During continuous working of plastic extruder, the barrel part will unavoidably suffer abrasion, which leads to increase of barrel inner diameter. Due to higher inner surface hardness, the worn out time of extruder barrel is usually later than screw. During the maintenance and repair work of barrel, the following points must be paid attention to:

1. In case barrel inner diameter increase is found, if there is still certain thickness of nitrided layer left, grind the inner hole of barrel by boring lathe to acquire a new diameter size, and prepare a new set of screw to match the new size.

2. Another way to fix the barrel is to restore the diameter by alloy casting. Thickness of alloy should be within 1-2mm. Further fine machining is required to get the necessary size.

3. Normally, the homogenizing zone of barrel is worn out faster than other positions.Boring processing can be applied to fix the size of barrel zone. Add a nitride treated alloy steel casing, with inner hole diameter referred to the screw diameter, and leave necessary screw gap.

4. Material for manufacturing screw and barrel

At present, the commonly used material for extruder screw and barrel manufacturing in domestic market is 45Cr, 40Cr and 38CrMoALA, while for imported brand screw and barrel, 34CrAlNI7 or CrMoV9 is mostly adopted. Yield strength of this kind of material can reach about 900 Mpa. After nitride treatment, it also acquires good resistence against abrasion and corrosion, with hardness exceeds 1000HV.