ISO 6624-2:2003

INTERNATIONAL ISO
STANDARD 6624-2
First edition
2003-10-01

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 6624-2:2003(E)
©
ISO 2003

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ISO 6624-2:2003(E)
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ii © ISO 2003 — All rights reserved

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ISO 6624-2:2003(E)
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
4.2 Type HKB — Barrel faced half keystone ring 7° . 2
5 Common features. 4
5.1 Type HK and HKB — Half keystone ring .4
5.2 Chamfered edges — Type HK and HKB rings — Outside and/or inside chamfered edges
(KA, KI) . 6
5.3 Type HK and HKB rings (fully faced, semi-inlaid) — Plating/coating thickness. 6
6 Force factors . 7
7 Dimensions. 7
Bibliography . 16

© ISO 2003 — All rights reserved iii

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ISO 6624-2:2003(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 6624-2 was prepared by Technical Committee ISO/TC 22, Road vehicles.
This first edition of ISO 6624-2 cancels and replaces ISO/TR 6624-2:1988, 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
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ISO 6624-2:2003(E)
Introduction
ISO 6624 is one of a number of series of International Standards dealing with piston rings for reciprocating
[2], [3], [4], [5] [6], [7] [8] [9]
internal combustion engines. Others are ISO 6621 , ISO 6622 , ISO 6623 , ISO 6625 ,
[10], [11] [12]
ISO 6626 and ISO 6627 .
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 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 selection.

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INTERNATIONAL STANDARD ISO 6624-2:2003(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 and HKB, having diameters of from 38 mm up to and including 160 mm, used in reciprocating
internal combustion piston engines.
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 6621-4, Internal combustion engines — Piston rings — Part 4: General specifications
3 Overview
The half keystone ring types are specified in Table 1 and Figures 1 and 2. Their common features and the
dimensions of those features are specified in Tables 2 and 3 and Figures 3 to 8. Tables 4 and 5 give the force
factors for the different ring types, while Table 6 gives the dimensions and forces of half keystone rings.
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
See Table 6 for dimensions and forces.
h values are calculated based on h + 0,05 mm.
3 1
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ISO 6624-2:2003(E)

Key
1 reference plane
2 mark
a
Nominal.
b
t = 0,006 × h .
1
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 1
(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):
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
See Table 6 for dimensions and forces.
h values are calculated based on h + 0,05 mm.
3
1
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ISO 6624-2:2003(E)

Key
1 reference plane
2 mark
a
Nominal.
b
t = 0,006 × h .
1
Figure 2 — Type HKB
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ISO 6624-2:2003(E)
Table 1 — Gauge width (h ) and barrel dimensions for symmetrical barrel faced compression rings
8
Dimensions in millimetres
a
h h h h tol. h t ,  t
h
1 25 26 26 27 2 3
8
1,0 0,25 0,50 ± 0,15 0,75 0,50
0,003.0,012
1,2 0,30 0,60 0,90 0,60
± 0,20
1,5 0,35 0,75 1,15 0,80
± 0,25
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 2,05 1,60
± 0,40
3,0 0,50 1,50 2,50 2,00
± 0,50
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 manufacturer and client.
8

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 1
(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):
Piston ring ISO 6624-2 HKB - 90 ×× 1,5 - MC12/CR2
××
5 Common features
5.1 Type HK and HKB — Half keystone ring
5.1.1 Uncoated rings

a) Type HK b) Type HKB
Key
1 mark
Figure 3 — Uncoated rings
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ISO 6624-2:2003(E)
5.1.2 Chromium plated or spray coated rings
5.1.2.1 Fully faced

a) Type HK b) Type HKB
Key
1 mark
Figure 4 — Fully faced rings
5.1.2.2 Semi-inlaid

a) Type HK b) Type HKB
Key
1 mark
Figure 5 — Semi-inlaid rings

5.1.2.3 Inlaid (not recommended for chromium plated rings)

a) Type HK b) Type HKB
Key
1 mark
Figure 6 — Inlaid rings

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ISO 6624-2:2003(E)
5.2 Chamfered edges — Type HK and HKB rings — Outside and/or inside chamfered edges
(KA, KI)

a) HK rings b) HKB rings
Key
1 mark

Figure 7 — Outside and inside chamfered edges (KA, KI)
Table 2 — KA and KI dimensions
Dimensions in millimetres
d KA KI
1
0,2 max. 0,2 max.
38 u d < 50
1
50 u d < 125 0,3 ± 0,1 0,3 ± 0,15
1
125 u d u 160
0,4 ± 0,1 0,4 ± 0,15
1

5.3 Type HK and HKB rings (fully faced, semi-inlaid) — Plating/coating thickness

a) Fully faced b) Semi-inlaid c) Inlaid
Figure 8 — Plating/coating thickness
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ISO 6624-2:2003(E)
Table 3 — Plating/coating thickness
Dimensions in millimetres
Chromium plating Spray coating Thickness
code code min.
CRF
— 0,005
CR1 SC1
0,05
CR2 SC2 0,10
a a
0,15
CR3 SC3
a a
0,20
CR4 SC4
a
Not recommended for rings h u 1,5.
1

6 Force factors
The tangential and diametral forces given in Table 6 shall be corrected when additional features or materials
2
other than grey cast iron with a modulus of elasticity, E , of 100 GN/m , or both, are used.
n
For common features, multiplier correction factors given in Tables 4 and 5 and the force correction factors
given in ISO 6621-4 shall be used.
Table 4 — Force correction factors for HK and HKB rings with features KA or KI
Factor
KA KI
0,98 0,98

Table 5 — Force correction factors for chromium plated and spray coated HK and HKB rings
(fully faced, semi-inlaid and inlaid type)
d Factor
1
CRF CR1 CR2/SC1 CR3/SC2 CR4/SC3 SC4
mm
38 u d < 50
1 0,81 0,70 0,64 — —
1
50 u d < 75
1 0,90 0,85 0,81 0,75 0,71
1
75 u d < 100
1 0,92 0,88 0,85 0,81 0,77
1
100 u d < 125
1 0,94 0,91 0,88 0,86 0,83
1
125 u d u 160
1 0,95 0,92 0,90 0,88 0,85
1

7 Dimensions
See Table 6.
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