ISO 6627:2022

INTERNATIONAL ISO
STANDARD 6627
Third edition
2022-02
Internal combustion engines — Piston
rings — Expander/rail oil-control
rings
Reference number
ISO 6627:2022(E)
© ISO 2022

---------------------- Page: 1 ----------------------
ISO 6627:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 6627:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.1
5 Ring types and designations .2
5.1 Types of expander/rail oil-control rings . 2
5.2 General features . 3
5.3 Designation examples . 4
6 Common features . 5
6.1 Expander . 5
6.1.1 Design considerations . 5
6.1.2 Without surface treatment . 5
6.1.3 Nitrided surface (NX). 5
6.1.4 Tab angle . 5
6.1.5 Expander dimensions . 6
6.2 Rail features . 6
6.2.1 Chromium-plated peripheral surface . 6
6.2.2 Nitrided surface codes NS010 to NS050 . 7
6.2.3 PVD coated peripheral surface . 7
6.2.4 Rail dimensions . 8
6.3 Expander/rail assembly . 10
7 Dimensions .10
8 Materials .11
9 Tangential force and nominal unit pressure .11
9.1 Tangential force, F . 11
t
9.2 Nominal unit pressure . 11
9.3 Classes of nominal unit pressure .12
Bibliography .13
iii
© ISO 2022 – All rights reserved

---------------------- Page: 3 ----------------------
ISO 6627:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). 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.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This third edition cancels and replaces the second edition (ISO 6627:2011), which has been technically
revised.
The main changes are as follows:
— previous nomenclature referred to the rails as segments;
— barrel faced rail was added;
— PVD specification for rails was added;
— figures and tables were revised;
— new dimension introduced for expander;
— applicable bore diameter range increased to 140mm.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 6627:2022(E)
Introduction
This document is one of a series of International Standards dealing with piston rings for reciprocating
internal combustion engines. Others are the ISO 6621 series, the ISO 6622 series, ISO 6623, the ISO 6624
series, ISO 6625 and the ISO 6626 series (see Clause 2 and the Bibliography).
The common features and dimensional tables included in this document represent a broad range of
variables. In selecting a ring type, the designer will above all need to consider the particular operating
conditions. Moreover, it is essential that the designer refers to the specifications and requirements of
ISO 6621-3 and ISO 6621-4 before completing the selection.
v
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 6627:2022(E)
Internal combustion engines — Piston rings — Expander/
rail oil-control rings
1 Scope
This document specifies the essential dimensional features of expander/rail oil-control rings, without
providing a complete product description (because expander-rail designs vary from piston-ring
manufacturer to piston-ring manufacturer, the interaction between the manufacturer and the client
will determine specific design details).
This document applies to expander/rail oil-control rings of nominal diameters ranging from 40 mm to
140 mm for reciprocating internal combustion engines for road vehicles and other applications. It also
applies to piston rings for compressors working under analogous conditions.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 6621-1, Internal combustion engines — Piston rings — Part 1: Vocabulary
ISO 6621-3, Internal combustion engines — Piston rings — Part 3: Material specifications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 6621-1 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Symbols and abbreviated terms
For the purposes of this document, the symbols and abbreviated terms in Table 1 apply.
1
© ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
ISO 6627:2022(E)
Table 1 — Symbols and abbreviated terms
Symbols and
abbreviated Description
terms
a Rail radial wall thickness
1
a Expander radial thickness excluding tab
8
a Expander radial thickness
9
a Assembly radial thickness
11
a Tab radial thickness
14
a Pad radial thickness
15
d Nominal ring assembly diameter (nominal bore diameter)
1
h Nominal assembly axial width
1
h Rail face contact width
24
h Barrel gauge width
8
h Expander axial width
9
h Rail axial width near inside diameter (ID), after coiling
10
h Rail axial width near outside diameter (OD), after coiling and surface treatment or plating
11
h Nominal rail axial width
12
h Expander axial width over pads
13
h Pad height
14
h Axial distance between height of expander tab and height of expander pad
28
p Nominal unit pressure
o
s Rail closed gap
1
t t Barrel face drop (barrel drop on peripheral surface)
2, 3
F Tangential force
t
F Specific tangential force
tc
θ Tab angle
CR1.CR2 Chromium-plating thickness
ES1.ES3 Types of expander/rail oil-control rings
PNH High nominal unit pressure
PNL Low nominal unit pressure
PNM Medium nominal unit pressure
PNR Reduced nominal unit pressure
PNV Very high nominal unit pressure
TT00…TT30 Nominal tab angle
NS010…NS050 Nitrided surface (rail)
NX003…NX025 Nitrided surface (expander)
PC001…PC020 PVD coa
...