Overview of Elastomers and O-Rings

Material Specifications:
The document details various elastomers such as butyl, styrene-butadiene, polyester urethane, and natural rubber, with specific brands and manufacturers mentioned. It references international standards like ISO and ASTM for testing and material analysis.

Material Determination:
Material compositions are best determined in a lab, though costly. Thermal analysis (TGA) per ASTM E-1131 can identify material groups, while density offers a simpler method.

Resilience and Hardness:
Elastomer groups like NBR, FPM, and EPDM have distinct resilience properties. Hardness is measured in Shore A or IRHD, tested according to DIN standards.

Compression Set:
Measured by DIN 53517 or ASTM D395, it indicates an elastomer's permanent deformation after stress removal. Lower values suggest higher quality.

Special O-Ring Types:
PTFE-FEP covered O-Rings combine elastomer elasticity with PTFE-FEP chemical resistance. Virgin PTFE O-Rings require special housing due to non-elastic behavior. Metal O-Rings and C-Rings suit high-temperature and high-pressure applications.

Chemical Resistance:
Chemical resistance is crucial as substances can cause elastomers to swell, affecting performance. The document summarizes chemical resistance for various materials.

Specifications and Material Use:
Outlines material use in mineral oils and temperature ranges, specifying materials like NBR, FPM, HNBR, and PTFE.

Synthetic Lubricants:
Synthetic fluids, mainly phosphoric acid esters, are poorly compatible with standard sealing materials. Recommended materials include FPM, FFKM, and PTFE.

Difficultly Flammable Fluids:
These are categorized into three groups per VDMA standards, each with specific temperature ranges and suitable materials.

Biological Oils:
Overview of biological oils like HETG, HEEG, and HEPG, detailing composition, temperature range, and applications.

Elastomer O-Rings:
Discusses limits of elastomer O-Rings, emphasizing temperature behavior, fluid resistance, and mechanical properties.

Chemical Effects and Compatibility:
Insights into chemical effects on elastomers, including swelling and shrinkage due to fluid penetration.

Resistance to Water and Oils:
Most elastomers suit cold water, but EPDM, MVQ, and HNBR are preferred for hot water and steam.

Lubricating Greases Compatibility:
Explains lubricating greases' composition and compatibility with different elastomers.

Elastomer Swelling and Hardness: Swelling leads to deterioration of physical properties. Some fluids extract substances, causing shrinkage and increased hardness.

Resistance to Water and Steam: Most elastomers suit cold water. For hot water above 100°C, EPDM, MVQ, and HNBR are preferred.

Resistance to Oils: Elastomers are not inherently resistant to mineral oils. The aromatic content affects swelling.

Compatibility with Lubricating Greases: Greases consist of a base fluid and a thickener. Mineral oil-based greases require elastomers resistant to mineral oils.

Compatibility with Vegetable and Animal Oils: Elastomers resistant to mineral oils can be used with vegetable and animal oils.

Compatibility with Brake Fluids: Brake fluids are glycols and glycol ethers. EPDM materials are suitable due to limited swelling and good resistance to heat and aging.

Compatibility with Fuels: Fuels cause swelling in elastomers. NBR with high acrylonitrile content and FPM are used.

Compatibility with Solvents: Swelling is influenced by polar or non-polar groups.

Compatibility with Acids: Inorganic acids are aggressive. FPM materials are generally resistant.

Compatibility with Bases: FPM elastomers are attacked by inorganic bases. EPDM is suitable.

Specifications and Material Properties:
Elastomers like EPDM, CR, HNBR, FPM, MVQ, and FFKM are noted for resistance to weathering and aging.

Food Contact Compliance:
Silicone elastomers are preferred for food contact due to inertness.

Chemical Compatibility:
FPM elastomers resist most inorganic compounds but are vulnerable to bases.

Medical Use Suitability:
Medical applications use white silicone for general purposes.

Metal Contact and Corrosion:
Corrosion can occur due to free sulfur or hydrochloric acid from elastomers.

Contact with Plastics:
Elastomers can cause discoloration or softening of plastics.

Electrical Properties:
Elastomers are generally electrical insulators.

Limits of the Use of Elastomer O-Rings:
1. Use in Vacuum: Vacuum sealing is challenging due to elastomer permeability.
2. Resistance to Radioactivity: Exposure to atomic radiation reduces elastomer tightness.
3. Pressurisation: O-Rings can handle up to 2000 bar in static applications.
4. Elevated Temperatures: High temperatures cause elastomer aging.
5. Low Temperatures: Elastomers become harder and stiffer.
6. Thermal Expansion: Elastomers expand more than metals.

Specifications and Procedures:
1. TR10 Low-Temperature Guideline: The TR10 value is determined by extending an elastomer strip.
2. Compression Set: Measures permanent deformation after load release.

Material Properties and Recommendations:
1. Acrylonitrile Butadiene Elastomer (NBR): Known for resistance to mineral oils.
2. Fluoroelastomer (FPM): Offers high resistance to temperature and chemicals.
3. Silicone Elastomer (MVQ): Features a wide temperature range.
4. Ethylene Propylene Diene Elastomer (EPDM): Resistant to ozone and weathering.
5. Chloroprene Elastomer (CR): Good resistance to aging.
6. Hydrogenated Acrylonitrile Butadiene Elastomer (HNBR): Offers improved temperature and fluid resistance.
7. Fluorosilicone Elastomer (MFQ): Similar to silicone but with better resistance to fuels.
8. Perfluoroelastomer (FFKM): Combines chemical resistance of PTFE with elastic properties.

