ISO 6624-2:2016

INTERNATIONAL ISO
STANDARD 6624-2
Second edition
2016-02-15
Internal combustion engines —
Piston rings —
Part 2:
Half keystone rings made of cast iron
Moteurs à combustion interne — Segments de piston —
Partie 2: Segments demi-trapézoïdaux fabriqués en fonte moulée
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Overview . 1
4 Ring types and designation examples . 1
4.1 Type HK — Straight faced half keystone ring 7° . 1
4.1.1 General features. 1
4.1.2 Designation . 2
4.2 Type HKB — Barrel faced half keystone ring 7° . 2
4.2.1 General features. 2
4.2.2 Designation . 4
4.3 Type HKBA — Asymmetrical barrel faced half keystone ring 7°(h ≥ 1,2 mm) . 4
4.3.1 General features. 4
4.3.2 Designation . 5
5 Common features . 5
5.1 Type HK, HKB and HKBA — Half keystone ring . 5
5.1.1 Uncoated rings . 5
5.1.2 Chromium plated or spray coated rings . 6
5.2 Chamfered edges — Type HK, HKB and HKBA rings — Outside and/or inside
chamfered edges (KA, KI) . 7
5.3 Type HK, HKB and HKBA rings (fully faced, semi-inlaid) — Plating/coating thickness . 7
6 Force factors . 8
7 Dimensions and forces . 8
Annex A (normative) Calculation of measurement width h of half keystone rings .17
Bibliography .18
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
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electrotechnical standardization.
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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
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The committee responsible for this document is ISO/TC 22, Road vehicles, Subcommittee SC 34,
Propulsion, powertrain and powertrain fluids.
This second edition cancels and replaces the first edition (ISO 6624-2:2003), which has been
technically revised.
ISO 6624 consists of the following parts, under the general title Internal combustion engines — Piston rings:
— Part 1: Keystone rings made of cast iron
— Part 2: Half keystone rings made of cast iron
— Part 3: Keystone rings made of steel
— Part 4: Half keystone rings made of steel
iv © ISO 2016 – All rights reserved

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.
INTERNATIONAL STANDARD ISO 6624-2:2016(E)
Internal combustion engines — Piston rings —
Part 2:
Half keystone rings made of cast iron
1 Scope
This part of ISO 6624 specifies the essential dimensional features of half keystone rings made of cast
iron, types HK, HKB and HKBA, having nominal diameters from 38 mm up to, and including, 160 mm,
used in reciprocating internal combustion piston engines for road vehicles and other applications.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. 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 Overview
The half keystone ring types are specified in Tables 1 and 2 and Figures 1 to 3. Their common features
and the dimensions of those features are specified in Tables 3 and 4 and Figures 4 to 9. Tables 5 and 6
give the force factors for the different ring types, while Table 7 gives the dimensions and forces of half
keystone rings.
The common features and dimensional tables presented in this part of ISO 6624 constitute a broad
range of variables and, in selecting a particular ring type, the designer shall 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 selection.
4 Ring types and designation examples
NOTE For the angle of half keystone rings, the same definition and measurement apply as for keystone rings
(see ISO 6621-2).
4.1 Type HK — Straight faced half keystone ring 7°
4.1.1 General features
Figure 1 shows the general features of piston ring type HK.
See Table 7 for dimensions and forces.
h values are calculated based on Annex A.
a
b
Key
1 reference plane (ring is positioned flat against datum A)
2 top side identification mark
a
Nominal.
b
t = 0,006 × h .
Figure 1 — Type HK
4.1.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-2, being a 7° half
keystone ring made of cast iron, with a straight-faced peripheral surface (HK), of d = 90 mm (90), of nominal
ring width h = 1,5 mm (1,5), made of heat treated martensitic spheroidal graphite cast iron, subclass 53 (MC53),
and having a chromium plated peripheral surface with a minimum thickness 0,1 mm (CR2). Parameters in
parenthesis are used in the ISO ring designation:
Piston ring ISO 6624-2 HK - 90 × 1,5 - MC53/CR2
4.2 Type HKB — Barrel faced half keystone ring 7°
4.2.1 General features
Figure 2 shows the general features of piston ring type HKB.
See Table 7 for dimensions and forces.
h values are calculated based on Annex A.
2 © ISO 2016 – All rights reserved

