US2541202A - Apparatus for removing entrained particles from liquid coolant - Google Patents

Description

Feb. 13, 1951 H 1 CALDWELL 2,541,202

APPARATUS FR REMOVING ENTRINED PRTICLES FROM LIQUID COOLANT U Filed Nov. 18, 1946 2 Sheets-Sheet 1 Figi Feb. 13, 1951 H. J. CALDWELL 2,541,202

APPARA FOR REMovING ENTRA:

PARTI s FROM LIQUID coom Filed Nov. 18, 1946 2 Sheets-Sheet 2 Q-Iarrq ci Caldwell @Mam 6315,11 m4. vhf.,

'dl'rramw Patented Feb. 13, 1951 APPARATUS FOB REMOVING ENTBAINED PARTICLES FROM LIQUID COOLANT Harry J. Caldwell, Rockford, lll.,

Barnes Drill Co., Rockford, lll., a corporation oi' Illinois auignorto Application November 18. 1946, Serial No. 710,564

3 Claims.

'Ihe invention relates generally to the removal of entrained particles of foreign material from liquid coolant used in machining operations to condition the same for reuse, and it is particularly concerned with the removal of entrained metal chips and abrasive particles. termed swarL from the coolant used in abrading operations. l

To overcome the disadvantages in the use oi' filters and settling tanks, continuous magnetic separators have been proposed and, as shown in the patented art, conventionally include electromagnets mounted within a rotating drum with the poles directed outwardly to gather entrained particles from a stream oi.' coolant or the like. In endeavoring to achieve the high ilux densities required in practical designs and thereby to increase the percentage oi swari' removed from the coolant, it has been considered necessary to resort to the use of windings providing a large number of ampere-turns- While it is true that higher flux densities may be obtained by increasing the current or the number oi turns oi' conductor or both, nevertheless I have found that, as a practical matter, all of such approaches to the problem are accompanied by a number of serious drawbacks.

In increasing the number of turns, for example, it is necessary to provide a correspondingly larger winding space. This may be accomplished in either of two ways, by increasing the radial length of the core or by increasing the pole span and the peripheral spacing between the magnets. The Jformer is objectionable since it not onlyin creases the drop in magnetomotive force in the core itself but also increases the face-to-face area oi the legs of the magnet. The latter correspondingly increases the leakage flux between adjacent legs. Since the flux passing directly between the legs follows a path lying within the drum, such ilux is totally wasted as far as the magnetic separation process is concerned. 'lil-I creasing the peripheral spacing of the magnets. to accommodate the windings is likewise objectionable since, for a given diameter of drum, it decreases the number of active poles which may be accommodated.

In those cases on the other hand where an attempt is made to obtain increased iiux density by the use of higher currents, it has been my obserration that inherent disadvantages are oi' a more serious nature. particularly where the substance being treated is a coolant. It is, of course, well known that the entire amount of electrical energy passing into an electromagnet must be dis- (Cl. ZIO-1.5)

sipated in the form oi heat. It is also a basic phenomenon that, for a given resistance, the heat given olf rises at an extremely rapid rate with increased current, increasing as the square of the latter quantity. Thus, a separator using electromagnets is actually a rather efllcient form oi electrical heater in which substantially all of the energy is effective to raise the temperature oi the coolant. As a result a much larger volume of coolant must be used to obtain an equivalent cooling effect. It might be expected that the amount of heat energy could be reduced by merely using a larger cross section of electrical conductor. Unfortunately, however, a separator drum of practical size has only a limited volume, and any appreciable reduction in winding resistance must be brought about at the expense of closer magnet spacing (thereby increasing the amount of flux wasted through leakage) or by using ineillcient magnetic cores of thin cross section.

During the course of producing .the improved separator to be subsequently described, I have found that certain features, not heretofore fully appreciated, are desirable in a coolant separator of the drum type. In the iirst place such a separator should not raise the temperature of the liquid being treated and should actually assist in cooling it. Secondly, I have found that the el.'- iiciency of the separator in removing particles depends to a marked extent on the coordination between the size and shape of the magnets, the spacing between adjacent magnets, and the magnetic conditions existing in the channel adjacent the poles and through which the liquid ows durlng treatment.

