US2790938A

US2790938A - Magnetic chucks

Info

Publication number: US2790938A
Application number: US297948A
Authority: US
Inventors: Edwin H Brandenburg
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-07-09
Filing date: 1952-07-09
Publication date: 1957-04-30
Anticipated expiration: 1974-04-30

Description

April 30, 1957 E. H. BRANDENBURG MAGNETIC CHUCKS 2 Sheets-Sheet 1 Filed July 9. 1952 R mm ef E 3 9 V 1 1 mm B .m w/ E W p 30, 1957 E; H. BRANDENBURG 2,790,938

MAGNETIC CHUCKS Filed July 9, 1952 2 She'ets-Sheet 2 23 I6 24 W 24 /I7 W\ W; \yxr 2 A% mg 9 9 22 a viii/i111!!! raw! IIIIIIIII- 9 INVENTOR. Edwin H. Brandenburg United States Patent O MAGNETIC CHUCKS Edwin H. Brandenburg, Lakewood, Ghio Application July 9, 1952, Serial No. 297,948

9 Claims. (Cl. 317-463) This invention relates to electromagnets of the lifting or holding class.

While the invention may be applied to various kinds or types of lifting magnets and holding magnets, and used in various arts, it is particularly applicable to holding work pieces to be worked by a machine tool; and in order to make a concrete disclosure of the invention herein, as required by law, I have chosen to illustrate and describe it as embodied in a so-called magnetic chuck for holding work pieces in a lathe.

Magnetic chucks are known having a work contacting surface upon which ferrous work pieces may be laid and magnetically held against slipping (when subjected to the force or torque of a tool working the piece), by magnetic flux produced by a winding and flowing from one end of the winding core through the work contacting surf-ace into the work piece, and out of the work piece back into the work contacting surface and thence by a return magnetic path of the structure to the other end of the winding core.

The work contacting surface of such known chucks is thus in two parts on two pole pieces of a magnetic circuit separated from each other magnetically, and functioning as two magnetic pole faces of opposite polarity namely: a magnetic pole face of one polarity (say north) where the flux leaves the surface and enters the work piece, and a pole face of south polarity where the flux reenters the surface.

It has been proposed to have the two pole faces in a common plane, and to separate them by non-magnetic spacing material flush with the said plane, so that the whole work contacting surface is smooth and planar and the work piece can be freely moved on the surface to position it or to center it on a pilot; before the current energizing the winding is turned on.

It has also been proposed to shape the opposite-polaritypole-faces so that the space between them and the spacing material therein is of suitable uniform width, say A, and follows a zig-zag path or pat-tern. By this means if a work piece covers enough of said surface, it may overlap the said space at several points and will thus lie upon a plurality of north and south pole faces and accordingly be more firmly gripped upon the surface.

With such arrangements, a single electromagnetic winding provides a plurality (greater than two) of alternating north and south pole faces in the work contacting planar surface.

This principle of design has been proposed for rotary magnetic chucks for lathes. They are generally circular aroundthe rotational axis; and the flux emanates from the said surface at the axis; and the zigzag path or patterns of the space separating the pole faces in some case defines generally the contours of a star, concentric with the rotational axis; that is, there are teeth on a central part of the said surface radiating outwardly, and similar teeth on an outer part of the surface radiating inwardly, the teeth on each part projecting into notches between teeth on the'other part.

2,790,938 Patented Apr. 30, 1957 ice There is a fundamental objection to prior chucks that have a star pattern as referred to, namely; there are practical maximum and minimum limits to the number of teeth and therefore limits to the number of alternate pole faces that may be provided around the axis of the chuck, and accordingly, a limit to the maximum additive effectiveness of the pole faces. If there are many teeth in the design, they will be so close together and therefore so thin, circumferentially, as to have too small a pole face area. If they are too few, then at points remote from the axis where the holding effect must be greatest (to resist tool torque) the pole faces will be so few that their holding effect will be too little. This will be explained more fully hereinafter.

This primary defect of prior chucks of this type is overcome in the present invention by providing a small number of teeth adjacent to the axis and radiating away therefrom, and wide, circumferentially, at their roots, and, farther out radially, where the circumference is greater, fanning out into a great number of branch teeth.

By this means, a work piece of small diameter which requires small holding force, is held on the surface by a few alternating pole faces; and work pieces of larger diameter requiring more holding force are held by a greater number of alternate pole faces; and all of the radially extending portions of the inwardly and outwardly radiating teeth are of ample width and area.

