US2994122A - Method of forming low flux loss bonds in permanent magnet assemblies - Google Patents

Description

Aug. 1, 1961 sFzdM ERKER ETAL P MANENT MAGNET ASSEMBLIES Original Filed Oct. 19, 1955 METHOD FlG.l

LOW FLUX LOSS BONDS I INVENTORS SIEGFRIED ZUERKER, BENJAMIN J. SAGGESE,

THEIR ATTORNEY.

United States Fatent g 2,994,122 METHOD OF FORMING LOW FLUX LOSS BONDS IN PERMANENT MAGNET ASSEMBLIES Siegfried J. Zuerker, Utica, and Benjamin J. Sa'ggese,

Liverpool, N.Y., assignors to General Electric Company, a corporation of New York Original application Oct. 19, 1955, Ser. No. 541,436, now Patent No. 2,894,182, dated July 7, 1959. Divided and this application Mar. 9, 1959, Ser. No. 797,964

2 Claims. (Cl. 29-15556) This application is a division of co-pending application for Electro-Acoustic Transducer, Serial Number 541,436, filed October 19, 1955, issued July 7, 1959, as US. Patent No. 2,894,182 which is assigned to the same assignee as the present application.

This invention relates to an improved structure for the magnetic component of a transducer device.

It is an object of this invention to provide a novel magnetic structure for a transducer, such as a loudspeaker which permits fabrication at a reduced cost.

It is another object of this invention to provide a novel magnetic structure for loudspeakers, which structure has a configuration permitting it to be molded out of a powdered magnetic material.

It is still another object of this invention to provide a novel magnetic structure for loudspeakers, wherein the magnetic structure may be assembled to the rest of the speaker assembly by the use of a portion of the magnetic structure itself so that the cost of assembly is reduced.

In the prior art wherein one component of magnetic material has been soldered to another, it has been found necessary to first coat the components with a suitable base before applying the solder. This method of bonding results in a relatively thick eflective air gap between the two members and a consequent increase of reluctance in the circuit. Therefore, it is a further object of this invention to provide a novel method of bonding magnetic materials so that the eifective air gap between the materials is minimized.

It is still a further object of this invention to provide a novel means and method of bonding components of magnetic structures to one another so that the cost of assembly of these components is reduced and the sensitivity of the structures are increased.

Briefly, the objects of this invention are achieved in one form by the provision of a unitary structure forming a portionof the magnetic circuit of a loudspeaker, which unitary structure has provided thereon an integral means supporting the magnetic structure on the speaker basket. A second portion completes the magnetic circuit and is assembled to the remainder of the magnetic structure by the use of a bonding material which reduces the equivalent air gap normally existing between the second portion and the rest of the magnetic structure and thereby cuts down the consequent flux loss and yields a more sensitive instrument.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims. Our invention itself, however, both as to its structure and method of assembly, will best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

FIGURE 1 is a cross-sectional side view of a speaker embodying our invention; and

FIGURE 2 is a rear view of the speaker illustrated in FIGURE 1.

Referring now to FIGURE 1 of the drawing, it may be seen that the speaker is constituted by the supporting frame or basket 1. At the outer periphery of the basket a flange 2 supports the outer edge of a frusto-conical known in the art. Also, in the manner well known the art, we provide a flexible spider 6, which is secured at its outer periphery to the basket as shown at 7. A moving or voice coil 8 is wound on the voice coil form 5 and drives the diaphragm 3 in accordance with the varying electrical signals representing sound intelligence impressed thereon. The construction described is substantially that construction well known in the art and constitutes no part of our invention.

In accordance with our invention, we provide aper-,

. manent magnet '9 which may have a cylindrical configuration and is disposed, as illustrated in the drawing, just to the rear of the basket 1. The magnet may, if desired, be constituted by an electromagnet or may be a permanent magnet formed from the material known by the trade name Alnico V which is commonly used in the 1 art for this purpose. A pole plate 10 of magnetic material may be secured by any suitable means to the front of the magnet 9 or may be held by the action of the magnet itself and provides a path to carry magnetic flux to a region surrounding the voice coil 8. Alternatively the pole plate 10 may be eliminated and the magnet9 extended to the region occupied by the pole plate. A

cup or yoke structure 11, which is formed as a tube and which may have a circular cross-section, encompasses the magnet 9 and also constitutes a portion of the magnetic circuit of the device. The remainder of the magnetic circuit is completed by the bottom plate 12 which may be formed from a soft steel or other magnetic mate- 1 rial and is secured to the rear end of the magnet 9 and engages the inner surface of the larger inner diameter end of the cup. A forward portion of the cup 11 is provided with a portion extending radially inward as shown at 13 and presents a smaller inner diameter. In combination with the pole plate 10, the portion -13 forms an air gap 1 4 in which the voice coil 8 is situated, whereby the electrical conductors constituting this coil may be transversed by the magnetic flux emanating from the magnet 9. The extent of the inwardly directed portion is selected inaccordance with the principle well known in the art so that the required spacing between the outer periphery of the magnet 9 and the inner wall of the cup 11 is at an optimum to maintain fringe flux losses between these two members at a The forward end of the portion 13 is provided with a means whereby the cup may be secured to the basket 1 by positioning extension 13, in an opening in the rear portion 15 of the basket 1 and peening it over to engage the frame in the manner indicated by reference numeral 16.

