Optimisation of corrosion protection and prevention at Thermo King.

Abstract

Corrosion of metals affects their function in many engineering applications, limits the useful life, and thereby causes increased costs for industry estimated at up to €300 billion per annum in the United States'. The prevention of corrosion is of major economic significance, and is a subject of intrinsic scientific interest due to the complex chemistry involved. The chemical protection of metals has to be moderated to conform to increasingly demanding environmental standards. There are relatively few effective alternatives to traditi* onal phosphate coatings dati*ng from2 1 869. In the case of refrigeration technology, the refrigeration cycle is largely conducted on metallic equipment exposed to repeated episodes of the thermal cycle. The metals used in portable or truck mounted refrigeration equipment must resist corrosion for periods of ten years in aggressive environments. In this project a scientific examination of the process steps used by Thermo King, a leading refrigeration manufacturer, was conducted. In this project, with the full support of the Thermo King Corporation, the process steps in the phosphate protection process were simulated in the laboratory to characterise various chemical changes and monitor changes over time. A study on the literature and technology of alternative corrosion protection relevant to the current processes was conducted. Accelerated corrosion tests were carried out on metallic samples used in the Thermo King production of refrigeration units. These samples were also characterised by scanning electron microscopy. Implementation of the findings in Thermo King had four major effects; 1. Decrease in phosphate levels to meet IPC licence requirements, for the first time in Thermo King 2. Substantial cost reduction through water conservation 3. The improved performance of Thermo King’s spray treatment line resulted in obtaining 700 hours, in a salt spray chamber in accordance with ASTM B177. This improved accelerated corrosion test result is 75% higher than was achievable prior to this project. 4. Preliminary investigations on the alternatives to phosphate coating were conducted, on silane and autophoretic technologies. These technologies showed promising results however further research is required. Suggestions are made for future research to obtain a better understanding of underlying principles, and to achieve improved performance from corrosion inhibition techniques.