Glass fiber has low density, excellent dielectric insulation properties, superior thermal insulation, as well as thermal absorption and expansion characteristics.
I. Density
The density of fiberglass ranges from 1.5 to 2.0, just one-quarter to one-fifth that of ordinary carbon steel and about two-thirds lighter than lightweight aluminum. Despite its lightness, its mechanical resistance is impressively high.
In some aspects, it can even approach the level of ordinary carbon steel. For example, certain epoxy fiberglass materials achieve tensile, flexural and compressive strengths in excess of 400MPa. When considering relative strength, fiberglass not only significantly outperforms ordinary carbon steel, but can also match and even surpass the level of some special steel alloys.
A comparison of the density, tensile strength, and relative strength of fiberglass and various metals is presented in Table 1.
table 1
| Material names | Density | Tensile strength (Mother) |
Specific Strength |
| Advanced Alloy Steel | 8.0 | 1280 | 160 |
| A3 steel | 785 | 400 | 50 |
| LY12 Aluminum Alloy | 2.8 | 420 | 160 |
| Cast iron | 7.4 | 240 | 32 |
| Epoxy fiberglass | 1.73 | 500 | 280 |
| Polyester Fiber | 1.8 | 290 | 160 |
| Phenolic fiberglass | 1.8 | 290 | 160 |
Strength/weight ratio: Refers to the tensile strength per unit of density, that is, the relationship between the tensile strength of a material and its density, indicating the extent of its light weight and high strength properties.
II. Electrical properties
Glass fiber has excellent electrical insulation properties, making it suitable as an insulation component in instruments, motors and electrical appliances. Maintains good dielectric properties even under high frequency conditions. Replacing paper and cotton cloth with glass fiber cloth in insulation materials can improve the insulation degree of these materials.
Using the same resin can improve at least one grade. Fiberglass makes up one-third to one-half of the total amount of insulation materials. In some large engines, such as 125,000 KW engines, hundreds of kilograms of fiberglass are used as insulation material.
Furthermore, fiberglass is not affected by electromagnetism and has good transparency in microwaves. Table 2 presents the dielectric properties of some types of glass fiber.
table 2
| Types of fiberglass | Dielectric constant | Dielectric Loss Tangent |
| Styrene Butadiene Glass Fiber | 3.5~4.0 | (3.5~5.0)*10 -3 |
| DAP fiberglass | 4.0~4.8 | (0.9~105)*10 -2 |
| Polybutadiene glass fiber | 3.54.0 | (4.5~5.5)*10 -3 |
| Polyvinyl Acetate 307 Fiberglass | 4.0~4.8 | (0.9~1.5)*10 -3 |
| Epoxy Fiberglass 6101 | 4.7~5.2 | (1.7~2.5)*10 -2 |
III. Thermal properties
Glass fiber has excellent thermal characteristics, with a specific heat capacity 2 to 3 times greater than that of metals, and lower thermal conductivity, which is only 1/100 to 1/1000 that of metallic materials.
Furthermore, certain varieties of fiberglass have remarkable resistance to instantaneous high temperatures. For example, phenolic-based high-silica fiberglass forms a carbonized layer under extremely high temperatures, effectively protecting rockets, missiles, and spacecraft from the high temperatures of 5,000 to 10,000 K and the high-velocity air flows they create. must withstand when passing through the atmosphere. Table 3 describes the thermal properties of some materials.
Table 3
| Materials | Specific heat (KJ (Kg·K)) |
Thermal conductivity (w/(m·k)) |
Linear Expansion Coefficient ɑ10 -5 /°C |
| Polyvinyl Castings | 0.17 | 0.17 | 6~13 |
| Iron | 0.46 | 75.6 | 1.2 |
| Aluminum | 0.92 | 222 | 2.4 |
| Wood | 1.38 | 0.09~0.19 | 0.08~0.16 |
| Fiberglass | 1.26 | 0.40 | 0.7~6 |
As illustrated in Table 3, fiberglass has exceptional thermal insulation properties, an advantage that metallic materials simply cannot compete with.
