[glass fiber] What is fiberglass?

2019-03-14 10:53

Glass fiber (original name: glass fiber or fiberglass) is an inorganic non-metallic material with excellent performance. It has many advantages, such as good insulation, heat resistance, good corrosion resistance and high mechanical strength, but the disadvantage is sex. Crisp, poor wear resistance. It is made of glass ball or waste glass by high-temperature melting, drawing, winding, weaving and other processes. The diameter of the monofilament is several micrometers to twenty micrometers, which is equivalent to one hair. 1/20-1/5, each bundle of fiber strands consists of hundreds or even thousands of monofilaments. Glass fiber is commonly used as a reinforcing material in composite materials, electrical insulating materials and thermal insulation materials, circuit boards and other fields of the national economy.



First, chemical properties


Melting point 680 °C


Molecular Structure


Boiling point 1000 °C

Density 2.4-2.7g/cm3



Second, the main ingredients


Its main components are silica, alumina, calcium oxide, boron oxide, magnesium oxide, sodium oxide, etc., according to the alkali content of the glass, can be divided into alkali-free glass fiber (sodium oxide 0% to 2%, belonging to aluminum Borosilicate glass), medium alkali glass fiber (8% to 12% sodium oxide, sodium or calcium silicate glass containing boron or boron) and high alkali glass fiber (more than 13% sodium oxide, sodium calcium) Silicate glass).



Third, the main features


Raw materials and their applications: Glass fiber is more resistant to temperature than non-combustible, non-combustible, anti-corrosive, heat-insulating, sound-insulating, high tensile strength and good electrical insulation. However, it is brittle and has poor abrasion resistance. Used to make reinforced plastics or reinforced rubber. As a reinforcing fiber, glass fiber has the following characteristics. These characteristics make the use of glass fiber much wider than other kinds of fibers, and the development speed is far ahead of its characteristics as listed below:


(1) High tensile strength and small elongation (3%).

(2) High modulus of elasticity and good rigidity.

(3) The amount of elongation in the elastic limit is large and the tensile strength is high, so the absorption impact energy is large.

(4) It is an inorganic fiber, which is incombustible and chemically resistant.

(5) The water absorption is small.

(6) Scale stability and heat resistance are good.

(7) It has good processability and can be used as a product of different forms such as strands, bundles, felts and woven fabrics.

(8) Transparent and transparent to light.

(9) The development of a surface treatment agent excellent in adhesion to a resin is completed.

(10) The price is cheap.

(11) It is not easy to burn, and it can be melted into glassy beads at high temperature.



Fourth, material classification


Glass fiber can be divided into continuous fiber, fixed length fiber and glass wool according to its shape and length. According to glass composition, it can be divided into alkali-free, chemical-resistant, high-alkali, medium-alkali, high-strength, high-elasticity and alkali-resistant ( Alkali resistant) glass fiber, etc.


The main raw materials for the production of glass fiber are: quartz sand, alumina and pyrophyllite, limestone, dolomite, boric acid, soda ash, thenardite, fluorite and the like. The production methods are roughly divided into two categories: one is to directly form the molten glass into fibers; the other is to first make the molten glass into a glass ball or rod with a diameter of 20 mm, and then remelt it in various ways to make a diameter of 3 ~ Very fine fiber of 80 μm. An infinitely long fiber drawn by a mechanical drawing method by a platinum alloy plate is called a continuous glass fiber and is generally called a long fiber. Non-continuous fibers made by rolls or air streams, called fixed length glass fibers, are commonly referred to as short fibers.


Glass fiber is divided into different grades according to composition, nature and use. According to the standard level, E-class glass fiber is most commonly used, widely used in electrical insulation materials; S grade is special fiber.


