US2160405A - Magnetic work holder - Google Patents

Description

May 30, 1939. F. R. MALLALIEU MAGNETIC WORK HOLDER Filed April 8, 1958 2 Sheets-Sheet l INK/,m

IgM/MMM ,@@wwdiw May 30, 1939- F. R. MALLALIEU 2,160,405

MAGNETIC WORK HOLDER Filed April 8, 1938 2 Sheets-Sheet 2 f6 15 za 1l. 23j/,941?? HQA? f f /1 Patented M., 3o, .1939

I UNITED STATES PATENT or-"FICEY vanimes MAGNETIC wonx noLDEn man nnoaemk Maumee, oxford. ra; application april s. 193s, serai No. 200.862

'I'he present invention relates to a magnetically energized work holder for articles of magnetic material and in. which the magnetic hold- 'ing members are energized by permanent mag- A nets.

A purpose of the invention is to surround and support multiple pole pieces of a permanent magnet and of one polarity by a common work table of soft iron or the like and of opposite polarity.

lo A further purpose is to open and close the magnetic circuit of a magnetic work holder without movingv a permanent magnet energiizng the circuit and at a portionof the circuit intermediate the magnet and the magnetic poles presented l5 to and holding the magnetic work, opening the circuit to release the work without disturbing the work.

A further purpose is to include a soft iron slide in the external magnetic circuit of a permanent magnet energizing a magnetic work holder, locating the slide intermediate the magnet and the work and using the slide as means to release the hold of the magnetic work holder without needing to move the magnet nor one or other of the pole members presented to and holding the work. 4

A further purpose is to provide a magnetic slide to be in continuous magnetic connection to one pole of a permanent magnet and connecting .30 selectively to either or neither of two magetic members that magnetically connect respectively to the other pole of the `magnet and to a magnetic work table. v

Afurther purpose is to employ the power of ,35 magnetic alloys to a fuller Iextent than has been 45 completely cover the face.

A further purpose is to simplify and cheapanv; the construction of permanent magnet wolf? holders.

Further purposes vwill appear in the specification andin the claims. I have elected to show one main-form only of Ymy invention, showing however detail modifications Vand selecting amain form 'and modificau tions 'thereof that well illustrate the principles V 18 Claims. (CL 1715-467) involved and are practical and eillcient in operation.

' a different position from that of Figure 2. The

energizing and release positions are shown re- 15 spectively in Figures 2 and 2a. Figure 2a also indicates in dot-and-dash line a third position of the slide.

Figures 3a and 4a arev fragmentary views corresponding generally to Figures 3 and 4 respec- 20 tively, with the magnetic circuit-closer, or slide, in different positions, closed in Figures 3 and 4 and open in Figures 3a and 4a. Figure 3a indicat in dot-and-dash line a third position of the slide or circuit-closer. 25

Figure 5 is a fragmentary elevation showing the chuck of the present invention applied to rotary machinery.

. Like numerals refer -to like parts in all figures.

Describing in illustration and not in limitation and referring to the drawings: f

In previous permanent magnet chucks or work holders, difllculty has in some cases been encountered through failure to provide means for diverting the flux to release the work. In other devices of the kind, whereas release has been provided for, such release is often incomplete and such previous chucks do not develop the full holding forces of the permanent magnets employed.

In the following description. the constructions 4o of certain embodiments of the invention will ilrst be considered, before explaining the special advantages o! these constructions.

Throughout the specincation and claims the term "soft iron" is intended to mean any suitable magnetic material, soft iron, soft steel or the dike, having the property of becoming immedihtely magnetic when subjected to magnetmng force and of effectively losing its magnetism with removal of the magnetizing force.

In the illustration the magnetic chuck or work holder comprises essentially a permanent magnet Il, a soft iron table Il, multiple pole pieces Il, non-magnetic'members Il that support and magneticallyinsulate the pole pieces from the ss table, and soft iron connections respectively from the pole pieces I2 to one pole of the magnet I0 and from the soft iron table II to the other pole of the magnet I0. The work table and pole pieces are preferably substantially flush, although they may be curved to conform to the shape of the work.

