Zinc Flake Coatings
A Complete Guide to Zinc Flake Coatings (ISO 10683)
High-Performance Corrosion Protection for Critical Fasteners
For high-strength, safety-critical fasteners, selecting the right coating is paramount. While electroplating is common, the ultimate in high-performance, controlled, and reliable corrosion protection is often found in zinc flake coating systems.
These advanced coatings provide exceptional durability at a very low thickness and, most importantly, they completely eliminate the risk of hydrogen embrittlement. This guide explores the technology, the application process, the leading proprietary systems, and how they are defined by international standards.
What is a Zinc Flake Coating?
A zinc flake coating is a non-electrolytically applied finish. Unlike plating, which uses an electric current, this process is a highly controlled method where a liquid coating is applied to a component and then heat-cured.
The coating itself consists of a mixture of tiny zinc and (often) aluminium flakes held within an inorganic binder. During the curing process, the binder hardens and the metallic flakes align into a dense, interlocking structure. This creates a powerful barrier that provides sacrificial (cathodic) protection, similar to galvanizing but in a much thinner and more precise layer.
*The Key Advantage: No Hydrogen Embrittlement Risk* ⚙️
This is the single most important reason for choosing zinc flake coatings for high-strength fasteners (Grades 8, 10, 12, and above).
- Hydrogen embrittlement is a phenomenon where hydrogen atoms can enter high-strength steel during acid cleaning and electroplating, causing the material to become brittle and fail unexpectedly under load, sometimes catastrophically.
- Because the zinc flake process does not use electrolysis or acid pickling, the primary sources of hydrogen are completely eliminated. This makes it the safest and most reliable coating choice for critical applications in automotive, construction, wind energy, and aerospace.
How Are Zinc Flake Coatings Applied? The Dip-Spin Process
For fasteners and other small components, the most common application method is dip-spin.
- Stage 1: Surface Preparation
- The parts are first meticulously cleaned to remove oils and dirt, typically using an alkaline solution. Crucially, this avoids the use of acid. Shot blasting may also be used to prepare the surface.
- Stage 2: Application
- The parts are loaded into a mesh basket, which is then submerged (dipped) into a tank containing the liquid zinc flake coating.
- Stage 3: Spinning
- The basket is immediately raised and spun at high speed (centrifuged). This spinning action removes all excess coating and ensures a smooth, even, and consistent layer thickness across all parts.
- Stage 4: Curing
- The coated parts are transferred to an oven and baked at a specific temperature. This curing process hardens the binder and creates the final, durable metallic coating. For systems requiring a topcoat, this process is repeated.
Technical Comparison of Proprietary Zinc Flake Systems
The following table provides specific technical values for some of the most common proprietary zinc flake systems, allowing for a direct comparison. These systems are often interchangeable as long as they meet the required ISO 10683 designation.
| PROPRIETARY SYSTEM | GRADE | TYPE | TYPICAL THICKNESS (µm) | FRICTION COEFFICIENT (µ cof) | SALT SPRAY TEST (Hours, ISO 9227) | ISO 10683 Designation | EN 13858 Designation | CURING TEMPERATURE (°C) |
|---|---|---|---|---|---|---|---|---|
| GEOMET® | 321 | Basecoat | 6-10 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 |
| 500A | Basecoat + Lubricant | 6-10 | 0.12-0.18 | >720 | flZnnc-L-f720 | flZn-8-nc-L | ~240 | |
| 500B | Basecoat + Lubricant | 6-10 | 0.09-0.14 | >720 | flZnnc-L-f720 | flZn-8-nc-L | ~240 | |
| 720 | High Performance Basecoat | 8-12 | N/A (defined by topcoat) | >1000 | flZnnc-f1000 | flZn-10-nc-T | ~240 | |
| GEOBLACK® | System (Black) | 8-12 | 0.12-0.18 | >1000 | flZnnc-L-f1000 | flZn-10-nc-L | ~240 | |
