ISO 6624-3:2017

Internal combustion engines — Piston rings — Part 3: Keystone rings made of steel

ISO 6624-3:2017 specifies the essential dimensional features of keystone rings made of steel, types T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 160 mm, used in reciprocating internal combustion piston engines.

Moteurs à combustion interne — Segments de piston — Partie 3: Segments trapézoïdaux en acier

General Information

• Status: Published
• Publication Date: 26-Apr-2017
• ICS: 43.060.10 - Engine block and internal components
• Technical Committee: ISO/TC 22/SC 34 - Propulsion, powertrain and powertrain fluids
• Drafting Committee: ISO/TC 22/SC 34/WG 4 - Piston rings
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 11-Oct-2022

Relations

• Revises: ISO 6624-3:2001 - Internal combustion engines — Piston rings — Part 3: Keystone rings made of steel
• Effective Date: 04-Nov-2015

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 6624-3
Second edition
2017-04
Internal combustion engines —
Piston rings —
Part 3:
Keystone rings made of steel
Moteurs à combustion interne — Segments de piston —
Partie 3: Segments trapézoïdaux en acier
Reference number
ISO 6624-3:2017(E)
ISO 2017
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ISO 6624-3:2017(E)
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© ISO 2017, Published in Switzerland

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ii © ISO 2017 – All rights reserved
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ISO 6624-3:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative reference ......................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Overview ....................................................................................................................................................................................................................... 1

5 Ring types and designation examples ............................................................................................................................................ 1

5.1 Type T — Straight faced keystone ring 6° ....................................................................................................................... 1

5.1.1 General features................................................................................................................................................................ 1

5.1.2 Designation ........................................................................................................................................................................... 2

5.2 Type TB — Symmetrical barrel faced keystone ring 6° ....................................................................................... 2

5.2.1 General features................................................................................................................................................................ 2

5.2.2 Designation ........................................................................................................................................................................... 4

5.3 Type TBA — Asymmetrical barrel faced keystone ring 6° ................................................................................ 4

5.3.1 General features................................................................................................................................................................ 4

5.3.2 Designation ........................................................................................................................................................................... 5

5.4 Type TM — Taper faced keystone ring 6° ........................................................................................................................ 5

5.4.1 General features................................................................................................................................................................ 5

5.4.2 Designation ........................................................................................................................................................................... 7

5.5 Type K — Straight faced keystone ring 15° .................................................................................................................... 7

5.5.1 General features................................................................................................................................................................ 7

5.5.2 Designation ........................................................................................................................................................................... 7

5.6 Type KB — Symmetrical barrel faced keystone ring 15° ................................................................................... 8

5.6.1 General features................................................................................................................................................................ 8

5.6.2 Designation ........................................................................................................................................................................... 8

5.7 Type KBA — Asymmetrical barrel faced keystone ring 15° ............................................................................ 9

5.7.1 General features................................................................................................................................................................ 9

5.7.2 Designation ........................................................................................................................................................................... 9

5.8 Type KM — Taper faced keystone ring 15° .................................................................................................................10

5.8.1 General features.............................................................................................................................................................10

5.8.2 Designation ........................................................................................................................................................................10

6 Common features ..............................................................................................................................................................................................10

6.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Outside and inside rounded edges ...................10

6.2 Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) — Internal bevel

top side........................................................................................................................................................................................................11

6.3 Type TM or KM rings with partly cylindrical machined (LM) or lapped (LP)

peripheral surface .............................................................................................................................................................................12

6.4 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Plating or coating configuration .........................12

6.4.1 Chromium plated or spray coated rings ...................................................................................................12

6.4.2 Nitrided surface .............................................................................................................................................................14

6.4.3 PVD rings .............................................................................................................................................................................15

7 Force factors ...........................................................................................................................................................................................................15

Bibliography .............................................................................................................................................................................................................................23

© ISO 2017 – All rights reserved iii
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ISO 6624-3:2017(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. 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. 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 on 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 the following

