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D1459-93 – Standard Test Method Technical Guide
📋 Scope, Types, and Ordering Information
This specification covers clear silicone varnished glass fabrics supplied as sheets, rolls, and tapes for use as electrical insulation. The materials are classified as Class 180 electrical insulating materials per IEEE Standard No. 1, with values stated in inch-pound units (excluding temperature, which is reported in degrees Celsius). The standard defines two product types: Type A for applications where primarily electrical properties are required, and Type B for applications where primarily physical properties are needed. Orders must specify the form, type, desired nominal thickness, width, length, and packaging details.
⚙️ Materials, Manufacture, and Dimensional Compliance
The glass fabric must be treated with a baking type of silicone varnish that fully penetrates the fabric to produce a smooth, non-tacky surface substantially free of wrinkles, creases, and blisters. Strict manufacturing constraints prohibit splicing; a maximum of two pieces is permitted per multiple of 25 yd (23 m) for rolls of full-width cloth and per multiple of 36 yd (33 m) for rolls of tape. The dimensional tolerances for thickness are rigorously defined: materials up to and including 5 mils (0.13 mm) must not vary by more than ±0.5 mil (0.013 mm) from nominal, while materials exceeding 5 mils must not vary by more than ±10 % from nominal. Full-width rolls are supplied trimmed at a width of 36 ± 1 in. (900 ± 25 mm), and tape widths must be held to a tolerance of ±1/32 in. (0.8 mm).
📊 Key Physical Properties and Test Methods
The following tables summarize the critical property requirements and material classifications per ASTM D1459–93.
| 🎯 Parameter | 📏 Specification / Tolerance |
|---|---|
| Warp Breaking Strength | Not less than the values prescribed in Table 1 of the standard for the corresponding type and nominal thickness. |
| Thickness (≤ 5 mils / 0.13 mm) | ± 0.5 mil (0.013 mm) from nominal |
| Thickness (> 5 mils) | ± 10 % from nominal |
| Width (Full-width Rolls & Sheets) | 36 ± 1 in. (900 ± 25 mm), trimmed |
| Width (Individual Tapes) | ± 1/32 in. (0.8 mm) from specified width |
| 🟦 Material Type | ⚡ Primary Performance Emphasis |
|---|---|
| Type A | Primarily Electrical Properties |
| Type B | Primarily Physical / Mechanical Properties |
💡 Technical Tip: Evaluate your application’s critical stress factor carefully. Type A is optimized for high dielectric strength and insulation integrity, while Type B is formulated for enhanced mechanical robustness and breaking strength. Incoming inspection should pay close attention to the stringent ±0.5 mil thickness tolerance for materials under 5 mils, using sampling practices defined in ASTM D 3636.
📌 Manufacturing Constraint: Splicing is strictly prohibited by Section 6.2 of the standard. For full-width cloth, a maximum of only two pieces is permissible per multiple of 25 linear yards (23 m) in any one roll. For tape, no more than two pieces are allowed per multiple of 36 linear yards (33 m). Verify this with your supplier’s certification report.
❓ Frequently Asked Questions
🔍 What does the Class 180 thermal classification specifically signify for this material?
Class 180 refers to the thermal endurance classification of the electrical insulation system as defined by IEEE Standard No. 1. It indicates the material is designed for continuous reliable operation at a total temperature of 180 °C.
💡 How should I decide between specifying Type A or Type B silicone varnished glass cloth?
Choose Type A when the primary design requirement is superior electrical performance, such as high dielectric breakdown resistance. Choose Type B when the application demands higher mechanical durability, such as resistance to tearing or breaking under physical stress during fabrication or service.
⚡ What are the specific test methods required to qualify this material?
The primary testing standard is ASTM D 902, which governs the testing of flexible resin-coated glass fabrics. Thermal endurance evaluations are conducted according to ASTM D 1830 using the curved electrode method, and all quality sampling procedures must follow ASTM D 3636.
📌 What unit system does the standard use, and how are tolerances applied?
The standard mandates inch-pound units as the standard, with temperature expressed in degrees Celsius. Thickness tolerances are extremely specific: ±0.5 mil (0.013 mm) for nominal thicknesses up to and including 5 mils, and ±10 % of nominal for thicknesses above 5 mils.