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abstract
This paper introduces and reviews the present situation and the latest progress of the production of mandrel for composite insulators, as well as the technological principle and product features of traditional pultrusion, vacuum assisted pultrusion and injection and pultrusion. Compared with the traditional process, the vacuum assisted pultrusion process has improved the transparency and stability of the products, while the injection pultrusion has fundamentally solved the shortcomings of the open dip, ensuring the consistency of the product characteristics. This paper also puts forward the problems that need to be solved and solved.

Keywords composite insulator, epoxy mandrel and pultrusion process

New pultruslon processes of epoxy core for composite Insulators. Abstract The pullrusion process and its recently development of epoxy core for composite insulators is reviewed. The traditional process, vacuum-aid process and Injection pultrusion process are introduced briefly also. Comparing with traditional process, the core by vacuum-aid process is more transparent and consistent in performance. The injection pultrusion process eliminates the disadvantages of open-to-air impregnating system and ensures the consistency of core performance. The problems to be resolved or studied are suggested in final. Key words composite insulator,epoxy core,pultrusion process.

Preface

One of the most important parts of the composite insulators is the core, it is not only the internal insulation of composite insulators that bear components are mechanical load of composite insulator, its quality is an important guarantee for the reliability of composite insulators. No matter is the composite insulator manufacturer or mandrel manufacturers are aware of this, on the one hand, composite insulator manufacturers put forward more specific and higher requirements on the insulator rod; on the other hand the mandrel manufacturers are constantly innovation, improve product quality. In recent years the development of heat resistant, acid resistant, transparent mandrel mandrel mandrel and injection pultrusion rod, in the production process of the development of vacuum pultrusion process and injection pultrusion process, has made considerable progress, this paper first introduces the characteristics of pultrusion process development and production process of different mandrel.

Progress of pultrusion process of epoxy mandrel in China
Pultrusion technology began in 50s, first registered in the United States patent application, 60s, 70s, 80s at the fastest speed of development in recent years, the growth rate of pultruded products is maintained at more than 10%. Pultrusion process has attracted the attention of all countries, all kinds of pultrusion equipment and processes are emerging, such as vertical pulling, horizontal pulling, bending, extrusion, injection, pultrusion and so on.The rise of China's epoxy insulator and pultrusion rod of composite insulator is synchronous, all from the last century, the early 80s began to rise, pultrusion equipment guide, including pre molding, epoxy resin dip tank, molding, traction machine. The process is: after the glass fiber yarn and pre forming die after (some manufacturers do not, after dipping the groove) open, under atmospheric pressure, the glass fiber is soaked, after molding after curing, pulled by a tractor. Most of the equipment used is crawler traction, as shown in figure 1.

This process has several obvious disadvantages, first of all is the product of the porosity is large, difficult to obtain transparent products, so that the internal defects of the mandrel (such as ground thrum, inclusion, dipping is not sufficient) is not easy to find; second is affecting the quality of products by the environment, especially the influence of environmental temperature and humidity; third is the curing characteristics of plastic pot adhesive varies with the extension of time, the consistency of the characteristics of the product can't be guaranteed. So some manufacturers in high humidity and high temperature season production or take in the dipping part is additionally provided with air conditioning, dehumidifiers, often for glue and other methods, trying to solve these problems, but the effect of these methods is limited.

Vacuum assisted pultrusion
In order to solve ordinary pultrusion rod porosity is large, opaque products, our two 00 year development of vacuum assisted pultrusion process, the features of this process is repeated dipping, vacuum assisted and minimize the contact area of the rubber and the atmosphere, so as to improve the performance of the product. Glass fiber multi-layer by first dipping into the pre forming die extruding glue, glue containing glass fiber into the vacuum impregnation system, eliminate pores and further dipping to reduce pores and ensure that the glass fiber fully soaked in vacuum condition, as shown in figure 2.

This process has achieved better results in the relatively dry environment in Northwest China. The performance of the products has been improved obviously in the following aspects:
Products of low porosity and high transparency, the product defect is easy to delete, such as the thrum, inclusions, lack of glue etc；
Multi layer dipping reduces the contact area between the gel and the atmosphere, thus reducing the environmental impact of the product；
Many times vacuum assisted impregnation makes glass fibers fully saturated;
The above aspects ensure the stability of the vacuum pull mandrel, which is more stable than that of the ordinary pultrusion.

