Coating Machine

Coating Machine

The coating machine is specialized post-processing equipment used in fertilizer production lines to apply surface coatings to granular fertilizers. It is a core piece of equipment for upgrading the commercial value of various granular fertilizers—such as organic, compound, blended, and slow/controlled-release fertilizers—by providing benefits like anti-caking properties, controlled nutrient release, and enhanced visual appeal. Using either powder dusting or liquid coating processes, the machine applies a uniform functional coating to the surface of the granules, ensuring the finished product achieves the ideal state of being non-caking, resistant to pulverization, and capable of controlled nutrient release.

Although finished granules possess their basic commercial form after granulation, drying, and cooling, they remain susceptible to issues such as caking, pulverization, and nutrient loss during storage and transportation. By applying one or more layers of coating materials (such as anti-caking agents, slow-release coatings, or colorants) to the granule surface, the coating machine effectively improves surface properties, physical strength, and nutrient release characteristics. The resulting granules feature smooth surfaces and uniform color; this not only enhances the product's commercial value and market competitiveness but also imparts value-added functions such as slow release, controlled release, and long-lasting efficacy.

The equipment typically features a horizontal rotary drum design, with an inclined rotating drum serving as the main body. It utilizes the synergistic action of the rotating drum and internal lifting flights to create a uniform curtain of material; coating agents are evenly applied via a spray system or powder duster, while hot air assists in drying to rapidly cure the coating layer. The coating machine integrates seamlessly with upstream and downstream equipment (such as coolers, screeners, and packaging machines), serving as the final "quality enhancement" step in the post-processing section of the fertilizer production line.

Structural composition of the equipment

The coating machine features a scientifically sound, compact overall structure and consists primarily of the following core components:

(I) Rotating Drum: The main vessel of the equipment, consisting of a rotating cylinder inclined slightly relative to the horizontal plane. The drum is fabricated from high-quality carbon steel plate; internal diameters range from Φ800mm to Φ1800mm, with lengths customized according to process requirements. The interior is lined with polypropylene or acid-resistant stainless steel plates, offering excellent corrosion resistance and anti-sticking properties. The exterior is equipped with riding rings and a large gear ring for support and power transmission, respectively.

(II) Lifting Flight System: Core working components installed on the inner wall of the drum. These flights continuously lift and scatter fertilizer granules, creating a uniform curtain of material across the drum's cross-section to ensure thorough contact between the coating agent and every granule. The flights typically feature an arc-shaped or spiral blade design and are evenly distributed along the inner wall. The curvature of the arc-shaped plates is usually oriented opposite to the drum's rotation direction to enhance material agitation.

(III) Spraying and Coating System: Comprising components such as spray pipes, nozzles, oil pumps, and powder feed pipes. The spray pipe runs along the drum's axis, with multiple nozzles arranged circumferentially in the middle section. The feed, oil, and powder pipes extend from the inlet side into the drum at progressively increasing lengths; this arrangement allows fertilizer granules to mix sequentially with the coating oil and dispersing powder, achieving a uniform, multi-stage coating effect. Nozzles may utilize either single-fluid or dual-fluid designs.

(IV) Drive System: Includes the electric motor, speed reducer, pinion gear, and large gear ring. The motor drives the reducer via a pulley and belt; the pinion on the output shaft meshes with the large gear ring fixed to the drum, rotating the drum at a low speed. The drive system operates smoothly and with low noise.

(V) Support Assembly: Includes support roller and thrust roller assemblies. The drum is supported on the support rollers via its riding rings, while thrust rollers prevent axial shifting of the drum. (VI) Feeding/Discharging and Auxiliary Devices: These include the feeding device, discharge outlet, hot air duct, screen, heating jacket, and slag discharge port. Some models are equipped with high-pressure air supply lines and hot air ducts to assist with drying and curing. The screen is used to filter out substandard granules.

