Structure and Operation Process of a 4m×10m Large-Scale Spray Booth

As a core piece of equipment for the surface coating of industrial products such as automobiles, construction machinery, and large components, the 4m×10m large-scale spray booth must have a structural design that balances ventilation efficiency, paint mist capture capability, operational safety, and coating quality stability. Its operation process follows the standardized logic of "pre-treatment - spraying - drying - finishing" to ensure both improved coating results and production efficiency. The following is a detailed analysis of its core structure and complete operation process.

I. Core Structure of the 4m×10m Large-Scale Spray Booth

Designed around the core concept of "closed space + high-efficiency ventilation + precise temperature control", this spray booth consists of six major modules: the main frame, air purification system, paint mist treatment system, heating and drying system, lighting system, and control system. These components work together to create a stable coating environment.

1. Main Frame: Foundation for Load-Bearing and Sealing

The main frame is welded from hot-rolled section steel (Q235B), with 0.8mm-thick color steel plates for external cladding and 1.2mm-thick fire-resistant rock wool boards attached internally. This design not only ensures structural strength (capable of withstanding a wind pressure of ≥0.5kPa) but also achieves excellent thermal insulation and soundproofing effects.The internal dimensions of the spray booth are 4m (width) × 10m (length) × 3.5m (height), accommodating the entry, exit, and flipping operations of large workpieces such as truck cabs and construction machinery components. A double-opening electric rolling door is installed at the entrance/exit, with a door opening size of 3.8m × 3.2m. Sealing strips are fitted to ensure airtightness, preventing paint mist leakage and dust ingress.The floor is made of 20mm-thick epoxy resin, with an anti-slip surface treatment. A 50mm-deep drainage groove is arranged around the perimeter to facilitate the collection and discharge of paint residue and wastewater.

2. Air Purification System: Creating a Clean Coating Environment

The air purification system adopts a three-stage filtration mode ("primary filtration - intermediate filtration - high-efficiency filtration") to ensure the dust content of the air entering the spray booth is ≤0.5mg/m³, preventing dust from affecting coating surface quality.

• Air Supply System: Four sets of air supply fans (with a total air volume of 80,000m³/h and air pressure of 1,200Pa) are installed on both sides of the spray booth’s top. After large dust particles are removed by the primary air filter (Grade G4, filtration accuracy of 5μm) at the top of the booth, the air enters the intermediate filter bags (Grade F8, filtration accuracy of 1μm) for secondary filtration. Finally, it passes through high-efficiency air filters (Grade H13, filtration accuracy of 0.3μm) and is uniformly delivered into the spray booth in a laminar flow pattern. The air velocity is controlled at 0.3-0.5m/s to avoid paint mist diffusion caused by airflow disturbance.

• Air Exhaust System: Four sets of exhaust fans are installed on both sides of the spray booth’s bottom, forming an "upper supply and lower exhaust" airflow pattern with the air supply system. This ensures paint mist settles downward under the combined action of gravity and airflow, preventing it from adhering to the workpiece surface. After being purified by the paint mist treatment system, the exhaust air is discharged outdoors through the exhaust duct.

3. Paint Mist Treatment System: Key to Environmental Protection and Compliance

This system uses a combined "water curtain capture + activated carbon adsorption" treatment method, achieving a paint mist purification efficiency of ≥98% and meeting the requirements of the Integrated Emission Standard for Air Pollutants (GB 16297-1996).

• Water Curtain Capture Device: A U-shaped water curtain tank is installed at the bottom of the spray booth, containing a dedicated paint mist coagulant solution (concentration: 0.5%-1%). A water pump circulates the solution to form a uniform 10-15mm-thick water curtain in the tank. When paint mist enters the water curtain area with the airflow, it is captured by the water curtain and flows into the paint residue sedimentation tank. After sedimentation and filtration, the paint residue is cleaned regularly, and the wastewater is recycled to reduce water waste.

• Activated Carbon Adsorption Device: The exhaust air treated by the water curtain still contains small amounts of organic waste gas (e.g., toluene, xylene). It needs to pass through an adsorption tank filled with granular activated carbon (iodine value ≥1,000mg/g). After the organic waste gas is adsorbed and purified by the activated carbon, the purified gas is discharged through a 15m-high exhaust stack. The activated carbon is replaced every 3-6 months to ensure adsorption efficiency.

