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D1764-97 – Standard Test Method Technical Guide
📋 Types, Classes, and Grades of Compounds
ASTM D1764-97, also approved as SAE J19, provides a classification system for compounded latex materials used in dipped automotive goods and coatings. The standard divides compounds into two primary types based on their service requirements:
Type LR (Non-Oil Resistant): Formulated from natural rubber, synthetic rubber, or combinations thereof. These compounds are intended for general service where specific resistance to petroleum-based fluids is not required. Applications include general-purpose boots and coated fabrics.
Type LS (Oil Resistant): Exclusively formulated from synthetic rubber or rubber-like materials. These compounds are designed for environments requiring sustained resistance to petroleum-based fluids, such as engine bay components and fuel system coatings.
Grade designations within each type use a numerical code combined with optional suffix letters (e.g., LR420, LSC515). Suffix letters define additional property requirements, such as low-temperature brittleness or staining resistance, allowing for precise material specification.
⚠️ Critical Note on Test Specimens: The physical property requirements in this standard are based strictly on standard laboratory-dipped films. Finished products may yield different results due to geometry and processing variation. When this occurs, the purchaser and supplier must mutually agree on acceptable deviations by comparing laboratory film results against the performance of actual parts.
⚙️ Performance Requirements and Testing
All compounds must conform to the physical property limits established in the standard after vulcanization. Testing is conducted using standardized ASTM methods on laboratory-prepared dipped films. The following tables summarize the mandatory requirements for the primary grades.
| 📏 Property | 🎯 Requirement (Grade LR420) | ⚡ Test Method |
|---|---|---|
| Durometer Hardness (points) | 45 ± 5 | ASTM D2240 |
| Tensile Strength, min [MPa (psi)] | 14.0 (2000) | ASTM D412 |
| Ultimate Elongation, min (%) | 500 | ASTM D412 |
| Heat Aged (70 h @ 70°C): Δ Hardness, max | ±5 | ASTM D573 |
| Heat Aged: Tensile Strength, min [MPa (psi)] | 10.5 (1500) | ASTM D573 / D412 |
| Heat Aged: Ultimate Elongation, min (%) | 400 | ASTM D573 / D412 |
| Permanent Set @ 400% Elongation, max (%) | 10 | ASTM D412 |
| 📏 Property | 🎯 Requirement (Grade LSC515) | ⚡ Test Method |
|---|---|---|
| Durometer Hardness (points) | 55 ± 5 | ASTM D2240 |
| Tensile Strength, min [MPa (psi)] | 10.5 (1500) | ASTM D412 |
| Ultimate Elongation, min (%) | 400 | ASTM D412 |
| Oil Immersion (22 h @ 100°C) | As specified in standard (ASTM Reference Oils) | ASTM D471 / D5964 |
📌 Suffix Letter Designations: The standard allows suffix letters to be appended to the grade number to specify additional testing requirements. Common suffixes mandate testing for low temperature brittleness (ASTM D746), contact/migration staining (ASTM D925), or specific compression set limits. Always verify the complete grade designation for your application.
🧪 Key Measured Properties
Durometer Hardness: Measured in accordance with ASTM D2240, this value defines the indentation resistance of the latex compound. Tolerances of ±5 points ensure consistent sealing force and flexibility for components like coated clips and protective boots.
Tensile Strength and Ultimate Elongation: Evaluated per ASTM D412, tensile strength indicates the maximum stress the material can withstand before rupture, while ultimate elongation defines its maximum stretch capability. The high minimum elongation of Type LR grades (500%) is critical for applications requiring tight-fitting coatings and flexible diaphragms.
Fluid and Heat Resistance: Heat aging (ASTM D573) assesses the compound’s ability to retain flexibility and strength after prolonged thermal exposure. For Type LS compounds, oil immersion testing (ASTM D471) using IRM reference oils per ASTM D5964 simulates service conditions involving contact with petroleum-based fluids under hood or in chassis environments.
❓ Frequently Asked Questions
🔍 What is the fundamental difference between Type LR and Type LS compounds in this standard?
Type LR compounds are intended for general service where specific resistance to petroleum-based fluids is not required and can be made from natural or synthetic rubber. Type LS compounds are explicitly formulated for oil resistance and must be made from synthetic rubber or rubber-like materials.
📌 Are the property values in the standard directly applicable to finished automotive parts?
The specified values apply directly to standard laboratory-dipped films. Finished products may exhibit different physical properties due to geometry, thickness, and processing effects. The standard explicitly allows purchasers and suppliers to agree on acceptable deviations based on comparative testing between films and actual parts.
💡 What are the required minimum tensile and elongation values for the LR420 grade?
For Grade LR420, the unaged compound requires a minimum tensile strength of 14.0 MPa (2000 psi) and a minimum ultimate elongation of 500%. Following heat aging for 70 hours at 70°C, the minimums decrease to 10.5 MPa (1500 psi) for tensile strength and 400% for elongation.
⚡ Which ASTM test method governs the oil immersion testing for Type LS compounds?
Oil immersion testing for Type LS compounds is conducted per ASTM D471. The standard specifies immersion for 22 hours at 100°C (212°F). The specific reference oils used are ASTM No. 1, No. 2, and No. 3 (now IRM 901, 902, and 903 as designated by ASTM D5964) to evaluate volume swell and property retention.