All products that come cut of industry consist of at least one – and often many – types of materials. The most obvious example is the automobile. A car contains a wide variety of materials, ranging from glass to steel to rubber, plus numerous other metals and plastics.www.mapeng.net 马棚网机械资讯

The number of materials which are available to the engineer in industry is almost infinite. The various compositions of steel alone run into the thousands. It has been said that there are more than 10000 varieties of glass, and the number of plastics are equally great. In addition, several hundred new varieties of materials appear on the market each month. This means that individual engineers and technicians cannot hope to be familiar with all the properties of all types of materials in their numerous forms. All he can do is try to learn some principles to guide him in the selection and processing of materials.www.mapeng.net 马棚网机械资讯

The properties of a material originates from the internal structure of that material. This is analogous to saying that the operation of a TV set depends on the components and circuits within that set. The internal structures of materials involve atoms, and the way atoms are associated with their neighbors into crystals, molecules, and microstructures.www.mapeng.net 马棚网机械资讯

It is convenient to divide materials into three main types: (1) metals, (2) plastics or polymers and (3) ceramics.www.mapeng.net 马棚网机械资讯

Characteristically, metals are opaque, ductile, and good conductors of heat and electricity. Plastics ( or polymers), which usually contain light elements, and therefore have relatively low density, are generally insulators, and are flexible and formable at relatively low temperatures. Ceramics, which contain compounds of both metallic and nonmetallic elements, are usually relatively resistant to severe mechanical, thermal, and chemical conditions.www.mapeng.net 马棚网机械资讯

Metals are divided into ferrous and non-ferrous metals. The former contain iron and the latter do not contain iron. Certain elements can improve the properties of steel and are therefore added to it. For example, chromium may be included to resist corrosion and tungsten to increase hardness. Aluminum, copper, and the alloy, bronze and brass, are common non-ferrous metal.www.mapeng.net 马棚网机械资讯

Plastics and ceramics are non-metals; however, plastics may be machined like metals. Plastics are classified into two types- thermoplastics and thermosets. Thermoplastics can be shaped and reshaped by heat and pressure but thermosets cannot be shaped because they undergo chemical changes as they harden. Ceramics are often employed by engineers when material which can withstand high temperatures are needed.www.mapeng.net 马棚网机械资讯