The production of fiberglass began in China in 1958, and the main molding process is hand lay-up. According to incomplete statistics, more than 70% of fiberglass is hand lay-up formed. With the vigorous development of the domestic fiberglass industry, the introduction of advanced technology and equipment from abroad, such as large-scale automatic winding machines, continuous waveform plate production units, extrusion molding units, etc., the gap with foreign countries has greatly shortened. Even if large-scale equipment has absolute advantages such as high production efficiency, guaranteed quality and low cost, hand laid fiberglass is still irreplaceable by large equipment in construction sites, special occasions, low investment, simple and convenient, and small customization. In 2021, China's fiberglass production reached 5 million tons, with a significant portion being hand laid fiberglass products. In the construction of anti-corrosion engineering, most of the on-site fiberglass production is also done by hand laying techniques, such as fiberglass lining for sewage tanks, fiberglass lining for acid and alkali storage tanks, acid resistant fiberglass flooring, and external anti-corrosion of buried pipelines. Therefore, the resin fiberglass produced in on-site anti-corrosion engineering is all hand laid process.
Fiberglass reinforced plastic (FRP) composite materials account for over 90% of the total amount of composite materials, making it the most widely used composite material today. It is mainly made of fiberglass reinforced materials, synthetic resin adhesives, and auxiliary materials through specific molding processes, and hand laid FRP technology is one of them. Hand laid fiberglass has more quality defects compared to mechanical forming, which is also the main reason why modern fiberglass production and manufacturing prefer mechanical equipment. Hand laid fiberglass mainly relies on the experience, operation level, and maturity of construction personnel to control quality. Therefore, for hand laid fiberglass construction personnel, skill training and experience summary, as well as using failed cases for education, to avoid repeated quality defects in hand laid fiberglass, causing economic losses and social impact; The defects and treatment solutions of hand laid fiberglass should become an essential technology for fiberglass anti-corrosion construction personnel. The application of these technologies is of positive significance for ensuring the service life and excellent corrosion resistance effect of anti-corrosion.
There are many quality defects in hand laid fiberglass, big and small. In summary, the following are important and directly cause damage or failure to fiberglass. In addition to avoiding these defects during construction operations, subsequent remedial measures such as maintenance can also be taken to meet the same quality requirements as the overall fiberglass. If the defect cannot meet the usage requirements, it cannot be repaired and can only be reworked and reconstructed. Therefore, using hand laid fiberglass to eliminate defects as much as possible during the construction process is the most economical solution and approach.
1. Fiberglass cloth "exposed white"
Fiberglass cloth should be fully soaked with resin adhesive, and exposed white indicates that some fabrics have no adhesive or very little adhesive. The main reason is that the glass cloth is contaminated or contains wax, resulting in incomplete dewaxing; The viscosity of the resin adhesive material is too high, making it difficult to apply or the resin adhesive material is suspended on the glass cloth eyelets; Poor mixing and dispersion of resin adhesive, poor filling or too coarse filling particles; Uneven application of resin adhesive, with missed or insufficient application of resin adhesive. The solution is to use a wax free glass cloth or a thoroughly dewaxed cloth before construction to keep the fabric clean and not contaminated; The viscosity of the resin adhesive material should be appropriate, and for construction in high temperature environments, it is important to adjust the viscosity of the resin adhesive material in a timely manner; When stirring dispersed resin, mechanical stirring must be used to ensure even dispersion without clumping or clumping; The fineness of the selected filler must be greater than 120 mesh, and it should be fully and evenly dispersed in the resin adhesive material.
2. Fiberglass with low or high adhesive content
During the production process of fiberglass, if the adhesive content is too low, it is easy for the fiberglass cloth to produce defects such as white spots, white surfaces, layering, and peeling, resulting in a significant decrease in interlayer strength and a decrease in the mechanical properties of fiberglass; If the adhesive content is too high, there will be "sagging" flow defects. The main reason is missed coating, resulting in "low glue" due to insufficient coating. When the amount of glue applied is too thick, it leads to "high glue"; The viscosity of resin adhesive material is improper, with high viscosity and high adhesive content, low viscosity, and too much diluent. After curing, the adhesive content is too low. Solution: Effectively control viscosity, adjust the viscosity of resin adhesive at any time. When the viscosity is low, adopt multiple coating methods to ensure the content of resin adhesive. When the viscosity is high or in high temperature environments, diluents can be used to dilute it appropriately; When applying glue, pay attention to the uniformity of the coating, and do not apply too much or too little resin glue, or too thin or too thick.
