Figure 3. Galling wear

Galling Wear

Figure 4. Abrasion wear

Abrasion Wear

This type of wear is commonly caused by a severe misalignment of the shaft in relation to the barrel or a non-uniform flow characteristic of the feed in the barrel.

This is the normal, expected wear of the extruder screw from typical operations.

Abrasion wear appears as a rounded, smooth radius on the front (leading) side of the flight at the outside diameter. This is caused by leakage flow of the extrudate across the outside diameter of the screw. This is normal, expected wear of the extruder screw.

The arrow in this photo indicates examples of typical abrasive wear; see also Figure 4. ■

Galling wear appears as rough surfaces on the outside diameter of the screw.

Galling wear (also known as forging) can be seen as rough surfaces on the outside diameter of the screw. The screw flights may have a welded, gouged or even torn appearance with a sharp edge on the back (lagging) side of the flight. This is commonly caused by a severe misalignment of the shaft in relation to the barrel or a non-uniform flow characteristic of the feed in the barrel.

The photo at left, detailed by the arrow, shows an example of typical galling damage, as does Figure 3.

Abrasion wear appears as a rounded, smooth radius on the front (leading) side of the flight at the outside diameter.