| PLUS® XL | Lubricating Topcoat (Clear) | 1-2 | 0.06-0.09 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| PLUS® L | Lubricating Topcoat (Clear) | 1-2 | 0.08-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| PLUS® VL | Lubricating Topcoat (Clear) | 1-2 | 0.09-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| PLUS® M | Lubricating Topcoat (Clear) | 1-2 | 0.12-0.18 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| PLUS® ML | Lubricating Topcoat (Black) | 1-2 | 0.10-0.16 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| DELTA-PROTEKT® | DELTA-TONE® 9000 | Basecoat | 8-12 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 |
| DELTA-PROTEKT® KL100 | Basecoat | 8-12 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 | |
| DELTA-PROTEKT® KL105 | Basecoat | 8-12 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 | |
| DELTA-PROTEKT® VH 301 GZ | Lubricating Topcoat | 1-2 | 0.09-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| DELTA-SEAL® Silver GZ | Lubricating Topcoat (Silver) | 1-2 | 0.09-0.15 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| DELTA-SEAL® Black GZ | Lubricating Topcoat (Black) | 1-2 | 0.09-0.15 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 | |
| Magni® | 560 | System (Black) | 8-12 | 0.10-0.16 | >720 | flZnnc-L-f720 | flZn-8-nc-L | ~220 |
| 565 | System (Base + Topcoat) | 8-12 | 0.10-0.16 | >720 | flZnnc-L-f720 | flZn-8-nc-L ~ | ~220 | |
| 575 | System (High Perf.) | 10-15 | 0.09-0.15 | >1000 | flZnnc-L-f1000 | flZn-10-nc-L | ~220 | |
| 590 | System (High Perf. Black) | 10-15 | 0.09-0.15 | >1000 | flZnnc-L-f1000 | flZn-10-nc-L | ~220 | |
| 594 | System (High Perf.) | 10-15 | 0.10-0.16 | >1000 | flZnnc-L-f1000 | flZn-10-nc-L | ~220 | |
| Atotech | Zintek® 200 | Basecoat | 8-10 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 |
| Zintek® 300 B | Basecoat (Black) | 8 - 10 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~240 | |
| Techseal® Silver WL | Lubricating Topcoat | 1 - 2 | 0.09-0.15 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| Techseal® Black S | Lubricating Topcoat (Black) | 1 - 2 | 0.08-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| Coventya | FINIGARD® 105 | Basecoat | 8-12 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~210 |
| FINIGARD® 112 | High Perf. Basecoat | 8-12 | N/A (defined by topcoat) | >1000 | flZnnc-L-f1000 | flZn-10-nc-T | ~210 | |
| FINIDUR® 110 | Topcoat (Sealer) | 1-2 | Variable/Not Defined | System Dependent | (Used to meet -T spec) | (Used to meet -T spec) | ~180 | |
| FINIDUR® 111 | Lubricating Topcoat | 1-2 | 0.09-0.15 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| FINIDUR® 131 | Lubricating Topcoat | 1-2 | 0.08-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| FINIDUR® 180 | Lubricating Topcoat (Black) | 1-2 | 0.10-0.16 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~180 | |
| Keim-Additec | SILAR® 320 | Basecoat | 8-12 | N/A (defined by topcoat) | >720 | flZnnc-f720 | flZn-8-nc-T | ~260 |
| SILAR® TOP L | Lubricating Topcoat | 1-2 | 0.09-0.14 | System Dependent | (Used to meet -L spec) | (Used to meet -L spec) | ~200 |
Note: Friction coefficient values are typical and can be adjusted based on specific topcoats and customer requirements.
Understanding the ISO 10683 Designation
The code used in the ISO standard provides a precise technical description of the coating. Let's break down an example: *flZnnc-L-f720*
- flZn - The chemical symbol for a Zinc Flake coating.
- nc - Stands for "no chromium", meaning it is Cr(VI)-free and RoHS compliant.
- -L - Indicates the system includes a lubricant (either integrated or as a topcoat).
- -f - Refers to the coating thickness, in this case 'fine' (typically 5-12 µm).
- 720 - The minimum hours the coating must resist red rust in a salt spray test (ISO 9227).
Trojan Special Fasteners and Zinc Flake Coatings
At Trojan Special Fasteners Limited, we understand the critical nature of high-performance coatings. We can source and supply fasteners finished with a wide range of proprietary zinc flake systems.
Whether your drawing specifies GEOMET® 500A by name or calls for a coating compliant with BS EN ISO 10683 flZnnc-L-f720, our expert team can ensure your components meet the exact technical requirements for your project, providing you with the flexibility and quality assurance you need.