Black Spots या Yellowing को Zinc Electroplating में कैसे Control करें? (Full Detailed Solution)

Zinc Electroplating में जब component par black spots, yellowish layer ya uneven color दिखाई देता hai, to iska मतलब process ke kisi na kisi step mein dikkat ho rahi hai. Yeh sirf visual issue nahi hota, balki product ki quality, corrosion resistance aur client satisfaction pe direct impact daal sakta hai.

🔍 Common Causes of Black Spots & Yellowing

Surface Preparation Poor Hai: Degreasing, acid pickling ya electro-cleaning sahi nahi hone par contaminants surface par reh jaate hain.
Zinc Bath Contaminated Hai: Iron, copper, lead contamination se plating layer uneven ya black ho sakti hai.
Current Density Zyada ya Kam Hai: High current se burning, low current se dull finish ya yellowing ho sakta hai.
Passivation Galat Timing Mein Ho Raha Hai: Over timing se flaking, aur short timing se spotting ho sakti hai.
Water Rinse Proper Nahi Hai: Acid drag-over ya passivation salt residue surface pe reh jaata hai.

🛠 Step-by-Step Solution (Best Practices)

1. Surface Preparation Sudharo

Hot soak degreasing: Use Alkaline cleaner @ 60°C for 5-7 minutes.
Electro-cleaning: Reverse polarity @ 6-9 V for 2-3 minutes. Water rinse properly after each step.

2. Acid Dipping

Use 10-15% HCl dip for 10-20 seconds to activate surface.
Avoid over-pickling, otherwise hydrogen embrittlement ho sakta hai.

3. Zinc Bath Maintenance

Filter bath weekly to remove metallic contamination.
Maintain Zinc metal content @ 8–12 g/L and check for Iron impurity.
Add brightener/booster properly in measured amount.

4. Current Density Optimize Karo

Maintain 1.5–2.5 A/dm² for uniform deposition.
Jyada thickness ke liye high current mat use karo. Burn marks aa sakte hain.

5. Rinsing Steps Perfect Rakho

3-stage rinse system: Cold water, overflow rinse & final DM water rinse.
Each rinse mein water ko daily replace karo to avoid salt deposit.

6. Passivation Timing & Temperature

Trivalent blue: 5–15 seconds @ 25–30°C
Black: 10–30 seconds depending on product & temperature
Don’t overdo! Warna peeling/shadow spots ayenge.

7. Drying & Handling

Hot air drying @ 80–90°C for 10 minutes.
Don't touch bare hands se – gloves ka use karein.

✅ Final Tips to Avoid Yellowing/Black Spots

Daily bath analysis & top-up schedule banao.
Drag-out loss control karo with good rinsing system.
Passivation tanks ko weekly replace karo.
Proper training & SOP follow karao staff ko.

🔚 Conclusion

Agar aap in sari steps ko dhyan se follow karte ho to Black Spots ya Yellowing jaise problems bilkul eliminate ho jaayengi. Yeh detailed SOP aapke staff aur quality team dono ke liye ek ready-made solution hai. Kisi expert se baar-baar puchhne ki zarurat nahi padegi.

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