Manufacturability and reliability of suspension composite insulators
As the country has increased the construction and transformation of power lines in the past ten years, the consumption of various insulators has increased, especially the consumption of suspension composite insulators has increased rapidly. There are about 3 million composite insulators in operation in my country. Compared with porcelain and glass insulators, suspension composite insulators have compact structure, high strength, light weight, good elasticity, not easily broken, not easily damaged by humans, excellent water repellency, no cleaning, long leakage distance, no zero value measurement, less Maintenance, installation and transportation are convenient. It has been widely used all over the world. However, if there is no guarantee through scientific design and perfect production technology, the insulators put into operation are prone to quality problems and even serious accidents.
1. Umbrella skirt and sheath forming process
At present, the main processes for producing suspension composite insulators at home and abroad are: integral extrusion sheathing, integral molding and integral injection molding.
The production cost of the overall extruded sheath and umbrella is low, and the production is convenient. The cold-shrinkable cable terminal can easily meet the requirements of customers with multiple specifications and small quantities. However, the room temperature vulcanized rubber is used for manual bonding between the umbrella skirt and the sheath, which is prone to interface bubbles, weak bonding, breakdown and other mechanical and electrical performance quality problems, and the easy aging of room temperature vulcanized rubber relative to high temperature vulcanized rubber cannot be solved. The problem belongs to the relatively backward production technology. The overall moulding is easy to put into production equipment, and the price is low. However, due to the poor flow of solid silicone rubber, especially at room temperature, the flow performance is very poor, and it is difficult to fill the mold cavity with a larger umbrella skirt or a more complex structure, which is likely to cause more surface defects and the inevitable core rod eccentricity And damage problems, which affect the quality of the product after the network is connected to the operation.
Integral injection molding is recognized as a high degree of automation, high efficiency, and stable quality. Experts at home and abroad consider it to be the most advanced vulcanization process, and it is the third generation of composite insulators. Umbrella skirt and sheath are molded with the same material at one time, and there is no interface problem of different materials in the umbrella extrusion process; silicone rubber is plasticized at a higher temperature before injection into the mold cavity to improve the fluidity of silicone rubber during injection. The injection mold is injected into the cavity under high injection pressure, so as to solve the problem of local lack of glue in compression molding. However, if there is no guarantee of perfect technology and effective management, the products produced are also prone to quality problems.
Common problems and solutions in production with injection molding process:
Mandrel eccentricity and damage problems. High temperature and high pressure silicone rubber is injected into the mold cavity from one side of the core rod, which may easily cause the eccentricity of the core rod and uneven thickness on both sides of the sheath. The serious situation is that the core rod is not protected. After long-term operation, the core rod may be brittle and may cause serious accidents. . This problem can be solved in two ways. The first is to improve the fluidity of silicone rubber. It can be easily solved by using liquid silicone rubber instead of solid rubber. Secondly, in the mold design, multiple positioning and reasonable methods of improving the fluidity of the solid glue are used to solve the problem, which can ensure that the deviation is within 0.2mm and does not damage the mandrel. Its performance can completely meet or exceed that produced by other processes. product.
The problem of difficulty in demolding, due to the characteristics of high-voltage suspension composite insulators with multiple umbrella skirts, European-style cable joints determine that the contact surface between the silicone rubber and the mold is large during integral molding, and the problem of difficult demolding is likely to occur. If it is difficult to demold, The mandrel sticking mold will crack, the lack of glue will affect the appearance, the yield will be low, and the reliability will be significantly reduced. The solution to this problem: First, adjust the silicone rubber formula to appropriately increase the proportion of mold release materials. The second is to choose imported steel for the mold cavity material, and improve the polished finish, improve the processing technology of the mold, or the inner cavity is electroplated with chromium.
The problem of temperature difference damage to the mandrel in segmented molding. At present, several domestic manufacturers have achieved one-time injection molding of products of 220kV and below, without segmented molding. Insulators above 500kV use segmented molding technology. Since the vulcanization temperature of silicone rubber is generally around 170°C, the core rod is in the mold. The cavity temperature and the indoor temperature reach about 150°C. Different power heaters are used at the connection to heat up in sections to eliminate the problem of excessive temperature stress caused by sudden temperature changes. After the improvement of this method, the problem of damage to the mandrel due to temperature stress has never been found.
2. Mandrel and hardware connection process
There are currently three main methods for connecting mandrels and fittings at home and abroad: bonding, wedge bonding and crimping. Due to the aging problem of the adhesive, low temperature embrittlement and low efficiency, the bonding effect is greatly affected by human factors, etc., it has been seldom used; the wedge connection is divided into inner wedge and outer wedge, and the inner wedge will damage the mandrel. It is used by a small number of manufacturers to reduce the mandrel and mechanical strength. The external wedge has been rarely used due to unstable connection strength and complex process, high drop rate; if the crimping type adopts perfect process control, it will be greatly improved For production efficiency and product quality, most domestic and foreign manufacturers currently use crimping methods. The relationship between crimping technology and quality will be discussed below.
