Introduction

Choosing the correct material for an O-ring is critical to ensuring the reliability of industrial systems. O-rings are used in various application systems, including hydraulic and pneumatic drives, dampers, ventilation systems, and electromechanical devices. Incorrect material selection may lead to unexpected leaks, component extrusion, reduced service life, or even failures. This article provides the technical basis for selecting O-ring material considering chemical compatibility, temperature ranges, mechanical properties, and standards. United-D offers reliable components compliant with DSTU, EN, and ISO requirements.

Fundamental Principles

O-rings are elastic seals that provide a seal between two surfaces. They are made from various thermoplastic elastomers, each of which has defined physical and mechanical properties. The material selection depends on temperature conditions, chemical environment, pressure and mechanical compatibility.

Key physical properties that determine the material selection include:

Temperature range (low-temperature and high-temperature resistance)
Chemical resistance to liquids (kerosene, hydraulic fluid, oil, water, exhaust gases)
Mechanical properties (elasticity, strength, deformation resistance)
MTBF (Mean Time Between Failures) and aging resistance
Electrical conductivity or insulation (for electromechanical devices)

Technical specifications and standards

Material selection for the O-ring should comply with the requirements of the following standards:

DSTU 3004-95: Specifies requirements for elastomers and their use in industrial systems.
EN 13168: Standard defining the test methods and classification of elastomers.
ISO 281: Sets the requirements for leakage tests for seals.
ISO 3601: Defines the standard sizes of O-rings and their classification.
IEC 60947-2: Requirements for electrical equipment, including electrical seals.

Each material has defined temperature ranges, chemical resistance, and mechanical properties:

Material	Temperature range, °C	Chemical resistance	Mechanical properties	Standard
NBR (NBR)	-30 to +100	Oil compatible, kerosene compatible, water compatible, but not resistant to ethers, amines, alcohols	Average elasticity, high strength	ISO 3601, EN 13168
FKM (FKM)	-20 to +200	Compatible with hydraulic fluids, exhaust gases, oils, but not resistant to alcohols, ethers	High elasticity, high strength	ISO 3601, EN 13168
EPDM (EPDM)	-50 to +150	Water compatible, hydrolyzed water compatible, but not oil and ether resistant	High elasticity, high moisture resistance	ISO 3601, EN 13168
FFKM (FFKM)	-100 to +300	Compatible with all chemicals, including aggressive gases	High elasticity, high service life, high strength	ISO 3601, EN 13168

Selection criteria and calculation

To select the correct O-ring material, the following steps need to be performed:

Determine the temperature range of the environment in which the O-ring will be used.
Assess the chemical environment (type of liquids, gases, moisture).
Determine mechanical loads (pressure, rotation, vibration).
Use the table below for comparing materials.
Perform the calculation of the O-ring size based on pressure and the wall thickness of the pipe or hydraulic drive.

Parameter	Formula	Units of measurement	Explanation
O-Ring Size	d = d_internal + 2 * t	мм	The O-ring size is determined based on the internal diameter of the pipe and the wall thickness.
Pressure	P = F / A	bar	Pressure is determined based on force and area of action.
Mean Time Between Failures (MTBF)	MTBF = T / (C * F)	years	It is determined based on time consumption and frequency of incidents.

Setup and Installation

Installation of the O-ring shall be carried out in accordance with the following recommendations:

Use special fluids for cleaning surfaces before installation.
Ensure smooth installation without noticeable forces, to avoid damage.
Use special clips or clamps for securing the O-ring.
Perform tightness tests after installation.
Perform regular checks for leakage and deformation.

Causes of Ejection and Analysis of Causes

O-rings may be extruded for various reasons, including:

Incorrect material selection (incorrect chemical resistance or temperature range)
High pressure or vibration
Incorrect installation
Material aging or degradation
Presence of aggressive liquids or gases

Visual signs of O-ring extrusion include:

Surface cracks or pitting
Shape change or stretching
Appearance of turns or liquids
Increase of resistance during installation

Prediction of Ejection and Condition Monitoring

The following methods are used for predicting the extrusion of the O-ring:

Напружено-деформований аналіз: Використовується для визначення навантажень і відповідності до стандартів.
Pressure monitoring: Measurement of pressure in the system to detect leaks.
Temperature monitoring: Temperature measurement to detect deviations from standard ranges.
Humidity monitoring: Measurement of humidity to detect its effect on material stability.
Visual Condition Check: Regular checks for signs of wear.

Material Comparison Table

Material	Temperature range, °C	Chemical resistance	Mechanical properties	Standard	Price per unit
NBR	-30 to +100	Oil and kerosene compatible	Average elasticity	ISO 3601	€ 1.20
FKM	-20 to +200	Hydraulic fluid compatible	High elasticity	ISO 3601	€ 2.50
EPDM	-50 to +150	Water compatible	High moisture resistance	ISO 3601	€ 1.80
FFKM	-100 to +300	Compatible with all chemical liquids	High strength	ISO 3601	€ 5.00

Conclusion

Choosing the correct material for an O-ring is critical to ensuring the reliability of industrial systems. United-D provides reliable components compliant with DSTU, EN and ISO requirements. Use our e-catalog to obtain high-quality components that meet your technical specifications.

Go to UNITEC-D e-catalog

List of references

ISO 3601:2007 — Plastic Elastomers — O-Rings.
EN 13168:2009 — Testing and Classification of Elastomers.
DSTU 3004-95 — Elastomers and their use in industrial systems.
IEC 60947-2:2011 — Electrical equipment for measurement and control.
UNITEC-D Whitepaper: Materials for O-Ring — Technical Documentation.