Project Background:
With the ongoing upgrade and improvement of municipal infrastructure across China, manhole covers and grates—critical components of urban drainage systems—are facing increasing demands for corrosion resistance, aesthetic appearance, and product consistency. This project was commissioned by a large cast iron product manufacturer based in East China. The client regularly undertakes municipal orders and has stringent requirements for production capacity, changeover efficiency, and product uniformity. The project's objective was to establish a highly automated, fast color-changing, energy-saving, and environmentally friendly powder coating line within the existing factory, capable of coating over 400,000 manhole covers and grates annually.
Project Overview:
Commissioning Date: April 2024
Total Line Length: Approximately 70 meters
Floor Area: Around 750㎡
Annual Design Capacity: About 420,000 standard manhole covers and grates (each approx. 600×400mm)
Product Characteristics: Heavy-duty cast iron parts requiring thick-film anti-corrosion coating, continuous batch production, and diverse color requirements for different regions
Process Flow and Core Equipment Configuration:
Automatic Powder Coating Booth
Dimensions: 6.8 meters long, dual-side door structure
Equipped with 8 automatic electrostatic spray guns mounted on a reciprocating tracking system
Interior features anti-static coating and dust-removal negative pressure balance to maintain clean air
Auxiliary function: reserved window for manual touch-up to meet the needs of irregular parts
Control system supports automatic recognition of workpiece type and calls corresponding spray program
Large Cyclone + Secondary Recovery System
Primary cyclone recovery efficiency: ≥96.8%
Secondary unit: fully enclosed filter cartridge with automatic reverse-blow cleaning
Recovered powder is automatically sieved and stored to avoid cross-color contamination
Dust emission concentration controlled within 15mg/m³, in compliance with GB16297 standards
Fast Color Change System
Multi-color switching module supports up to 6 powders simultaneously, with one-button color change execution
Cleaning process: electrostatic guns, powder feed lines, and booth can be cleaned within 6 minutes
Special design of “short pipelines + independent powder hoppers” reduces color residue
Effectively enhances responsiveness to diverse municipal orders in different regions (e.g., blue, black, gray anti-rust coatings)
Bridge-Type Curing Oven
Oven design: tiered upper-lower layout, total length 13.2 meters, saving floor space
Temperature zones: preheating – curing – cooling, supporting curve-based temperature control
Temperature control accuracy ±2℃, with uniform air duct distribution ensuring consistent curing of thick cast iron coatings
Energy-saving design uses high-density insulation cotton and variable frequency hot air system, saving about 18% energy compared to traditional ovens
C-Shaped Automatic Conveyor Line
Conveyor structure: dual-rail closed-loop C-shaped track, with high-temperature alloy hangers for heavy parts (30kg each)
Hanger spacing: standard 1.2 meters, adjustable for different product sizes
Conveyor speed: adjustable from 1.5 to 3.5m/min, supports synchronized process operation
Full line is PLC-controlled with real-time monitoring of operational status, energy consumption, and efficiency
Project Results:
Coating thickness stabilized at 80–100μm, with adhesion passing GB/T 9286 cross-cut test at grade 0
Achieved daily switch among three colors with continuous batch production, increasing line efficiency by over 40%
Powder waste in the spray booth reduced by nearly 30%, saving about 12 tons of powder annually
Daily production capacity consistently reaches 1,800 units, meeting simultaneous municipal project supply demands
This production line has become the most critical coating stage in the client’s manufacturing system. It not only significantly improves product appearance and consistency but also enhances overall production efficiency and responsiveness to orders. The client has now begun planning a second similar line to support newly acquired sanitation equipment project orders.
