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New pultrusion processes of epoxy core for composite insulators

Time: 2021.01.06

Abstract  The pultrusion 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

  1. Foreword

The one of the most important components of polymer insulator is Epoxy Glass Rod, It make sure an inner-insulation of composite insulator, in addition, it is a part which undertaking a mechanical load of composite insulator. The quality of Epoxy Glass rod is a key guarantee to polymer insulators. Both Epoxy Glass Rod and polymer insulator manufacturer have a common awareness on this point. One side the polymer insulator manufacturer requested a more specific and higher quality on epoxy glass rod, the other part the epoxy glass rod manufacturer introducing and improving their quality continuously. In recent years, they developed high temperature rod, anti-acid rod, transparent rod and injection pultruded rod. On production process sector developed vacuum-aid process and injection pultrusion process and has been made a great progress. This article will introduce the development of pultrusion process and the properties of different production processes.

  • The progress of pultrusion process

The pultrusion technology started at 50 decades in USA. It was applied in 60s and developing in 70s, and develop fastest in 80s. In recent years, the increase rating of pultrusion products maintain 10% and above. The pultrusion technology has caught attentions of almost every countries. There are lots of equipment and processes surge in the market, for instance vertical pultrusion, horizontal pultrusion, bending and winding products, injection pultrusion etc. The pultrusion equipments including yarn inductor, shape performer, resin impregnating tank, shape former and puller. In China, the rise of epoxy glass rod is sync with composite insulators, they all start at 80s of 20 century.

Figure 1 Traditional Pultusion Process

There are some significant defects of this process, the first is big porosity, nontransparent of products, and internal defects like impurity, twisted, and non-soaking etc. The second is the product quality is easily effect by the environment especially air and temperature. The third is the product consistent can’t be assured as the characteristics of the resin in the tank changed with the time. So, some manufacturers installing A/C, desiccator and change resin frequently, but these method are less working.

1) Vacuum-aid pultrusion process

To solve the rod problems of porosity and nontransparent by tranditional pultrusion process, we developed the vacuum-aid pultrusion process. The characteristics of this process are multiple impregnations, vacuum-aid and try to reduce the contact area between resin and air, then improve the properties of product.

The glass fiber is divided into several layers and enters the preform die after the first dip.

The glass fiber containing a certain amount of resin enters the vacuum impregnation system to avoid the porosity and mare sure the fiber glasses are totally impregnated. As shown in figure 2.

Figure2 vacuum-aid process

This process achieved a good result in the dry environment of Northwest districts of China. By comparison with common pultrusion process, the products that gained from this process having several significant characteristics as below:

a) Less porosity, high transparent, easy to avoid the product defects, like impurity, cracks and scars, lack of resin etc.

b) Multiple layers of impregnation reducing the contact area between resin and air, reducing the influence that the environment to products.

c) The glass fiber was totally impregnated by multiple vacuum-aid impregnations.

d) The above sectors ensued a higher characteristics of products compare to the products of common pultrusion process.

Definitely, by comparison with traditional processes, this production process has a huge progress. Its appearance makes a gradually rise of transparent rods in civil market of China. But this process has not totally solve the problems of the temperature’s effected on the rod characteristic and new epoxy resin and old epoxy resin.

2) Injection pultrusion process

To solve the problems from the root that porosity, nontransparent as well as the temperature effects on the rods, we developed the Injection Pultrusion process and applied the national patent and passed it.

Figure 3 Injection pultrusion process

Key features:

a) The fiber glass has totally been soaked, there are little porosities in finished product, very good mechanical and electrical characteristics of the rod

b) The supplying system of epoxy resin could be easily isolated with the air, the rod’s features can’t be effected by the environment.

c) The injecting resin aways keeping as new resin.

d) Easily to get transparent product, making the defects can be found and avoided for instance Impurity and twisted of yarn.

e) Less effects on environment and the operators.

The stability and consistent of the rods has been big problems to the open type process of manufacturers, this problem has also brought lost to the manufacturers of composite insulators. The injection pultrusion process solved above problems perfectly.