Screws

The screw is perhaps the most important working component in plastic processing. Screw geometry is a very dynamic field of knowledge, and a critical look at it, from time to time, is both useful and necessary.

Euro-Stel screws are renowned worldwide for their high quality in terms of offering the ideal ratio between plasticizing capacity, yield and wear resistance. We supply screws for all types of machines, with diameters ranging from 15 mm to 360 mm, and with lengths up to ten metres. These can be for thermoplastic, thermoset materials and rubbers.

Euro-Stel supplies screws with every possible geometry. And that means from the simplest three-point screw to the most complex geometries. Over the years, we have accumulated a level of experience in plastics processing that allows us to be highly successful in developing in-house Euro-Stel geometries for the widest range of applications.

The exceptional quality of Euro-Stel screws can be attributed to the particularly efficient homogenizing section. Available types:

• All-round EUROSTEL mixing screw with EUROSTEL homogenizing section
• High efficiency EUROSTEL screw with EUROSTEL homogenizing section and barrier
• Depending on the application, we supply all the variants and combinations of them.

Which screw is right for you?

The application for which the screw will be used determines the type of steel the screw will made of and the thermal treatment that will be applied. For example, we have nitrided steel or chrome steel screws, on which the screw profile can be supplied with or without armour.

We can apply nitriding to these types of screw or, optionally, a special surface lamination to the core. In addition, we also have hardened screws made of tool steel and powder metal technology types, which are resistant to extreme abrasion and/or corrosion. Finally, there are the screws in superalloys (Hasteloy-Inconel) for special applications

The screw geometry not only determines the plasticizing behaviour and yield of a screw, but also its wear behaviour. Experience teaches us that if the geometry is poor, good metallurgy and good screw quality will not contribute significantly to the product’s wear resistance.

Poor geometry leads to high pressure peaks in the compression zone during plasticizing. So, despite a good choice of materials, these increased pressures will still cause a great deal of wear on the screw and, of course, the barrel too.

Principle of the EUROSTEL mixing section

The molten substance is passed through a mixing gap, which leads it from screw flight to screw flight along a hot barrel wall. Meanwhile, the molten substance is mixed, resulting in the excellent homogeneity properties that this mixing section offers. This condition allows significant compression reduction, to the advantage of higher plasticizing power and lower process pressure. The last unmelted granulate residue melts during the short passage of the overflow flanks, because it is guided automatically along the hot barrel wall.

Characteristics of the EUROSTEL mixing unit

• Excellent mixing quality
• Increased plasticizing power
• Uniform melt temperature distribution
• Smaller master batch required
• Less power consumption

All-round EUROSTEL mixing screw with EUROSTEL mixing section

this screw can be considered a conventional three-zone screw but it has a EUROSTEL mixing section fitted at the end, in the measuring zone. Depending on the materials to be processed, this screw has a variable or non-variable spiral coil, which can change over the full length of the screw. The EUROSTEL mixing section makes a number of significant differences in comparisontothe conventional three-zone screw:

• Much lower compression ratio (this is no longer needed for homogeneity)
• Better mixing behaviour by turning the molten substance in the mixing section
• Higher plasticizing performance due to compression reduction and increased flank height in the pump zone
• Reduced screw and barrel wear by avoiding extreme process pressure. particularly in compression
• Little or no thrust pressure needed to assist homogenization
• Lower temperature setting in the emission range due to temperature homogeneity of the melt and elimination of a “cold” melt zone

The EUROSTEL mixing screw is an all-round screw with a broad spectrum, improved plasticizing results, e.g. in quality and efficiency, and long lifespan (screw and barrel!). This screw proves its special features best when colouring with a master batch. It is possible that users do not exploit all the advantages of the EUROSTEL mixing screw, for example by not colouring them all. There is one point that will benefit everyone, the wear reduction.

High efficiency EUROSTEL screw with EUROSTEL mixing section and barrier

The high efficiency EUROSTEL screw is an extended version of the EUROSTEL mixing screw. This screw has an additional barrier section. Unlike the mixing screw, the geometry of the high efficiency screw is designed for special applications. The molten substance is separated from the solids early, in the barrier section, which permits higher rotational speeds combined with higher plasticizing capacity. The mixing section ensures permanent and high-quality plasticizing. The concept of the barrier section takes into account the special characteristics of the plastic to be processed such as its melting point, viscoelasticity and pressure or mixing sensitivity.

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Revisie schroeven

Al van bij onze oprichting reviseert en herstelt Euro-Stel allerhande schroeven. Gebruikte schroeven worden met de grootste zorg onder handen genomen om ze terug zo goed als nieuw te maken!
De hoofdreden voor schroefrevisie is slijtage. Regelmatig krijgen we echter ook schroeven binnen met mechanische breuken.

Een typisch voorbeeld hiervan zijn schroeven met gebroken terugslagkleppen die met hun schroefdraad vastzitten op de schroef en waarbij de schroefdraad dient gerecupereerd of hersteld te worden om een nieuwe terugslagklep te kunnen monteren.

Alles over schroefslijtage en -herstelling

Wanneer schroeven onherstelbaar versleten of beschadigd zijn, kunnen wij nieuwe schroeven aanbieden volgens model of in Euro-Stel-uitvoering.

Er is geen algemeen geldende beschrijving of oorzaak voor schroefslijtage. De belangrijkste vorm is echter slijtage aan de buitenste schroefdiameter door wrijving tussen de schroefflank en de cilinder. De werkende oppervlaktedruk en enorme krachten die aan de basis hiervan liggen en die negentig graden ten opzichte van de transportrichting werken, worden meestal onderschat.

Men mag er in geen geval van uitgaan, dat de schroef in de cilinder “zwemt”. Als dit het geval was, zouden de slijtagebeelden van schroef en cilinder niet congruent mogen zijn, wat zij alleszins altijd zijn. Alleen de graad van slijtage is verschillend: deze is kleiner in de cilinder, omdat deze in vergelijking met de schroef over een groter oppervlak beschikt.

Abrasieve additieven zoals glasvezel zijn niet de oorzaak van de slijtage, maar versterken deze wel. De grote oorzaak is altijd de druk die in het betrokken schroefdeel heerst, bv. in de compressiezone.
Als het slijtagebeeld extreme kenmerken vertoont (zoals diepe groeven aan het loopvlak van de flank, sterke braamvorming aan de zijkanten van de flank en een korte levensduur) dan kan men zich de vraag stellen of de schroefgeometrie wel geschikt is. Dat kan voor ons namelijk de reden zijn waarom wij regenerering afraden; binnen de kortste keren doen dezelfde slijtagesymptomen zich opnieuw voor.

Als er “normale” slijtage optreedt en het basismateriaal is nitreerstaal – doorgehard staal kan niet geregenereerd worden – dan kan de schroef door flankpantsering vernieuwd worden. Hierbij wordt tijdens het lasproces op de bovenkant van de flank een pantsering aangebracht. De keuze van de pantserlaag is afhankelijk van de toepassing. De metallurgie van de cilinder (paring) en het type te verwerken materiaal (verwerkingstemperaturen) bepalen welke pantserlaag wordt opgelast.

De meest courante herstellingen zijn:

• Aanbrengen van een nieuwe pantserlaag in de juiste legering op de spiraal van de schroef. Bij de herstelling van een reeds gepantserde schroef wordt de oude pantserlaag verwijderd en een bufferlaag aangebracht.
• Polijsten
• Richten
• Nitreren indien nodig
• Ontchromen, verchromen indien nodig
• Herstellen van schroeven beschadigd in hun aandrijving
• Herstelling bevestiging terugslagklep