Introduction

FRP (Fiberglass Reinforced Plastic) water tanks have captured over 30% of the storage tank market in construction, fire protection, and industrial sectors due to their corrosion resistance, light weight, and ease of installation. In 2023, China's annual production exceeded 1.2 million cubic meters, with compression-molded products accounting for 65%. Drawing on decades of experience at Beijing Yuanhui FRP Co., Ltd., this article dissects the complete production workflow—from raw material formulation to final inspection.

1. Material Selection and Ratio Control

1.1 Resin and Reinforcement Compatibility

The core materials are unsaturated polyester resin (UPR) and E-glass fiber. Beijing Yuanhui uses 196# weather-resistant resin with a tensile strength of 65 MPa and flexural modulus of 3.2 GPa, paired with medium-alkali woven roving (800 g/m²) to withstand 1.5 MPa water pressure. The resin-to-catalyst (MEKP) ratio is strictly 100:1.8~2.2, adjusted to 100:2.5 when ambient temperature drops below 15°C.

1.2 Fillers and Additives

To reduce shrinkage (target ≤0.3%) and enhance flame retardancy, 5% aluminum hydroxide and 2% fumed silica are added. Each batch is tested with a Brookfield viscometer to maintain resin viscosity between 300 and 500 mPa·s.

2. Hand Lay-Up Process

2.1 Mold Preparation and Release Layer

Steel or polyester molds with surface roughness RA ≤ 0.8 μm are used. Three coats of mold release wax (15-minute intervals) are applied, followed by PVA release film. Beijing Yuanhui reports mold life exceeding 1,500 cycles; acetone wiping is performed before each use.

2.2 Layering and Impregnation

Standard panel thicknesses of 5 mm, 8 mm, and 10 mm require specific layer counts. For an 8 mm panel, four layers of 450 g/m² chopped strand mat and two layers of 800 g/m² woven roving are stacked with a 45° offset to avoid stress concentration. Resin consumption is 35~40 g/m² per layer, applied using a spiral roller. Hand lay-up must be completed within 30 minutes to prevent pre-curing.

3. Compression Molding and Curing Control

3.1 Molding Parameters

Beijing Yuanhui uses a 500-ton four-column hydraulic press. Molding temperature is set at 135~145°C with a hold time calculated at 2 min/mm of thickness. For an 8 mm panel: heat at 3°C/min to 140°C, hold for 16 minutes, then cool naturally to 60°C before demolding. Pressure is maintained at 12~15 MPa with three 5-second degassing cycles to eliminate bubbles.

3.2 Curing Verification

Three samples per batch undergo Barcol hardness testing (per GB/T 3854), requiring a minimum hardness of 45. Differential scanning calorimetry (DSC) ensures a curing degree of ≥92%. In 2024, Beijing Yuanhui achieved a 98.7% batch pass rate; rejected panels are crushed and reused as filler.

4. Assembly and Quality Assurance

4.1 Panel Cutting and Sealing

CNC cutting machines achieve ±0.5 mm precision. SMC-molded panel edges are chamfered 2 mm, and silicone sealant (tensile strength ≥2.5 MPa) is used for joints. Bolt holes are spaced at 300 mm intervals. Beijing Yuanhui's patented locking structure reduces leakage probability to below 0.1%.

4.2 Hydrostatic Testing

Each tank undergoes a 72-hour full-water test at a water height of 3.6 m (0.036 MPa static pressure). Ultrasonic wall thickness gauges check for deviations within ±0.3 mm. Per GB 50242, more than three leak points render the tank non-compliant. In 2023, Beijing Yuanhui achieved a 99.2% first-pass rate.

Conclusion

FRP water tank production has fully transitioned from hand lay-up to compression molding, with precise material ratios and curing control being the decisive factors for a 25-year design life. Beijing Yuanhui FRP Co., Ltd. has reduced single-panel cycle time from 45 to 28 minutes by integrating automated molding lines and DSC inspection, while maintaining a scrap rate of just 0.3%. For buyers, selecting suppliers with full traceability significantly lowers downstream maintenance costs.