Coating Machine

The coating machine is a core piece of equipment in the post-processing stage of fertilizer production lines, responsible for functionalizing the granule surface; its operational stability directly determines the finished product's anti-caking performance, slow-release characteristics, and commercial appearance. Given that the machine relies on the coordinated operation of multiple subsystems—including mechanical drives, spraying systems, hot-air systems, and electrical controls—and continuously processes materials containing oily or powdery coating agents, standardized operation and scientific maintenance are crucial. Any oversight in these areas can lead to uneven coating, granule agglomeration, equipment clogging, or even safety incidents.

The machine operates in a unique environment characterized by the presence of rotating, tumbling granules alongside atomized oily liquids and powdery materials; these substances tend to deposit and form scale on the inner drum walls and nozzles, thereby compromising long-term operational stability. Mastering correct operating and maintenance procedures, as well as troubleshooting techniques, is essential to ensuring the machine's long-term, efficient, and stable performance and maintaining consistent coating quality.

Standardize operational procedures

(I) Pre-start Inspection: A comprehensive inspection of the equipment must be conducted before every startup. Check the drive system for proper belt tension and gear lubrication. Verify that the spray system pipelines are clear and the nozzles are free of clogs. Ensure the coating agent supply is sufficient and has not deteriorated. Check the interior of the drum for residual material. Inspect the sealing mechanism for integrity. Verify that the hot air system is operating normally.

(II) Correct Startup Sequence: The coating machine must be started following a strict sequence. First, start the coating drum and allow it to rotate empty at the set speed. Second, once the drum is running normally, activate the conveying system to begin feeding material. Third, activate the spraying system only after a stable curtain of material has formed inside the drum. This sequence is crucial: starting the drum before feeding prevents material from piling up in a stationary drum; forming the material curtain before spraying prevents localized material agglomeration caused by excessive coating application.

(III) Operational Monitoring Points: Operators must continuously monitor key parameters during equipment operation. Monitor the drum rotation speed to ensure it remains within the set range (typically 6–15 rpm). Monitor the stability of the coating agent spray rate. Observe the material inside the drum to ensure uniform tumbling and check for sticking or clumping. Listen for any abnormal vibration or noise during operation. Inspect the discharged granules to ensure the coating is uniform.

(IV) Correct Shutdown Sequence: The shutdown sequence is the reverse of the startup sequence. First, stop the material feed. Second, turn off the spraying system. Third, purge any residual coating agent from the pipelines. Fourth, stop the drum rotation only after the material inside has been fully discharged.

Structural composition of the equipment

The coating machine features a scientifically sound and rational structural design, comprising the following core components:

(I) Support Assembly: The rotating section of the machine body is supported by this assembly, which bears significant loads. The support roller frame is fabricated from welded medium-carbon steel plate and channel steel, adhering to strict quality control and specialized manufacturing processes. The support rollers mounted on the frame are made of wear-resistant materials, significantly extending the equipment's service life. The frame utilizes integrated casting technology and features lifting hooks at its four corners to facilitate loading, unloading, and transport.

(II) Drive Assembly: The drive frame is constructed from welded high-quality channel steel. The main motor and speed reducer mounted on the frame are of reliable quality. The motor drives the main shaft via a pulley, V-belt, and speed reducer, thereby operating the machine body. Power transmission between the speed reducer and the main shaft is achieved through a nylon pin coupling.

(III) Large Gear Ring: Fixed to the machine body, this component meshes with the drive pinion to rotate the body. It is made from advanced wear-resistant materials to ensure a longer service life.

(IV) Rolling Tires: Mounted on both sides of the machine body to support the entire structure.

(V) Machine Body: The core component of the coating machine, fabricated from welded medium-carbon steel plate in compliance with rigorous quality control and specific manufacturing standards. The drum features a polypropylene lining or an acid-resistant stainless steel liner. Internally, the drum is equipped with a screen mesh, a heating jacket, and a discharge port; certain models also include high-pressure air supply pipes and hot air ducts to assist the process.

(VI) Auxiliary Systems: These include components such as screw conveyors, mixing tanks, and oil pumps, responsible for the transport, mixing, and supply of the coating agent.

