, according to the sponsor. Furthermore, an improvement in quality is said to require the application of new processes and innovative raw materials.

Topics covered during the conference will include the following: Optimization of machine and rotor design for the production of silica tire tread compounds; dependency of the silanization efficiency on process conditions and chemical modifications; comparison of machine concepts for continuous mixing of rubber compounds; application and optimization of a continuous compounding line for the production of technical rubber goods and tire parts; materials handling for continuous compounding--polymer granulation and storage; advanced dust stop systems for internal mixers; surface technology and wear mechanisms of dust stop sealing rings; lubricating properties and effects of process oils for use in dust stop systems; comparative investigation of tangential rotor geometries; numerical and practical simulation and evaluation of rotor geometries; new approach to the problem of filler dispersion in rubber; and identification and quantification of dispersion mechanisms.

In an accompanying exhibition, rubber processors, suppliers of raw materials, rubber machinery and equipment, as well as research institutes, will be given the opportunity to display and advertise their products and services.

Chairmen of the conference are Edmund Haberstroh of the University of Aachen, Germany, and Robert H. Schuster of the Deutsches Institut fur Kautschuktechnologie, Germany.

Registration for this conference costs EUR 600. Further information is available from the conference secretary, tel.: [phone]; fax: [phone].

Descriptions of the three major research projects that will be introduced to the public during this conference are as follows:

SATPRO--system analysis for the production of technical rubber goods and tires

New developments in the area of raw materials and compounds also require innovations on the side of processing equipment. In this context, the rubber mixing process is of special importance due to its influence on quality and costs of the final products.

The project SATPRO (system analysis for the production of technical rubber goods and tires) was funded by the European Commission within its fifth frame program. The project was initiated to find improved technical solutions for the processing of two of these new raw material and compound developments. Each of these developments was addressed in a separate work package.

The reason for the widely spread application of silica as an active filler in tire tread compounds can be seen in improved tire properties. However, silica mixing by means of traditional mixing technology goes along with a reduction of mixing capacity and an increase of mixing costs. This is due to the tact that in contrast to traditional mixing processes, silica mixing requires the performance of a chemical reaction which consists of binding an additional compound ingredient, an organosilane, to the surface of the silica particles. This process is called hydro-phobation.

With the goal of developing a so-called silanization reactor, trials were conducted within the SATPRO project in order to optimize both the silica mixing process itself and the mixing equipment. All measures taken targeted an acceleration of the equilibrium reaction. In addition to a close temperature control, measures were to be addressed that would lead to an efficient removal of the reaction product ethanol. Starting on a laboratory scale, different process conditions, changes in construction and recipe modifications were investigated with regard to their influence on the silanization reaction. The most promising results were verified on pilot production scale in order to be transferred to industrial scale with subsequent test tire production. By means of the newly developed technology, it was not only possible to reduce processing times, but also to significantly improve safety relevant to tire properties. These facts could be proved within an independent tire test program.

Motivated by the availability of free flowing polymers as currently given or as to be expected in the future, the second work package within the SATPRO project dealt with a further development of the continuous mixing process. The aim was to apply this technology within a direct extrusion concept, a combination of continuous compounding and subsequent profile extrusion. Investigations were carried out for applications of the tire and the mechanical rubber goods sector.

The investigations started with a neutral screening of some of the available machine concepts for continuous mixing. Within a round robin test, a planetary roller extruder, a multi-screw extruder and two different concepts of a co-rotating twin-screw extruder were evaluated with respect to their applicability to the continuous mixing of selected recipes. The criteria for evaluation were the achieved compound properties, aspects of integration into a production surrounding and the obtained output levels in relation to the applied machine size, taking into account the critical temperature level to prevent pre-scorch. The purpose of the screening was the selection of the most suitable machine for subsequent development.

All following investigations were conducted by means of a co-rotating twin-screw extruder with a diameter of 58 mm. In this part of the project, work focused on an optimization of the machine concept and the mixing process with the aim of increasing both compound quality and output level for the two selected areas of application. While the investigations for the mechanical rubber goods were carried out on various EPDM-based compounds, the investigations for the tire sector were conducted on an innerliner compound. Within the trials, different mixing philosophies were compared, such as one-stage vs. two-stage mixing, as well as different alternatives for dosing compound ingredients. Furthermore, the focus was kept on the stability of the process and on quality assurance aspects. Applying the best suited philosophy, compounds were continuously mixed and integrated into a subsequent hose and test tire production, respectively. This was followed by an evaluation of the final products' properties. Based on the findings regarding the possible scenarios of continuous mixing, costs were compared with those of the application of traditional batch mixing.

Since only a few polymers are actually available in a free flowing form currently, the usage of ground polymer bales was also analyzed in order to broaden the potential fields of application of continuous mixing. This work includes a comparison of different parting agents on the storability of the polymers and on the properties of the compound in which they are used.

The SATPRO project was coordinated by the Institute of Plastics Engineering of the University of Paderborn, Germany. Other project partners include ThyssenKrupp Elastomertechnik GmbH, Vredestein Banden B.V., Trelleborg Industri AB, along with other consumer organizations and universities.

Improved end product quality by rotor optimization

The production of rubber products, such as tires for cars or seals for technical products, always begins with the production of a rubber mixture in an internal mixer. Subsequently, various processing steps (injection molding, extruding, etc.) follow, and at the end of the manufacturing chain, the uncured rubber products are vulcanized to a rubber part.

