Introduction

FRP (Fiberglass Reinforced Plastic) water tanks are widely used in construction, municipal, and chemical industries due to their lightweight, high strength, corrosion resistance, and long service life. The production process directly determines mechanical performance and durability. Beijing Yuanhui FRP Co., Ltd., with over a decade of experience, provides insights into the complete production flow, focusing on hand lay-up and spray-up molding techniques, along with key quality control points.

1. Raw Material Selection and Formulation

1.1 Reinforcement and Resin System

E-glass fiber mat (300-600 g/m²) and woven roving are standard reinforcements. The matrix resin is typically isophthalic unsaturated polyester or vinyl ester resin for balanced water resistance and cost. Beijing Yuanhui uses a standard ratio of resin:MEKP = 100:1.5-2.0 (by weight) with 0.2-0.5% cobalt promoter. Filler content (calcium carbonate, talc) is limited to 15% to avoid strength reduction; exceeding this caused delamination in a municipal project, where filler reached 22% and interlaminar shear strength dropped below 10 MPa.

2. Mold Preparation

Steel or FRP molds are used with surface roughness Ra ≤3.2 μm. Process: clean mold → apply release agent (3-4 layers, 15-minute intervals) → inspect. Beijing Yuanhui monitors mold temperature at 25±2°C using infrared thermometers. Insufficient release agent (<3 layers) increases demolding force by 30%, risking product damage.

3. Molding Processes: Hand Lay-Up vs. Spray-Up

3.1 Hand Lay-Up

Suitable for small batches or complex shapes. Steps: gel coat application (0.3-0.5 mm), fiber mat lay-up with resin impregnation (void content <2%), layer-by-layer buildup (0.5-1.0 mm per layer). For a 0.6 MPa tank, 12-15 layers are needed. Beijing Yuanhui reports fiber content of 30-35% and flexural strength ≥200 MPa for hand lay-up products.

3.2 Spray-Up Molding

Ideal for mass production, boosting efficiency by 40%. Chopped glass fibers (25-50 mm) and resin are sprayed simultaneously. Key parameters: gun pressure 0.4-0.6 MPa, distance 300-400 mm, resin-to-glass ratio 2.5:1. In 2023, Beijing Yuanhui produced 1,000 standard tanks for an industrial park using spray-up, reducing cycle time from 4 to 2.5 hours per tank and scrap rate from 5% to 1.2%.

4. Curing, Demolding, and Post-Processing

4.1 Curing Conditions

Room-temperature curing takes 24 hours at 25°C; heat curing at 60-80°C for 4-6 hours. Beijing Yuanhui uses a staged process: 2-hour precuring at ambient, then 50°C for 2 hours, followed by cooling. This increases heat deflection temperature by 8-10°C.

4.2 Demolding and Inspection

Demolding uses pneumatic ejectors and wedges to avoid damage. Inspection covers appearance (no voids, cracks, white spots), dimensional tolerance (±2 mm), Barcol hardness (≥35), and hydrostatic test (1.5× design pressure for 30 min). Beijing Yuanhui maintains a pass rate above 99.2%.

4.3 Post-Treatment and Assembly

Trimming, drilling (diamond bits), and fitting flanges with EPDM gaskets. Each tank has a production record with ≥10-year traceability.

Conclusion

FRP water tank production requires strict control over material formulation, mold precision, molding parameters, and curing. Hand lay-up suits custom products, while spray-up excels in efficiency and consistency. Beijing Yuanhui FRP Co., Ltd. achieves stable quality with an annual output of 5,000 tanks through standardized processes. Automation and online monitoring are the next frontiers for industry advancement.