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. Die breakage is most common in almost all feed mills. We can analyze a few parameters before or at the time of installation for getting a better die life. Die breakage can mainly be classified into 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 a manufacturer's point of view in concern with die breakage.
High chrome material has a carbon content of 0.35% and chromium 12.5 % (minimum range) as major alloying elements.
Anything below this range may lead to under/poor performance of pellet die in terms of strength and wear & tear. Die manufacturers must ensure that material composition must be in the optimum range and material is free from forging defects before the start of manufacturing.
After the number of machining processes, die must be heat treated in high-end vacuum furnaces as per specified heat treatment cycle including hardening followed up by tempering. Poor heat treatment and low HRC leads to lesser die life and poor performance.
Fitting size tolerance at the die surface is a very important factor in die performance. Loose fitment may lead to fatigue failure of Ring /holder bolts and pellet die. Also, the thickness of die not matching the feed formulation and application also leads to Die breakage or poor die life.
Operational: Around 85 % of die breakage problems associated with poor handling and incorrect die usage. Few of the factors are as mentioned:
1. Die Fitment: The Fitment of die plays a significant role in the life of the die. While changing die carefully examine the condition of the die seating surfaces with rear & front ring. If the rings have been used for a long period of time, the operator must check the clearance between die and rear/front rings. Loose fitment of die and ring may lead to fatigue failure of die bolts and Die.
2. Play in Holder assembly: worn-out die holder/ bearing seats allow the die to move slightly during the operation. This may generate vibration in the pellet mill leading to fatigue failure, die rollover or premature end of Die.
3. Iron Particles: Too much sand or iron impurities in the feed, can increase the wearing of the die & rollers. So it is important to remove the impurities in the raw materials. When any foreign particle comes in direct contact with the die surface, it blocks the die surface. When roll shells exert pressure on the clogged surface extreme forces are generated which after some time may lead to Die breakage. So it is always recommended to clean the magnets at regular intervals.
4. Improper selection of shear pins: Shear pin prevents the breakage of dies by stopping the pellet mill in case of any iron tramp in between die & roller shell. If the shear force more than the safety factor acts to it, it will break itself & prevent the die breakage. So the proper selection of the shear pin is very important. It should neither be too ductile nor too brittle, neither too long neither too short, neither too weak nor too strong.
5. Incorrect assembly of stay plates and studs. The Support stud used in the assembly needs to be assembled in a proper manner. Any kind of misalignment and loose fitment may cause vibration in pellet mill & die which may lead to fatigue failure and die breakage.
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.