For extrusion experts it is recommended to visit EXTRUDEX – stand B42 in hall 16 – to form an impression of HELIBAR® (see attachment). This single-screw extruder affords immense advantages with regard to energy savings and durability.
“At the beginning there was the demand by SOPLAR to increase the throughput on the blow moulding machines for bottles by between 30 and 50 percent with the use of new extruders.” As a result, the academically qualified engineer Eberhard Grünschloß developed a new single screw extruder which he called
HELIBAR® (helix = spiral, combined with ‘bar’ = barrier or barrel). In mid-1999, EXTRUDEX Kunststoffmaschinen GmbH, in Mühlacker, Germany, patented this technology. Since then, the system has been continuously improved, refined, tested, and declared a ‘runner’ – not with regard to RPM, but certainly when it comes to energy efficiency, economy, reliability, endurance, and longevity. “Even after three years of continuous production, REHAU (as international global polymer processing company supplying products to the construction, automotive, and industry sectors) has not been able to discover discernible wear in the HELIBAR® processing unit”, Eberhard Grünschloß quotes the core clause from a paper published on the subject.
The HELIBAR® energy consumption can be lower – between 10 and 60 per-cent – than usual because of the reduced cooling demand and the smaller size at equal output. Tests have revealed:
- a 10 percent improved energy saving rate compared with state-of-the-art extruders of grooved bushing design,
- 20 percent more efficient compared with older machines – achieved by retrofitting the process unit (screw/cylinder), and keeping the existing gear system/motor,
- up to 60 percent better when replacing the complete unit, i.e. a 90 screw diameter (OD) extruder with a 60 OD HELIBAR®.
Helmut Wahl, CEO of EXTRUDEX, attributes the advantage to the fact that the ‘lack’ of wear – even when processing aggressive raw materials containing additives and/or masterbatch – is due to the low pressure within the feed section of the extruder: “In addition, this factor is equally responsible for the low energy requirement, aided by lower friction heat and a reduced cooling requirement, not forgetting the option of complete cylinder insulation”, adds Wahl.
Consequently, the heating capacity is utilized to a much greater extent with HELIBAR®, achievable by the direct heat transfer from the electric heaters to the polymer: “… because the cylinder is grooved, because the developing melt is immediately being pressed into the grooves, and because the melt layer between the hot cylinder and the cold solid material can thus be kept much thinner. Subsequently, the heat transfer between the hot cylinder and the cold solid material is considerably improved and the solid material can be melted much faster. At the same time, much improved material feeding is achieved, as the shear stress between the cylinder and the cold polymer increases – similar, for instance, to the displacement of water by the tread on car tyres”, as Grünschloß explains the physics in context.
The throughput rate of HELIBAR® is optimized by the use of spiral grooves which, in addition, are characterized by improved self cleaning and less friction. Added to that is the extremely advantageous pressure built-up capability of up to 800 bar at the screw tip; this feature is particularly important in extrusion blow moulding of up to 12 bottles along melt paths of considerable distance. The advantage of the groove technology is accompanied by low RPM at equal throughput and pressure build-up. This leads to the conclusion that, for instance, the smaller 45 OD screw HELIBAR® can easily compete with a larger 60 OD extruder of grooved bushing design: “Here is our leading edge when it comes to lower heat emission, reduced space requirements and a smaller and low-cost drive system”, continues manager Wahl.
The HELIBAR® cooling system can, in 90 percent of cases – dependant on the die/mould and type of material – do without an expensive water cooling system: “The less expensive air cooling system is entirely sufficient, frequently offering the passive variant (free convection) when processing HDPE and many PP types. In addition, the mixing of virgin materials with regrind material and masterbatch does not present HELIBAR® with a processing challenge”, the inventor Grünschloß summarizes.
The breadth of application of HELIBAR® ranges at present from extrusion blow moulding processes for bottles, using HDPE, PP, and PET, etc. (drinks, foodstuffs, cosmetics, chemical/medical solutions, cleaning agents, motor oil, fuel and many more), to sheet and film extrusion as well as cable coating on large equipment right through to operations with smaller 25 to 30 mm screw diameter HELIBAR® models as co-extruders for the processing of PA, EVOH and PVDF and up to seven layers.
The demand for ever smaller batches and more frequent change in materials and colour – also in the field of cable coating – makes HELIBAR® the economic workhorse. The advantage of self-cleaning: reduced material wast-age with the smaller HELIBAR® models when compared with larger extruders. The frequently posed question about possible deposits in the cylinder grooves is answered by Grünschloß as follows: “At a thickness of between 0.5 and 1 mm, the grooves are extremely flat which makes purging a much faster process when compared with the considerably deeper screw channels.”
High pressure build-up ability and pressure stability, as well as excellent colouring and mixing quality using masterbatch – these are the differentiating positive factors for efficient extrusion blow moulding, regular pipe or corrugated pipe extrusion and for cable coating.