The work-holding face of the chuck is the top face `presented by the members II, I2 and' I3, the magnetic work being intended to seat on the table II across any number of the pole-pieces I2 (here a few only are shown, but by breaking the ilgures it is intended to indicate that any number of pole pieces may be employed).

4 portion of the magnetic circuit of the magnet I0.

' bers u and ls.

The magnet I0 is shown conventionally as a bar in the -igures, intended to be polarized vertically, that is, parallel to its shorter dimension. Soft iron connection is provided from one magnet pole at the top I4 to the multiple pole-piece inserts I2 and soft iron connection is provided from the other-,magnet pole I5 at the bottom to A'the table I I.

In practice the magnet III `may be made up of preferred to use a single magnet.

The soft iron connection between the table II and the bottom pole I5 of the magnet is through soft-iron sides I5. The soft iron connection between the multiple pole inserts I2 and the top pole I4 includes a soft iron member that in Figure 2 is a conductor bar I1, stationary and integral with the pole inserts I2, and that in Figures 3 and liis a slidable conductor bar I8.

The pole members II and I2 presented to the magnetic work are effectively energized only when they are in closed soft-iron connection with thepoles I5 and I4 of the magnet and one of the main features of the present invention is to deenergize the pole members II and I2 by opening the soft-iron connection of either to the magnet-thereby releasing the magnetic hold of the chuck upon the work without either moving the magnet or disturbing the work.

In Figures 2 and 2a, the magnet pole Il is continuously in connection with the pole pieces I2 through the conductor bar I'I. The soft iron connection between the table II and the bottom pole I5 of the magnet includes a soft-iron slide I0. This slide I9- presents its upper face continuously -to the downwardly directed pole I5 oi.'`

the magnet and its lower face slides along a non-magnetic base plate 20 secured to the magnetic side walls I8. It is adapted to be shifted, as by means of a suitable non-magnetic screw connection 2| with the side wall, selectively to occupy settings respectively for energization of the work holder, for work release and for'appllcation of a keeper to the magnet.

In the chuck energizing position, Figure 2, the slide, all the way to the right, engages at 22 the soft iron side I6 of the table-thereby securing a continuous soft iron connection between the table II and magnet In the work release position, full-line Figure 2a, the slide I9 has been shifted to a midposltion, opening a gap at 23 in the soft-iron connection between the table II and the magnet pole. In the magnetic-keeper position the slide has been shifted all the way to the left into enpole I5 through -the mein-y 'extensions 21 adapted in one position of the slide, that of Figure 3, to register with the lower ends of the pole-piece inserts I2 of they table. 'I'his is the chuck energizing position.

By shifting the slide to the position of Figure 3a, as by means of non-magnetic screw mechanism 28, the polar extensions 21 are intermediate the pole pieces I2 and in contact with the insulation I3', and the resultant gaps in the soft-iron connection between the pole pieces I2 and the magnet pole I4 provide for effectively releasing the magnetic hold of the chuck without moving the magnet or disturbing the work.

In the form of Figures 4 and 4a, the structure lis similar to the structure of Figures 3 and 3a except that the table II is throughout flush with the bottoms of the pole pieces I2, and no conductor block 29 is needed, as explained below.

It will be understood that when the conductor bar I8 of Figure 3 is moved to the release position shown in fullline in Figure 3a, the magnetic circuit to thework is interrupted, but no keeper is applied to the magnet. Further movement to the position shown in dot-and-dash line in Figure 3a forms a closed magnetic circuit from the magnet pole Il, through the conductor bar I8, through the soft iron conductor block 29, the

table II, the side wall I6, the bottom wall 26 and finally to the magnet pole I5.

