Meccanica, Pelleting
Nov 21, 2015
La Meccanica
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PDI = Durability

Measuring Pellet Quality

Pellet quality does have economic importance; it should not be left to chance.

Fines are generally formed by mechanical action on the pellets during transport. These forces may be classified as impact, compression, and shear. Impact shatters the pellet surface and any natural cleavage planes in the pellet; compression forces crush the pellet; shear forces cause abrasion of the edges and surface of the pellet.

The pellets need to be highly durable so that they do not break up and create fines in downstream handling operations.  The tougher or more durable the pellet the better.   Many factors affect pellet quality or durability.

Pellet durability or quality is commonly referred to by the term PDI or Pellet Durability Index.  This is a number that describes the percentage of remaining pellets that are not reduced to fines after being agitated under controlled time and conditions by various mechanical means.

Durability of pellets shall be determined by tumbling the test sample for 10 seconds at 500 rpm, in a dust-tight enclosure.

The construction of this device is illustrated in the photo.

MVC-007F MVC-008F MVC-009F

Screens. Fines shall be determined by screening a sample on a wire sieve having openings just smaller than the nominal pellet diameter.

Test procedure. A sample of pellets to be tested will be sieved on the appropriate sieve to remove fines.

Place a 500 grams sample of sieved pellets or crumbles in the tumbling can device. After tumbling for 10 seconds, the sample will be removed, sieved, and the percent of whole pellets calculated.

Pellet durability will be defined as: PDI = Durability =  Weight of pellets after tumbling  x (100) / Weight of pellets before tumbling

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