Step 1: The semi-wet material crusher determines the granule's "foundation." Regardless of the subsequent granulation method, raw material fineness is the initial critical factor. Fermented organic materials typically have a moisture content of 30%–50%, characterized by high viscosity and fibrous content. The semi-wet material crusher employs a dual-stage rotor structure: the upper stage performs coarse crushing and breakup, while the lower stage handles fine crushing and homogenization; a screenless bottom design prevents clogging caused by wet material. Achieving a fineness of over 60 mesh is essential for smooth granule surfaces and uniform structural strength. Insufficient fineness results in coarse particles that cannot be fully encapsulated during granulation, leading to rough surfaces and internal "sandwich" defects.

Step 2: The granulation method determines the granule's "framework." Modern organic fertilizer granulators (including "two-in-one" models) utilize wet agglomeration; materials roll into spheres on the pan surface using their own moisture, achieving a pelletization rate exceeding 90%. The "two-in-one" model integrates mixing and granulation into a single unit, eliminating intermediate conveying steps and offering strong compatibility with high-moisture materials (25%–45%). In contrast, double-roller press granulation technology represents the dry method: powder is compressed into dense sheets under high pressure, then crushed and screened. This process requires no added water or drying, producing granules with a strength exceeding 30N—making them ideal for long-distance transport.

Step 3: The rounding machine determines the granule's "market appeal." Granules emerging from the granulator often feature burrs, sharp edges, or slight flattening. The ball-shaping machine utilizes rotational friction and centrifugal force to make the granules rub and roll against each other within the pan; this smooths out edges, improves sphericity by 30%–50%, and simultaneously increases compressive strength. Rounded granules perform more reliably during packaging, transport, and mechanical sowing, and command a higher market price. Typically positioned between the granulator and the screening machine, the rounding machine creates a continuous closed-loop system: fine "return" powder is re-granulated, while qualified granules proceed to the rounding and shaping stage.

Step Four: The coating machine determines the granule's "functionality." It evenly sprays a coating agent onto the granule surface to form a hydrophobic film. This film enhances visual luster while enabling slow-release capabilities—controlling the nutrient release rate and minimizing losses due to leaching. The coating agent dosage is usually kept between 0.5% and 2%; application must be uniform, as excessive thickness locally can impede release, while insufficient thickness fails to provide the desired slow-release effect.

An alternative approach: mixing without granulation. Bulk Blending (BB) fertilizer production lines and mixers follow a completely different path; raw materials such as urea, ammonium phosphate, and potassium chloride are already granular, so the line performs only physical mixing. The core of the BB fertilizer mixing process is "shape-preserving mixing," utilizing a twin-shaft paddle mixer for gentle blending. The process takes 2–5 minutes, achieving a coefficient of variation (CV) for uniformity of ≤5% and keeping granule breakage below 0.5%. Excessive mixing time or speed can abrade granule surfaces, actually exacerbating moisture absorption and segregation.

From crushing, granulation, and rounding to coating, each step adds value to the granules. Granulation determines "usability," rounding determines "marketability," and coating determines "value." Before selecting a production line, it is essential to clarify the target market and the intended method of application for the final product.