The glass used to produce glass fiber is different from the glass of other glass products. The glass components used in commercially available fibers are as follows:


E-glass

Also known as alkali-free glass, it is a borosilicate glass. At present, it is the most widely used glass component for glass fiber. It has good electrical insulation and mechanical properties. It is widely used in the production of glass fiber for electrical insulation. It is also widely used in the production of fiberglass for glass reinforced plastic. Its disadvantage is that it is easy to be Inorganic acid is eroded and therefore not suitable for use in an acidic environment.


C-glass

Also known as medium alkali glass, it is characterized by chemical resistance, especially acid resistance is better than alkali-free glass, but the electrical properties are poor, the mechanical strength is lower than that of alkali-free glass fiber by 10% to 20%, usually the foreign medium-alkali glass fiber contains certain The amount of boron trioxide, while China's medium alkali glass fiber is completely free of boron. In foreign countries, medium-alkali glass fiber is only used to produce corrosion-resistant glass fiber products, such as glass fiber surface felts, and also used to strengthen asphalt roofing materials. However, in China, alkali glass fiber occupies more than half of glass fiber production. (60%), widely used in the reinforcement of FRP and the production of filter fabrics, dressing fabrics, etc., because it is more competitive than alkali-free glass fiber.


High-strength glass fiber

It is characterized by high strength and high modulus. Its single fiber tensile strength is 2800 MPa, which is about 25% higher than that of alkali-free glass fiber. The elastic modulus is 8600 MPa, which is higher than that of E-glass fiber. The FRP products produced by them are mostly used in military, space, bulletproof armor and sports equipment. However, due to the high price, it is still not popularized in civilian use, and the world's output is about several thousand tons.


AR fiberglass

Also known as alkali-resistant glass fiber, alkali-resistant glass fiber is glass fiber reinforced (cement) concrete (referred to as GRC) rib material, is 100% inorganic fiber, is an ideal substitute for steel and asbestos in non-load bearing cement components. Alkali-resistant glass fiber is characterized by good alkali resistance, can effectively resist the erosion of high alkali substances in cement, strong grip strength, high modulus of elasticity, impact resistance, tensile strength, high flexural strength, non-combustible, antifreeze and temperature resistance. It has strong humidity change ability, excellent crack resistance and impermeability, and is characterized by high designability and easy molding. Alkali-resistant glass fiber is a new type of environmentally-friendly reinforcement widely used in high-performance reinforced (cement) concrete. material.


A glass

Also known as high alkali glass, it is a typical sodium silicate glass, which is rarely used for the production of glass fiber due to poor water resistance.


E-CR glass

It is an improved boron-free alkali-free glass for the production of glass fiber with good acid and water resistance. Its water resistance is 7-8 times better than that of alkali-free glass fiber. The acid resistance is also superior to that of alkali glass fiber. New varieties developed for underground pipelines, storage tanks, etc.


D glass

Also known as low dielectric glass for the production of low dielectric glass fibers with good dielectric strength.

In addition to the above glass fiber components, a new alkali-free glass fiber is now available, which is completely free of boron, thereby reducing environmental pollution, but its electrical insulation properties and mechanical properties are similar to those of conventional E-glass. There is also a glass fiber with a double glass composition which has been used in the production of glass wool and is said to have potential in the field of FRP reinforcement. In addition, there is fluorine-free glass fiber, which is an improved alkali-free glass fiber developed for environmental protection.


Identification of high alkali glass fiber

The simple method of testing is to put the fiber in boiling water and cook for 6-7 hours. If it is a high-alkali glassy fiber, after boiling water, the fibers in the warp and weft directions are all loosened.


According to different standards, glass fiber classification methods are many, generally divided into two aspects: length and diameter, composition and performance.



Fifth, the production process


There are two kinds of glass fiber production processes: two-forming-drawing method, one-time forming-pool kiln drawing method.

There are many processes in the drawing process. The glass material is first melted into a glass ball at a high temperature, and then the glass ball is secondarily melted, and the glass fiber strand is formed by high-speed drawing. This kind of process has various disadvantages such as high energy consumption, unstable molding process and low labor productivity, which is basically eliminated by large glass fiber manufacturers.