It has been attempted heretofore to obtain this general result by complicated configuration patterns other than star patterns, and a correspondingly complicated zig-zag spacer; which, because of the complications, are prohibitively costly to make.

It is one of the objects of the invention to provide a holding magnet having the improved construction feature above described.

Other objects are to provide generally an improved holding magnet adaptable to be fabricated in an improved manner; with improved economy; and with improved facility of assembling and diassembling.

Another object is to provide a holding magnet, having a work engaging planar surface divided up into numerous pole faces of alternate polarity in an improved manner, and energized by a single winding; and the pole faces formed to exert greater holding force per square inch of the said surface and per ampere turn of the winding than is possible with prior magnets.

Another object is to provide a holding magnet having a unitary work engaging disc made of two co-planar parts with teeth of each meshed with notches of the other, and spaced apart by a zig-zag space of generally star pattern filled with non-magnetic bonding material poured into the space and solidifying therein, and bonding the parts together; and improved structural means comprising a nonmagnetic element for holding the two parts in said spaced relation during solidifying of the material and bonded to the disc by the solidified material.

Other objects will be apparent to those skilled in the art to which the invention appertains.

The invention is fully disclosed in the following description taken in connection with the accompanying drawing in which Fig. 1 is a view of the work contacting surface, of a holding magnet embodying the invention, the view being a top plan view of the parts of Fig. 2;

Fig. 2 is a sectional view of the embodiment of the invention and may be considered as taken from the plane 2-2 of Fig. 1;

Fig. 3 is a view similar to a portion of Fig. 2 illustrating a modification;

Fig. 4 is a fragmentary sectional view from the warped plane 4-4 of Fig. 1; and,

Fig. is a view similar to Fig. 4 but from the warped plane 5-5 of Fig. 1;

Fig. 6 is a View similar to Fig. 4 but from the warped plane 6 6 of Fig. 1;

Referring to the drawing, the magnet proper comprises a tubular outer side wall 1, and a bottom wall 2, and a cylindrical central core 3, coaxial with the side Wall 1, all integral and of steel or cast iron; and a preformed wind ing 4 around the core 3 and housed within the sidewall 4.

A shank 5 extends from the bottom wall coaxial of the core 3 to be gripped in. a lathe chuck or the like.

A steel flange 6 extends radially outwardly from the top of the side wall 1, being in the form of an annular plate, mounted on top of the wall 1 by screws 7-7.

A circular disc-like pole piece 8 is mounted on the end of the core 3. In some cases, the pole piece 8 can be omitted by making the core 3 longer.

An annular flat plate 9 of non-magnetic metal of suitable thickness, is seated in annularly recessed portions 10-10 and 11-11 of the pole piece 8 and flange 6 respectively, and will be described later.

The outer end 12 of the pole piece 8, and the outer face 13 of the flange 6, are machined to be in a common plane 15 and at right angles to the axis of the shank, so as to rotate in the plane without wobble.

Indicated generally at 16 is a separately made disc like structure, comprising radially inner and outer parts A and B.

The inner part A is made from a steel plate and genorally in the form of a star, having teeth 26-26 made by cutting notches 27-27 inwardly toward a center point of the plate. The distance of the bottom of the notches from the center being about the same as the radius of the pole piece 8.

The teeth 26 at their roots are wide circumfcrentially, and the notches are narrow.

For example in an illustrative case, the pole piece 8 may have a radius of 1%" and there may be only eight teeth, 26, about A" wide at their roots, and the notches 27 maybe about A wide at their bottoms.

The sides of the notches 27 are radial from the plate center point, and the notches are therefore V-shaped and become wider proceeding outwardly radially.

The sides of the teeth 26 are correspondingly radial and each tooth 26 as a whole therefore becomes wider, proceeding outwardly radially.

The outer end of each tooth 26, has Vshaped

notches

23, 29 cut in it. In the illustrative case there are two such notches, 28 and 29 and they divide the outer part of the tooth 26 into three teeth, 30, 31 and 32.

The bottoms of the

notches

28 and 29 in the il1ustrativc case may be, roughly, twice as far from the disc center as the bottoms of the notches 27.

The teeth 30-31-32 are rounded at their radially outer ends, and because of the V-shape of the notches 28-29, they taper radially outwardly.

The middle tooth 31 of the three

teeth

30, 31 and 32 is larger than the other two, being wider at its root than the other two, and its outer end extending beyond the ends of the other two.

