In the production of pellets using a granulating machine, irregularly shaped pellets can occasionally appear. Experienced feed manufacturers are usually aware of the root causes and can quickly address these issues. However, inexperienced or new feed producers might struggle to identify the problem and often seek external assistance or rely on support from the granulator manufacturer. Below are the seven most common pellet abnormalities, along with their causes and solutions. These insights are derived from my extensive experience in developing and commissioning granulators for feed production, providing valuable guidance for those in the industry.
**1. Pellets Are Bent with Cracks on One Side**
This issue typically arises when pellets exit the ring die. In production, if the cutter is positioned too far from the ring die’s surface and its edge becomes dull, the pellets are more likely to be torn or broken rather than cleanly cut. As a result, you’ll notice numerous cracks on one side, while the other remains relatively intact. These pellets often break further during cooling or transportation, leading to excessive waste.
Improvement Measures:
- Increase the compression force applied by the ring die on the feed, effectively raising the compression ratio. This enhances the pellet's density and hardness.
- Ensure the feed ingredients are ground to a finer consistency. If molasses or fats are added, ensure they’re evenly distributed and used sparingly to maintain pellet firmness.
- Adjust the cutter’s distance from the ring die’s surface. Ideally, this gap should not exceed the diameter of the pellets being produced. Alternatively, replace the cutter with a sharper blade. For smaller pellets, use thinner blades placed closer to the ring die.
- Utilize binding agents to enhance internal cohesion within the pellets.
**2. Horizontal Cracks Across the Entire Pellet**
Similar to the first case, this defect appears as a split across the pellet’s cross-section. It happens frequently with fluffy feeds rich in fiber. When such feeds are pressed into the ring die’s holes, the fibers expand, causing a bark-like texture on the pellet surface.
Solutions:
- Increase the compression ratio of the ring die.
- Control the fineness of fibrous ingredients, ensuring their maximum length does not exceed one-third of the final pellet size.
- Reduce the feed throughput rate to allow more time for densification.
- Extend the conditioning time, possibly using multi-layer conditioners or kettle conditioners.
- Monitor moisture levels and urea content to avoid excessive bark formation.
**3. Vertical Cracks in Pellets**
Vertical cracks occur in certain feed formulations that include fluffy, slightly elastic raw materials. These materials expand during the conditioning process and then rebound under pressure, creating vertical fissures.
Strategies to Mitigate:
- Modify the feed formula, though this may increase costs.
- Optimize steam quality, favoring saturated steam to minimize moisture addition.
- Lengthen the die holes to prolong the feed’s residence time.
- Incorporate binders to reduce cracking.
**4. Radiant Cracks Emerging from a Single Point**
This defect suggests the presence of large particulates in the feed. These larger components fail to absorb sufficient moisture and heat during conditioning, unlike finer materials, leading to inconsistent softening and subsequent cracking upon cooling.
Improvement Steps:
- Regulate the feed material’s thickness and uniformity to ensure all components are adequately conditioned.
**5. Uneven Pellet Surfaces**
Uneven surfaces arise when coarse particles or semi-crushed materials remain in the feed mixture. These particles resist softening during conditioning, resulting in harder, larger granules that don’t blend well with others. Additionally, steam bubbles trapped in the feed can form air pockets during pressing, rupturing under pressure and leaving an uneven surface—especially common in fiber-rich feeds.
Enhancement Methods:
- Control the feed’s thickness during conditioning to ensure thorough softening.
- Limit steam usage in fiber-heavy formulas to prevent bubble formation.
By addressing these issues systematically, feed producers can significantly improve pellet quality and reduce wastage, ultimately boosting efficiency and profitability.
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