Equipment Introduction
The coating machine, also known as a rotary drum coating machine, is a core post-processing piece of equipment in granular fertilizer production lines. It physically coats fertilizer granules with a uniform protective film or functional layer, preventing clumping, improving appearance, extending fertilizer effectiveness, and reducing nutrient loss. A complete set of equipment typically consists of a screw conveyor, mixing tank, oil pump, main unit, and induced draft fan (or air compressor), and can employ either powder coating or liquid coating processes.
The main unit of this equipment uses a polypropylene lining or acid-resistant stainless steel, providing excellent corrosion resistance and adapting to the complex chemical environment of the fertilizer industry. Its internal structure is specially designed according to process requirements, making it a highly efficient equipment specifically for compound fertilizers.
Equipment Structure
The entire machine can be divided into five core parts, each working in concert to ensure a continuous and stable coating process:
1. Support Frame: The support frame supports the rotating parts of the entire machine body and bears significant force. The support roller frame is welded from medium carbon steel plate and channel steel, and undergoes strict quality control. The support rollers are made of high-quality corrosion-resistant and wear-resistant materials, and the support roller frame uses integrated casting technology. Lifting hooks are located at the four corners for easy loading, unloading, and transportation.
2. Transmission Frame: The transmission frame is welded from channel steel. Both the main motor and the reducer are reliable products conforming to ISO standards. The motor drives the reducer via pulleys and V-belts, and then transmits power to the main shaft via nylon pin couplings or cross couplings, ensuring smooth transmission and easy maintenance.
3. Large Gear Ring: Fixed to the machine body, it meshes with the split pinion on the drive shaft. Made of high-tech wear-resistant materials, it drives the cylinder to rotate in opposite directions and is a crucial link in the overall power transmission of the machine. 4. Roller Belt (Track): Fixed to both sides of the machine body, mounted on support rollers, it supports the entire rotating cylinder and evenly distributes the cylinder's weight to the support frame.
5. Machine Body: The cylinder, welded from high-quality carbon steel plates, is the core working chamber for material coating. The inner wall of the cylinder is typically equipped with lifting plates (elevating plates) to continuously lift and scatter the particles, ensuring full contact with the coating agent. Simultaneously, the cylinder has a slight inclination angle (usually 2.5°) to allow the material to move slowly from the feed end to the discharge end.
In addition, the complete set of equipment is also equipped with:
1) Screw conveyor: for quantitatively conveying particles to be coated;
2) Mixing tank/oil pump: for preparing and conveying liquid coating agent;
3) Spray system: including adjustable spray bars and atomizing nozzles to evenly spray the coating agent in a fine mist;
4) Exhaust fan: to accelerate airflow within the cylinder, promoting solvent evaporation and coating layer solidification.
Raw Materials for the Equipment
1. Materials to be Coated
1) Form: Dry granular fertilizer (particle size typically 2–6 mm), such as compound fertilizer granules, organic fertilizer granules, urea granules, etc.
2) Moisture Content: Before entering the coating machine, ensure the granules are fully dry (moisture content generally <10%). Wet granules will severely affect the coating effect and the adhesion of the coating layer.
2. Coating Materials
Depending on the process objectives, the following materials may be selected:
| Coating Type | Common Materials | Function |
|---|---|---|
| Anti‑caking Agent | Talc powder, zeolite powder, kaolin, diatomaceous earth | Isolate moisture and prevent particle adhesion |
| Liquid Coating | Paraffin wax, grease, vegetable oil, molasses, resin | Form hydrophobic protective film and improve surface gloss |
| Slow‑release / Controlled‑release Material | Sulfur, polymer, polyurethane, inorganic salt | Control nutrient release rate |
| Functional Additive | Trace elements, beneficial bacterial agents, colorants | Supplement nutrition, distinguish product types and enhance functions |
Working Principle of the Equipment
The coating machine operates on a combination of mechanical tumbling and uniform spraying:
1. Cylinder Rotation and Material Tumbling: The main motor drives the belt and pulley, transmitting power to the drive shaft via a reducer. A split pinion on the drive shaft meshes with a large gear ring fixed to the machine body, causing the machine to rotate. Material is added from the feed end; as the cylinder rotates, internal lifting plates continuously lift and scatter the particles, forming a uniform material curtain.
