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D1931-99 – Standard Test Method Technical Guide
📐 Scope and Referenced Standards
This specification covers the requirements for fully cured silicone rubber-coated glass fabric in sheet form, full-width rolls, and tapes used as electrical insulation. It provides the dimensional, physical, and electrical requirements necessary to ensure product reliability and performance in demanding electrical applications.
The standard D1931-99 (Reapproved 2004) specifically addresses materials made from glass fabric coated with a fully cured silicone rubber. This combination provides excellent thermal stability, flexibility, and dielectric strength. The classification of terms used within this standard is defined in accordance with ASTM D1711, while the specific sampling and test procedures are governed by ASTM D1458.
⚙️ Material Quality and Dimensional Requirements
The glass fabric and silicone rubber must be of good commercial quality. The final coated product must be free of blisters, wrinkles, creases, and any conductive dust or dirt that may have accumulated due to static charge during processing. For rolls, strict guidelines are provided for splicing. As a general rule, 90% of a shipment must contain no splices. The remaining 10% may have a single splice, which must be clearly flagged. Any splicing agreement must be mutually arranged between the purchaser and the seller.
Dimensional tolerances are strictly defined to ensure consistency in manufacturing and assembly. The following table summarizes the primary width requirements for full-width rolls and tapes.
| 🟦 Form | 📏 Specified Width | 🎯 Tolerance |
|---|---|---|
| Full-Width Rolls / Sheets | 91 cm (36 in.) | ± 2 cm (± 1 in.), trimmed ≥ 89 cm (35 in.) |
| Tapes ≤ 38 mm (1.5 in.) | As Specified | ± 0.8 mm (1/32 in.) |
| Tapes > 38 mm (1.5 in.) | As Specified | ± 1.6 mm (1/16 in.) |
💡 Tip: When ordering, ensure the purchase order clearly specifies the desired nominal thickness, width, length, and whether mica dusting is required to match the intended application.
📊 Physical Properties and Rejection Criteria
Conformance to the physical and electrical requirements is determined according to the test methods prescribed in ASTM D1458. The material must meet the specific property values outlined in Table 1 of the standard, which dictates key performance parameters for the coating and fabric substrate.
| ⚡ Property | 🔬 Test Method | 🎯 Requirement |
|---|---|---|
| Dielectric Breakdown Voltage | ASTM D1458 | Refer to Table 1 of Standard |
| Tensile Breaking Strength | ASTM D1458 | Refer to Table 1 of Standard |
| Visual Defects & Workmanship | Section 5 / D1458 | Free of blisters, wrinkles, and dust |
The purchaser retains the right to reject shipments that do not conform to agreed-upon packaging and marking requirements. Furthermore, a rigorous statistical sampling plan is specified for acceptance testing.
🚨 Warning: According to Section 9.2, if 20% or more of the sample rolls or sheets fail to conform to any single requirement in Sections 5 (Materials/Manufacture), 6 (Dimensions), or 8 (Physical/Electrical Properties), this constitutes cause for rejection of the entire shipment without the need for further testing.
❓ Frequently Asked Questions
🔍 What specific forms of insulation are covered by ASTM D1931-99?
The standard covers fully cured silicone rubber-coated glass fabric in sheet form, full-width rolls, and tapes intended for use as electrical insulation.
💡 What are the width tolerances for slit tapes according to the standard?
For tapes with a width of 38 mm (1.5 inches) or less, the tolerance is ±0.8 mm (1/32 inch). For tapes wider than 38 mm, the tolerance is ±1.6 mm (1/16 inch).
⚡ Which ASTM test method is referenced for determining the physical and electrical properties?
All sampling and testing for conformity to the physical and electrical requirements of this specification must be performed according to ASTM D1458.
📌 What is the automatic rejection criterion for an entire shipment of this material?
If 20% or more of the sample rolls or sheets fail to meet any one of the requirements covering materials/manufacture, dimensions, or physical/electrical properties, the entire shipment is subject to rejection without further testing.