With the foregoing in view, it is one object of the invention to provide an improved separator of the rotating drum type which effects a continuous and substantially complete removal of entrained metal chips and abrasive particles from a coolant without raising the temperature there-- of.

Another object oi the present invention is to provide a magnetic separatorin which the magnets are not only or a size and shape, relative to the drum, which enables the setting up oi' high flux densities in the liquid channel butin which the legs are so spaced and proportioned as to enable the ilux wasted through leakage within the drum to be reduced to a minimum. More particularly, it is an object to produce a drum type magnetic separator in which the gap between the poles of a given magnet and the spacing of the poles of adjacent magnets is coordinated with the magnetic gap in the liquid channel in a manner to increase the proportion of the total flux made available for separation purposes.

It is a further object to provide a continuous magnetic separator in which commutators, slip rings and similar modes of supplying power to the rotating drum are obviated together with their attendant disadvantages and in which maintenance of the magnetic elements as a result of extended use or as a result of the entry of water or other liquid into the magnet chamber are substantially eliminated. It is a related object to provide a drum typ separator which 1s of simple inexpensive construction and which is inherently durable, giving trouble-free operation for a period normally in excess of the life of the machine tool with which it is used.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment illustrated in the accompanying drawings, in which:

Figure 1 is a side elevational view of a separator for liquid coolant embodying thel features of the invention.

Fig. 2 is a vertical sect'ic'nia'lview'oi the apu paratus taken substantiallyon line- 2 2 of M831.' v

Fig. 3 is a transverse sectional view of the apparatus taken on the line 3-3 of Fig. 2.

Fig. 4 is a perspective view of one of the permanent magnets forming apparatus.

While the invention is susceptible of various modications and is capable of being practiced with a wide variety of apparatus, I have shown the drawings and will describe herein the pre` ferred form of the invention. I do not. however..

ticles are to be removed is directed in a relatively thin wide stream through an elongated annularfchannel I3 defined jointly by the outer peripheral surface of the rotatably supported drum I4 and an arcuate apron I5 partially encircling the drum and which is 'constructed of iron or other magnetic material. The channel I3 is shown as having the same radial thickness throughout its length. If desired, however, the inlet end of the apron I5 may be spaced slightly farther from the drum Il than the outlet end, thus producing a liquid stream of gradually decreasing thickness toward the outlet. Such alternative construction has been found advantageous where the liquid vehicle is of amore viscous nature. insuring removal ofthe finest particles of magnetic material.

To vprovide the magnetic field for collecting magnetizable particles from the liquid stream, the drum Il is arranged to carry a plurality of magnet assemblies i6 (Fig. 2) positioned to establish magnetic ileldsv transversely 4of the channels I3 and'movable. along the channel upon rotation of the drum. Arcuate sealing members I1, supported at opposite sides of the apron .Il and having sliding contact with the surface of the-drum, close the sides of the channel I3 and confine the iluid therein.

a. part of the improved As'willbe seen by reference toFlg. l of the.

drawings, the apron I6 merges at one end into an vinlet tank Il located at one side of the drum yand having a baille I! over which liquid is discharged into the channel substantially above the rotational axis of the drum. The liquid c001- ant to be treated is delivered through an openins in the bottom of the tank Il. and an inlet duct 2l by a suitable pump P which draws used intend to limit the invention to such exemplary .disclosure but intend to cover all modifications f and alternative constructions falling within the spirit'and scope of the invention as expressed f in theappended claims.

