Useful Information for Designing Your Own Magnetic Shielding

MuShield high permeability magnetic shielding material is a non-oriented 80% nickel-iron-molybdenum alloy which offers extremely high initial permeability and maximum permeability with minimum hysteresis loss.

It meets military specification MIL-N-14411 C (MR), and ASTM A-753-78 standard specification.

DC MAGNETIC PROPERTIES

Coercive force from H=1.0 Oe, Oersted 0.008 to 0.02

Hysteresis loss from H=1.0 Oe, erg/cm³ per cycle 18 to 24

DC MAGNETIC PROPERTIES
Form	µ at B = 40 G	µ max	Ho from H=1 Oersted
Bar, Wire	50,000	200,000	0.02 max.

DC hysteresis loss from
H = 1 Oe, erg/cm³ per cycle . . . 16
Induction, gauss . . . . . . . . . . . . 7,300
Residual Induction, gauss . . . . 3,500
(Split strip or split rod specimens)

AC MAGNETIC PROPERTIES, 60 Hz
Minimum Limits

Thickness in. mm		µ 40 G	µ 200 G	µ 2000 G
0.025¹	0.635	35,000	40,000	55,000
0.014¹	0.356	55,000	65,000	95,000
0.006¹	0.152	65,000	85,000	135,000
0.002²	0.051	70,000	90,000	220,000

¹ Ring laminations 1 1/2" (38.1 mm)
OD x 1" (25.4 mm) ID specimens
² Tape toroid specimen

PHYSICAL PROPERTIES:

Specific gravity	8.74
Density -- lb/in³	0.316
kg/m³	8747
Thermal conductivity
Btu-in/ft²/hr/°F	240
W/m· K	34.6

MuShield Magnetic Shielding Material
Type analysis:

Carbon	0.02%	Nickel	80.00%
Manganese	0.50%	Molybdenum	4.20%
Silicon	0.35%	Iron	Balance

Electrical Resistivity
ohm-cir mil/ft	349
microhm-mm	580
Temperature coefficient of electrical resistivity
per °F from 0/930°F	0.0006
per °C from -17.8/499°C	0.0011
Curie temperature	860°F (460°C)
Melting point	2650°F (1454°C)
Specific heat, Btu/lb · °F	0.118
kJ/kg · K	0.494

COEFFICIENT OF THERMAL EXPANSION

Temperature		Coefficient
°F	°C	10 ^-6 /°F	10 ^-6 /°C
-103 to 77	-75 to 25	6.00	10.80
-58 to 77	-50 to 25	5.94	10.70
-11 to 77	-25 to 25	5.78	10.40
77 to 122	25 to 50	6.83	12.30
77 to 212	25 to 100	6.89	12.40
77 to 392	25 to 200	7.09	12.76
77 to 572	25 to 300	7.22	13.00
77 to 752	25 to 400	7.39	13.30

Heat Treatment

Hydrogen anneal: For maximum softness and optimum magnetic and electrical properties, MuShield anneals finished parts in an oxygen-free dry hydrogen atmosphere with a dew point below -40° F (-40° C) for two to four hours at 2050° F (1121° C) to 2150° F (1177° C). Furnace cool to 1100° F (593° C) from 1100/700° F (593/371° C), cool at a rate between 350° F (194° C) and 600° F (334° C) per hour. Oil, grease, lacquer and all other contaminants must be removed before annealing. Individual parts are separated by an inert insulating powder such as magnesium or aluminum oxide during hydrogen annealing.

Shielding Properties

MuShield Magnetic Shielding Materials. Because of its very high permeability and very low coercive force, MuShield's materials are particularly well suited for magnetic shielding applications. "Annealed, Deep Drawn Quality" strip can be fabricated into shields by bending, drawing or spinning: where joining is required, spot welding or tungsten inert gas welding -- with or without a base metal filler rod -- can be used. To develop the best shielding characteristics, shields must be annealed at 1900° F(1040° C) or higher as described under Heat Treatment after all fabricating operations have been completed. In general, higher annealing temperatures yield higher permeability and better shielding characteristics.

Workability

Machinability: High Perm Material machines somewhat like austenitic stainless alloys and develops gummy chips, but it does not work harden as rapidly as the stainless alloys. Work hardened bars (Rockwell B 90 minimum) offer the best machining characteristics. Lard oil should be used for drilling and machining operations which must be done at slow speeds. If sulfur-bearing and water-soluble cutting compounds are used, the parts should be thoroughly cleaned within 48 hours and heat treated. High-speed steel or carbide tools are suggested for cutting operations.

Cold Forming: For best blanking characteristics, strips should be purchased in the cold rolled condition Rockwell B 90 minimum. For best forming characteristics, strips should be purchased as cold rolled annealed for forming. For best drawing characteristics, strips should be purchased as annealed, Deep Drawn Quality.

Welding: High permeability materials are readily welded by following the usual practices for ferrous alloys.

If a filler material is required, use the same analysis. Finish annealed parts can be soft or hard soldered.

Do not Braze or solder prior to final heat treatment.

REFERENCES FOR MACHINING
Operation Speed*			Feed		Tool
	sf/m	m/s	i/r	mm/r	Materials
Turning	50	0.254	0.0007/ 0.002	0.018/ 0.051	M42
Drilling	35	0.18	0.001/ 0.004	0.025/ 0.102	M42
Milling	40	0.20	0.002/ 0.005	0.051/ 0.127	M2
Tapping	10/15	0.05/ 0.08	- -	- -	M1 or M2
*For carbide tools, double the sf/m

MECHANICAL PROPERTIES
BAR
	As Cold Drawn	As Hydrogen Annealed at 2050° F (1121° C)	After Process Anneal at 1600° F (871° C)
Tensile Strength, ksi	97	79	90
MPa	669	545	620
Yield point, ksi	69	22	33
MPa	414	152	228
Proportional limit, ksi	19	19	28
MPa	131	131	193
Elongation %	37	64	57
Reduction of area, %	71	70	74
Modulus of elasticity in tension 10³ ksi	33.7	33.3	31.4
10⁶ MPa	232	230	217
Rockwell B hardness	97	62	85
Izod impact, ft-lbs	120	85	85
J	163	115	115

STRIP
	Cold Rolled	As Hydrogen Annealed at 2050° F (1121° C)	After Process Anneal at 1600° F (871° C)
Tensile strength, ksi	135	77	98
MPa	931	531	676
Yield point, ksi		21	38
MPa		145	262
Proportional limit, ksi		15	35
MPa		103	241
Elongation %	4	38	38
Rockwell B hardness	100	58	85

CORROSION RESISTANCE:
High Perm Material is moderately resistant to moisture and atmospheric corrosion.