Magnetic Particle Inspection is a non-destructive examination technique used to detect surface and slightly subsurface flaws in most ferromagnetic materials such as iron, nickel, and cobalt, and some of their alloys. Below are five important factors with magnetic particle inspection.
1. Not all metals can be used
When it comes to the metals used you need to understand the composition of your parts and what metals can be magnetised as only iron, nickel and cobalt can be magnetised.
One of the most common metals to be tested with magnetic particle inspection that cannot be magnetised is aluminium which is used predominantly in aircrafts given that it is lightweight, strong and inexpensive. If you’re unsure of what can and cannot be magnetised grab a magnet and see if the metal sticks.
2. Change the bath
Making sure that your work space is clean and not contaminated is important when it comes to Magnetic Particle Inspection. Elements such as oil, grease, sand and dirt can be introduced to your bath by inspected components. Getting oil in the water bath is also of primary concern. These contaminants will impede the testing performance and can disguise indications - ideally the bath should be changed when foreign matter exceeds 30% of settled solids.
3. It’s not about more current
You are less likely to see indications if you hit a part with more amps. This is because the fluorescent particles will be attracted to the flux leakages of the entire part. This will create a bright background that will hide the indications operators are looking for. It’s important not to saturate your field and mask defects because you need sharp contrast with the background of the part to easily spot indications.
4. Part cleaning is necessary
Cleaning your parts properly will decrease the contamination to your bath and will help increase the visibility of the indications on the part itself. This is key in the pre-testing phase and you should clean them before sending them to the magnetic particle testing area. Doing so will improve the quality of your inspections and it will also reduce the amount of times you need to change your bath.
5. Perform daily checks
As well as part cleaning you will also want to perform daily check so that your bath and machine are in optimal working condition. Checking areas such as bath concentration and UV lamp intensity daily or at the start of every shift will improve quality and inspection performance. There are many other checks including ambient white light, that can play a large factor in the inspector’s ability to see indications.