How do you indicate surface coatings in mechanical drawings?

Short Answer:

In mechanical drawings, surface coatings are indicated using symbols, notes, or specific codes placed near the surfaces that need treatment. These coatings include paint, plating, galvanizing, powder coating, and more. They help protect the part from rust, wear, or improve its appearance.

The surface coating is usually mentioned in the surface finish symbol, general notes, or as a text annotation near the drawing view. Standard codes like ISO 2063, ISO 1302, or BIS equivalents are followed to maintain uniformity and clarity in documentation.

Detailed Explanation:

Indicating surface coatings in mechanical drawings

Surface coatings are very important in mechanical design. After a part is manufactured, it often requires a coating or surface treatment to protect it from corrosion, increase its lifespan, or enhance its appearance. These treatments include painting, anodizing, chrome plating, galvanizing, nitriding, powder coating, etc.

In engineering drawings, the details of such coatings must be clearly indicated so that the workers or contractors who handle manufacturing and finishing know exactly what surface treatments to apply. Properly indicating surface coatings ensures correct production, reduces errors, and follows the design requirements accurately.

Common methods to indicate surface coatings

  1. Notes and callouts
  • Surface coatings are often mentioned as general notes on the drawing sheet or next to the relevant part.
  • The note should include the type of coating, thickness, standard code, and area of application.

Example:

  • “Apply zinc plating as per ISO 2081 to all exposed surfaces.”
  • “Powder coat, black, 60 microns thick on outer surface only.”
  1. Surface finish symbol with coating note
  • Sometimes, the surface finish symbol (as per ISO 1302) is used and accompanied by a coating description above or below the symbol.
  • The check mark (⌃) symbol may include additional text.

Example:

  • A surface finish symbol with the note “Anodize 25µm” written above it indicates that anodizing is to be done on that surface.
  1. Part or area labeling
  • In complex parts, specific areas might need coating while others may not.
  • These areas are clearly marked with leader lines or labels, showing where the coating starts and ends.

Example:

  • “Coat highlighted surface with epoxy paint, RAL 5012.”
  1. Material and process table
  • Some detailed engineering drawings include a materials and processes block, which mentions:
    • Coating name
    • Method (e.g., electroplating, spray painting)
    • Thickness
    • Relevant standard

This ensures all surface-related instructions are grouped in one place.

  1. Symbols from standards
  • Specific coatings may be represented using standard codes or abbreviations, such as:
    • Zn for zinc plating
    • Cr for chromium plating
    • Phos for phosphating
    • Anod for anodizing

These codes are often combined with finish symbols or included in the BOM (Bill of Materials).

Guidelines for applying surface coating indications

  • Always follow standard practices like ISO, BIS, ASME, or company-specific guidelines.
  • Clearly mention the coating type, thickness, area, and standard.
  • Avoid writing general instructions—be specific about what to coat and how.
  • If multiple coatings are required on the same part, show each step in a sequence.

Importance of correct coating indication

  • Ensures durability and protection of the part in its working environment
  • Helps achieve aesthetic and functional requirements
  • Guides manufacturing and quality control teams
  • Avoids costly rework or product failure
  • Maintains consistency across production batches
Conclusion:

Surface coatings in mechanical drawings are indicated through symbols, annotations, and notes that mention the type, thickness, and area of coating as per standard practices. These indications ensure the part receives the correct surface treatment after manufacturing. By using surface finish symbols, general notes, or material tables, engineers can communicate coating requirements clearly and accurately. This helps maintain product quality, appearance, and performance over time.