I. Definition and classification of engineering plastics
Engineering plastics is a specific name. Its broad sense refers to the plastic with high performance and may replace the metal material; narrow sense refers to the strength and heat resistance than the general-purpose plastics (PE, PP, PVC, ABS and other thermoplastics), can be used as a structural material for industrial use and has a functional role in the structure of the high-performance plastics.
Plastics can be divided into two categories: thermoplastic (melt flow when heated) and thermosetting (three-dimensional structure insoluble when heated). Engineering plastics can also be divided into two categories of special engineering plastics and general engineering plastics. The so-called general engineering plastics often refers to thermoplastic polyamide (PA). Polyformaldehyde (POM), polycarbonate (PC), modified polyphenylene ether (PPO, also abbreviated as PPE), polyester (PBT and PET) and so on five, and special engineering plastics often refers to the above five kinds of engineering plastics in addition to the performance of the more excellent. According to the use temperature, the general use temperature is 150℃. Below the general engineering plastics (generally 100 ℃ -150 ℃), more than 150 ℃ for the special engineering plastics, special engineering plastics are divided into 150 a 250 ℃ class (including general engineering plastics, including compounds) and more than 250 ℃ class. The higher the use of temperature, the price also increases.
Second, the characteristics of engineering plastics:
Compared with metal materials:
(1) Advantages:
(a) small specific gravity: 1.0 - 2.0, about one-sixth of the iron, reducing the weight of the effect of large;
(b) good processing, high production efficiency;
(c) resistant to water and various chemicals corrosion;
(d) good self-lubrication, small coefficient of friction
(e) can be free coloring;
(f) easy to be compounded with glass fibers and a variety of fillers;
(g) excellent electrical insulation;
(h) excellent thermal insulation, thermal conductivity of about one-hundredth of iron, copper two-thousandths of a percent. one hundredth of iron and less than two thousandths of copper;
(i)It can reduce cost and save resources and energy.
(2) Disadvantages:
(a) low heat resistance, low softening point;
(b) low mechanical strength, tensile strength is generally about one-tenth of steel;
(c) poor dimensional stability, the coefficient of linear expansion of about five times that of steel;
(d) poor durability, fatigue is easy to produce by gravity for a long period of time, and long-term ultraviolet radiation in the outdoors, easy to reduce performance. The role of the outdoor long-term ultraviolet light, easy to reduce performance.
Three, the use of engineering plastics
1. According to the use of classification engineering plastics are roughly divided into; one is the strength, drug resistance, abrasion resistance and other requirements of the functional parts; the other is the shrinkage rate, dimensional accuracy, appearance, and other requirements of the mechanical parts. Generally speaking: the former for the crystalline engineering plastics, the latter for the non-crystalline engineering plastics. Practical applications often require the performance of both. The use of glass fiber (GF) or carbon fiber (CF) reinforced engineering plastics are more suitable for this requirement.
2. Engineering plastics in automotive, electrical and electronic applications accounted for more than half, while the main use of general-purpose plastics is extrusion molding (51%) and non-industrial products (21%).