The other part B of the disc is made from a circular steel plate having an unbroken continuous annular peripheral portion 24, and inwardly thereof having notches 35-36-37-323 cut in it, providing teeth 39-40-41- 42 so formed that the notches of the outer part B can be telescoped over the teeth of the inner part A and the teeth of each part will project into the notches of the other part with a substantially uniform clearance space 33 all around and between the teeth of the two parts.

The aforesaid annular non-magnetic plate 9 is rigidly mounted on the undersidcs of the two parts A and B of the disc, by a circular series of screws 46-46 projected up through the plate and screwed in the part A (see Fig. 4), and by a circular series of screws 47-47 screwed similarly through the plate 9 and into the part B (see Fig. 6).

The plate thus predisposes the parts A and B with the said clearance space 33 of uniform width at all points.

The clearance space is then filled with non-magnetic bonding material 33A of a kind that can be poured and thereafter will solidify.

A suitable material is metal composed of copper and antimony which is used in various arts, a commercial form being sold under the name Cerro-Matrix.

Such alloys will melt at a conveniently low temperature in a ladle over an open flame and can then be poured into said clearance space. The plate 9 as will be understood closes the clearance space on its underside, giving it the form of an upwardly open channel or trough. When the material cools and solidifies it has the property of forming a firm bond with the steel of the parts A-B and with the plate 9, making an integral rigid unitary structure of the three parts.

After the disc 16 is thus completed, it may be handled as a separate unit, and the upper and lower faces of the parts A-B, may be machined off to accurate parallel planes; and the plate 9 trued up as to its thickness and inner and outer diameters, and the disc as a whole is then mounted with the inner face 18 coincident with the aforesaid common plane 15, and with the plate 9 in the said recess, by circumferentially spaced screws 19-19 projected upwardly through peripheral portions of the flange 6 and screwed into the radially outer part B of the disc; and by screws 20-20 projected downwardly through the central portion of the disc part A and through the pole piece 8 and screwed into the end of the core 3.

The heads of the screws 20-20 are preferably flat heads and flush with or below the disc face 17.

When the disc structure 16 is thus mounted in place, it will be apparent that the pole piece 8 (when utilized) is also mounted on the core 3 by the screws 20-20; and that upon detaching and removing the disc 16 upon unscrewing the screws 19-19 and 20-20, the disc 16 and plate 9 may then be lifted off as a unit, thereby giving access to the winding to remove it for repair or replacement.

In some cases, see Fig. 3, the center of the disc part A may have a coaxial hole 21 and the pole piece 8 may have a coaxial threaded hole 22, and a pilot body 23, having a threaded shank 24, may have the shank screwed into the hole 22 to mount the pilot body on the disc, the pilot body serving to center work pieces on the outer face 17 of the disc; and to accurately position the pilot body, the outer face 17 may have a coaxial recess 25 in which the pilot body fits.

In such cases therefore, the pole piece 8 may be as sembled as a part of the disc structure 16 by means of the pilot; and when the screws 20-20 and 19 have been removed, the disc 16 and plate 9 and pole piece 8 may all be removed as an assembled unit as shown in Fig. 3 for the purposes mentioned.

If preferred however, when a pilot is used, the disc hole 21 may be threaded and the pilot shank 24 screwed into it and not be long enough to go on into the pole piece 8; in which case the first described assemblv and disassembly method would be utilized.

In the illustrative case referred to, and as shown in the drawing, there will be on the part A, eight large teeth 26, and twenty-four small teeth comprised of eight groups of teeth 30-31-32; and on the outer part B, there will be eight repetitions of three teeth 39-40-41 or a total of 24 teeth.

When the disc 16 is made and mounted as above described, the outer planar face 17 constitutcs the surface upon which a work piece may be placed and centered thereon by the pilot 23 when a pilot is utilized.

When the winding 4 is energized, the flux has a path through the core 3, and pole piece 8 into the part A, and

into the work piece, and out of the work piece into the part B, and thence to the peripheral portion 24 of the part B to the flange 6, and by way of the wall 1 and bot. tom 2 to the other end of the core 3.

The non-magnetic gap occupied by the plate 9 con strains the flux to flow radially all the way out to the peripheral portion of the disc part B before returning to the core 3.

If the work piece is of small diameter, it may overlap only the inner ends of the teeth 26 and 39-42 and the flux may flow from the teeth 26 through the work piece to the teeth 3942, thus providing eight north pole faces and eight south pole faces on the disc at small radius.

