The granulation process is known for its fast particle size and effective results. A special filter screen is designed and carefully used to sieve the material. The friction filter rod helps crush the sieved solid particles, making this technology widely applied in the pharmaceutical, chemical, and food industries. This machine can replace traditional swinging pellet machines and represents a new generation of pellet equipment. During the production of granulated pellets, sometimes abnormal appearances occur. For less experienced or new feed manufacturers, these issues may go unnoticed. In the following sections, we will discuss seven common causes of abnormal granular materials and provide improvement methods for reference in feed production.
**1. Pellets are bent with many cracks on one side**
This issue typically occurs when the pellets exit the ring die. If the cutter is positioned too far from the ring die surface or if the blade is dull, the particles may be torn rather than cleanly cut as they pass through the die holes. This results in many cracks on one side, which can lead to breakage during cooling or transportation, increasing the number of fines produced.
Improvement methods include:
a) Increasing the compression force of the ring die by raising the compression ratio, which enhances pellet density and hardness.
b) Ensuring finer grinding of feed ingredients. If molasses or fat is added, it should be evenly distributed and properly controlled to improve pellet compactness and prevent softening.
c) Adjusting the distance between the cutter and the ring die surface—ideally not exceeding the diameter of the pellets. A sharper blade can also be used, especially for small-diameter pellets.
d) Using a binding agent to strengthen internal bonding within the particles.
**2. Horizontal cracks across the entire pellet**
Similar to the first issue, but the pellet is not bent. This happens when fluffy feeds with high fiber content are processed. As the pellets are extruded, the fibers expand, creating horizontal cracks that resemble bark-like surfaces.
To address this:
- Increase the compression force of the ring die.
- Control fiber length to ensure it does not exceed one-third of the pellet size.
- Reduce production speed to increase pellet density.
- Extend conditioning time using multi-layer or kettle conditioners.
- Monitor moisture and urea levels in the feed, as excess water or urea can cause similar issues.
**3. Vertical cracks in the pellets**
Some feed formulations contain fluffy, slightly elastic raw materials that swell during tempering. When compressed into pellets, the moisture and elasticity cause vertical cracks.
Improvement methods:
- Adjust the formula, though this may increase costs.
- Use high-quality steam, preferably dry and saturated, to reduce added moisture.
- Decrease production speed or increase the effective cavity length to allow more time in the die.
- Add a binder to reduce crack formation.
**4. Radiating cracks from a central point**
This appearance indicates the presence of large particles in the feed. These particles do not absorb moisture and heat as effectively as smaller ones, leading to uneven shrinkage and cracking upon cooling.
Improvement methods:
- Ensure uniform and fine grinding of all ingredients to promote even softening during conditioning.
**5. Uneven surface on the pellets**
This occurs when the feed contains large, unground particles or when steam bubbles are present. These bubbles create uneven surfaces when the pellets are extruded, especially in fiber-containing feeds.
Improvement methods:
- Control the fineness of the feed to ensure all ingredients are fully softened.
- Avoid excessive steam when processing fibrous materials to prevent bubble formation.
**6. Whisker-like pellets**
Excessive steam can accumulate in fibers or powders, causing pressure changes that rupture the pellets, resulting in protruding fibers that look like whiskers. This is common in high-starch, high-fiber feeds.
Improvement methods:
- Use low-pressure steam (0.1–0.2 MPa) to allow proper moisture and heat absorption.
- Ensure the steam pipeline after the pressure-reducing valve is long enough (at least 4.5 meters) to avoid steam accumulation.
- Pay close attention to steam pressure regulation and the placement of the pressure-reducing valve.
**7. Pellets with inconsistent color, commonly called “flower materialâ€**
This issue occurs when individual particles vary in color due to uneven mixing or improper conditioning. It often appears in feeds with varying ingredient compositions.
Improvement methods:
- Ensure consistent mixing and proper conditioning to achieve uniform color and texture in the final product.