QLQ zinc alloy surface finishing equipment and process QLQ zinc alloy surface finishing equipment and process

Professional Zinc Alloy Surface Finishing Solutions

Nickel/Tin Plating

Barrel Nickel & Tin Plating — Bright, Matte, Pearl & Solderable Finishes

Nickel (bright pH 4.2-4.6, 50-55 °C, matte, pearl) and tin (solderable, electronics) plating for small parts in barrel. Pinhole prevention with wetting agents.

Why Barrel Nickel & Tin

Nickel provides hardness, brightness and corrosion resistance. Tin provides solderability for electronic components. Both are barrel-processed daily for small hardware.

Bright Nickel

Mirror finish, pH 4.2-4.6, 50-55 °C

Matte & Pearl Ni

Satin sheen, fingerprint resistant

Tin — Solderable

Essential for electronic components

Pinhole Prevention

Wetting agents + filtration

Barrel vs Rack — Nickel/Tin Comparison

Key parameter differences between barrel and rack for nickel and tin plating

ParameterBarrel PlatingRack Plating
Bright Ni current density0.5-2 A/dm²2-6 A/dm²
Nickel pH4.2-4.64.0-4.8
Temperature50-55 °C50-65 °C
Barrel rotation (Ni)8-12 rpmN/A
Tin current density0.5-1.5 A/dm²1-3 A/dm²
Cost per part (Ni)Lower (mass batch)Higher (individual)
Wetting agent needHigher (rotation aerates)Standard
Pinhole sensitivityHigher (part-contact shadows)Lower (fully exposed)
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Barrel Nickel & Tin — Process Steps

Five finishes from a single barrel line: bright, matte, pearl, tin, and Ni-Sn alloy

1Bright Nickel Plating

Workhorse finish for most hardware. Sulfamate or Watts-type bath. Barrel rotation vs. rack: lower current density (0.5-2 A/dm²) to compensate for barrel masking.

Key Parameters
pH: 4.2-4.6
Temperature: 50-55 °C
NiSO₄·6H₂O: 240-300 g/L
NiCl₂·6H₂O: 45-60 g/L
H₃BO₃: 30-40 g/L
Current density: 0.5-2 A/dm²
BeforeIndustrial bright nickel plating roller rotating in a tank on an automated production line
AfterHand holding a shiny silver nickel-plated small hardware component with scattered similar parts on a blue background.

2Matte & Pearl Nickel

Matte nickel uses no brightener — just a pure nickel deposit with matte finish. Pearl nickel adds micro-matting agents for a soft satin sheen. Barrel lines achieve this consistently.

Key Parameters
Matte Ni: No brightener, same basic bath
Pearl Ni additive: 0.5-2 mL/L matting agent
Pearl effect: Micro-dispersed inert particles

3Tin Plating (Barrel)

Tin for solderability on electronic components and food-contact parts. Acid tin (methane sulfonate) or alkaline stannate. Barrel rotation prevents 'tin whisker' contact damage.

Key Parameters
Tin (acid): Sn²⁺ 20-40 g/L, MSA 100-200 g/L
Tin (alkaline): Sn⁴⁺ 20-40 g/L, KOH 10-20 g/L
Current density: 0.5-1.5 A/dm²
Barrel rotation: 6-10 rpm

4Nickel-Tin Alloy (Gun Color Base)

Ni-Sn alloy (60:40 or 50:50) forms the base for gun metal color. Barrel-compatible with tight parameter control.

Key Parameters
Ni:Sn ratio: 60:40 to 50:50
Current density: 0.5-1.5 A/dm²
pH: 4.5-5.0
Temperature: 45-55 °C

5Pinhole / Pit Prevention

Barrel plating is prone to pinholes because parts contact each other and trap gas bubbles. Wetting agent + barrel reciprocation + filtration are the three defenses.

