I. Common Quality Problems Related to Plating Layer
1. Uneven Plating or Localized Absence of Plating
Causes: Uneven current distribution, poor contact of the plating fixture, poor deep plating ability in deep recesses of the workpiece (difficult deposition in low current areas).
Manifestations: Inconsistent surface gloss, over-plating at edges and corners, thin plating or even missed plating in deep holes or inner walls.
Improvement Measures: Optimize the layout of the electroplating tank, use auxiliary anodes, adjust the current density and plating solution composition (e.g., control the CrO₃:SO₄²⁻ ratio to 80-100:1).
2. Pinholes and Pitting
Causes: Inadequate degreasing during pretreatment, residual oil or oxides on the surface, hydrogen bubbles adhering during electroplating forming insulating points, preventing metal deposition.
Manifestations: Tiny pores extending from the plating layer to the substrate, reducing corrosion resistance.
Improvement Measures: Strengthen alkaline washing and ultrasonic cleaning; add wetting agents to reduce surface tension; regularly filter the plating solution to remove particulate impurities.
3. Chromium layer appears mottled, hazy, or dull.
Causes: Insufficient passivation or activation of the undercoat (e.g., nickel layer) after polishing; excessive saccharin or chloride ion content in the plating solution.
Appearance: Uneven surface gloss, with localized hazy or grayish-white areas.
Improvement Measures: Control nickel plating process parameters to ensure sufficient activation before chromium plating (immersion in 3%–5% sulfuric acid for 2 minutes); regularly analyze and purify the plating solution.
4. Plating layer peeling, delamination, or flaking.
Causes: Incomplete degreasing during pretreatment; rust or oxide film on the substrate surface; ineffective removal of hydrogen embrittlement.
Appearance: Easily peels off under light pressure, especially noticeable under bending or impact conditions.
Improvement Measures: Strictly adhere to the degreasing, pickling, and activation processes; perform a dehydrogenation treatment at 200–220℃ for 3 hours after plating.
II. Dimensional and Geometric Tolerance Issues
1. Out-of-tolerance outer diameter or poor straightness
Causes: Improper clamping during machining, tool wear, unreasonable grinding parameters, or uneven stress release after heat treatment.
Symptoms: Excessive tightness or looseness during assembly, affecting guiding accuracy.
Improvement Measures: Use a centerless grinder to ensure outer diameter accuracy; implement closed-loop control of "trial cutting + inspection" during machining; control straightness ≤0.08mm/m during straightening.
2. Inadequate coating thickness
Causes: Insufficient electroplating time, low current efficiency, abnormal plating solution temperature or concentration.
Symptoms: Decreased wear resistance and shortened lifespan.
Improvement Measures: Strictly monitor plating solution parameters (temperature 50-55℃, current density 30-60 A/dm²), and use an X-ray thickness gauge for real-time detection.
III. Materials and Process Management Issues
1. Excessive Trivalent Chromium Ions
Impact: Causes graying and roughness of the plating layer, and reduces the ability to deep plated.
Control Method: Reduce Cr³⁺ concentration through large-area cathodic electrolysis and maintain plating solution balance.
2. Foreign Metal Impurity Contamination (e.g., iron, copper ions)
Sources: Workpiece drop, anodic corrosion, introduction by chemical raw materials.
Consequences: Causes pinholes, roughness, and reduced adhesion.
Treatment: Regularly dilute the plating solution or use ion exchange for purification.
3. Hydrogen Embrittlement Risk
Mechanism: Large amounts of hydrogen are released during electroplating, and hydrogen atoms penetrate the substrate, reducing the material's toughness.
Prevention Measures: All high-strength chromium plating rods must undergo hydrogen removal treatment to prevent sudden breakage during service.
