Marine forged shafts are the core components of a ship's power transmission system, used to connect the main engine (such as diesel engines, gas turbines) with the propeller, transmitting torque and thrust while withstanding complex mechanical loads (torsion, bending, impact) and harsh marine environments (seawater corrosion, vibration, low temperature). Their performance directly affects the ship's navigation safety, economy, and reliability, requiring high strength, corrosion resistance, fatigue resistance, and low magnetic properties (especially for military vessels). They are indispensable key components of the ship's power system.
Materials
1. Carbon steel/low alloy steel (such as 35 steel, 45 steel, 40Cr):
- Low cost, moderate strength, suitable for medium and low load scenarios, requires coating for corrosion protection.
2. High-strength alloy structural steel (such as 18Cr2Ni4WA, 38CrMoAl):
- High strength, fatigue resistance, partially low magnetic (e.g., 18Cr2Ni4WA used for military vessels), 38CrMoAl has high wear resistance after nitriding.
3. Stainless steel (such as 316, duplex steel 2205):
- Resistant to seawater corrosion, suitable for harsh environments like ocean-going and LNG ships, high cost.
4. Ductile cast iron (such as QT600-3):
- Low cost, good shock absorption, used for light loads or non-critical parts.
Classification of marine forged shafts
1. Classification by shaft system position:
- Thrust shaft: transmits axial thrust generated by the propeller to the hull, maintaining axial positioning of the shaft system.
- Intermediate shaft: connects the main engine and tail shaft, transmits torque, compensates for installation errors and hull deformation.
- Tail shaft (propeller shaft): passes through the stern tube to connect the propeller, bearing torque, thrust, and seawater corrosion.
2. Classification by material:
- Carbon steel forged shaft: such as 35 steel, suitable for conventional ships, lower cost.
- Low magnetic steel forged shaft: such as 18Cr2Ni4WA, used for military vessels to reduce magnetic field signals.
- Stainless steel forged shaft: strong corrosion resistance, suitable for coastal or ocean-going ships.
3. Classification by structural form:
- Integral forged shaft: formed in one piece, high reliability, commonly used in small and medium-sized ships.
- Segmented combined shaft: facilitates manufacturing and maintenance of large ships.
Scope of application
1. Ship types:
- Warships, ocean-going cargo ships, oil tankers, container ships, fishing vessels, engineering ships.
2. Power systems:
- Low-speed diesel direct drive systems, gearbox drive systems.
3. Special requirements:
- Military vessels (low magnetic stealth), LNG ships (low temperature tolerance), icebreakers (impact resistance).
Process introduction
1. Smelting and forging:
- Using "EAF (Electric Arc Furnace) + LF (Ladle Furnace) + VD (Vacuum Degassing)" smelting to ensure purity of composition.
- Multiple forging heats (e.g., 2-3 heats): upsetting → drawing out → forming, forging ratio ≥4, grain refinement.
2. Heat treatment:
- Post-forging normalizing/annealing to relieve stress, quenching and tempering after rough machining.
- Low magnetic steel shafts require solution treatment (1080-1120°C) for uniform microstructure.
3. Machining process:
- Rough turning with allowance → ultrasonic flaw detection → finish turning to size → grinding (surface roughness meets standards).
4. Strengthening and protection:
- Surface quenching (HRC 50-60) or nitriding of shaft journals to improve wear resistance.
- Tail shaft copper sleeve coating + fiberglass epoxy resin anti-corrosion layer.
5. Quality inspection:
- Non-destructive testing: GB/T 6402 Level 1 flaw detection, or ISO 10893-3 ultrasonic standard.
- Magnetic permeability testing, grain size inspection (≥ grade 5), mechanical performance testing.
Keywords
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Marine forged shaft
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