Capability

Surface Finishing

Zinc, nickel, passivation and PVD in one plant

Zinc / NiPassivationPVD720 h salt spray

Line-up of coated screws in different finishes

Surface Finishing · Bekasi plant

Process overview

Zinc, nickel, passivation and PVD in one plant

Finish is where a functional fastener becomes a product feature. The same screw can be a dull grey part inside a housing or a black decorative element on a visible surface, and the difference is a few micrometres of coating. But finish also carries the corrosion specification, the friction coefficient that determines torque-to-preload, and in some cases the electrical contact resistance.

We operate barrel plating for zinc and nickel, passivation and electropolishing for stainless, and PVD chambers for TiN, CrN, TiCN and DLC. Coating thickness is measured by X-ray fluorescence at multiple points including the thread root, where coverage is always thinnest and where salt spray failures actually begin.

Step by step

How the process runs

Each step has a defined control point. The sequence is not arbitrary — changing it changes the result.

Pre-treatment

Degreasing, pickling and activation to remove oil, oxide and scale so the coating adheres uniformly.

Barrel plating

Zinc, zinc-nickel or nickel deposited in rotating barrels with current and chemistry controlled per bath.

Post-treatment

Trivalent chromate, topcoat or sealer applied to enhance corrosion resistance and control friction.

Passivation

Stainless parts are passivated in nitric or citric acid to restore the chromium oxide layer after cutting and tumbling.

PVD coating

Parts are cleaned, ion etched and coated in a vacuum chamber with rotating fixtures for uniform coverage.

Baking

High-strength plated parts are baked to release hydrogen before or after post-treatment as the specification requires.

Inspection

Coating thickness by XRF, appearance against a master, adhesion and salt spray on a sampled basis.

Specification

Process window and capability

The numbers below define what the process can hold repeatably. They are not laboratory bests.

Zinc thickness

5 – 12 µm

Zinc-nickel thickness

8 – 15 µm, 12–15% Ni

Nickel thickness

3 – 8 µm

PVD thickness

2 – 5 µm

Salt spray, zinc trivalent

96 – 240 h

Salt spray, zinc-nickel

480 – 720 h

Salt spray, Dacromet

720 – 1,000 h

Passivation standard

ASTM A967 / ASTM A380

Friction coefficient

0.10 – 0.25 depending on system

Colour options

Clear, blue, black, gold, gunmetal, rainbow

Equipment

What the line is built on

Capacity figures are per machine and assume a standard part. Complex geometry reduces throughput.

Equipment	Specification
Barrel plating lines	Zinc, zinc-nickel, nickel; 5 – 20 kg barrels
Passivation line	Nitric and citric, ASTM A967 / A380
PVD chambers	Multi-arc and magnetron sputtering, 2 – 5 µm
XRF thickness gauge	Multi-point, including thread root
Salt spray chambers	Neutral 5% NaCl, ASTM B117
Adhesion test	Rockwell C indentation for PVD

Process control

What is checked, and when

A control that is not recorded is not a control. Each item below generates a record linked to the lot code, retained for the programme duration.

Quality & certifications

Bath chemistry analysis daily

Coating thickness by XRF at head, shank and thread root

Appearance against retained master sample

Adhesion by tape or Rockwell indentation for PVD

Salt spray per ASTM B117 on sampled lots

Hydrogen embrittlement bake record for 10.9+

Friction coefficient by torque-tension test

RoHS / REACH declaration per finish

Questions

Surface Finishing FAQ

Practical questions from sourcing and engineering teams.

Considering a process change? If a tolerance or finish is not achievable on our current line, we will say so before quoting rather than after the first lot.

Why measure coating at the thread root?

Because that is where it is thinnest and where corrosion starts. A coating that measures 10 µm on the head may be 4 µm at the thread root, and the salt spray result will follow the thin point, not the average.

Does coating change the thread fit?

Yes. A 10 µm coating adds up to 20 µm diametrally. For Class 6g this is usually acceptable, but for tight fits we either gauge after coating or mask the thread. Zinc-nickel at 15 µm is the usual point where this becomes a design issue.

Can I have a black finish that is not paint?

Yes. Black oxide, black zinc, black PVD and DLC are all available. Black oxide is cheapest but has limited corrosion resistance; DLC is hardest and most durable; black zinc offers the best corrosion per unit cost.

Do you passivate to ASTM A967?

Yes, in nitric or citric chemistry depending on the alloy and the customer specification. We can supply passivation records and copper sulphate test results where required.

Related capabilities

What happens before and after

These processes are usually sequenced with the one above.

Capability

Cold Forging

Two-, three- and four-station cold heading machines form micro screw blanks from wire without cutting, preserving grain flow through the head and shank.

Capability

Heat Treatment

Controlled atmosphere heat treatment for case depth, core hardness and hydrogen embrittlement relief — with batch records for every lot.

Micro screws with a green pre-applied locking patch

Capability

Precoating & Patch

Automated application of locking and sealing elements at a controlled thread position, with break-loose torque verified per batch.

Precision screw samples prepared for laboratory inspection

Capability

Quality Laboratory

An in-house laboratory covering dimensional metrology, hardness, torque, salt spray and material verification — so results are not outsourced and delayed.

Need surface finishing for your part?

Send the drawing and the annual volume. We will confirm feasibility, tolerance and lead time in the quotation.

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