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D2644-12 – Standard Test Method Technical Guide
📐 Scope, Sampling, and Referenced Documents
ASTM D2644 – 12 (Reapproved 2018) provides standardized tolerances for yarns spun on the woolen system, covering all fiber types and blends. The standard establishes benchmarks for yarn number, twist, breaking strength, extractable matter, and commercial mass, ensuring consistency across manufacturing lots and facilitating contractual agreement between suppliers and purchasers.
These tolerances apply to any yarn manufactured on the woolen system, regardless of fiber composition (including yarns containing no wool). For tolerances covering cotton or worsted system yarns, refer to ASTM D2645. Sampling is performed as directed in the applicable material specification or, in the absence of one, in accordance with Practice D2258/D2258M.
Key referenced test methods include D1907/D1907M for yarn number, D1422/D1422M and D1423/D1423M for twist, D1578 and D2256/D2256M for breaking strength, D2257 for extractable matter, and D2494 for commercial mass. Terminology standards D123 and D4849 govern the definitions used within this specification.
💡 Technical Note: While this standard is published under the jurisdiction of woolen system yarns, its scope explicitly covers all fibers spun on that system. This universal applicability makes D2644 a cross-fiber benchmark for yarns processed on the woolen spinning platform.
⚙️ Mechanical Tolerances: Strength, Yarn Number, and Twist
The mechanical properties of the yarn are subject to strict limits. The average breaking force of a lot must equal or exceed the specified minimum value. Linear density and twist are held to specific percentage tolerances to ensure downstream processing performance.
| 🟦 Property | 📏 Specification Range / Test Method | 🎯 Tolerance Requirement |
|---|---|---|
| Breaking Strength | D1578 (Skein) or D2256/D2256M (Single Strand) | Average ≥ Specified Minimum |
| Yarn Number | 500 tex to 165 tex (0.6 to 1.86 woolen run) | ± 7.5 % of Specified Value |
| Yarn Number | Finer than 165 tex (1.86 woolen run) | ± 5.0 % of Specified Value |
| Twist (Average) | D1422/D1422M or D1423/D1423M | Specified Value ± 7.5 % |
| Twist (Package Variation) | Comparison of Highest vs Lowest Avg Package Twist | ≤ 15.0 % of the Lower Average Twist |
⚠️ Critical Quality Note: Although the average twist tolerance is ±7.5 %, the standard enforces a strict 15.0 % limit on variability between packages. The package with the highest average twist must not exceed the package with the lowest average twist by more than 15.0 % of the lower value, which is essential for maintaining consistent dye uptake and fabric hand.
📊 Extractable Matter and Commercial Mass Requirements
D2644 sets distinct maximum limits for extractable matter based on the spinning preparation method, as determined by Test Method D2257. It also governs commercial mass to ensure accurate invoicing, referencing Test Method D2494.
| 🟦 Yarn Type / Preparation Method | 📏 Test Method | 🎯 Maximum Extractable Matter (%) |
|---|---|---|
| Dry-spun | D2257 | 2.0 |
| Oil-spun, Semi-scoured | D2257 | 15.0 |
| Oil-spun, Scoured (Blends, ≤ 50 % wool) | D2257 | 4.0 |
| Oil-spun, Scoured (All wool or > 50 % wool) | D2257 | 10.0 |
For commercial mass, the standard stipulates that the invoice mass adopted by the specific trade branch, as determined by the supplier, must not exceed the commercial mass determined by Test Method D2494. This requirement protects against discrepancies in transactional weight calculations for yarn shipments.
❓ Frequently Asked Questions
🔍 What types of yarns are covered by ASTM D2644?
This standard applies to any yarns spun on the woolen system, irrespective of the fiber composition. This includes 100 % wool, blends with other natural or synthetic fibers, and yarns containing no wool at all.
💡 How do the yarn number tolerances differ based on linear density?
Coarser yarns from 500 tex (0.6 woolen run) down to 165 tex (1.86 woolen run) have a tolerance of ±7.5 %. Yarns with a linear density finer than 165 tex require a stricter tolerance of ±5.0 % of the specified value.
⚡ What is the maximum extractable matter for oil-spun scoured yarns with high wool content?
For oil-spun scoured yarns composed of all wool or more than 50 % wool, the average percent extractable matter must not exceed 10.0 %. If the wool content is 50 % or less, the limit is tightened to a maximum of 4.0 %.
📌 Which test methods are referenced for measuring twist under this standard?
Twist in single spun yarns is measured using Test Method D1422/D1422M (the untwist-retwist method). For specific constructions requiring a direct count, Test Method D1423/D1423M (direct-counting method) is used.