New powdered material with extreme properties
HA72 makes wear back down

Abrasion und Korrosion sind besondere Herausforder­ungen an Compoundier-­Extruder. Mit einem neuen Werkstoff für die Gehäusebuchsen von Zweischnecken­extrudern gelingt es KraussMaffei Berstorff, diesem Problem noch besser zu ­begegnen als bisher.

Text Andreas Weseler  Photos KraussMaffei Berstorff
ZE 65 BluePower
ZE 65 BluePower
Twin-screw extruder with optimal wear resistance

The name of the “wonder material” sounds quite unspectacular: 72HA. Behind the short form name hides an iron-based powder metallurgical alloy with high carbon and chromium contents. Its chemical composition guarantees excellent wear resistance against abrasion and corrosion. But not only that: The dual-stage manufacturing process from parts made from 72HA also makes machining substantially easier. 

In the first step, the blanks are formed during the HIP process. HIP stands for hot isostatic pressing – in a heated pressure vessel, the powder mixture is simultaneously pressed and sintered. The workpiece generated by this process stands out thanks to its high material density but does not yet have the desired final strength for the finished part. It is easy to work with the workpiece while it is still in this soft state. It is not hardened until afterward. The iron base of 72HA makes this process possible.

Longer replacement intervals

Andreas Madle, Process Engineer of Development for Plastics Technology at KraussMaffei Berstorff, emphasizes the advantages of the new material. “This material offers optimized wear resistance when subjected to abrasive and corrosive stress. This results in a noticeable extension of replacement intervals for the housing bushings. Furthermore, 72HA is a much more attractive option than previous materials in terms of price.” The new generation of housing bushings is now available for the state-of-the-art ZE BluePower twin-screw extruder series.

Low wear
Low wear
ZE BluePower housing with oval bushing made of the new 72HA material.

Last but not least, the production process meets the special bushing requirements for the ZE BluePower series. These sleeves have a special elliptical shape. Producing this shape in conventional manu facturing is a demanding task, but it has a lot of advantages. First of all, it enables optimized positioning of the cooling and heating cartridge holes and thus effective tempering of the housing elements.  In addition, the oval geometry prevents bushing collapse in the gusset area. This facilitates heat transfer from the outer body to the bushing. The bushing is also axially secured in the housing by a special collar. This prevents leaks at the sealing surfaces of the barrel connections that could otherwise occur without axial securing due to differences in thermal expansion between the bushing and the outer body. “We can use the new metallic material to manufacture the complex geometry of the completely through- hardened bushings without any problems,” Madle says in praise.

Contact

Andreas Madle
andreas.madle@kraussmaffei.com

Process Engineer of Development for Plastics Technology