Shaft parts are one of the typical parts often encountered in machines. It is mainly used to support the transmission zero

Components, transmit torque and bear load. Shaft parts are rotating parts whose length is greater than the diameter, and are generally composed of the outer cylindrical surface, conical surface, inner hole and thread of the concentric shaft and the corresponding end surface. According to different structural shapes, shaft parts can be divided into optical shafts, stepped shafts, hollow shafts and crankshafts.

Shafts with a length-to-diameter ratio of less than 5 are called short shafts, and those with a ratio greater than 20 are called slender shafts. Most shafts are between the two.

The shaft is supported by a bearing, and the shaft section matched with the bearing is called the journal. Axle journals are the assembly benchmark of shafts. Their accuracy and surface quality are generally required to be high. Their technical requirements are generally formulated according to the main functions and working conditions of the shaft, usually the following items:

(1) Dimensional accuracy. In order to determine the position of the shaft, the bearing journal usually requires high dimensional accuracy (IT5 ~ IT7). Generally, the dimensional accuracy of the shaft journal for assembling transmission parts is relatively low (IT6～IT9).

(2) Geometric shape accuracy The geometric shape accuracy of shaft parts mainly refers to the roundness, cylindricity, etc. of the journal, outer cone, Morse taper hole, etc. Generally, the tolerance should be limited within the dimensional tolerance range. For the inner and outer round surfaces with higher precision requirements, the allowable deviation should be marked on the drawing.

(3) Mutual position accuracy The position accuracy requirements of shaft parts are mainly determined by the position and function of the shaft in the machine. Generally, it is necessary to ensure the coaxiality requirements of the shaft journal of the assembled transmission parts to the supporting shaft journal, otherwise it will affect the transmission accuracy of the transmission parts (gears, etc.) and generate noise. For ordinary precision shafts, the radial runout of the matching shaft section to the supporting journal is generally 0.01～0.03mm, and high precision shafts (such as main shafts) are usually 0.001～0.005mm.

(4) Surface roughness Generally, the surface roughness of the shaft diameter matched with the transmission part is Ra2.5～0.63μm, and the surface roughness of the supporting shaft diameter matched with the bearing is Ra0.63～0.16μm.

Blanks and materials of folded shaft parts
(1) Shaft parts blanks Shaft parts can be selected as blanks, forgings and other blank forms according to use requirements, production types, equipment conditions and structure. For shafts with little difference in outer diameter, bar materials are generally used; for stepped shafts or important shafts with large outer diameters, forgings are often used, which saves materials and reduces the workload of machining. Improve mechanical properties.

According to different production scales, there are two types of blank forging methods: free forging and die forging. Free forging is mostly used for small and medium batch production, and die forging is used for mass production.

(2) Material of shaft parts Shaft parts should select different materials and adopt different heat treatment specifications (such as quenching and tempering, normalizing, quenching, etc.) according to different working conditions and usage requirements to obtain certain strength, toughness and Abrasion resistance.

45 steel is a common material for shaft parts. It is cheap and after quenching and tempering (or normalizing), it can obtain better cutting performance, and it can obtain comprehensive mechanical properties such as higher strength and toughness. After quenching, the surface hardness can be Up to 45～52HRC.

Alloy structural steel such as 40Cr is suitable for shaft parts with medium precision and high speed. After quenching and tempering and quenching, this kind of steel has better comprehensive mechanical properties.

Bearing steel GCr15 and spring steel 65Mn, after quenching and tempering and surface high-frequency quenching, the surface hardness can reach 50-58HRC, and has high fatigue resistance and good wear resistance, which can be used to manufacture high-precision shafts.

The main shaft of the precision machine tool (such as the grinding wheel shaft of the grinder, the spindle of the jig boring machine) can choose 38CrMoAIA nitride steel. After quenching and tempering and surface nitriding, this steel can not only obtain high surface hardness, but also maintain a soft core, so it has good impact resistance and toughness. Compared with carburized and hardened steel, it has the characteristics of small heat treatment deformation and higher hardness.

No. 45 steel is widely used in machinery manufacturing, and the mechanical properties of this steel are very good. But this is a medium carbon steel, and its quenching performance is not good. No. 45 steel can be quenched to HRC42~46. Therefore, if the surface hardness is required and the superior mechanical properties of 45# steel are desired, the surface of 45# steel is often quenched (high-frequency quenching or direct quenching), so that the required surface hardness can be obtained.

Note: No. 45 steel with a diameter of 8-12mm is prone to cracks during quenching, which is a more complicated problem. The current measures adopted are rapid agitation of the sample in water during quenching, or oil cooling to avoid cracks.

National Chinese Brand No. 45 No. UNS Standard No. GB ​​699-88

Chemical composition (%) 0.42-0.50C, 0.17-0.37Si, 0.50-0.80Mn, 0.035P, 0.035S, 0.25Ni, 0.25Cr, 0.25Cu

Shape ingot, billet, bar, tube, plate, strip state without heat treatment, annealing, normalizing, high temperature tempering

Tensile strength Mpa 600 Yield strength Mpa 355 Elongation% 16

Folding in the field of mold repair
The mold welding consumable model for No. 45 steel is: CMC-E45

It is the only welding rod for medium-hardness steel with good bonding properties, suitable for air-cooled steel, cast steel: such as ICD5, 7CrSiMnMoV… etc. Auto sheet metal cover molds and large metal sheet metal stamping molds for drawing and repairing stretched parts, and can also be used for hard surface production.

In addition, there are some things to pay attention to when using:

1. Before construction in a damp site, the electrode should be dried at 150-200°C for 30-50 minutes.

2. Generally preheating above 200°C, air cooling after welding, stress relief is best if possible.

3. Where multilayer surfacing welding is required, use CMC-E30N as a primer to get a better welding effect.

Hardness HRC 48-52

Main ingredients Cr Si Mn C

Applicable current range:

Diameter and length m/m 3.2*350mm 4.0*350mm
The 45 gauge steel of our factory is used to make the mold base on the mold.