Wheel-type abrasive-impelling device

Dec. 9, 1958 w. h. mead 2,863,261

WHEEL-TYPE ABRASIVE-IMPELLING DEVICE

Filed Oct. IS, 19S6 2 Sheets-Sheet 1

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INVENTOR.

William H. Mead

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ATTORNEY

Dec. 9, 1958 w. _H. mead 2,863,261

WHEEL-TYPE ABRASIVE-IMPELLING- DEVICE

Filed Oct. 15, 1956 2 Sheets-Sheet 2

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INVENTOR.

kV/zzMM H. Mead

VaUmL.

attorney

United States Patent Office

2,863,261

Patented Dec. 9, 1958

2,863,261

WHEEL-TYPE ABRASIVE-IMPELLING DEVICE William H. Mead, Oakland, Calif.

Application October 15, 1956, Serial No. 615,856

Claims. (Cl. 51—9)

This invention relates to a wheel-type abrasive-impelling device.

_ Machines in which abrasive is impelled toward a workpiece from a wheel have long been known, an example being shown by Linderman in Patent No. 2,247,391 filed July 1, 1941. However, quite a few problems have remained without solution until the present invention solved them.

One object of this invention is to increase the efficiency of abrasive-throwing wheels by reducing the wear that has been inherent in prior-art abrading wheels. This wear has been caused by the constant friction of highspeed abrasive particles against the interior surface of the wheels and the retention discs used to control the outward flow of abrasive. This wear has required constant maintenance and frequent replacement of parts, even with vaneless wheels.

Another object of the invention is to prevent wear on the* interior surface of the cup-like wheel itself by providing a structure which causes the abrasive to collect in a series of frusto-conical shells sloped along the angle of equilibrium. The disc surfaces are substantially covered and remain so, while the additional moving abrasive being fed in simply slides over the relatively stationary abrasive particles in the steps. In this way, the grit can only wear against, itself and not against the wheel.

Another problem solved by this invention relates to the fact that the angle of repose of static granular material is necessarily greater than the angle of equilibrium of the same material, when centrifugal force is applied. Because of this fact there has to be some means for axially* foreshortening the cup of a centrifugal abrasive wheel if the abrasive is to be red to the cup by gravity. In other words, if an abrasive material whose static angle of repose is about 40° is to be fed by gravity into the cup of a wheel, the hopper spout has to slope down at approximately 45° (or at least greater than 40°) or else there* will be no flow of abrasive through it. But if. the radius of the cup is equal to or greater than its axial length as it must be in order to get the spout into the center of the cup closely adjacent the inner radial wall—how is the abrasive to be kept from falling off around the entire periphery of the wheel? Its angle of repose under the centrifugal force is a relatively flat one as compared with the angle of the static material, say 27° as compared with 40°. On the other hand, if the axial length of the cup is longer than the radius, how can the abrasive be properly fed by gravity into the cup?

The previous approach to this problem has been to space an annular disc away from the radial wall of the cup and introduce the abrasive in between, using the disc to hold it in. But this requires another part subject to wear by the abrasive.

Another object, therefore, of the present invention is to provide a wheel with an open type of cup design in which the angle of equilibrium can be balanced with the angle of repose of the static material. This is accomplished by means of a stepwise construction of the cup so that the abrasive, instead of rnoving radially out to the periphery, is moved in a generally conical path, the steps being balanced to provide a general resultant slope corresponding to an angle somewhat greater than 5 that of the angle of repose of the static material, i. e., about 45, while the angle of repose of the abrasive on each step* is the relatively low angle suitable for retaining the grit on the periphery.

_ Another important object of the invention is to pro10 vide a cup-type abrasive wheel especially for use with ferromagnetic abrasive particles such as steel grit and shot. In this form of the invention a plurality of coaxial magnet rings of different diameter comprise most or all of the axial portion of the steps. The magnets 15 act to control the movement of ferromagnetic particles. Ferromagnetic particles are quite heavy and, when introduced into the center of the cup-type of abrasive wheel, tend to bounce or skip along out to the periphery and then to fall off the edge indiscriminately instead of being 20 taken off by* the discharge means. Thus a great deal of abrasive is wasted. The magnetic rings, which are described in detail below, control these ferromagnetic particles and prevent them from skipping, while the stepwise structure itself serves to prevent lighter particles 25 (such* as sand, garnet, walnut shells, and the like) from skipping when those abrasives are used.

Another object of the invention is to provide a particularly effective* disposition of magnets in such a wheel.

Another object of the invention is to provide a struc30 ture for preventing the short-circuiting of the respective magnetic rings.

Other objects and advantages of the invention will appear from the following description of preferred embodiments of the invention.

In the drawings:

* Fig.* 1 is a view in front elevation of an abrasiveimpelling wheel embodying the principles of the invention.

_An ,^Flg’ ^{2 is a view in side} elevation and in section of the 40 wheel of Fig. 1.

In* this invention a wheel or cup 10 is supported for rotation upon a shaft 11 of an electric motor 12, or may be driven by any other appropriate means. The ** shaft 11 is attached to a drive hub 13 which, in turn 4a is bolted to a radially-extending wall 14 of the cup 10 on the opposite side from the open mouth 15 thereof, thereby leaving the interior 16 of the cup 10 completely unobstructed. A gravity feed is provided from a hopper ka ¹⁷ above the cup 10 through a metering device 18 and condrnt 19 into the cup interior 16 and toward the axis 20 thereof. Necessarily, this gravity feed lies at an angle greater than the angle of repose of the abrasive which, tor most suitable materials, means that it may lie at about 45°.

