Company provides background to consolidate metric and AS 568B inch standards
 ISO 3601, the standard covering O-Rings, has recently been revised to ensure standards between units of measure |
ISO 3601, the standard covering O-Rings, has recently been revised to ensure standards between units of measure. ISO 3601 consolidates the long established AS 568B inch standard with the existing metric ISO 3601 and importantly, as it retains its original designation, means modification of documentation may not be required. Those involved sought out a new standard in order to meet the needs of American, European and Asian manufacturers.
Until the harmonization between the AS and ISO standards, it was not possible to specify housing dimensions and retaining rings. Now two parts have been added to the standard that define these, while still in revision is a section on elastomer materials.
ADVERTISEMENT
Class A corresponds to the American standard AS 568B in its current format. Class B allows production of O-Rings in technically acceptable and economical metric sizes related to inch sizes, which can then fit into metric grooves. Also, in Class B, the five standard cross sections are replaced with a table of tolerances using a formula.
“Changes to the existing standard were needed to reflect what was happening in the market place,” says Bernd Murthum, O-Ring Product Manager for Trelleborg Sealing Solutions, who was the convener on the ISO working group responsible for this latest revision of the ISO 3601 O-Ring standard. “Discussions to harmonize the two standards have been ongoing for a number of years.”
The revised standard not only successfully embraces both the AS and ISO standard tolerance in a single standard, but also extends cross sections covered. “ISO 3601 and AS 568B only describe five standard cross sections.
In reality, in the market place there are many more. Common practice was to use the principles of the ISO over a broader range of cross sections. This is now recognized in the revised standard.”
Trelleborg Sealing Solutions has a high level of expertise in specification of O-Rings and other sealing elements within a wide range of industrial, aerospace and automotive applications.
Design engineers can contact one of over 40 marketing companies worldwide for further information on this O-Ring standard or selecting the optimum sealing element for their specific application.
The five parts of the now valid O-Ring standard ISO 3601-2:2008 are as follows:
ISO 3601-1: 2008
Revised - Inside diameters, cross sections, tolerances and designation codes
- Dimensions are expressed in both metric and inch measurements
- Class A is identical with AS568B
- Class B is similar to the tolerances of the previous ISO 3601-1: 2002
- Includes an equation to calculate the tolerance for the O-Ring inside diameter
- Range for O-Ring cross section diameter tolerances from 0.8 mm to 8.4 mm
ISO 3601-2: 2008
New - Housing dimensions for general applications
- Covers technology for measuring surface roughness of O-Ring housings
- Design recommendations for O-Ring squeeze, elongation and compression as well as maximum groove fill
- Equation for calculation of O-Ring cross section reduction caused by the elongation of the O-Ring inner diameter
ISO 3601-3: 2005
Partially revised - Quality acceptance criteria for O-Ring surfaces
ISO 3601-4: 2008
New – Retaining ring specifications
- Covers spiral Back-up Rings, solid type (cut/ uncut), concave type (cut/ uncut)
- Gives tolerances for outer and inner diameters for rod and piston applications
- Design recommendations but no size list for preferred housing dimensions
ISO 3601-5:2002
Currently in revision – Suitability of elastomeric materials for industrial applications
- Will replace general information on material groups with detailed information of more practical use to design engineers
- Will comprise a selection table with important material groups related to the compatibility to fluids and operating temperatures