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PDI; an Important Factor in Feed Quality & Production


Pellet quality is usually expressed as the Pellet Durability Index(PDI) and measured by using a tumbling can device, in which the pellet sample to be tested is first sieved to remove fines, then tumbled in the tumbling can devise for a defined period of time. Then after tumbling, we compare the fines produced during tumbling with actual weight.

PDI = weigh of the pellet after tumbling / weight of Pellet before tumbling x 100

At PDI lower than 85 pellet tends to break during crumbling; producing more fines which result in more recycling of feed and low final output.

Factors that affect PDI are:

1. Formulation: In today’s dynamic world, Nutritionists face the challenge of formulating feeds using available raw materials at the lowest possible cost while meeting the feed specifications, while the production managers face the challenge of producing the good quality pellets from these ingredients at the optimum mill setting. Pellet quality is proportionally dependent on several factors, with diet/feed formulation being the most important.

Raw materials affect pellet quality depending on their “binding properties” and its proportion in the formulation. From our experience, we know that starch gelatinization is the most important factor for achieving the desired pellet quality.

Dietary inclusion of oil has a positive effect on animal growth but an adverse effect on pellet quality.

Oil also reduces the friction generated between the die and the feed particles, which subsequently reduces the compression pressure required to produce good pellets and also decreases the starch gelatinization rate. Inclusion of natural pelleting aids can help overcome these bottlenecks and improve pellet quality, increase pellet throughput and lower the power consumption.

High starch-containing raw materials like wheat generally contribute to good quality pellets. Formulation governs approx.40 % in pellet quality & PDI.

2. Grinding Size: Better grinding helps in better absorption of steam due to the increased surface area which leads to better conditioning and a good level of gelatinization of starch. Good gelatinization increases pelleting properties and PDI index. Grinding governs approx. 20 % in pellet quality.

3. Conditioning: Minimum 1.5 to 2.0 % moisture should be added in the conditioning process. Also, temperature above 80 helps to achieve good gelatinization level which leads to better binding properties and good PDI.

Proper steam of good quality is required for better performance of machines and production of quality feed. Steam parameters required are:

1. Dry Saturated Steam Minimum 8.5-9 kg/cm2 at the boiler.

2. 2-2.5 Kg/Cm2 after PRV

3. Good & reputed make boiler, Water softener.

4. Proper Steam traps, insulation of steam line and supporting valves.

Conditioning governs approx. 20 % in Pellet Quality & PDI.

4. Die configuration: Selecting a die as per formulation is very important. As Broiler contain fewer fibers and more oil %age (soft formulation), which provides better pelleting properties, less frictional load on pellet die. Hence, we can use a compression ratio of 1:12, 1:13 & even more.

Using high compression ratio for layer feed may lead to poor die life, die chocking, non-uniform PDI, more power consumption in layer feed, low output, more wear & tear.

And using low compression dies in soft broiler formulation may lead to poor PDI (Pellet Durability Index – Pellet Strength). Considering all the above factors using a separate die for both layer & broiler feed is a better and cost-effective solution. Die selections govern approx. 10-15 % in pellet quality & output.

The above information is based on data collected from our existing customers & internet sources and is only for your reference. As expertise in feed mill engineering only, Lark Engineering will not be responsible for any type of loss occur due to above-stated information.

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