GB/T 17879-2023 Gear - Surface temper etch inspection after grinding, chemical method
1 Scope
This document specifies procedures and requirements for the detection and classification of localized overheating on ground surfaces by chemical etch methods.
The process described in this document is typically used on ground surfaces; however, it is also useful for the detection of surface anomalies that result from post-heat treatment machining such as hard turning, milling, deburring and chamfering processes. Surface metallurgical anomalies caused by carburization or decarburization are also readily detectable with this process.
The methods described in this document are more sensitive to changes in surface hardness than most surface hardness testing methods. Some methods which have been used in the past are no longer recommended.
This document is applicable to steel parts such as gears, shafts, splines and bearings. It is not applicable to nitrided parts and stainless steel parts.
Note: This process, although at times called "nital etch", is not intended to be confused with other processes also known as "nital etch".
The surface temper etch procedure is performed after grinding and before additional finishing operations such as superfinishing, shot peening and honing.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
4 Apparatus and requirements
4.1 Container materials
Container materials shall not react with the solutions contained, nor damage the parts to be processed. All containers should be labelled with the solution contained and covered when not in use. Containers should be labelled according to relevant regulations.
4.2 Inspection area
The area to be inspected shall be sufficiently illuminated to be free of shadows and reflections. The light intensity should not be lower than 2,200lx (≈200 foot candles).
4.3 Cleaner
An alkaline cleaner, vapour degreaser or equivalent cleaning process shall be used.
4.4 Timing device
A suitable timing device shall be used for the uniform processing of all parts in a group.
4.5 Grey scale reference
A suitable grey scale reference should be used.
Figure 1 is an example of a suitable grey scale reference. Use of a sample part with known indications to exhibit surface tempering is also recommended.
Figure 1 is an approximate reproduction of a commercially available grey scale. The reproduction shown in this image is not accurate due to variance in graphic reproduction quality and is provided for reference only. It shall not be used for inspection in conformity with this document.
The grey scale card should be replaced at regular intervals.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Apparatus and requirements
4.1 Container materials
4.2 Inspection area
4.3 Cleaner
4.4 Timing device
4.5 Grey scale reference
5 Reagents
5.1 Cleaning materials
5.2 Nitric acid
5.3 Hydrochloric acid
5.4 Alcohol
5.5 Water
5.6 Alkaline solution
5.7 Rust-preventive oil
6 Inspection procedure
6.1 General
6.2 Cleaning
6.3 Etching
7 Inspection criteria
7.1 Visual appearance and classification
7.2 Surface hardness effects
8 Temper etch discoloration removal
9 Rework of surface-tempered parts
10 Operator qualification
11 Maintenance and control
12 Safety and environmental precautions
13 Specifications and documentation
Bibliography