Key Parameters
Wetting agent: 1-3 mL/L (anti-pit)
Barrel reciprocation: 20-50 mm stroke
Filtration: Continuous 5-10 μm
Air agitation: Gentle (avoid over-oxidation)

6Rinse & Protection

Nickel rinse — anti-tarnish dip (0.5-1% Cr³⁺ or organic) for bright nickel. Tin rinse — DI water only (chromates interfere with solderability).

Key Parameters
Ni anti-tarnish: 0.5-1% Cr³⁺ or organic
Tin protection: DI rinse only
Drying temp: < 80 °C
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Nickel & Tin Application Guide

Choose the right finish and process for your part

FinishAppearanceHardness (HV)Thickness (μm)Best ForBarrel-Friendly?
Bright NickelSilver mirror350-5005-15General hardware, sliders★★★
Matte NickelSatin matte300-4505-15Minimalist designs, tools★★★★
Pearl NickelSilk sheen300-4005-10Luxury bags, handbags★★★
Tin (Acid)Bright white10-203-10Electronics, PCB contacts★★★★
Tin (Alkaline)Matte white10-203-10Food contact, cookware★★★★
Ni-Sn (Gun base)Grey-black500-6003-8Gun color precursor★★★★

📌 Nickel & Tin Cheat Sheet

Ni pH4.2-4.6
Ni temperature50-55 °C
Barrel Ni current density0.5-2 A/dm²
Tin current density0.5-1.5 A/dm²
Barrel rotation (Ni)8-12 rpm
Wetting agent1-3 mL/L
Ni thickness typical5-15 μm
Barrel vs rack Ni current0.5-2 vs 2-6 A/dm²
⚠ Pinholes in barrel nickel — the hidden defectPinholes are the #1 hidden defect in barrel nickel. Gas bubbles get trapped between contacting parts in the rotating barrel. The fix: (1) increase wetting agent to 2-3 mL/L, (2) add barrel reciprocation (vertical 'bobbing' motion during rotation), (3) filter continuously at 5 μm. Pinholes that look acceptable in the bath may corrode through within weeks in service — especially in humid environments.

FAQ

Can bright nickel and matte nickel run in the same barrel?
Not simultaneously — brightener contamination ruins the matte finish. Run matte nickel in a dedicated bath or schedule bright nickel first, then a full carbon treatment before matte runs.
What causes 'burning' in barrel nickel?
Same as acid copper — too much current for the barrel geometry. Nickel is less tolerant than copper. Keep barrel Ni current density at 0.5-2 A/dm². Above 2.5 A/dm² in barrel, expect burning at barrel door edges.
Tin plating for electronics — matte vs bright?
Matte tin is preferred for electronics: bright tin additives can co-deposit organics that degrade solderability over time. Matte tin has superior shelf life for solderability. Always specify matte tin for connectors and terminals.
How do I test nickel adhesion on barrel parts?
Simple bend test: bend 10 parts per batch 90° and inspect for peeling. Cross-cut (ISO 2409) for flat surfaces. In barrel lines, adhesion issues trace back 90% of the time to insufficient activation before nickel — never to the nickel bath itself.
What is the right barrel rotation speed for nickel?
8-12 rpm for most barrel sizes. Too slow (<6 rpm): parts at the bottom get thick Ni while top parts barely plate. Too fast (>15 rpm): excessive foaming of wetting agent and mechanical damage to parts.

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Nickel-tin: alloy ratio is the whole game

Tin in depositColourCorrosionNote
60-70%Warm champagneExcellentStandard decorative range
Below 55%Grey, dullReducedTin depletion - analyse and replenish
Above 75%Yellowish, softReducedHard to control, prone to tarnish

Titrate tin daily in production; ratio drift is the main cause of colour complaints.

FAQ

Can nickel-tin replace nickel under gold?

Yes, it gives a warmer undertone that suits gold and champagne finishes. Test the colour chip first.

Why does the deposit turn yellow over time?

Tin-rich surface oxidising, or a missing seal. Check the ratio and add a seal coat.