Physical Properties of Plastics（5）
Wear refers to the mechanical damage process in which the particles are continuously separated from the friction surface during the friction process of plastics, resulting in the continuous change of the size of friction parts. It is also called wear or abrasion. Hardness plastic hardness refers to the resistance of plastics to other hard objects. Generally, there are Rockwell hardness and shore hardness.
Shore hardness refers to the depth pressed by the indenter needle under the specified pressure and time. Shaw indenters can be divided into two types: type A and type D. The applied load weight is 1. 0、5。 0 kg, pressing time is 15 seconds, type A is suitable for soft plastics, and type D is suitable for semi-hard plastics; When type A is used to measure more than 95% of the measuring range, type D shall be used. When type D measures more than 95% of the measuring range, Rockwell indentation shall be used. Fatigue strength refers to the strength of plastic failure in an environment with static failure force and a small amount of alternating cycle; Fatigue load sources include tension and compression, bending, torsion, impact, etc.
Creep refers to the characteristics of plastic changing with time under the continuous action of fixed external force under certain temperature and humidity conditions. This deformation characteristic increases with the increase of load, decreases with the decrease of load, and its deformation also gradually recovers. The sources of creep include tensile creep, compressive creep, bending creep and so on. Endurance strength endurance strength refers to the time function that the ability of plastics to withstand static load for a long time decreases from high to low.
For example, the plastic strength before loading is 1000 hours, while after loading, it may be only between 50% and 70%. Linear expansion coefficient linear expansion coefficient refers to the number of centimeters of plastic elongation per centimeter when the temperature rises by 1 ℃. The linear expansion coefficient of plastics is generally about ten times that of steel.
Specific heat refers to the unit of heat required when 1 gram of plastic is difficult to rise by 1 degree Celsius. Thermal conductivity refers to the unit of heat that a certain unit of area and thickness of plastic can pass through. The thermal conductivity of plastic is very small, only about 1% of that of steel, so it is a good thermal insulation material. Heat resistance plastic heat resistance is a characteristic that reflects the relationship between temperature and deformation of plastic parts. Heat resistance is more important for temperature related plastic parts.