NUTRITION ▶▶▶
Factors affecting feed pelleting quality and efficiency
The quality of pellet feed is mainly reflected in the vulnerability, the hardness, the appearance and the length of pellets. However, raw materials have a major influence on pelleting quality and efficiency including the following aspects:
BY MR. HAO BO CHAIRMAN OF ZHENG CHANG GROUP
1. The influence of the particle size of raw material on pelleting quality and efficiency
Raw materials come in coarse, medium and fine particles. Generally, coarse particles have a diameter greater than 3 mm. Medium and fine particles have good pelleting prop- erties, low energy consumption and less abrasion due to the effect of the die and roller. Compared to coarse particles, me- dium and fine particles have more of their surface area in contact with steam during conditioning. Steam can easily penetrate the cores of small particles and cause physical and chemical changes, which improves the quality of pelleting. In addition, coarse-particle raw materials are more likely to crack after pelleting. Medium and fine materials ensure the high density of pressed particles, and are better able to pass through the die holes, with less abrasion and thus higher output. But if the materials are crushed too fine, production costs will rise. The ideal particle size is a reasonable combina- tion of coarse, medium and fine materials. For Ф2 mm prawn feed, 85% of the raw materials should pass through a 40- mesh sieve. Now the minimum diameter of the ring die hole is 0.8mm, so the maximum diameter of raw materials for pelleting should not be more than a third of the diameter of the die hole, i.e., the raw materials must pass through the 60-mesh sieve (0.267 mm) after crushing to meet the particle size requirement.
2. The influence of feed density on pelleting efficiency Pelleting efficiency is related to the density of raw materials. Light materials have a density below 0.33 t/m³, whereas heavy materials have a density of more than 0.4 t/m³. When pelleting, light materials lead to low output, while heavy ma- terials ensure high output. For example, when using alfalfa with a density of 0.22 t/m³, the output is 4 t/h. For cottonseed powder with a density of 0.53 t/m³, the output is 16 t/h.
The quality of the pellets can be influenced by the type of raw materials used.
3. The influence of protein content on pelleting efficiency High-protein raw materials (generally with a high density), such as soybean powder and cottonseed powder, are extrud- ed by the die and roller technique, resulting in friction heat, which is conducive to pelleting. However, for high-protein feed (such as calf feed and concentrated feed), a large amount of powder or urea should be added to enhance pelleting.
4. The influence of fat content on pelleting efficiency Fat is a great lubricant for pelleting. It can increase output, re- duce abrasion and prolong the service life of the roller and die. The feed itself contains fat, and we can also add fat be- fore pelleting. Too much fat content (e.g., 6%) will affect pel- leting, since the particles may become soft making them dif- ficult to shape. If particles with high fat content (more than 3%) are required, 1% – 2% fat can be added during mixing, and the rest can be added by spraying after pelleting.
5. The influence of fibre content on pelleting efficiency Fibre has an adverse effect on pelleting. It may reduce output and increase abrasion due to the die hole. There are two types of fibre: stringy fibre, such as alfalfa, sweet bud stem, sweet potato stem, etc., and shelled fibre, such as oat, soy- bean, cottonseed, peanut shell, etc. The stringy fibre can ab- sorb steam and soften during conditioning, and play the role of binding particles, thus improving particle strength; howev- er, shelled fibre cannot absorb steam and thus play a role in the dispersion of particles and this affects particle quality.
▶ ALL ABOUT FEED | Volume 28, No. 2, 2020 23
PHOTO: SERHII DERKACH
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