4. Aging resistance
All materials face the problem of aging and fiberglass is no exception; it just varies in rate and severity. Under exposure to atmospheric conditions, moist heat, water immersion and corrosive media, the performance of fiberglass decreases. Prolonged use can result in decreased gloss, color changes, resin detachment, fiber exposure and delamination, among other phenomena.
However, with advances in science and technology, necessary anti-aging measures can be taken to improve its performance and extend the product's useful life.
For example, when fiberglass was subjected to natural aging tests in Harbin, the smallest decline in panel tensile strength was observed, less than 20%; followed by flexural strength, generally no more than 30%; the greatest decrease was observed in compressive strength, which also showed greater fluctuation, generally between 25% and 30%. See Table 4 below.
Table 4
| Mechanical properties | Types of fiberglass | Starting Strength (MPa) |
Strength after 10 years | Strength after 10 years |
| Residual Force (MPa) |
Strength Decline Rate (%) |
|||
| Tensile strength | Epoxy | 290.77 | 244.22 | 16 |
| Polyester | 293.21 | 228.73 | 22 | |
| bending strength | Epoxy | 330.06 | 260.68 | 21 |
| Polyester | 292.04 | 224.91 | 23 | |
| Compressive strength | Epoxy | 216.58 | 160.23 | 26 |
| Polyester | 199.43 | 139.65 | 30 | |
| Curvature Module | Epoxy | 1.73*10 4 | 1.11*10 4 | 36 |
| Polyester | 1.59*10 4 | 1.02*10 4 | 36 |
Additionally, exposure to external elements such as wind, rain and sunlight can lead to shedding of the resin layer on fiberglass surfaces. Regular maintenance is necessary to avoid this.
V. Long-term heat resistance and flame resistance
The heat and flame resistance of fiberglass depends on the type of resin used. The continuous operating temperature cannot exceed the thermal distortion temperature of the resin. Commonly used epoxy and polyester fiberglass are flammable. For structures that require fire resistance, resins or fire retardants must be used. Therefore, caution is required when using fiberglass.
Typically, fiberglass cannot be used for long periods under high temperatures. For example, the strength of polyester glass fiber begins to decrease at temperatures above 40°C to 45°C, and that of epoxy glass fiber begins to decrease above 60°C.
In recent years, high temperature resistant varieties of glass fiber have emerged, such as cycloaliphatic epoxy glass fiber and polyimide glass fiber. However, its long-term operating temperature is only between 200-300°C, which is significantly lower than the long-term operating temperature of metals.
Given these five aspects of physical properties, it is clear that fiberglass differs from materials such as metals and ceramics. Therefore, to maximize its advantages, it needs to be used properly. For example, fiberglass has excellent performance at low temperatures as its strength does not decrease.
So even when outdoor temperatures drop to -45°C to -50°C in northern winters, fiberglass does not become brittle. Outdoor structures such as cooling towers and rain shelters remain safe for use in northern winters.
On the other hand, in high temperature environments, specific resins and formulas for fiberglass are required. For continuous use at 100°C, a high temperature resistant formula and specific molding process conditions are required. Otherwise, the glass fiber may be damaged under continuous operation at temperatures above 100°C.
SAW. Chemical Properties of Fiberglass
The main chemical property of fiberglass is its excellent resistance to corrosion. It does not rust or corrode like metallic materials or rot like wood. It is almost immune to erosion by means such as water and oil. It can replace stainless steel in chemical plants for manufacturing tanks, pipes, pumps, valves, etc.
In addition to having a long useful life, it also does not require protection measures against corrosion, rust or insects, reducing maintenance costs. Fiberglass is widely used for its resistance to corrosion. In some major industrialized countries, more than 13% of corrosion-resistant products are made from fiberglass, with usage increasing annually. It is also commonly used in our country, mainly to coat metal equipment to protect the metal.
The corrosion resistance of fiberglass depends mainly on the resin used. Although the resin used for fiberglass is corrosion resistant, if applied directly to metal surfaces it can cause severe cracking and will not prevent leaks or protect the metal.
Adding a certain amount of fiberglass to the resin can transform potential serious cracks into numerous smaller cracks. The chance of these small cracks forming a continuous crack is minimal and can also serve to prevent new cracks. This helps prevent penetration and corrosion by chemical solutions.