Glass fiber process flow chart



The pool kiln drawing method melts raw materials such as pyrophyllite into a glass solution in a kiln, removes the bubbles, transports them to the porous drain plate through the passage, and pulls the glass fiber strands at high speed. The kiln can be connected to hundreds of drain plates through multiple channels for simultaneous production. The process is simple, energy-saving and consumption-reducing, stable in formation, high-efficiency and high-yield, and is convenient for large-scale and fully automated production, and has become an international mainstream production process. The glass fiber produced by the process accounts for more than 90% of the global production.



Six, test standards


Glass fiber has high tensile strength and small elongation (3%). The test method standards are: GB/T14338-1993

Synthetic staple fiber: test method for crimping, GB/T 15232-1994

Textile glass mat: Determination of tensile breaking strength, GB/7689.5

Determination of tensile strength and elongation at break of glass fiber, GB T15232-1994

Determination of tensile breaking strength of textile glass mats, GB/T 7689.5-2001


The single fiber tensile strength test is to use a high strength and high modulus fiber strength meter capable of testing glass fibers.



Seven, security protection


1. In case of accidental contact with the eyes, rinse immediately with plenty of water and seek medical advice.

2. Wear appropriate protective clothing.

3. Do not inhale dust.

4. Avoid contact with skin and eyes.



Eight, the main purpose


1, no roving

The roving is a bundle of parallel or parallel monofilaments. The roving of the roving can be divided into: alkali-free glass roving and medium-alkali glass roving. The glass fiber used to produce the glass roving has a diameter of 12 to 23 μm. The number of rovings is from 150 to 9600 (tex). The roving can be directly used in some composite material forming methods, such as winding and pultrusion processes. Because of its uniform tension, it can also be woven into a roving-free roving fabric. In some applications, the roving is further chopped. .


(1) roving for jetting

The roving used for FRP injection molding has the following properties:

1 good cutting property, less static electricity generated during continuous high-speed cutting;

2 The efficiency of dispersing into the original yarn after cutting without roving is high, that is, the beam splitting rate is high, usually requiring more than 90%;

3 The short-cut raw yarn has excellent overmolding and can cover all corners of the mold;

4 resin soaked quickly, easy to be flattened by the roller and easy to drive air bubbles;

5 The original yarn tube has good decomposing performance and uniform density of coarse yarn, which is suitable for various spray guns and fiber conveying systems. The roving for jetting is made up of a plurality of raw yarns, each of which contains 200 glass monofilaments.


(2) SMC roving

SMC is a sheet molding compound, which is mainly used for pressing automobile parts, bathtubs, water tank plates, septic tanks, various seats, and the like. SMC uses roving to cut Sin sheet into lin (25mm) length and disperse it in resin paste. Therefore, the requirement for SMC roving is good short cut, less wool and excellent antistatic property. The chopped strand does not stick to the knife roll during cutting. For colored SMC, the roving is to be impregnated with resin in a high pigment content resin paste. Usually SMC roving is generally 2400 tex, and in some cases 4800 tex is also useful.


(3) Untwisted roving for winding

The winding method is used to manufacture glass pipes, storage tanks, and the like of various calibers. The number of rovings used for winding is from 1200 to 9600. Winding large pipes and storage tanks tend to be direct roving, such as 4800 tex direct roving.


The requirements for roving for winding are as follows:

1 into a good band, in the form of a flat ribbon;

2 The roving of the flawless roving is good, and it does not turn off when it is retracted from the bobbin, and does not form a "bird's nest"-like chaotic silk;

3 uniform tension, no drape;

4 line density is uniform, generally less than ± 7%;

5 The flawless roving has good permeability and is easy to be wetted and saturated by the resin when passing through the resin tank.