Application scope of the equipment

Coating machines are primarily utilized in the post-processing stage of fertilizer production. In the manufacture of compound and blended fertilizers, they are suitable for applying anti-caking and slow-release coatings to granular products. For organic and bio-organic fertilizers, they facilitate the application of anti-caking coatings and bio-inoculant coatings to granules. In the slow- and controlled-release fertilizer sector, the equipment is used to produce polymer-coated slow/controlled-release fertilizers and sulfur-coated urea. It also supports the production of specialty fertilizers, such as those coated with bio-inoculants or agrochemicals. Additionally, these machines can be used for granule coating applications in industries such as food processing and pharmaceuticals. The equipment accommodates processes requiring both dry powder and liquid coating agents and supports production capacities ranging from 10,000 to 200,000 tons per year.

Types of usable raw materials

The coating machine can process two main categories of raw materials:

Materials to be coated: Various types of 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 (e.g., anti-caking powder, talc powder, bentonite, dispersing powders); liquids (e.g., coating oil, liquid anti-caking agents, paraffin-based coating agents, PVA-based coating agents, polymer emulsions); slow-release materials (e.g., sulfur, resin, tung oil, polyurethane); and functional additives (e.g., colorants, microbial agents, plant nutrient solutions, trace elements).

The working principle of the equipment

The coating machine operates on the following principle: the main motor drives a belt and pulley system, transmitting power through a speed reducer to the drive shaft; a split gear mounted on the drive shaft meshes with a large ring gear fixed to the machine body, enabling counter-rotation. Material enters from the feed end, mixes with powder or liquid inside the rotating drum, and subsequently discharges from the outlet.

The specific operational process comprises the following stages:

Feeding and Distribution Stage: Granular fertilizer enters the higher end of the inclined, rotating drum via the feeding mechanism. As the drum rotates at a steady speed, internal lifting flights continuously scoop up and scatter the granules, creating a uniform curtain of material within the drum.

Spraying and Coating Stage: Coating material is evenly applied to the surfaces of the tumbling granules using either a spray system (for liquid coating) or a powder applicator (for powder coating). The action of the lifting flights causes the material to tumble and mix continuously, ensuring the coating agent uniformly encapsulates each granule.

Fluidization and Curing Stage: As the drum rotates, the fertilizer granules are thoroughly mixed with and coated by the coating agent while being conveyed toward the discharge end. An induced-draft fan accelerates airflow within the drum; some models are equipped with high-pressure air lines and hot-air ducts to assist with drying and curing.

Discharge Stage: The fully coated granules are discharged from the outlet.

Equipment operating instructions

(I) Installation and Commissioning: Upon arrival at the site, install the equipment in coordination with the process flow, marking the required elevation and horizontal positioning. The unit is installed at an incline, typically between 2 and 5 degrees (adjustable according to user requirements). Wedge-shaped shims placed between the machinery bases and the foundation must not exceed 30–35 mm in thickness; use these shims to adjust the base heights to achieve the required 5-degree tilt. Once the bases are properly adjusted, place the cylinder onto the support frame and adjust the support rollers. Install the drive assembly. After verifying the proper alignment of the support rollers, drive mechanism, and cylinder, pour the concrete foundation; allow 8–10 days for the concrete to cure before commencing a no-load test run.

(II) Pre-start Checks: Check the drive system belt tension and gear lubrication. Ensure the spray system pipelines are clear and nozzles are free of clogs. Verify sufficient coating agent supply. Check the cylinder interior for residual material. Inspect the sealing devices for integrity. Ensure the grounding wire is properly connected.

(III) Operation: Start the coating machine cylinder first, then activate the feeding system, and finally start the spraying system. During operation, monitor the drum rotation speed, coating agent spray volume, and the uniformity of the coating on the discharged granules. While the machine is running, do not crawl underneath the unit, perform internal inspections or repairs, or remove protective guards. Do not touch the motor or electrical wiring without wearing insulated gloves.

(IV) Shutdown Procedure: Stop feeding first; shut down the machine only after the cylinder has been emptied of material and the spraying system has been turned off with residual fluid drained from the lines. Perform cleaning and maintenance after shutdown.