Already at the beginning of the process chain, when the raw materials are mixed, the quality of the final product is determined by the type of machine used (tangential or intermeshing) and the mixing units used (rotors), the raw materials and by the type of process. The geometry of the rotors deployed in the internal mixers plays an important role. In the past, their development was accomplished by means of an extensive empirical methodology, in which the practical experiences of the developers came into effect. This method was very expensive and accordingly slow.

In the European project ROTOR (Computer optimized rotors for internal mixers: An innovative way of enhancing the quality of rubber parts and tires), the practical experiences in the area of rotor development are supported by the simulation of flow processes and filler dispersion within the internal mixer. The main goal of the project was the simulation supported development and testing of new rotors on industrial scale for tire mixers (tangential) and internal mixers of the technical rubber goods industry (intermeshing), with which rubber mixtures of higher quality can be manufactured.

The existing software products for the simulation of the mixing process, which were suitable for the evaluation of the mixing quality before the beginning of the project only under certain conditions, are being refined sustainably (few criteria for the description of distributive mixing and no mathematical model for the description of the disagglomeration process had been considered). An important factor in this context is the quantitative description of the destruction of the filler pellets and their incorporation into the mixture during the mixing process. These so-called dispersion kinetics are experimentally determined and mathematically described with specified carbon black pellets which are used in the rubber industry. These dispersion models are implemented into the existing simulation software and allow the simulation of the dispersion quality obtained in the mixing process.

Then the new rotors were tested in industrial machines with a multiplicity of different mixtures. Physical measuring techniques and practice tests on finished rubber parts help to evaluate the quality of the mixture.

Partners in the ROTOR project included Michelin, ThyssenKrupp Elastomertechnik GmbH, Polyflow SA, Optigrade and various universities.

Critical analysis and further developments of alternative dust stop systems

The main objective of the national research project, "Reduction of emission at the dust stops of internal mixers," is the development of an optimal dust stop system. The processing of rubber compounds which consist of a multitude of different substances requires that no ingredients of this heterogenous mixture can escape from the mixing chamber. The emission of these fluid and finely dispersed ingredients into the environment is restricted by the use of so-called dust stops. First, the finely dispersed ingredients are pasted by means of an oil film. In the next step, the high pressure in the mixing chamber squeezes the paste created outwards along the rotor shafts. In order to restrict the flow of the disposal, a pair of rings seals the rotor shafts at each end.

In this way, the emission of the finely dispersed substances can generally be avoided. Nevertheless, disposal, consisting of oil, various chemicals and fillers, is still created. Rising requirements concerning economic as well as ecological standards in the production process, and the demand for higher quality standards regarding the product itself, necessitate the development of an optimized sealing system. This sealing system should not only provide a longer service life of the sealing rings, but at the same time should reduce the amount of oil needed and the amount of disposal. In this manner, the operational costs for sealing rings, oil and waste disposal can be reduced. A different approach from the constructive possibilities for optimization is the use of lubricant-free dust stops. Based on analyses of abrasion and service life, the risks and chances of the aforementioned sealing system were examined in extensive field tests. This work is completed by a functional analysis of the production process.

Additional process analyses with production machines give further information about the potential optimization of operational parameters. Exemplary parameters in this context are the contact pressure, in addition to the type and amount of different process oils. The influence and performance of the process oils on restricting dust emission were investigated in field and laboratory tests of a different examination. In this separate work package, the material properties and the application areas of the lubricants were determined by means of analytic chemical, physical and tribological techniques.

Cooperating in this research project were Veritas AG, Bottcher-Gelsdorf GmbH, ThyssenKrupp Elastomertechnik GmbH and various institutes and universities.

Paper call

Alliance for the Polyurethane Industry. Papers and posters are solicited to be presented at the Polyurethanes Technical Conference and Trade Fair, to be held October 19-22 in Houston, TX.

This conference and trade fair is said to present an opportunity to reach an audience of more than 1,500 manufacturers and processors of polyurethane-based products across all industrial sectors. Papers and posters may address innovations and developments in flexible slabstock, flexible molded PU, equipment and machinery, cast elastomers, thermoplastic polyurethanes, integral skin, RIM, binders/fillers, adhesives and sealants, or fundamentals.

The API also encourages papers and posters on breakthrough technology in polyurethane markets or chemistry, developing markets such as medical and fiberboard, and product areas such as rigid foam insulation or coatings.

Presentation submissions may also focus on issues such as combustibility, transportation, recreation and security, as well as environmental and stewardship issues, including emissions, regulatory developments, waste management and related topics.

The highly successful Polyurethanes Conference 2004 saw 17 authors picked from a competitive field to receive awards for their papers and posters, as judged by their peers, according to the API.

Paper abstracts are due by January 31. Poster abstracts are due by May 2. Further information, such as submission instructions, paper guidelines and templates, can be found at the API's web site, www.polyurethane.org.

The Alliance for the Polyurethane Industry promotes the sustainable growth of the polyurethane industry, in accordance with the principles of Responsible Care, by identifying and managing issues that could impact the industry, in cooperation with user groups.

Rubber group news

The Ohio Rubber and Plastics Group will hold a technical meeting February 10 at the Martin Center in Akron, OH. Further information is available from Dave Schwarz [phone].

The Ontario Rubber Group will hold a technical meeting February 8 at the Holiday Inn in Cambridge, Ontario, Canada. Details are available from Phil Ballet [phone].

The Wisconsin Rubber Group will hold a technical meeting February 1 at the Clarion Hotel in Milwaukee, WI. Details are available from [e-mail].