In the course of overcoming the disadvantages of prior art magnetic separators of the drum type, I have found that permanently magnetic material, for example highly retentivesintere'd magf netic material, may be effectively employed in 4. a novel manner to obtain a number Aof important practical advantages. It is, of course, recognized 'that permanent magnets have been used for magnetic separating 'purposes in the past. For example, magnetic plugs and arrestors of Alnico have been employed to attract and therefore immobilize 'magnetizable particles in automotive lubricating systems. Furthermore, prior art .patents disclosing specific electromagnetic separator structures have contained the suggestion that permanent magnets could be employed in such structure as a less desirable alternative. The latter indicates not only that the advantages residing in the use of permanent magnets have not been appreciated but that such material has been consideredand its use rejected.. In the discussion which follows, on the other hand, it will be seen that the structure disclosed is such as to fully utilize in a novel `and effective manner the inherent characteristics of improved permanently magnetic material. Y

A Referringnow to the drawings, the magnetic separator indicated generally at III will be seen to consist of a drive portion II and a separating portion I2`through which the coolant is directed for treatment. As shown. to best advantage in Fig. 3, the coolant from which entrained pareures a smooth cylindrical 'shell 2l of brass, aluminum or otherl which the apparatus is associated.

coolant through a pipe 2I from the machine with Fluid is discharged from the other end of'the channel-I3 into a discharge tank 22 from which it is carried by a pipe 23 to a sump or reservoir for reuse in the machine. The end of the apron I! over'whichthe liquid ilows into the tank 22 is located substantially below the level of the upper edge of the baille Ilfthus enabling the vliquid to ilow by gravity through the channel 'I3 from the tank I8 to the tank 22. The channel I2, ofcourse, remains filled ,at all times and the relative positioning of the inlet and outlet `in 1 flow o f liquid over the surface of thedrum Il.

.As-shownl in Fig. 2, thedrum Il comprises a suitable non-magnetic material assembled be-A tween circular end plates 26 and 21. Buch plates are reinforced by radially extending ridges or vanes 28 connected at their outer ends to an annular flange 29' having axially extending projections 30 thereon which are utilized to support the magnetic elements in peripherally spaced relation.

In accordance with the invention permanent magnets are provided for setting up the magnetic eld in the annular space I3, such magnets being so constructed and arranged as both to reduce the loss in magnetism in the magnets themselves (due to the drop in magnetic potential therein) and to reduce the portion of the aux which is lost within the drum due to leakage. In

-the present instance this is accomplished by the ,shown in Fig: 2 such magnets 3|A arepreferably aunado axially alined, here four abreast, and polarized in the same direction so as to present a substantially continuous magnetized strip extending the width of the shell Il.

Further in accordance with the invention the legs SIS and SIN of each of the magnets li are separated by a gap which is coordinated with the average thickness of the annular channel Ii through which the liquid passes. Referring to the magnet shown in the lowermost position in Fig. 3, the path of useful dux is shown dotted at P, the return path forsuch flux lying within the apron II which, as above stated, is of magnetic material. Interposed in the ilux path are two non-magnetic gaps di and di, the lengths of which are determined by the thickness of the annular channel I3. It will be apparent, however, in view of the fact` that a magnetic potential diilerence exists between the poles IIS and IIN. that there will be a tendency for the ilux to pass between such poles directly without passing through the apron It. In the practice of the invention such ilux is considerably reduced by so constructing the magnet ll that the gap G between the poles thereof is at least approximately twice the average distance between the poles of the magnet and the portion oi.' the magnetic apron which is opposite such magnet. Stated another way, the non-magnetic gap G between the poles of an individual magnet should be approximately equal to or somewhat greater than the total nonmagnetic path which the flux must transverse in crossing the gap to the magnetic apron. In accordance with the usual practice in magnetic calculations the drop in magnetic potential through the apron l may, for practical purposes, be assumed negligible with respect to the drop across the nonmagnetic gaps d1 and d2.

It might be assumed. using a gap of width G which is just equal to the sum of the gaps d1 and dz, that leakage would take place within the drum across the gap G. While some flux will unavoidably Dass directly between the two poles, it is to be noted that the magnetized areas soon acquire tufts 3l composed of magnetic particles or swarf which, because of its magnetic nature, become a part of the ilux path and correspondingly reduce the total length of the gaps d1 and de to a value which is much less than the spacing between the drum It and the apron I5. With the 'separator in normal operation and using distances di and d: in the proportions shown, it has been found that substantially all of the flux originating in a magnet 3| passes across the gaps di and d: and through the apron It. It has been found further that4 such radial passage of flux insures that the "swarf is effectively removed regardless of whether the particles are being carried in the coolant stream adjacent the drum or adjacent the apron. Ordinarily, however, coolant passes through4 the channel Il sudiciently rapidly so as to produce turbulence, and this fact facilitates the removal of the particles.