4. Heating and Drying System: Improving Coating Curing Efficiency

The system adopts an "electric heating + hot air circulation" mode, supporting switching between spraying and drying operating conditions to meet the curing requirements of different coatings.The heating elements are stainless steel electric heating tubes with a total power of 120kW, controlled independently in four groups. Temperature sensors monitor the indoor temperature in real time to achieve precise temperature control (temperature control accuracy: ±2℃). During drying, the air supply fan filters the outside air and sends it to the heating chamber, where it is heated to the set temperature (adjustable between 50-80℃) by the electric heating tubes. The heated air is then uniformly delivered into the spray booth through the hot air circulation duct, with a circulation air volume of 60,000m³/h. This ensures uniform indoor temperature, enabling rapid curing of the coating on the workpiece surface and shortening the production cycle.

5. Lighting and Control Systems: Ensuring Operational Convenience and Safety

• Lighting System: Forty sets of explosion-proof LED lights (each with a power of 36W and a color temperature of 5,000K) are installed on the top and both sides of the spray booth. Designed with anti-glare features, these lights ensure an indoor illuminance of ≥800lux without shadow dead zones, allowing operators to observe coating effects easily. Meanwhile, the explosion-proof rating reaches Ex d IIB T4, meeting safety requirements for flammable and explosive environments.

• Control System: It adopts a PLC programmable controller + 10-inch color touchscreen control mode, integrating functions such as fan start/stop, temperature adjustment, lighting control, and fault alarm. Operators can set operating parameters for spraying, drying, and other conditions via the touchscreen, and the system displays real-time data such as indoor temperature, air velocity, and filter resistance. In case of fan failure, excessive temperature, filter blockage, or other issues, the system automatically triggers an audible and visual alarm and cuts off the power supply to relevant equipment to ensure operational safety. Additionally, the system is equipped with emergency stop buttons, fire extinguishers, and other safety facilities to further enhance operational safety.

II. Standardized Operation Process of the 4m×10m Large-Scale Spray Booth

The operation process of the spray booth strictly follows the sequence of "workpiece pre-treatment - equipment inspection - spraying operation - drying and curing - workpiece removal - equipment cleaning" to ensure coating quality and production safety. The operation cycle for a single batch of workpieces (e.g., large truck cabs) is approximately 4-6 hours.

1. Workpiece Pre-Treatment: Laying the Foundation for Quality Coating

Before entering the spray booth, the workpiece undergoes surface pre-treatment to remove oil, rust, dust, and other impurities, preventing them from affecting coating adhesion. The specific steps are as follows:① Rinse the workpiece surface with a high-pressure water gun (pressure: 5-8MPa) to remove floating dust and loose impurities;② Soak or spray the workpiece with a dedicated degreaser (e.g., alkaline degreaser) and let it stand at room temperature for 10-15 minutes to remove surface oil;③ Phosphatize the workpiece surface with a phosphating solution (temperature: 35-45℃, time: 8-12 minutes) to form a uniform phosphating film and enhance coating adhesion;④ Rinse the residual chemicals on the workpiece surface with clean water, then send it to a drying chamber (temperature: 80-100℃) for drying to ensure the moisture content of the workpiece surface is ≤0.5%.Pre-treated workpieces must enter the spray booth within 2 hours to avoid secondary pollution.

2. Equipment Inspection and Preparation: Ensuring Stable System Operation

Before the workpiece enters, operators conduct a comprehensive inspection of the spray booth equipment:① Check whether the power connections of the air supply/exhaust fans, heating system, lighting system, and other equipment are normal. Start the fans to test the stability of the airflow pattern and whether the air velocity meets the requirement of 0.3-0.5m/s;② Check the resistance of the primary, intermediate, and high-efficiency filters. If the resistance exceeds the set value (primary ≥150Pa, intermediate ≥300Pa, high-efficiency ≥500Pa), replace the filters promptly;③ Check the concentration and liquid level of the paint mist coagulant solution in the water curtain tank. Replenish the solution if insufficient to ensure a stable and uniform water curtain;④ Check the adsorption status of the activated carbon adsorption tank. Replace the activated carbon in advance if it is saturated;⑤ Start the control system, set the spraying operating parameters (indoor temperature: 20-25℃, humidity: 40%-60%), and prepare for the workpiece to enter once the indoor environment stabilizes.

