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Pellet Press Settings

To the Better Physical Pellet Quality through the Pellet Press Settings

Published: November 3, 2010
By: M.Sc. Dejan Miladinovic (Norwegian University of Life Sciences- Fôrtek), Ph.D. Birger Svihus
The primary objective of pelleting is to produce a palatable, high quality product with minimum production expense. Manipulation of the feed pellets during the storage, transporting, and transfer to feeding lots seriously reduces the number of feed pellets that finally reach the feed pans. It seems that the best solution for this problem is to increase the Pellet Durability Index (PDI) of the feed pellets using different settings in the manufacturing process and different raw ingredients.
The factors influencing pellet quality such as grinding, mixing, conditioning process, pelleting techniques and cooling are fertile ground for pellet quality improvement.
Norwegian University of Life Sciences (UMB) has carried out research as a part of the Feed Manufacturing Technology (FMT) Master of Science program. The research experiments were carried out at Centre for Feed Technology, an experimental feed plant associated with the university.
Pellet press settings - Gap between the rolls and pellet-press die influence the PDI
Previous research has shown that increased pressure generated in the die hole increases the physical properties of the feed pellets. Elevated pressure seriously depends on the coefficient of friction (CF%) between conditioned feed compound and die wall, plastic properties of conditioned material and its conditioning time. In the gap between the die wall and roller, a layer of feed material with a specific thickness is forming. This layer of the feed material and its thickness directly influences formation and compaction of the material inside the pellet press die-hole by roller/die frictional force.
Research has been performed with different roller/die pellet press settings in order to find the best roller/die gap settings related to increased physical properties of feed pellets. Results showed that by increasing the roller/die gap, several layers of feed mash are created and CF% is increasing (figure 1).
 To the Better Physical Pellet Quality through the Pellet Press Settings - Image 1
Figure 1. Layers of feed mash and coefficient of friction areas during the pelleting process
Increasing the roller/die gap to 2 mm, as well as reducing feeder rate by 50%, resulted in significantly (P<0.05) increased PDI (table 1). This is probably caused by prolonged kneading effect time. Obviously, by decreasing the feeder rate, CF% helps forming higher PDI values, but energy consumption and production capacity reaches commercially non satisfactory level and reduced production capacity. In addition to the CF% influence on PDI, larger roller/die distance forms better pressing angle. This produces higher pressure on the material that enters the die hole, thus material in the hole as well (figure 2). All this leads to better-compacted particles into the single feed pellets and elevates physical properties of the animal feed.

To the Better Physical Pellet Quality through the Pellet Press Settings - Image 2
Figure 2. Angle of Pressure "Angle of nip"

Table 1
To the Better Physical Pellet Quality through the Pellet Press Settings - Image 3
When roller/die gap set to be too big, that often results irritating choke-ups. Opposite, if rollers are adjusted hard against the die, some damages of the die-hole inlets and die blockages are possible.
Pressing angle between the die and roller and the gap between them increases the total amount of fine particles, as shown in figure 3. This shows the grinding ability of the pellet press produced by the roller/die kneading effect. This effect might be used for better control of the particle size and energy consumption in the process of grinding.

