Key Manufacturing Processes Of Quenched And Tempered Piston Rods

Key Manufacturing Processes of Quenched and Tempered Piston Rods
The key manufacturing processes for quenched and tempered piston rods encompass six major steps: material selection, pre-treatment, quenching and tempering heat treatment, machining, surface treatment, and quality inspection. Details are as follows:
1. Material selection
Based on the working conditions of the piston rod (e.g., load, environmental corrosion), medium-carbon steel (e.g., 45# steel), alloy structural steel (e.g., 40Cr, 35CrMo), or stainless steel (e.g., 304, 316) are prioritized. These materials must exhibit high strength, high toughness, and corrosion resistance. Non-destructive testing (e.g., ultrasonic inspection) is used to ensure the absence of internal defects such as cracks or inclusions.

2. Pre-treatment
Forged blanks undergo annealing or normalizing to eliminate forging stress and improve machinability. For example:
45# steel: Normalizing (heated to 840–860°C, held, then air-cooled).
40Cr steel: Annealing (heated to 850°C, held, then furnace-cooled).

3. Quenching and tempering heat treatment
Quenching:
The piston rod is heated above its critical temperature (e.g., 840–860°C for 45# steel, 850°C for 40Cr steel), held for a specific duration, and rapidly cooled (e.g., oil or water quenching) to form a martensitic structure.
Tempering:
Immediately after quenching, high-temperature tempering (e.g., 550–650°C for 45# steel, 600–650°C for 40Cr steel) is performed, followed by air cooling. This produces a tempered sorbitic structure, balancing strength, hardness, plasticity, and toughness.

4. Machining
Rough Machining:
Turning and milling are used to remove excess material and preliminarily shape the outer diameter, threads, and other features.
Precision Machining:
Grinding and roller burnishing improve dimensional accuracy and coaxiality. Roller burnishing creates a work-hardened layer, enhancing wear resistance and reducing surface roughness (to Ra ≤ 0.2 μm).
Straightening:
Post-heat treatment deformation is corrected through straightening to ensure straightness (generally ≤ 0.15 mm).

5. Surface treatment
Chrome Plating:
A hard chromium layer (0.03–0.05 mm thick) is electroplated onto the surface to improve corrosion resistance and surface hardness (up to HV 800–1000). Post-plating grinding or polishing achieves a surface roughness of Ra 0.2–0.4 μm.
Nitriding:
Gas or ion nitriding forms a nitride layer (50–100 μm deep) on the surface, increasing hardness (up to HV 1000–1200) and wear resistance while maintaining core toughness.
Thermal Spraying:
Techniques like high-velocity oxygen fuel (HVOF) spraying apply tungsten carbide (WC) or ceramic coatings to further enhance wear and corrosion resistance.

6. Quality inspection
Dimensional Accuracy:
Coordinate measuring machines (CMM) and external micrometers are used to inspect dimensional accuracy, coaxiality, cylindricity, and other geometric tolerances.
Hardness Testing:
Hardness testers verify surface and core hardness to ensure compliance with design requirements.
Non-Destructive Testing (NDT):
Ultrasonic and magnetic particle testing detect internal and surface defects such as cracks or inclusions.
Surface Roughness Measurement:
Surface roughness testers ensure the surface finish meets operational requirements.