Anodising and Plating Finish Specifications

Understanding Surface Finishing in Modern Manufacturing

Surface finishing processes play a critical role in determining the performance, longevity, and aesthetic quality of manufactured components. For industries across Atlantic Canada—from marine equipment manufacturers in Halifax to aerospace suppliers in the Greater Moncton area—selecting the appropriate anodising or plating specification can mean the difference between a component that lasts decades and one that fails prematurely in service.

At its core, surface finishing serves multiple functions: corrosion protection, wear resistance, electrical conductivity or insulation, thermal management, and visual appearance. The harsh maritime climate of Nova Scotia, with its salt-laden air and significant humidity variations, makes proper surface treatment specifications particularly crucial for equipment operating in our region.

This comprehensive guide examines the technical specifications, standards, and practical considerations that engineers and technical managers must understand when specifying anodising and plating finishes for their manufacturing projects.

Anodising Processes and Specifications

Anodising is an electrochemical process that converts the surface of aluminium (and certain other metals) into a durable, corrosion-resistant oxide layer. Unlike plating, which deposits material onto a surface, anodising grows the protective layer from the base material itself, creating an integral bond that won't peel or flake.

Type I: Chromic Acid Anodising

Chromic acid anodising produces the thinnest oxide layer, typically ranging from 0.5 to 2.5 micrometres. This process operates at temperatures between 32°C and 38°C with voltage levels of 20 to 22 volts. Key specifications include:

• MIL-A-8625F Type I and Type IB (non-chromic acid alternative)

• Minimal dimensional change, making it ideal for precision components

• Excellent paint adhesion properties

• Superior fatigue resistance compared to thicker anodic coatings

• Commonly specified for aerospace applications where weight and dimensional tolerances are critical

Due to environmental regulations regarding hexavalent chromium, many Canadian manufacturers are transitioning to Type IB alternatives using tartaric-sulphuric acid processes that achieve comparable performance without the hazardous materials concerns.

Type II: Sulphuric Acid Anodising

The most widely specified anodising process, Type II sulphuric acid anodising, produces oxide layers between 2.5 and 25 micrometres thick. Standard specifications include:

• MIL-A-8625F Type II (conventional) and Type IIB (thin film)

• Class 1: Non-dyed (natural clear finish)

• Class 2: Dyed finishes in various colours

• Operating temperature: 18°C to 22°C

• Current density: 12 to 16 amps per square decimetre

For Maritime applications, Type II anodising with proper sealing provides excellent protection against the corrosive salt air environment common throughout Nova Scotia's coastal regions. Components for fishing vessels, marine hardware, and outdoor signage frequently specify this treatment.

Type III: Hard Anodising

Hard anodising, also known as hard coat anodising, produces exceptionally thick and durable oxide layers ranging from 25 to 100 micrometres. This process requires lower temperatures (0°C to 5°C) and higher current densities to achieve its distinctive properties:

• Surface hardness: 60 to 70 Rockwell C equivalent

• Wear resistance comparable to hard chromium plating

• Electrical insulation up to 800 volts

• Operating temperature resistance to 200°C continuous

• Dimensional growth of approximately 50% of total coating thickness per surface

Engineers must account for dimensional changes when specifying hard anodising. A component requiring a 50-micrometre coating will experience approximately 25 micrometres of growth per surface, necessitating undersizing of mating features.

Electroplating Specifications and Standards

Electroplating deposits a metallic coating onto a substrate through electrolytic reduction. Unlike anodising, plating can be applied to virtually any conductive material and offers a broader range of functional properties.

Zinc and Zinc Alloy Plating

Zinc plating remains the most cost-effective corrosion protection method for ferrous metals. Canadian manufacturers typically specify according to ASTM B633 or ISO 2081 standards:

• Fe/Zn 5: 5-micrometre minimum thickness for mild indoor environments

• Fe/Zn 8: 8-micrometre minimum for moderate indoor/outdoor exposure

• Fe/Zn 12: 12-micrometre minimum for severe outdoor conditions

• Fe/Zn 25: 25-micrometre minimum for marine and industrial atmospheres

Conversion coatings (chromates) applied after zinc plating significantly enhance corrosion resistance. Modern trivalent chromate processes have largely replaced hexavalent chromates in Canadian facilities, offering comparable performance while meeting environmental regulations.

For applications in Nova Scotia's demanding coastal environment, zinc-nickel alloy plating (typically 12-15% nickel content) provides three to five times greater corrosion resistance than pure zinc, making it increasingly popular for automotive and marine fasteners.

Nickel and Chromium Plating

Nickel plating serves both decorative and functional purposes. Engineering specifications typically reference ASTM B689 for electroless nickel or ASTM B456 for electrolytic nickel-chromium systems:

• Electroless nickel (EN): Uniform coating regardless of geometry, typically 12 to 75 micrometres

• High-phosphorus EN (10-13% P): Superior corrosion resistance, non-magnetic

• Mid-phosphorus EN (6-9% P): Balanced hardness and corrosion resistance

• Low-phosphorus EN (2-5% P): Maximum hardness (up to 68 HRC after heat treatment)

Decorative chromium plating over nickel underlayers creates the brilliant, corrosion-resistant finish common on consumer products and automotive trim. However, functional hard chromium plating (industrial chrome) serves entirely different purposes, providing extreme hardness (850-1000 HV) and low friction coefficients for hydraulic cylinders, bearing surfaces, and tooling.

Precious Metal Plating

Electronics and aerospace applications frequently require precious metal plating for conductivity, solderability, or contact resistance properties:

• Gold (ASTM B488): Type I (99.7% pure) to Type III (99.0% minimum with hardeners)

• Silver (ASTM B700): Excellent conductivity, typically 2.5 to 13 micrometres for electrical applications

• Palladium and palladium-nickel: Cost-effective gold alternatives for connector applications

Atlantic Canada's growing aerospace sector, including maintenance, repair, and overhaul facilities throughout the region, regularly specifies these coatings according to stringent aerospace material specifications (AMS) requirements.

