Introduction

FRP (Fiberglass Reinforced Plastic) water tanks are widely used in construction, municipal, and fire protection sectors due to their light weight, high strength, corrosion resistance, and long service life. Beijing Yuanhui FRP Co., Ltd., with over 20 years of production experience and an annual output exceeding 3,000 units, provides a reliable benchmark for process analysis. This article breaks down the entire production workflow based on real manufacturing data.

1. Raw Material Preparation and Formulation

1.1 Resin System Selection

For standard water tanks, 196# orthophthalic unsaturated polyester resin is common. For potable water tanks, RF-1008 isophthalic resin with styrene emission below 3.5% is mandatory. Beijing Yuanhui uses DSM-brand resin to ensure batch consistency.

1.2 Glass Fiber Reinforcement

E-glass chopped strand mat (450 g/m²) and continuous filament roving (2400 tex) are used. Fiber content is controlled at 35%–45% by weight. Below 30% weakens mechanical strength; above 50% causes poor resin wet-out.

1.3 Additive Ratios

MEKP catalyst: 1.5%–2.0%; cobalt naphthenate accelerator: 0.3%–0.5%. Below 15°C ambient temperature, accelerator is increased to 0.6%. In summer, 0.1% inhibitor is added to prevent premature gelation.

2. Mold Preparation and Molding Process

2.1 Mold Surface Treatment

Semi-permanent PVA release agent is applied in 3 coats (20 min intervals), followed by a gel coat layer of 0.4–0.6 mm thickness. Spray gun pressure: 0.5 MPa, fan angle: 45°. At Beijing Yuanhui, gel coat thickness is monitored with a wet-film gauge.

2.2 Hand Lay-Up vs. Spray-Up

Bottom and side panels use hand lay-up: one layer of mat, resin impregnated, air bubbles removed, repeated to 3 mm per layer. Roof panels and stiffeners use spray-up, boosting efficiency by 40%. Inter-layer time must not exceed 30 minutes to avoid delamination.

2.3 Curing and Demolding

Room-temperature curing for 24 hours, followed by post-cure at 50°C for 4 hours and 80°C for 2 hours. Pneumatic ejectors apply demolding force ≤5 kN. Shrinkage after demolding: 0.2%–0.4%, compliant with GB/T 8237.

3. Assembly and Sealing

3.1 Panel Cutting and Drilling

CNC waterjet cutting with accuracy ±0.5 mm. Flange width: 15 mm; bolt hole spacing: 200 mm. In a recent 200 m³ fire tank project, 48 panels were cut with 100% hole alignment.

3.2 EPDM Gasket Installation

Compression ratio: 30%–40%. Over-compression causes seal failure. Recommended torque: M10 bolts at 25 N·m, M12 at 35 N·m. Beijing Yuanhui uses EPDM gaskets rated from -40°C to 120°C.

3.3 Internal Bracing

For tanks taller than 2 m, stainless steel 304 or FRP tie rods are installed at 1.2 m spacing. Cross points are wrapped with roving. Hydrostatic test: fill with water, hold 72 hours; deflection ≤5 mm passes.

4. Quality Inspection and Shipment Standards

4.1 Physical Property Testing

Every batch is tested for Barcol hardness (≥40), resin content by burn-off (35%±3%), and flexural strength (≥150 MPa). Beijing Yuanhui applies internal standards 15% above national requirements.

4.2 Leak Testing

Pneumatic test at 0.1 MPa for 30 min, pressure drop ≤0.01 MPa. Hydrostatic test at 1.5× working pressure. Example: a tank with 0.3 MPa working pressure passed 0.45 MPa test with zero leakage for 2 hours.

4.3 Coating and Packaging

Inner surface: two coats of food-grade resin, total dry film thickness ≥0.3 mm. Outer surface: polyurethane topcoat. Wooden crate with foam padding and corner protectors. Transport damage rate: below 0.5%.

Conclusion

FRP water tank production integrates material science, mold engineering, and quality control. Beijing Yuanhui FRP Co., Ltd. ensures a service life exceeding 15 years through precise resin formulation, molding parameters, assembly accuracy, and rigorous testing. Buyers should request batch test reports and verify resin brand, fiber content, and sealing procedures.