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D2518-99 – Standard Test Method Technical Guide
This article provides a technical overview of ASTM D2518-99, the American National Standard for Woven Glass Fabrics for Electrical Insulation. This specification is applicable to straight-cut plain weave greige fabrics produced from continuous-filament yarns intended for use in coated or treated electrical insulating materials. The standard emphasizes dimensional and compositional controls to ensure reliability in insulation applications.
📐 Scope and General Provisions
The scope covers fabrics suitable for electrical insulation, excluding glass fabric tapes and laminating fabrics. All values are stated in inch-pound units with SI equivalents in parentheses. The standard references several ASTM test methods for verifying compliance, including D1777 for thickness and D3775 for fabric count.
📊 Dimensional Tolerances and Material Composition
Fabrics must conform to the construction and mechanical properties defined in Table 1. Width and roll length are controlled to ensure consistency. The yarns used must be Types ECD, ECE, or ECG per Specification D578, and the fabric must contain only standard weaving sizes without extraneous lubricants.
| 🟦 Parameter | 📏 Specification | 🎯 Tolerance |
|---|---|---|
| Width | As per agreement | ±0.5 in. (13 mm) |
| Roll Length | Nominal value per Table 1 | Within 10% of nominal; 10% of rolls may be shorter but not below 30% of nominal |
| Sizing Content | Average ≤4.5 weight % | Styles 104 and 1610: ≤6.0 weight % |
⚙️ Composition and Workmanship Requirements
The yarn in the fabric must meet the requirements of Types ECD, ECE, and ECG from Specification D578. The fabric is a plain weave greige type with controlled sizing. The amount of sizing is critical: for general use, the average sizing must not exceed 4.5 weight %, but Styles 104 and 1610 allow up to 6.0 weight %. For applications requiring high wet dielectric strength, such as per Specification D1931, a maximum sizing of 2.6 weight % is recommended. Workmanship and quality are judged in accordance with Practice D3636.
💡 Tip: When specifying fabric for critical insulation, always reference Note 1 regarding reduced sizing content to enhance electrical properties.
⚠️ Caution: Always measure fabric width outside the selvedge to ensure compliance with the ±0.5 in. tolerance.
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D2518-99?
To specify requirements for straight-cut plain weave greige glass fabrics used as base materials for coated or treated electrical insulation.
💡 Which yarn types are required in this standard?
Yarns must conform to Types ECD, ECE, or ECG as defined in Specification D578.
⚡ What are the limits on sizing content?
The average sizing must be ≤4.5 weight %, except Styles 104 and 1610 which allow ≤6.0 weight %. For wet dielectric strength, ≤2.6 weight % is recommended.
📌 How are width tolerances applied?
The fabric width, measured outside the selvedge, must not differ from the specified value by more than ±0.5 in. (13 mm).