Innovations for rubber mixing in the Tyre Industry
Two major innovations show important steps for cost reduction and quality improvement in the tyre industry: A new generation of tangential batch mixers and the tandem technology. Both technologies were developed in the companies of the HF Mixing Group, one of the leading manufacturers of mixers and mixing room systems for the rubber processing industry.
Tangential mixing technology
The BM305N and BM440N BANBURY tangential mixers unify all the advantages of the successful developments realised over the years from each of the HF Mixing Group’s mixer companies around the world – Farrel, Harburg- Freudenberger, and Pomini. In a ‘Best-of-Best’ approach the HF Mixing Group today offers its customers the most advanced and optimum BANBURY design. This also includes a new machine size, the BM 700 N.
Standard features of the BANBURY mixer are for example the end-frame design for enhanced dust stop access or the two-piece water cooled rotor end plate, which improves the heat transfer for the process and allows a better control of the dust stop temperature. Another new development is the totally newly designed hydraulic dust-stops, which significantly improve the sealing performance. Besides these features a better batch discharge is reached by the wide drop door adopted; a keel bottom weight increases productivity and improves distributive mixing. For enhanced corrosion and abrasion resistance a new hard coating for the mixing chamber body was introduced.
These N-Series mixers have increased net chamber volumes for higher throughput and are available with the latest rotor technologies such as NST-SC, MD-SC and ZZ4-SC as well as a hydraulic power unit with iRAM (intelligent RAM) control.
The combination of all these new features confirms that this complete redesign of the HF Mixing Group’s previous tangential mixers exceeds and convinces customers around the world of the highest innovative energy, which the Group displays on a daily basis.
The Banbury Mixer BM700N is the latest development of the mixer with tangential rotors designed to offer greater efficiencies in rubber mixing.
It was a logic step forward and unifies the experiences with the former GK 650 N and the F 620 – two big tangential mixers, which the group companies have successfully brought into the market in the past. Of course it now contains also all the “best of best” ideas, realized on the sizes BM 305 and BM 440 already. The BM700N is also
equipped with super cooled rotors, developed specifically for the new mixer. The super-cooling design leads to a 50 per cent higher cooling efficiency. The length to diameter ratio is significantly improved compared to the F620. It enables better homogenization as a result of the improved L/D ratio, and this results in much shorter mixing times, thus higher productivities can be realized. Also, the compact rotor geometry and higher cooling provides better energy efficiency.
The removed throat restrictors allows to fit a keel bottom ram thus improving the distributive mixing performance by eliminating any dead zones whilst additionally increasing the mixer net chamber volume. The end frames have no throat restriction, just a very simple throat plate and are split for easy maintenance. Often there are lifting capacity restraints in the mill room, therefore access to the rotor is improved.
The BM700N’s rotor end plates have an optimised water-cooling design, which provides an increased surface area for heat transfer medium.
The machine’s door top seals the mixing chamber tightly as it is driven underneath the rotor end plates, this prevents the typical wear found on tangential mixers’ drop doors.
The drop door is bigger compared to the F620, which leads to a shorter batch discharge and less material hang up. The faster discharge results in shorter mixing times, and the dwell times can be reduced from batch-to-batch, thus saving a number of seconds between each batch.
Replacing a 620 L tangential mixer with the BM700N means much higher outputs can be achieved up to 15%.
Mixed doubles – The HF tandem process
The widespread success of tandem technology began with an idea from Dr Julius Peter (Continental AG). He discovered that separating the two main tasks in the rubber mixing process – dispersion and distribution – carried a number of clear advantages. The tandem process was born out of this idea and was patented by Peter as long ago as 1987. Tandem technology involves connecting two machines in series – or more precisely, on top of one another, with each machine optimised to perform one of the two mixing tasks.
The first machine is responsible for dispersion, which means breaking down mixture components such as the fillers. Distribution takes place in the second machine (or stage), which involves achieving the most homogeneous mix within the rubber compound. If reactive compounds are processed, the chemical reaction also chiefly takes place in this machine. Both machines are connected in series so that they function together as one continuous mixing process.
The ‘premixed’ material from the first stage is not temporarily stored, but immediately moved on to the second stage, which performs the concluding distribution task while the next batch of material is being premixed in the first stage. This perfectly synchronised, permanent two-stage process signifies a quantum leap in mixing technology. It soon became clear that it would not only result in enormous benefits in relation to the silica compounds used for manufacturing tyres – an area of development on which there is currently a great deal of focus – but also in relation to the numerous other mixing requirements such as remill and carbon black manufacturing stages.
Above all, the temperature profile which is absolutely essential for inducing the chemical reactions during the mixing process can be better controlled by separating the stages. Consequently, the properties and quality of the compound can be positively influenced. There is a further effect: by separating the tasks and concentrating on one at a time, and as a result of the relatively smaller compound weight in the larger lower machine, it can be operated at a higher speed. This improves the quality of the compound thanks to the higher gravitational forces and the greater number of times the compound is moved around.
Experience shows that a Tandem mixer can improve the throughput rate by up to 25 per cent when working with carbon black compounds and even by up to 100 per cent with silica compounds. The resulting potential for cutting costs and increasing output is obvious. Depending on the mixing line, in an average-sized mixing room for tyre production (approx. 100,000 tonnes of rubber compound p.a.) this can soon add up to savings of almost one million euros per year.
The early decision taken by HF to focus on tandem technology and continue to optimise this process is paying dividends. The pioneering automation technology, the numerous, individually configurable applications and the exemplary global service network should also be mentioned. An increasing number of companies from the rubber and tyre industry clearly recognise the enormous benefits, because demand for the machines supplied by the HF Mixing Group is greater than ever.