US2380616A - Magnetic system - Google Patents

Description

July 3l, 1945. J, sNOEK ET AL MAGNETIC SYSTEM Filed Mair 5, 1941 /A/x/fA/TO/25 JACOB Lou/S SNOW BY )f3 WW A TTORNEY Patented July 31, 1945 assume s PATENT OFFICE mamme srs'ram Jacob Louis Snoek and LultJe Mons, Eindhoven,

Netherlands; vested in the Alien Property Cus- VApplication May s, 1941, seran No. 391,020

1n the Netherland June zo, 1940 (ci. zz-zoo) selected with reference to that direction of the lClaim.

This invention relates to such magnet -systems comprising one' or more air gaps which either have an electric energization or are provided with one or more permanent magnets and which are built up from material of good magnetic conductivity at inductions higher than 10,000 gauss.

In such magnet systems the total weight of the system with a ileld intensity of from 6000 to 8000 gauss in the air-gap with the utilisation of a permanent magnet having a .(BHhnx lower than 2,000,000 will be substantially governed by the quality of the magnet steel used. In this case it is amply suillcient that the material of magnetic conductivity employed for the other parts of the circuit should be normally fired soft iron. 'I'he use oi material having special magnetic properties does not'give any particular advantage. If. however, in the construction of the system use is made of a magnet steel whose (BHMm is higher than 2,500,000, say 5,000,000, it is possible to ensure a considerable increase of the field intensity in the air gap or else a considerable saving in weight of the magnet system with identical ileld intensity in the air gap if the 'soft iron is replaced =by material of higher conductivity at a high induction.

In the use of electrical energization oi magnetic circuits also a considerable reduction of the quantity of magnetic material or else a reduction in energization can be obtained itat high inductions use is made of material having a particularly high permeability.

It iswell-known' that for the purpose of obtaining the maximum ileld intensity in the air gap or of reducing the dimensions of the circuit use may be made at given points of material exhibiting very high magnetic conductivity. at inductions higher than 10,000 gauss. As an example of such material, it has been proposed to use -an ironcobalt alloy containing substantially equal parts of iron and cobalt. Because of the magnetic isotropy of the composing crystals this alloy has a high permeability in all directions independent of the crystal orientation.

According to the invention, the magnetic 'material used is an alloy contalning'a substantial proportion of iron. and thus having a positive cristal anisotropy, but having added to it one or more elements in such amounts that while coolin'r from the solidiflcation temperature down to ordinary temperature the alloy only traverses the magnetic transition point (Curie point), the cooling of the fusion being directed in such manner that the solldilcation gives rise to directional crystals (columnar crystals) whose direction is magnetic eld which is to be expected in the magnet system.

It has ybeen found that the orientation of these columnar crystals is such that a [1,0,0] direction or axis oi the crystals extends parallel with the direction of the columns. Since with materials exhibiting 'positive crystal anisotropy the v[1,0,0] direction has a very high magnetic conductivity at inductions which closely approach magnetic saturation, the direction of the columnar crystals with such material is always a direction of good magnetic conductivity. For other directions the magnetic conductivity is generally much lower due to the arbitrary 'orientation of the columnar crystals about their long axis.

The use of this material leads to a decrease of `the magnetic leakage in the proximity of the air 'gap and thus to an increase of the ileld intensity in the air gap.

Besides, the iron alloy according -to the invention is more easily machined than the well-known iron-cobalt alloys.

For parts of the magnetic circuit in which the lines of force are curvilinear, such as in pole pieces, the said alloy comprising directional columnar crystals cannot -be used directly. since columnar crystals can only grow out along a straight line. By jumping-.UD or upsetting, the material may, however, be shaped into such form that the desired correlation of the crystal orientation to the direction of the lines of force is obtained. After the jumping-up operation the material must, however, b'e reilred in order that the internal stresses produced may be removed.

In order that the invention may be clearly understood and readily carried into effect it will now be described more fully with reference to the accompanying drawing, in which: l

Figs. 1 and 2 are diagrams of the variation of the solidiiication temperature and the transition points of iron-aluminium and iron-silicon alloys, respectively.

Fig. 3 shows ahcasting and cooling method with a view of obtaining directional columnar crystals.

