In the production of biomass pellet machine, sometimes pellets with abnormal appearance will appear. Experienced pellet machine manufacturers will know what the cause of this situation and can quickly eliminate it. For insufficient experience or new wood pellet manufacturers, sometimes they will not find the crux of the problem. Only ask for help from the outside world or pellet machine manufacturers.

Below, we will introduce the causes and improvement methods for the occurrence of seven common abnormal appearance wood pellets. This is a summary of Taichang Company's years of experience in the development and commissioning of pellet machine for comparison and reference in the production of wood pellets.

1. wood pellets are curved and have many cracks on one side

This phenomenon usually occurs when the wood pellets leave the ring mold. In production, when the cutting knife position is adjusted far away from the surface of the ring die and the blade edge is blunt, the pellets are easily knocked and cut off by the cutting knife rather than being cut off when extruded from the die hole. At this time, some of the pellets bent to one side and the other side has many cracks. When these wood pellets enter the cooler for cooling or transportation, they often break from these cracks, resulting in too much wood pellets or too short pellets produced.　

Improvement method:

Increase the compression force of the ring die on wood pellets, that is, increase the compression ratio of the ring die, thereby increasing the density and hardness of the pellets; crush the wood raw material woods to finer to improve the density of the wood pellets and prevent the wood pellets from being soft; adjust the distance between the cutter and the surface of the ring die, usually the distance between the knife edge and the outer surface of the ring die is not greater than the diameter value of the produced wood pellets, or replace it with a sharp cutting blade;

2. Horizontal cracks cross the entire wood pellets

Somewhat similar to the phenomenon in case 1, cracks occur in the cross-section of wood pellets, except that the pellets are not bent. This can occur when fluffy woods containing more fiber are granulated. This kind of wood pellet is often when the wood is squeezed into the granulated holes of the ring die. Since it contains fibers that are longer than the pore size, when the pellets are extruded, the expansion of the fibers causes the pellets to produce transverse cracks in the cross-section, creating a fir-bark-like wood pellet appearance.

The improvement method is to increase the compression force of the ring die on wood pellets, that is, increase the compression ratio of the ring die; control the fineness of the fibers, and its maximum length cannot exceed one-third of the pellet size; reduce the yield to reduce the speed of the wood die pellets passing through the mold holes and increase the density;

3. The biomass pellet machine produces vertical cracks

During the production process, some customers cannot dry the raw materials evenly due to the type of dryer selection, resulting in uneven moisture content of the raw materials. After being compressed and granulated by the mold, it will bounce open due to the action of moisture and the elasticity of the raw materials itself, resulting in vertical cracks.

The improvement method is: improve the drying effect of the dryer and increase the effective length of the mold hole.

4. wood pellets produce radiation cracks from a source point

The main reason for this situation is that the woods contain relatively large woods. Raw materials with similar fiber levels will only be squeezed and fused to each other when granulating. If there are larger fibers, it will affect the interaction between the fibers. It is not as easy to soften like other finer raw materials. When cooling, due to the different degree of softening, the shrinkage amount is different, resulting in radiation cracks.

The improvement method is to properly control the thickness and uniformity of the powdered feed raw materials, and add simple sieve powder and sieve woods with larger pellets before granulation.

5. Uneven surface of the pellet material

This situation is that the powder used for granulation contains large pellets of raw materials that have not been crushed or semi-crumbed. Because the pellets are relatively hard and large, they cannot be well combined with other raw materials when passing through the mold holes of the granulator, making the pellets appear uneven. The improvement method is to properly control the thickness of powdered raw materials.

6. The color of the pellets is inconsistent between individual pellets or individuals, commonly known as "flower materials"

It is mainly manifested as the color of individual pellets extruded from the ring die is darker or lighter than that of other normal pellets, or the surface color of individual pellets is inconsistent. The main reasons for this phenomenon are as follows:

There is a re-granulation material in the granulation chamber to be made. The granulated pellets can only become finished products after being cooled and sieved. The screened fine powder or small pellets often enter the process flow and are re-granulated, usually entering the mixer or granulated bin. Since this return material is re-granulated, it is sometimes produced when mixed with other raw materials that are unevenly or are mixed with small pellets of the return machine.

The inner wall finish of the ring mold aperture is inconsistent. Due to the inconsistent finish of the die hole, the resistance and extrusion pressure the pellets are subject to during extrusion are different, and the color changes are inconsistent. In addition, some ring dies have burrs on the small hole walls, and the pellets will scratch the surface when extruded, resulting in different surface colors of individual pellets.

For the four reasons for the production of "flower materials" listed above, the improvement method is very clear. Control the return material. For pellets that are prone to "flower materials", the return material and the raw materials should be mixed and crushed again; a ring mold with guaranteed quality is used to control the finish of the mold holes, and if necessary, sand the mold holes before use.

In short, for the abnormal appearance pellets that appear in the wood pellet machine production, several representative forms of expression are discussed above, and some abnormal appearance phenomena of some pellets are not listed here because they are not representative. From the above discussion, we can see that the causes of these phenomena are multifaceted and are not completely isolated from each other. This requires that when we deal with such problems in actual work, we should analyze more and grasp the key to the problem in order to solve the problem. I hope this article can help you.