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Inside Look on Dies for Wood Pellet Making Machine
- Jan 30, 2018 -

What Is A Pellet Die?


A pellet die implies a metal part comprising of either flat or ring-shaped holes, in which the roller uses to force raw materials under pressure to make pellets. Ideally, the pellet die is driven by the motor of a pellet mill. The features and overall size of the pellet is dependent on the size of holes alongside the thickness of pellet die.


Functions Of A Pellet Die


Apparently, pellet dies work along with the roller to execute the pellets during the process of pelletizing. The force of the roller acts on the feed stocks in contact with the die, consequently compressing and extruding the pellets. Conversely, the radial force coming from pellet dies resists the feed stock that flows through the holes of the die. And, since the two resilient forces interact together, the feed stocks are manufactured into pellets.


The pelletizing chamber distributes the feed stocks evenly across the face of pellet die. This is where the rollers and the cross face of pellet dies press the feed stocks, consequently forcing them through the die holes to mold pellets. The pellets are usually cut off and shaped when extruded out of the pellet die.


Types Of Pellet Dies


Ring Die Type Mill (normally used in large wood pellet plant)


The two common die designs used in wood pellet machine at the contemporary market include the flat die and ring die. A flat die is small in size, light in terms of weight, easy to clean, easy to maintain, and cheaper than its ring die counterpart. On the contrary, ring dies are large in size, durable, heavy in weight, high capacity, and are expensive. Ring dies don’t wear easily and feature low energy consumption as well.


Core Parts of Flat Die Pellet Machine (flat type pellet mill die and roller)


Flat die is adopted by homemade pellet machines or small wood pellet machines for the low production cost and low purchase price. The ring dies, on the other hand, are installed in the large scale pellet machines as they suit the high productivity. Regardless of the shape of the die, the die is used to determine the overall performance of the pellet production line. This simply implies that the pellet die is a vital component of a wood pellet mill.


The Design Of Pellet Dies


The pellet die design is crucial since the pellet die directly affects the quality of pellet along with the production capacities of pellet mill. The same design may equally pose a huge impact on operation performance and working die life. The following factors determine the pellet die design:




The thickness of wood pellet making machine is a decisive factor that needs to be considered. The thickness of the die may further be divided into effective thickness and total thickness. The total thickness implies the overall thickness of the die, which is bigger in comparison to the effective thickness of the die.

The effective thickness of the die implies the working thickness of the pellet die, whereby the pellets are molded. Usually, the die tends to be studier when it’s thicker. The increments of a pellet die thickness differ by just 1/4” between 11/4” and 5” thick.


The thickness influences the flow of materials through the die. If it’s quite deep, the biomass materials lack adequate compression to make pellet. Nevertheless, if it’s quite shallow, the biomass materials get the machine blocked thus shortening the service life of the machines.


Relief depth


This refers to the depth difference between the pellet die effective thickness and total thickness. The overall design of the relief depth is used in enhancing the strength of a pellet die by adopting thicker die. Similarly, the design of relief depth is used to promote the flowing rate of the feed stock.



Pellet Die Design




Pellet dies are made of metals that determine the working life along with the features of pellet dies. In general, pellet dies are made of metals like stainless steel, alloy, and “Chrome-Plus” stainless steel, among others.


Alloy pellet die is suitable for palletizing some common feedstocks. Nevertheless, stainless steel pellet die performs better. Stainless steel provides better resistance to agents of corrosion, scoring, and pitting. The “Chrome-Plus” stainless steel pellet die is the best for pelletizing ingredients that boast strong corrosive or abrasive qualities.


Inlet diameter and angle


The inlet of die holes is countersunk into taper shape, allowing the feed stock to seamlessly flow into the die holes. The inlet angle can be somewhere in the region of 30o-40o on small hole dies.


Drill pattern


The type of die hole is another essential aspect worth your consideration. Presently, the state-of-the-art step-shaped die is the most successful and mature design that suits pellets production, particularly when it comes to wood pellet production. This design extends the service lifespan for a ring die that’s well-known to be vulnerable to agents of wear and tear.


Hole count


The hole count refers to the total number of die holes present in a die. Kindly note that the higher the number of holes, the better the production capacity and the lower the pellet die strength. The hole count directly influences the pellet die production capacity alongside the die working life.




The pellet die specs may include the inlet angle, inlet diameter, total & effective thickness, hole count, drill pattern, and relief depth. The C.R. Stark’s study suggests that the die specifications comprising of the factors mentioned herein may largely influence the quality of the pellet.