(Photo credit: Otto Systems)
PET injection system
As is well known, big trade fairs cast their shadows ahead. In this shadow, Otto Systems is building its new PET system for drinktec 2022.
An interview by Otto Appel with Stefan Zatti and Beda Grob Otto Systems AG
We accept the invitation of Stefan Zatti, CEO, and Beda Grob, CTO, to get to know the new PET-Series of Otto Systems at BMB, the partner and supplier of the injection moulding mashine in Brescia in northern Italy. What had happened since the rollout of the first system, which we had reported on in detail in the THREE:2017 issue of our comPETence magazine?
Zatti: Four weeks to go - on 29 August, the trucks loaded with our new PET system will leave here. On 30 August at eight in the morning, the trucks will arrive at the drinktec exhibition centre in Munich. In front of the hall where Robbie Williams will give a concert on 27 August. So, if you like, there is a lot of sound in our project.
Grob: The whole team is now going into the final sprint. We expect the 96-cavity mould of the new generation from Otto Hofstetter to arrive in the next few days. We will integrate it into the PETSeries 240 here and put into operation with the side entry take-out robot and the post mould cooling system. The process settings will be optimised and fine-tuned for drinktec with a view to perfect preform quality.
Grob: The PET-Series 160 presented in March had all the integration features with our newly developed robot and the complete merging of Software and Control in one system.
Zatti: The specialty of having a fully integrated high-performance system available for small production batches, which is compatible with selected topentry moulds and, as a variant, is capable of producing preforms up to 400 mm in length, has been an excellent success.
Grob: First of all, the exterior. We say in our language: You eat with your eyes. From our point of view, the appearance of a technological system also plays an important role. This is where we started and focused our attention on compactness. But of course, during the realisation of the 240 ton platform, we questioned each movement axis once again and fine-tuned its conception and dimensioning as well as the potential for parallel movements. As a result, the overall system and energy efficiency could be further increased. Why? Because our customers expect optimum performance with minimum energy consumption and maximum system availability. Looking at the mechanical and technological details, you will see that we have focused on the system approach.
Grob: The system concept is essential for us, and we consistently pursue this at the technological level and, of course, in the sense of thinking in terms of series. It is based on consistently transferring comprehensive know-how from granulate to quality preform into system technology.
Grob: For example, the plasticising screw, the injection plunger with static mixer, the mould hot runner through to the valve gate system at the gate and the preform itself are rheologically regarded as ONE technological system and consistently designed from A-Z.
Grob: The implementation of the PETSeries model range follows the guideline of standardisation and modularisation. The core system, which we call PETSeries, includes the clamping side and the injection side of the machine as well as the robot with the machine-side installations for preform post-cooling. These are the standardised system modules. For example, the 160 or 240 clamping unit can be combined modularly with the 100 mm shotpot injection unit. The modules are standardised and the interfaces are identical.
Zatti: Every mould intended for a model range with post-mould cooling equipment can also be implemented like a module in the PET-Series. Everything related to the preform geometry and the preform itself builds on the experience of our Swiss company and is individually adapted to the preform requirements in each case. It is very important - also to complete the system idea - that with over 40 years of experience of Otto Hofstetter AG in the PET mould business, an enormous know-how is available for the development and optimisation of preform designs. We must never lose sight of the fact that the end product of our PET-Series customers are preforms.
Grob: We have further developed some technological highlights and implemented them with BMB, such as the kinematics of the electric and very energy-efficient clamping unit. Further fine-tuning of the toggle geometry and optimisations in the parameter settings of the drive control have once again resulted in an improvement in the dynamic of the kinematics. The conceptual design with the so-called cross-head platen, which moves in the system, and the central force application provide excellent values regarding platen parallelism and deflection and guarantee minimum mould wear.
Zatti: All in all, the smooth movements of the clamping unit allow us to achieve lock-to-lock times of less than two seconds. That is standard in the highperformance range. We ran 1.9 seconds in the tests and will show maximum 2.0 seconds at drinktec. Generally, we aim to run under two seconds as standard.
