A Study on the Occurrence of Discouloration / Blackening / Dezincification / Corrosion on 7.62 mm Ball Ammunition Manufactured by Ordnance Factory Varangaon

Abstract

This study examines the persistent degradation of 7.62 mm ball ammunition from Ordnance Factory Varangaon (OFV), characterized by unwanted changes in appearance and structural integrity. Using a combined analytical and qualitative approach, the research assesses the success of modified protective treatments, the role of sulfur-based contaminants, and the effects of storage and packaging. Key results demonstrate that sulfur, originating from packaging and wax, is a significant cause of surface blackening. Furthermore, while the new protective coating process requires thorough confirmation, relying solely on immersion cleaning proves insufficient for preventing recurring corrosion. The research concludes by suggesting ways to refine the protective coating process, investigate new cleaning techniques, and establish a system of continuous assessment to enhance product quality and user satisfaction. This research provides insights into quality management within ammunition manufacturing, emphasizing the need for robust evaluation, process verification, and innovative approaches to solve longstanding corrosion and degradation problems.

Introduction

Since 2012, multiple depots reported blackening (discoloration) of 7.62mm belted ammunition cartridge cases. Initial inspections by SQAE(A) Varangaon from 2013 onward identified the issue and approved hand rumbling with toluene and cotton as a temporary rectification method. Later, CQA(Met) confirmed chromic acid solution effective in removing black stains, though toluene remained in use.

A Board of Officers (BOO) investigated and recommended stricter quality control on packing materials, including millboard, wax, and gaskets, which were found to contribute sulfur contamination—identified as the primary cause of blackening. The presence of sulfur in wax, cleaning chemicals, and packing materials was confirmed by tests from various labs including CSIR-NML.

A Study Group and Task Force formed by CQA(A) recommended switching packing materials to PPC (polypropylene corrugated sheets) and adopting dip cleaning methods using chemical solutions developed by CSIR-NML for better rectification. OFV made changes in manufacturing, including chemical passivation and removal of previous cleaning steps, but continued blackening issues persisted, partly due to proprietary chemicals whose specifications were not disclosed.

Trials and testing from 2015 to 2024 included different cleaning and passivation methods. The chromate passivation process at OFV was found to be non-compliant with specifications (JSS 0461-01) and inconsistently applied, possibly causing poor passivation and contributing to blackening.

Recommendations include fully automating the chromate passivation process, replacing packing carton materials with non-sulfur-containing alternatives, and continuing dip cleaning as a corrective method until better processes are implemented. Some blackened lots were segregated, rectified, and reissued after proof testing, while worst-affected rounds were discarded.

Despite ongoing improvements, blackening remains a concern, with debates over whether it is caused by storage environment, chemical contamination, or natural brass aging. Recent audits stressed the need for strict adherence to specifications and improved packaging to prevent recurrence.

Conclusion

This study investigated critical facets of the revised passivation process validation, the efficacy of dip cleaning, and the contentment with implemented corrective measures. Utilizing a range of statistical techniques, including chi-square tests, logistic regression, paired t-tests, and ordinal regression, several key findings were identified. Initially, the validation of the altered passivation procedure (H1) revealed no notable correlation between respondent experience and their assessment of the validation. This implies that experience did not impact perceptions of the process\'s efficacy. Secondly, the dip cleaning\'s effectiveness (H4) was statistically insignificant, as both the paired t-test and logistic regression demonstrated that it did not substantially mitigate corrosion recurrence. This underscores the necessity to investigate alternative or complementary cleaning approaches to better address corrosion issues. Concerning satisfaction with corrective actions (H5), the analysis indicated that although overall contentment was average, the passivation process\'s effectiveness significantly predicted increased satisfaction. However, satisfaction levels remained consistent across different roles, suggesting a shared perception of the corrective measures. These results point to the potential for enhanced overall satisfaction among stakeholders by improving the passivation process\'s effectiveness. In conclusion, the hypothesis testing outcomes emphasize the significance of refining the passivation process and seeking alternative solutions to boost both effectiveness and satisfaction. While some hypotheses did not yield significant outcomes, they offer valuable insights into areas demanding further study and potential enhancements. Subsequent research could concentrate on pinpointing additional factors influencing corrosion recurrence and satisfaction, and also on evaluating novel methods to improve the general efficacy of corrective actions.

References

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Copyright

Copyright © 2025 Col. Remesh VP, Prof. Sameer Narkhede. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.