ISO 6624-4:2003

INTERNATIONAL ISO
STANDARD 6624-4
First edition
2003-10-01

Internal combustion engines — Piston
rings —
Part 4:
Half keystone rings made of steel
Moteurs à combustion interne — Segments de piston —
Partie 4: Segments semi-trapézoïdaux en acier




Reference number
ISO 6624-4:2003(E)
©
ISO 2003

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ISO 6624-4:2003(E)
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ii © ISO 2003 — All rights reserved

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ISO 6624-4:2003(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 Type HK and HKB rings — Outside and inside rounded edges. 5
5.3 Type HK and HKB rings (fully faced and inlaid) — Plating/coating thickness. 6
5.4 Type HK and HKB rings — Nitrided case depth . 7
6 Force factors . 8
7 Dimensions. 8
Bibliography . 18

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ISO 6624-4:2003(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 6624-4 was prepared by Technical Committee ISO/TC 22, Road vehicles.
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 6624-4:2003(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 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.

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INTERNATIONAL STANDARD ISO 6624-4:2003(E)

Internal combustion engines — Piston rings —
Part 4:
Half keystone rings made of steel
1 Scope
This part of ISO 6624 specifies the essential dimensional features of half keystone rings made of steel, 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 to 5 and Figures 3 to 8. Table 6 gives the force factors
for the different ring types, while Table 7 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 6624-4:2003(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 6624-4, being a 7° half keystone ring
made of steel with a straight faced peripheral surface (HK), of nominal diameter d = 60 mm (60), of nominal ring width
1
h = 1,2 mm (1,2), made of CrSi alloyed steel subclass 62 (MC62), and having a chromium plated peripheral surface with
1
a minimum thickness of 0,1 mm (CR2):
Piston ring ISO 6624-4 HK - 60 × 1,2 - MC62/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 6624-4:2003(E)

Key
1 reference plane
2 mark
a
Nominal.
b
t = 0,006 × h .
1
Figure 2 — Type HKB
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ISO 6624-4:2003(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
1,2 0,30 0,60 ± 0,20 0,90 0,003.0,012 0,60
1,5 0,35 0,75 1,15 0,80
± 0,25
1,75 0,35 0,85 1,35 1,00
± 0,30
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 2,50 2,00
± 0,50
0,005.0,020
3,5 0,55 1,75 2,95 2,40
± 0,50
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 6624-4, being a half keystone ring
made of steel with a barrel faced peripheral surface (HKB), of nominal diameter d = 60 mm (60), of nominal ring width
1
h = 1,5 mm (1,5), made of martensitic steel 11%Cr (min.) subclass 65 (MC65), and nitrided on the peripheral surface and
1
side faces (NT) to a depth of 0,050 mm min. on the peripheral surface (050), with an associated side face depth of
0,015 mm min.:
Piston ring ISO 6624-4 HKB - 60××××1,5 - MC65/NT050
5 Common features
5.1 Type HK and HKB — Half keystone rings
5.1.1 Nitrided rings

a) Type HK b) Type HKB
Key
1 mark
Figure 3 — Nitrided rings
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ISO 6624-4:2003(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 Inlaid (not recommended for chromium plated rings)

a) Type HK b) Type HKB
Key
1 mark
Figure 5 — Inlaid rings
5.2 Type HK and HKB rings — Outside and inside rounded edges

Figure 6 — Outside and inside rounded edges

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ISO 6624-4:2003(E)
Table 2 — h and h dimensions
x y
Dimensions in millimetres
h h h
1 x y
max. max.
1,2 0,25 0,3
1,5
0,3 0,35
1,75
2,0
2,5
0,3 0,4
3,0
3,5

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


a) Fully faced b) Inlaid
Figure 7 — Plating/coating thickness

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

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ISO 6624-4:2003(E)
5.4 Type HK and HKB rings — Nitrided case depth

Key
1 mark
Figure 8 — Nitrided case depth
Table 4 — Nitrided case depth of peripheral surface and bottom side face
Dimensions in millimetres
Nitrided case depth min.
Code
Peripheral surface Bottom side face
NB030 0,03 0,010
NB050 0,05 0,015
NB070 0,07 0,020
NB090 0,09 0,020
NB110 0,11 0,030
NB130 0,13 0,030
NOTE Nitrided case depth on top side face and on inside surface not
specified.

Table 5 — Nitrided case depth of peripheral surface and side faces
Dimensions in millimetres
Nitrided case depth min.
Code
Peripheral surface Side faces
NT030
0,03 0,010
NT050 0,05 0,015
NT070
0,07 0,020
NT090 0,09 0,020
NT110 0,11 0,030
NT130
0,13 0,030
NOTE Nitrided case depth on inside surface not specified.


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ISO 6624-4:2003(E)
6 Force factors
The tangential and diametral forces given in Table 7 shall be corrected when additional features are being
used.
For common features, multiplier correction factors given in Table 6 shall be used. The force correction factors
for the ratio m/(d − a ), as given in ISO 6621-4, shall be used.
1 1
Table 6 — Force correction factors for chromium plated, spray coated and nitrided HK and HKB rings
Factor
d
1
NB030…NB130
CRF CR1 CR2/SC1 CR3 SC2 CR4/SC3 SC4
mm
NT030…NT130
38 u d < 50
1 0,80 0,71 — 0,63 — — 1,03
1
50 u d < 75
1 0,87 0,81 0,75 0,75 0,69 0,64 1,03
1
75 u d < 100
1 0,91 0,86 0,82 0,82 0,78 0,74 1,03
1
100 u d < 125
1 0,93 0,89 0,86 0,
...