Process analysis of surface quenching of crankshaft using high-frequency induction quenching machine and characteristics of induction coil

As an important part of the internal combustion engine, the crankshaft, together with the cylinder, piston, connecting rod and other parts, constitute the engine's power plant. Therefore, the crankshaft is required to have high strength, high wear resistance and long service life. In order to meet these performance requirements of the crankshaft, the crankshaft needs to be heat treated. So, which type of induction heating equipment is better for crankshaft heat treatment? The heat treatment of crankshafts generally uses quenching, high-frequency induction heating quenching and flame quenching. Today, we will introduce high-frequency induction heating quenching. Induction hardening is an energy-saving heat treatment technology that can significantly improve the efficiency of heat treatment and organize production according to the production rhythm. Therefore, it can be called a low-cost heat treatment technology.

1. The crankshaft adopts high-frequency induction quenching machine for heat treatment technology

High-frequency induction heating quenching and cooling adopts the crankshaft shaft diameter to be quenched in turns and surface quenching is performed separately. The quenching temperature of the crankshaft is 860~900℃. A small hole for supplying cooling water is drilled on the inner wall circumference of the inductor (ring). The diameter of the hole is is 1.5~2.5mm, and the water pressure is usually 0.15~0.35MPa. Heating 75~150℃/s. Self-tempering treatment is performed at 300℃, while the tempering process in the furnace is (180~220)℃×(1.5~2)h. After tempering, the hardness becomes 52-57HRC. The process and technical requirements for crankshaft surface quenching heat treatment are shown in the table below.

Process and technical requirements for crankshaft surface quenching heat treatment

After the crankshaft is quenched by a high-frequency induction hardening machine, the rounded corner R where the shaft diameter and the crank are connected are not quenched, so a large tensile stress will be generated and the fatigue strength of the crankshaft will be reduced. For high-power automobile crankshafts, a heat treatment process is adopted in which the shaft diameter and fillet are simultaneously quenched. The characteristic of this method is that on the basis of the original semicircular inductor, the thickness of the effective arc section section is changed and a magnet is attached. The purpose It is to make the crankshaft fillet R and the shaft diameter be heated and quenched under a strong inductor at the same time to obtain an ideal quenching effect and a certain residual compressive stress. Commonly used quenching cooling media include water, PAG and oil. PAG is used as the quenching medium for materials such as 42CrMoA and 50CrMoA. After treatment, the crankshaft has the characteristics of uniform surface hardness, deep hardened layer, and few quenching cracks and grinding cracks. Most tempering adopts the self-tempering method. Generally, tempering at a temperature of (140~180)℃×2h in a hot air furnace or low-temperature resistance furnace is enough.

2. Characteristics of crankshaft sensor:

Induction heating surface quenching of the crankshaft is an important process in the heat treatment process and is a necessary measure for hardening the crankshaft shaft diameter. There are two common types of crankshaft inductors, one is a full-turn separate inductor, which is used for surface quenching of the crankshaft under stationary conditions, and the other is a half-turn quenching inductor, where the crankshaft rotates within the inductor. The frequency selection is based on the diameter of the shaft. Generally, if the diameter is less than 50mm, it is 8000HZ, and if it is larger than 50mm, it is 2500Hz.

The heating temperature of the crankshaft is 860~900℃ (taking 45 steel as an example). The heating time is generally related to the power, and the cooling time is 0.9 to 1.2 times the heating time. At this time, the water pressure is 0.015-0.4MPa, and the water temperature is 18-50°C. The heating temperature used for the ductile iron crankshaft is 900~950℃. After self-tempering at about 300℃, it still needs to be supplemented with tempering at 180~220℃.

The half-turn sensor of the crankshaft is the most commonly used and has a wide range of applications. It is composed of four main parts: effective ring, outer protective plate, positioning block and quenching cooling device. In its structure, the effective circle is made of anisotropic copper tube welding layer, which is welded into a series of "8"-shaped semicircular induction conductors. The shape of the effective circle is composed of four axial conductors and four arc conductors. "mouth"-shaped coils are then connected in series to form a "LV" shape, which is buckled on the shaft diameter in a semicircular arc. The gap between the 8 effective wires and the surface of the shaft diameter is 1.5~2mm. Relying on four axis wires A transverse magnetic field is generated, and the current induced in the axis direction heats the shaft diameter. The crankshaft rotates at 60 to 100r/min and is cooled by spraying water. Generally, a "II" shaped silicon steel sheet magnet is installed on the wire. This half circle has the following characteristics:

1. The depth of the hardened layer and the width of the area are uniform, and the crank arm is not heated.

2. Adjust the distribution curve of the hardened layer to achieve quenching of the shaft diameter fillet.

3. Reduce or eliminate quenching cracks, especially the existence of inclined oil holes, which are easy to produce cracks. By making the axial current generated parallel to the oil holes, the tendency of quenching cracks can be greatly reduced.

4. Reduce the quenching deformation of the crankshaft.

Zhengzhou Gou's is a company specializing in the production and sales of crankshaft quenching equipment and high-frequency induction annealing machines. The equipment uses IGBT modules, making the equipment more environmentally friendly and energy-saving. At the same time, the induction coil of the equipment is also very convenient to install and disassemble. Of course, you can also customize it according to your needs. The workpiece is customized to suit your induction coil.