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Demagnetizing steel shaft

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Gregory

Member
I have a steel shaft out of my gearbox of my vehicle
The shaft is magnetized and I wish to demagnetize the shaft
Can i make something to do this if so how do i go about this project.
 

Mike_2545

Super Moderator
If you hold the steel shaft near a transformer winding, like the kind you find in an aquarium air pump, only larger, it will demagnetize your shaft.
 

crutschow

Well-Known Member
Most Helpful Member
Any source of a strong AC magnetic field will remove the magnetism. If you can find an old magnetic tape degausser, that would work well.
 

MikeMl

Well-Known Member
Most Helpful Member
Demagnetizers produce a strong Alternating Magnetic field. They are usually AC line powered, and draw many amps while operating. I have a commercial eraser for old reel-to-reel magnetic tape, which also works for screwdrivers and small objects. I have another larger homemade one that I use to demagnetize the steel tubes in aircraft fuselages when swinging a magnetic compass.

The large one I made by peeling the cross bar off a 120V power transformer core. This reduced the inductance of the transformer primary, so it draws a lot of current when connected to 120VAV, so I use a Variac to reduce the voltage.

The correct way to "demagnetize" is to slowly move the item past the gap in the core. Keep the item moving slowly, smoothly. Do not switch off the AC with the item still in the gap, otherwise the current decay transient can leave the item locally magnetized; rather move the item away while the coil is still powered, or slowly reduce the AC voltage with the Variac.

It takes some practice to do this right. I use a small Boy-Scout compass to assess how well something is demagnetized (or not).
 

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Sceadwian

Banned
A note of caution, those things eat credit cards for lunch =) So leave your wallet at home that day, or at least a few feet away.
 

dknguyen

Well-Known Member
Most Helpful Member
You can also heat it up. I forget how hot though.

EDIT: Google seems to say steel is 500C so that's probably too hot.
 
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ccurtis

Well-Known Member
1. You can hit it with a hammer some number of times, since ordinary steel has low coercivity. Hold it at one end in a vise and hit the other end, or hold one end on a hard surface and hit the top end so that the hammer energy is transmitted though the shaft.

2. Wrap a bunch of turns of wire around the shaft to make an electromagnet. Wire a 120 watt incandescent household lamp in series with the electromagnet to limit the current. Use a household lamp dimmer to power the series combination. Slowly bring up the current using the dimmer, then slowly bring the current down to off. The more turns of wire, or the greater the load (say a 400 watt space heater) the stronger the demagnetizing field will be.

edit 3. You can use another magnet to stroke the shaft with an opposing magnetic field.
 
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tcmtech

Banned
Most Helpful Member
If I remember correctly the Currie point for steel is higher than the tempering point so you wont want to do the heat method.
Your transmissoin shafts are hardened steel and if you take that hardness away they will be very short lived! If everything is clean inside the transmission there is no reason to demagnetize it.

Most likely it was that way from the factory. Many high strength gear steels are induction hardened and tempered. Also it is common to use magnetic grippers on the robots that do the manufacturing and assembly work. This would also be a likey source of the magnetizing in the first place.

I would just leave it alone if I was you!
 

Gregory

Member
I was working at a allimiun smelter were there is high magnetic fields where I was driving my work ute around the plant for 2 years which caused the gearbox bearings gears and shaft to become magenized .
 

Hero999

Banned
So how is that causing a problem?
 

tcmtech

Banned
Most Helpful Member
Why do you think that it needs to be demagnetized?
IF the fields were that powerful the whole truck needs to be demagnetized too!

How bad is this magnetization anyway? Do other metal objects jump right off the table and attach them selves to it? Or is it more likey that some small shavings or bits of metalic bits slightly stick to it?

Magnetism is a rather natural action of iron based materials.
If you take and Iron based rod and hit it hard several times it will become slightly magnetized too!
The vibration of gears meshing or residual magnetization from the manufacturing process is more likely the source of the magnetization than the smelter plant.

I work on salvage yard magnet cranes and I also haul loads of iron with my pickups. I have had 30Kw electromagnets activated right in the box of my trucks many times. And they have the force to actualy lift the back end off the ground.
SO far the worst I have ever had to do was reset the compass on my pickup.
 

Gregory

Member
The Bearings and shavft and gears had steel worn particles on the working area which in turn caused the bearings to destroy themselves.
To prevent the shaft picking up steel particles then it is wise to demagnetized as the magnetism can be passed to other parts of the gearbox.
 

tcmtech

Banned
Most Helpful Member
Even If everything is non magnetic how do you plan to keep the gear oil from carrying the metallic particles back around into the gears and bearings again? :confused:
That oil carries far more metallic particles that you may think! :eek:

Good luck demagnetizing or finding something that is not already magnetized to some degree!

Just for curiosity sake I checked a bunch of old tractor transmission and engine parts I have around. Everything that is not cast iron has some residual magnetic charge to it!
I just used some fine cast iron dust from my band saw to check everything.
The dust it self is not magnetized but every bearing and tempered high carbon steel shaft I could Find is slightly magnetized! ;)
Even a pair of bearings that I purchased brand new two days ago that have never even been out of my pickup yet still showed a slight magnetic charge! :D
 

Mikebits

Well-Known Member
Even If everything is non magnetic how do you plan to keep the gear oil from carrying the metallic particles back around into the gears and bearings again? :confused:
That oil carries far more metallic particles that you may think! :eek:

Good luck demagnetizing or finding something that is not already magnetized to some degree!

Just for curiosity sake I checked a bunch of old tractor transmission and engine parts I have around. Everything that is not cast iron has some residual magnetic charge to it!
I just used some fine cast iron dust from my band saw to check everything.
The dust it self is not magnetized but every bearing and tempered high carbon steel shaft I could Find is slightly magnetized! ;)
Even a pair of bearings that I purchased brand new two days ago that have never even been out of my pickup yet still showed a slight magnetic charge! :D
Perhaps it is your magnetic personality... :)
 

Sceadwian

Banned
You sure that's not much oil making the dust stick tcm?
 

Hayato

Member
If you take out farm tractors engine oil sumps, you'll see a lot of iron dust inside. So it's pretty normal. Just keep your engine and tranny oil always up to date.
 
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