As previously stated, the channel I3 may alternatively be of tapered thickness without departing from the invention Thus the thickness of the channel I3 at the end or right-hand portion (as shown in Fig. 3) may, if desired, be much less than one-half of the distance of the gap G between the poles. Under such conditionsthe reluctance of the dux path through the coolant will be considerably less et the end of the channel than the reluctance of the flux path G directly between the poles or the magnet, and conse quently very little direct leakage between the poles willoccur. Asagivenmagnetiscausedto rotate in a clockwise direction from the end position, the nonmagnetic gap through the coolant will become longer tending to increase the reluctance. However, during the course of such rotation, the magnet acquires an increasing amount of sw and by the time such magnet has reached a left-hand position of the channel, sufficient swart would ordinarily be accumulated to compensate, to a great extent, for the increased reluctance of the ilux path. Thus, even though the channel I3 were of tapering thickness, the ilux density in the channel I3 would tend to remain more nearly constant and the leakage between the poles of the magnet would continue a constant low value.

Reference has been made to the fact that the nonmagnetic path G between the magnet poles should be coordinated with the spacing between the drum and apron I5. I have also found that the speciilc structure of the magnet disclosed is a primary factor in the efficient removal of the entrained particles, such structure being shown in detail in Fig. 4. It has been found desirable to construct the magnets 3| -with a radial dimension or height which does not exceed the distance between the centers of the poles, which may be rei'erred to as "pole span and to further shape the magnet in such a way that the ilux follows a substantially semicircular path therein. In this way, a maximum difference in magnetic potential between the poles may be achieved with a minimum drop in magnetic potential through the magnet itself due to the reluctance of the latter.

An additional practical advantage of using magnets constructed as shown is the fact that direct leakage between the poles is reduced to a minimum. This can be more fully appreciated by assuming that magnets of a considerably greater height and having long parallel legs were used. `Under such conditions such legs would have a correspondingly increased face-to-fa lateral extent. Thus, even though a somewhat greater magnetomotive force may be obtained, such eiect would be largely dissipated due to leakage between the poles and little, if any, additional magnetism would be produced in the annular channel I3. Conversely, the magnet should preferably not have a height, compared to its pole span, which is much less than that illustrated since this shortens the length of the path within the magnet to too great an extent. thereby reducing the available magnetcmotive force at the poles. Referring to Fig. 4, it will also be noted that the yoke portion 3iY of the magnet is larger in cross section than the leg portions or poles 3IS, SIN. Such construction reduces the drop in magnetomotive force within the magnets themselves and makes up for the reduction in cross section caused by the holes for the passage oi' the bolts 32. Still another design feature which has been found to he advantageous is the fact that the pole faces have a rounded contour which very closely matches theperipheral contour of the drum Il. This facilitates the formation of two tufts of swarf" on each of the poles instead of merely one,

In order to further increase the magnetic efiiciency of the separator, the neighboring poles of the adjacent magnets are caused to be of unlike polarity. It is believed that the increased einciency is due to the flux designated as F' in Fig. 3 which passes across the annular channel t3 and through the apron I5. In orderV to taire full advantage of such additional flux, I have found that it is desirable to space v'erueapoausnupsnabmmnnacwln adiacent by an amount G' as shown. Such spacing should preferably be approximately equal to the gap G between the poles of a given magnet Il since this tends to reduce flux leakage between adjacent magnets. lGap G may be somewhat less than the distance, G however, if it is desired to achieve maximum compactness of design.

