Related knowledge of enameled wire

Enamelled wire is a major type of winding wire, consisting of a conductor and an insulation layer. The bare wire is annealed and softened, then painted and baked multiple times. However, it is not easy to produce products that meet both standard requirements and customer requirements. It is influenced by factors such as raw material quality, process parameters, production equipment, and environment. Therefore, the quality characteristics of various enameled wires are different, but they all have four major properties: mechanical, chemical, electrical, and thermal.

Enamelled wire is the main raw material for products such as motors, appliances, and household appliances. Especially in recent years, the power industry has achieved sustained and rapid growth. The rapid development of household appliances has brought a wider range of applications for enameled wire, which has led to higher requirements for enameled wire. Therefore, it is inevitable to adjust the product structure of enameled wire, and the corresponding raw materials (copper, paint), enameling process, process equipment, and testing methods are also urgently needed for development and research.

At present, there are over a thousand manufacturers of enameled wire in China, with an annual production capacity of over 250000 to 300000 tons. But overall, the situation of enameled wire in China is a low-level repetition, which can be summarized as "high production, low grade, and outdated equipment.". In this situation, high-quality enameled wires for household appliances still need to be imported, let alone participate in international market competition. Therefore, efforts should be doubled to change the current situation, so that China's enameled wire technology can keep up with market demand and squeeze into the international market.

1) Acetaldehyde enameled wire

Formaldehyde enameled wire is one of the earliest developed varieties in the world. It was introduced to the market by Germany and the United States in 1930, and the Soviet Union also developed rapidly. There are two types: polyvinyl formal and polyvinyl acetal. China also successfully researched them in the 1960s. Although the temperature resistance level of this enameled wire is low (105 ° C, 120 ° C), it is widely used in oil immersed transformers due to its excellent high-temperature hydrolysis resistance. This characteristic has been recognized by countries around the world. Currently, there is still a small amount of production in China, especially acetaldehyde enameled flat wire used to make transposition wires for large transformers.

2) Polyester enameled wire

In the mid-1950s, West Germany was the first to successfully develop polyester enameled wire paint based on dimethyl terephthalate. Due to its good heat resistance and mechanical strength, wide range of paint making processes, and low price, it has become the main product dominating the enameled wire market since the 1950s. However, due to the poor heat resistance and impact resistance of polyester enameled wire, as well as its susceptibility to hydrolysis under high temperature and humidity conditions, polyester enameled wire as a single coating was no longer produced in West Germany and the United States in the late 1970s. However, it is still widely produced and used in Japan, China, and Southeast Asia. The statistics from 1986 indicate that the production of polyester enameled wire in China accounted for 96.4% of the total production. After 10 years of effort, the variety of enameled wire has been developed, but there is a significant gap compared to developed countries.

A lot of work has also been done on polyester modification in China, including research and development on THEIC modification and imine modification. However, due to the slow adjustment of the structure of enameled wire, the production volume of these two types of paints is still not large. So far, the issue of voltage drop in modified polyester enameled wires still needs to be taken seriously.

3) Polyurethane enameled wire

Polyurethane enameled wire paint was developed by Bayer in Germany in 1937. Due to its direct solderability, high frequency resistance, and dyeing properties, it is widely used in fields such as electronics and electrical appliances. At present, foreign countries are extremely concerned about improving the heat resistance level of polyurethane enameled wire without affecting its direct welding performance. F-grade and H-grade polyurethane enameled wires have been developed successively in Europe, the United States, and Japan. Due to the rapid development of color televisions, Japan's development of a long length polyurethane enameled wire for FBT color televisions without salt water pinholes has attracted the attention of countries around the world, and it is still Japan's leader.

The development of domestic polyurethane enameled wire is slow. Although some factories produce ordinary polyurethane paint, due to poor craftsmanship and surface quality issues, the paint mainly relies on imports. F-grade polyurethane has also been developed domestically, but has not yet formed production capacity. Large length non pinhole polyurethane paint has also been successfully developed and put on the market, mainly used for making black and white TV FBT coils.

4) Polyester imine enameled wire

Due to the improvement of heat resistance through modification of polyester with imine, the usage of polyester imine enameled wire in the world has sharply increased since the 1970s. In Europe and America, this enameled wire has completely replaced single coated polyester enameled wire. Currently, representative products in the world are the Terebe FH series products from Germany and the Isomid series products from the United States. At the same time, we have also developed directly solderable polyesterimide enameled wires, which have been widely used as windings for small motors, simplifying welding processes and reducing motor manufacturing costs. Some Japanese companies also use direct soldering polyester imine paint as the primer for self-adhesive enameled wires for color TV deflection coils, simplifying the process. Domestic polyester imine paint has successively introduced manufacturing technology from Germany and Italy, and has also been successfully developed independently. However, due to unstable raw materials and other reasons, a large number of polyester imine paints used as cold resistant composite enameled wire primers in China still rely on imports. Only a small number of single coated polyesterimide enameled wires are coated with domestic paint, but voltage instability is still a concern for manufacturers. Direct soldering polyesterimide paint has been successfully developed by the Cable Research Institute.

5) Polyimide enameled wire

Polyimide is currently the highest heat-resistant enameled wire paint among organic enameled wires, with a long-term usage temperature of over 220 ° C. This paint was successfully developed by the United States in 1958. Polyimide enameled wire has high heat resistance, good resistance to solvents and refrigerants. However, due to its high cost, poor storage stability, and toxicity, its widespread use has been affected. At present, this enameled wire is used in certain special occasions, such as coal mine motors, space instruments, etc.

6) Polyamide imide paint

Polyamide imide paint is currently known as the king of enameled wire paint due to its comprehensive performance, high heat resistance, mechanical properties, resistance to refrigerants, and chemical resistance. This paint is currently mainly used for its unique properties and is widely used as a topcoat for composite coated enameled wires, improving the heat resistance of composite wires and reducing costs. At present, it is mainly used to coat cold resistant enamel wire in China, with a small amount of production domestically, mainly imported from the United States, Italy, and Germany.

7) Composite coated enameled wire

To improve the temperature resistance level and develop special purpose enameled wires, composite insulation layers are generally used. Compared with single coated enameled wire, composite coated enameled wire has the following advantages: (1) it meets special usage requirements, such as self-adhesive enameled wire for complex frameless forming, and cold resistant enameled wire for refrigerators, air conditioning compressors, etc., which can be met through composite coating structure; (2) By compounding various insulation layers to make up for their strengths and weaknesses, and improving and enhancing their performance to meet usage requirements, such as polyester/nylon composite coated enameled wire which improves thermal shock performance and winding performance, it is suitable for hot impregnation process and can be used for motor windings that experience instantaneous overheating due to overload; (3) It can reduce the cost of certain enameled wires, such as polyester imide, polyamide imide composite coated enameled wires replacing single coated polyamide imide enameled wires, which can greatly reduce costs.