6 Reasons Why Your Wood Pellets Appearance Abnormal

6 Reasons Why Your Wood Pellets Appearance Abnormal

According to the pellet making process, there are many reasons which can result in different quality wood pellets, for example the raw material type and size, raw material moisture, pellet making machines, cooling section, crushing section and screening section. The quality and power of the https://www.tcpel.com/pellet-machine/pellet machine affect the production efficiency of the entire production line and affect the quality of the finished pellets. Here we have listed the 6 abnormal wood pellets appearances you may come across during pellet making, and reason for this, and also solution to help you improve that, keep on reading.

6 different wood pellets appearance

1. The wood pellets are bent and cracked

This result usually occurs when the pellets leave the ring die. In production, when the position of the cutter is adjusted far away from the surface of the ring die, and the knife edge is blunt, the wood pellets are easily broken or torn by the cutter when extruded from the ring die hole instead of being cut. At this time, some wood pellets are bent towards the one side and the other side show many cracks.

Such pellets often break from these cracks when they enter the cooler for cooling or during transportation, resulting in the production of pellets with too much powder or too short pellets.

  • Improvement methods: increase the compression ratio of the ring die; grind the raw materials into finer pieces; adjust the distance between the cutter and the surface of the ring die, or replace it with a sharper cutting blade.

2. The wood pellets have transverse and horizontal cracks

Cracks occur in the cross-section of the wood pellets, and the wood pellets are not bent. This can happen when you are making pellets with fluffy materials which contains high amounts of fiber. Since it contains fibers that are longer than the pore diameter, when the pellets are extruded, the expansion of the fibers causes transverse cracks in the cross section of the wood pellets.

  • Improvement methods: Increase the compression ratio of the ring die; control the crushing fineness of the raw materials, the maximum length cannot exceed one-third of the wood pellets diameter; reduce the output to reduce the speed of the wood pellets passing through the ring die holes. Note that too high moisture will also cause this problem.

3. Vertical cracks occur in wood pellets

The raw material contains fluffy and slightly elastic raw materials, and the moisture content is uneven. After compression and pellet making through the ring die, it will bounce open due to the action of moisture and the elasticity of the raw material itself, resulting in vertical cracks.

  • Improvement methods: Change the proportion of raw materials; reduce or evenly adjust material moisture; increase the compression ratio of the pellet machine ring die.

4. The crack changes from one point to a radiation direction

The main reason is that the raw materials contain relatively large particles. They are not so easy to soften as other finer raw materials. When cooling, due to different degrees of softening, the percentage of shrinkage is different, resulting in radial cracks and powdering. The powder rate will also increase.

pellet mill cooler

  • Improvement method: It is recommended to control the thickness and uniformity of raw materials.

5. The surface of the wood pellets appears uneven.

This is probably because the raw material contains large particles. Since the particle size of the raw material is hard and large, it cannot be well combined with other raw materials when passing through the ring die hole. The change in pressure causes the wood pellets to appear uneven.

  • Improvement method: Control the fineness of raw materials.

6. The colors of individual pellets are inconsistent

This situation is mostly caused by repeated pellet pressing of recycled materials in the pelletizing bin, or the inner surface of ring die aperture is inconsistent, and the resistance and extrusion force experienced by the pellets during extrusion are different, resulting in inconsistent color changes. In addition, there are burrs on the surface of the ring die, and the wood pellets will scratch the surface during extrusion, causing the surface color of individual wood pellets to be different.

  • Improvement method: Mix the recycled materials and raw materials and crush them again; use high-quality ring die to ensure the smoothness of the mold holes.


Above are some main bad quality wood pellets appearances reasons and solution, find the reason behind them, you can improve your pellet making efficiency and make higher quality wood pellets. If you have any questions during pellet making, welcome to discuss with our technician.

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