Why is an iron cover needed for a solenoid?

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    Iron Solenoid
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Discussion Overview

The discussion revolves around the necessity of an iron cover for a solenoid, focusing on the implications for magnetic circuits, flux concentration, and the resulting force generated by the solenoid. Participants explore theoretical and conceptual aspects of magnetic fields and their behavior in relation to solenoids.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants suggest that closing the magnetic circuit with a metal casing helps to focus the magnetic flux lines, potentially increasing the force generated by the solenoid.
  • Others argue that the magnetic force is proportional to the square of the magnetic flux density, implying that a higher flux density leads to greater force.
  • It is noted that concentrating the magnetic field within a smaller area (the gap where the armature is placed) can yield a higher flux density compared to a more dispersed field.
  • A participant mentions that using a high-permeability jacket can significantly reduce leakage flux, which may enhance the magnetic flux inside the solenoid.
  • There is a reference to historical designs of magnets, such as horseshoe shapes, which were used to achieve a worthwhile flux density.

Areas of Agreement / Disagreement

Participants express varying views on the mechanisms by which an iron cover affects the solenoid's performance. While there is some agreement on the importance of magnetic flux density, the exact relationship between the casing and force generation remains contested.

Contextual Notes

Some assumptions about the magnetic circuit and the definitions of flux density are not explicitly stated, which may affect the clarity of the arguments presented. The discussion does not resolve the mathematical relationships involved.

yaxlei
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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.
 
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yaxlei said:
but how does it increase the force generated by the solenoid ?

by concentrating the magnetic field in the coil of the solenoid
 
yaxlei said:
but how does it increase the force generated by the solenoid ?
The magnetic force is proportional to the square of the magnetic flux density.
 
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alan123hk said:
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.
 
alan123hk said:
The magnetic force is proportional to the square of the magnetic flux density.
yaxlei said:
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.
 

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