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The screw is an important, if not the most important tool in plastics processing. Every now and then, it deserves a critical analysis, especially when things are moving as screw geometry is regarded.

The Euro-Stel screws have an excellent reputation worldwide because of their high quality. Quality means the perfect ratio between plasticizing capacity, output and wear resistance.
We supply screws for all kind of machines, ranging from diameter 15 mm up to diameter 360 mm with a maximum length of ten metres, both for thermoplastics, thermosetting plastics and rubbers.

The intended application for the screw will determine the steel grade to be used as well as the corresponding thermal treatment. For instance: screws in nitride or chromium steel can have a spiral, which is armoured or not. This kind of screws can be nitrated or a special surface lamination can be applied to the core. Apart from that, we also supply hardened screws in tool steel or powder metal, which resists to extreme abrasion and/or corrosion. Finally, we offer screws in super-alloys (Hasteloy-Inconel) for special applications.

The geometry of the screw determines not only the plasticizing behaviour and the output of the screw, but the wear behaviour as well. Experience tells us that a good metallurgy and quality of the screw do not contribute to the wear resistance of the product if the screw geometry is inappropriate.
An inappropriate geometry leads to high pressure peaks in the compression zone during the plasticizing process. Notwithstanding the choice of the proper material, these pressures can still cause considerable wear to the screw and the cylinder.

Euro-Stel supplies screws with all kinds of geometries, for the simple three-zone screw to the most complex geometries. Throughout the years, we have acquired a lot of experience as plastics processing is regarded, which enabled us developing our own Euro-Stel geometries for a wide range of applications.

The essential element, which is responsible for the high quality of the Euro-Stel screws, is the particularly efficient homogenisation component.

There are different kinds of screws:
• all-round EUROSTEL mixing screw with EUROSTEL homogenising part
• high-output EUROSTEL screw with EUROSTEL homogenising part and barrier
• application-dependent: all kinds of variants and combinations of these types

Principle of the EUROSTEL mixing part

The melted mass is led through a mixing gap, thus flowing from thread to thread along a hot cylinder wall. At the same time, this mass is being mixed, where the excellent homogenising properties of this mixing part are revealed. This situation enables a considerable reduction of the compression in favour of a higher plasticizing capacity and a lower process pressure.
The final granules that are not melted finally melt during the short passage of the overflow flanks, where they are automatically led along the hot cylinder wall.

Features of the EUROSTEL mixing part
• excellent mixing quality
• higher plasticizing capacity
• uniform temperature distribution of the melted mass
• less master batch required
• lower energy consumption

All-round EUROSTEL mixing screw with EUROSTEL mixing part

This screw can be considered as a conventional three-zone screw, however with a EUROSTEL mixing part in the metering zone at the end of the screw. Depending on the materials to be processed, this screw has a variable helical pitch, which can change throughout the length of the screw.
The EUROSTEL mixing part however offers some considerable advantages compared to the conventional three-zone screw:
• lower compression ratio (no longer required for the homogeneity)
• improved mixing behaviour because of the melted mass being revolved in the mixing part
• higher plasticizing capacity because of the compression reduction and the higher flank height in the metering zone
• less wear to screw and cylinder because of the absence of extreme process pressures, especially during the compression
• few or no back-pressure required for the homogenisation
• lower temperature setting in the ejection zone because of the temperature homogeneity of the melted mass and the omission of the “cold” melting area.

The EUROSTEL mixing screw is an all-round screw with a wide spectrum, improved plasticizing results such as quality and output and a long life (of screw and cylinder!). This screw reveals its special features preferably when colouring with master batch.
Perhaps the users of the EUROSTEL mixing screw do not use all advantages of this screw, e.g. not all users are colouring. They however all benefit from the reduced wear.

High-output EUROSTEL screw with EUROSTEL mixing part and barrier

The high-output EUROSTEL screw is an extension of the EUROSTEL mixing screw and has a supplementary barrier part.
Contrary to the mixing screw, the geometry of the high-output screw is developed for special applications. In the barrier part, the melted mass is prematurely separated from the solid substances, which allows for higher revolving speeds in combination with an increased plasticizing capacity. The mixing part ensures a permanent and perfect plasticizing quality. The design of the barrier part takes the special properties of the plastic to be processed into account, e.g. melting point, visco-elasticity and pressure or mixing sensitivity.

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