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D3933-98 – Standard Test Method Technical Guide
📐 Scope and Significance of Phosphoric Acid Anodizing (PAA)
This standard guide, designated as D3933 – 98 (Reapproved 2017), specifically describes the requirements for phosphoric acid anodizing of aluminum and its alloys intended for structural adhesive bonding. The procedure outlined in Section 1 is based on the commercial practice of numerous agencies and organizations and may be revised or supplemented to include methods based on proven performance.
Per Section 4 (Significance and Use), surface preparation is a critical step for obtaining durable adhesive bonds. Improper preparation can produce seemingly acceptable bonds that can degrade rapidly over time. Experience has demonstrated that when adhesively bonded aluminum surfaces are prepared in accordance with this guide, they produce relatively reproducible, durable bonds in structural assemblies.
⚙️ Process Facility Requirements and Apparatus Control
Section 5 of the standard defines strict environmental controls for the PAA process. Surface preparation and drying facilities must be located separately from other activities or equipment to preclude contamination by substances detrimental to adhesion. The workflow must be arranged so that parts flow from the beginning of surface preparation to the priming operation without being touched.
| 🟦 Facility Control Element | 📏 Specification Requirement |
|---|---|
| Facility Location | Separate from other activities or equipment to prevent contamination. |
| Workflow Design | Parts flow from start of preparation to priming without touching. |
| Air Supply Filtration | Filters or traps for airborne dust, moisture, and oil on all air lines and ducts. |
| Equipment Maintenance | Periodically check, clean, or replace filters to ensure proper operation. |
📊 Standard References and Key Materials
The standard specifies that the anodizing bath must use Orthophosphoric Acid conforming to Federal Specification 0-0-670, Technical Grade. General terminology for the process is defined in ASTM D907 (Terminology of Adhesives), while further context on metal preparation is available in ASTM D2651. It is also a requirement that the surface preparation of metal systems used for qualification and quality-control testing be agreed upon between the manufacturer and the user.
| 🟦 Document / Material | 📏 Specification / Title |
|---|---|
| Orthophosphoric Acid | 0-0-670, Technical Grade (Federal Specification) |
| Adhesive Terminology | ASTM D907 – Terminology of Adhesives |
| Metal Surface Preparation | ASTM D2651 – Guide for Preparation of Metal Surfaces for Adhesive Bonding |
⚠️ Safety and Regulatory Compliance: The standard explicitly notes that it does not purport to address all safety concerns. Users must establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. A specific precaution is given in Section 5.5 of the full document.
💡 Best Practice for Reproducibility: The values stated in SI units are to be regarded as the standard for this guide. Consistent success with the PAA method is heavily dependent on the strict segregation and cleanliness protocols defined in the Apparatus section to ensure the formation of reproducible, durable bonds.
❓ Frequently Asked Questions
🔍 What is the current status of this standard?
This guide is designated as D3933 – 98 (Reapproved 2017). It was originally approved in 1980, last revised in 1998, and received its last reapproval in 2017.
💡 Why is phosphoric acid anodizing specified for structural bonding?
Experience has shown that this specific surface preparation method produces relatively reproducible and durable adhesive bonds. The guide details the critical steps to avoid rapid degradation of bonds over time, which can occur with improper preparation.
⚡ What chemical specification is required for the process?
The standard requires Orthophosphoric Acid conforming to Federal Specification 0-0-670 (Technical Grade) to ensure consistent chemistry in the anodizing bath.
📌 What unit system is used in this standard guide?
The values stated in SI units are to be regarded as the standard. Values given in parentheses (inch-pound) are provided for informational purposes only.