Granules produced by a disc granulator already possess decent sphericity, yet their surfaces often feature burrs, sharp edges, and slight flattening. The function of a spheronizer is to place these semi-finished granules into a rotating disc where they rub and roll against one another, smoothing out edges and polishing the surface. This process improves sphericity by 30%–50% and simultaneously increases compressive strength. However, a spheronizer is not a standard component of a disc granulation line; its inclusion depends on the target market and the intended application of the granules.
First, consider the product’s destination. If the granules are intended for BB fertilizer (bulk blending) or mechanical spreading, spheronization is virtually essential. Granules with poor sphericity and sharp edges exhibit poor flowability during blending—leading to bridging and material blockages—and are prone to clogging machinery outlets during mechanical spreading. Conversely, if the granules are to be broadcast-applied locally or used as a base fertilizer for compound fertilizers, sphericity requirements are lower; the spheronization step can be omitted, allowing investment to be allocated to the more critical granulation and drying stages.
Second, consider the granulation method. Granules produced by disc granulators are naturally quite round, so spheronization yields a noticeable improvement. In contrast, granules from double-roller extrusion lines are typically cylindrical or irregularly flaky with sharp edges and a high angle of repose; while spheronization significantly improves flowability for blending or mechanical spreading, it also increases equipment and operating costs. For high-end granular fertilizer production using new organic fertilizer granulators or “two-in-one” organic fertilizer granulators, adding a spheronization step after screening is also recommended to ensure a more uniform and marketable appearance.
Third, there is a specific “red line” requirement for bio-organic fertilizers. In bio-organic fertilizer granulation and production lines, the spheronizer (rounding machine) must operate at low temperatures. Functional microorganisms die off in large numbers when exposed to temperatures exceeding 60°C; since friction during the spheronization process generates heat, excessive rotational speeds or prolonged residence times can cause local temperatures to surpass 55°C. Consequently, spheronizers for bio-organic fertilizer require low rotational speeds and short residence times, with cooling air ducts installed if necessary, to ensure granule temperatures remain within a safe range.
Fourth, consider the spheronizer’s position within the disc granulation production line. A typical workflow involves: granulation discharge → screening → feeding compliant granules into the spheronizer → recycling fine powder for re-granulation. Spheronized granules feature smooth surfaces, allowing for more uniform subsequent coating and greater resistance to crumbling during storage. Skipping the spheronization step results in granules with rough edges, where coating agents tend to accumulate unevenly, thereby compromising the slow-release performance.
Spheronization is not a universal necessity but rather a tool that amplifies product positioning. The target market and intended application determine whether spheronization is required and to what degree it should be performed. Answering this question before selecting a production line is more meaningful than simply comparing equipment prices.