Magnetic rubber inspection
Magnetic rubber inspection is a non-destructive testing method that utilizes a liquid rubber containing suspended magnetic particles to detect surface and near-surface discontinuities in ferromagnetic materials.
The technique involves applying the rubber to the area to be inspected on a magnetized component and then exposing it to a magnetic field, which allows the magnetic particles to migrate to areas of leakage caused by discontinuities.
This method is particularly effective for detecting very fine cracks and can be used in difficult-to-reach areas, such as inside gear teeth.
The process typically requires a dam of modeling clay to contain the rubber compound in the region of interest, and the rubber must cure for 10 to 30 minutes before examination.
Magnetic rubber inspection is advantageous for its ability to reveal finer cracks than other magnetic techniques and is often used in conjunction with other inspection methods.
What is the typical input power requirement for bench machines?
220V or 440V alternating current
The power can be single-phase or three-phase depending on the model.
Ohm’s law shows the relationship of current and voltage, as follows:
What is advisable to keep as short as practical in a circuit?
The cable
This helps minimize resistance and maintain current flow.
True or false: Electromagnetic Yokes can burn the test surface on heat-treated parts.
FALSE
They are safe for use on heat-treated parts.
What is the maximum acceptable ambient light for most specifications during testing?
20 lx (2 ftc) at the test surface
This is measured with the ultraviolet light on.
Magnetic Rubber – MPI Technique
Purpose:
Detects internal or complex surface cracks using a rubber compound with magnetic particles.
How It Works:
Magnetic particles mixed into liquid rubber.
Applied to part and cured under magnetic field.
Rubber is removed and inspected for trapped particles at defects.
Benefits:
Ideal for threads, holes, and recesses.
Creates a permanent defect replica.
High sensitivity for internal surfaces.
Limitations:
Slower process.
Not suitable for high-volume inspections.
What is the typical intensity level for ultraviolet lights used in magnetic testing according to ASTME 1444?
1000 μW/cm2 minimum at 381 mm (15 in.) from the part surface
Many specifications require a minimum intensity of 1200 μW/cm2.
What are the types of light used during the magnetic particle testing process?
- Visible light
- Ambient light
- Ultraviolet light
Each type plays a specific role during testing and inspection.
What do alternating current coiled and crossed cables act as?
Inductors
They further reduce current flow.
What does the shot timer in bench machines typically adjust between?
0.5 s to 1.0 s
It is usually set between 0.6 s and 0.9 s for optimal performance.
According to Ohm’s law, what must be very low in a circuit?
Total circuit resistance. I = V/R
Ohm’s Law is a fundamental principle in electronics and electrical engineering that states the relationship between current (I), voltage (V), and resistance (R) in a circuit. The law can be expressed with the formula I = V/R, which means that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance. This principle is essential for understanding how electrical circuits operate.
This includes cables, connectors, etc.
What are Permanent Magnet Yokes primarily used for?
- Inspections without electric power
- Inspections in explosive environments
Their field strength is low compared to electromagnetic yokes and they are not recommended for general inspection applications.
What types of current do multidirectional units use?
- Full-wave direct current
- Half-wave direct current
- Alternating current
They are equipped for both magnetization and demagnetization processes.
What is the electromagnetic spectrum?
Defines radiant energy by wavelengths
It includes long and short radio waves, microwaves, infrared waves, visible waves, ultraviolet waves, X-rays, gamma rays, and cosmic rays.
How is amperage expressed in magnetic inspection?
- Amperes
- Ampere turns
Ampere turns is the magnetizing current times the number of turns.
Prods & clamps for electrical conduction
What is the best source of data about specific test equipment?
The equipment supplier
Data can also be obtained from equipment shows, industry specifications, and military specifications.
What is the benefit of using a direct current yoke?
Useful for weld inspection due to adequate penetration
It can provide either half-wave direct current or pulsed direct current.
What effect do external cables have in a circuit?
They act as resistors and cause line voltage drop
This drop is measured in ohms per meter (feet).
What is the minimum intensity of visible light required when using fluorescent particles?
1000 lx (100 ftc)
This is necessary to aid in the evaluation of indications.
What is the maximum output of heavy-duty power supplies?
Up to 20,000 A full-wave direct current
These power supplies are suitable for large stationary and special equipment.
What is a dual prod used for?
Allows the inspector to hold both prods with one hand while the other is free to apply powder or wet suspension
Most frequently used on weld inspections.
What is the primary use of bench machines?
Wet, general purpose equipment for batch lots
Bench machines are rugged production machines especially useful when a fully automatic machine is not economical.
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Defects27
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Magnetic Particle Vocabulary53
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End of Chapter Questions - All190
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ASNT Magnetic Particle Level I Review Questions92
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ASNT Magnetic Particle Level II Review Questions79
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ASNT Magnetic Particle Level III Review Questions61
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Chapter 1 & 2: Study Guide Summary97
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Chapter 3 : Study Guide Summary43
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Chapter 4: Study Guide Summary64
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Chapter 5: Study Guide Summary24
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Chapter 6: Study Guide Summary41
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Chapter 7: Study Guide Summary32
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Chapter 8: Study Guide Summary34
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Chapter 9: Study Guide Summary58
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Chapter 10: Study Guide Summary16
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Chapter 11: Study Guide Summary46
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Chapter 12: Study Guide Summary27
