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Crankshafts

Crankshafts used in power-dense engines face millions of high-amplitude stress cycles, particularly in commercial transport, marine propulsion, and industrial generators. To meet these demands, we employ closed-die forging and multi-stage heat treatment to refine the microstructure and align grain flow along key stress paths. This enhances crack initiation resistance and improves load-bearing durability.

Material Specification

Forged Steel SAE 4340 (AMS 6414) or EN-GJS-700-2 Cast Iron

Balancing Specification

ISO 1940-1 G6.3 Grade (Residual unbalance ≤ 1 g·mm/kg at operating speed)

Surface Finish

Journal surfaces – 0.2–0.4 μm Ra; Non-functional surfaces – 1.6–3.2 μm Ra

Hardness

Journals – 55–62 HRC (case-hardened); Core – 28–35 HRC

Fillet Radii

2.0–5.0 mm (Roller-burnished to 400–600 MPa compressive residual stress)
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Product Description

Each crankshaft forging undergoes ultrasonic inspection to detect sub-surface inclusions that often trigger fatigue cracks under low-cycle and high-cycle fatigue conditions. This ensures consistent quality and long-term performance in demanding operational environments.

Dimensional Tolerances

Journal diameters – ±0.013 mm; Bearing widths – ±0.05 mm; Total length – ±0.2 mm

Concentricity/Runout

Main journals – ≤ 0.03 mm TIR; Crankpins – ≤ 0.04 mm TIR (per SAE J1246)

Stroke Length (Throw)

60–200 mm (±0.1 mm tolerance; application-specific)

Heat Treatment Process & Depth

Induction hardening – 1.5–3.0 mm case depth; Tempered at 150–200°C to relieve stresses

Certification Standards

ISO 9001:2015, IATF 16949, ASTM A536 (cast), SAE J404 (material composition)

Technical Advantages

Failure of journal surfaces due to oil film breakdown, micro-welding, or edge loading often traces back to improper geometry control during machining. Our crankshafts are precision-machined using five-axis CNC systems with in-process metrology to maintain taper, roundness, and cylindricity well within 3–5 μm. Strict control of oil groove placement, chamfering, and fillet radii ensures stable hydrodynamic lubrication, especially in high-speed or boundary-lubricated engine cycles. This prevents uneven wear patterns and bearing seizure. 

Thermal gradients during engine operation cause crankshaft warpage when residual stresses remain uncontrolled. We apply sub-zero treatments and staged tempering to equalize internal stresses after hardening. Post-process stress relief is verified using X-ray diffraction-based residual stress mapping. This ensures dimensional stability during operation, preserving bearing alignment and preventing deviation in rotational axis under real-world thermal cycles. 

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Industry Applications

Automotive Internal Combustion Engines

Converts reciprocating piston motion into rotational torque while withstanding high-cycle fatigue, torsional loads, and lubrication-induced thermal gradients. 

Marine Diesel Propulsion Systems

Transfers linear force from large-bore pistons into propulsive torque under high bending stress and prolonged low-speed operating conditions. 

Locomotive Engines

Manages large dynamic loads and cyclic bending stress with precise journal alignment and optimized counterweight distribution for smooth operation. 

Aerospace Auxiliary Power Units (APUs)

Operates at high RPM with strict tolerances for vibration control, fatigue resistance, and minimal mass imbalance in compact environments. 

Power Generation Gensets

Converts combustion energy into rotational motion under sustained load with controlled thermal expansion and long-duration dimensional stability. 

Oil and Gas Reciprocating Compressors

Translates crank-slider motion into compressed gas flow, handling severe dynamic forces, rod side loads, and off-center load fluctuations. 

Crankshafts

Controlled Surface Hardness for Wear-Prone Zones

Surface degradation in journals, pins, and thrust faces is often due to abrasive wear, adhesive wear, or cavitation. Our hardening processes involve selective induction heating followed by immediate quenching with constant surface temperature monitoring via pyrometry. 

Stress concentration at fillets between crank webs and pins often serves as the origin for fatigue cracks under torsional or bending loads. All crankshafts undergo deep fillet rolling using programmable hydraulic presses with defined rolling forces and dwell times. 

Crankshafts

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Having Doubts? Our FAQ

Check all our Frequently Asked Question

How does Frigate ensure crankshaft core strength during high bending moment applications?

Frigate uses closed-die forging to align grain flow along stress paths, improving core strength under heavy bending loads. The forging is followed by normalizing and quenching-tempering processes to achieve a uniform tempered martensitic structure. This enhances impact toughness and minimizes brittle fracture risk during torque transmission. Metallurgical tests verify hardness gradients and core ductility per design requirements.

What measures does Frigate take to control torsional vibration in long-stroke crankshafts?

Torsional vibration modes are simulated using finite element modeling before finalizing crank geometry. Frigate adjusts web thickness, counterweight design, and crank throw layout to avoid resonance at operating speeds. Dynamic balancing is done in multiple planes to reduce critical speed amplification. Final validation includes frequency response testing under load-simulated conditions.

How does Frigate maintain journal surface integrity during high-speed machining operations?

All journal surfaces are rough-turned, stress-relieved, and finish-ground using controlled-feed CNC systems. Cutting parameters are optimized to prevent thermal damage and surface tearing. Frigate uses CBN grinding for fine tolerances and micro-finish control. Surface roughness is kept below Ra 0.2 µm to ensure proper oil film stability.

How does Frigate verify the dimensional accuracy of critical crankshaft features post-machining?

Frigate performs in-process probing during CNC operations to reduce stack-up errors. Final inspection is conducted using high-resolution coordinate measuring machines (CMMs). Each crankshaft is checked for concentricity, runout, and parallelism within micrometer-level tolerances. Inspection data is logged and shared with the customer if PPAP or ISIR compliance is required.

What material testing protocols does Frigate follow for aerospace-grade crankshafts?

Frigate sources aerospace-grade alloys with certified mill test reports and verified chemical compositions. Microstructure is inspected for cleanliness, grain size, and carbide distribution per AMS standards. Charpy impact, tensile, and hardness tests are performed on each batch to ensure material consistency. All data is documented for traceability under AS9100 quality systems.

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LOCATIONS

Registered Office

10-A, First Floor, V.V Complex, Prakash Nagar, Thiruverumbur, Trichy-620013, Tamil Nadu, India.

Operations Office

9/1, Poonthottam Nagar, Ramanandha Nagar, Saravanampatti, Coimbatore-641035, Tamil Nadu, India. ㅤ

Other Locations

  • Bhilai
  • Chennai
  • Texas, USA
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Crankshafts

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