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Analysis and solutions of abnormal appearance of pellet feed (useful experience)
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Analysis and solutions of abnormal appearance of pellet feed (useful experience)

1.      Pellet feed is curved and with many cracks

Cause analysis:

This phenomenon is often generated when pellets leave the ring die. When a cutter location is far away from the die surface, and blade is dull, the pellets extruded from die is broken by cutting knife instead of being cut off. At this time, there are part of pellet feed bending toward one side, and the other side presents many cracks. 

Improvement measures:

1)      Increase the compression force of the ring die on feed. Namely, increase the compression ratio of die to increase the density and hardness value of pellet feed;

2)      Crush the raw material more finely. If there are molasses or fat added, should improve uniformityof their distribution and control adding amount, so as to improve compactness of the pellet feed and prevent feed from being soft;

3)      Adjust the distance between the cutting knife and the surface of ring die, or to replace with a sharp blade;

4)      Use bonding additive to improve the bonding force inside of the pellet.

2. Horizontal crack crosses the whole pellet feed.

Cause analysis:

Similar to the phenomenon in case 1, the crack occurs in the cross-section of pellets, but the particles do not bend. This happens in the process of producing the fluffy pellet feed, which contains more fiber. Because the fiber is longer than the pore diameter, when the particle is extruded, the fibers’ expansion effect causes cross-sectional crack, producing the pellets with the appearance like fir tree’s bark.

Improvement measures:

1)      Increase the compression force of the ring die on feed. Namely, increase the compression ratio of the ring;

2)      Control the crushing fineness of the fiber, its maximum length shall not exceed one third of pellet size;

3)      Reduce the output to lower the speed of getting through die, to increase the density;

4)      Extend tempering time, use multi-layer conditioner or caldron conditioner;

5)      When the powder contains too much water or urea, it is possible to produce feed with the appearance of fir bark. Therefore, we should control the content of water and urea.

3. The particles have vertical cracks

Cause analysis:

Feed formula contains fluffy and elastic raw material, it will swell after passing through the conditioner. After the compression of ring die, the feed will bounce off and generate vertical cracks, due to the effect of water and elasticity of raw material.

Improvement measures:

1)      Change the recipe, but it is possible to increase the cost of raw materials;

2)      Use saturated dry steam;

3)      Reduce output or increase the effective length of ring’s hole, so as to increase the time of feed in it.

4)      Adding a binder also helps reduce the vertical cracks.

4. The particles have a radiat crack

Cause analysis:

This phenomenon means that there are large pellet raw materials in pellet feed, it is difficult to fully absorb moisture and heat in the steam. It is not as easy softening as the other thinner material, and during the process of cooling, different degree of softening causes difference shrinkage, which also results in radial crack, and further increases the pulverization rate.

Improvement measures:

Control the thickness and uniformity of raw materials, so that all raw materials can be softened uniformly

5. Uneven surface of pellet feed

Cause analysis: 

There are complete or half crushed large pellet raw materials in powder, in the process of the maturing, they are not completely softened. Therefore, when passing through the ring die, they cannot be well connected with the other raw materials, causing the particles uneven. In addition, there is steam soak in the raw material after maturing, steam bubble causes air bubble in the process of compressing into particles. At the moment of the pellets out of the die, the pellet’s surface becomes uneven because the change of pressure. Any feed containing fiber may cause this phenomenon.

Improvement measures: 

1) Properly control the thickness of the powder feed, thus all raw materials can be softened during maturing.

2) For the raw materials with more fiber, since it is easy to include steam bubbles, do not add too much steam into the formula.

6. Whisker pellet feed

Cause analysis: 

If there is too much steam, the superabundant steam will accumulate into the fiber or powder. However, when the pellet is extruded out of the die, due to the dramatic change of pressure, the particles will burst and this will push the fiber or pellet materials convex the surface, forming a prick whisker, especially during the feed production with high starch and fiber. When there is more steam into it, it will get worse.  

Improvement measures:

Better maturing.

A.    The feed with high starch and high fiber should use (0.1-0.2 Mpa) low-pressure steam, so that the moisture and heat in the steam can be fully released to feed for absorption;

B.     If the steam pressure is too high, or the downstream piping of pressure reducing valve is too close to the conditioning device, generally it should be longer than 4.5 m, the steam definitely will not well release the moisture and heat. Therefore, part of the steam accumulates in feed ingredients after maturing, it leads to whiskers pellet effects which was described above. Anyway, it should pay special attention to the installation position of steam pressure’s control system and pressure reducing valves, to check whether they are in the right position or not.


7. The color of pellets is different, called " colored feed ".

Cause analysis:

A.    It is common in the production of aquatic feed, it mainly shows that the color of pellets extruded from die is darker or lighter than the other normal pellets. Moreover, the color of a single pellet’s surface is different. All of these may affect the whole batch of feed appearance.

B.     The formula of aquatic feed is complex. It contains variety of raw material, some have little composition addition, causing the mixed effect is not ideal;

C.     The water content of raw materials used for pelleting is inconsistent;

D.    It contains the return machine used for duplicate pelleting;

E.     The inner wall of ring die has different degree of finish.


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