Author: Marco Solinas
Subtitle: Design choices for a high-performance industrial packaging blow moulding machine
Discontinuous process based on accumulator headhas been for decades the standard blow moulding technology to produce drumswith volumes from 60 liters (15 gallons) upwards, including the well-known220-liter (55-gallon) “L-ring” drums.
In the last ten years, the move to continuousextrusion – which in the previous decade involved the jerrycans, the “smallestbrothers” in the rigid industrial packaging family – has been imposing itsadvantages also on the drums production. Among those advantages, the shortestcycle time, the lower power consumption and the better product quality. The riskof parison sagging – inherent in any continuous extrusion process with a longcycle time – has been overcome by using Very High Molecular Weight Polyethylene(VHMW-PE) with greater melt strength and by intensive post-cooling (whichallows de-moulding at higher temperature, resulting in a significantly shortercycle time). The combination of those two factors made possible the use of thecontinuous extrusion process for heavy items like the 220-liter (55-gallon)“L-ring” drums.
The next choice to make for a continuousextrusion process is whether moving the mould to catch the parison from theextrusion head (so called “shuttle” layout) or moving the parison from theextrusion head into the mould (so called “parison transfer” layout). Thislatter has been the ST BlowMoulding preferred option, to prevent theencumbrances of the rails on the floor and of the large chains to house thecooling hoses (which are needed in the “shuttle” layout to follow the cyclicmovement of the carriage that holds the mould).
Vertical or horizontal parison transfer? Thefirst one grants the fastest movement (hence the shortest cycle time), but itrequires so much extra headroom as the parison length (because the parison isextruded above the mould). The second one does not need any extra headroom(because the parison is extruded at the side of the mould), but the sidewaysmovement to the mould takes longer (to prevent the parison from swinging). Sincethe industrial packaging industry looks for the maximum performance to stay ontop of the competition, the new ECT 880 by ST BlowMoulding has been designed accordingto the vertical parison transfer concept.
The challenge of the vertical parison transfer
The vertical parison transfer requires theextrusion head to be located on the same vertical axis of the mould, at adistance to allow the parison to be completely extruded between the head andthe mould before the mould opens for the next cycle. When the mould opens and theblown item is de-moulded, the parison is put into the mould cavity by a fastvertical movement of the parison transfer grippers.
The obvious consequence of the distancerequired to extrude the parison above the mould is that the extrusion headbecomes difficult to approach. In a blow moulding machine for “L-ring“ drumsthe head is about 4.5 m from the floor and almost 2 meter above the mould: howto reach it for centering the die, tuning the SFDR, changing the head tooling orjust cleaning it? In the design of the ECT 880, ST BlowMoulding has decided toconvert this weak point of the vertical parison transfer layout into a “plus”for safety, ergonomics, and maintenance efficiency.
First of all, a “service room” easilyaccessible by stairs has been arranged at the mezzanine under the extrudersplatform. Electric and pneumatic connections are provided in the service room,as well as a full set of tools for any maintenance need of the extrusion head. Apassageway sliding on linear rails can be easily pushed from the service room tothe extrusion head; together with the backwards movement of the overhanging platformthat houses the extruders and the head, it provides an ergonomic access to thehead tooling.
Bringing the head tooling to such a height withno risk – neither for the operator nor for the machine – has been the secondissue to be solved. On this purpose, the service room of the ECT 880 isequipped with an electrical winch to lift the head tooling from the floor, andwith a swivel arm to bring the head tooling under the extrusion head. The swivelarm is equipped with specific devices to adjust accurately the head tooling underthe extrusion head.
“Adiabatic” extrudersfor VHMW-PE
In thermodynamics, a physical process is named“adiabatic” when it does not involve any heat exchange between the system andthe surrounding environment. In the technical language, the term “adiabatic”has been slightly relaxed to include any process that virtually does not include any heat exchange. That is why at STBlowMoulding the term “adiabatic” is used to identify the extruders that do notresort to fans to keep the melt temperature under control; on the contrary, theextruders are insulated with a double layer of glasswool to prevent any heat loss.Since any heat exchange between the machine and the environment is a net lossof energy, preventing it with a thick insulation and avoiding the use ofcooling fans result in a significant energy saving.