Grob: Of course, the effective lock-to-lock time depends on the preform design. The shorter a preform, the faster the removal times, as a result of shorter strokes. It is worth mentioning that our clamping unit, despite the highest dynamics, enables the production of preforms over 200 mm in length. Our competitors, who have optimised for mass production, have reduced the strokes even further.
Grob: For the start of the series production of the system, we have further developed the screw design - based on a barrier concept. With this, we realise a stable and high specific throughput with a flat pressure profile along the plasticising screw. This means that we are energy-efficient, have a uniform and high specific melting capacity in every segment of the screw and thus an excellent plasticising performance with very gentle melt preparation.
Zatti: We achieve excellent behaviour when processing rPET and do not see any process fluctuations or instability. We will process 100% rPET at drinktec, dyed with liquid colour.
Grob: The complete drive unit on the injection side has become more compact: The main pump motor and the heat exchanger have been arranged more ergonomically and, due to the performance data achieved in the border area of injection, only three bladder accumulators could now be arranged in series - instead of 2 + 2.
Zatti: Another optimisation: The water pipes run in the machine frame for a central water feed from the mould area to the rear. In most cases, PET systems are positioned against a wall at the end of the injection unit. So it makes sense to feed in all media from the rear.
Grob: In general, we have optimised the installation area and the housings to save space. For example, the robot housing has a sliding door instead of a protruding swing door. This allows the system to be positioned as close as possible to a wall on the “non-operator side”. A small footprint is often a strong argument with customers, because space is scarce and costs money. These and other measures have made the entire machine slimmer and more elegant.
Grob: The take-out area with the water cooling in the take-out plate and the preform internal air cooling in the transfer plate are central to the preform after-cooling and thus crucial for perfect geometric shaping of the preforms. And of course, we have also optimised here: We opted for three post-cooling stations as standard. We have deliberately dispensed with a vertical robot movement for a fourth station. We are convinced that with three cooling stations, we can cover the majority of fast-running applications without any loss of cycle time. With thickwalled preforms, it is indeed the case that a fourth station would help, but in these applications, it is typically not the hundredth of a second that counts.
Zatti: In our system approach, the mould series was explicitly adapted to this process. Each pitch and compartment number has an exact row spacing in the mould so that the largest preform that fits into an insert group has enough space for three post-cooling stations in the removal plate.
Grob: In principle, implementing a fourth station would also be possible. However, our current solution not only saves investment costs, but also ensures high stability and positioning accuracy of the highly dynamically operated takeout axis. This is an advantage because an additional vertical movement of the entire take-out mechanism is often underestimated in terms of stability in the system and susceptibility to wear. We have therefore decided in favour of safety, standardisation and cost optimisation.
Zatti: The removal plate with the water-cooled sleeves passes through three stations. When the preforms are transferred, the transfer plate with the blow-cooling pins - which is now stateof-the-art - takes over the preforms. Most suppliers in the market offer two blow-cooling stations and the picker on the third station. In our PET-Series, the third station is a combined station. The blow-air cooling is equipped with a kind of slide function in the air chamber to switch to vacuum for picking the perform. In this way, we partially compensate for the supposed disadvantage of only three stations with a third blow-cooling station. We call this innovation “pickblow-combi” - and it will be on show at drinktec.
Grob: With the 160 robot of the first generation, we designed a demonstration system with a reserve in the installed power. The motor and drive with the control unit are identically dimensioned in the new system, although larger and heavier take-out plates for up to 96 cavities are used. The overdimensioning of the demonstration system gave us plenty of scope for testing and optimising the settings of the acceleration ramps. We have now installed the same unit as a series solution on the PET-Series 240 and achieve the same dynamic movements. The power peaks are now no longer at 50-60% of the installed power but around 80%. In principle, we have dimensioned something smaller, benefiting energy efficiency. On the PET-Series 240, we have only raised the mechanics and linear guides to the next dimension to cope with the higher loads. This ensures smooth running, safety and mechanical engineering quality.
