Microsoft Word C027929e doc Reference number ISO 6624 3 2001(E) © ISO 2001 INTERNATIONAL STANDARD ISO 6624 3 First edition 2001 08 15 Internal combustion engines — Piston rings — Part 3 Keystone rings[.]
Type T — Straight faced keystone ring 6°
See Table 12 for dimensions and forces.
1 Reference plane a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
This example features a piston ring designed in accordance with ISO 6624-3 specifications, made from CrSi alloyed steel (subclass 62 MC62) It is a 6° keystone ring with a straight-faced peripheral surface (T), featuring a nominal diameter of 90 mm and a ring width of 2.5 mm The piston ring's peripheral surface is fully chromium plated, with a minimum chromium plating thickness of 0.1 mm (CR2), ensuring durability and corrosion resistance.
Piston ring ISO 6624-3 T - 90 ´´´´ 2,5-MC62/CR2
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Type TB — Symmetrical barrel faced keystone ring 6°
See Table 12 for dimensions and forces.
1 Reference plane a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
4,0 0,60 2,00 ±0,60 3,40 0,005 0,023 2,8 a Gauge widthh 8 , informative only, shall be used only if agreed between manufacturer and client.
This article describes a piston ring that complies with ISO 6624-3 standards, made of martensitic steel (11% Cr minimum), subclass 65 (MC65) It is a 6° keystone steel piston ring with a barrel-faced peripheral surface (TB), designed for a nominal diameter of 90 mm and a ring width of 2.5 mm The ring is nitrided on the peripheral surface and side faces to a minimum depth of 0.070 mm on the peripheral surface and at least 0.020 mm on the side face, ensuring enhanced durability and wear resistance.
Piston ring ISO 6624-3 TB - 90 ´´´´ 2,5-MC65/NT070
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Type TBA — Asymmetrical barrel faced keystone ring 6°
See Table 12 for dimensions and forces.
2 Mark a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
0,013 0,045 a h25 may be lowered for rings with reduced edge dimensions. b t2 ort3 or both may be varied as agreed between manufacturer and client.
This example features a piston ring designed in compliance with ISO 6624-3 standards, made of martensitic steel (17% Cr minimum), classified as subclass 66 (MC66) It is a 6° keystone steel ring with an asymmetrical barrel-faced peripheral surface (TBA), having a nominal diameter of 90 mm and a ring width of 2.5 mm The piston ring is nitrided on both the peripheral surface and side faces to enhance wear resistance, achieving a minimum nitriding depth of 0.070 mm on the outer surface and at least 0.020 mm on the side faces This design ensures optimal sealing, durability, and performance in engine applications.
Piston ring ISO 6624-3 TBA - 90 ´´´´ 2,5-MC66/NT070
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Type TM — Taper faced keystone ring 6°
See Table 12 for dimensions and forces.
2 Mark a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
Code Taper Tolerance a Internal twist feature designs
For chromium-plated rings featuring a tapered peripheral surface that has not been ground, the tolerance must be increased by 10 units; for example, the M3 tolerance should be adjusted to +70, and the M3 with internal features to +80 Additionally, the M1 tolerance is not applicable for rings with a partially cylindrical peripheral surface.
4.4.2 Designation © ISO 2001 – All rights reserved 9
Type K — Straight faced keystone ring 15°
See Table 13 for dimensions and forces.
1 Reference plane a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
The example piston ring is designed in compliance with ISO 6624-3 standards, featuring a steel, 15° keystone profile with a straight-faced peripheral surface (K) It has a nominal diameter of 90 mm and a ring width of 2.5 mm, crafted from CrMoV alloyed steel (subclass 61, MC61) The piston ring also includes a fully faced chromium-plated peripheral surface with a minimum thickness of 0.1 mm, ensuring durability and corrosion resistance.
