What is the best shape for magnetic particles used in the dry powder method?

In the dry powder method of magnetic particle testing, the optimal shape for magnetic particles is a mixture of elongated and globular particles. This combination is effective because elongated particles are capable of aligning more easily along magnetic field lines, allowing for enhanced sensitivity in detecting discontinuities. They can bridge small gaps in defects, leading to a more effective indication of flaws.

On the other hand, globular particles contribute to a uniform coverage of the test area, which is crucial for ensuring that the entire surface is inspected thoroughly. The mixture of these particle shapes achieves a balance between sensitivity and coverage, improving both the likelihood of detecting defects and the quality of the indications produced.

Using only round or flat particles would not provide the same level of effectiveness. Round particles might not align as efficiently in the magnetic field, while flat particles tend to settle or stack, leading to less effective coverage and potentially missing subtle indications. The combination of elongated and globular shapes thus offers the best performance in the dry powder method for magnetic particle testing.