Application scope of the equipment

The application scope of the coating machine is clearly defined and focused, centering primarily on the post-processing stage of fertilizer production. In the fertilizer sector, it serves as core equipment for surface treatments—such as anti-caking, slow-release, and coloring coatings—within production lines for granular fertilizers like compound fertilizers, blended fertilizers, organic fertilizers, bio-organic fertilizers, and slow/controlled-release fertilizers. Regarding slow/controlled-release fertilizers, the machine is suitable for producing polymer-coated varieties, achieving precise nutrient release control through multi-layer coating. It also supports the production of specialty fertilizers, including sulfur-coated urea, coated bio-fertilizers, and pesticide-impregnated fertilizers. Additionally, the equipment is applicable to granule coating processes in industries such as food processing and pharmaceuticals, and it accommodates requirements for combined treatments using both dry powder and liquid coating agents.

Types of usable raw materials

The types of raw materials that the coating machine can process primarily include:

Materials to be coated: Various granular fertilizers, such as organic fertilizer granules, compound fertilizer granules, blended fertilizer granules, urea granules, bio-fertilizer granules, and magnetized fertilizer granules.

Coating materials: Powders (including anti-caking powder, talc powder, bentonite, dispersing powders, etc.); liquids (including coating oil, liquid anti-caking agents, paraffin-based coating agents, polyvinyl alcohol-based coating agents, polymer emulsions, etc.); and slow-release materials (including sulfur, resin, tung oil, polyurethane, etc.). Other materials include colorants, microbial agents, plant nutrient solutions, etc.

The working principle of the equipment

The working principle of the coating machine relies on the synergistic effect of mechanical tumbling, atomized spraying, and hot-air drying. Its operational process comprises the following stages:

Feeding and Distribution Stage: Cooled granular fertilizer enters the higher end of an inclined rotary drum via the feeding mechanism. As the drum rotates at a steady speed, lifting flights continuously scoop up and scatter the granules, creating a uniform curtain of material inside the drum. The feed pipe, oil pipe, and powder pipe extend to varying lengths, ensuring that fertilizer granules first mix with the coating oil at the feed end and subsequently mix with the dispersed powder.

Atomized Spraying Stage: Coating material is evenly sprayed in atomized form onto the surfaces of the tumbling granules via a spray system. Single-fluid nozzles produce atomized droplets larger than 100 μm, while dual-fluid nozzles utilize compressed air to achieve a droplet size of 50–80 μm. The material continuously tumbles and mixes under the action of the lifting flights, ensuring the coating agent uniformly encapsulates every granule.

Fluidization and Curing Stage: As the drum rotates and conveys the fertilizer granules toward the discharge end, they undergo more thorough mixing with the coating oil and dispersed powder, resulting in a stable coating. Hot air supplied through a duct accelerates the curing of the coating layer.

Discharge Stage: The coated granules are discharged through the outlet. Some models are equipped with a screen, facilitating the easy retrieval of the finished coated product.

Equipment operating instructions

Pre-start checks: Ensure all bolts on the equipment are securely tightened. Check that the spray system pipelines are clear and the nozzles are free of clogs. Verify that the supply of coating agent is sufficient. Confirm that the hot air system is operating normally.

Start-up sequence: First, start the coating drum; next, activate the feeding system; finally, turn on the spraying system. This sequence prevents material from clumping due to an excess of coating in specific areas.

Operational monitoring: Adjust the drum rotation speed (typically 6–15 rpm) based on material characteristics and coating requirements. Control the spray volume of the coating agent (typically 0.5%–2% of the granule weight). Monitor the uniformity of the coating on the discharged granules. Observe the equipment for any abnormal vibration or noise during operation.

Shutdown procedure: Stop the feeding process first; shut down the machine only after the material has been fully discharged from the drum, the spraying system has been turned off, and any residual coating agent has been cleared from the pipelines.

Application of the equipment in the production line

The coating machine represents the final step in the post-processing section of the fertilizer production line. It is preceded by the rotary cooler, from which cooled granules at ambient temperature are transported into the coating machine. It is followed by the automatic packaging line, where the finished, coated granules proceed for packaging.

The complete post-processing workflow is as follows: granulation → drying → cooling → screening → coating → packaging. The coating machine integrates seamlessly with the upstream and downstream equipment to form a complete post-processing production line. After coating, the granules are linked to the automatic packaging line via a buffer silo; the capacity of this silo should be sufficient to hold at least 30 minutes' worth of production output.