Development And Performance Evaluation Of Durability Testing Machine

2.2.5    Drop test
Drop test is used to test the durability of bulk materials, including coal, ore, and pellets. Sahoo and Roach (2005a) showed that the strength of coal can be determined by shatter tests. A five-meter drop tower was used to facilitate dropping the coal onto different surfaces  The differ  rent impact surfaces are steel plate, conveyor Belt and coal stockpile. The coal was contained in a hopper with a release at the bottom that allowed the coal to be dropped from various heights. The size of the coal used in the test was 20-30 mm. They used the term ―strength index‖ to describe the empirical measurement. Sahoo and Roach (2005b) performed a new drop test procedure to measure the strength of the coal. The procedure was based on repeated drops. They found that:
 1) fines generated from the coal in handlings were due to larger vertical drops;
2) disintegration of coal increased proportional to increased drop velocity;
3) replacing larger sample size with smaller sample size can reduce the fines produced; and
 4) replacing larger drop heights with smaller drop heights can also reduce the fines generated.
The drop test is meant to measure the amount of dust in a situation close to reality. Pellets are dropped freely from a certain height. The dust produced from the drop is removed and remaining unbroken pellets is weighed to determine the percentage of breakage. The sample can be dropped as a single pellet or a number of pellets all together. Another possibility of dropping pellets is to put them in a physical pack (Adapa, 2007).
2.3    Durability Tester
I.    Briquette durability test
II.    Pellet durability test
III.    Durability test of cubes
2.3.1    Briquettes Durability Test
The briquette durability is estimated by using a dustproof rotating drum prototype. The drum has an internal diameter and a 598mm depth (volume 168 l). It is equipped with a baffle (200_598) mm, perpendicular to the wall surface of the cylinder. In the tests, presented here the rotation speed was fixed at 21 rpm. A test portion of 2 l sample material, from which fine particles had been removed, was weighed to the nearest 0.1 g and placed in the drum for 105, 210, 315, 410 and 630 rotations. After each tested rotation number, the sample material was removed from the drum and screened mechanically or manually for 30 s using a 40mm metal wire cloth according to ISO 3310-1. The particles remaining on the sieve (sieve oversizes) were weighed to the nearest 0.1 g. Both, sieve over- and undersizes were returned into the drum and the tumbling was continued until the subsequent tested rotation number was achieved.
Tumbling, sieving and weighing procedures were continued until each sample was exposed to 630 rotations. The DU was calculated from the mass share of the sieve oversizes to the total initial mass. The results are given in percentage as the mean value of five replications (ASABE 2019)
2.3.2    Pellet Durability Test
The ASAE S 269.4 standard describes a tumbling device made of a rectangular container in aluminum or stainless steel with inner dimensions of (300_300_125) mm. In order to enforce the tumbling effect the box is equipped with a 230mm long baffle, which extends 50mm into the container. The baffle is affixed symmetrically to a diagonal of one side of the box. Rivets and screws are kept to a minimum and they are well rounded. The container rotates on an axis, which is centered perpendicular to the sides of the box. The rotation speed is fixed to 50 rpm. In the trials described here, a 500 g sample was tumbled for 500 rotations before being sievedmanually with a 3.15mm round hole sieve according to ISO 3310.2 8. The DU is expressed as the percentage in mass of the pellets remaining on the sieve to the total sample weight. It is calculated as the mean value of three replications.