If the work piece is of large diameter it may overlap all of the smaller teeth 30-31-32 of the part A and all of the teeth 39404142 of the part B and the flux may flow into the work piece from teeth 30-3132 and out at teeth 39404142 thus providing 24 north pole faces and 24 south pole faces on the disc of larger radius.

In practice the torque exerted by the cutting tool on the rotating work piece held by the magnet and tending to make the work piece slip, increases with the radius on which the tool cuts; and the holding effect or holding torque of the pole faces opposing the tool-exerted-torque increases with the number of alternate pole faces and the radius at which the pole faces are disposed and the area of the pole faces.

These factors are compensated in the arrangement of pole faces above described. For small tool cutting diameter and small tool torque, a few pole faces on small radius are sufficient, and this is provided for by the sixteen pole faces of the teeth 26 on part A and the teeth 40-42 on part B, on small radius.

For greater tool cutting diameter and tool torque, a greater number of pole faces at longer radius are needed and this is provided for by the forty-eight pole faces of teeth 30--3132 on part A and of teeth 39-40, 41 on part B.

To increase the holding torque for extreme diameter of cutting tool torque, the teeth 31-31 are made extra long and the pole faces thereof act on an extremely large radius.

The holding torque of the pole faces of the teeth at any given radius depends upon the number of pole faces of alternating polarity and upon the area thereof.

When the teeth of a chuck are arranged in the kinds of star patterns of the prior art, it the number of teeth be increased in the attempt to increase the number of pole faces to increase the holding torque, their width and the width of their pole faces (considered circumferentially), and their area decrease.

A minimum space must always be provided between alternate teeth, to prevent short circuiting the flux of adjacent teeth, and if the number of teeth be increased too far, the width of the pole faces begins to approach a vanishing width. There is thus a maximum limit to the number of teeth beyond which there is no gain.

In the arrangement herein described, the number of teeth is increased, beginning at a great radial distance from the center, where the circumferential dimension is great, and the width of the teeth and their area are therefore not curtailed.

Thus the invention provides for a greater ratio of the number of teeth to the available area than heretofore possible or practical, and provides it at the larger radii where the tool torque is large.

This is reflected in greater holding torque for a given size of chuck; and in a smaller winding and fewer ampere turns, and decreased heat dissipation therefrom; and, in general, in a more efiicient chuck for a given amount of material.

The above described structure of the parts provides as referred to for low manufacturing cost and cheap assem' bly, and for concurrent accessibility to the winding.

The electric contact arrangement for supplying current to the winding 4 during rotation of the chuck by the lathe, has not been shown, as being well known. Threaded holes at 4343 are provided for attaching the rotating electrical circuit parts to the magnet; and holes at 44 and 45 are provided for terminal wires from the winding.

1 claim:

1. In a holding magnet, a magnetic circuit comprising a central core and a side wall circumscribing the core both extending from a base and spaced apart radially, providing space for a winding within the wall and surrounding the core; a unitary disc element comprising a central part magnetically connected to the free end of the core and an outer part having a peripheral portion magnetically connected to the free end of the wall; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, intermeshed with radially inwardly extending teeth and notches between them provided on the outer part; the teeth of the outer part comprising long teeth and short teeth, the long teeth extending inwardly toward the center of the central part and terminating at a chosen radial distance therefrom; the teeth of the inner part comprising body portions between the said long teeth of the outer part and the body portions outwardly beyond said chosen radial distance being divided into a group of teeth; the sides and ends of the intermeshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts together in a unitary structure; and all of the teeth being elongated in generally radial directions and being free from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central core and side wall are caused to be radial.

2. In a holding magnet, a magnetic circuit comprising a central core and a side wall circumscribing the core both extending from a base and spaced apart radially, providing space for a winding within the wall and surrounding the core; a unitary disc element comprising a central part magnetically connected to the free end of the core and an outer part having a peripheral portion magnetically connected to the free end of the wall; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, intermeshed with radially inwardly extending teeth and notches between them provided on the outer part; the teeth of the outer part comprising long teeth and short teeth, the long teeth extending inwardly toward the center of the central part and terminating at a chosen radial distance therefrom; the teeth of the inner part comprising body portions between the said long teeth of the outer part and the body portions outwardly beyond said chosen radial distance being divided into a group of teeth; of difierent lengths; the sides and ends of the intermeshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts together in a unitary structure; and all of the teeth being elongated in generally radial directions and being free from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central core and side wall are caused to be radial.

