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The Working Principle and Processing Technology of the Crankshaft, Understand the Whole Process!

The crankshaft is the most important part in the engine. It receives the force from the connecting rod and converts it into torque, which is output through the crankshaft and drives other accessories on the engine to work. The crankshaft is subjected to the combined action of the centrifugal force of the rotating mass, the periodically changing gas inertial force and the reciprocating inertial force, so that the crankshaft is subjected to bending and torsional loads. Therefore, the crankshaft is required to have sufficient strength and stiffness, and the journal surface needs to be wear-resistant, work evenly, and have good balance.

 

The crankshaft is the main rotating part of the engine. After the connecting rod is installed, it can undertake the up and down (reciprocating) movement of the connecting rod and turn it into a cyclic (rotating) movement.

Crankshaft

The crankshaft is mainly made of carbon structural steel or ductile iron, and has two important parts: the main journal and the connecting rod journal. The main journal is installed on the cylinder block, the connecting rod journal is connected with the big end hole of the connecting rod, and the small end hole of the connecting rod is connected with the cylinder piston, which is a typical crank-slider mechanism.

The lubrication of the crankshaft mainly refers to the lubrication of the connecting rod big end bearing bush and the crankshaft connecting rod journal and the lubrication of the fixed points at both ends. The rotation of the crankshaft is the power source of the engine and the source power of the entire mechanical system.

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1. How the Crankshaft Works

The crankshaft is one of the most typical and important parts in the engine. It bears the force from the connecting rod and converts it into torque, which is output through the crankshaft and drives other accessories on the engine to work, and drives the auxiliary equipment of the internal combustion engine to work. The crankshaft is subjected to the combined action of the centrifugal force of the rotating mass, the periodically changing gas inertial force and the reciprocating inertial force, so that the crankshaft is subjected to bending and torsional loads.

2. Machining Technology of Crankshaft

(1)External Milling of Crankshaft Main Journal and Connecting Rod Journal

During the processing of crankshaft parts, due to the influence of the structure of the disc milling cutter itself, the cutting edge and the workpiece are always in intermittent contact with impact. Therefore, the gap link is controlled in the entire cutting system of the machine tool, which reduces the vibration caused by the movement gap during the machining process, thereby improving the machining accuracy and the service life of the tool.

(2)Crankshaft Main Journal and Connecting Rod Journal Grinding

The tracking grinding method takes the center line of the main journal as the center of rotation, and completes the grinding of the crankshaft connecting rod journal in one clamping (it can also be used for main journal grinding). The grinding method of the connecting rod journal is controlled by CNC. The feed of the grinding wheel and the rotary motion of the workpiece are linked by two axes to complete the feed of the crankshaft. The tracking grinding method uses one clamping and completes the grinding of the crankshaft main journal and the connecting rod journal in turn on a CNC grinding machine, which can effectively reduce equipment costs, reduce processing costs, and improve processing accuracy and production efficiency.

(3)Crankshaft Main Journal, Connecting Rod Journal Fillet Rolling Machine

The application of rolling machine is to improve the fatigue strength of crankshaft. According to statistics, the crankshaft life of ductile iron crankshaft after fillet rolling can be increased by 120% to 230%; the life of forged steel crankshaft after fillet rolling can be increased by 70% to 130%. The rotational power of the rolling comes from the rotation of the crankshaft, which drives the rollers in the rolling head to rotate, and the pressure of the rollers is implemented by the oil cylinder.

The most common fatigue damage of the crankshaft, the main force-bearing part of the engine, is metal fatigue damage, that is, bending fatigue damage and torsional fatigue damage. The probability of the former is greater than that of the latter. Bending fatigue cracks first occur at the connecting rod journal (crank pin) or the main journal fillet, and then develop towards the crank arm. Torsional fatigue cracks occur in poorly machined oil holes or fillets, and then develop in the direction of the axis. Metal fatigue failure is the result of the variable stress that changes periodically with time. Statistical analysis of crankshaft failure shows that about 80% is caused by bending fatigue.

3. Crankshaft Maintenance Precautions

1) During the repair of the crankshaft, carefully check the crankshaft for defects such as cracks, bending and twisting, as well as the wear of the main bush and the connecting rod bush, to ensure the gap between the main journal and the main bush, the connecting rod journal and the connecting rod bush. The fit clearance is within the allowable range.

2) Crankshaft cracks mostly occur at the transition fillet between the crank arm and the journal, and at the oil hole in the journal.

3) When repairing and reassembling the crankshaft, ensure the balance of the flywheel.

4) After the internal combustion engine has major accidents such as burning tiles and ramming the cylinder, it is necessary to conduct a comprehensive overhaul of the crankshaft.

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