Subsequently, Global O-Ring and Seal defines the quality acceptance criteria of all O-rings to be in accordance with ISO Grade N which classifies surface imperfections and specifies maximum acceptable limits for these imperfections. This information can be viewed in PDF format here. Stricter tolerance and inspection requirements can be achieved upon customer request. Class A O-rings have equivalent tolerances to those used in AS, which are tighter than the tolerances for Class B O-rings, and are suitable for industrial or aerospace applications when the application or the housing require tighter tolerances. Class B O-rings have slightly wider tolerances and are suitable for general-purpose applications. ISO Quality Acceptance Criteria ISO was originally developed for general-purpose O-rings, but over the years this standard has been revised and refined to include three grades N, S, CS of defects depending upon the application.
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ISO All rights reserved. ISO copyright office Case postale 56? CH Geneva 20 Tel. Normative references Terms and definitions Inside diameters, d1, cross-sections section diameter , d2, and tolerances Designation codes Methods of measuring for receiving inspection Identification statement reference to this part of ISO Annex A normative Recommended inside diameter tolerances and cross-section tolerances for non-standard custom O-ring values Annex B informative Example method of measuring for receiving inspection The work of preparing International Standards is normally carried out through ISO technical committees.
Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights.
ISO shall not be held responsible for identifying any or all such patent rights. This fifth edition cancels and replaces the fourth edition ISO , which has been technically revised. ISO consists of the following parts, under the general title Fluid power systems — O-rings:? Part 1: Inside diameters, cross-sections, tolerances and designation codes? Part 2: Housing dimensions for general applications? Part 3: Quality acceptance criteria? Part 4: Anti-extrusion rings back-up rings? ISO — All rights reserved Not for Resale ISO E Introduction In fluid power systems, power is transmitted and controlled through a fluid liquid or gas under pressure within an enclosed circuit.
To avoid leakage or to seal different chambers of a component from each other, sealing devices are used. O-rings are one type of sealing device. The dimensions and tolerances specified in this part of ISO are suitable for any elastomeric material, provided that suitable tooling is available. For materials that shrink differently from this standard NBR compound, a special mould can be required to maintain the mean diameters and the tolerance limits listed.
For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document including any amendments applies. Figure 1 — Typical O-ring configuration 6 Inside diameters, d1, cross-sections section diameter , d2, and tolerances 6. The tolerance of class B O-rings is based on Equation A. Class A O-rings have tighter inside diameter tolerances than class B O-rings and are suitable for industrial or aerospace applications when the application or the housing require tighter tolerances.
Class B O-rings have dimensions and tolerances suitable for general-purpose applications. The inside diameter tolerances are based on Equation A. For information, Figure 2 shows a graphical comparison of the inside-diameter tolerances for class A and class B O-rings. Tolerances for inside diameters for non-standard custom class A O-rings are listed in Table A. Equation A. In marginal cases, the compliance with the limits of the shape deviations and surface imperfections should be considered besides the dimensional tolerances.
See ISO Annex B provides possible methods for such a procedure for information. Volume ref. Class A Class B? This annex provides directions for determining the tolerances that should be applied to the inside diameter, d1, and cross-section, d2, of such O-rings.
Table A. Applies to class B only. Differences between tolerance values are due to conversion of dimensions from metric to inch and rounding rules. Actual measurements shall be taken at ambient temperature, and no lubrication shall be used on either the gauges or the O-rings during the inspection process. O-rings shall be handled in such a way as to avoid dimensional distortion. If the latter instrumentation is used, the cross-section dimension of the O-ring shall be centred under the contact button and the O-ring shall be rotated so the parting line projection, if any, does not interfere.
Care should be taken that the contact pressure does not significantly affect the accuracy of the reading. It is necessary to have a gauge for each cross-section size. The top of each step shall be sized so that when an O-ring with the minimum inside diameter and maximum cross-section diameter is dropped freely in a radial plane over the step, the top of the step and the top of the O-ring are in the same plane.
Similarly, the bottom of each step shall be sized so that an O-ring with the maximum inside diameter and maximum cross-section diameter just clears the flat-bottom step of the gauge. The height gauge is arranged so that the tolerance spread is indicated for the particular O-ring measured. A micrometer adjustment shall be provided to permit realignment of the pointers for readings taken at the outside surfaces of, rather than the centreline of, the O-ring. The length of the taper gauge can vary depending on the O-ring applications.
If the O-ring falls into the predetermined groove without stretching, then it shall be considered to be within tolerance.
ISO 3601 Metric O-Rings