A, shaft parts function, structure characteristics and technical requirements
Shaft parts is one of the most frequently encountered in typical machine parts. It is mainly used to support transmission parts, transmission and torque under load. Hengding hub represents shaft is a rotating body parts, the length is greater than the diameter, generally by the concentric shaft and the outer cylindrical surface, conical surface, hole and the thread and the corresponding end composed. According to the different structural shapes of shaft parts can be divided into the optical axis, stepped shaft, hollow shaft and crankshaft etc..
Axis aspect ratio of less than 5 is called the short axis is bigger than 20 is called the slender shaft, most shaft in between.
Shaft bearing, and bearing with the shaft segment called the journal. The journal is the axis of the assembly base, their precision and surface quality generally higher, according to its general technical requirements and working conditions of the main function of shaft making, usually has the following items:
(a) the size precision plays the supporting role journal in order to determine the position of the shaft, usually requires high dimensional precision (IT5 ~ IT7). The shaft neck size precision assembly transmission of the general requirements for low (IT6 ~ IT9).
(II) geometry precision the axis class components geometry shape precision is mainly refers to the shaft neck, outside the cone, Morse taper hole and roundness, cylindricity and so on, in general should be the tolerance limit in size within the tolerance range. High precision internal and external circular surface, should be marked on the drawing of the allowable deviation.
(three) the mutual position precision of position accuracy of shaft parts demand is mainly decided by the axis in the position and function of machinery. Is necessary to ensure the assembly transmission parts journal bearing journal concentricity requirements, otherwise it will affect the transmission parts (gear) transmission accuracy, and noise. The general accuracy of the shaft, the shaft with radial bearing journal beating is 0.01 ~ 0.03mm, the high precision of the shaft (such as spindle) is usually 0.001 ~ 0.005mm.
(four) surface roughness and transmission parts matched with the shaft diameter of the surface roughness is Ra2.5 ~ 0.63 m, the supporting shaft and bearing the diameter of the surface roughness is Ra0.63 ~ 0.16 M.
Two, shaft parts and blank material
(a) shaft blank of shaft parts can be used according to the requirements, the production conditions and equipment types, structure, selection of bars, forging blank form. Outer diameter difference between the small shaft, generally the main bar; and outer diameter difference between the large stepped shaft or shaft, often used in forging, so as to save materials and reduce the workload of processing machinery, improve the mechanical properties.
Hendin hub said depending on the production scale, there are two kinds of free forging and die forging forging blank. Small batch production of free forging, a large number of mass production using die forging.
(II) of shaft parts material shaft parts should be according to the different working conditions and requirements for the use of the use of different materials and by different heat processing specification (such as quenching and tempering, normalizing, quenching and so on), to obtain a certain strength, toughness and wear resistance.
45 steel is commonly used in shafts, it is cheap, after quenching and tempering (or normalizing), can get better cutting performance, but also can obtain the comprehensive mechanical properties of high strength and toughness, the quenched surface hardness of up to 45 ~ 52hrc.
40Cr and other alloy structural steel is suitable for the high precision and high speed shaft parts, this kind of steel after quenching and tempering, has good comprehensive mechanical properties.
GCr15 bearing steel and spring steel 65Mn, after quenching and tempering and surface high frequency quenching, the surface hardness of up to 50 ~ 58HRC, and has a high fatigue resistance and good wear resistance, can be manufactured with high precision shaft.
Precision machine tool spindle (such as grinding wheel spindle coordinate boring machine) can be used 38CrMoAIA steel nitride. After tempering and surface nitriding, the steel is not only able to obtain a high surface hardness, but also can maintain a soft core, so the impact toughness is good. Compared with carburizing and quenching steel, it has a very small heat treatment deformation, higher hardness characteristics.
