www.mapeng.net 马棚网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 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:
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(1) Disassembly for inspection and repair;
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(2) Modular design where a product consists of a number of subassemblies. Modular design aids manufacturing as well as transportation.
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There are three main classifications of fastener, which are described as follows:
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(1) Removable. This type permits the parts to be readily disconnected without damaging the fastener. An example is the ordinary nut-and-bolt fastener.
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(2) Semi-permanent. For this type, the parts can be disconnected, but some damage usually occurs to the fastener. One such example is a cotter pin.
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(3) Permanent. When this type of fastener is used, this intended that the parts - will never be disassembled. Examples are riveted and welded joints.
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The following factors should be taken into account when electing fasteners for a given application:
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(1) Primary function;
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(2) Appearance;
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(3) A large number of small size fasteners versus a small number of large size fasteners (an example is bolts);
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(4) Operating conditions such as vibration, loads and temperature;
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(5) Frequency of disassembly:
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(6) Adjustability in the location of parts;
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(7) Types of materials to be joined;
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(8) Consequences of failure or loosening of the fastener.
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The importance of fasteners can be realized when referring to any complex product In the case of the automobile, there are literally thousands of parts which are fastened together to produce the total product. The failure or loosening of a single fastener could result in a simple nuisance such as a door rattle or in a serious situation such as a wheel coming off. Such possibilities must be taken into account in the selection of the type of fastener for the specific application.
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Springs are mechanical members which are designed to give a relatively large amount of elastic deflection under the action of an externally applied load. Hooke’s Law, which states that deflection is proportional to load, is the basis of behavior of springs. However, some springs are designed to produce a nonlinear relationship between load and deflection. The following is a list of the important purposes and applications of springs:
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(1) Control of motion in machines. This category represents the majority of spring applications such as operating forces in-clutches and brakes. Also, springs are used to maintain contact between two members such as a cam and its follower.
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(2) Reduction of transmitted forces as a result of impact or shock loading. Applications here include automotive suspension system springs and bumper
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springs.
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(3) Storage of energy. Applications in this category are found in clocks, movie cameras and lawn
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