Glass fiber is not only stable against a variety of acids, alkalis, salts and low concentration solvents, but also resistant to atmospheric, seawater and microbial effects.
However, for different corrosive media, appropriate resin, glass fiber and their products must be selected. The use of glass fiber for anti-corrosion has become increasingly popular in recent years, demonstrating the advantages of low anti-corrosion investment, long service life and substantial savings on stainless steel materials, leading to significant economic benefits.
Typically, the corrosion resistance of fiberglass is assessed by measuring its change in mass when placed in different corrosive media. A smaller mass change indicates better corrosion resistance, and a larger mass change indicates lower corrosion resistance.
Table 5 lists the mass proportions of various types of glass fiber in different concentrations of acid and alkaline solutions, while Table 6 shows the retention rate of flexural strength of polyester glass fiber in acids, alkalis and other media .
Table 5
| Average | Average Concentration | Age | 307 polyester fiberglass | Styrene fiberglass | Furan-epoxy fiberglass | 634 epoxy polyester fiberglass 193 | DAP fiberglass | 197 polyester fiberglass | Polybutadiene glass fiber |
| Sodium Hydroxide | 5.2% | 366 | -5,426 | +0.5091 | +0.7122 | +10.85 | +1,023 | +9744 | +0.531 |
| Sodium Hydroxide | 29.2% | 366 | -17.21 | +0.103 | -0.49 | +12.07 | +2,301 | +0.522 | +0.174 |
| Sodium Hydroxide | 48.3% | 386 | -8.85 | -1,432 | -1.28 | -0.604 | +8.34 | -1.84 | -1.78 |
| Sulfuric acid | 5.6% | 365 | +0.472 | -0.155 | +4.74 | -0.0371 | -0.012 | -0.212 | – |
| Sulfuric acid | 28.8% | 365 | +5,855 | +1,199 | +17.38 | +0.032 | +1,795 | +1,217 | +4,338 |
| Sulfuric acid | 48.3% | 365 | +1,565 | +0.115 | +6,193 | +0.321 | +0.434 | +0.339 | +0.428 |
| Hydrochloric acid | 4.7% | 365 | -0.6762 | -3,350 | +3,987 | +0.044 | -0.7414 | -2,083 | – |
| Hydrochloric acid | 15.2% | 365 | -6.254 | -6.74 | +0.7428 | +3,878 | -8,371 | -7,211 | – |
Table 6
| Resin grade | 191# | 189# | 196# | 197# | 198# | 199# | |
| Original Strength (MPa) | 259 | 267 | 278 | 295 | 337 | 290 | |
| Steel Hydroxide | 5% | 8.75 | 5.96 | 12:10 | 8:30 p.m. | 6.24 | 27.10 |
| Steel Hydroxide | 30% | – | – | – | – | – | 10:60 p.m. |
| Sulfuric acid | 5% | 50.6 | 55.5 | 45.5 | 43.4 | 47.0 | 69.8 |
| Sulfuric acid | 30% | 58.5 | 45.1 | – | 38.6 | 40.0 | 64.5 |
| Hydrochloric acid | 5% | 70.5 | 55.3 | 68.5 | 46.8 | 49.2 | 69.8 |
| Hydrochloric acid | 30% | 50.6 | 45.2 | 45.0 | 39.7 | 28.1 | 71.0 |
| Nitric acid | 5% | 69.8 | 50.3 | 59.5 | 56.2 | 52.2 | 75.0 |
| Hydrochloric acid | 30% | 50.6 | 45.2 | 45.0 | 39.7 | 28.1 | 71.0 |
| Nitric acid | 5% | 69.8 | 50.3 | 59.5 | 56.2 | 52.2 | 75.0 |
| Nitric acid | 30% | 57 | 40.2 | 53 | 39.6 | 36.6 | 64.6 |
| Benzene | 21.9 | 24.4 | 21 | 28.8 | 55.2 | 88 | |
| Transformer Oil | 81.5 | 74 | 75.1 | 66.5 | 69.4 | 84.8 | |
| Gasoline | 85.5 | 75.7 | 74.8 | 79.6 | 74.0 | 89.6 |
* Immersion time is one year.
