Material Preparation
Angel hair is material formed when granulate in a vacuum conveying line rubs at high speed against the pipe wall, and especially the elbows, melts and is stripped off as fine, thread-like fibers. It is common with soft materials with a low melting point, such as PE and PP. It clogs filters, bridges at the hopper inlet and spoils dosing precision.
The cause is frictional heat: as the conveying speed increases, the impact energy of the granulate on the elbow increases and the contact point momentarily reaches the melting temperature. The solution is to reduce the speed, increase the elbow radius and, if necessary, use glass or specially surfaced elbows.
Wear resistant steel elbows protect the pipe but do not solve angel hair; they are two different problems. A glass elbow reduces angel hair with its smooth surface, but is short-lived with glass-fiber raw material.
With soft polyolefins, above all PE-LD and PP. With hard materials such as PA, PC and PET, dust (fine fragments) forms instead of angel hair; its cause is the same friction.