Demagnetization (2)

Question 1

Step Down Demagnetization

Answer 1

Place the part in the coil or between the clamp heads and decay current values going from maximum to minimum to effectively demagnetize the part.

Question 2

AC Tunnel Coil

Answer 2

• one of the more common means of demagnetizing

- coil is energized with a rapidly reversing, constantly diminishing AC.

Question 3

Manual Demagnetization

Answer 3

Using a portable coil, simultaneously energize the coil while moving the part through and away from the coil (about 3-5ft)
- repeat until remnant fields are acceptable

Question 4

To demagnetize a part, the current value must be ____ to or ____ than the current value that was used to test the part.

Answer 4

equal to or less than

Question 5

For complex geometric parts, demagnetization is often more successful if the part is ______ and ______.

Answer 5

rotated and turned

Question 6

Demagnetization via heat treatment

Answer 6

heat treatment temperatures often exceed the curie point causing the material to lose and ferromagnetic properties, cooling it regains them but will not retain the magnetic field.

Question 7

Demagnetization using DC

Answer 7

current is slightly reduced then completely reversed in direction (1 to 1.5 seconds per step)

Question 8

Contact yoke demagnetization methods

Answer 8

• energized in contact and pulled up and away
• energized and twisted
• energized and dragged away

Question 9

Non-contact yoke demagnetization method

Answer 9

parts are passed between the poles and withdrawn while the yoke is energized

Question 10

Special demagnetization techniques (3)

Answer 10

• rubber mallet
• positioning
• transient

Question 11

Rubber Mallet Demagnetization

Answer 11

• not recommended

- striking a part with a rubber mallet during the demagnetization operation.

Question 12

Positioning Demagnetization

Answer 12

Longer parts can be magnetized by earths poles, this is why it is recommended that demagnetizing coils/coils should be positioned so that the part has its long axis positioned in an east-west direction.

Question 13

Transient Demagnetization

Answer 13

• for large, strong fielded parts
• place part in demagnetizing coil, current turned on and off 5-10x, reinitiate the current and pull the part out of the coil with current on.

Question 14

Small cylinder demagnetization

Answer 14

in an AC coil when the L/D ration is 1 or less, rotating the part 180° motions while withdrawing from energized coil.

or use two pole pieces to assist in increasing the L/D ratio for demagnetization

Question 15

Circular field demagnetization

Answer 15

convert field into longitudinal and the demagnetize as, field will exhibit poles.