40 PROCESSING TECHNOLOGY
Revised global O-ring standard harmonises US, Europe and Asia
ISO 3601, the standard covering O-Rings, the most commonly used seal, has been revised to meet American, European, as well as Asian needs.
ISO 3601, la norme portant sur O-Rings, le plus couramment utilisé le sceau, a été révisé pour répondre à l’Amérique, d’Europe, d’Asie, ainsi que les besoins.
ISO 3601, die Norm für O-Ring, die am häufigsten verwendeten Siegel, wurde überarbeitet, um in Amerika, Europa sowie Asien Bedürfnisse.
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SO 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.
“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 is the convener on the ISO working group responsible for this latest revision of the ISO 3601 O-Ring standard.
The American AS 568B standard dates back
over 50-years. Originally, the high cost of tools to produce O-Rings meant that inch O-Rings were used in metric housings. Elastomer O-Rings have a relatively large tolerance field between the minimum and maximum effective cross-section; where at the lower limit there will be sufficient squeeze to fill the sealing groove and at the higher, it will not extrude beyond the sealing gap. This characteristic meant that AS 568B O-Rings with widened tolerances could effectively fit into metric housings. These wider tolerances were reflected in ISO
3601, initially drafted back in the early 1980s. America, who account for a third of the world’s market for O-Rings continued to use tolerances as specified by the AS standard while the rest of the world work to Europe’s widened tolerances.
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Fig. 1. A selection of O-Rings. The revised standard embraces AS and ISO tolernaces.
“Discussions to harmonise the two standards
have been ongoing for a number of years,” continues Murthum. The revised standard not only successfully embraces both the AS and ISO standard tolerances in a single standard but also extend 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 recognised in the revised standard.” 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 and inch sizes, which can then fit into metric grooves. Also, in Class B there is now a table of tolerances covering cross-sections from 0.8 to 8.4 mm. Until the harmonisation 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. “One thing the working group ensured was that the ISO designation remained the same,” adds Murthum. “With such a long established standard this was important and means that
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