ISO 6627:2011

INTERNATIONAL ISO
STANDARD 6627
Second edition
2011-08-01

Internal combustion engines — Piston
rings — Expander/segment oil-control
rings
Moteurs à combustion interne — Segments de piston — Segments
racleurs régulateurs d'huile/Ressorts d'expansion




Reference number
ISO 6627:2011(E)
©
ISO 2011

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ISO 6627:2011(E)

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ii © ISO 2011 – All rights reserved

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ISO 6627:2011(E)
Contents Page
Foreword . iv
Introduction . v
1  Scope . 1
2  Normative references . 1
3  Symbols and abbreviated terms . 1
4  Ring types and designations . 3
4.1  Types of expander/segment oil-control rings . 3
4.2  General features . 4
4.3  Designation examples . 5
5  Common features . 5
5.1  Expander-spacer . 5
5.2  Segment features . 7
5.3  Expander/segment assembly . 10
6  Dimensions . 10
7  Materials . 13
7.1  Expander-spacer . 13
7.2  Segments . 13
8  Tangential force and nominal contact pressure . 13
8.1  Tangential force . 13
8.2  Classes of nominal contact pressure . 13
Bibliography . 15

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ISO 6627:2011(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
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. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 6627 was prepared by Technical Committee ISO/TC 22, Road vehicles.
This second edition cancels and replaces the first edition (ISO 6627:2000), which has been technically revised.
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ISO 6627:2011(E)
Introduction
ISO 6627 is one of a series of International Standards dealing with piston rings for reciprocating internal
combustion engines. Others are ISO 6621, ISO 6622, ISO 6623; ISO 6624, ISO 6625 and ISO 6626 (see
Clause 2 and the Bibliography).
The common features and dimensional tables included in ISO 6627 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 refer to the specifications and requirements of ISO 6621-3 and ISO 6621-4
before completing the selection.

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INTERNATIONAL STANDARD ISO 6627:2011(E)

Internal combustion engines — Piston rings —
Expander/segment oil-control rings
1 Scope
This International Standard specifies the essential dimensional features of expander/segment oil-control rings,
without providing a complete product description (because expander-spacer design varies from piston-ring
manufacturer to piston-ring manufacturer, the interaction between the manufacturer and the client will
determine specific design details).
This International Standard applies to expander/segment oil-control rings of nominal diameters ranging from
40 mm to 125 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 referenced documents are indispensable for the application 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 6621-2, Internal combustion engines — Piston rings — Part 2: Inspection measuring principles
ISO 6621-3, Internal combustion engines — Piston rings — Part 3: Material specifications
ISO 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications
ISO 6626, Internal combustion engines — Piston rings — Coil-spring-loaded oil control rings
3 Symbols and abbreviated terms
For the purposes of this International Standard, the symbols and abbreviated terms in Table 1 apply.
Table 1 — Symbols and abbreviated terms
Symbol
abbreviated Description
terms
a Segment radial wall thickness

1
a Spacer radial thickness
8
a Expander radial thickness
9
a Assembly radial thickness
11
a Seating tab height
14
d Nominal ring assembly diameter (nominal diameter)
1
h Nominal assembly width
1
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ISO 6627:2011(E)
Table 1 (continued)
Symbol
abbreviated Description
terms
h Segment contact face width
24
h Expander width
9
h Segment width near inside diameter (ID), after coiling
10
h Segment width near outside diameter (OD), after coiling and surface treatment or plating
11
h Nominal segment width
12
h Spacer width
13
p Nominal contact pressure
o
p Unit contact pressure
ou
s Segment closed gap; stagger gap
1
F Tangential force
t
F Specific tangential force
tc
 Tab angle
CR1.CR2 Chromium-plating thickness
LM Piston rings with partly cylindrical machined peripheral faced
LP Piston rings with lapped stripe over the whole circumference
ES1.ES4 Types of expander/segment oil-control rings
PNH High nominal pressure
PNL Low nominal pressure
PNM Medium nominal pressure
PNR Reduced nominal pressure
PNV Very high nominal pressure
TT00…TT30 Nominal seating tab angle
NS010…NS050 Nitrided surface (segment)
NX003…NX025 Nitrided surface (expander-spacer)