The “adiabatic” extrusion technology has been extensivelyapplied for many years by ST BlowMoulding in polyethylene processing because ofits outstanding efficiency. However, some concern still survived about the riskof overheating the melt when plasticizing VHMW-PE, because of its very highviscosity. After some modifications of the barrel and screw design, the“adiabatic” extruders has proven to be very effective also in processingVHMW-PE with the lowest melt flow rates (HLMFI = 2 g/10 min @ 190 °C and 21.6kg).
Thanks to this technology, the specific energyconsumption of the ECT 880 in CoEx3 version has been measured below 0.32 kWh/kgat a production rate of 50 drums/hour (drum net weight 8.5 kg). At thisproduction rate, no one of the three extruders exceeds 45% of its maximum throughtput.The specific energy consumption of the ECT 880 in single layer configurationhas been calculated below 0.29 kWh/kg (in the same working conditions).
The HMI made as easy as a smartphone
How can you really get advantage of a high-performancemachine, if only few super-skilled people can use it? With that in mind, the STBlowMoulding software team has developed for the ECT 880 a new generation web-basedHMI. Using that interface is as easy as using a smartphone, because most functionswork on the same principle. According to the logged-in user, the interface is customizedto his profile (either production, or setting, or maintenance, or quality): onlythe corresponding area of competence are visible and accessible. Even the radialparison thickness control has been made intuitive by a graphics thatdynamically shows the actual movement of the head tooling. Quick log-in throughpersonal badge and transponder is the standard.
The operating manual of the machine is availableon the HMI: the “help on line” function directly gives access to the content ofthe manual corresponding to the page currently displayed on the screen. Thepneumatic / hydraulic / electric schematics are also dynamically accessiblefrom the HMI: you can scroll them by sliding the fingers on the screen orenlarge them by spreading apart two fingers – like on a smartphone. Inaddition, a chat line is available on the HMI to get in touch with the STBlowMoulding service team and get advice in real time whilst working at themachine.
Predictive maintenance to avoid productionlosses
Preventing productionlosses due to machine downtime and optimizing maintenance interventions are keyfactors not to jeopardize the high productivity of a top-performing machine. Traditionally,maintenance has been carried out according to a fixed schedule: components arereplaced at constant intervals of working hours, which do not take intoconsideration the varying circumstances of the machine being maintained. Predictivemaintenance aims to get the maximum life out of the equipment whileminimizing the risk of failure by monitoring the actual status of the machinecomponents.
ST BlowMoulding has integrated predictivemaintenance tools into the ECT 880 machine to an extent never attained before:
· “Smartcomponents” have been used for the first time ever on anextrusion-blow moulding machine: according to the MTTF curve (Mean Time ToFailure), a warning information is given when that component has to be replacedbecause the risk of a failure has increased beyond the threshold;
· A number ofcomponents (hydraulic pumps, proportional valves, heating bands, utilityfluids) are permanently monitored; their working conditions are compared withthe ideal ones to detect possible long-term deviations; if that is the case, amessage is automatically forwarded to the maintenance team for theintervention.
The efficient maintenance plan that can be scheduled on predictiveinformation prevents not only the downtime caused by unexpected failures andlast-minute maintenance activities, but also the unnecessary costs caused by apremature replacement – based on a preventive maintenance concept – of partsthat are still operational.
Continuous extrusion is gaining more and moreground to blow-mould large industrial packaging items. The vertical parisontransfer is the most effective single-cavity machine layout for the drumsproduction to get the fastest cycle time, the lowest power consumption and themost compact machine footprint – as long as a sufficient headroom is available.
Selecting the most advanced technologies for everystep of the process – adiabatic extruders for the most efficient plasticization,W. Müller extrusion heads for the perfect parison distribution, Feuerherm PWDS®/SFDR®units for the most accurate dynamic radial thickness control – is the STBlowMoulding choice to stay at the forefront.
Developing solutions to operate and maintainthe machine in an easier, quicker and safer way is the focus of the STBlowMoulding design. These factors significantly contribute to increase theoverall production efficiency and quality consistency. In this continuousimprovement process, new targets have been already set on the way to the“intelligent machine”.
Machine identity card
Machinename: ECT 880 CoEx3
Firstpresentation: K 2019
Productapplication: 3-layer 220-liter (55-gallon)“L-ring” drums
Productionrate: Up to 50 drums/h (withpost-cooling)
Powerconsumption: < 32 kWh/kg (CoEx3version)
Extruders: HEX 60/30 + HEX 120/28+ HEX 60/30
Extrusionhead: W. Müller S1/400 ReCo3
Dynamicradial control: Feuerherm PWDS®/SFDR®
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