3. Fiberglass surface becomes sticky
During the construction process of fiberglass reinforced plastic, products are prone to surface sticking after coming into contact with air, which lasts for a long time. The main reason for this sticky defect is that the humidity in the air is too high, especially for the curing of epoxy resin and polyester resin, which has a delaying and inhibiting effect. It may also cause permanent sticking or incomplete long-term curing defects on the surface of fiberglass; The ratio of curing agent or initiator is inaccurate, the dosage does not meet the specified requirements, or the surface becomes sticky due to failure; Oxygen in the air has an inhibitory effect on the curing of polyester resin or vinyl resin, with the use of benzoyl peroxide being more pronounced; There is too much volatilization of crosslinking agents in the surface resin of the product, such as too much volatilization of styrene in polyester resin and vinyl resin, resulting in imbalance in proportion and failure to cure. The solution is that the relative humidity in the construction environment must be below 80%. About 0.02% paraffin or 5% isocyanate can be added to polyester resin or vinyl resin; Cover the surface with plastic film to isolate it from the air; Before resin gelation, it should not be heated to avoid excessive temperature, maintain good ventilation environment, and reduce the volatilization of effective ingredients.
4. There are many bubbles in fiberglass products
Fiberglass products produce many bubbles, mainly due to excessive use of resin adhesive or the presence of too many bubbles in the resin adhesive; The viscosity of the resin adhesive is too high, and the air brought in during the mixing process is not expelled and remains inside the resin adhesive; Improper selection or contamination of glass cloth; Improper construction operation, leaving bubbles; The surface of the base layer is uneven, not leveled, or there is a large curvature at the turning point of the equipment. For the solution of excessive bubbles in fiberglass products, control the resin adhesive content and mixing method; Add diluents appropriately or improve environmental temperature to reduce the viscosity of resin adhesive; Choose untwisted glass cloth that is easily soaked by resin adhesive, free from contamination, clean and dry; Keep the base level and fill the uneven areas with putty; The dipping, brushing, and rolling process methods selected based on different types of resin adhesive and reinforcement materials.
5. Defects in fiberglass adhesive flow
The main reason for the flow of fiberglass products is that the viscosity of the resin material is too low; The ingredients are uneven, resulting in inconsistent gel and curing time; The amount of curing agent used for resin adhesive is insufficient. The solution is to add active silica powder appropriately, with a dosage of 2% -3%. When preparing the resin adhesive, it must be thoroughly stirred and the amount of curing agent used should be adjusted appropriately.
6. Delamination defects in fiberglass
There are many reasons for the delamination defects in fiberglass, and in summary, there are several main points: wax or incomplete dewaxing on the fiberglass cloth, contamination or moisture on the fiberglass cloth; The viscosity of the resin adhesive material is too high, and it has not penetrated the fabric eye; During construction, the glass cloth is too loose, not tight, and has too many bubbles; The formulation of resin adhesive is not appropriate, resulting in poor bonding performance, which can easily cause slow or fast curing speed during on-site construction; Improper curing temperature of resin adhesive, premature heating or excessive heating temperature can affect the interlayer bonding performance. Solution: Use wax free fiberglass cloth; Maintain sufficient resin adhesive and apply vigorously; Compact the glass cloth, remove any bubbles, and adjust the formulation of the resin adhesive material; Resin adhesive should not be heated before bonding, and the temperature control of fiberglass that requires post curing treatment needs to be determined through testing.
7. Poor curing and incomplete defects of fiberglass
Fiberglass reinforced plastic (FRP) often exhibits poor or incomplete curing, such as soft and sticky surfaces with low strength. The main reasons for these defects are insufficient or ineffective use of curing agents; During construction, if the ambient temperature is too low or the air humidity is too high, water absorption will be severe. The solution is to use qualified and effective curing agents, adjust the amount of curing agent used, and increase the ambient temperature by heating when the temperature is too low. When the humidity exceeds 80%, fiberglass construction is strictly prohibited; It is recommended that there is no need for repair in case of poor curing or long-term non curing quality defects, and only rework and re lay.
In addition to the typical cases mentioned above, there are many defects in hand laid fiberglass products, whether they are large or small, which can affect the quality and service life of fiberglass products, especially in anti-corrosion engineering, which can affect the anti-corrosion and corrosion resistance life. From a safety perspective, defects in heavy-duty anti-corrosion fiberglass can directly lead to major accidents, such as leaks of acid, alkali, or other strongly corrosive media. Fiberglass is a special composite material composed of various materials, and the forming of this composite material is constrained by various factors during the construction process; Therefore, the hand laid fiberglass forming process method looks simple and convenient, without the need for many equipment and tools; However, the molding process requires strict requirements, proficient operating techniques, and an understanding of the causes and solutions of defects. In actual construction, it is necessary to avoid the formation of defects. In fact, hand laying fiberglass is not a traditional "handicraft" that people imagine, but a construction process method with high operating skills that is not simple. The author hopes that domestic practitioners of hand laid fiberglass will uphold the spirit of craftsmanship and regard each construction as a beautiful "handicraft"; So the defects of fiberglass products will be greatly reduced, thereby achieving the goal of "zero defects" in hand laid fiberglass, and creating a more exquisite and flawless fiberglass "handicraft".
Post time: Dec-11-2023
