DKHV: “Angel hair” and “molten granules” in material pipes

Both phenomena are still frequently seen in extrusion, our experiences with their occurrence and measures to avoid them:

material pipes molten granules


  • High granulate velocity in the pipe system and during unloading of the silo trucks.
  • Edges due to different wall thicknesses of bends and pipe.
  • Too small pipe bends (radius) and pipe diameter (Ø).
  • Negative pressure or air volume of the vacuum supply too high.
  • Pipe connections not butt-jointed.
    Pipe connections not butt-jointed.


Avoidance or countermeasures:

  • Throttling of the vacuum volume to reduce the granulate speed with ball valves.
    separator wall mounting
  • Special “angel hair” separators
    Special Special
  • Checking the entire pipe system for wall thicknesses and joints.
  • Bends with a large radius (optimum: R = 500 mm).
    Bends with a large radius
  • Specification of unloading times or use of own blowers when unloading the silo trucks.
  • Bends must be made of stainless steel, aluminium bends are not suitable!
  • Replace pipes with shot-blasted pipes (inside) to reduce friction energy.
  • Additional compressed air cleaning of the pre-filters, prevents rapid clogging of the filter surface.
    Pre-filter without compressed air cleaning
  • T-pieces for reducing material speed.

We would be happy to advise you on the problem of “angel hair” and “molten granules”.

With best regards
Yours, Detlef Kaul