Development And Performance Evaluation Of Durability Testing Machine

CHAPTER TWO
LITERATURE REVIEW
2.1    Definition of durability
According to MC Graw –Hill (2003) define durability is define as the     quality of equipment structure or goods of continue to be useful after an extended period of time and usage. According to Houghton Miffli  Harcourt (2016) define durability as a good or product made to withstand repeated use over a relatively  period, usually several years or more. Furthermore Farlex Clipart (2003) define durability as permanence by virtue of the power to resist stress or force.
      Cambridge Business English Dictionary define durability as the fact of something continue to be used without getting damage.
     In the work of,  Cooper (1994)he defined durability as the ability of a product to perform its require function over a length period under normal condition of use without excessive expenditure or maintenance or repair.
2.2      Durability measurement equipment and methods
2.2.1     Tumbler
According to American Society of Agricultural Engineers Standard S269.4 (ASABE 2006) this durability test unit is made of a rectangular stainless steel container with inner dimension of 300 mm x 300 mm x 125 mm. Figure 2.1 shows the unit. One baffle is placed inside the container to enforce the tumbling effect. The rotation speed is adjusted to 50 rpm and the rotation time is 10 minutes. 500 g of sample is used. The percent of pellets remained unbroken to total sample weight is reported as durability index. The treated sample is sieved using round screen holes of 3.15 mm. This unit is used in North America and Europe. The European standard is CEN/TS 15210-1 (2005). There are some disadvantages associated with the Tumbler device which makes the machine less valuable. The disadvantages may be attributed to three factors:
i.     Low resolution - The measured durability for low quality pellets would not be reliable or realistic. For instance, Temmerman et al. (2006), used 11 types of
pellets for durability measurement by Tumbler. The pellets had different sizes and were collected from different countries. The results showed that all the measurements fell within a very narrow range of 91-99%.
ii    Amount of sample – The 500 g of sample materials needed for each test is a large amount. When the measurements cannot be done in the plant, this could become a constraint for the repeated Tumbler tests in laboratory.
iii    Testing time - The 10 minutes of time required for each Tumbler test is too long. This may not be practical for industry when they need to measure durability over and over during the process. A faster method is preferred.
These characteristics provide the main motivation for investigating another type of equipment which yields more reliable and realistic test results in terms of the range of durability measurements for wood pellets (Adapa ,2007)