Piston ring ISO 6624-3 K - 90 ´´´´ 2,5-MC61/CR2
Copyright International Organization for Standardization
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Type KB — Symmetrical barrel faced keystone ring 15°
See Table 1 for symmetrical barrel dimensions See Table 13 for dimensions and forces.
1 Reference plane a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
Type KBA — Asymmetrical barrel faced keystone ring 15°
See Table 2 for asymmetrical barrel dimensions See Table 13 for dimensions and forces.
1 Reference plane a Due to manufacturing processing, side angle tolerances are not cumulative.
This piston ring complies with ISO 6624-3 standards, featuring a 15° keystone design with an asymmetrical barrel-faced peripheral surface (KBA) Made of martensitic steel (minimum 17% Cr, subclass MC66), it has a nominal diameter of 90 mm and a ring width of 2.5 mm The ring is nitrided on the peripheral surface and side faces to a minimum depth of 0.070 mm on the peripheral surface and a minimum of 0.020 mm on the side faces, ensuring enhanced durability and corrosion resistance.
Piston ring ISO 6624-3 KBA - 90 ´´´´ 2,5-MC66/NT070
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Type KM — Taper faced keystone ring 15°
See Table 3 for taper See Table 13 for dimensions and forces.
2 Mark a Due to manufacturing processing, side angle tolerances are not cumulative. b Nominal.
This example describes a piston ring that complies with ISO 6624-3 standards, made of CrMoV alloyed steel (subclass 61 MC61) It is a steel, 15° keystone ring with a 10° tapered faced peripheral surface (KM1) and a nominal inner diameter of 90 mm, along with a ring width of 2.5 mm The piston ring features a fully faced chromium-plated peripheral surface with a minimum thickness of 0.1 mm, ensuring durability and resistance to wear.
Piston ring ISO 6624-3 KM1 - 90 ´´´´ 2,5-MC61/CR2 © ISO 2001 – All rights reserved 13
Type T, TB, TBA, TM, K, KB, KBA, KM rings — Outside and inside rounded edges
Outside and inside rounded edges are shown in Figure 9 and Figure 10; their dimensions are given in Table 4.
Figure 9 — Outside and inside rounded edges
Dimensions in millimetres h 1 h x h y max max.
Type T, TB, TBA, TM, K, KB, KBA, KM rings (positive twist type) — Internal bevel top side
An internal bevel is not recommended for the 15° keystone rings with ring width h 1 given in the "nominal value of ring width" column 1 of Table 13.
Figure 11 — Internal bevel top side (IF)
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Type TM or KM rings with partly cylindrical machined (LM) or lapped (LP) peripheral surface
Figure 12 — Partly cylindrical peripheral surface
Dimensions in millimetres h 1 h 24 max. h 24 max. each side of gap up to 30°
Partly cylindrical peripheral surfaces shall be visible.
Type T, TB, TBA, TM, K, KB, KBA, KM rings — Plating or coating configuration
5.4.1 Chromium plated or spray coated rings
Semi-inlaid types are not recommended. © ISO 2001 – All rights reserved 15
See Figure 13. a) T or K rings b) TB or KB rings c) TBA or KBA rings d) TM or KM rings
Inlaid types are not recommended for chromium plated rings See Figure 14. a) T or K rings b) TB or KB rings c) TBA or KBA rings d) TM or KM rings
Copyright International Organization for Standardization
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See Figure 15. a) T or K rings b) TB or KB rings c) TBA or KBA rings d) TM or KM rings
Table 8 — Nitrided case depth of peripheral surface
Code Nitrided case depth min.
NP130 0,130 © ISO 2001 – All rights reserved 17
Table 9 — Nitrided case depth of peripheral surface and side faces
NOTE The nitrided case depth on the inside surface is not specified.
The tangential and diametral forces given in Tables 12 and 13 shall be corrected when additional features are used.
The force correction factor for the ration m/d 1 – a 1 given in ISO 6621-4 shall be used.
For common features, the multiplier correction factors given in Tables 10 and 11 shall be used.