Undoubtedly, this process has greatly improved compared with the traditional process, it appears that the gradual rise of the domestic epoxy transparent mandrel, but this process is not completely solve the influence of environmental temperature on the product characteristics and the new and old times "problem (the problem of glue application period). The new gum is just adding glue groove good glue, the curing characteristics; the old glue refers to the residual glue groove in glue, because anhydride (curing agent) and air H2O reaction and adhesive curing reaction to change adhesive curing characteristics.

Injection pultrusion

In order to fundamentally solve the pressure for open dipping prone glass fiber impregnated impermeable and bubble entrainment, product performance is affected by environmental factors and the disadvantages of the process for the production of resin has higher requirements of the shortcomings existing units to develop new technology of injection of garbage and declared a national patent and passed the identification.

Through the glass fiber yarn guide and pre molding, into a continuous resin transfer molding mold, the mold to stable pressure and flow into the special resin and the glass fiber is fully saturated with and remove air bubbles; curing mold and fully saturated with a bubble free glass fiber into the mold in the traction machine. In order to achieve continuous resin transfer molding (Continuous Resin Transfer Molding Pultrusion Process CRTM) or injection pultrusion

Its characteristics:
The glass fiber is fully soaked, and the FRP products have less micro bubbles and excellent mechanical and electrical properties;
The resin supply system is easy to isolate from the atmosphere, and the performance of the product is not affected by the environment;
The injection of the resin has always maintained the same curing characteristics (always "new gum");
Easy to obtain transparent products, products defects (such as inclusions, yarn, etc.) easy to find and delete.
Little impact on the environment and the operators.

The stability and consistency of mandrel performance, has been open dipping rod manufacturers are difficult to solve and the headache problem, this problem has also brought losses to the composite insulator manufacturer, especially in high humidity and high temperature to 5 in October (in the South can be larger and longer) injection. Pultrusion process in addition to solve the problem of environment influence, also solve the problem of glue application period, it does not exist "old 'gum problems, always is the' new gum", so to ensure product consistency and stability.

At present, China's production process of composite insulator core is mainly the traditional process, the biggest problem is the temporal and seasonal variation characteristics of the product is large, the mandrel manufacturers should strengthen the control, closely monitor the change characteristics of products, high temperature mechanical properties and color of a relatively simple method is to monitor product changes, such as hot bending strength the value should take active measures below a certain value, such as the change in the resin glue, can not join the dye to ensure that the color is consistent, of course if there are conditions by vacuum or injection pultrusion is a good solution; secondly, because most of the mandrel mandrel opaque, manufacturers should try to eliminate the defect in the mandrel. As thrum, inclusion, lack of plastic, hard rubber block, local crack; third, should strengthen the glass fiber and raw materials, especially the control of the curing agent, the process. Rule fourth written by fan; special standard rod composite insulator, technical conditions and requirements of the reference is not complete.

In addition to the above problems, some basic problems should be paid attention to, first of all is the glass fiber content, according to the domestic often accepted view, glass fiber with high content of some good, diameter of mandrel glass fiber content of 18mm is 81 (weight indicator) 83%, while the foreign products of glass fiber content is low for. Such as: Glassforms line suspension insulator core rod with 73-80% line pillar and cross arm mandrel with 70-77%, so low content of fiber core can not be produced domestically, it presents a problem, that is the level of glass fiber content means what; followed by domestic production with mandrel releasing agent. These release agent are not included in the fixed reaction, with the passage of time, the release agent to the surface of the mandrel and the silicone rubber mandrel or mandrel and a metal accessory interface or diffusion interface, thus affecting the long-term performance of insulator. Foreign liquid metal vertical curing pultrusion die mandrel, the content of glass fiber production can be adjusted in a large range, and not with resin release agent.

How to ensure the quality stability of core technology research, a new method to remove the release agent and mandrel with different content of glass fiber, standard mandrel pultrusion process is pultrusion process need to solve future problems of various properties of the mandrel; glass fiber content (including fatigue characteristics) influence, making mandrel standard is the foundation a study of composite insulator industry, manufacturers need to pay attention to the mandrel.

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