Internal combustion engines - Piston rings - Part 1: Keystone rings made of cast iron
1Key Takeaways
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.
2Expert Interpretation
This article provides an in-depth analysis of the ISO 6624-1:2017 international standard's technical requirements for 70-200mm cast iron trapezoidal piston rings. It covers the dimensional parameters, mechanical properties, surface treatments, and correction factors for eight ring types (T/TB/TBA/TM/K/KB/KBA/KM). It also provides comparative data and engineering application guidance for rings with 6° and 15° taper angles.
Analysis of the core content of the standard
ISO 6624-1:2017 specifies the key technical requirements for cast iron trapezoidal piston rings in the 70-200mm diameter range, which are mainly suitable for reciprocating internal combustion engines. The standard includes the following key elements:
| Ring type classification | Cone angle | Face type | Typical application |
|---|---|---|---|
| Type T/K | 6°/15° | Straight face | Basic seal |
| Type TB/KB | 6°/15° | Symmetrical barrel face | High load condition |
| Type TBA/KBA | 6°/15° | Asymmetric barrel surface | Directional lubrication |
| Type TM/KM | 6°/15° | Conical surface (10'-120') | Quick running-in |
Key Technical Parameters
1. Dimension Tolerance System
The standard establishes a strict dimensional control system. Key parameters include:
- Radial wall thickness (a1): Tolerance range ±0.15mm~±0.20mm
- Ring width (h1): Phosphate treated rings allow special tolerances of +0.01/-0.024mm
- Closing gap (s1): controlled by diameter, maximum 0.6±0.3mm
2. Mechanical performance requirements
Based on the benchmark force value of gray cast iron (elastic modulus 100GN/m²):
| Ring type | Tangential force Ft(N) | Radial force Fd(N) | Force ratio Fd/Ft |
|---|---|---|---|
| 6° trapezoidal ring | 9.9-65.8 | 21.3-76.8 | 2.15 |
| 15° trapezoidal ring | 11.2-63.4 | 24.0-74.2 | 2.15 |
Surface Treatment Technology
Plating/Coating Configuration Scheme
The standard defines three surface treatment methods and their correction factors:
- Full Surface Treatment: Applicable to chrome plating (CR1-CR4) and PVD coating (PC series)
- Semi-Inlaid Treatment: Spray coating (SC series) retains a 0.1-0.3mm untreated area on the edge
- Full Inlaid Treatment: Only the working surface is treated, with a force correction factor of 0.77-0.87
Typical Application Cases:
TB-90×2.5-MC53/SC4E indicates a 6° symmetrical barrel-surface trapezoidal ring with a diameter of 90mm and a width of 2.5mm, made of ductile iron and semi-inlaid with a 0.2mm spray coating.
Standard Evolution and Implementation Recommendations
Major Technical Changes
- Added PVD coating thickness requirements (Table 8)
- Updated spray coating technical parameters
- Refer to the force calculation method for 15° trapezoidal rings
Engineering Application Recommendations
- When selecting a ring type, the material specification of ISO 6621-3/4 should be referred to simultaneously.
- The taper tolerance of chrome-plated rings needs to be increased by an additional 10'.
- Inner chamfer design is not recommended for 15° trapezoidal rings.
- The maintenance dimension should use the radial wall thickness of the adjacent smaller nominal diameter.