Approvals and Material Codes:
1. Food and Drug Administration (FDA) Approvals: For foodstuffs and drinking water applications.
2. DVGW Gas Approval: For gas sealing applications.
3. Oxygen Clearance Certificate (BAM): For oxygen applications.
4. ASTM Material Codes: Standardized codes for material identification.

Temperature Stability and Water Resistance Tests:
1. Temperature Stability: Conducted according to ASTM D746.
2. Water Resistance: Conducted according to ASTM D471.

Surface Treatments for O-Rings:
Various treatments like halogenation, molykoting, and PTFE spraying are discussed.

Surface Treatment of Metal O-Rings and C-Rings:
Coatings enhance sealing effects, especially for gas and vacuum seals.

Design Notes for O-Rings:
1. Introduction: O-Rings are used in static and dynamic applications.
2. Static Applications: O-Ring compression is higher in static conditions.
3. Compression: The mounted O-Ring must be deformed to initiate sealing.
4. Groove Profiles and Surface Finish: Groove volume should be larger than the O-Ring's cross-sectional area.
5. Axial Seals for Static Applications: Groove location and pressure direction are crucial.
6. Special Groove Profiles: Dovetail grooves hold the O-Ring firmly.
7. Material and Surface Considerations: O-Rings with a hardness of 70 to 90 IRHD/Shore A are standard.
8. Additional Considerations: Factors like pressure, material hardness, and lubrication are critical.

Design Notes for Radial Seals in Static Applications:
Discusses radial seals, groove location, and surface roughness specifications.

Special Applications: Vacuum Use:
Specific guidelines for O-Ring design and seating in vacuum applications.

Material Recommendations:
Standard materials for normal vacuums, FPM, CR, and FFKM for high vacuum.

Dynamic Applications:
Lower compression to minimize friction and wear.

Hydraulic Dynamic Applications:
Guidelines for groove dimensions and avoiding enclosed O-Rings.

Specifications and Design Notes:
Detailed specifications for O-Rings in various applications.

Compression and Groove Dimensions:
Guidelines for determining compression and groove depth.

Surface Finish:
Adherence to specified surface finishes is crucial.

Dynamic Pneumatic Applications:
Permissible compression range and calculation examples.

Special Applications:
Specifications for immersed mounting and rotary applications.

Tables and Diagrams:
Includes tables and diagrams for groove profiles and compression values.

Design Specifications and Notes:
Guidelines for O-Rings as drive belts in low-torque applications.

Limitations:
Avoid contact with liquids, minimum bending radius, and other limitations.

Surface Roughness:
Importance of surface roughness for durability and wear.

Compression and Force Requirements:
Table for groove depth and graph for compressive force.

Pressure Considerations:
High pressure in static applications, fluid pressure limits in dynamic applications.

Material and Surface Quality:
Importance of material and surface quality for effective sealing.

Design Notes and Specifications:
O-Ring damage under pressure, permissible clearance, and back-up rings.

Static and Dynamic Sealing Applications:
Design considerations for static and dynamic applications.

Material Hardness and Testing Methods:
Hardness testing methods and material resistance.

Lubrication and Viscosity:
Importance of lubrication in static and dynamic applications.

Viscosity-Temperature Characteristics: Importance of viscosity-temperature behavior in mineral oils.

Friction and Lubrication: Proper lubrication reduces friction and wear.

Stick-Slip Effect: Affects slow stroke movements, mitigated by high VI oils.

Wear and Tear: Common types of wear and measures to reduce it.

Running Speed and Contamination: Service limits for piston and rod speeds.

Back-up Rings: Prevent migration into sealing gaps.

Design Notes: Guidelines for designing grooves for back-up rings and O-Rings.

Specifications:
Specifications for PTFE O-Rings and design notes for metal O-Rings.

Surface Finish:
Surface roughness specifications for contact surfaces.

Accidental Damage and Limitations:
Common causes of O-Ring failure and prevention measures.

O-Ring Surface Cracking and Rapid Decompression: Causes and prevention of surface cracks and rapid decompression.

Manufacturing Tolerances and Standards: Tight dimensional tolerances and standards for O-Rings.

Quality Grades and Defect Limits: O-Rings categorized into Grade N and Grade S.

Storage Guidelines: Storage conditions for elastomer components.

Manufacturing Tolerances, Storage, and Standards:
Specifications and standards related to O-Rings.

DIN Standards:
Various DIN standards for O-Rings.

Aviation Standards:
DIN standards for aerospace equipment.

International Standards:
ISO standards for O-Rings.

British, French, Italian, and Swedish Standards:
Standards for O-Ring dimensions.

Extended Standards for Elastomer Components:
DIN standards for rubber products.

Testing and Quality Assurance:
DIN and ISO standards for testing elastomers.

Groove Dimensions and Applications:
Recommendations for groove dimensions.

O-Ring Specifications and Availability:
Variety of O-rings offered by Angst + Pfister.

Groove Dimensions for O-Rings:
Guide to groove dimensions.

O-Ring Groove Design:
Tables for determining groove dimensions.

Standards and Dimensions:
References to American/British standards for O-ring dimensions.

Static Applications:
Specifications for static applications.

Overview: Technical specifications and guidelines for O-Rings.

Specifications: Dimensions of O-Rings according to different standards.

Procedures and Recommendations: Advises against using O-Rings without mounting recommendations for dynamic applications.

Standards and Norms: References several standards and permissible tolerances.

Key Data from Tables: Extensive data on O-Ring dimensions.

Critical Information: Notes on O-Rings without specific mounting recommendations.