With the permanent magnets constructed and arranged as shown. it has been found that the two tufts 3l formed on eachof the poles are substantially equal in size. This has the advantage that a maximum amount of swarf" may be built up on each of the poles before the collection reaches a radial height sumciently great to cause the swarf to drag on the magnetic apron I5. An additional advantage residing in the formation of two tufts is that the latter practically doubles the nltering or screening effect to which "additional reference will be made. Studies have shown that the formation of a pair of tufts of magnetic material is facilitatedvby -the use. of magnets having vpole faceswhich are relatively great in peripheral extent such as those shown in Fig. 3. This is believed due to the fact that like poles are induced in the tufts at the region thereof adjacent the drum. Since the surface of the drum is well lubricated and since like poles repel, such tufts tend to move as far away from one another as theycan without leaving the region of high flux density. Still another contributing factor to the formation of a pair of equal tufts is believed to be the unlike polarity of the neighboring poles of adjacent magnets. As a practical matter it has been found that the formation of tufts in pairs as illustrated greatly increases both the eillciency of the separator in removing the entrained particles and the maximum amount of such material which can be removed per unit time.

The above-described structure, which has been found to be extremely emcient in practice, is contrasted with conventional separators in which a considerable proportion of the available flux is lost within the drum through leakage. This structure is to be particularly contrasted with that employed in electrically energized separators in which the core structure is dictated almost completely by the necessity for linking the magnet with a coil of high ampere-tum capacity. By

using the structure shown and by employing sintered highly retentive material, a magnetic separating eect is achieved which' could only be achieved in the case of electromagnets by using a considerably larger drum and at a considerably greater manufacturing cost.

In order to cause the magnets to be Vtransported successively to the inlet end and in order ytheho yusing 4l.

The shaft 4l' is driven from the worm wheel. 41 through a generally well known type of reduction gearing including a stationary ring gear and a planetary pinion. In the present instance the pinion 5I, rotatably mounted on an arm 52 proliecting laterally from the worm wheel 4I, is in mesh with both a stationary ring gear 54 and with a gear 53 fixed to the shaft 40. The gears 53 and 54 are provided with different numbers of teeth, the latter causing the pinion 5i to turn the gear 52 and the shaft 40 at a very slow rate and in a clockwise direction, as viewed in Fig. 1, in response to the rotation of the worm wheel 41.

Due to the magnetic field set up by the magnet assembly I5 in cooperation with the magnetic apron i5, the magnetizable particles entrained in the coolant are attracted to the shell in the vicinity of the magnet pole and collect in a series of tufts 33 standing out from the drum I4 as shown in Fig. 3 and extending lengthwise of the shell transversely of the channel il. The tufts 3l, which gradually increase in size as they are carried forwardly against the liquid stream, form a radial screen across the-channel through which the liquid coolant is forced to pass. The collected magnetic particles are thus enabled to mechanically filter out and entrap the nonmagnetic particles entrained in the coolant. It will be understood that some of the nonmagnetic particles normally adhere to the magnetic particles in any case and such particles, of course, are retained in the collected mass.

Continued rotation of the `drum eventually `withdraws the collected tufts 33 in succession from the liquid stream while fresh masses are formed adjacent magnetic assemblies moved into the vicinity of the channel I3. The operation of the apparatus is thus vcontinuous and newly formed tufts with unimpaired -nltering capacity are regularly brought into service. In practice it has been noted that substantially all solid particles are removed from the coolant.

The collected tufts II of magnetic and non'- magnetic particles may be removed from the surface ofthe shell 25 in any desired manner. The means provided for this purpose in the exemplary apparatus comprises a scraper blade (Fig. 3) ,extending lengthwise 'of the drum and having a sharp forward edge contacting the outer surface of the shell 25. The scraper blade 5I is rigidly fastened in a chute 5l which is plvotally supported on a shaft 5I carried between laterally spaced lugs 59 projecting forwardly from the housing 45. The pivotal axis of thechute 51 is located so that the weight of the chute tends to to enable the collected swarf to be readily scraped' oil' the drum I4, such drum is supported for rotation about a central axis. Support for the drum is provided, in this instance, by shaft40 having one end extending through central hubs 4l formed in the respective end plates 28 and 21 and anchored thereto by appropriate set screws 42. 'Ihe other end of the shaft is journaled in spaced bearings 43 ,and 44 formed in a housing 45 enclosing the driving portion Il of the separator.

