General Introduction

Magnifer 7904(1J85) is a soft magnetic nickel-iron alloy with about 80 % nickel, 4.2 - 5.2 % molybdenum, a saturation induction of approx. 0.8 T, the highest technically obtainable permea-bility, and a very low coercive force.

Typical applications of Magnifer 7904 are:

***Toroidal tape-wound cores – integrating current trans-formers for earth-leakage circuit breakers, instrument
transformers, inductive components
***Laminations – transformer laminations, transformer coresfor modems with special transformer characteristics,
stamped rings for electronic earth-leakage circuit breakers
***Shieldings – to protect against magnetic interference, in the form of shielding films, shielding cans and spatial
shielding arrangements
***Stepping motors – stamped parts for analogue watch mechanisms
***Relay parts – components for electromagnetic relays
***Other solid components – with a low coercive force

General magnetic properties

The magnetic properties of Magnifer 7904 can be varied by appropriate heat treatments. In toroidal tape-wound cores, the initial permeability µ4 can reach 160 000 to 380 000 and the maximum permeability 320 000 to 480 000 at a frequency of 50 Hz and a strip thickness of 0.065 mm. The static coercive force is then typically Hc ≤ 1 A/m. The hyste-resis loop can be set to curved, rectangular or flat.

Fabrication

Forming

The usual processes can be used. Fabrication data may be obtained from the table of mechanical properties. In the "annealed for deep drawing” condition, the minimum Erich- sen depth is 8 for sheets of 1 mm thickness. The magnetic condition after final annealing is exclusively the final condition for fabrication of certain parts. It is not suitable as the initial condition for any further working operations, as the magnetic properties would be drastically lowered. The cold-rolled state is the most suitable for stamping.

Machining

The cold-worked condition is best suited for machining opera- tions. The material exhibits characteristics similar to those of stainless steels. Low cutting speeds, cooling cutting oils, and carbide or high-speed-steel cutting tools are required; the latter must be kept sharp.

After machining is completed, residual films of oil, grease or dirt must be removed as completely as possible before annealing the parts. Oils with added sulphur are entirely unsuitable.

Welding

The best process is usually spot welding, although other weld- ing processes are also suitable in principle. We are pleased to advise on the best process in special cases.

Corrosion resistance

Corrosion resistance in a humid atmosphere is good, but this is not the case in aggressive media.

Forms supplied

strip, ribbon, sheet, bar and wire.