Coating questions, answered

Zinc flake coating is a non-electrolytic protective finish made of overlapping zinc and aluminium flakes held in an inorganic binder. Parts are dip-spun or sprayed, then cured in an oven. Because no electric current is used, there is no hydrogen embrittlement risk, which is why it is the preferred finish for high-tensile fasteners.

GEOMET® is a water-based, hexavalent-chrome-free zinc flake coating system developed by NOF Metal Coatings. It provides cathodic corrosion protection in a thin film, typically applied by dip-spin. Aum Dacro Coatings is a licensed GEOMET® applicator for NOF Metal Coatings, Japan.

Both are zinc flake systems from the same family. DACROMET® is the earlier generation and contains hexavalent chromium; GEOMET® is the chrome-free successor. For any part going into an ELV- or RoHS-regulated assembly, GEOMET® is the correct specification.

A zinc flake basecoat is typically applied in the range of 8–12 µm, rising to roughly 10–20 µm once a top coat is added. The exact figure depends on the system specified and the customer drawing. The film is thin enough to preserve thread fit on fasteners, which is one of its main advantages over hot-dip galvanising.

Performance is measured as hours to red rust under neutral salt spray to ISO 9227 or ASTM B117. Zinc flake systems commonly reach several hundred hours, and basecoat-plus-topcoat combinations can be specified well beyond that. The figure achieved depends on the system, film thickness and part geometry, so it is agreed against your drawing requirement at enquiry stage.

Yes. GEOMET® and the other zinc flake systems we apply are Cr(VI)-free. This is what allows coated parts to be used in assemblies subject to EU ELV (2000/53/EC), RoHS and REACH obligations.

No. Hydrogen embrittlement is a risk associated with electrolytic processes, where atomic hydrogen is generated at the part surface. Zinc flake is applied without electric current and cured thermally, so the mechanism does not occur. This is the main reason it is specified for high-strength fasteners of grade 10.9 and above.

For high-tensile fasteners and parts needing long salt-spray life at low film thickness, zinc flake is usually the better choice, and it avoids hydrogen embrittlement. Zinc electroplating remains a sound choice where electrical conductivity, a bright decorative finish, or lowest cost per part is the priority. We run both, so we can advise against your actual requirement.

A top coat is a second layer applied over the zinc flake basecoat. It is used to raise corrosion performance, control the coefficient of friction, add colour, or improve chemical resistance. Friction control matters most on threaded fasteners, where consistent torque–tension behaviour is required at assembly.

Torquer is our friction-controlled coating range for threaded fasteners. It is specified when the assembly process needs a predictable and repeatable coefficient of friction so that applied torque translates into the intended clamp load. Torque–tension behaviour is verified to ISO 16047.

Zinc nickel is an electroplated alloy coating, usually containing 12–15% nickel, that offers markedly better corrosion resistance than plain zinc plating and performs well at elevated temperature. It is commonly specified for brake components, underbonnet parts and applications with a galvanic contact requirement against aluminium.

Thermal diffusion, sometimes called sherardising, forms a zinc–iron alloy layer by heating parts in a zinc powder medium. The coating grows into the substrate rather than sitting on top of it, giving excellent adhesion and edge coverage. It suits parts with complex geometry and those needing abrasion resistance.

PTFE and related fluoropolymer coatings are applied where low friction, non-stick release or chemical resistance is needed rather than corrosion protection alone. They are sprayed and sintered, and are often specified for sliding components, seals and parts in aggressive media.

Zinc alkaline is an electroplating process using an alkaline, cyanide-free electrolyte. It gives more uniform thickness distribution than acid zinc, particularly on complex shapes, which makes it well suited to stampings and formed components.

It means the plating line is monitored and regulated by a supervisory control and data acquisition system, so bath chemistry, current, temperature and cycle times are logged automatically rather than recorded by hand. The practical benefit is repeatability between batches and a traceable record for audit.

The standards most often referenced on our work are ISO 10683 for non-electrolytically applied zinc flake coatings on fasteners, ISO 9227 and ASTM B117 for salt spray testing, ISO 16047 for torque–clamp force, ISO 4042 for electroplated fastener coatings and ISO 2178 for coating thickness measurement.

Yes. Neutral salt spray testing to ISO 9227 and ASTM B117 is part of our routine quality control, alongside coating thickness and coating mass checks. Test reports can be issued with supply where your specification calls for them.

For most of our work thickness is measured magnetically to ISO 2178, and coating mass is determined to ISO 10683 where the specification is written in grams per square metre rather than microns. Both methods are used depending on how the customer drawing is dimensioned.

Yes. Most of our work is to customer or OEM specification rather than to a generic finish. Send us the drawing and the coating callout, and we will confirm whether we can meet it as written or propose the closest qualified equivalent.

Job coating, also called contract or jobbing coating, means we coat parts that you supply and return them to you finished. We do not manufacture the components themselves. Parts arrive at the plant, are processed through the agreed route, inspected and despatched back.

Automotive and mobility, railways, wind and solar energy, oil and gas, telecommunications, metallic and electrical construction, and construction and agricultural machinery. Our customers include fastener, stamping, casting and precision component manufacturers.

We operate five units in India: two at Manesar in Haryana, one at Bilaspur in Haryana, one at Chennai in Tamil Nadu and one at Sanand in Gujarat, with the corporate office in Gurugram. Capacity and available coatings differ by unit, so parts are routed to the plant equipped for the finish you need.

Yes — our quality management system is certified to IATF 16949:2016 alongside ISO 9001:2015, with ISO 14001:2015 and ISO 45001:2018 for environment and occupational health and safety. Coating line assessment is carried out to AIAG CQI-12 and process audits to VDA 6.3. Certification scope varies by unit and current certificates are available on request.

Yes. We produce part approval documentation to the submission level your programme requires, including control plans, process flow, measurement system analysis and capability studies.

There is no single figure — it depends on the coating, the part and the line it runs on, since dip-spin work is batched by basket volume. Send us your part details and expected annual quantity and we will confirm what is practical.

Lead time depends on the coating route, batch size and current line loading. We confirm a committed date against each order rather than quoting a blanket figure. For regular schedules we plan capacity in advance so despatch is predictable.

Send us the part drawing, the coating specification or performance requirement, the annual volume and the plant region that suits you. That is normally enough for us to quote. You can reach us through the contact page, or by email and phone.

Our plants are in India and most of our work supplies Indian manufacturing, including parts that are subsequently exported by our customers. For direct export enquiries, contact us with the destination and volume so we can confirm what is workable.

Part size and weight limits differ between units and between coating routes, since dip-spin, rack and spray lines each have their own envelope. Send the part dimensions and weight and we will confirm which of our plants can process it.