Glass fiber reinforced plastic is based on the original pure plastic, adding glass fiber and other additives to improve the rigidity of the material, so as to improve the use range of the material.
Basics:
Glass fiber reinforced plastic is based on the original pure plastic, glass fiber and other additives are added, so as to improve the use range of materials. Generally speaking, most of the glass fiber reinforced materials are mostly used in the structural parts of the product, which is a kind of structural engineering material;Such as: PP ABS PA66 PA6 PC POM PPO PET PBT PPS
Advantages: 1 After glass fiber reinforcement, glass fiber is a high-temperature resistant material, therefore, the heat-resistant temperature of reinforced plastics is much higher than that before without glass fiber, especially nylon plastics
2. After the glass fiber is strengthened, due to the addition of glass fiber, the mutual movement between the polymer chains of the plastic is restricted, so the shrinkage rate of the reinforced plastic is reduced a lot, and the rigidity is greatly improved.
3. After glass fiber reinforcement, the reinforced plastic will not stress crack, and at the same time, the impact resistance of the plastic is greatly improved
4. After the glass fiber is strengthened, the glass fiber is a high-strength material, which also greatly improves the strength of the plastic, such as: tensile strength, compressive strength, bending strength, which is much improved
5. After glass fiber reinforcement, due to the addition of glass fiber and other additives, the combustion performance of reinforced plastic decreases a lot, and most of the materials cannot be ignited, which is a flame retardant material
Disadvantages: 1 After the glass fiber is strengthened, due to the addition of glass fiber, it will become opaque if it is transparent before the glass fiber is added. 2 After glass fiber reinforcement, the toughness of all plastics decreases, and the brittleness increases
3. After the glass fiber is strengthened, due to the addition of glass fiber, the molten viscosity of all materials increases, the fluidity becomes poor, and the injection pressure increases much more than that without glass fiber
4. After the glass fiber is strengthened, due to the addition of glass fiber, the fluidity is poor, in order to normal injection molding, the injection temperature of all reinforced plastics should be increased by 10 -30 compared with before without glass fiber
5. After the glass fiber is strengthened, due to the addition of glass fiber and additives, the moisture absorption performance of the reinforced plastic is greatly enhanced, and the original pure plastic that does not absorb water will also become absorbent, so it must be dried during injection molding.
6. After the glass fiber is reinforced, in the injection molding process, the glass fiber can enter the surface of the plastic product, making the surface of the product very rough and spotted. In order to achieve a higher surface quality, it is best to use a mold temperature machine to heat the mold during injection molding, so that the plastic polymer can enter the surface of the product, but it cannot achieve the appearance quality of pure plastic.
7. After the glass fiber is reinforced, the glass fiber is a material with high hardness, and the additives are very corrosive gases after high temperature volatilization, which is very abrasive and corrosive to the screw and injection mold of the injection molding machine. Glass fiber reinforced plastic product process From the product performance consideration, all glass fiber reinforced products require a certain length of glass fiber after shredding, generally in 04-0.8mm, in order to play a reinforcing role: the glass fiber is too short, only the role of filling, and the waste of its reinforcing performance;If the glass fiber is too long, it will affect the enhancement effect due to the poor interface between the glass fiber and the material, and the surface of the product is too rough and not smooth enough, and the surface performance is not good.
Conditions affecting the shearing of glass fiber: (1) The material must be melted more than 85% at the mouth of the glass fiber, otherwise the glass fiber will be sheared to pieces due to serious friction between the glass fiber and the material
2) The temperature at the mouth of the glass fiber should not be too low, and it must be above the melting point of the material produced, otherwise the glass fiber will be sheared and broken due to the material being too cold. This problem has been taken into account in the general process table, and it is necessary to pay attention to ensure that the temperature fluctuation is not large.
1. Reinforced PP products When producing reinforced PP products, the glass fiber is difficult to cut and is related to the glass fiber used. When the production is not smooth, there will be such a phenomenon: because the glass fiber is too long, often the die die hole is blocked, causing a broken strip, judgment method: a clump of glass fiber can be seen at the die die, the section of the finished product can be clearly seen into a clump of glass fiber or a glass fiber cut on the surface of the particle, the strip is soft but not brittle, the strip can not be completely broken, and there will be a layer of skin after the reluctance. Or it can be judged from the broken sound: the sound of the strip with poor reinforcement effect is heavier, and the sound of the strip with good reinforcement effect is more brittle when it is broken. It is commonly known as "glass fiber does not melt". If the strip is severely broken during production and the strip is soft, the performance of the finished product will definitely be reduced. According to the above characteristics of PP material, the screw shear from the back of the glass fiber mouth to the head section is very strong during the production of reinforced PP. In order to avoid the phenomenon of "glass fiber does not melt", in addition to ensuring the strong shear behind the screw glass fiber mouth, the wear size of the screw barrel also has a great impact on it. When the machine is worn too much, it is often used to reduce the temperature behind the glass fiber mouth, especially the temperature between the glass fiber mouth and the vacuum mouth, and increase the melt viscosity to improve the shear and avoid "glass fiber does not melt". However, the temperature after the glass fiber mouth should not be reduced too much, so as not to shear the glass fiber too broken and the performance will be reduced.
