Improving the quality of electroplated fasteners requires comprehensive optimization from material selection, process control, post-treatment and quality management.
Author: Anna
Improving the quality of electroplated fasteners requires comprehensive optimization from material selection, process control, post-treatment and quality management. The following are the key measures:
1. Pre-treatment of substrate
Cleaning and degreasing: Thoroughly remove oil, rust and oxides on the surface of fasteners, using ultrasonic cleaning or chemical degreasing (such as alkaline degreasing agent).
Acid washing activation: Remove the oxidized layer with dilute hydrochloric acid or sulfuric acid to avoid over-corrosion (control the concentration, time and temperature).
Sand blasting/grinding: Enhance the surface roughness and improve the adhesion of plating layer (applicable to high-strength fasteners).
2. Plating process optimization
Plating layer selection:
Zinc plating: commonly used, need to be combined with passivation (blue and white, colored zinc, black zinc) to improve corrosion resistance.
Nickel plating: higher corrosion and wear resistance, suitable for harsh environments.
Zinc-nickel alloy (Zn-Ni): better corrosion resistance than pure zinc, suitable for automotive, aerospace.
Process parameter control:
Current Density: Avoid excessive high levels resulting in rough or burnt plating.
Temperature: keep it stable (e.g. zinc plating at room temperature, nickel plating needs 50-60°C).
pH: Monitor and adjust regularly (e.g. alkaline zinc plating solution pH 12-14).
Plating time: Ensure uniform plating thickness (can be optimized by Hall tank test).
Additive management: Use brightener and leveler to improve the appearance of the plated layer, and filter the bath regularly to remove impurities.
3. Post-treatment key steps
Passivation treatment:
Chromate passivation (Cr(VI) or Cr(III)) to improve corrosion resistance, with attention to environmental compliance.
Chromate-free passivation (e.g. silicates, molybdates) is suitable for environmentally demanding scenarios.
Sealing treatment: Sealing of the passivated plating (e.g. coating with silane or wax) to reduce porosity.
Dehydrogenation treatment:
High strength fasteners (≥10.9 grade) need to be baked at 200-230°C for 2-4 hours to prevent hydrogen embrittlement.
4. Quality inspection and control
Plating thickness: Tested by magnetic thickness gauge or X-ray fluorescence meter, in accordance with ISO 4042 or ASTM B633.
Adhesion test: bending test, thermal shock test or scribing method.
Corrosion resistance: Salt spray test (e.g. neutral salt spray for more than 72 hours without white rust).
Hydrogen embrittlement test: Delayed fracture test or stress ring test for high strength parts.
5. Environment and equipment management
Plating solution maintenance: regularly analyze the composition, filter to remove particulate impurities and prevent contamination.
Equipment maintenance: check anode, conductive system, temperature control device to ensure stability.
Environmental protection measures: Waste water treatment (heavy metal recovery, neutralization and precipitation), in line with RoHS/REACH requirements.
6. Personnel and Standards
Operation training: Standardize plating, passivation and testing process to reduce human error.
Standardized operation: according to ISO 4520 (galvanizing), ASTM F1941 (fastener plating) and other standards.
Countermeasures for common problems
Blistering of plating layer: Check whether the pre-treatment is thorough or whether there are defects in the base material.
White rust/red rust: Optimize passivation process or add sealing treatment.
Poor thread fit: control the thickness of plating (threaded parts can be partially shielded or back to the teeth treatment).
Through systematic optimization of the above links, the corrosion resistance, adhesion and mechanical properties of plated fasteners can be significantly improved to meet the high standards of the automotive, construction, electronics and other industries.