URL: w w w . i s o .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 second edition cancels and replaces the first edition (ISO 6624-3:2001), which has been technically

revised. The main changes compared to the previous edition are as follows:
— PVD rings were included; and
— updates were made regarding technology improvements.
A list of all the parts in the ISO 6624 series can be found on the ISO website.
iv © ISO 2017 – All rights reserved
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ISO 6624-3:2017(E)
Introduction

ISO 6624 is one of a number of series of International Standards dealing with piston rings for

[2].[3],[4],[5] [6],[7] [8]

reciprocating internal combustion engines. Others are ISO 6621 , ISO 6622 , ISO 6623 ,

[9] [10],[11], [12] [13]
ISO 6625 , ISO 6626 and ISO 6627 .

The common features and dimensional tables presented in this document constitute a broad range of

variables and, in selecting a particular ring type, the designer must bear in mind the conditions under

which it will be required to operate.
[4]

It is also essential that the designer refers to the specifications and requirements of ISO 6621-3 and

ISO 6621-4 before completing a selection.
© ISO 2017 – All rights reserved v
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INTERNATIONAL STANDARD ISO 6624-3:2017(E)
Internal combustion engines — Piston rings —
Part 3:
Keystone rings made of steel
1 Scope

This document specifies the essential dimensional features of keystone rings made of steel, types T,

TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 160 mm, used in

reciprocating internal combustion piston engines.
2 Normative reference

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 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications

3 Terms and definitions
No terms and definitions are listed in this document.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
4 Overview

The keystone ring types are specified in Tables 1 to 3 and Figures 1 to 8. Their common features and

the dimensions of those features are specified in Tables 4 to 9 and Figures 9 to 15. Tables 11 and 12 give

the force factors for the different types of rings, while Table 13 and Table 14 give the dimensions and

forces of keystone rings 6° and 15°, respectively.
5 Ring types and designation examples
5.1 Type T — Straight faced keystone ring 6°
5.1.1 General features
See Table 13 for dimensions and forces.
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ISO 6624-3:2017(E)
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 1 — Type T
5.1.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6°

keystone ring with straight-faced peripheral surface (T), of nominal diameter d = 90 mm (90) and nominal ring

width h = 2,5 mm (2,5), made of CrSi alloyed steel, subclass 62 (MC 62), and having a fully faced chromium

plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the

ISO ring designation:
Piston ring ISO 6624-3 T - 90 x 2,5-MC 62/CR2
5.2 Type TB — Symmetrical barrel faced keystone ring 6°
5.2.1 General features
See Table 13 for dimensions and forces.
2 © ISO 2017 – All rights reserved
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ISO 6624-3:2017(E)
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 2 — Type TB
Table 1 — Symmetrical barrel dimensions
Dimensions in millimetres
h h h h t , t h
1 25 26 27 2 3 8
Tolerance
2,0 0,40 1,00 ±0,30 1,60 1,2
0,003...0,015
2,5 0,45 1,25 ±0,40 2,05 1,6
3,0 0,50 1,50 2,50 2,0
±0,50 0,005...0,020
3,5 0,55 1,75 2,95 2,4
4,0 0,60 2,00 ±0,60 3,40 0,005...0,023 2,8

Gauge width h , informative only, shall be used only if agreed between the manufacturer and

customer.
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ISO 6624-3:2017(E)
5.2.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6°

keystone ring with barrel faced peripheral surface (TB), of nominal diameter d = 90 mm (90) and nominal ring

width h = 2,5 mm (2,5), made of martensitic steel (11 % Cr min.), subclass 65 (MC 65), nitrided on the peripheral

surface and side faces (NT) to a depth of 0,070 mm min. on the peripheral surface (070), and with an associated

side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring designation:

