1. Properties of insulating materials
Insulating materials in household appliances are related to the quality and performance of electrical products, so the critical position of insulating materials in electrical products is beyond doubt. There are many home appliance types, and each product type’s insulating materials requirements differ. However, to ensure the safety of home appliances, the insulating materials used for home appliances should meet the following criteria. 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 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 a 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.
Good heat resistance, flame retardant properties
In using the appliance, due to the continuous flow of current, the long-time, uninterrupted use will lead to the appliance’s temperature rising, the insulation material in the external temperature increases, its conductivity will rise, and the insulation performance will be significantly reduced. As a result, there is a risk of softening and firing the insulation material, which can devastate the entire appliance or circuit system. So, the insulation material has elemental electrical resistance but must also be heat-resistant and flame-retardant at high temperatures.
Good anti-aging properties
Insulation materials exposed to heat, electromagnetic fields, light exposure, oxidation, mechanical forces, and the ravages of microorganisms for extended periods will experience depreciation loss, gradually weakening their insulation performance and strength. The two aspects of electricity and heat are the most critical factors affecting the degree of aging of insulation Οee materials, so the aging resistance of insulation materials after long-term use directly affects the service life of home appliances.
Good moisture resistance
Moisture and humidity are generally precautionary when using electrical products, as moisture will lead to a short circuit in the entire circuit. Using insulation material as a physical medium may lead to the material having cracks or capillaries. If the external environment of the insulation material is relatively wet, water molecules may penetrate the insulation material through these fine lines or pores. After the insulation material is damp, the insulation performance will be affected, and 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; they have 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 humans: 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 fundamental. China’s GB4706 series of standards has 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.
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 when operating electrical appliances. Whether the electrical appliances usually work or not, 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 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. Chapterr 29 of the standard limits 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 to resist leakage start ability, to ensure the safe use of products in specific environmental conditions.
Safety requirements of mechanical properties
Parts made of insulating materials and their structures should have sufficient mechanical strength to resist external forces. Mechanical strength is the maximum load per unit area that can be withstood 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.
Heat and flame resistance safety requirements
Electrical products in thregularal 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 and flame resistance to ensure their safety. 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 entirely 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. The 30.2.2 and 30.2.3 tests are 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 decide whether or not it passes.
Safety requirements for moisture resistance
Insulation material components are in the microscopic existence of capillary pores and inevitable cracks because the diameter of water molecules is much smaller than these capillary pores and cracks, so water molecules can easily penetrate the insulation material. 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 considerably deteriorate, resulting in the electrical properties of electrical products being damaged. Therefore, electrical products should have sufficient moisture resistance to maintain good electrical performance and 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. Therefore, when selecting insulation materials, it is essential to ensure the quality of the materials and consider the use of home appliances and other factors so that appliances in use ensure lasting safety.
