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D3992-94 – Standard Test Method Technical Guide
🧶 Scope and Significance
These specifications are applicable in the classification, by fineness grade, of the fiber in wool top, mohair top, wool yarns, mohair yarns, wool fabrics, and mohair fabrics of the worsted type. They provide a standardized basis for the acceptance of commercial shipments. (Refer to Scope 1.1 and Significance 5.1).
📊 Grade Specifications and Tables
The grade of wool top shall conform to the requirements in Table 1, and the grade of mohair top shall conform to Table 2. These tables outline the average fiber diameter and fiber diameter distribution for each grade.
| 🟦 Grade Designation | 📏 Average Fiber Diameter (µm) | 📐 Distribution ≤30 µm | 🎯 Distribution ≤50.1 µm |
|---|---|---|---|
| 56s | 28.10 | 64% | 1% |
For complete list of grades and detailed specifications, refer to the full ASTM D3992 standard.
| 🟦 Grade Designation | 📏 Average Fiber Diameter (µm) | 📐 Distribution Requirements |
|---|---|---|
| Refer to the standard for detailed specifications. | ||
💡 Accurate Measurement: Ensure that fiber measurements are extensive enough to meet the confidence limits specified in Test Method D2130 for reliable grade assignment.
⚙️ Test Method and Grade Determination
Testing should be performed in accordance with Test Method D2130, using microprojection to measure fiber diameter. A minimum number of fibers must be measured to achieve confidence limits of ±0.4 µm at a 95% probability level (Annex A1 of Test Method D2130). This precision is critical for accurate grading.
For grade assignment, compare the observed average fiber diameter and fiber diameter distribution with the specifications in Table 1 (wool top) or Table 2 (mohair top). If the observed values correspond to a single grade, assign that grade. If the fiber diameter distribution does not meet the requirements for the grade to which the average fiber diameter corresponds, assign a dual grade designation, with the second designation being one grade coarser than the grade indicated by the average diameter. Assignment of grade is illustrated in the standard by examples such as the 56s grade for wool top (Section 7).
⚠️ Dual Grade Designation: If fiber distribution does not align with the average diameter grade, a dual grade is required, indicating a distribution coarser than typical. This ensures accurate representation of fiber characteristics.
❓ Frequently Asked Questions
🔍 What is the primary test method for fiber diameter?
The primary test method is Test Method D2130, which uses microprojection to measure the diameter of wool and other animal fibers. This method is essential for determining fiber fineness.
💡 How is confidence limit important in testing?
Confidence limits of ±0.4 µm at 95% probability ensure the mean fiber diameter is accurately estimated, which is crucial for correct grade assignment per the standard.
⚡ What are the referenced documents for grading?
Key referenced documents include D3991 for wool and mohair fineness, D2252 for alpaca, D123 for textile terminology, and D4845 for wool terminology. Federal standards also provide official grade definitions.
📌 Can these specifications be used for acceptance testing?
Yes, these specifications are considered satisfactory for classifying wool top or mohair top by grade and provide a basis for acceptance of commercial shipments, as noted in the significance and use section.