2. Single reinforced nylon natural color product At present, the biggest problem of this product is discoloration. There are six causes of discoloration: Sequence of change. (1) If flame retardant products are produced before the switch, whether it is flame retardant PBT or other flame retardant products, or even flame retardant nylon products, due to the influence of flame retardants, single-reinforced nylon natural color products will often change color, and the impact is long-term, sometimes as long as a shift. Among them, bromine flame retardants have the greatest impact. (2) In addition, if a dark-colored product was produced before the change of production, it often changes color. This aspect has a lot to do with production planning. If the flame retardant product or dark product is produced and the nylon natural color product is reinforced, it is often necessary to carry out high-grade cleaning, and if the cleaning machine is not clean, it will often change color. The moisture content of raw materials, including the moisture content of the drying material and the moisture content of the glass fiber. Nylon is very sensitive to moisture, and it is easy to hydrolyze when exposed to water, and it is charred and discolored. Therefore, the drying material, glass fiber and other raw materials must pay attention to waterproofing, the mixing section should be mixed and divided as little as possible, the window must be closed, the glass fiber must be placed by the window to prevent wetting, and the mixing section and the extrusion section need to be closely coordinated, so as to avoid the mixture being exposed for too long. Especially on rainy or cloudy days, the moisture content in the air is high, and the raw materials are more likely to absorb water. Selection of machine and screw. Generally, nylon 6 products can be produced in 75 machines and 70 machines, while nylon 66 products are generally produced in 70 machines, and it is easy to change color if it is arranged to be produced in 75 machines. Types of fiberglass. Generally, the color of glass fiber is the most stable in production, followed by glass fiber, and the color of glass fiber is the most unstable in production. Therefore, some high-grade nylon products must be produced with boulder ** glass fiber. Process control. (1) Temperature control If the temperature at the cutting block is too high, the nylon is easy to change color, and the cutting block is generally in the area before the glass fiber mouth and the area before the vacuum port. (2) The speed of the main engine, the larger the speed of the main engine in the production of 70 machines, the better, and the speed of the main engine is too large during the production of 75 machines, but it is easy to change color, and the color is the most stable at 350rpm, and the speed of the main engine is appropriately increased to 400rpm in order to increase the speed of the main engine. Recipe reasons. When there is modified Baso4 Micro in the formulation, the color of the finished product is often gray and yellow. Production is normal after the ingredient is removed. The reason may be that the ingredient coats the surface of the antioxidant, causing the latter to not have its effect. Description: The discoloration problem of nylon needs to be coordinated and prevented in all aspects, and prevention is the main thing. After nylon discoloration, the color is generally adjusted by adjusting the speed, feeding, current and temperature of the host, but the general effect is limited, and prevention is the main thing. 3. The color of nylon 66 natural color products is unstable The reason for the unstable color of this type of product is not very clear, and it has been observed for a long time that its influencing factors are consistent with nylon 6 natural color products, and generally have the following types: The influence of color in raw materials The color of the raw materials themselves is unstable. The performance of the nylon resin used in the formulation is unstable Some nylon resins may have many small molecules in them, which are easy to degrade and discolor. The degree of vacuum displayed by the vacuum gauge has a great influence on the color of the finished product's appearance. In general, the color stability of nylon 66 natural color products is a weak link in the nylon process, and the cause of its discoloration has not been well analyzed. In the future, it will still be a key problem to be solved in the process. 4. Some nylon black products mainly refer to nylon products with high glass fiber content (more than 40%). Because the glass fiber content in this type of product is very high, the following problems are prone to occur in the production of this type of product: Carbonization and broken strip Because the glass fiber content in this type of product is very high, a lot of heat is generated with the shear of the screw in production, and the temperature in the melt is difficult to control, resulting in melt carbonization and broken strips. The measures taken are to reduce the speed of the main engine and reduce the temperature between the glass fiber port and the vacuum port to reduce shear. Use ** glass fiber, control the temperature, use the die head with a small die hole, move the pelletizer to the direction of the machine head, and pass the water appropriately. Vacuum return material is mainly caused by the high content of glass fiber, resulting in a high viscosity of the melt. During production, the number of mold holes should not be too small, or the filter plate should be removed or replaced with a hollow filter plate.
5. Flame retardant reinforced nylon products These products often contain components with low melting points, so it is necessary to pay attention to cleaning the hopper and feeding screw of the mixing section and extrusion section when producing such products, so as to avoid agglomeration and uneven blanking. Among them, the natural color products need to control the black spots and color stability, so we should pay attention to the cleaning grade, the impact of the product before the switch, and the selection of screws and machines. 6. Reinforced alloy and reinforced ABS products These two types of products contain ABS raw materials, and the degradation temperature of ABS materials is very low, so they are easy to carbonize, which is the most important problem that needs to be paid attention to in production. Therefore, attention should be paid to the following during production: Temperature control The temperature of each zone, especially the temperature at the shear block, must be well controlled, which is the most important condition. Screw selection Because it is necessary to pay attention to the performance and processing of the finished product at the same time, it is necessary to choose different screws according to the different glass fiber content of the products produced. Products with high glass fiber content need to choose screws with weak shear, and when the glass fiber content is low, for smooth production, screws with strong shear are generally used. Main engine speed When producing reinforced alloys or ABS products with high glass fiber content, reducing the main engine speed is very helpful to avoid or reduce carbonization. Types of glass fiber Generally, the production of glass fiber is the smoothest. In addition, in the production of these products, there is often a phenomenon of "glass fiber does not melt", at this time, in order to make the glass fiber shear smoothly, the method of reducing the temperature between the glass fiber mouth and the vacuum port is generally adopted to improve the melt strength to shear the glass fiber. However, care must be taken when lowering the temperature in these areas, as too much can cause the glass fibers to be sheared and crushed, degrading the performance of the finished product.