melt flow improvement, black spot prevention

chemisch resistente siebwechsler und Ventile


Non stick effects, plastic degradation
and corrosion prevention in screen
changer flow channels and granulators


Lunac 1 coatings in screen changers act like a PTFE non stick coating and
resist acids like a full nickel alloy machine part without the typical problems


Conditions can be very demanding and divergent in screen changers. Often, flow channels have to deal with sticking and corrosion problems. Additionally, the central piston(s) and bore(s) have to deal with high mechanical loads, regularly leading to galling and seizing problems. For this reason, these mechanically loaded surfaces are often plated with Lunac 2+. Lunac 1 applied to flow channels proved to be very effective in eliminating the formation and deposition of plastic degradation products. The spectrum of (sticking or corrosive) plastics that can be processed in these Lunac 1 coated parts, such as : CPVC, PC, PVDF, PFA, HIPS, PU, ECTFE etc. is surprisingly large. Many feed back experiences are derived from screen changer applications and remarkably long-lasting. Some Lunac 1 coated screen changers are in operation for over 20 years already.




Generally, the Lunac 1 melt flow channel treatment is carried out as follows:

  1. Flow channels are (pre) finished to Ra < 0.2 - 0.3 µm (Rz < 2 µm)
  2. Deposition of 45-60 µm / 1.8 - 2.4 mil Lunac 1
  3. The coated flow channels will be polished further down to Ra <0.03 µm
  4. If any significant wear is expected, the coating will be hardened to HRc 65
    (very important: Lunac will not develop micro crack (last picture) after being
    exposed to (hardening) temperatures over 290°C / 554 F) and preserve the corrosion
    resistance which is even higher than the resistance of Hastelloy C ® in 50% HCl / 4% HF.
  5. If major bore and piston surface problems are to be expected, 70-80 µm / 2.8 - 3.2 mil
    Lunac 2(hc)+ is first applied to these surfaces before the side channels are drilled.
    Check out Lunac 2+ treatments. for important details.







 
This screen changer has been coated with both

-Lunac 1 in all flow channels to prevent the molten plastic from sticking and degrading and

-Lunac 2+ in the main bore and on the piston outer surfaces to prevent the sliding parts from galling and explicitly deposition of plastic degrading products as well. For reasons of ultimate precision Lunac 2+ is ground afterwards with diamond to a final clearance of only 0.02-0.03 mm / 0.79-1.18 mil.
 
corrosion resistant screen changer with non stick properties

















Non stick granulator plate with hard metal replacement coating and inner Lunac 1 coating
Because of the good corrosion resistance and internal non stick properties, it is often worth the effort to plate all extrusion channels (as small as Ø 5 mm / 0.197") with Lunac 1 and the frontal side with Lunac 2+ to withstand the adhesive (knifes) and abrasive (product) wear at this location (hard metal replacement).