In the form of Figure 4, when the conductor bar I8 slides to the "position of Figure 4a (enlargement lII on the end of the screw feed may provide a stop), the conductor bar first interrupts the magnetic circuit through the work and then by engagement at IIIA with the bottom of the table II, applies a keeper to the magnet.

In manufacturing the chuck of the present invention, the table I I and sides I6 may desirably be a casting, produced with the slots in the required positions. The pole pieces may then be inserted in the slots and melted lead poured into the spaces to provide the insulation I3 or I3'.

The table II-and pole pieces I2 are then surface ground on the upper face in Figure 2 and on both faces in Figures 3 and 4. I'he magnet is desirably ground on its two pole faces and rigidly held in thev construction in any suitable manner as by engaging screws from the end walls, not shown. The operating handle may, if desired, be removable.

Anvadvan'tage of the present invention is that expensive and relatively weak non-magnetic all'oys are reduced to a minimum in the present construction, which can employ chiefly inexpensive steel castings. Machine work is reduced to a minimum. The necessity for grinding a number of magnets together in a set is wholly avoided.

It will be understood that an important advantage of the present invention is the facility with which keeper action may be applied to the magnet when desired without the use of any complicated construction and without the necessity for applying a plate to the working surface oi' the chuck. Inprevious permanent magnet chucks, complete breaking of the magnet circuit in the release position has not been accoma,1oo,sos

'pushed or intended. Instead. a panini snoricircuiting or shunting of lines of torce through an auxiliary circuit has previously been used.

In view of the complete breaking of the magnetic circuit and the ample keepei` action. the most powerful of the modern magnet steels may be used,since on theonehand there is no danger of partial holding of the work in the release position as was the case in prior art constructions where complete breaking of the magnetic c ircuit` was not employed, and, on the other hand, the magnet is held at highest emciency by the keeper.

In accordance with the present invention, a considerably larger proportion of active magnetic material tllls the space within the chuck. Almost twice as much magnet area is possible with .the present invention as with prior constructions.

The device of the present invention is particularly desirable to hold small work. In the present construction, it is very easy to provide a num-ber of small pole pieces (inserts), as it is only necessary to provide the table Il with the number and size of pole pieces desired and then to cut the required number of slots in the bar l1 ot Figure? or the Abar' II of Figures 3 and 4. No need for re-design of the magnets themselves is caused by this change, as was the case in prior art constructions. Where a piece of work does not cover the entire active face of the chuck, all the flux of the magnet upto the point of saturation of the conductors and of. the work is concentrated on the particular pole piece or pole pieces which are active in holding the work. In usual prior art constructions, each pole piece was supplied with ilux from one magnet alone of a plurality oi' magnets,` with consequent lowering of the proportional force.

By virtue of the emciency of the construction from a magnetic standpoint and the possibility of increased magnetic area, the increased holding ilux as compared with prior art constructions in which the work is released by shunting of flux, is substantially as follows:

Factor by which the area of the magnet may be increased -2 Factor by which the strength of the magnet may be increased 1.5

Cumulative sum 3 For a given lholding area the holding force is proportional to the square of the total flux available. 'Ihus e factor by which the holding 'force may be increased in the present construction, over prior art chucks, is 9.

This ignores several small disturbing factors, but they are of minor significance. It is thus clearly evident that .the invention makes possible a very new and unobvious result in the production of markedly greater, holding forces than were previously thought possible.

In designing the chuck of the` present invention, it is not, as might be supposed, desirable to isolate conductors of Opposite polarities too widely from one another. The spacings of conductors of opposite polarity should be such that there' is suiilcient leakage flux to prevent great self-demagnetization in the release position or in case the device isleft in the on position with no work on the face.

