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D2645-07 – Standard Test Method Technical Guide
📐 Scope and Applicability
ASTM D2645 establishes standard tolerances for all yarns spun on the cotton or worsted systems. This includes both carded and combed yarns composed of any fiber or blend of fibers. The standard specifically excludes cotton tire cords, novelty yarns, and fancy yarns from its scope.
Critical scope limitation: These tolerances apply exclusively to yarns sampled directly from packages. Yarns that have been extracted from greige or processed fabrics are not subject to these tolerances and must be evaluated under separate standards.
⚙️ Sampling and Test Methods
Sampling is a critical prerequisite for compliance. Per Section 4, samples must be taken as directed in the applicable material specification, or in the absence of such a specification, according to Practice D2258/D2258M for sampling yarn for testing.
The standard references a suite of ASTM test methods to verify conformance to the tolerances:
- Linear Density (Yarn Number): D1907/D1907M (Skein Method)
- Breaking Strength: D1578 (Skein Form) or D2256/D2256M (Single-Strand Method)
- Twin Measurement: D1422/D1422M (Untwist-Retwist) or D1423/D1423M (Direct-Counting)
- Appearance Grading: D2255/D2255M
- Extractable Matter: D2257
📊 Key Tolerances and Requirements
The core tolerances outlined in Section 5 define the acceptance criteria for yarn lots produced on the cotton or worsted systems.
| 🟦 Property | 📏 Tolerance Requirement | 🎯 Test Method |
|---|---|---|
| Breaking Force (Strength) | The average breaking force of the lot must be equal to or greater than the specified minimum value. | D1578 or D2256/D2256M |
| Yarn Number (Linear Density) | The average yarn number for cotton or worsted system yarns must conform to the published tolerance limits (expressed as a percentage of the specified value). | D1907/D1907M |
| Twist Direction | The direction of twist in each package or end must be consistently designated and conform to the required S or Z specification. | D1422/D1422M or D1423/D1423M |
💡 Key Application Tip: The primary pass/fail criterion for strength under D2645 is a “minimum lot average” requirement. Individual low-strength packages may be permissible provided the overall lot average meets or exceeds the specified minimum breaking force.
⚠️ Important Note on Referenced Standards: D2645 references several historical documents that have been withdrawn (e.g., D541, D681, D738). Users must ensure they are applying the most current active versions of cited test methods, such as D1907/D1907M and D2256/D2256M, for compliance testing.
❓ Frequently Asked Questions
🔍 What are the main exclusions from the tolerances in D2645?
D2645 explicitly excludes cotton tire cords and novelty or fancy yarns. Furthermore, it does not apply to yarns spun on the woolen system (which are covered by D2644), nor to yarns removed from greige or processed fabrics.
💡 How is the yarn number tolerance applied in practice?
Section 5.2.1 requires the average yarn number of the entire lot to conform to the specific limits defined in the standard, which are calculated as a percentage of the nominal specified value. This ensures the linear density is consistent with the intended yarn count.
⚡ What is the difference between average strength and minimum strength in this standard?
D2645 specifies a minimum average requirement for breaking force. This is distinct from a “minimum individual” value specification. The lot is solely evaluated on its mean performance, which must be equal to or greater than the specified minimum.
📌 Which terminology standards govern the language used in D2645?
Two key terminology standards are referenced: D4849 (Terminology Related to Yarns and Fibers) for the main technical terms specific to D13.58, and D123 (Terminology Relating to Textiles) for all other general textile terminology.