Magnetic particle Inspection (MPI) is one of non-destructive testing (NDT) methods for investment castings. Compared to other NDT methods, Magnetic particle Inspection focuses on the detecting of outside casting defects , such as cracks, seams, inclusions, porosity, ect. Main MPT process for investment castings is to apply magnetic particles to find invisible defects, without harming the part in any way.
The test method process is quick and simple in principle and application. It is highly sensitive to the detection of surface and slightly subsurface linear indications, and indications appear on the actual test investment casting part. The test method process may often work through contaminant layers and coating thickness, and the method lends itself to automation and high-volume production inspection. Besides, it is less expensive than other more sophisticated methods of quality assurance.
Advantages of Magnetic Particle Inspection:
- It is quick and relatively uncomplicated.
- It gives immediate indications of defects.
- It shows surface and near surface defects, and these are the most serious ones as they concentrate stresses.
- The method can be adapted for site or workshop use.
- It is inexpensive compared to radiography.
- Large or small castings can be examined.
- Elaborate pre-cleaning is not necessary.
Disadvantages of Magnetic Particle Inspection:
- It is restricted to ferros castings – usually iron castings and steel castings, but cannot be used on austenitic stainless steel castings.
- It is messy.
- Most methods need a supply of electricity.
- It is sometimes unclear whether the magnetic field is sufficiently strong to give good indications.
- The method cannot be used if a thick paint coating is present.
- Spurious, or non-relevant indications, are probable, and thus interpretation is a skilled task.
- Some of the paints and particle suspension fluids can give a fume or fire problem, particularly in a confined space.
MPI in CFS foundry
Quality control is quite important for us to deliver high quality products. To be more professional and reliable, we are equipped with MPI equipment in CFS foundry, so that we can do MPI directly. The MPI in our foundry is wet method, which provides improved sensitivity for the detection of very fine surface flaws. We can detect a discontinuity with maximum depth 1/4 inch, but usually 0.050 to 0.100 inch depth is enough. For heat treated castings or machined castings, magnetic particle inspection should be done once casting blanks are completed. And there is no need to carry on further heat treatment or machining operation if there is any defects. Investment casting with defects tested by MPI will not be delivered to our customers.
Of course, we can also do other NDT for investment castings, such as X-Ray Examination, Hardness Testing, Dye Penetrant Inspection, Leak Testing, ect. Pls contact us for your next casting project with such requirement.