1, Properties of insulating materials
The use of insulating materials in household appliances is related to the quality and performance of electrical products, so the important position of insulating materials in electrical products is beyond doubt. There are many types of home appliances, and the requirements for insulating materials are different for each type of product. However, in order to ensure the safety of home appliances, the insulating materials used for home appliances should meet the following requirements:
a. Good dielectric properties
Dielectric properties of insulation materials, including resistance, leakage current, dielectric constant, dielectric strength, dielectric loss, etc., are used to indicate the dielectric properties of the applied voltage conditions and changes in the quality of insulation. Any insulation material in the applied voltage will have leakage current flow through the insulation material, in this process, the current in the insulation material surface resistance encountered for the surface resistance, the resistance value is generally between 107 ~ 108Ω; in the insulation material through the resistance encountered in the medium for the volume resistance. Under the same conditions, the volume resistance is greater than the surface resistance. The dielectric constant is the growth multiple of the capacitance between the two plates in the presence of dielectric and the capacitance in the vacuum state. The ability of the insulating material to resist electrical breakdown is called electrical strength, while dielectric loss is the electrical energy consumed by the dielectric heating under the applied voltage. In daily use, dust or moisture can affect the dielectric properties of the insulation material.
b. Good heat resistance, flame retardant properties
In the process of using the appliance, due to the continuous flow of current, the long time uninterrupted use will lead to the temperature of the appliance rise, the insulation material in the external temperature increases, its own conductivity will rise, while the insulation performance will be significantly reduced. As a result, there is a risk of softening and fire of the insulation material, which can bring devastating damage to the whole appliance or even the whole circuit system being used. So the insulation material has the basic electrical resistance, but also must be able to have heat-resistant, flame retardant properties at high temperatures.
c. Good anti-aging properties
Insulation materials in the long-term use of heat, electromagnetic fields, light exposure, oxidation, mechanical forces, and the ravages of microorganisms, there will be depreciation loss, this depreciation loss will make the insulation material insulation performance and insulation strength gradually weakened. The two aspects of electricity and heat are the most important factors affecting the degree of aging of insulation Οee material, so the aging resistance of insulation materials after long-term use directly affects the service life of home appliances.
d. Good moisture resistance
Moisture and humidity are generally a precaution in the use of electrical products, moisture will lead to a short circuit of the entire circuit. Insulation material as a physical medium, its own process leads to the material itself may have cracks or capillaries. If the external environment of the insulation material is relatively wet, water molecules may penetrate into the insulation material through these fine lines or pores. After the insulation material is damp, not only the insulation performance will be affected, but also the insulation material will gradually corrode, the insulation performance of the whole appliance will be reduced, and the safety index will be lowered.
2, Standard safety requirements
The development and popularization of household electrical appliances have brought great social benefits, it has reduced household chores, enabled users to have more time for study, entertainment, and rest, and gained a lot of conveniences. However, electrical appliances also bring many hazards to human beings: fire, electric shock, harmful rays, electromagnetic interference, etc. Among them, fire is the most dangerous and directly related to people’s lives and properties. Therefore, the safety characteristics of household appliances are particularly important. China’s GB4706 series of standards have made strict regulations on the safety characteristics of household appliances, and the following is a description of the safety requirements for insulation materials in conjunction with the standards.
(1) Safety requirements of electrical performance
In electrical products, the role of insulating materials is to isolate conductive parts of different potentials and polarities from each other for energy conversion. Insulation materials are subjected to the electric field in the operation of electrical appliances, whether the electrical appliances can work normally, insulation materials play a decisive role to a certain extent. The greater the resistivity of the insulation material, the better the insulation performance, and the smaller the leakage current. In GB4706, chapter 13 of the apparatus under the working temperature leakage current and electrical strength makes provisions for testing the electrical performance of the apparatus at working temperature. Leakage current generally refers to the current flowing through the insulation part under the action of high DC voltage. Leakage current measurement and insulation resistance in the measurement of the essence of the same, to a certain extent, reflect the insulation state of electrical products. Chapter 29 of the standard puts limits on the leakage resistance index for different material groups. The leakage start resistance test is a simulation of the accelerated test under very harsh conditions to test whether the insulation materials will form leakage traces so that the solid insulation materials can be distinguished in a short period of time to resist leakage start ability, to ensure the safe use of products in specific environmental conditions.
(2) Safety requirements of mechanical properties
Parts made of insulating materials and their structures should have the sufficient mechanical strength to resist external forces. Mechanical strength is the maximum load per unit area that can withstand when subjected to external forces. Chapter 21 in GB4706 is dedicated to the mechanical strength test, the electrical properties of the apparatus should not be affected after the test. The general standard of Article 21.2 also provides for solid insulation of easy-to-reach parts that should be strong enough to prevent the piercing of sharp tools. So the mechanical properties of the insulation material should not be ignored as well.
(3) heat and flame resistance safety requirements
Electrical products in the normal use of the process will have the phenomenon of heat, resulting in insulating material parts heat temperature rise, resulting in higher electrical conductivity of insulating materials, and insulation performance decline; at the same time, if the temperature is too high, will also cause the softening of insulating material parts, and even aging, reducing its mechanical properties; in some conditions, insulating materials will also have the risk of fire. Therefore, insulating materials must have a certain degree of heat resistance, and flame resistance, to ensure the safety of use. In GB4706 general standard 30.1: for non-metallic materials made of external parts, insulation materials used to support charged parts (including connections) additional insulation live to strengthen the insulation of thermoplastic material parts, its deterioration can lead to apparatus does not meet this standard, should be fully heat-resistant. Through the ball pressure test on the parts concerned to determine compliance. In standard 30.2, the non-metallic material parts used in the apparatus required for ignition and flame spread should have resistance. Which 30.2.2 and 30.2.3 test is a special tests on the insulating material parts of the current-carrying connections. The flame resistance of the insulating material is generally determined by the scorching wire test to determine whether it passes.
(4) Safety requirements for moisture resistance
Insulation material components in the microscopic existence of capillary pores and certain cracks, because the diameter of water molecules is much smaller than these capillary pores and cracks, so the insulation material is easy to be penetrated by water molecules. The water molecules in the dampness enter the insulating material through condensation, adsorption, absorption, diffusion, breathing, etc. After the insulating material absorbs the dampness, the insulating performance will be greatly deteriorated, resulting in the electrical properties of electrical products being damaged. Therefore, electrical products should have sufficient moisture resistance to maintain their good electrical performance, to provide safety protection. Chapter 15 of GB4706 is for different appliances in the possible moisture conditions under the security requirements.
In summary, the performance of insulation materials is closely related to the safety characteristics of household appliances, so in the selection of insulation materials, both to ensure the quality of insulation materials, but also to consider the use of home appliances and other factors, so that appliances in use to ensure lasting safety.