The basics of crankshaft

The most important component of an engine. It takes the force from the connecting rod and converts it into torque output through the crankshaft and drives the other accessories on the engine to work. The crankshaft is affected by centrifugal force of rotating mass, periodic gas inertia force and reciprocating inertia force, which makes the crankshaft bear the action of bending and torsional load. Therefore, the crankshaft is required to have sufficient strength and stiffness, and the journal surface should be wear-resistant, uniform and balanced.

In order to reduce the mass of the crankshaft and the centrifugal force generated during movement, the crankshaft journal is often hollow. Each journal surface is provided with an oil hole for oil introduction or extraction to lubricate the journal surface. In order to reduce stress concentration, the connection of the spindle neck, the crank pin and the crank arm are connected by a transitional arc.

The role of the crankshaft counterweight (also known as counterweight) is to balance the rotating centrifugal force and its moment, and sometimes the reciprocating inertial force and its moment. When these forces and moments themselves are balanced, the balance weight can also be used to reduce the load on the main bearing. The number, size and placement of the balance weight should be considered according to the number of cylinders of the engine, the arrangement of cylinders and the shape of the crankshaft. The balance weight is generally cast or forged into one with the crankshaft, and the high-power diesel engine balance weight is manufactured separately from the crankshaft and then bolted together.

Casting technology
Smelting
Obtaining high temperature and low sulfur pure hot metal is the key to producing high quality ductile iron. Domestic production equipment is mainly based on cupola, and hot metal is not pre-desulfurization treatment; This is followed by less high purity pig iron and poor coke quality. Molten iron is melted in cupola, desulfurized outside the furnace, and then heated and adjusted in induction furnace. In China, the detection of molten iron composition has been generally carried out by vacuum direct reading spectrometer.
moulding
The air impact molding process is obviously superior to the clay sand molding process, and can obtain high-precision crankshaft castings. The sand mold produced by this process has the characteristics of no rebound deformation, which is especially important for the multi-throw crankshaft. Some domestic crankshaft manufacturers from Germany, Italy, Spain and other countries to introduce the air impact molding process, but the introduction of the entire production line is only a very small number of manufacturers.
Electroslag casting
Electroslag remelting technology is applied to the production of crankshaft, so that the performance of cast crankshaft may be comparable to that of forged crankshaft. And has the characteristics of fast development cycle, high metal utilization rate, simple equipment, superior product performance and so on.

Forging technology
The automatic line with hot die forging press and electric hydraulic hammer as the main engine is the development direction of forging crankshaft production. These production lines will generally adopt advanced technologies such as precision cutting, roll forging (cross wedge rolling) forming, medium frequency induction heating, finishing hydraulic press finishing, etc. At the same time, they are equipped with auxiliary machines such as manipulators, conveyor belts and mold change devices brought back to the turntable to form a flexible manufacturing system (FMS). The FMS can automatically change the workpiece and die and automatically adjust the parameters, and constantly measure during the working process. Display and record data such as forging thickness and maximum pressure and compare with fixed values to select the best deformation for quality products. The entire system is monitored by a central control room, enabling unmanned operation. The crankshaft forged by this forging method has the full fiber of the internal metal flow line, which can increase the fatigue strength by more than 20%.