Piston ring ISO 6624-3 TB - 90 x 2,5-MC 65/NT070
5.3 Type TBA — Asymmetrical barrel faced keystone ring 6°
5.3.1 General features
See Table 13 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 3 — Type TBA
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ISO 6624-3:2017(E)
Table 2 — Asymmetrical barrel dimensions
Dimensions in millimetres
a b b
h h h h t t
1 25 26 27 2 3
Tolerance
2,00 0,40 0,60 ±0,20 1,50 0...0,007 0,009...0,030
2,50 0,45 0,70 1,80 0,011...0,035
±0,25 0...0,008
3,00 0,55 0,80 2,10 0,012...0,038
3,50 0,60 0,90 2,40 0,012...0,040
±0,30 0...0,009
4,00 0,65 0,95 2,80 0,013...0,045
h may be lowered for rings with reduced edge dimensions.
t or t or both may be varied as agreed between the manufacturer and customer.
2 3
5.3.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6°

keystone ring with asymmetrical barrel faced peripheral surface (TBA), of nominal diameter d = 90 mm (90)

and nominal ring width h = 2,5 mm (2,5), made of martensitic steel (17 % Cr min.), subclass 66 (MC 66), nitrided

on the peripheral surface and side faces (NT) to a minimum depth of 0,070 mm on the peripheral surface (070),

and with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO

ring designation:
Piston ring ISO 6624-3 TBA - 90 x 2,5-MC 66/NT070
5.4 Type TM — Taper faced keystone ring 6°
5.4.1 General features
See Table 13 for dimensions and forces.
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ISO 6624-3:2017(E)
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 4 — Type TM
Table 3 — Taper
Dimensions in minutes
Code Taper Tolerance Internal twist feature designs
Tolerance
+50 +60
M1 10
0 0
M2 30
M3 60
+60 +70
0 0
M4 90
M5 120

For chromium plated rings with a tapered peripheral surface that is not ground, the tolerance shall be increased by 10

+70 +80
(e.g. M3 = 60 tolerance: ; M3 with internal features = 60 tolerance: ).
0 0
M1 not for rings with partly cylindrical peripheral surface.
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ISO 6624-3:2017(E)
5.4.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 6°

keystone ring with 10´ taper faced peripheral surface (TM1), of nominal diameter d = 90 mm (90) and nominal

ring width h = 2,5 mm (2,5), made of martensitic steel (11 % CR min.), subclass 65 (MC 65), and having a fully

faced chromium plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis

are used in the ISO ring designation:
Piston ring ISO 6624-3 - TM1 x 2,5-MC 65/CR2
5.5 Type K — Straight faced keystone ring 15°
5.5.1 General features
See Table 14 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 5 — Type K
5.5.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15°

keystone ring with straight-faced peripheral surface (K), of nominal diameter d = 90 mm (90) and nominal ring

width h = 2,5 mm (2,5), made of CrMoV alloyed steel, subclass 61 (MC 61), and having a fully faced chromium

plated peripheral surface with a minimum thickness of 0,1 mm (CR2). Parameters in parenthesis are used in the

ISO ring designation:
Piston ring ISO 6624-3 K - 90 x 2,5-MC 61/CR2
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ISO 6624-3:2017(E)
5.6 Type KB — Symmetrical barrel faced keystone ring 15°
5.6.1 General features

See Table 1 for symmetrical barrel dimensions. See Table 14 for dimensions and forces.

Dimensions in millimetres
Key
1 reference plane
Due to manufacturing processing, side angle tolerances are not cumulative.
Nominal.
Figure 6 — Type KB
5.6.2 Designation

EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-3, being a steel, 15°

keystone ring with barrel faced peripheral surface (KB), of nominal diameter d = 90 mm (90) and nominal

ring width h = 2,5 mm (2,5), made of martensitic steel (17 % Cr min.), subclass 66 (MC 66), nitrided on the

peripheral surface and side faces (NT), to a minimum depth of 0,090 mm on the peripheral surface (090), and

with an associated side face depth of a minimum of 0,020 mm. Parameters in parenthesis are used in the ISO ring

designation:
Piston ring ISO 6624-3 KB- 90 x 2,5-MC 66/NT090
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ISO 6624-3:2017(E)
5.7 Type KBA — Asymmetrical barrel faced keystone ring 15°
5.7.1 Gen
...