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D1423 – Standard Test Method Technical Guide
The ASTM D1423/D1423M −16 (Reapproved 2022) standard, formally titled Standard Test Method for Twist in Yarns by Direct-Counting, establishes a precise direct-counting procedure for determining the amount and direction of twist in various yarn structures. This method relies on physically untwisting a clamped specimen to quantify the number of complete turns per unit length. The standard is applicable to yarns in package form or, with special precautions, taken from fabrics. It emphasizes that values stated in either SI units or inch-pound units are to be regarded separately as standard, and the two systems shall not be combined.
📐 Scope and Yarn Classification
This test method covers the determination of twist at the completion of any stage of twisting in single (spun or filament), plied, cabled, or novelty (exclusive of long-term repeat patterns) yarns. The procedure for spun yarns in Section 9.2 is also applicable to rovings. For plied yarns, it determines the twist of the plied structure and the twist of the single yarn before plying. For cabled (hawser) yarns, it determines the cable twist, the plied yarn twist after plying but prior to the last twisting operation, and the original single yarn twist before plying. Specific procedures are included for determining the twist of components as they lie in the final structure, including plied yarns made with direct cabling technology.
The standard explicitly limits its validated precision to yarns that extend 5.0% or less when tension is increased from 2.5 mN/tex to 7.5 mN/tex [0.25 to 0.75 gf/tex]. Using this test method for yarns with higher extensibility requires independent handling of bias and precision, and the specific tension used must be explicitly reported.
| 🟦 Parameter | 📏 Specification |
|---|---|
| Yarn Extension Limit (Standard Precision) | ≤ 5.0% under load change (2.5 to 7.5 mN/tex) |
| Standard Tension Range | 2.5 to 7.5 mN/tex |
| Equivalent Tension Range (gf/tex) | 0.25 to 0.75 gf/tex |
| Applicability to Rovings | Yes (per spun yarn procedure in 9.2) |
⚙️ Test Procedure and Specimen Conditioning
Specimens must be conditioned in accordance with Practice D1776 for Conditioning and Testing Textiles. The linear density of the yarn (yarn number) is typically determined in accordance with Test Method D1907 or Test Method D1059 to facilitate the calculation of twist factor or twist multiplier. The core procedure involves mounting the yarn specimen under the defined tension range and inserting a pin or needle to isolate the specimen length. The yarn is then untwisted until the fibers or component strands are parallel, and the number of turns is directly counted.
| 🎯 Yarn Structure | ⚡ Twist Determinations |
|---|---|
| Single (Spun / Filament) | Twist amount and direction in the final structure |
| Plied Yarn | Plied twist and single yarn twist before plying |
| Cabled (Hawser) Yarn | Cable twist, plied twist (post-plying), single twist (pre-plying) |
| Direct Cabling Technology | Single and plied component twists in the final structure |
📊 Key Measured Properties and Interpretation
The direct-counting method yields the exact twist per unit length, expressed as Turns per Inch (tpi) or Turns per Meter (tpm). The direction of twist is reported as “S” or “Z”. The standard also facilitates the calculation of twist factor or twist multiplier using the measured linear density. Key terminology for these properties is formally defined in Terminology D4849, with additional references in Terminology D123 and Terminology D3888.
⚠️ Critical Limitation: This test method is not validated for yarns that extend more than 5.0% under the standard tension change (2.5 to 7.5 mN/tex). Results from testing such yarns are independent of the bias and precision determined for this standard, and the specific tension used must be explicitly documented in the report.
📌 Related Standards and Notes: For a more rapid but less accurate method of determining twist in single spun yarns, refer to Test Method D1422 (Untwist-Retwist Method). Note 2 of the standard specifically states this test method (D1423) has been evaluated for use in determining twist in open-end yarns and is not recommended.
❓ Frequently Asked Questions
🔍 What is the primary scope of ASTM D1423?
It covers the direct-counting determination of twist amount and direction for single, plied, cabled, and novelty yarns, as well as rovings, at any stage of twisting.
💡 What are the standard tension limits for this test?
The standard tension range is 2.5 to 7.5 mN/tex (0.25 to 0.75 gf/tex). Yarns extending more than 5.0% within this range require reporting the specific tension used.