POWDERED-IRON CORES in-house manufactured
When a powdered-metal core of compact material is made, it is also encumbered with severe eddy-current losses. In order to reduce these losses, the volume of the core must be subdivided into a large number of electrical sectors isolated from each other.
This is accomplished one-dimensionally using a tape wound core and three-dimensionally using a powdered-metal core. Such cores have magnetic properties totally different to those of the compact core.
For many applications, an air gap must be applied additionally to the tape wound core. In the case of the metal-powder core, the air gap can then be adjusted to the particle isolation and the complete core distributed homogeneously.
The magnetic flux passes alternatingly in the powdered-metal core between magnetic sectors and non-magnetic interstices. This results, inter alia, in a significantly slighter stray field being generated in the cores with the air gap. Powdered-metal cores are thus especially suitable for all applications involving DC magnetic bias.
The initial permeability of powdered-metal cores depends essentially on the material and achieves µ 90 in the case of pure-iron core and µ 160 in the case of cores consisting of molybdenum-permalloy powder (81Ni 17Fe 2Mo).
Only carefully selected powders of high chemical purity are capable of developing the required magnetic properties.
The powder particles are effectively isolated from one another in the first step of the production process. Prior to pressing, a binder is added to generate the necessary mechanical stability. After pressing, the cores are adjusted to the required mechanical properties in a final annealing operation.
The parameters of the powder cores can be systematically adjusted between broad ranges by varying pressing conditions, particle isolation and suitable heat treatments.
The many diverse core geometries provided by PTR HARTMANN (toroidal, E-core, EF-core, cylinder core, tubular core, block core and profile core, modular and one-piece structured pot cores) on a powdered-iron basis permit great flexibility in the choke design.
Toroidal cores are fitted with a plastic coating to electrically isolate them from the winding and to protect them against harmful ambient influences. The epoxy-paint coating of the toroidal cores permits high dielectric strength with minimum paint-film application.