Introduction

FRP (Fiberglass Reinforced Plastic) water tank manufacturing is a precise engineering process rather than simple hand lay-up. At Beijing Yuanhui FRP Co., Ltd., raw materials account for 42% of the cost, labor and equipment depreciation 31%, and the quality loss rate remains below 0.8%. This article breaks down the entire production workflow, from SMC sheet preparation to final packaging.

1. Material Selection & Formulation

1.1 Resin System

For potable water tanks, food-grade isophthalic polyester resin (e.g., DSM 430 series) is mandatory, with styrene emission <5% and oxygen index ≥28. In 2019, Beijing Yuanhui optimized the gel time from 12 to 8.5 minutes, increasing interlaminar shear strength from 14.2 MPa to 16.8 MPa.

1.2 Reinforcement Materials

E-glass chopped strand mat (450 g/m²) and bidirectional woven roving (800 g/m²) are used in alternating layers. When ambient humidity exceeds 75%, a silane coupling agent pretreatment is required; otherwise, the water absorption rate jumps from 0.3% to 1.2%.

2. Molding Processes: Hand Lay-Up vs. Compression Molding

2.1 Hand Lay-Up (for Custom Shapes)

After applying mold release wax, layers are placed sequentially: surface veil (30 g/m²), structural layers (3×450g mat + 2×800g cloth). Each layer is compacted with a grooved roller. Beijing Yuanhui’s data show fiber content varies between 32%-38% in hand lay-up, so vacuum bagging (-0.08 MPa) is used to narrow the range to ±2%.

2.2 Compression Molding (for Standard Panels)

SMC molding parameters: temperature 140-145°C, pressure 12-15 MPa, hold time = panel thickness × 1.5 min/mm. For a 1.2m×1.2m standard panel, the cycle time is 4 minutes 20 seconds, yielding a Barcol hardness of 45—significantly higher than the 35 achieved by hand lay-up.

3. Curing, Demolding & Post-Processing

The exothermic peak must be controlled below 150°C, with a heating rate of 1.5°C/min. Beijing Yuanhui uses a three-stage curing curve: 80°C/1h → 120°C/1.5h → natural cooling, achieving 99.2% cure degree. After demolding, flash is trimmed, and a silicone sealant (2mm ±0.3mm) is applied to the flange surface.

4. Leak Testing & Quality Assurance

4.1 Hydrostatic Pressure Test

Per GB/T 17219, the tank is filled with water and pressurized to 1.5 times the working pressure for 24 hours. The leakage rate must ≤0.05%. Beijing Yuanhui’s pass rate is 99.7%, with most failures occurring at flange joint micro-cracks, which are repairable via local reinforcement.

4.2 Water Quality Testing

Following the Hygienic Safety Standard for Drinking Water Equipment, tests cover heavy metals (Pb<0.01mg/L), volatile phenols (<0.002mg/L), and oxygen consumption (<2mg/L). 2% of each batch is tested; 2023 reports show zero exceedances.

Conclusion

The three critical control points in FRP tank production are material ratio, temperature profile, and seal integrity. Beijing Yuanhui FRP Co., Ltd. has extended product lifespan from the industry average of 12 years to 18 years through formulation optimization and vacuum-assisted processes. Buyers should focus on SMC storage conditions (5-25°C, humidity <65%) and cure degree reports, as these directly determine long-term weatherability.