Particles (2)

Question 1

What are MPI particles made of?

Answer 1

precipitated soft iron, coloured or dyed (black, red, fluorescent), high permeability and low retentivity.

Question 2

MPI particle characteristics include:

Answer 2

• ferromagnetic
• high permeability (max response to leakage fields)
• low retentivity (no retaining residual fields)
• high contrast and visibility

Question 3

MPI particle size and shape:

Answer 3

• 0.05mm to 1.5mm

- round to irregular/elongated shape

Question 4

What does particle shape do in relation to a leakage field?

Answer 4

smaller particles attract to lower level leakage fields

larger particles have the ability to bridge larger gaps

Question 5

Elongated particles are more commonly found in ____ form.

Answer 5

dry-visible form

Question 6

Dry powders carry the ____ range of particle sizes and shapes.

Answer 6

largest range of particle sizes and shapes.

uniform small rounded particles are more commonly found in wet MPI

Question 7

Particle densities range:

Answer 7

5-8 times that of water. when coated with dye pigments density tends to be less.

Question 8

Describe the importance of particle mobility

Answer 8

the ability of particles to move quickly over the part surface detecting leakage fields.

• particle size and shape
• relative viscosity of suspension liquid

Question 9

How can an inspector assist with particle mobility?

Answer 9

• blowing
• AC, half-wave rectified AC
• vibrating the part
• promoting natural draining action
• low velocity compressed air