Casting Soft Magnetic Alloys Fe-cr-mo

Objective: product magnetic retainer with strong magnetic force, small volume has been gradually developed. But the product magnetic retainer cannot meet the specific requirement of many patients with limited natural roots, shape, direction of root channel and patients with implant. In this study, the casting keeps were made with the magnetizable low coercivity Fe-Cr- Mo alloy, the product keepers by forging has the same ingredient like the casting keeper. The purpose of this study is to find the possibility of using casting keeper in clinic by comparetively investigating the difference about microstructure , retentive forces and corrosion resistance. Methods: first, one Z-lproduct keeper was used as a mould to reconstruct 50 keepers by casting technology. Z- 1 keepers are made in the 4 military medical university. Second, 31 sets were chosen from S0keepers without casting defect for experiments. 1. metallography analysis A casting keeper and a product keeper were chosen. They were inlayed, polished and eroded according the request of metallography. Then they were observed, analysed and took a picture under the light-microscopy. 2. The retentive force experiment 20 casting keepers were chosen and randomly divided into two groups. The top surface of 10 specimens were ordinarily polished and smoothed in manual operation. Another group specimens were smoothed through a lathe. 10 product keepers constitute a contrast group . A Z- I magnetic part was used in this experiment for all samples . The retentive force was evaluated with a cross-head speed of 0.5mm/mm .Thresults were statistically significant among the three groups. 3,The test of the corrosion resistance The electro-chemical method was used in this study to investigate the rate of electrochemical corrosion of casting keepers in artificial saliva C35.5+0.5 Ph5.0 using product keepers as control. Results 1. casting keeper is made of multi-phase whereas product keeper is closed to single phase. It indicated casting keeper has a lower corrosion resistance ability than product keepers. 2. The product keeper mean retentive force is 847.1 g; lathe group 804.5g; manual group 676.5g . The result shows that there was a significant difference between the manual group and the product group or the lathe group. But no significant difference between the product group and lathe group. 3. The negative polarization curve indicates that there was a significant difference between the rates of electrochemical corrosion of the two kind of keepers. The product group mean electric current density is 2.566uA/cm2, casting group 1 .976uA1cm2. But about pitting corrosion potential, there is a opposition result. Product group mean pitting corrosion potential is 0.5093V; casting group: 0.2644 V. Conclusion It can be concluded that casting keeper can replace product keeper in clinical cases, although the casting keeper has failure about their retentive force and corrosion resistance. If we improve manual polishing skill and use thermal treatment technology, the casting magnet can largely used in the clinic.