Lesson 7 Fasteners and Springs 紧固件和弹簧 机械专业专业英语教学用书.ppt

Lesson 7 Fasteners and Springs 紧固件和弹簧 Fasteners are devices which permit one part to be jointed to a second part and，hence，they are involved in almost all designs．The acceptability（满意程度）of any product depends not only on the selected components，but also on the means by which they are fastened together．The principal purposes of fasteners are to provide the following design features： Lesson 7 Fasteners and Springs 紧固件和弹簧 （l）Disassembly for inspection and repair； 为检查和维修提供拆卸的方便； （2）Modular design where a product consists of a number of subassemblies．Modular design aids manufacturing as well as transportation． 为由许多部件组成的组合式设计提供方便。采用组合式设计可以便于生产制造和运输。 There are three main classifications of fasteners，which are described as follows： 紧固件可以分为以下三类： Lesson 7 Fasteners and Springs 紧固件和弹簧 l．Removable (可拆式)．This type permits the parts to be readily disconnected without damaging the fastener. An example is the ordinary nut-and-bolt fastener. 2．Semipermanent半永久式．For this type，the parts can be disconnected，but some damage usually occurs to the fastener．One such example is a cotter pin (开口销)． 3．Permanent永久式．When this type of fastener is used，it is intended that the parts will never be disassembled．Examples are riveted and welded joints (铆接和焊接)． Lesson 7 Fasteners and Springs 紧固件和弹簧 The following factors should be taken account when selecting fasteners for a given application： （1）primary function;（2）appearance;（3）a large number of small size fasteners versus a small number of large size fasteners（an example is bolts）；（4）operating conditions such as vibration，loads and temperature;（5）frequency of disassembly；（6）adjustability in the location of parts;（7）types of materials to be joined；（8）consequences of failure or loosening of the fastener． Lesson 7 Fasteners and Springs 紧固件和弹簧 The importance of fasteners can be realized (认识) when referring to any complex product．In the case of the automobile，there are literally (逐字的，照字面的) thousands of parts which are fasten