To the Better Physical Pellet Quality through the Pellet Press Settings - Image 4
Figure 3. Roller/die gap and particle size distribution
Effects of Die Whole Diameter and Die Thickness on Pellet Quality
Pellets are sensitive to shearing actions at the places where they are cut off after leaving the die. Through this impact, newly created surfaces are sensitive to further deterioration. Therefore problems related to the feed pellet quality, die whole diameter and die thickness have been studied through the "Pellet Quality" project at the Department for Animal and Aquacultural Sciences at UMB. The aim of the study was to observe how the same die-hole diameter with different die thicknesses affects the pellet quality in relation with the different feeder rates.
The same die-hole diameter (3.5mm) and different die thickness (50mm and 60mm) were used, with additional feeder rate change, from 500 kg/h to 1000 kg/h. Holmen Pellet Test showed highest durability value (PDI=90.1%) in samples for 3.5mm die-hole and 60mm die thickness configuration with the feeder rate 500 kg/h. Significantly lower PDI values (P<0.05) was demonstrated for 1000 kg/h feeder rate independent on die thickness (figure 4). This is caused by lower pressure in the die-holes and higher feed mash acceptance in the pellet press, which makes the newly formed feed pellets more vulnerable for abrasion and cracks. The highest durability loss (3.3%) was found with 50mm die thickness and 1000 kg/h feeder rate.
 To the Better Physical Pellet Quality through the Pellet Press Settings - Image 5
Figure 4. Holmen Test results- feeder rate and die thickness influences PDI values

Similar research, studying the variation of the die-hole diameter, illustrated a strong positive effect of decreased diameter on PDI values (figure 6). This effect was obvious even if diet composition changed.

To the Better Physical Pellet Quality through the Pellet Press Settings - Image 6
Figure 5. Influence of die-hole diameter on PDI values of two different diets
In addition to the tale of the results presented above themselves, these results also show how important pellet press settings are for the technical quality of the pellets, and thus for the profitability of the pelleting process.
Related topics
Dejan Miladinovic
Fôrtek- Norwegian University of Life Science
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Dejan Miladinovic
Fôrtek- Norwegian University of Life Science
24 de mayo de 2011

Thomas, M can be found by following this link

Dejan Miladinovic
Fôrtek- Norwegian University of Life Science
24 de mayo de 2011

In case you want to know or understand better the physical quality of feed pellets I would suggest you sci. papers written by Thomas Meno (Physical quality of pelleted animal feed http://www.sciencedirect.com/science/article/pii/0377840196009492) as well as Behnke (http://amena.mx/wp-content/uploads/2010/11/13KBehnke.pdf). Overall, pay attention to your cooling / drying!

Regarding binding and binders I would suggest you to:

- Increase the % of Limestone inclusion (e.g. 0,5%)
- Include pre-gelatinized starch in small % and/or some protein gels in the case your product requires high protein content as shrimp feed pellets, etc.. (e.g. Ajinomoto)
- Include some binders as lignosulphonate (1 - 1,5%) Click here 

Amir Attar
Javaneh khorasan
7 de noviembre de 2010
there were some practical information for feed mills thanks to author
Dejan Miladinovic
Fôrtek- Norwegian University of Life Science
4 de noviembre de 2010
This article is meant to help the operational officers as well in order to understand that the small adjustment can create the opportunities and hence the added value of better physical properties of pelleted feed products.
24 de mayo de 2011
Thomas Meno (Physical quality of pelleted animal feed http://www.sciencedirect.com/science/article/pii/0377840196009492 this article i could not read it. but Behnke was realy good. please send me another link for the first or the article please, That Benke write about glycerol, is reccomend to put this product in the pellet mill, because maybe i will try to do it. Jordache
24 de mayo de 2011
thank you for help. i need to know how resolve this problem. i will read the topic related.
23 de mayo de 2011
you can tell something about the components of mill that affects the pellets quality , if i use products with high humidity, pellets are nor durability. you may help with this? what binder can i use in this condition?
Dr Jaydip Mulik
10 de noviembre de 2010
Dear Sir, Thanks a lot!!! As your study taught how small things can change the whole world This will guide those people who are working with pellet feed manafacturing industries to create the difference. Thanks & regards, Dr Jaydip
Krishan Agarwal
8 de noviembre de 2010
the article is very educative to all those people who are engaged in pellet feed manufacturing activities .the die hole and thickness of die makes difference on pellet durability,a very importent aspect like have been explained. thanks
Saikim Gimbang
4 de noviembre de 2010
A very good information for feedmillers managers, may be conditioners (starch) and raw materials such as corn make a huge difference on the PDI.
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