Table 10 — Force correction factors for chromium plated or spray coated T, TB, TBA, TM, K, KB, KBA and
KM rings with features IF and taper
Table 11 — Force correction factors for chromium plated, spray coated or nitrided T, TB, TBA, TM, K, KB,
KBA and KM rings d 1 Factor
NP030 NP130 mm CRF CR1 CR2/SC1 CR3/SC2 CR4/SC3 SC4 NT030 NT130
Copyright International Organization for Standardization
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Table 12 — Dimensions of T, TB, TBA, TM keystone rings 6°
Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
Copyright International Organization for Standardization
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Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
For intermediate sizes (e.g repair sizes), the radial wall thickness of the next smaller nominal diameter should be applied.
The values for F_t and F_d provided in Table 12 are based on steel with a standard modulus of elasticity (E_n) of 210 GN/m² Multiplying factors, as specified in ISO 6621-4, should be applied to account for different conditions Mean forces are calculated considering the nominal radial wall thickness (a₁) and the average trapezoidal ring width (h₃), ensuring accurate assessments for structural design and analysis.
Table 13 — Dimensions of K, KB, KBA, KM keystone rings 15°
Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
Copyright International Organization for Standardization
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Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
Keystone ring width Closed gap Tangential force
Nominal value of ring width
For phos- phated PO surface:
For phos- phated PO surface:
For phos- phated PO surface:
For intermediate sizes (e.g repair sizes), the radial wall thickness of the next smaller nominal diameter should be applied.
The values for F t and F d provided in Table 13 apply to steel with a common modulus of elasticity (E n) of 210 GN/m² Multiplying factors, as outlined in ISO 6621-4, should be applied to adjust these values Mean force calculations are based on the nominal radial wall thickness (a₁) and the mean trapezoidal ring width (h₃), ensuring accurate design parameters for structural assessments involving steel components.
NOTE 2 For the sole purpose of this part of ISO 6624, the assumed average ratio F d /F t is 2,15.
NOTE 3 For measurement of keystone ring width see ISO 6621-2 item 3.2.1.
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[1] ISO 1101, Geometrical Product Specifications (GPS) — Geometrical tolerancing — Tolerances of form, orientation, location and run-out.
[2] ISO 6621-1, Internal combustion engines — Piston rings — Part 1: Vocabulary.
[3] ISO 6621-2:— 2) , Internal combustion engines — Piston rings — Part 2: Inspection measuring principles.
[4] ISO 6621-3, Internal combustion engines — Piston rings — Part 3: Material specifications.
[5] ISO 6621-4:— 3) , Internal combustion engines — Piston rings — Part 4: General specifications.
[6] ISO 6621-5, Internal combustion engines — Piston rings — Part 5: Quality requirements.
[7] ISO 6622-1:— 4) , Internal combustion engines — Piston rings— Part 1: Rectangular rings made of cast iron.
[8] ISO 6622-2:— 5) , Internal combustion engines — Piston rings — Part 2: Rectangular rings of narrow width.
[9] ISO 6623:— 6) , Internal combustion engines — Piston rings — Scraper rings made of cast iron.
[10] ISO 6625, Internal combustion engines — Piston rings — Oil control rings.
[11] ISO 6626, Internal combustion engines — Piston rings — Coil-spring-loaded oil control rings.
[12] ISO 6626-2:— 7) , Internal combustion engines — Piston rings — Part 2: Coil-spring-loaded oil control rings of narrow width made of cast iron.
[13] ISO 6627, Internal combustion engines — Piston rings — Expander/segment oil-control rings
2) To be published (Revision of ISO 6621-2:1984)
3) To be published (Revision of ISO 6621-4:1988)
4) To be published (Revision of ISO 6622-1:1986)
5) To be published (Revision of ISO/TR 6622-2:1988)
6) To be published (Revision of 6623:1986)
Copyright International Organization for Standardization
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