Development And Performance Evaluation Of Durability Testing Machine

2.2.3    Ligno tester
The principle of this equipment is indicated in the Austrian Standard  (1998) . Pellets are exposed to shocks caused by air stream that induces the particles to collide against each other and the walls of equipment. The test box has a four-sided pyramid form and air stream comes from below the box. Before the experiment, the fines have to be removed from the sample by sieving. 100 g of sample is placed in the box and air stream of 70 mbar is blown for 60 s into the Lingo tester. The produced dust is removed and the remaining pellets are weighed and durability is calculated.
Temmerman et al. (2006) showed that the Ligno tester tends to suffer a higher variability between experiments and this affects the repeatability of durability measurement. The unit is more complicated in terms of operation and structure. Air Facility needs to be available and this may cause problem in some cases particularly when it is used as in-plant equipment.(Adapa,2007)   
2.2.4     Holmen tester
The Holmen pellet tester Fig 2.3 is a pneumatic system which simulates a more rigorous treatment of pellets. A 100-g sieved sample of pellets is introduced in a stream of air. Feed pellets are conveyed around in a closed circuit at an air velocity of about 20 m/s for a standard time (0.5 to 2 min) based on the pellet diameter. The air and pellets are circulated through right-angled bends, impinging repeatedly on hard surfaces. Pellet attrition will then happen. After treatment, the samples are sieved again with a sieve having an opening of about 80% of the pellet diameter. The Holmen tester was used for measuring pellet durability and described by Payne et al. (1994) as well as Thomas and van der Poel (1996). Thomas and van der Poel (1986) made a comparison between the Holmen tester and the Tumbler tester for animal feed pellets, and concluded that the Holmen tester gave results in a wider range and in a shorter time span (for instance, 60-95% durability with a testing time up to 5 min) than the Tumbler tester (for instance, 91-98% durability with testing time up to 20 min). Similar to the Ligno tester, the Holmen tester also suffers from very strict requirement for air supply, which is not practical for in-plant applications (Adapa,2007).