Equipments& Materials For MPI.doc

Above left is a photo of a typical qqi shim the photo

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Above left is a photo of a typical QQI shim. The photo on the right, shows the indication produced by the QQI when it is applied to the surface a part and a magnetic field is established that runs across the shim from right to left. Pie Gage
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The pie gage is a disk of highly permeable material divided into four, six, or eight sections by nonferromagnetic material. The division serve as artificial defects that radiate out in different directions from the center. Diameter of the gage is ¾ to 1 inch. The divisions between the low carbon steel pie sections are to be no greater than 1/32 inch. The sections are furnace brazed and copper plated. The gage is placed on the test piece copper side up, and the test piece is magnetized. After particles are applied, and excess removed, the indications provide the inspector the orientation of the magnetic field. The principal application is on flat surfaces such as weldments or steel castings where dry powder is used with a yoke or prods. The pie gage is not recommended for precision parts with complex shapes, for wet-method applications, or for proving field magnitude. The gage should be demagnetized between readings. Several of the main advantages of the pie gage are: it is easy to use and it can be used indefinitely without deterioration. The pie gage has several disadvantages, which include: it retains some residual magnetism so indications will prevail after removal of the source of magnetization, it can only be used in relatively flat areas, and it cannot be reliably used for determination of balanced fields in multidirectional magnetization. Slotted Strips Slotted strips, also known as Burmah-Castrol Strips, are pieces of highly permeable ferromagnetic material with slots of different widths. They are placed on the test object as it is inspected. The indications produced on the strips give the inspector a general idea of the field strength in a particular area. Advantages of these strips are: they are relatively easily applied to the component; they can be used successfully with either the wet or dry method when using the continuous magnetization; they are repeatable as long as orientation to the magnetic field is maintained and they can be used repetitively. Disadvantages include: they cannot be bent to complex configuration; and they are not suitable for multidirectional field applications since they indicate defects in only one direction. Magnetic Particles As mentioned previously, the particles that are used for magnetic particle inspection are a key ingredient as they form the indications that alert the inspector to defects. Particles start out as tiny milled (a machining process) pieces of iron or iron oxide. A pigment (somewhat like paint) is bonded to their surfaces to give the particles color. The metal used for the particles has high magnetic permeability and low retentivity. High magnetic permeability is important because it makes the particles attract easily to small magnetic leakage fields from discontinuities, such as flaws. Low
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  • Fall '19
  • Magnetism, Magnetic Field, Ultraviolet, Magnetic Particle Inspection

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