Figs. 4, 5 and 6 show three forms of construction of elements thus cast of a magnet system.

l Referring to Figs. 1 and 2. the line l0 indicates the variation of the solidiilcation temperature of l and alpha phases with temperature. On cooling from the solidiilcation temperature to ordinary temperature an alloy of iron-aluminium containing more than 11/?% of A1 traverses no longer the gamma-phase but permanently remains in the alpha-phase. Thus, a crystal formation is set up which. with the correct manner of cooling, leads to columnar crystals. The line I2 indicates the variation of the magnetic transition point. This point is therefore always traversed during cooling so that the casting eventually cooled exhibits magnetically conductive properties, as is the ca'se with an iron-silicon alloy comprising more than 2/z% of silicon or an addition of silicon and aluminium in conjunction to the extent of more than 2%.

On the other hand, however, the addition of aluminium and silicon decreases the maximum induction obtainable of the alloy so that it is acivisable that only this minimum quantity of aluminium or silicon should be used.

Fig. 3 illustrates the method of casting and directional cooling with a view of obtaining co1- umnar crystals in the desired direction. A castlng mould I3 having no bottom is placed on an artificially cooled copper plate I4. The casting mould is surrounded by a furnace I5.

The casting mould I3, which .in the present case is intended for the formation of a central pole of the magnet system of an electro-dynamic loudspeaker, has poured into it a quantity of a liquid iron-aluminium or iron-silicon alloy of the required composition. The furnace I5 is caused to assume a temperature of about 1200 C. so that the casting mould is itself also heated. The supply of heat to the furnace IE is decreased so that the casting slowly cools entirely. The lowermost part of the casting I5 is in direct contact with the cooled plate I4; hence all heat will be withdrawn from the casting in the direction of the arrow III.

There will be a formation of columnar crystals one of the axes of which extends parallel With the longitudinal axis of the cylindrical piece IB. It has now been found that lthe [1, 0, 0] direction extends parallel with the long axis of the coluninar crystals so that the maximum magnetic conductivity coincides with the direction of heat withdrawal, in the present case the longitudinal axis of the cylinder I6. It is to be expected that the direction of the magnetic field in a central pole of an electro-dynamic magnetic system also extends along this axis.

Fig. 4 shows a form of construction of a cy1indrical component member 20 of a magnet system. s described with reference to Fig. 3, this piece has cooled to such extent during solidiflcation that the il, 0. 0l direction of the columnar crystals extends parallel with the longitudinal axis of the piece. The piece should be placed in such manner in a magnetic circuit that the field also extends in the direction of the' longitudinal direction. These conditions occur, for example. with the central pole oi' an electro-dynamic magnet system.

The form of construction shown in Fig. 5 comprises a disc-like plate 2I in which a centrai cy lindrical aperture 22 is formed. Component members of this kind are used, yfor example, as the annular pole plate of an electro-dynamic magnet system. The magnetic field to be expected extends radially in such a pole so that the withdrawal of heat, during solidiflcation of such a piece should occur at the outer circumference and in this case the [1, 0, 0l direction of the co1- umnar crystals is also radial.

Since columnar crystals can only grow out along a straight line component members of magnet systems in which the direction of the magnetic field diverges from the straight line cannot be built up directly from material crystallised in columnar crystals, since the magnetic conductivity is substantially less outside the [1, G, [Il direction of the crystal. As a matter of fact it is. however, possible for such component members to be adapted for the object sought if the material is given such a form by jumping-up that the direction of the columnar crystals is altered to accord with the direction to be expected ofthe magnetic field. It is necessary 1that after jumping-up the internal stresses set up by firing should be removed although this results in the particularly favourable crystal form being slightly lost.

Fig. 6 shows a form of construction of the central pole pin of an electro-dynamic magnet system. The uppermost part 2l which forms the pole piece proper is so deformed by jumping-up of the cylindrical pin 23 that the direction of the columnar crystals is bent-oil radially to the sides so that it is altered to accord With the direction of the lines of force that laterally emerge towards air gap.

What we claim is:

A method of producing magnetically conductive material, according to which use is made of material of positive crystal anisotropy Containing a major proportion of iron, which consists in add ing to said material such component ingredients that while cooling from the solidification point down to ordinary temperature only the magnetic transition point is traversed and no phase-change occurs in the material as it solidifies, pouring said material in the fused state into a casting mould, and then cooling the cast material in a given direction in such a manner as t0 give rise to col umnar crystals in the direction of maximum magnetic conductivity.

JACOB LOUIS SNOEK. LUITJE ALONS.

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