Specification Documentation and Quality Requirements

Proper specification documentation ensures consistent results and facilitates quality control. A complete finish specification should include:

Essential Specification Elements

• Base material: Alloy designation, temper, and any pre-treatment requirements

• Process type: Specific anodising or plating process (e.g., MIL-A-8625F Type III Class 2)

• Thickness requirements: Minimum, maximum, or range with measurement locations

• Coverage requirements: Significant surfaces versus non-significant areas

• Post-treatment: Sealing, chromate conversion, or other supplementary processes

• Acceptance criteria: Visual standards, adhesion tests, thickness verification methods

Common Testing and Verification Methods

Quality assurance for surface finishes typically involves multiple verification techniques:

• Thickness measurement: Eddy current (ASTM B244), magnetic induction (ASTM B499), or X-ray fluorescence methods

• Adhesion testing: Bend tests, tape tests (ASTM D3359), or thermal shock methods

• Corrosion resistance: Salt spray testing (ASTM B117) with hours to first corrosion specified

• Hardness testing: Microhardness (Knoop or Vickers) for thin coatings

• Porosity testing: Ferroxyl tests for nickel, copper sulphate tests for chromium

For critical applications, statistical sampling plans according to ANSI/ASQ Z1.4 (formerly MIL-STD-105) ensure adequate quality coverage without requiring 100% inspection.

Environmental and Regulatory Considerations

Canadian environmental regulations significantly impact surface finishing operations and material selections. Engineers must consider these factors when developing specifications:

CEPA and Provincial Requirements

The Canadian Environmental Protection Act (CEPA) and Nova Scotia's Environment Act regulate emissions, effluent discharge, and hazardous material handling for surface finishing operations. Key considerations include:

• Hexavalent chromium restrictions affecting chromic acid anodising and hard chrome plating

• Cadmium plating limitations (though aerospace exemptions may apply)

• Wastewater treatment requirements for metal-bearing effluents

• Air emission controls for process tanks and drying operations

RoHS and REACH Compliance

Products exported to European markets must comply with RoHS (Restriction of Hazardous Substances) and REACH (Registration, Evaluation, Authorisation, and Restriction of Chemicals) directives. This affects finish specifications for:

• Hexavalent chromium in conversion coatings and plating

• Cadmium in any plating application

• Lead in solders and certain alloy platings

Many Maritime manufacturers serving export markets now specify trivalent chromium processes and zinc-nickel alternatives to ensure global market access.

Application-Specific Recommendations

Different industries and applications demand tailored surface finishing approaches. The following recommendations reflect common requirements across Atlantic Canadian manufacturing sectors:

Marine and Offshore Applications

The demanding maritime environment of Nova Scotia's coastline requires robust corrosion protection:

• Aluminium components: Type III hard anodising with PTFE impregnation for wear surfaces

• Steel fasteners: Zinc-nickel plating (minimum 12 micrometres) with trivalent passivation

• Electrical connectors: Tin-nickel alloy or gold plating over nickel barrier layers

• Hydraulic components: Hard chromium or electroless nickel with phosphorus content above 10%

Food Processing Equipment

Nova Scotia's significant seafood processing industry requires finishes that meet food safety standards:

• Electroless nickel (high phosphorus) for excellent cleanability and corrosion resistance

• Anodised aluminium with FDA-compliant sealing processes

• Electropolished stainless steel as an alternative to plating where appropriate

Defence and Aerospace

Military and aerospace specifications demand rigorous process control and documentation:

• MIL-A-8625 for aluminium anodising with specific type and class designations

• AMS 2404 (electroless nickel), AMS 2406 (zinc-nickel), AMS 2460 (cadmium where permitted)

• QPL (Qualified Products List) approved processors for critical applications

• Full material traceability and certification documentation

Cost Considerations and Specification Optimisation

Balancing performance requirements with economic constraints requires careful specification optimisation. Key factors affecting surface finishing costs include:

• Coating thickness: Thicker coatings require longer process times and more material

• Surface preparation: Complex geometries or poor surface quality increase pre-treatment costs

• Process type: Precious metal plating significantly exceeds zinc or anodising costs

• Quality requirements: Aerospace-grade certification adds substantial overhead

• Batch size: Setup costs favour larger production quantities

Engineers should specify only what the application truly requires. Over-specification wastes resources, while under-specification risks premature failure. Consulting with experienced finishing specialists early in the design process often identifies opportunities for cost reduction without compromising performance.

Partner with Sangster Engineering Ltd. for Your Surface Finishing Specifications

Developing appropriate anodising and plating specifications requires expertise in materials science, manufacturing processes, and application requirements. At Sangster Engineering Ltd. in Amherst, Nova Scotia, our professional engineering team brings decades of experience helping Maritime manufacturers optimise their surface finishing specifications.

Whether you're designing new products, troubleshooting coating failures, or seeking to reduce costs while maintaining quality, our engineers can provide the technical guidance you need. We understand the unique challenges of manufacturing in Atlantic Canada's demanding environment and can help you select specifications that ensure long-term performance and reliability.

Contact Sangster Engineering Ltd. today to discuss your anodising, plating, and surface finishing specification requirements. Our team is ready to help you achieve optimal results for your manufacturing projects across Nova Scotia, New Brunswick, Prince Edward Island, and beyond.

Partner with Sangster Engineering

At Sangster Engineering Ltd. in Amherst, Nova Scotia, we bring decades of engineering experience to every project. Serving clients across Atlantic Canada and beyond.

Contact us today to discuss your engineering needs.