a
Key
1 reference plane (ring is positioned flat against datum A)
2 top side identification mark
a
Nominal.
Figure 2 — Type HKB
Table 1 — Symmetrical barrel dimensions and gauge width (h )
Dimensions in millimetres
a
h h h h tol. h t , t h
1 25 26 26 27 2 3 8
1,2 0,30 0,60 ±0,20 0,90 0,002.0,012 0,60
1,5 0,35 0,75 ±0,25 1,15 0,80
1,75 0,35 0,85 ±0,30 1,35 1,00
0,003.0,015
2,0 0,40 1,00 ±0,30 1,60 1,20
2,5 0,45 1,25 ±0,40 2,05 1,60
3,0 0,50 1,50 ±0,50 2,50 2,00
0,005.0,020
3,5 0,55 1,75 ±0,50 2,95 2,40
a
Gauge width (h ) only informative; may be used only if agreed between the manufacturer and the customer.
4.2.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-2, being a 7° half
keystone ring made of cast iron, with a barrel faced peripheral surface (HKB), of d = 90 mm (90), of nominal ring
width h = 1,5 mm (1,5), made of non-heat-treated 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 6624-2 HKB - 90 × 1,5 - MC12/CR2
4.3 Type HKBA — Asymmetrical barrel faced half keystone ring 7°(h ≥ 1,2 mm)
4.3.1 General features
See Table 7 for dimensions and forces.
h values are calculated based on Annex A.
a
Key
1 reference plane (ring is positioned flat against datum A)
2 top side identification mark
a
Nominal.
Figure 3 — Type HKBA
4 © ISO 2016 – All rights reserved

Table 2 — Asymmetrical barrel dimensions
Dimensions in millimetres
a b b
h h h h tol. h t t
1 25 26 26 27 2 3
1,2 0,28 0,43 0,90 0…0,005 0,005…0,016
±0,15
1,5 0,35 0,50 1,15 0.0,006 0,007.0,022
1,75 0,35 0,55 1,35 0,008.0,025
±0,20 0.0,007
2,0 0,40 0,60 1,50 0,009.0,030
2,5 0,45 0,70 1,80 0,011.0,035
±0,25 0.0,008
3,0 0,55 0,80 2,10 0,012.0,038
3,5 0,60 0,90 ±0,30 2,40 0.0,009 0,012.0,040
a
h may be lowered for rings with reduced edge dimensions.
b
t and/or t may be varied as agreed between the manufacturer and the customer.
2 3
4.3.2 Designation
EXAMPLE Designation of a piston ring complying with the requirements of ISO 6624-2, being a 7° half
keystone ring made of cast iron, with an asymmetrical barrel faced peripheral surface (HKBA), of d = 90 mm
(90), of nominal ring width h = 1,5 mm (1,5), made of non-heat-treated 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 6624-2 HKBA - 90 × 1,5 - MC12/CR2
5 Common features
5.1 Type HK, HKB and HKBA — Half keystone ring
5.1.1 Uncoated rings
1 1
a) Type HK b) Type HKB c) Type HKBA
Key
1 top side identification mark
Figure 4 — Uncoated rings
5.1.2 Chromium plated or spray coated rings
5.1.2.1 Fully faced
1 1
a) Type HK b) Type HKB c) Type HKBA
Key
1 top side identification mark
Figure 5 — Fully faced rings
5.1.2.2 Semi-inlaid
1 1 1
a) Type HK b) Type HKB c) Type HKBA
Key
1 top s
...