Large crankshafts are core transmission components in heavy machinery and power systems, mainly used to convert reciprocating motion (such as piston movement) into rotational motion and output high torque to drive equipment operation. Their working environment is complex, requiring them to withstand cyclic alternating loads (such as gas pressure, inertial forces, centrifugal forces, etc.), thus they must possess extremely high strength, stiffness, wear resistance, and fatigue resistance. Large crankshafts are widely used in ships, construction machinery, internal combustion engines, generator sets, and other fields, serving as an important indicator of a country's mechanical manufacturing level.

Crankshaft Classification

1. By structural type:

- Integral crankshaft: forged or cast as a whole, suitable for medium and small or high-speed equipment, with a compact structure and high reliability.

- Composite crankshaft: composed of multiple main journal sections, crank arms, and other parts connected by interference fit, welding, or bolts, suitable for ultra-large equipment (such as ten-thousand-ton class marine diesel engines), facilitating manufacturing, transportation, and maintenance.

- Inserted cast crankshaft: high-strength materials (such as alloy steel) are embedded on the base body, balancing cost and performance.

2. By application scenario:

- Marine crankshaft: used for low-speed, high-power diesel engines, with huge dimensions (length can exceed 20 meters, weight hundreds of tons).

- Construction machinery crankshaft: used in excavators, mining equipment, etc., bearing high impact loads.

- Energy sector crankshaft: used in generator sets, compressors, etc., emphasizing high reliability and long service life.

3. By material and process:

- Forged crankshaft: made of high-strength forged steel (such as 42CrMo, 35CrMo), suitable for high-load scenarios.

- Cast crankshaft: made of ductile cast iron (QT700-2), lower cost, suitable for medium and low loads.

Specifications

1. Size range:

- Length: from several meters to tens of meters (e.g., the 12S90ME-C crankshaft is 23 meters long).

- Diameter: main journal diameter can exceed 2 meters.

- Weight: single piece weight ranges from tens to hundreds of tons (e.g., the world's heaviest W12X92 crankshaft weighs 488 tons).

2. Material properties:

- High-strength alloy steel with yield strength ≥ 800 MPa, surface hardness HRC 50-60.

- Nitriding layer depth of 0.3-0.5 mm to enhance wear resistance.

- Surface roughness: key journals Ra ≤ 0.8 μm to ensure low friction loss.

Design Parameters

1. Dimensional parameters

- Crank pin diameter and length: determined by cylinder diameter, affecting crankshaft strength and stability.

- Main journal diameter and length: determine the fit between crankshaft and bearings.

- Crank arm thickness and width: affect crankshaft stiffness and strength, requiring reasonable design.

2. Strength parameters

- Bending and torsional load capacity: the crankshaft must withstand centrifugal forces of rotating mass, cyclic gas inertial forces, and reciprocating inertial forces simultaneously, thus requiring sufficient strength and stiffness.

- Surface strengthening techniques: such as fillet rolling strengthening, journal surface quenching, etc., to improve fatigue strength and wear resistance.

3. Machining accuracy

- Roundness and cylindricity: the standard cylindricity value of journals is 0~0.005 mm, with a usage limit of 0.05 mm.

- Surface roughness: journal surfaces should be smooth without dents, depressions, cracks, or other defects.

4. Balance

- Counterweight design: based on the number of engine cylinders, cylinder arrangement, and crankshaft shape, reasonably design the number, size, and placement of counterweights to balance rotational centrifugal forces and their moments.

Scope of Application

1. Large ships: low-speed diesel engines driving propellers (e.g., 21,000 TEU container ships).

2. Heavy construction machinery: mining excavators, large bulldozers, oil drilling rigs, etc.

3. Energy equipment: high-power generator sets, natural gas compressors, industrial pump units.

4. Railway locomotives: internal combustion locomotive power systems, suitable for long-term high-load operation.

Key Features

1. Ultra-high strength and reliability:

- Using full fiber forging or electroslag remelting processes to ensure continuous metal flow lines without internal defects.

2. Fatigue resistance design:

- Fillet rolling strengthening, surface quenching, and other processes significantly improve fatigue life.

3. Lightweight and energy-saving:

- Hollow journals and topology-optimized structures reduce weight and improve equipment fuel economy.

4. Precision manufacturing:

- CNC grinding and online inspection technologies ensure micron-level machining accuracy.

5. Corrosion resistance and durability:

- Surface coatings or special alloy treatments adapt to harsh marine environments, with a design life of ≥ 20 years.

Process Introduction

1. Forging process:

- Hot forging: Using a ten-thousand-ton hydraulic press, multiple steps of upsetting, bending, and forging are performed to form a full fiber structure.

- Segment forging + assembly: Ultra-large crankshafts are segment forged and then assembled by hot fitting, overcoming equipment limitations.

2. Casting process:

- Airflow impact molding: High-precision sand molds reduce casting defects.

- Electroslag remelting: Improves material purity and uniformity, comparable to forging performance.

3. Machining process:

- CNC turning and tracking grinding: Ensures journal roundness and coaxiality.

- Deep hole machining: Precision oil hole design optimizes lubrication and cooling.

4. Strengthening treatment:

- Medium frequency induction quenching: Controllable surface hardening layer depth enhances wear resistance.

- Nitriding + fillet rolling composite process: Comprehensively improves fatigue and corrosion resistance.

5. Inspection technology:

- Non-destructive testing (ultrasonic, magnetic particle inspection) to detect microcracks.

- Dynamic balancing test bench simulates actual working conditions and adjusts to the optimal balance state.