The driving mechanism indicated at 46 comprises a worm wheel 41 (Fig. 2) loosely mounted on the shaft 40 within the housing 45 and adapted to be driven by a worm 4B fast on a vertical shaft 4l. The latter is drivingly coupled to a motor M which. as shown in Fig. 1, is mounted ina 7s to.

hold the blade 55 tightly against the shell 25. The collected material is accordingly scraped from the surface of the shell during the rotation of the drum and the chute 5l serves to direct such material into a convenient waste receptacle 6I.

A separator constructed as disclosed may be almost continuously operated for a period of several years or longer without requiring attention or maintenance. Because of the absence of any electrical supply, corrosion of slip ring contacts and short circuiting caused by leakage of liquid to within the drum are obviated. At the same time, the improved structure reduces magneticA leakage of flux to a minimum and, for the amount of magnetic material employed, has an 'emciency in removing swarf" which greatly surthe prior art separators previously referred This is a continuation in part of the Harry J. Caldwell application Serial 507,270, illed on October 22, 1943, now abandoned, and application Serial 540,818, led June 17, 1944, now Patent 2,466,839.

I claim as my invention:

l. A separator for effecting the removal of entrained metal and abrasive particles from a liquid coolant used in the operation of an abrading arranged in spaced relation about the circumference of said drum and of alternating polarity, individual ones of said magnets having a substantially semicircular ilux path, the height of a given magnet as measured along a radius of said drum being substantially no greater than the span of the poles thereof measured about the circumference of the drum, so that a maximum amount of the drop in magnetomotive force will take place outside of said drum, and a scraper blade riding on said drum exteriorly of said channel for removing collected particles as said drum is rotated.

2. In a separator for effecting the removal of entrained metal and abrasive particles from a liquid coolant used in the operation of an abrading machine, the combination comprising a rotatable drum having a thin wall of nonmagnetic extending around a portion of said drum and radially spaced therefrom to provide an arcuate channel for the flow of coolant about the periphery of said drum, a plurality of U-shaped permanent magnets mounted within said drum and presenting their poles outwardly against the wall thereof, said magnets being arranged side by side in groups having like poles alined longitudinally oi said drum, said alined poles of the several groups being arranged in spaced relation about the circumference ternating polarity,

of sid drum and of a1- individual ones o! said magnets havingV a pole span such that the gap between the poles is at least approximately twice the average distance from the poles of said magnets to said magnetic apron so that the pole-topole reluctance of the flux path in the arcuate channel is less than that of between the poles within the drum.

3. In a separator for eiecting the removal of entrained metal and'abrasive particles from a liquid coolant used in the operation of an abrading machine, the combination comprising a rotatable drum having a thin Wall of nonmagnetic material, an arcuate apron of magnetic material extending around a portion of said drum andradially spaced therefrom to provide an arcuate channel for the flow of coolant about the periphery of said drum, a plurality of U-shaped permanent magnets mounted within said drum and presenting their poles outwardly against the wall thereof, said magnets being arranged side by side in groups having like poles alined longitudinally of said drum, said alined poles of the several groups being arranged in spaced relation about the circumference of said drum and of alternating polarity, said magnets having a. pole span and spacing such that the gaps between the poles of individual magnets and between the neighboring poles of adjacent magnets respectively are at least approximately twice the, average distance from the poles of said magnets to said magnetic apron so that the reluctance of the magnetic path in the arcuate channel is less than between the poles Within the drum.

Y J. CALDWELL.

REFERENCES CITE@ The following references are of record in the nie of this patent: material, an arcuate apron of magnetic material 40 UNITED STATES PATENTS OTHER REFERENCES Barnesdrit Magnetic Automatic Coolant Beparators for Honing or Grinding Machines," Bulletin 151A, Barnes Drill Co. Publication.

the ilux leakage path the reluctance of leakage paths

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