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Product Description
The crankshaft for compressor is the core transmission component in reciprocating compressors, primarily responsible for converting the rotational motion from the motor or prime mover into the reciprocating linear motion of the piston. It drives the piston via the connecting rod to complete the gas intake, compression, and discharge processes within the cylinder. During operation, the crankshaft is subjected to torque and inertial loads, with its structural strength, machining precision, and material quality directly determining the compressor's operational stability and service life.
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In reciprocating compressor systems, the crankshaft assembly, together with components such as the connecting rod, crosshead, and piston rod, forms a complete power transmission chain. As the starting point of the entire machine's power transmission, the crankshaft requires high precision in journal dimensions, coaxiality, surface quality, and fatigue strength. Totem Machinery can provide customized design and machining for compressor crankshafts based on different compressor specifications, speeds, and load conditions to meet diverse industrial application needs.
Machining Process
The machining process for a reciprocating compressor typically begins with a forged blank, followed by multiple precision machining and surface treatment steps to gradually form a finished crankshaft that meets assembly and operational requirements.
Crankshaft Forged Blank
The image below shows the forged crankshaft blank. The crankshaft is forged from high-strength alloy steel, with the forging process designed to achieve continuous metal grain flow. This provides a solid material foundation for withstanding alternating torque and bending moments during subsequent operation.
Semi-Finish Turning
Building upon rough machining, this operation performs semi-finish turning on the crankshaft blank. It aims to further improve the dimensional accuracy and geometric tolerances of all journals and end faces, leaving an appropriate and uniform allowance for subsequent finishing operations. This step is critical for establishing a reliable foundation for final precision.
Turning the Eccentric Outer Diameter (Crankpin)
This step specifically machines the crankpin (also known as the connecting rod journal). Using a precision eccentric fixture or controlled via CNC programming, turning is performed at an offset position from the rotational center to form the crankshaft’s distinctive eccentric geometry. This is the essential process that enables the crankshaft’s core function—converting rotational motion into reciprocating motion.
Finish Turning of Both Crankshaft Ends
This operation involves final precision turning of features at both crankshaft ends, such as flanges and shaft extensions. It ensures that the flatness, perpendicularity, and relevant mating dimensions meet drawing specifications, providing accurate reference surfaces for subsequent dynamic balancing, gear, or pulley installation.
Positioning on the Grinding Machine
Prior to grinding operations, the crankshaft is precisely mounted on a dedicated grinding machine using high-precision centers, chucks, or specialized fixtures. This setup and alignment process ensures the crankshaft’s rotational axis is concentric with the machine spindle axis, forming the essential foundation for achieving concentricity across all journal grinding operations.
Finish Grinding of the Main Journals
High-precision CNC grinding machines are employed to perform the final grinding of the main journals, which support the crankshaft’s rotation. This process achieves extremely tight dimensional accuracy (to micron levels), strict roundness and cylindricity, and excellent surface finish, ensuring smooth, low-friction operation within the engine bearings.
Finish Grinding of the Crankpins (Connecting Rod Journals)
Precision grinding is performed on the eccentrically positioned connecting rod journals (crankpins). This is one of the most challenging operations in crankshaft machining, requiring simultaneous adherence to strict standards for phase angle between pins, diameter, roundness, and surface roughness. It directly affects engine smoothness and reliability.
Finish Grinding of Other Crankshaft Journals
In addition to the main and connecting rod journals, this step involves final precision grinding of other functional journals such as seal journals and gear journals. It ensures all journals meet design specifications for dimensions, geometric tolerances, and surface quality, satisfying overall assembly and sealing requirements.
Packaging & Shipping
1. Inner Protective Layer
All critical surfaces of the product, such as machined areas, mating surfaces and end faces, are coated with anti-rust oil or other suitable protective agents. The parts are then wrapped with VCI (Volatile Corrosion Inhibitor) paper or similar protective materials to isolate air and moisture and reduce the risk of corrosion during transportation and storage.
2. Cushioning and Fixation Layer
Cushioning materials including pearl cotton, foam or rubber pads are applied around the product to absorb vibration and impact. According to the product structure, customized supports or positioning blocks are installed inside the package to prevent rolling or movement and to keep the product stable during transport.
3. Outer Reinforced Packaging
The outer packaging adopts a reinforced export wooden case or other high-strength packaging with sufficient load-bearing capacity, suitable for sea, land or air transportation. Handling marks such as center of gravity, lifting points, moisture protection and anti-tilt symbols can be added based on customer requirements for easier handling and identification on site.
4. Customized Packaging Options
Packaging solutions can be adjusted according to customer requirements, including protection level, cushioning method, fixing structure and outer case design, to suit different transportation conditions, destination ports and project site requirements.
