During tumbling, pellets abrade
and produce fines due to impact, and shearing of pellets over
each other and over the wall of the tumbling can. After
tumbling 500 g of pellets for 10 min at 50 rpm, the pellets are
sieved using a sieve size of about 0.8 times the pellet diameter.
The PDI or durability is calculated as the ratio of weight after
tumbling over the weight before tumbling, multiplied by 100.