In other words, a leakage path of substantially the same reluctance in any position of the slider is provided internally between the two poles of the magnet by properly spacing oppositely polarized conductors. and this path serves (and becomes important in its, service when the main circuit is of high reluctance, as when the device is on with no work on the face or oi!) to always carry ilux from pole to pole of the magnet, at all times providing av relatively low rel ctance ilux path, preventing partial demagne tion oi the magnet. In this way, in effect, a keeper circuit is at all time acting, and thus, except rarely when the work holder is not to be used for a long period of time, it is not neceary to apply the full iron keeper circuit provided in any of the embodiments shown and such circuits are optional and not necessary to the operation of the devices. e

As stated above', the reluctance of the leakage path provided is constant irrespective of the position of the slider. Thus, although this path functions in the "on position of the device also, it does not unduly rob the working face of the holder of useful ilux, as the leakage path is made to have a high lreluctance relative to the re- 1uctance.of the. active face when holding work, although it exhibits a relatively low reluctance in respect to the reluctance of the main circuit when opened in the off position or when in the "on position with no work on the face.

The leakage path is thus operative at all times -as a bleeder circuit, irrespective of the podtion of the conductor bar. When the iron keeper" circuit is applied, however, the leakage path is eflectively inoperativey and wholly negligible.

It will be understood that the chuck or work holder of the present invention may be used for any service where such devices are desired, whether the chuck be stationary or moving, and regardless of the character of the motion. Figure 5 shows a chuck 32 according to the invention, rotatably mounted in a lathe 33 (the live center end only being shown). The active magnetic holding face is shown at N.

In view of my invention and disclosure variations and modications to meet individual whim or particular need will doubtless become evident to others skilled in the art to obtain all or part of the benefits of my invention without copying the structure shown and I therefore claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention what I claim as new and desire to secure by .Letters Patent is:

1. In a magnetic work holder, a rst magnetically conducting member exposed to contact with the work, n plurality of second magnetically conducting members magnetically insulated from the first magnetically conducting member and likewise exposed to contact with the work, a permanent magnet having two poles, -a magnetic conductor connecting the iirst magnetically conducting member to one of the magnet poles, a

magnetic conductor connecting all of said second magnetically conducting members to the other magnet pole and means for interrupting the connection between a magnet pole and the corresponding magnetically conducting member or members.

2. In a magnetic work holder, a first magnetically conducting member exposed to contact with the work, a plurality of second magnetically conducting members magnetically insulated from the ilrst magnetically conducting member and likewise exposed to contact with the work,aperma nent magnet having two poles, a magnetic lcoriductor connectingthe ilrst magnetically conducting member to one of the magnet poles, a magnetic conductor connecting all of said second magnet- 'ically conducting members to the other magnet pole and common means for interrupting the connection between amagnet pole and the corresponding magnetically conducting member or members, and for connecting one magnet pole with the other magnet pole.

3. In a magnetic work holder, a first magnetically conducting member exposed to contact with thevwork, a plurality of second magnetically conducting members magnetically insulated from the first magnetically conducting member and likewise exposed to contact with the work, a permanent magnet having two poles, a magnetic' and in a further position of sliding, to close a keeper magnetic circuit across the magnet. 4

4. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened to the table, a permanent magnet having poles of reverse polarity, a soft iron connection from one of the poles to the table, another soft iron connection from the other oir the poles to the pole pieces and means for opening and closing one of the soft iron connections.

5. In a magnetic work holder, a soft iron table having slots, soft iron pole pieces in the slots and magnetically insulated from the table, a permanent magnet having poles, soft iron connections from one pole of the permanent magnet to the table and from the other pole of the permanent magnet to all of said pole pieces and slidable means for interrupting one of the connections and for applying a keeper to the magnet.

6. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened to the table, a permanent magnet having Apoles of opposite polarity, a soft iron 'connection from one of the poles to the table, another soft Y iron connection from the other of the poles to the pole pieces, one of the said connections including a slide and means for operating the slide selectively to open and close the magnetic circuit.

