Why is an iron cover needed for a solenoid?

[yaxlei]

Hi everyone,

I've heard that it's better to close the "magnetic circuit" of a solenoid by adding a metal casing around the coils, but I don't get why : people say that it's for focusing the magnetic flux lines but how does it increase the force generated by the solenoid ?

Thanks if you reply, have a nice day.

 

[davenn]

but how does it increase the force generated by the solenoid ?

by concentrating the magnetic field in the coil of the solenoid

 

[alan123hk]

but how does it increase the force generated by the solenoid ?

The magnetic force is proportional to the square of the magnetic flux density.

 

[sophiecentaur]

The magnetic force is proportional to the square of the magnetic flux density.

. . . . . and having the same flux across a small area of gap gives a much higher flux density than when the flux is spread over the whole of space around the coil. You put the armature where the gap is and that gives more force.

The old magnets were nearly all Horseshoe shaped so that you could get a worthwhile flux density somewhere, at least. Modern permanent magnets of all shapes can be strong enough to do a useful job.

 

[rude man]

The magnetic force is proportional to the square of the magnetic flux density.

Hi everyone,

I've heard that it's better to close the "magnetic circuit" of a solenoid by adding a metal casing around the coils, but I don't get why : people say that it's for focusing the magnetic flux lines but how does it increase the force generated by the solenoid ?

Thanks if you reply, have a nice day.

With the hi-mu jacket the leakage flux is greatly reduced.
Analytically, when you run the usual amperian loop inside & outside the solenoid there is less of the B integral outside the coil. So that means more flux inside.