Application
Dense Phase Conveying of Plastic Pellets
Answer in brief
Angel hair is the reason plastics plants move to dense phase.
At high velocity a pellet sliding along the pipe wall melts at the contact point and leaves a streamer behind; at low velocity it does not.
- Keep the velocity below the threshold where streamers form.
- Watch the line finish, since a rough or hot wall makes it worse.
- Expect to trial the actual pellet grade.
Reviewed October 21, 2026 · Updated October 21, 2026
The problem
Streamers and fines block screens and appear as defects in the finished part, and they are generated by the conveying line rather than by the process.
Soft and coated grades are the most sensitive.
Desired outcome
A conveying line that reaches the rate over the required distance while keeping the product and the pipework in the condition the process needs.
Process approach
Dense phase systems move pellets as a slow bed, which removes the sliding contact that creates streamers.
Line internal finish, bend radius and the absence of sharp transitions all affect the result, and some plants use treated or roughened bore pipe for the same reason.
Trials with the actual grade establish the velocity threshold, which differs between materials.
- Velocity threshold established per grade.
- Bend radii and line finish specified, not left to the installer.
- Screening before the extruder to catch what still forms.
Selection factors
- Pellet grade, hardness and surface coating.
- Required rate and distance.
- Acceptable streamer and fines content.
- Line material and internal finish.
- Static control across the conveying system.
Common failure modes
- Velocity above the streamer threshold for a soft grade
- Sharp bend transitions generating fines
- Line finish not specified, leaving it to the installer
- Screening omitted because dense phase was assumed to be clean
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