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D1731-09 – Standard Test Method Technical Guide
📋 Scope and Types of Surface Preparations
These practices describe procedures for the preparation of hot-dip aluminum surfaces for painting. The standard covers two types of surface preparations: Solvent Cleaning and Chemical Treatments. Service conditions will dictate the type of surface preparation that should be selected, as variations in surface treatment produce end conditions which differ and do not necessarily yield identical results when paints are applied.
🧼 Solvent Cleaning Methods
Solvent cleaning can be performed using three methods as outlined below. Method 1 involves manual swabbing or dip washing with a solvent such as mineral spirits or high flash solvent naphtha, but it is difficult to produce a clean surface due to potential redeposition. Method 2 is solvent spray cleaning in accordance with Method A, Procedure 1 of Practice D609. Method 3 is vapor degreasing using trichlorethylene or perchlorethylene vapor, which does not disturb the natural oxide film and may be adequate for some applications.
| 🟦 Method | 📏 Description | 📐 Notes |
|---|---|---|
| Method 1 | Manual swabbing or dip washing | Risk of contaminant redeposition |
| Method 2 | Solvent spray cleaning per D609 | Effective for light soils |
| Method 3 | Vapor degreasing with trichlorethylene or perchlorethylene | No disturbance of oxide film |
Tip: Solvent cleaning does not disturb the natural oxide film, making it suitable for applications where oxide integrity is important.
🧪 Chemical Treatment Methods
Chemical treatments are available from various sources as proprietary compounds. The standard cautions that hexavalent chromium methods are not recommended due to carcinogenicity. Method 1 uses alkaline cleaners, but etching solutions such as caustic soda should be avoided as they can dissolve the aluminum coating and expose the base metal. Inhibited alkaline cleaners can be used to remove grease, oil, and other organic solids without etching. After alkali cleaning, the surface should be thoroughly rinsed with clean water.
| 🟦 Method | 📏 Description | ⚡ Key Considerations |
|---|---|---|
| Method 1 | Alkaline Cleaners | Avoid etching; use inhibited cleaners; rinse thoroughly |
Warning: Hexavalent chromium methods are not recommended as hexavalent chromium is a known carcinogen. Always follow safety protocols.
❓ Frequently Asked Questions
🔍 What is the purpose of solvent cleaning?
Solvent cleaning removes organic contaminants like grease and oil from the hot-dip aluminum surface, but it does not disturb the natural oxide film.
💡 Why should etching alkaline solutions be avoided?
Etching alkaline solutions such as caustic soda can dissolve the aluminum coating, potentially exposing the base metal and compromising the surface integrity.
⚡ What are the safety considerations for chemical treatments?
Chemical treatments may involve hazardous materials and procedures. Users should establish appropriate safety, health, and environmental practices and determine regulatory limitations.
📌 Which surface preparation method is adequate for mild service conditions?
Solvent cleaning, particularly vapor degreasing, may be adequate for some applications where the oxide film is not disturbed.