ISO 6624-1:2017

Internal combustion engines - Piston rings - Part 1: Keystone rings made of cast iron

ISO 6624-1:2017 specifies the essential dimensional features of keystone rings made of cast iron, types T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 200 mm, used in reciprocating internal combustion piston engines.

Moteurs à combustion interne — Segments de piston — Partie 1: Segments trapézoïdaux en fonte

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: 9092 - International Standard to be revised
• Start Date: 01-Nov-2023
• Completion Date: 13-Dec-2025

Relations

• Revises: ISO 6624-1:2001 - Internal combustion engines - Piston rings - Part 1: Keystone rings made of cast iron
• Effective Date: 04-Nov-2015

Overview

ISO 6624-1:2017 - "Internal combustion engines - Piston rings - Part 1: Keystone rings made of cast iron" specifies the essential dimensional features and designation rules for keystone piston rings made of cast iron. It covers ring types T, TB, TBA, TM, K, KB, KBA and KM, intended for reciprocating internal-combustion piston engines with nominal diameters from 70 mm up to and including 200 mm. The 2017 (3rd) edition updates coating/PVD thickness guidance and reflects technological improvements.

Key topics and technical requirements

• Ring types and geometries
  • Type T / K - straight-faced keystone rings (T = 6°, K = 15°)
  • Type TB / KB - symmetrical barrel faced
  • Type TBA / KBA - asymmetrical barrel faced
  • Type TM / KM - taper faced (multiple taper codes)
• Dimensional features
  • Essential dimensional tables, figures and designation examples for nominal diameters and widths
  • Separate tables for 6° and 15° keystone variants, plus common feature tables
• Materials and subclasses
  • Cast-iron ring material options and subclass examples (e.g., MC12, MC22, MC32, MC53) are used for designation
• Surface treatments and coatings
  • Uncoated, chromium plated, PVD coated, spray coated, phosphate or ferroxide coatings - configurations and minimum thickness classes are referenced
  • PVD coating thickness included in this edition
• Force factors and mechanical data
  • Tables of force factors and ring forces to guide design and selection
• Manufacturing features
  • Options for machined or lapped peripheral surfaces, internal bevels/chamfers and twist features
• Designation format
  • Standardized example format: Piston ring ISO 6624-1 T-90 × 2,5-MC12/CR2

Applications - who uses this standard

• Engine designers and powertrain engineers - to select ring geometry and material compatible with piston/cylinder designs
• Piston ring manufacturers and foundries - to produce keystone rings to standardized dimensions, tolerances and coating classes
• OEMs and suppliers - for procurement specifications and part designation consistency
• Quality, testing and inspection labs - to verify dimensional conformity, surface treatment and force characteristics
• Aftermarket and service - to match replacement rings to engine requirements

Related standards

• Normative reference: ISO 6621-4 (Piston rings - General specifications)
• ISO piston-ring series: ISO 6621, ISO 6622, ISO 6623, ISO 6625, ISO 6626, ISO 6627 - consult these for complementary requirements and full ring-system specifications

Keywords: ISO 6624-1, piston rings, keystone rings, cast iron, internal combustion engines, ring dimensions, ring coatings, ring designation, engine design.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 6624-1
Third edition
2017-04
Internal combustion engines —
Piston rings —
Part 1:
Keystone rings made of cast iron
Moteurs à combustion interne — Segments de piston —
Partie 1: Segments trapézoïdaux en fonte
Reference number
©
ISO 2017
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved

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 . 6
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° . 7
5.6.1 General features. 7
5.6.2 Designation . 8
5.7 Type KBA — Asymmetrical barrel faced keystone ring 15° . 8
5.7.1 General features. 8
5.7.2 Designation . 9
5.8 Type KM — Taper faced keystone ring 15° . 9
5.8.1 General features. 9
5.8.2 Designation .10
6 Common features .11
6.1 Type T, TB, TBA, TM, K, KB, KBA, KM rings — Inside chamfered edges (KI) .11
6.2 Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) internal bevel or
internal step 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/coating configuration .13
6.4.1 Uncoated rings .13
6.4.2 Chromium plated, PVD coated or spray coated rings .14
7 Force factors .16
8 Dimensions .16
Bibliography .24
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
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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 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 third edition cancels and replaces the second edition (ISO 6624-1:2001), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— PVD coating thickness has been included with a new Table 8;
— updates have been made regarding technology improvements.
iv © ISO 2017 – All rights reserved

Introduction
ISO 6624 belongs to the series of International Standards dealing with piston rings for reciprocating
internal combustion engines. Others are ISO 6621, ISO 6622, ISO 6623, ISO 6625, ISO 6626 and ISO 6627
(see Bibliography for details).
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 refer to the specifications and requirements of ISO 6621-3 and
ISO 6621-4 before completing a selection.
.
INTERNATIONAL STANDARD ISO 6624-1:2017(E)
Internal combustion engines — Piston rings —
Part 1:
Keystone rings made of cast iron
1 Scope
This document specifies the essential dimensional features of keystone rings made of cast iron, types
T, TB, TBA, TM, K, KB, KBA and KM, having diameters from 70 mm up to and including 200 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 8 and Figures 9 to 16. Tables 9 and 10 give
the force factors for the different types of ring, while Table 11 and Table 12 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 10 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 1 — Type T
5.1.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast
iron, 6° keystone ring with a straight faced peripheral surface (T), of nominal diameter d = 90 mm (90) and
nominal width h = 2,5 mm (2,5), made of grey cast iron, subclass 12 (MC12), and having a 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 6624-1 T-90 × 2,5-MC12/CR2
5.2 Type TB — Symmetrical barrel faced keystone ring 6°
5.2.1 General features
See Table 10 for dimensions and forces.
2 © ISO 2017 – All rights reserved