(4) roving with roving

Pultrusion is used to manufacture a variety of profiles with consistent cross-sections, characterized by high glass fiber content and high unidirectional strength. The pultrusion roving may be a combination of a plurality of strands of yarn or a straight roving having a linear density ranging from 1100 to 4400. The various performance requirements are generally the same as for winding rovings.


(5) roving for weaving

An important use of rovings is to weave woven woven or unidirectional roving fabrics of various thicknesses, most of which are used in hand lay-up FRP forming processes. There are the following requirements for the use of roving for strong making:

1 good wear resistance;

2 good banding;

3 Weaving roving for weaving requires forced drying before weaving;

4 The tension of the roving is uniform, and the drape should meet certain standards;

5 flawless rovings have good deconstructability;

6 flawless roving has good permeability.


(6) Pre-formed roving

In the preform process, the roving is short-cut and sprayed on a web of a predetermined shape, while a small amount of resin is sprayed to fix the fiber web, and then the formed fiber web is transferred into a metal mold, and the resin is thermoformed. That is the product. The performance requirements for the roving for this process are essentially the same as for the roving without jetting.


2, flawless roving fabric

The gingham fabric is a plain roving plain weave fabric, which is an important substrate for hand lay-up glass reinforced plastic. The strength of the woven fabric is mainly in the warp and weft direction of the fabric. For the case where the warp or weft strength is required, it can also be woven into a one-way woven fabric, which can arrange more roving in the warp or weft direction. .


The quality requirements of the other cloth are as follows: 1 uniform fabric, straight edge, smooth surface of the cloth, no stains, fluffing, creases, wrinkles, etc.; 2 warp, weft density, area weight, cloth width and roll length Meet the standard; 3 wound on a strong paper core, neatly wound; 4 rapid, good resin permeability; 5 fabrics of the laminate material dry and wet mechanical strength should meet the requirements.

The composite material paved with gingham is characterized by low interlaminar shear strength, poor pressure resistance and fatigue strength.


3, glass fiber mat

(1) Chopped strand mat

The glass strands (sometimes also used as rovings) are cut to a length of 50 mm, which are randomly and evenly laid on the mesh belt, and then applied with an emulsion binder or a powdered powder on the cloth. Cut the original silk felt. Chopped mat is mainly used in hand lay-up, continuous board and counter-molding and SMC processes. The quality requirements for chopped strand mat are as follows:

1 The area quality is uniform along the width direction;

2 chopped strands are evenly distributed in the felt surface, no macropores are formed, and the binder is evenly distributed;

3 has a moderate dry felt strength;

4 excellent resin infiltration and permeability.


(2) continuous raw silk felt

The glass strand formed during the drawing process or the continuous strand retracted from the original strand is laid in a figure-eight shape on a continuous moving web belt and bonded by a powder binder. The fibers in the continuous glass fiber mat are continuous, so the reinforcing effect on the composite material is shorter. Mainly used in pultrusion, RTM, pressure bag method and glass felt reinforced thermoplastic (GMT) and other processes.


(3) Surface felt

FRP products generally require the formation of a resin-rich layer, which is typically achieved with a medium alkali glass surface felt. This kind of felt is made of medium alkali glass (C), so it gives chemical resistance to glass fiber reinforced plastic, especially acid resistance. At the same time, because the thin felt and the diameter of the glass fiber are fine, more resin can be absorbed to form a resin-rich layer. The texture of the glass fiber reinforced material (such as gingham) is used to modify the surface.


(4) Needle felt

Needle felt is divided into chopped fiber needle felt and continuous silk needle felt. The chopped fiber needle felt is a short cut of 50 mm roving, placed on a substrate placed on a conveyor belt, and then needled with a barbed needle. The needle pierces the chopped fiber into the substrate. In the middle, the crochet pulls some fibers up to form a three-dimensional structure. The substrate used may be a woven fabric of glass fibers or other fibers which have a fluffy feel. Its main uses include thermal insulation materials, lining materials, and filter materials.