Zatti: The system is also state-of-theart in terms of energy recuperation. In addition to the deceleration energies of the robot axes, those of the clamping unit are also fed back into the system.
Grob: The motion sequences were further optimised through the integration of Heidenhein Control and our software development for the robot. In addition to the control settings optimisations for the acceleration ramps, all robot movements were synchronised with the clamping unit and the ejector, and the maximum potential in parallel movements was exploited. A lock-to-lock time of 2 seconds is suddenly easy to achieve because the movements run smoothly into each other.
Grob: We have completely redesigned the control cabinet and were able to reduce the overall height considerably. The mould needles are no longer temperature-controlled but only assigned a percentage control variable. This is because we are following a standard in the market to be able to supply compatible moulds. Since our top-entry mould customers are used to having the information of the nozzle needle temperatures available, we equip up to 6 nozzle packages of their choice with thermocouples on the PET-Series. Our customers enormously appreciate this “service”. We have also paid special attention to simple and intuitive navigation on the new large-format touchscreen panel.
Grob: I am proud to say that, similar to the system’s appearance, the operator panel is also a feast for the eyes. The design has a very clear structure for easy and intuitive operation. All menu-guided pages contain only essential information. Let’s look at the mould temperature as an example: mould and hotrunner are shown on a single page with all heating zones. They are arranged as they are installed in the mould. In the main menu at the top, you choose whether you want to see the set value, the actual value, the current heating power or the pin assignment at the connector or in the control cabinet in the zone fields, e.g. for maintenance purposes. A menu appears below the mould and below the hotrunner, in which you enter the set value - that’s all. Everything on a single page. That is our understanding of system integration.
Zatti: We notice from the market that small systems are in demand. From manufacturers who can deliver quickly. Our 160 is small. Larger suppliers are rather hesitant about this segment or don’t have a solution in their range. So we are quite unique in the 160 system, while there are several suppliers of 240s. At drinktec, we will present the new 96-cavity mould on the PET-Series 240. For preforms with neck finishes up to a maximum of 26 mm, this is a highly efficient system: with a preform weight of 9.8 g and a wall thickness of 1.86 mm, it produces around 60,000 preforms per hour.
Zatti: In BMB we have a perfect partner. This is undoubtedly also due to the family-run company structure and philosophy. That builds on similar values as our Swiss parent organisation, Otto Hofstetter Holding. It’s perfectly compatible: BMB has the equipment, the capacities, the manufacturing and the willingness to provide us with that. We bring the know-how for PET. And we have Beda Grob, who has made the PETSeries what it is today. In the medium term, the production of the systems is to be located in Uznach.
Zatti: That was indeed a lengthy decision-making process. We haven’t shown a mould on the exhibition stands of Otto Hofstetter for years. At Otto Systems, we are facing a completely new situation: with the PET-Series, a completely new system has been developed, and we want to inspire our customers with it. What is the best way to do that? Can it be done purely virtually? For sustainability reasons, that would be my preference. In the end, we decided otherwise because the physical presentation does make a difference. Because you can see the engineering performance, the quality. Maybe it’s enough to bring the system to a trade fair just this once. After all, everyone is talking about energy efficiency and sustainability. Consequently, we should consider whether this should not also be a topic for our trade fair planning in the future.
Zatti: Well, that’s an exciting question. There are so many imponderables. Does the pandemic play a role? What is the effect of the highly increased travel costs? Has air traffic normalised by then? And the geopolitical situation certainly does not play an insignificant role either. I expect drinktec 2022 to be a European-oriented fair. I hope for the USA, and customers will also come from South America. The fact that drinktec and K-Show take place a few weeks apart will probably lead to customers deciding to go to one or the other trade fair. For us, drinktec is THE trade fair for PET. Otto Systems and the PET division of Otto Hofstetter will be there with their full power. At the K Show, Otto Hofstetter will focus on its medical sector and packaging.
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