Micro-Penetrant Impregnation Technology Applied to Castings Surface Treatment before Heat Treatment
Introduction
Heat treatment is an integral part of manufacturing processes in order to optimally modify the properties of a workpiece to satisfy product requirements. While its application is not exclusive to castings, there are certain features of castings which should be taken into account when applying the technology. The aesthetic, mechanical, metallurgical, and corrosion properties of castings are greatly affected by surface preparation prior to heat treatment. This includes the removal of internal irregularities, the correction of surface hardness, and the filling of micro-pores. Micro-Penetrant Impregnation (MPI) technology is a tool which can be used to achieve these goals.
Theory
Micro-Penetrant Impregnation is a process that fits in the category of surface treatments before heat treatment. The basic concept of this method consists of a compound that easily seeps into the smallest pores of the surface, strengthening it by filling the irregularities in the casting. The development of this technology has gained importance in recent years due to its ability to protect casting from a variety of industrial processes and reduce costs associated with pre- and post-treatment operations.
The overall performance of the process depends on the type of fluid used and the concentration of the solution. The most common fluid used in this process is an acid etchant, as it accelerates the absorption of the compound into the micro-pores. The acid etchant is then mixed with an impregnator, which is a compound specifically developed to penetrate and solidify the micro-pores of the casting. This mixture is applied to the surfaces and penetrates delicately and deeply into the pores. When it solidifies, it forms a protective layer on the surface that provides maximum protection against corrosion, abrasion, and other environmental damage.
Procedures
The main procedures of applying MPI technology are largely straightforward. The first step of the process is to thoroughly clean the workpiece. This is typically accomplished by washing it with detergent, hot water, and compressed air. The second step is the application of the etchant/impregnator solution. This solution is usually applied by spraying, dipping, or brushing it onto the desired area. Once the solution is applied, it is then left to sit for a period of time (typically 5–25 minutes). This allows the solution to fully penetrate the micro-pores.
The third step is the curing of the penetrant. This is accomplished by heating the impregnated area up to a specific temperature. The temperature will be specified by the manufacturer of the penetrant, as different penetrants have different curing temperatures. The fourth step is the post-treatment operations such as polishing, painting, and other desired aesthetic finishes.
Conclusion
In conclusion, Micro-Penetrant Impregnation (MPI) technology is an efficient and cost-effective way to improve the aesthetic, mechanical, metallurgical, and corrosion properties of castings. This process can be used to correct surface irregularities, improve surface hardness, and fill micro-pores. It is also relatively straightforward, and can be accomplished with the appropriate etchant and impregnator solution. Therefore, it is beneficial to consider utilizing MPI technology when preparing surfaces of castings for heat treatment.