7. In a magnetic chuck, -a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and yfastened to the table,'a permanent magnet having poles of opposite polarity, a soft iron connection from one of the poles to the table, another soft iron connection from the other of the poles to the pole pieces, the soft iron connection from one of the po`es to the table ,including a slide and means for operating the slide selectively to open cuit breaker in contact with the other pole piece and contacts connecting the magnetic circuit breaker to the table in one position, to the conductor bar in another position and to neither in a third position.

9. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened to the table, a permanent magnet having poles ci' opposite polarity, asoft iron connection from one of the magnet poles to the table, another soft iron connection from the other of the magnet poles to the pole pieces, one of said connections including a slide having three positions at which respectively it closes the magnetic work circuit, opens the said magnetic work circuit and at a more Widely open position closes a keeper magnetic circuit across the magnet, and means for operating the slide.

10. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened. to the table, a permanent magnetv having poles of reverse polarity, a soft iron connection from one of the magnet poles to the table,

f. another soft iron connection from theA other of the magnet poles to the pole pieces, the soft iron connection from one of the poles to the table including a slide connecting magnetically continuously to the said one pole and in three selective positions connecting magnetically selectively to either the table, or,to the other pole or to neither.

11. In a magnetic work holder, a table of soft iron having a substantially flat face and having a plurality of slots, soft iron pole pieces in the slots substantially flush with the surface of the table, nonmagnetic metal occupying space between the pole pieces and the table, serving to position and magnetically insulate the pole pieces, a permanent magnet having poles, a movable conductor bar continuously in contact with one pole of the magnet and connecting said pole to the pole pieces in one position and to the table in another position and connections from the other pole of the magnet to the table.

12. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened to the table, a permanentl magnet having poles of opposite polarity, a soft iron connection from one of the poles to the table, another soft iron connection from the other of the poles to the .pole pieces, the said last connection including a slide and means for operating the slide selectively to open and close the magnetic circuit, the said slide magnetically connecting continuously to the magnet and having multiple slide poles that in one position of the slide register with and are presented to the inner ends of the said pole pieces Within the perforations, and the said slide intermediate the slide poles being inwardly recessed to clear the slide in its respective positions. respectively from the table and the said pole pieces.

13. In a magnetic work holder, a table of soft iron having a substantially flat face and having a plurality of slots, soft iron pole pieces in the slots substantially flush with the surface oi the table, nonmagnetic metal occupying space between the pole pieces and the table, serving to position and magnetically insulate the pole pieces, a permanent magnet having poles, a movable conductor bar continuously in contact with one pole of the magnet and connecting said pole to the pole pieces in one position and to the table in another position and to neither in a third position and connections from the other pole ot the magnet to the table.

14. In a magnetic chuck, a soft iron table having perforations, soft iron pole pieces within the perforations and magnetically insulated from and fastened to the table, a permanent magnet having poles of opposite polarity, a soft iron connection from one of the poles to the table, another soft iron connection from. the other of the poles to the pole pieces, the said last connection including a slide and means for operating the slide selectively to open and close the magnetic circuit, the said slide magnetically connecting continuously to the magnet and having multiple slide poles that in one position of the slide register with and are presented to the inner ends of the said pole pieces within the perforations. and the said slide intertable, soft iron pole pieces distributed over the table and magnetically insulated from it, a permanent magnet having poles of opposite polarity, a soft iron connection from one of the poles to the table, another soft iron connection from the other of the poles to the pole pieces, means for opening and closing one of the soft iron connections and a leakage flux' path from one magnet pole to the other maintained when said one of the soft iron connections is open and also when it is closed.

16. A magnetic chuck having an active face, side Walls part at least of which are of magnetic material in magnetic contact with the active face, a permanent magnet occupying the bulk of the space within the side walls, having one pole in magnetic contact with the active face and one pole in magnetic contact with the side walls, whereby the entire magnetic space is engaged in conveying ux to the active face and the return circuit is affected through the side Walls, and means for completely interrupting the magnetic circuit and cutting oiI ow of ux to the active face.

FRANK RHODEBACK MALLALIEU.

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