Dimensions in millimetres
Key
1 reference plane
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 2 — Type TB
Table 1 — Symmetrical barrel dimensions
Dimensions in millimetres
a
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 3,40 2,8
±0,60 0,005.0,023
4,5 0,65 2,25 3,85 3,2
a
Gauge width h , informative only, shall be used only if agreed between manufacturer and customer.
5.2.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast iron, 6°
keystone ring with a symmetrical barrel faced peripheral surface (TB), of nominal diameter d = 90 mm (90) and
nominal ring width h = 2,5 mm (2,5), made of heat-treated martensitic spheroidal graphite cast iron, subclass 53
(MC53), and having a semi-inlaid spray coating on the peripheral surface with a minimum thickness of 0,2 mm
(SC4E). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-1 TB-90 × 2,5-MC53/SC4E
5.3 Type TBA — Asymmetrical barrel faced keystone ring 6°
5.3.1 General features
See Table 10 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 3 — Type TBA
4 © ISO 2017 – All rights reserved

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
4,50 0,70 1,05 ±0,35 3,20 0.0,010 0,015.0,050
a
h may be lowered for rings with reduced edge dimensions.
b
t or t or both may be varied as agreed between manufacturer and customer.
2 3
5.3.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624–1, being a cast iron,
6° keystone ring with an 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 heat-treated martensitic spheroidal graphite cast iron,
subclass 53 (MC53), and having a semi-inlaid spray coating on the peripheral surface with a minimum thickness
of 0,2 mm (SC4E). Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-1 TBA-90 × 2,5-MC53/SC4E
5.4 Type TM — Taper faced keystone ring 6°
5.4.1 General features
See Table 10 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 4 — Type TM
Table 3 — Taper
Dimensions in minutes
Internal twist feature de-
a
Code Taper Tolerance signs
a
Tolerance
+50 +60
b
M1 10
0 0
M2 30
M3 60
+60 +70
0 0
M4 90
M5 120
a
For chromium plated rings with a tapered peripheral surface that is not ground, the tolerance
+70 +80
shall be increased by 10 (e.g. M3 = 60 tolerance: ; M3 with internal features = 60 tolerance: ).
0 0
b
M1 not for rings with partly cylindrical peripheral surface.
5.4.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron, 6°
keystone ring with a 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 heat-treated grey cast iron, subclass 22 (MC22), and phosphate-coated all
over (PO). Parameters in parenthesis are used in the ISO ring designation:
6 © ISO 2017 – All rights reserved

Piston ring ISO 6624-1 TM1-90 × 2,5-MC22/PO
5.5 Type K — Straight faced keystone ring 15°
5.5.1 General features
See Table 11 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 5 — Type K
5.5.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron,
15° keystone ring with a straight faced peripheral surface (K), of nominal diameter d = 90 mm (90) and nominal
ring width h = 2,5 mm (2,5), made of carbidic cast iron, subclass 32 (MC32), and ferroxide coated all over (FE).
Parameters in parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-1 K-90 × 2,5-MC32/FE
5.6 Type KB — Symmetrical barrel faced keystone ring 15°
5.6.1 General features
See Table 1 for symmetrical barrel dimensions.
See Table 11 for dimensions and forces.
Dimensions in millimetres
Key
1 reference plane
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 6 — Type KB
5.6.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron, 15°
keystone ring with a barrel faced peripheral surface (KB), of nominal diameter d = 90 mm (90) and nominal ring
width h = 2,5 mm (2,5), made of malleable cast iron, subclass 41 (MC41), and having an inlaid spray coating on
the peripheral surface with a minimum thickness of 0,2 mm (SC4F). Parameters in parenthesis are used in the
ISO ring designation:
Piston ring ISO 6624-1 KB-90 × 2,5-MC41/SC4F
5.7 Type KBA — Asymmetrical barrel faced keystone ring 15°
5.7.1 General features
See Table 2 for asymmetrical barrel dimensions.
See Table 11 for dimensions and forces.
8 © ISO 2017 – All rights reserved

Dimensions in millimetres
Key
1 reference plane
2 top side identification mark
a
Due to manufacturing processing, side angle tolerances are not cumulative.
b
Nominal.
Figure 7 — Type KBA — Correction of details “X” and “Y”: show asymmetry more detailed
5.7.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-1, being a cast iron 15°
keystone ring with an asymmetrical barrel faced peripheral surface (KBA) of nominal diameter d = 90 mm (90)
and nominal ring width h = 2,5 mm (2,5), made of malleable cast iron, subclass 41 (MC41), and having an inlaid
spray coating on the peripheral surface with a minimum thickness of 0,2 mm (SC4F). Parameters in parenthesis
are used in the ISO ring designation:
Piston ring ISO 6624-1 KBA
...