3. In a holding magnet, a magnetic circuit comprising a central core and a side wall circumscribing the core both extending from a base and spaced apart radially, providing space for a winding within the wall and surrounding the core; a unitary disc element comprising a central part magnetically connected to the free end of the core and an outer part having a peripheral portion magnetically connected to the free end of the wall; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, intermeshed with radially inwardly extending teeth and notches between them provided on the outer part; the teeth of the outer part comprising long teeth and short teeth, the long teeth extending inwardly toward the center of the central part and terminating at a chosen radial distance thereramas from; the teeth of the inner part comprising body portions between the said long teeth of the outer part and the body portions outwardly beyond said chosen radial distance being divided into a group of teeth; at least one of. which is longer than the others; the sides and ends of the intermeshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts together in a unitary strueture; and all of the teeth being elongated in generally radial directions and being free from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central core and side wall are caused to be radial.

4. In a holding magnet a disc like element having a plane surface upon which articles to be worked may be positioned; the disc like element comprising a central part and an outer part adapted, respectively, to be connected to the respective poles of a magnet to be energized with magnetic flux; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, intermeshed with radially inwardly extending teeth and notches between them provided on the outer part; the teeth of the outer part comprising long teeth and short teeth, the long teeth extending inwardly toward the center of the central part and terminating at a chosen radial distance therefrom; the teeth of the inner part comprising body portions between the said long teeth of the outer part and the body portions outwardly beyond said chosen radial distance being divided into a group of teeth; the sides and ends of the intermeshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts together in a unitary structure; and all of the teeth being elongated in generally radial directions and beingfree from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central part and outer part are caused to be radial.

5. In a holding magnet a disc like element having a plane surface upon which articles to be worked may be positioned; the disc like element comprising a central part and an outer part adapted, respectively, to be connected to the respective poles of a magnet to be energized with magnetic fiux; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, intermeshcd with radially inwardly extending teeth and notches between them provided on the outer part; the teeth of the outer part comprising long teeth and short teeth, the long teeth extending inwardly toward the center of ti e central part and terminating at a chosen radial distance therefrom; the teeth of the inner part comprising body portions between the said long teeth of the outer part and the body portions outwardly beyond said chosen radial distance being divided into a group o'f teeth; of different lengths; the sides and ends of the intermcshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts to gether in a unitary structure; and all of the teeth being elongated in generally radial directions and being free from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central part and outer part are caused to be radial.

6. In a holding magnet a disc like element having a plane surface upon which articles to be worked may be positioned; the disc like element comprising a central part and an outer part adapted, respectively, to'be connected to the 'espective poles of a magnet to be energized with magnetic flux; the central part of the disc element provided with generally radial outwardly extending teeth with notches between them, inter-meshed with radially inwardly extending teeth and notches between them pro ed into a group of teeth; at least one of which is longer than the others; the sides and ends of the intermeshed teeth and notches being spaced apart by a substantially uniform space filled with solid non-magnetic material, bonding the two parts together in a unitary structure; and all of the teeth being elongated in generally radial directions and being free from laterally projecting portions, whereby the main flux paths in the teeth toward and from the central part and outer part are caused to be radial.

7. The magnet described in claim 1 and in which the free end of the wall of the magnetic circuit is provided with a flange extending radially outwardly therefrom, and the peripheral portion of the outer part of the disc element is magnetically connected to a radially outer portion of the flange.

8. In a holding magnet, a magnetic disc element having a plane top surface upon which ferrous articles may be placed to be magnetically gripped; a radially inner portion and a radially outer portion of the disc element being adapted to be mounted respectively on the poles of a magnet; the inner portion provided with generally radial outwardly extending teeth and notches therebetween intermeshed with radially inwardly extending teeth and notches therebetween of the outer portion; the intermeshed teeth and notches sized to provide a clearance space all around all of the teeth and extending axially through the disc element; a plate of non-magnetic material on the bottom surface of the disc and covering the clearance space, and converting it into a trough, of which the side walls are the sides of the clearance space and the bottom wall is the plate and solidified non-magnetic bonding material in the trough, having the property of making an integral bond with the side walls of the trough.

9. A disc like element as in claim 8 and in which the bonding material also makes an integral bond with the non-magnetic plate at the bottom of the trough.

References Cited in the file of this patent UNITED STATES PATENTS 1,212,555 Pragst Jan. 16, 1917 1,312,092 Arter Aug. 5, 1919 1,554,236 Simmons Sept. 22, 1925 1,853,471 Storch Apr. 12, 1932