In this article, we discuss some of the most popular misconceptions regarding magnetic particle inspection. We have also provided you with the best solutions to take care of these misunderstandings. Magnetic particle inspection was developed in 1930 by Fotesre B and Alfred V. Since then, magnetic particle inspection has served as the technique of nondestructive testing.
It is possible to Use All Metals for Magnetic Particle Testing
Have a clear understanding of what your parts entail and what they are made of. It is vital to understand that only cobalt and nickel can get magnetized. Most of the steels and their alloys are perfectly magnetic, which is an important thing to note in this aspect.
At least 80% of aircraft materials are made of aluminium, which implies that it is the most common material used today. This is the case because it is inexpensive, lightweight, and predictable. It is the most common out of all other metals that have been tested with the magnetic particle inspection method. If at all you are doubting this fact, especially about what can be and can’t be magnetized, why not use a permanent magnet?
You Don’t Have to Change your Bath
Every environment has some sort of contamination. This is always the case, regardless of how clean your space might seem to be. Greases, oils, dirt, sand, and other solids get introduced to your bath via inspected components.
Make sure that you examine the particles and carrier amid bath concentration checks. By finding the differences in banding, colour, or layering in both the carrier and particles, you can ensure that no contamination happens in the magnetic particle inspection. If you notice any band that fluoresces brighter compared to the bulk of the materials, it means that there are excess unattached fluorescent pigments. Make sure that the bath is changed ASAP if that is the case. Generally, you want to ensure that the bath is changed as long as there are more than 30% of foreign materials.
Consider Using More Current
When running magnetic particle inspection tests, you should know that it is never a good idea to send more current via a single part. Once you have hit a given part with more amps, you might not see any indications. The reason behind this is that the fluorescent particles will get attracted to the flux leakages. The same will happen to the whole part. Due to this, a bright background will be created, and it will hide the indications being looked for by the operators.
Saturating your field is the last thing you want at this level of magnetic particle testing. If this happens, the defects get masked, but you need them for sharp contrasts alongside the background of the parts so that you can see the indications easily.
Consider working with an MT Level 3 to let you develop magnetic particle testing methods that are quite specific.
All Materials Magnetize the Same Way
In case the parts look the same but are crafted of widely different materials, a similar magnetic particle testing method will never be used. This makes sense since different materials tend to have different retentivity and permeability.
Permeability is a crucial factor to consider in magnetic particle inspection since it impacts the ease with which a magnetic current can travel through parts and then get attracted to flux leakages due to imperfections. The retentivity of a material can affect it perfectly; it can hold its original magnetic fields.
There is a solution to ensure that all materials get tested during magnetic particle testing. It can be done by checking the material. You should not assume that the same methods can be employed on parts that look similar. There are specific products available for Liquid Penetrant Testing.
You Don’t Need Part Cleaning in Magnetic Particle Inspection
It is important to ensure that the parts are pre-tested. This is an essential part of the entire process since it can ensure the highest possibility of detection. Once the part has been cleaned excellently, it will greatly reduce the contamination of your bath. At the same time, it will improve the visibility of the indication on the particular part.
It is Possible to Mag Through Coatings
As per the ASTM E709-15, thin nonconductive coatings like paint in the order of 1 and 2 mils (0.02 to 0.05mm) might not always interfere with the natural formation of the indications. However, they have to be removed at all points where there is a need for electrical contact to be made for the sake of direct magnetization.
Always Do Two Shots
In the process of trying to find cracks in both latitudinal and longitudinal directions, many machines require you to use two shots. The reason is that magnetic fields that are produced by two shots might have an impact on each other, which then erases in one of the two directions. There are two methods that can be employed in firing two shots and in inspecting a given part twice.
The first part involves looking for cracks that are available in just one direction. This is an application that was picked with a certified level three. It greatly relies on the intended application and geometry.
The next way of curbing firing to shots is with the help of a multi-directional mag bench. With these benches come many phase circuity that allows for the application of both magnetic fields to be employed simultaneously. This will then be done without significant interference with each other.
In any case, you care for the throughput, and you need both directions to be inspected for cracks, then you might need to use a multi-directional wet bench. It will ensure that the job gets done in a single shot and with only one UV lamp inspection of two.
Daily System Performance Checks Are not Important
In magnetic particle inspection, it is essential to run NADCAP and ATSM quality checks. The results must always be recorded. By running daily checks, you can ascertain that the machine and bath are in the best working condition. Your operators must ascertain that UV lamp intensity is at the best level all the rime. Note that there will always be more quality checks such as ambient white light, that can contribute to the ability of the inspector to see and comprehend the indications.
With daily checks, time and money can be saved in the long-term. There have always been instances that parts that are worth the entire day get retested because the machine was not calibrated in the right way, and nothing got magnetized. You can also detect indications easily by adding particles. Note that more particles are never better.
Conclusion
If you are only looking for a few parts to get tested during magnetic particle testing, it might not be worth the overall time to have the machine calibrated for the multiple directions shot. This is because an MD unit might only cut your overall time, especially if you are trying to get the parts processed in parts in improved volumes using the same test technique. In the case of more complicated parts in small volumes, it is advisable to consider standard magnetic particle testing and carry out at least two mag shots. Seek help from professionals if you are unable to do these on your own.