⁵⁵ „^Th15^{up M is} P^rovided with a coaxial series of steps 21. The steps 21 near the radial wall 14 are of smallest radius, so that the cup 10 is stepped outwardly both radially and axially toward the discharge lip 22 of the an ²³’ ^Therefore&gt; as abrasive is fed into the whirling wheel 10 and centrifugal force tends to accelerate it toward the rim 23, the abrasive moves over the steps 21. The first abrasive 24 fed in covers the steps 21 with a layer of abrasive that subsequently remains static by virtue of the angle of equilibrium of the material under ”0 the action of the centrifugal force. This angle of equilibrium is similar to, but is flatter than, the free angle of repose of the static material. Thus, the radially inner surface of the* static abrasive 24 forms on each succeeding step a conical frustum, over which subsequent abrasive travels without any direct contact, except at the edge of the steps 21.

It is apparent that the number of steps 21 may vary to,

2,863,261 in effect, form a true conical surface, but that is not desirable. From a practical standpoint, the steps 20 are related to that the effective angle formed by a line joining their edges is about 45° or greater, thereby permitting entry of the gravity feed conduit 19. In other words, the line joining their edges must be greater than the angle of free repose of the material.

At the periphery suitable discharge means 25 are provided; While this may be a rotating wheel of the type shown in the Linderman Patent 2,247,391,1 prefer to use an air discharge means as disclosed in co-pending application Serial No. 615,972 filed October 15, 1956, or, where steel grit is being used, a permanent magnet (as shown in Figs. 1 and 2) or an electromagnet to draw the material off in a manner disclosed and claimed by co-pending application Serial No. 615,842 filed October 15, 1956. The particular form of discharge means 25 forms no part of this invention.

In operation, the abrasive is fed from the hopper 17 through the metering device 18 and conduit 19 down into the wheel 1® and moves outwardly over the steps 21 toward the rim 23. The first abrasive fed in forms an initial layer 24 that remains substantially static, while the Subsequent abrasive travels over that abrasive and does not come in contact with the wheel as it moves out to theperiphery 22, where it is taken off the wheel 10 by the discharge device 25.

As stated earlier, when steel grit is used, a further control over its movement is advisable, since steel shot and grit are very heavy. This control is provided by using magnetic rings 30 as the axial portion of each step 21. Each ring magnet 30 may be cast as a unit or formed from a series of bar magnets, the north poles of all the magnets in one ring 30 facing one axial end of the cup 10 while the south poles face the other end. Some advantages in strength of field and control may be obtained by reversing the polarity of adjacent rings 30, so that the north poles of one ring face the wall 14 and in the next adjacent ring the south poles face the wall 14; and so on. It should be noted that the magnetic steps have no relation to whether a magnetic discharge 25 is used, but a magnetic discharge may well be used in the same apparatus.

Where magnetic rings 30 are used, it is sometimes desirable to prevent what may be described as a short-circuit of the magnet due to the steel particles being in direct contact with the magnetic rings 30. Avoidance of this and strengthening of the field in general may be provided by providing a covering 31 of plaster-of-Paris, brass, or other nonmagnetic material over each ring 30 to provide a generally frusto-conical surface, preferably somewhat concave, whose angle is somewhat flatter than that of the angle of equilibrium of the abrasive. Then the layer 24 of ferromagnetic abrasive deposits over the covering 31 and protects its surface from the moving particles of grit, which thus move only over the surface of the grit itself. For this purpose also, radial faces of the magnet rings 30 are preferably protected by overhanging rings 32 of brass or other nonmagnetic material. As shown, the overhang is relatively slight but may be extended to any desired degree.

It is important to obtain control over the ferromagnetic particles from the instant they come out of the spout 19. Therefore the innermost magnetic ring 30 is of rather small diameter and its field is strengthened by a plug 35 of magnetic material located along the axis 20 just opposite the outlet from the feed conduit 19. The space in between the plug 35 and magnet 3® and the area over the plug and magnet are filled with a covering 36 like the covering 31. As. the lines 37 of magnetic force shown in the drawings illustrate, there is a strong magnetic field tending to hold the particles at the center. This tends to impart to them an angular velocity, whence the centrifugal force slowly moves them out in a long spiral, with the velocity of the wheel itself at any given point being substantially the velocity of the particles. The slow outward movement provided by the central plug 35 and the' innermost magnet 30 and by the successive magnetic rings and steps 21 result in the ultimate in control of ferro5 magnetic abrasive.

Otherwise, operation of the magnetic device is substantially the same as that of the regular stepped device, the principal difference being that, since steel grit or shot is the abrasive material being used, the magnetic rings 10 30 exert a constant control over the abrasive, beginning at the inner portion near the feed conduit 19 and extending out toward the rim 23. The magnets provide a field which' is not subject to wear, and the magnets themselves are protected. The magnetic field acts upon the 15 grit particles as effectively as baffles or other mechanical parts would without having any of the disadvantages of mechanical baffles and without being subject to wear. The control is substantially complete, and the device can operate indefinitely without wear.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the descrip25 tion herein are purely illustrative and are not intended to be in any sense limiting.