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D2338-02 – Standard Test Method Technical Guide
The ASTM D2338-02 (Reapproved 2013) standard provides a straightforward, visual test method for evaluating the particle size of multicolor nitrocellulose lacquers. By utilizing a set of photographic reference standards, this method establishes a uniform nomenclature for classifying spray patterns and particle dimensions. This evaluation is critical for maintaining consistent visual aesthetics and quality in factory-applied coatings.
🔬 Scope and Significance of Particle Size Standards
This test method relies exclusively on photographic reference standards to determine particle size. It applies specifically to multicolor lacquers and is integral for both producers and users to establish a common language regarding particle size characteristics. The standard designations—Fine, Small, Medium, Large, and Extra Large—correspond to five photographic standards (ASTM Adjunct ADJD2338) which depict actual sprayed panels. Users compare their dried test panels directly against these visual references.
The values stated in SI units are regarded as the standard within the document, with imperial units provided for reference only.
⚙️ Test Procedure and Apparatus Specifications
Apparatus: The critical test equipment is a pressure-feed internal-mix type spray gun fitted with a 2.2 mm (0.086 in.) diameter tip and a wide-spray nozzle. The test substrate consists of coated white paper stock.
Procedure: Prior to testing, the lacquer sample must be mixed by pouring it from one container to another until a uniform consistency is achieved. The lacquer is then sprayed onto the coated white paper substrate. The fluid and atomizing pressures are adjusted to achieve specific spreading rates depending on the application style. For a complete covering, a rate of 3.7 to 4.9 m²/L (150 to 200 ft²/gal) is used. For a scatter coat application, which often provides a clearer view of individual particles, the rate is 4.9 to 7.35 m²/L (200 to 300 ft²/gal).
After the sprayed lacquer is thoroughly dry, the particle size on the panel is determined by direct visual comparison to the photographic reference standards.
💡 Technical Tip: The resulting particle size is highly sensitive to the specific spray conditions (fluid pressure, atomizing pressure, and technique). To ensure reproducibility, the exact spray conditions must be explicitly agreed upon between the purchaser and the seller prior to testing, as highlighted in Note 1 of the standard.
📋 Standard Spray Application Parameters
| 🟦 Application Type | 📏 Spreading Rate (SI Units) | 📐 Spreading Rate (Imperial Units) |
|---|---|---|
| Complete Covering | 3.7 to 4.9 m²/L | 150 to 200 ft²/gal |
| Scatter Coat | 4.9 to 7.35 m²/L | 200 to 300 ft²/gal |
🎯 Particle Size Nomenclature and Reference Standards
| 🟦 Standard Designation | 🎯 Comparison Method | ⚡ Reference Source |
|---|---|---|
| Fine | Visual comparison of dried sprayed panels against glossy photographic prints. | ASTM Adjunct ADJD2338 (5 photos) |
| Small | ||
| Medium | ||
| Large | ||
| Extra Large |
⚠️ Precision and Bias Consideration: Because this test method relies on visual judgment, it does not lend itself to a formal precision statement. However, the standard notes that there has been general good agreement between operators. No information on bias is available as no material with an accepted reference value exists for this specific type of measurement.
❓ Frequently Asked Questions
🔍 What is the main purpose of ASTM D2338-02?
The standard provides a standardized, reproducible test method using photographic reference standards to evaluate and classify the particle size of nitrocellulose-type multicolor lacquers. This promotes uniform nomenclature in industry communications between producers and users.
💡 What are the five standard particle size designations?
The standard identifies the following five distinct particle size categories: Fine, Small, Medium, Large, and Extra Large. These are identified by visually matching the dried sprayed sample to a provided set of five photographic standards.
⚡ What specific spray gun equipment is required for this test?
The specified apparatus is a pressure-feed internal-mix type spray gun equipped with a 2.2 mm (0.086 in.) diameter tip and a wide-spray nozzle. The substrate must be coated white paper.
📌 What are the required spreading rates for the test panels?
Two specific rates are defined: For a complete covering, the rate is 3.7 to 4.9 m²/L (150 to 200 ft²/gal). For a scatter coat application, the rate is 4.9 to 7.35 m²/L (200 to 300 ft²/gal). The chosen rate depends on the desired visual density for comparison.