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D2647-18 – Standard Test Method Technical Guide
📐 Scope and Classification of Crosslinkable Ethylene Plastics
ASTM D2647-18 (Reapproved 2024) provides a general classification system for crosslinkable ethylene plastics compounds. As stated in Section 1.1, the requirements specified are not necessarily directly suitable for determining the end-use suitability of a fabricated product, but rather serve as a material classification framework.
The specification defines two primary material types (Section 1.2):
- Mechanical Types: Where mechanical strength properties are of prime importance.
- Electrical Types: Where electrical insulating or conducting properties are of prime importance alongside mechanical properties.
⚠️ Important Testing Context: As per Note 1 of the standard, the materials covered are supplied commercially in an uncrosslinked form. Therefore, the parameters used for classification and specification are typically measured after the material has been cured (crosslinked).
📏 Classification Parameters and Referenced Test Methods
The classification parameters differ slightly between the two types. Mechanical types rely on four key properties, while electrical types add three electrical parameters to this baseline.
| 🦾 Property | ⚡ Mechanical Types | 🔬 Electrical Types | 📐 Test Standard |
|---|---|---|---|
| Ultimate Elongation | ✔️ | ✔️ | D638 |
| Elongation Retention (Aging) | ✔️ | ✔️ | D573 |
| Apparent Modulus of Rigidity | ✔️ | ✔️ | D1043 |
| Brittleness Temperature | ✔️ | ✔️ | D746 |
| Dielectric Constant | — | ✔️ | D150 |
| Dissipation Factor | — | ✔️ | D150 |
| Volume Resistivity | — | ✔️ | D257 / D991 |
Specimens must be conditioned according to Practice D618. The degree of crosslinking can be verified using Test Methods D2765 (Gel Content and Swell Ratio). Packaging of the material should follow Practice D3892 (Section 2.1).
💡 Test Method Note: For the volume resistivity of conductive and antistatic products, the standard specifically references Test Method D991. For general insulating materials, Test Methods D257 is the appropriate reference.
The standard values are expressed in SI units, with values in parentheses provided for information only (Section 1.5). The safety caveat in Section 1.6 applies to the test methods portion, placing responsibility on the user to establish safety practices.
❓ Frequently Asked Questions
🔍 What is the core difference between Mechanical and Electrical types in D2647?
Mechanical types are classified solely on their tensile elongation, aging retention, stiffness, and low-temperature brittleness. Electrical types must meet all these requirements plus specific standards for dielectric constant, dissipation factor, and volume resistivity (Sections 1.3, 1.4).
⚡ Which standards govern the electrical testing of these compounds?
Dielectric constant and dissipation factor are measured per D150. Volume resistivity is measured per D257 for insulating materials and D991 for conductive or antistatic materials (Section 2.1).
💡 Why are classification tests generally performed on cured specimens?
Because the material is commercially supplied in its uncrosslinked state. The mechanical and electrical properties specified are inherent to the crosslinked form. Therefore, testing is performed after curing to characterize the final material accurately (Note 1).
📌 What is the role of Test Method D1043 in this specification?
D1043 is the Test Method for Stiffness Properties of Plastics as a Function of Temperature by Means of a Torsion Test. It is used to determine the Apparent Modulus of Rigidity, which is a key classification parameter for both mechanical and electrical types (Section 1.3, 1.4).