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ISO 6627:2011(E)
4 Ring types and designations
4.1 Types of expander/segment oil-control rings
ES1

ES2

ES3

ES4

Key
1 centring pad (optional)
Figure 1 — Expander/segment oil-control ring designs
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ISO 6627:2011(E)
4.2 General features
The expander/segment assembly shall be in accordance with Figure 2.

a)  Assembly

b)  Expander-spacer c)  Segment
Key
1 seating tab
2 expander-spacer ends
3 peripheral surface
a
4 stagger segments gaps and expander ends (all three components); stagger angle should be larger than 30°
a
For assembly arrangement regarding tangential force, see ISO 6621-2.
b
Seating tab angle dimensions are defined in Table 3.
NOTE This is a schematic drawing of the four spring types shown in Figure 1.
Figure 2 — Expander/segment assembly
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ISO 6627:2011(E)
4.3 Designation examples
The following are examples of piston ring designations in accordance with this International Standard.
EXAMPLE 1 Expander/segment oil-control ring type ES1 (ES1) of nominal diameter d = 90 mm (90) and nominal
1
assembly width h = 3 mm (3,0), with segments made of unalloyed steel subclass 68 (MC68), a chromium-plated
1
peripheral surface of minimum thickness 0,05 mm (CR1), and with an expander made of 16 % Cr (min.) austenitic steel, of
material subclass 67 (MC67) and tangential force, F , according to the medium nominal contact pressure class (PNM):
t
Piston ring ISO 6627 - ES1-90 × 3,0-MC68/CR1-MC67/PNM
EXAMPLE 2 Expander/segment oil-control ring type ES2 (ES2) of nominal diameter d = 90 mm (90) and nominal
1
assembly width h = 2,5 mm (2,5), with segments made of 11 % Cr (min.) martensitic steel, subclass 65 (MC65), nitrided
1
on the peripheral and inside surfaces (NS020) to a minimum depth of 0,020 mm on the peripheral surface, and with an
expander made of 16 % Cr (min.) austenitic steel, of material subclass 67 (MC67), nitrided on the surface (NX), and
tangential force, F , according to the reduced nominal contact pressure class (PNR):
t
Piston ring ISO 6627 - ES2-90 × 2,5-MC65/NS020-MC67/NXPNR
EXAMPLE 3 Expander/segment oil-control ring type ES3 (ES3) of nominal diameter d = 90 mm (90) and nominal
1
assembly width h = 4,0 mm (4,0), with segments made of unalloyed steel subclass 68 (MC68), a chromium-plated
1
peripheral surface of minimum thickness 0,05 mm (CR1) with lapped stripe (h24) of 0,30 mm, and with an expander made
of 16 % Cr (min.) austenitic steel, of material subclass 67 (MC67) and tangential force, F , according to the high nominal
t
contact pressure class (PNH):
Piston ring ISO 6627 - ES3-90 × 4,0-MC68/CR1-MC67/PNH
5 Common features
5.1 Expander-spacer
5.1.1 Design considerations
In order to optimize the fit of the oil ring assembly into the engine cylinder bore, the following should be
considered in the design of the expander/segment oil-control rings:
 total circumferential deflection of the expander;
 piston groove depth;
 features on the lands adjacent to the oil ring groove;
 groove-corner radius.
5.1.2 Without surface treatment
The expander-spacer without surface treatment is typically used together with chromium-plated segments
(see 5.2.1).
5.1.3 Nitrided surface (NX)
The expander-spacer with a nitrided surface is typically used together with nitrided segments (see 5.2.2).
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ISO 6627:2011(E)
Table 2 — Expander-spacer nitrided case
Dimensions in millimetres
Code Nitrided case depth Tolerance
NX003 0,003
NX010 0,010
+ 0,012
NX015 0,015
 0
NX020 0,020
NX025 0,025
NOTE 1 The tolerance for NX applies
...