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D2252-18 – Standard Test Method Technical Guide
📐 Scope and Referenced Framework
ASTM D2252-18 provides a standardized specification for the classification of alpaca into distinct types based on fiber fineness. This standard is crucial for aligning production, preparation, and marketing efforts across the textile industry. The values stated in inch-pound units are regarded as the official standard, with SI unit conversions provided for informational purposes. The specification relies on a comprehensive framework of established test methods and terminologies:
| 🟦 Standard Designation | 📏 Title and Role |
|---|---|
| D123 | Terminology Relating to Textiles |
| D2130 | Test Method for Diameter of Wool and Other Animal Fibers by Microprojection |
| D4845 | Terminology Relating to Wool |
This specification serves as the primary guide for comparing the average fiber diameter of a specimen against the fineness specifications established for various alpaca types in Table 1, ensuring uniformity in trade and product development.
📊 Classification and Interlaboratory Precision
The core of the specification requires that the fineness of various alpaca types conforms to the average fiber diameter limits detailed in Table 1. Understanding the precision of the mandatory test method (D2130) is critical. An interlaboratory test was conducted involving six laboratories, each testing six distinct alpaca type samples. The resulting coefficients of variation (CV) for the average fiber diameters measured between laboratories are summarized below:
| 🎯 Alpaca Type Sample Code | ⚡ Interlaboratory CV (%) |
|---|---|
| HTB-CB | 3.2 |
| HAXB-CB | 4.7 |
| HAAB-CB | 3.8 |
| HAB-CB | 4.5 |
| HLPB-CL | 2.2 |
| HSKB-CL | 0.93 |
Note the significant variability in interlaboratory precision across different alpaca types, ranging from a CV of 0.93 % for type HSKB-CL to 4.7 % for type HAXB-CB. This data is essential for evaluating the reliability of test results when applying this specification.
⚙️ Testing Procedure and Statistical Requirements
All sampling and testing for the purposes of this specification must be conducted strictly as directed in Test Method D2130. This involves the use of microprojection to measure the diameter of individual fibers. To ensure the highest degree of accuracy in classifying alpaca fineness, the standard imposes a strict statistical criterion. The test must be carried out until at least the minimum number of fibers specified to attain confidence limits of the mean of ±0.5 µm at a probability level of at least 95 % has been measured. This specific sample size requirement is detailed in Annex A1 of Test Method D2130 and is a mandatory condition of this specification.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D2252-18?
This specification provides a standardized method for classifying alpaca fibers into types based on their average fiber diameter (fineness). It is intended to serve as a guide for the production, preparation, and marketing of alpaca fiber.
💡 Which test method is specified for measuring fiber diameter?
The standard mandates the use of Test Method D2130, “Test Method for Diameter of Wool and Other Animal Fibers by Microprojection,” for both sampling and testing.
⚡ What are the mandatory statistical requirements for classification?
The test must measure enough fibers so that the confidence limits for the mean fiber diameter are within ±0.5 µm at a 95 % probability level. This ensures reliable and consistent type classification.
📌 Where can I find the definitions of terms like “alpaca” and “fineness”?
Definitions for textile terms used in this specification, including alpaca, average fiber diameter, and fineness, are located in Terminology D4845. General textile terms not found there are defined in Terminology D123.