The construction of the magnetic portion of the speaker is such that the yoke or cup 13 may be molded using any suitable material capable of carrying magnetic flux. Thus, it is possible to utilize a powdered iron material for this portion of the assembly which may be fabricated by molding so as to considerably reduce the cost of this portion of the device. This particular advantage is gained by providing that the forward reduced inner diameter portion 13 of the cup constitutes the element completing the air gap, necessary for the operation of the voice coil.

As pointed out above, the magnetic circuit is completed by the bottom plate 12. The bottom plate, in addition to completing the magnetic circuit, also functions to make possible the use of material having a relatively low saturation value, and consequently relatively inexpensive materials, as it reduces the flux density by providing Patented Aug. 1, 196 1 spacing or securing ring,such

a path of ever increasing cross-section from its center to its periphery where it engages the cup 111. Thus, a. powdered iron material is capable of transmitting the required flux without incurring high osses due to high flux density.

A further feature of our invention is the manner in which the bottom plate 12 and the pole plate are secured to the permanent magnet 9. It has been the custorn in the prior art to solder such assemblies. The soldering operation has been carried out by coating the members with a base such as cadmium and by depositing pellets of solder and flux between the surfaces of the two members after the coating. Heat is then applied and the solder disperses over the two surfaces. However, the structure which thereby results is subject to the disadvantage of what amounts to a fairly large gap exists between the two members 9 and 12. This air gap may be on the order of 0.002 of an inch and the resulting flux losses serve to reduce the sensitivity of the device.

In accordance with our invention, we provide that the opposing surfaces of the pole plate 10, bottom plate 12 and the magnet 9 shall each be cleaned by the application of a suitable flux or a cleansing agent and then coated with a relatively thin coat of tinzinc. It has been found that a tin-zinc composition of from 73%- 83% tin and from. 27%17% zinc, by weight, yields a bond of sufficient strength to hold the members together. Within this range, a composition of 78% tin and 22% zinc, by weight, appears to yield a bond of optimum strength characteristics. We have found that electroplating the most effective method for forming a coating of tin-zinc on the surfaces to be joined. The members 9, 10 and 12 are then subjected to heat. The tin- Zinc forms, upon cooling, at strong bond to hold the members 9, 10 and 12 together. The equivalent air gap between these members is far less; than that obtained by other methods such as noted above and the consequent losses are avoided. The air gaps, obtainable by the use of method, are on the order of 0.0002 of an inch and an over-all increase in speaker sensitivity is obtained. Such an advantage permits either the construction of a more sensitive speaker or, sensitivity comparable to competing speakers is desired, a smaller magnet with its consequent cost reducing feature may be used. We have tound that if a fiurther decrease in the equivalent air gap is desired, pressure may be exerted on the elements 9, 10 and 12 to force out whatever bubbles or undue thickness of plating material may be present.

The bonding technique, described above, has particular utility in forming structures constituting a magnetic circuit wherein it is desirable to avoid flux losses. However, it is not limited in its application to loudspeaker magnetic structures, but obviously has general utility in fabricating magnetic devices of diverse characteristics.

While the present invention is described by reference to a particular embodiment thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the invention. We therefore, in the appended claims to cover all such variations as come within the true spirit and scopeof the foregoing disclosure.

What We claim as new and esire to secure by Letters Patent of the United States is:

l. A method of bonding a permanent magnet to a portion of a loudspeaker magnetic structure comprising the steps of, electroplating the magnet and the magnetic structure with tin-zinc, and subjecting them to heat to cause the tin-zinc to form a bond.

2. A method of bonding magnetic materials comprising the steps of electroplating a coating of tin-zinc on each surface of each member to be bonded, placing the plated surfaces in contact with each other, subjecting the members to heat to cause the tin-zinc to form a thin low flux loss bond.

References Cited in the file of this patent UNITED STATES PATENTS 440,952 Land NOV. 18, 1890 2,169,098 Howe Aug. 8, 1939 2,798,843 Slomin et a1 July 9, 1957 ,365 Erickson Feb. 25, 1958

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