LaiZhou ChengDa Machinery Co., Ltd.

Stable production of a pellet mill requires simultaneous attention to raw material status, equipment parameters, process conditions, and finished product indicators. Improper parameter adjustment can easily lead to die blockage, high fines content, loose pellets, and output fluctuations. In actual production, parameter windows should be gradually verified based on material characteristics.

Control of Raw Material Moisture and Particle Size

Raw material moisture is a fundamental parameter affecting pelleting stability. Pre-conditioning moisture is typically controlled around 12%–15%, while post-conditioning moisture is generally maintained between 15%–16.5%, with specific adjustments based on formula and finished product requirements. If moisture is too low, material friction increases and forming becomes difficult; if too high, slippage on the ring die inner wall may occur, potentially causing die blockage. Raw material particle size should also match the die hole diameter. Excessively coarse particles increase wear on the ring die and rollers, while excessively fine particles may affect pellet durability and permeability.

Conditioning Temperature and Steam Quality

The conditioning process directly affects starch gelatinization, material softening, and forming effectiveness. For livestock and poultry feed, conditioning temperature can reference 70°C–88°C; for aquatic feed, it can be appropriately increased, while for heat-sensitive materials, temperature should be reduced. Steam pressure should remain stable, with a common range of approximately 0.2–0.4 MPa. Condensate must be drained before entering the conditioner, and dry saturated steam should be used whenever possible. Unstable steam quality causes fluctuations in material moisture and temperature, thereby affecting main motor current and discharge uniformity.

Adjustment of Ring Die and Roller Gap

The gap between the ring die and rollers significantly impacts output, fines content, and die life. In conventional material production, the gap is typically controlled within 0.1–0.3 mm; it can be appropriately widened for high-fiber or difficult-to-pellet materials. If the gap is too small, die-roller friction intensifies, increasing heat and wear; if too large, the rollers slip easily, the material layer becomes excessively thick, output decreases, and fines content rises. During adjustment, observe whether the rollers are properly driven, aiming for smooth operation and uniform discharge.

Selection of Ring Die Compression Ratio

The compression ratio, defined as the ratio of effective die hole length to die hole diameter, reflects material extrusion intensity. A higher compression ratio produces denser pellets with lower fines content but increases discharge resistance and may reduce output. A lower compression ratio allows faster discharge, but pellets may become loose and uneven in length. Livestock and poultry feed, aquatic feed, biomass fuel, and straw-based materials have different compression ratio requirements, which should be selected based on material fiber content, moisture, and finished pellet hardness.

Feed Rate and Main Motor Current

Feed rate should match the main unit load. Production load can be assessed via main motor current, generally controlled at 85%–95% of rated current. Excessive feed rate can cause overload and die blockage; insufficient feed rate reduces output and increases unit energy consumption. When steam, moisture, or raw material formula changes occur, the feed rate should be promptly fine-tuned to maintain stable current.

Ring Die Speed and Cutter Position

Ring die speed affects material residence time in the die holes and extrusion effectiveness. Excessively high speed may produce looser pellets; excessively low speed limits output. Cutter position determines pellet length, typically controlled at 1.5–3 times the pellet diameter, adjusted according to product standards. Dull cutters or improper distance cause uneven pellet length and rough cross-sections.

Cooling and Finished Product Quality Monitoring

Pellets exit the mill at elevated temperatures and require timely cooling to bring pellet temperature close to ambient and reduce moisture to a suitable storage range. Excessively rapid cooling may cause surface cracking, while insufficient cooling can lead to moisture absorption and caking. During production, pellet appearance, length, fines content, hardness, and moisture should be regularly tested. When abnormalities are detected, priority checks should focus on whether moisture, conditioning temperature, die-roller gap, and compression ratio have deviated from set ranges.

In summary, pellet mill parameter control should center on "raw material moisture, conditioning conditions, die-roller gap, compression ratio, feed load, speed and cutter settings, and cooling monitoring." Parameter windows vary for different materials and formulas. It is recommended to record current, temperature, moisture, and finished product quality through small-batch trial production to establish a stable process parameter table.