[Zumba]

I've got a 115v, 1amp, 6x18 electromagnetic chuck. Power is delivered with a full-wave bridge rectifier and an reversing drum switch.

I have a hard time getting the chuck to release the part. It takes a bit of effort, and the problem is that it scratches the nicely ground face that is in contact with the chuck.

Will a variable transformer help? Lower the voltage gradually while switching the poles back and forth with the drum switch?

Seems like permanent magnets don't have this problem (like dial indicator stands). Never owned a permanent magnetic chuck.

Thanks...

[HillBilly]

Will a variable transformer help? Lower the voltage gradually while switching the poles back and forth with the drum switch?

That is the same logic used with the controllers that come with these chucks. The ON time with each polarirty change needs to be equal.

Darek

[Al_The_Man]

I am not that familiar with electromagnetic chucks, but have worked with large electromagnet lifts (100amp).
And the problem you may be seeing is when a reverse de-magnetizing energy is used, it is normally a short reverse shot, if the reverse is kept on too long it will have the same effect of retaining the attraction of the part.
I would have though they would normally have a automatic 1 shot timer to give the de-magnetizing pulse, rather than leave it to manual operation.
Al.

[HillBilly]

Here is a schematic of the OLD motor driver Neutrofier control as used on most Blanchards of that age. The on and off times were at least one second.

Darek

[Al_The_Man]

Interesting, it appears to use the same principal as a dial indicator base, i.e. magnetic (but motorized) shunt.
It is not clear when the limit switches are made, also I don't see a coil for the contactor? unless it is manual or other?
Al.

[HillBilly]

The contactor is cam driven by the same motor that drives the rotary switch. The contactor and rotary switch are shown in the park condition (full magnet power). When demag is initiated the rotary switch steps down the secondary reversing polarity at each step with the contactor until the last step and the limit switch stops it at the park location.

Darek

[Zumba]

Thanks for the replies.

Currently, I'm only using the drum switch to reverse the poles back and forth. It certainly helps. It goes from "stuck" to "releasable with some effort".

Knowing this, would buying the variable transformer really help in my situation?

[HillBilly]

I would say yes.

Darek

[dhiruj]

hi

we manufacture electro chucks and the controllers.. our customers also used to complain about this with our old design controller.. now we have developed a new electronic controller where, we give the demag pulses in steps to acheive demagnetization..

our test results with customers has been very sucessful even with very thin jobs....

you can visit our site www.sardamagnets.com

for any more details please feel free to contact us.

dhiruj

[vger]

If you have a suitable variable transformer you should be able to do the demag easily. You should be able to put AC on the coil from the variable. Just put a switch in line from the coil in the chuck to switch the chuck over to the variable transformer output. Flip the switch, turn the variable on and bring the voltage up, then down slowly.

Steve

[HillBilly]

Be careful when putting AC on a non laminated core electro magnet. You can burn it up real easy.

Darek

[vger]

Be careful when putting AC on a non laminated core electro magnet. You can burn it up real easy.

Darek

Yes, the core will heat up due to eddy currents. Assuming the chuck is fairly massive, you should be OK for short demag operation..

Steve

[amit_sarda]

magnetism depends on vasious factors.

stickness depends on the material of the job which is being grinded.

if the material is hardended steel or steel with high carbon content, it has a tendency to retain magnetism even after the electrical power is cut from the magnetic chuck.

there are a few methods with which we can remove the job.

1. after the demagnet operation has been done from your reversing drum switch (which should be spring loaded presently), try demagnetizing the job using a platent demagnetizer http://www.sardamagnets.com/showtable.asp?prodid=100 . This is a crude method, but can be used

2. you can use the digital controller like http://www.sardamagnets.com/showtable.asp?prodid=136. this is a variable DC demagnetization cycle. primarily what it does is it passes first DEMAG at 100% then MAG at 80% then DEMAG at 70% and like that for 2 seconds with variable power. this will reduce the induced magnetism in the job making it easier to release.

Amit Sarda
www.sardamagnets.com