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Factors Affecting Pellet Mill Die Life


Pellet Mill die covers more than 70 % of the total cost of the consumables in a feed mill. Getting an optimum life from pellet die is a big challenge for feed millers’.Factors behind die life may be classified in two categories:

1. Manufacturing
2. Operational

Manufacturing: Material, Heat treatment and dimensional size & tolerance – these are the three main factors to be considered or reviewed from manufacturer point of view in concern with die breakage.

High chrome material has carbon content of 0.35% and chromium 12.5 % (minimum range) 

Anything below this range may leads to different properties of pellet die in terms of strength and wear & tear. Die manufacturer must take care of these metallurgical properties while die manufacturing. Poor heat treatment and Low HRC leads to lesser die life and poor performance 

Fitting size tolerance at the die surface is very important factor in die performance. Loose fitment may leads to fatigue failure of Ring /holder bolts and pellet die. Also thickness of die not matching the feed formulation and application also leads to die breakage or poor die l

Operational: Around 85 % of die breakage problem associated with poor handling and incorrect die usage. Few of the factors are as mentioned.

1. Feed Formulation: Formulations rich in fiber content are hard, thus pelleting is difficult and therefore the die life is less in this case. Life of dies used for producing layer feed (high fiber, less oil, Calcite)is very less as compare to broiler feed.Raw materials containing marble powder/silica & other abrasive particles wear dies more rapidly.As good fat content in feed acts as a lubricant therefore formula containing 1.5-4% fat run smoother and are less abrasive due to less friction as the fat present in feed reduces friction.

2. Particle size of the mash(Grinding): A die producing pellets from consistent particle size mash will give good life as compared to die producing pellets from uneven and over size of particles particle size of mash will give subsequently less life. As a thumb rule the particle size should be in the range of 600-900 microns for good pellet quality, better results and good die life.

3. Conditioning & Moisture addition: A poorly conditioned mash also reduces the die life by increasing friction and load on pellet die. Conditioning parameters play very vital role in increasing die life. Minimum 2-2.5 % of moisture should be added through the conditioners and moisture range after conditioning should be 14-16 %.

4. Operator’sSkill: The operator should regularly check the
A. Gap between Die & Rollers, steam setting as per formulation, deflector /scrappers setting as per die wearing pattern, knife settings etc.

B. Observing wearing pattern of die; it is recommended to change the side of die (front side – Back side) for more uniform wear after 200-250  running hours.

C. Magnet cleaning at regular intervals.

5. Using other supporting parts to an optimum level: Some time we use the consumable parts more than their standard life but loose much more in feed quality and life of other parts which directly related to them. Like for an average die life cycle it is recommended to use 5 pieces (2.5 set) of roll shells for a better die life and uniform PDI feed quality. Hence using the roll shells & beaters more than recommended life results in great losses in terms of grinding texture, conditioning, pellet quality and specific energy consumption also reduces the die life.

6.  Using Same die for Broiler & Layer Feed: Broiler contain less fibers and more oil %age (soft formulation), which provides better pelleting properties, less frictional load on pellet die. Hence, we can use compression ratio of 1:12, 1:13 & even more.

Using high compression ratio for layer feed may leads 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 above factors using separate die for both layer & broiler feed is a better and cost effective solution. For Layer feed – Minimum hole size for die should be or more than 3.5 mm.

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 the above stated information.