Through crimping, the insulator fittings are plastically deformed and the core rod is compressed to generate strong friction and obtain the required tensile strength. The best crimping result should be that under the action of the crimping force, the fittings are fully deformed and fully adhered to the mandrel without excessive deformation, which will make the brittle mandrel brittle and maximize the deformation resistance of the fittings. It is extremely difficult to achieve this effect. It not only requires complex elastic-plastic performance calculations but also considers various external factors, which are generally solved by experience and a large number of tests.
At present, there are mainly three control methods for crimping:
One is the unidirectional movement of the mold. The crimping mold has only two upper and lower pieces. The hydraulic device pushes the mold to move up or down in a single direction to squeeze and plastically deform the hardware to achieve the crimping effect. Since the hardware, mandrel, machine and mold itself have certain processing tolerances, the plastic deformation of the hardware is uneven, and the crimping speed is too fast, and whether it is over-pressure can not be judged, the crimping quality is unstable, and the method is limited to a small number of manufacturers. For products with low voltage levels and low mechanical strength.
The second method is to use eight radially evenly distributed molds to generate a constant pressure under the action of an oil cylinder to control the crimping force of the fittings, and to monitor the quality of the mandrel with an acoustic emission monitoring system during the crimping process. Compared with the first method, this method has a qualitative improvement in the crimping effect, but it also has a flaw in the middle: one is that the concentricity and synchronization after the mold and the cylinder are matched cannot be very precise, and the second is that each batch of hardware or the same batch of materials They are not exactly the same. The materials of the ball head and socket are also different. There are also certain differences in the heat treatment process of the surge arrester manufacturers, resulting in different hardness of each hardware and different crimping forces. The existence of these two problems ultimately leads to the disadvantage of unstable crimping effect.
The third is a method in which eight radial molds are evenly distributed, and the crimping amount of flexible crimping is controlled through a one-time processing of force-increasing taper sleeves. The crimping process is also used with the acoustic emission monitoring system to monitor the quality of the mandrel. This solution solves: First, the plastic fittings are crimped with the brittle mandrel and the deformation is only 0.2～0.5mm. If the crimping speed is too fast, the mandrel will be damaged, and the rebound of the fittings will be increased, so that the fittings and the mandrel cannot be tightly combined. The problem of reduced crimping strength is that this solution adopts a slow and continuous crimping method of 3 to 5 seconds and a flexible crimping method of 0-9 seconds holding pressure, which not only greatly reduces the risk of mandrel crimping damage, but also improves the bond between the metal fittings and the mandrel. Crimping strength. Second, there are processing deviations between the fittings and the mandrel. Each batch or the same batch of parts has different dimensions and tightness. The pre-tightening pressure can be set during the crimping, and the gap between the fittings and the mandrel can be eliminated before the crimping amount is measured. To ensure that each product has the same crimping effect, the third is the synchronization and concentricity of crimping. When processing modules, first process the inner, outer circle, length, mounting holes, etc., and then cut into eight modules on average. The booster taper sleeve is also a one-time taper, and there is no problem with too many accumulated tolerances. , To ensure the overall concentricity and synchronization.
3. End sealing process
The brittle fracture of the insulator core rod will cause the most serious accident of the wire landing. If the mandrel is not effectively protected, the intrusion of moisture and corrosive gas is one of the most important factors causing the brittle fracture of the mandrel. The intensity of the electric field at the end is complex, which is where the most important protection is needed. At present, various manufacturers of end seals mainly use normal temperature vulcanized rubber to seal; use normal temperature vulcanized rubber to seal the formed sealing ring; use high temperature vulcanized rubber to seal the three methods at a time. The performance of room temperature vulcanized silicone rubber is different from that of high temperature injection. Its mechanical properties, electric corrosion resistance and aging resistance are far worse than high temperature vulcanized silicone rubber. Under high-voltage outdoor operation, the product is often exposed to electrical, mechanical and outdoor sunlight. Rainwater impact, end seal deterioration and moisture intrusion may occur after long-term operation, and it is difficult for the mandrel to get the protection it deserves. The seal on the high temperature silicone rubber is to inject the silicone rubber through the injection machine at high temperature and high pressure, and then vulcanize it in the mold as a whole with the sheath. The sealant fully fills all the gaps between the fittings and the mandrel; and it is tightly bonded with the fittings to completely root. In addition to the interface air bubbles sealed with room temperature glue, weak bonding, man-made defects, and hidden dangers, the reliability of the end seal is greatly improved.
Based on the above, the suspension composite insulator jacket adopts integral injection molding at one time, the hardware connection adopts flexible crimping with sonic abrasion tester, and the end seal adopts high-temperature silicone rubber. The production process of one-time integral sealing is the best and effective way to ensure the long-term operation of the product. Method.
Yichang Hengyuan Technology Co., Ltd. is a professional manufacturer of European-style cable connectors, plug connectors, cable branch boxes, American elbow connectors, high-voltage vacuum circuit breakers, high-voltage load switches, lightning arresters, zinc oxide arresters, tank arresters, overvoltage protectors, Counters, monitors, heat-shrinkable cable accessories, cold-shrinkable cable accessories, T-shaped heads, wall bushings, European cable accessories, American cable joints, transformer neutral point protection devices, fuses, isolating switches, PT cable heads, elbows Manufacturers of type cable joints, 10kV outdoor terminals, switch cabinets, cable intermediate joints, cable accessories and other products
