Introduction

FRP water tanks have captured over 35% of the industrial and civil water supply market due to their corrosion resistance, lightweight strength, and longevity. Beijing Yuanhui FRP Co., Ltd., with 15 years of manufacturing experience, presents the complete process chain from raw material batching to final product inspection, based on real production line data.

1. Raw Material Preparation and Ratio Control

1.1 Resin System Selection

We use isophthalic unsaturated polyester resin (e.g., DS-146) with a temperature range of -40°C to 90°C and shrinkage controlled within 0.2%. At Beijing Yuanhui FRP Co., Ltd., the ratio of resin to hardener (MEKP) is strictly maintained at 100:1.5-2.0, with curing temperature stabilized at 25°C ± 2°C.

1.2 Reinforcement Material Selection

E-glass chopped strand mat (450 g/m²) and SMC sheet (30% glass fiber) are used in composite layering. For a 10-ton tank, the bottom and side panels consist of 5 layers of mat plus 3 layers of SMC, achieving a total thickness of 8 mm. The top panel uses 4 mat layers plus 2 SMC layers, meeting GB/T 20678-2006 standards.

2. Mold Preparation and Surface Treatment

2.1 Mold Cleaning and Release Agent Application

Steel molds are cleaned with acetone to remove residual resin, then sprayed with semi-permanent release agent (e.g., Frekote 700-NC) three times at 20-minute intervals, forming a 0.1 mm release film. Beijing Yuanhui FRP Co., Ltd. tests show this process increases demolding success to 98.5%.

2.2 Gel Coat Spraying

Gel coat (with weather-resistant pigment) is sprayed at a 45° angle and 0.6 MPa pressure to a thickness of 0.4-0.6 mm. Common defects like pinholes and orange peel are resolved by adjusting spray distance to 30 cm.

3. Hand Lay-Up and Filament Winding

3.1 Hand Lay-Up Sequence

First, a surface mat (30 g/m²) is laid as a resin-rich layer, followed by alternating layers of chopped strand mat and SMC. Each layer is consolidated with an 8 mm steel bubble roller to eliminate air and ensure impregnation. Data from Beijing Yuanhui FRP Co., Ltd. shows interlayer shear strength of 12 MPa for 10 mm thick panels.

3.2 Winding Layer Reinforcement

For tank stiffeners and flanges, circumferential winding is applied at a 54.75° angle with tension controlled at 8-10 N per tow. For a 2 m diameter cylinder, 6 winding layers are required, each 0.3 mm thick, totaling 1.8 mm.

4. Curing, Demolding, and Post-Processing

4.1 Curing Curve Management

After 24 hours of room-temperature curing, parts are transferred to an oven for post-curing: 80°C for 4 hours, then natural cooling below 40°C before demolding. Beijing Yuanhui FRP Co., Ltd. uses a Barcol hardness tester, requiring hardness ≥ 35.

4.2 Trimming and Assembly

Excess flash is cut with diamond saws, and edges are chamfered to R5 using a grinder. Panels are pre-assembled on a jig; if gaps are ≤ 1 mm, silicone structural sealant is applied. Final assembly undergoes a water-fill test: fill to design level, hold for 72 hours, with leakage ≤ 0.1 L/day.

Conclusion

FRP water tank production demands precise coordination between materials science, process parameters, and quality control. Beijing Yuanhui FRP Co., Ltd. standardizes these 12 steps to boost first-pass yield from the industry average of 92% to 97.3%. For field engineers, we recommend monitoring SMC sheet storage humidity (< 30% RH) and resin gel time (20-30 minutes)—both directly impact interlaminar bond strength and service life.