3. Workpiece Entry and Positioning: Ensuring Operational Convenience

Use an electric hoist or forklift to move the pre-treated workpiece into the spray booth. Fix the workpiece on a rotatable tooling rack according to its size and coating requirements, ensuring all surfaces of the workpiece can be uniformly sprayed. The load-bearing capacity of the tooling rack must be ≥1.5 times the weight of the workpiece. After positioning the workpiece, close the electric rolling door of the spray booth to ensure airtightness and prevent paint mist leakage.

4. Spraying Operation: Precisely Controlling Coating Quality

The spraying operation combines "manual spraying + high-pressure airless spraying", with spraying parameters adjusted according to the coating type (e.g., acrylic paint, polyurethane paint). The specific steps are as follows:① Operators put on anti-static work clothes, gas masks, safety goggles, and other protective gear, and enter the operating area inside the spray booth;② Adjust the spraying equipment: set the pressure of the high-pressure airless sprayer to 15-20MPa, and select the nozzle diameter based on the coating viscosity (usually 0.4-0.8mm);③ Spray in the order of "top to bottom, left to right, inside to outside", with the spraying distance controlled at 20-30cm and a uniform spraying thickness (wet film thickness: 80-120μm) to avoid defects such as sagging and pinholes;④ Use a manual spray gun to touch up corners, gaps, and other parts of the workpiece to ensure full coating coverage;⑤ After spraying a single coating layer, let it stand for 5-10 minutes (leveling time) as required by the coating, then apply the next layer. Usually, 2-3 layers are applied, with a total dry film thickness of 100-150μm.

5. Drying and Curing: Accelerating Coating Film Formation

After completing all coating layers, operators exit the spray booth and close the operation door. Switch to the drying condition via the control system:① Set the drying temperature (adjusted according to the coating type, e.g., 50-60℃ for acrylic paint, 60-80℃ for polyurethane paint) and drying time (30-60 minutes);② Start the heating system and hot air circulation system to ensure the indoor temperature rises uniformly to the set value and remains stable;③ During drying, the system monitors the indoor temperature and humidity in real time. If abnormal temperature occurs, it automatically adjusts the heating power;④ After the drying time ends, turn off the heating system and keep the air supply/exhaust fans running for 10-15 minutes to cool the indoor temperature to room temperature, preventing coating cracking on the workpiece due to excessive temperature differences.

6. Workpiece Removal and Quality Inspection

After drying, open the electric rolling door of the spray booth and move the workpiece out using tooling equipment, then send it to the quality inspection area:① Inspect the appearance quality of the coating on the workpiece surface, ensuring no sagging, pinholes, bubbles, color differences, or other defects;② Use a coating thickness gauge to measure the dry film thickness, ensuring it meets technical requirements;③ Test the coating adhesion using the cross-cut method (adhesion grade ≥Grade 1);④ Qualified workpieces are sent to the next process, while unqualified ones undergo rework such as sanding and touch-up spraying.

7. Equipment Cleaning and Maintenance: Extending Equipment Service Life

After completing each batch of operations, conduct comprehensive cleaning and maintenance of the spray booth:① Turn off the power supply of all equipment, clean the residual coating in the spraying equipment, and rinse the spray gun, paint delivery pipeline, etc., with a dedicated solvent (e.g., banana oil, thinner) to prevent coating solidification and blockage;② Clean the paint residue in the water curtain tank, fish out the settled paint residue for proper disposal, and replenish the tank with new paint mist coagulant solution;③ Wipe the color steel plates and glass inside the spray booth to remove adhered paint mist;④ Check the operating status of all equipment, record equipment parameters and maintenance conditions, and prepare for the next operation.

III. Key Precautions

• Smoking and open flames are strictly prohibited inside the spray booth. Operators must receive professional training and be familiar with equipment operation and safety procedures.

• Flammable and explosive materials such as coatings and solvents must be stored in a dedicated hazardous materials warehouse. Large quantities of such materials are not allowed to be stored in the spray booth.

• Conduct regular maintenance of the equipment, focusing on checking vulnerable components such as filters, activated carbon, and electric heating tubes to ensure long-term stable operation of the equipment.

• In case of paint mist leakage, equipment failure, or other issues during operation, stop the operation immediately and activate emergency response measures to ensure the safety of personnel and equipment.

In summary, through its scientific structural design and standardized operation process, the 4m×10m large-scale spray booth can not only meet the coating needs of large workpieces but also ensure coating quality, operational safety, and environmental compliance. It is one of the core pieces of equipment in the industrial coating field.

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