Direct Magnetization:
In Direct Magnetization, current is passed directly through the component and we know that, whenever current flows, a Magnetic field is produced. As per Right-hand rule, the flow of current causes a circular magnetic field to form in & around the conductor.
When using the direct magnetization method, make sure that good electrical contact is established & maintained between the test equipment & the test component to avoid damage of the component due to overheating or arcing at high resistance points.
Right-hand rule:
Right-Hand rule says, if the person grasps a conductor in his right hand with the thumb pointing in the direction of the current, the fingers will point in the direction of the Magnetic field.
Direct Contact Technique - Head shot:
This technique produces circular magnetization by passing electric current through the part itself. Direct contact to parts is generally made by placing them between clamping heads. this is sometimes called the direct contact or head shot methd.
In this method, Current is passed through the components directly and a circular magnetic field produces in and around the component that creates poles on either side of any crack or discontinuity which runs parallel to the length of the part. The pole attract magnetic particles, which form an indication of the discontinuity.
When the magnetizing current is stopped, a residual magnetic field will remain within the component.
The strength of the induced magnetic field is proportional to the amount of current passed through the component.
Check out this video to know, how actually this Direct Contact (Head shot) Technique work.
Using Prods or Clamps Technique:
Prods are Handheld electrods that are pressed against the surface of the component being inspected to make contact for passing electrical current through the metal. The Passing current between the prods create a circular magnetic field around the prods that can be used in magnetic particle inspection.
Prods are made from copper and have an insulated handle to help protect the operator. One of the prods has a trigger switch so that the current can be easily and quickly turned on/off. Sometimes the two prods are connected by an insulator to facilitate one hand operation.
Check out this short video to know, how actually this Direct Contact (Using Prods) Technique work.