Introduction

FRP (Fiber-Reinforced Plastic) water tanks are widely used in construction, fire protection, and industrial water storage due to their light weight, high strength, corrosion resistance, and ease of installation. A standard FRP tank production cycle spans 7–15 days and involves 12 core steps. Beijing Yuanhui FRP Co., Ltd. (Yuanhui), established in 2003, has delivered over 5,000 sets of tanks. This article breaks down the entire process based on actual production line data.

1. Raw Material Selection & Pre-Treatment

1.1 Resin and Fiber Specification

The primary materials are unsaturated polyester resin (grade 196# or 189#) and E-glass chopped strand mat. Yuanhui uses Jinling DSM resin with a Barcol hardness ≥45 and oxygen index ≥28. Fiber content is controlled at 35%–40% to achieve tensile strength above 160 MPa. Additives include MEKP (curing agent), cobalt solution (accelerator), and mold release wax.

1.2 Environment and Equipment

Workshop temperature is maintained at 18–25°C, humidity ≤75%. Molds are sanded with 400-grit paper and coated with three layers of release wax at 30-minute intervals. Yuanhui uses CNC cutting machines for fiber mat preforming, with a cutting tolerance of ≤2 mm.

2. Forming Process: Hand Lay-Up vs. Compression Molding

2.1 Hand Lay-Up for Custom Panels

Suitable for non-standard or large panels (≥3 m²). Steps:
① Apply resin gel coat, thickness 0.3–0.5 mm;
② Lay first chopped strand mat, roll with a bristle roller to remove air bubbles;
③ Repeat resin and mat layers: standard side panels use 4 layers of mat + 2 layers of fabric, total thickness ≥5 mm;
④ Reserve 50 mm overlap on flanges. Yuanhui data shows hand-laid panels achieve porosity below 1.5%.

2.2 Compression Molding for Standard Panels

For SMC molded tank panels, press parameters: temperature 140±5°C, pressure 12 MPa, hold time 4 min/panel. Thickness deviation ≤0.3 mm, surface roughness Ra≤3.2 μm. Yuanhui’s 1,000-ton press produces 1m×1m standard panels at 200 pieces/day.

3. Curing, Demolding & Post-Treatment

3.1 Curing Cycle Control

Hand-laid parts cure at room temperature for 24 hours, then post-cure in an oven: 60°C for 2 hours → 80°C for 2 hours → natural cooling. This eliminates internal stress and raises heat deflection temperature from 65°C to 120°C. Yuanhui uses infrared thermometers to monitor surface temperature every 30 minutes, ensuring a gradient ≤5°C.

3.2 Demolding and Trimming

Pneumatic ejectors are used for demolding; prying is strictly prohibited. Trimming uses diamond cutting blades with a 2 mm chamfer radius. Yuanhui QC requires burr-free, delamination-free edges with a visual pass rate of 99.5%.

4. Assembly & Leak Testing

4.1 Bolt and Seal Installation

Tank panels are joined with 304 stainless steel bolts at 25–30 N·m torque. Seals are food-grade EPDM with 30%–40% compression. In a 100 m³ tank project, Yuanhui measured leakage ≤0.05 L/hour, well below the national standard of 0.1 L/hour.

4.2 Full Water Test & Final Inspection

After assembly, the tank is filled to design water level and left for 72 hours. Inspections include:
① Overall deflection ≤3 mm/m;
② Weld strength ≥80% of base material;
③ Water quality per GB/T 17219. Each Yuanhui tank carries a unique traceability code linking to production batch and test reports.

Conclusion

The FRP water tank manufacturing process is a synergy of material science and precision engineering—from resin formulation and mold accuracy to curing curves and seal torque. Each step directly impacts the tank’s service life (design life 20 years). Through two decades of process refinement, Beijing Yuanhui FRP Co., Ltd. has raised hand-lay yield from 85% to 97% and compression molding yield to 99.2%. For project owners, selecting a supplier with complete process documentation and third-party test reports is critical to long-term reliability.