Corrosive Wear

There are three types of wear that occur, often in combination, in barrels, screws, valves and other components. An understanding of nature and causes of adhesive, abrasive and corrosive wear is essential to the selection and use of these components.

Corrosive.JPG

This image is an example of severe corrosive wear.

Corrosive Wear

Corrosive wear results from acids and other chemicals that are generated in plastics processing which attack the surfaces of barrels and screws. Corrosive wear is characterized by pitting and usually occurs in the last few flights of the transition zone and in the metering zone. The pits can also collect melt, burn or degrade it and result in black or burned particles in the parts.

There are several resins that can generate acids at high temperature. They include polyvinyl chloride (which releases hydrochloric acid), acetals (formic acid), fluoroplastics (hydrofluoric acid) and cellulosics (acetic, butyric and propionic acids). In addition, flame retardants, coupling agents and some foaming agents release acids, including bromic and sulfuric acids. Despite their acid-generating characteristics, these resins can be successfully processed using the proper screw designs and corrosion-resistant component materials.

There are several causes of corrosive wear, some of which can be prevented through the proper design, manufacture and use of the machinery components.

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