WMV

selbstreinigende anti-haft Schichten fuer extruder und plastifizier-Schnecken


Non stick and black specks prevention
effects of Lunac 1 coated injection
molding and extrusion screws

 


I
mprovements with Lunac 1 coated screws and screw tips



The effects of a 40 ┬Ám (1.6mil) non-stick Lunac 1 coating on injection and extrusion screws are very interesting. The anti-black specks effects (see figure on the Lunac 1 page) with especially polar plastics (such as PET and PC) are until now almost unparalleled. Moreover the micro-crack free, corrosion resistant Lunac 1 is one of the very few coatings that is durably able to withstand corrosive plastics such as ABS, PVC or even most fluoro plastics such as pfa. In this way non-corrosion resistant high-tensile steel can be applied instead of expensive nickel alloys. This is accompanied with a long lasting non stick effect and therefore melt flow / melt conveying improvement. Lunac 1 can significantly slow down plastic from degrading and
almost always facilitates the screw cleaning remarkably, if still necessary. These effects are observed in +/- 85% of all problem cases. Lunac 1 coated screws are very well able to deal with colour changes (especially screws processing blue (L)LDPE can easily and completely be cleaned !). There are some important points of interest before a screw can be coated successfully. Please check out our report on the application of Lunac coatings in plastic processing machines and/or contact our technical staff. The feed back we received dealing with Lunac applications in plastic processing machines during more than ten years are bundled in a report on non stick and corrosion resistance experiences of Lunac coatings .












Various Lunac 1 coated screw parts. The 45-60 µm Lunac 1 coating is in contrast
with hard chromium very well capable to be distributed in the deep structures as well.
In this way the coating offers high long lasting corrosion resistance and non stick effects.








Black specks prevention:



Although a major measurement to reduce black specks formation in plastic processing equipment is to strive for an average 50% shot-to-barrel ratio. (and go as low as 20%, if the material is not too heat sensitive (such as PE) and raise to 80% if the material is very heat sensitive (such as CPVC), Lunac coatings add two major effects :

  • The Lunac non-stick effect reduces the residence time of the plastics close to the walls significantly.
  • The inert, crack- and iron-free nature of Lunac strongly inhibits chemical degradation of (polar) technical
    plastics. This can regularly be the dominant reason for black specks formation in a plastic processing machine!





    Lunac coated screws can perform very well as long
    as two major issues have been taken into account:

  • Flight tips need a stellite 12 replacement and the screw should not be nitrided before.
  • Barrels should be rinsed (with polyolefin or similar) when non-polyolefin plastics have
    been processed, before shutting down and profoundly be preheated before starting up.