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Polyethylene Powder for Rotomoulding: LDPE Pellets Cut to -30 Mesh in an Air-Cooled Mill (Feder, Wedco, US 3,428,260)
Rotational moulding needs polyethylene as a fine, free-flowing powder, but grinding heats the plastic until it softens and clogs the mill. Feder's mill throws the pellets off a fast impeller into toothed cutters, while the impeller itself pumps air through to keep the particles cool.
Result: low density polyethylene powder, -30 mesh, well suited to rotational moulding.
Source: Feder, US 3,428,260 (Wedco, 1969), Operating Example. Picture drawn by Youblob.
Advanced
Factory process
Instructions
1
1
Fit cutters for the mesh
Fit cutters for the mesh
Use 12 in cutters with 480 cutting edges for a -30 mesh product (240 edges give -12 mesh). Edges at 60° with a 0.010 in flat; a razor edge would not last. Clearance to the housing 1/4 in.
Tools needed:
Grinding Mill2
2
Run the impeller and cutters
Run the impeller and cutters
Drive the 18.5 in impeller at 2700 rpm and the cutters at 4200 rpm. The impeller pumps air through the housing, which cools the particles while they are cut.
Tools needed:
Grinding Mill3
3
Feed the pellets
Feed the pellets
Feed low density polyethylene pellets about 1/8 in across, in open circuit, at about 150 lb per hour; more overheats the plastic.
Materials for this step:
LDPE Pellets1 as requiredTools needed:
Grinding Mill4
4
Collect the powder
Collect the powder
Particles small enough pass the screen round the housing; the mill's own air carries them to a cyclone about 10 ft above it. The size spread is narrow, with few fines.
Tools needed:
Cyclone SeparatorMaterials
1- 1 as requiredPlaceholder
Tools Required
2- Placeholder
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