2. Coating Agent Application: Liquid Coating Process: Coating agents (such as paraffin wax, resin, coating oil, etc.) are evenly sprayed in a mist form onto the surface of the tumbling particles through atomizing nozzles. The nozzles are typically installed at a certain angle to the cylinder axis to ensure complete coverage of the particle flow. A pump draws the coating agent from the storage tank and delivers it through pipelines to the nozzles for atomization and spraying.
Powder coating process: Powdered coating agents (such as talc, diatomaceous earth, etc.) are evenly spread onto the surface of granules coated with liquid coating agents using a powder coating machine, forming a powder-liquid composite coating.
3. Uniform coating: Granules are tumbled inside the drum while being coated with the coating agent, ensuring each granule is evenly coated with a film. The coating thickness can be precisely adjusted by spraying time and flow rate. Under specific temperature conditions, the coating agent rapidly solidifies or forms a film on the granule surface.
4. Finished product discharge: Coated granules flow out from the discharge port. The equipment can continuously feed and discharge, enabling large-scale continuous production.
Applications of the Equipment
Coating machines have a wide range of applications, primarily concentrated in the fertilizer production industry:
1. Organic Fertilizer Production (Core Application): After organic fertilizer granulation, the coating machine performs surface treatment on the granules. Coated organic fertilizer granules have a brighter appearance, better anti-caking effect, and a longer shelf life. Widely used in the fine processing of commercial organic fertilizers and bio-organic fertilizers.
2. Compound Fertilizer and Blended Fertilizer Production: Used for anti-caking coating treatment of compound fertilizer and blended fertilizer granules. Effectively prevents compound fertilizers from clumping due to storage or moisture absorption.
3. BB Fertilizer (Blended Fertilizer) Production: One of the commonly used supporting equipment at the end of the BB fertilizer production line, used to improve the quality of the finished product.
4. Slow-Release and Controlled-Release Fertilizer Production: Achieves slow-release or controlled-release functions of fertilizer nutrients by coating with slow-release coating agents (such as resin, sulfur, etc.).
5. Functional Fertilizer Production: Micronutrients, functional microbial agents, humic acid, and other functional components can be added during the coating process to increase the added value of the fertilizer. 6. Other industries: Coating machines can also be used for surface treatment of other powdery and granular materials.
Common Faults, Causes, and Standardized Solutions
| Fault Phenomenon | Possible Causes | Solutions |
|---|---|---|
| Riding Ring Slippage | Loose riding‑ring end‑face clamping; insufficient clamping force in radial direction | Clamp riding ring and end‑face flange; use shims for even clamping (avoid excessive clamping which causes unit vibration) |
| Unit Offset | Worn supporting roller; worn riding ring | Adjust or replace supporting roller according to wear degree; repair or replace new riding ring |
| Gear Offset / Wear | Partial wear of pinion; loose connection flange between big gear and drum shell | Re‑install pinion reversely (replace if both sides worn); calibrate connection of big gear and drum shell |
| Drum Vibration | Loose bolts for supporting‑roller base; serious riding‑ring wear | Tighten connecting bolts to place supporting roller in correct position; lathe‑repair or replace riding ring according to wear condition |
| Uneven Coating | Nozzle blockage or poor atomization; improper drum speed; excessive material moisture content | Clean or replace nozzle; adjust drum speed to rated value; ensure dry feeding particles |
| Poor Discharge | Material accumulation inside cylinder; discharge port blockage | Clear accumulated material inside cylinder; unclog discharge port; check whether feeding capacity is over‑loaded |
| Bearing Overheating | Insufficient grease; bearing wear; drum out‑of‑level causing overload | Add grease periodically; replace worn bearing; re‑calibrate drum level and parallelism |
| Model | Barrel | Capacity | Power | |||
| Internal Diameter | Length | Inclination | Rotation speed | |||
| mm | mm | mm | ° | r/min | t/h | kW |
| BM1200×4000 | 1200 | 4000 | 3 | 14 | 1-5 | 5.5 |
| BM1400×4000 | 1400 | 4000 | 3 | 13 | 5~7 | 7.5 |
| BM1600×6000 | 1600 | 6000 | 3 | 12 | 7~15 | 11 |
| BM1800×8000 | 1800 | 8000 | 3 | 12 | 15~30 | 15 |
