1、Overview of shaftA shaft is one of the most important components in machines. Shafts are used to support rotating elements and transmit rotational motion and power. It is integral to any mechanical system in which power is transmitted from a prime mover,such as an electric motor or an engine, to oth
2、er rotating parts of the system. Rotating parts of machines are mounted on shafts which provide for a constant position of the axis of rotation of these parts.1.1 Types of shaftsAccording to the loads exerted on shafts, the shafts can be classified into three types: shafts , axle, spindle.1. ShaftsS
3、hafts are members intended for transmitting a torque along their axes and for supporting rotating machine components. Since the transmission of torque is associated with development of forces applied to the shafts ,such as forces acting on the teeth of gear , belt tension etc. , shafts are usually s
4、ubject to transverse forces and bending moments in addition to the torque.2. AxleAxle are members which support rotating components of machines but do not transmit a useful torque. They are commonly subject to bending moments and to torques, not taken into consideration in design ,due to friction fo
5、rces.Axles are classified as rotating and fixed , the former providing for better operation of the bearings and better location , and the latter being cheaper but requiring built-in bearing in the rotating members.3. SpindleShafts subject only to torque, just transmit motion from an input source to
6、an output work site , usually called spindle.With respect to the shape of their geometric axis , shafts are classified as straight shafts ,crankshafts and flexible shafts .Crankshafts are used to convert reciprocating motion into rotation or vice verse . They combine the functions of ordinary shafts
7、 which those of cranks in slider-crank mechanisms. In a separate group are the so-called flexible shafts with a geometric axis of variable shape.As to their shape , straight shafts are divided into plain shafts and stepped shafts. For the same mass , stepped shafts are more favorable than shafts of
8、constant cross section . Such a shape is convenient in manufacture and assembly ; the shoulders of the stepped shaft can carry large axial forces .Shafts may be hollow in design . A hollow shaft with a hole to outside diameter ratio of 0.75 is lighter by about 50% than a solid shaft of equal strengt
9、h and rigidity .With respect to the shape of their cross section , shafts may be plain , spline , and of special shape.1.2 Shaft materialsThe materials used for shafts are usually carbon steel and its alloy , most of shaft are made of round steel or forging , all kinds of heat treatment and surface
10、strengthening treatment can significantly increase the fatigue strength of axis. Carbon steel are cheaper than its alloy , and the sensitivity to the stress concentration is lower,so it is applicable to the general requirements of shaft. Alloy steel has higher mechanical properties and better than c
11、arbon steel quenching performance. In transmission power and reduce the size and quality, high wear resistance, corrosion and high temperature, low temperature, and alloy steel under the condition of shaft is often adopted.Under the general working temperature, the elastic modulus of all sorts of ca
12、rbon steel and alloy steel, so the same size of the carbon steel and alloy steel shaft stiffness.High strength cast iron and nodular cast iron can be used to make complex shape of the shaft, and has low price, good vibration absorbing resistance and abrasion resistance, and low sensitivity to the st
13、ress concentration of advantages, but the quality of a material is brittle.1.3 Structural design of shaftsThe structure of the shaft is affected by many factors , three major problems in the structure design should be considered , functional requirements , technological requirements and the strength
14、 of shafts .1. Functional requirementsIn order to ensure the fixed position of elements on the shaft , it is needed to fix each element on the shaft radially and axially . The radial location of elements on the shaft is usually realized by keys . If a shaft has several key ways along its length , it
15、 is good practice to align them in a single plane to avoid resetting the shaft in milling the key ways .Axial loads acting on shafts or on components mounted on the shafts are transmitted as follows:(1) light loads and as a safety measure to prevent displacement by chance forces by means of a locati
16、ng ring or setscrews holding the component ；(2) Medium loads by means of shoulder and nuts , fixed locating rings , or cone and nut;(3) Heavy loads by having the loaded components bear against shoulders of the shaft , or mounting the components with dual-nuts or an interference fit .Two-way axial securing of a shaft is not compulsory if it is held in place by a constant force which prevents displacement .2. Technological requirem
