On the cover: Machine downtime often results from a maintenance or wear issue, which is almost always avoidable.

continued from cover

been running this product for months without a problem and then all of a sudden …” 95% of the time the leading factor was either raw materials or typical maintenance/wear issues.

In the case of a maintenance or wear issue, it’s almost always avoidable.

The process of creating petfood requires mechanical energy. Product specifications, cell structure, pellet durability and raw materials will all dictate the amount of mechanical energy input required to produce a specific product. In due course, this mechanical energy input comes at a cost: equipment wear.

In the extrusion process, there are three primary types of wear (see Figure 1):

Figure 2. Corrosion wear

Corrosion Wear

Also known as chemical wear, this can be caused by salt, cavitation in a low-pressure area of the barrel or metal not compatible with the pH of the extrudate.

■ Chemical;

■ Galling;

■ Normal processing (abrasion) wear.

Figure 1. Three primary types of extruder wear

Chemical or corrosion wear is seen as rough-sided indentions on the surface of screws and liners. This wear may be caused by any of the following:

■ Metal not compatible with the pH

of the extrudate;

■ Salt;

■ Cavitation in a low-pressure area of

the barrel.

The arrows in the photo at right point to examples of typical corrosion damage; for another example, see Figure 2.

Barrel Surface

Metal Chemical Contact Corrosion

> FLOW DIRECTION

Normal Wear

The types of wear that happen during the extrusion process affect different parts of the extruder screw.

Chemical or corrosion wear is seen as rough-sided indentions on the surface of screws and liners.