WO2017014767A1

WO2017014767A1 - Control cage for centrifugal blast wheel machine

Info

Publication number: WO2017014767A1
Application number: PCT/US2015/041516
Authority: WO
Inventors: Raymond Paul BITZEL Jr.; Michael Dwayne REAVES; Christoph Baer; Jürgen WRUCK
Original assignee: Wheelabrator Group Limited
Priority date: 2015-07-22
Filing date: 2015-07-22
Publication date: 2017-01-26

Abstract

A centrifugal blast wheel machine includes a wheel assembly configured to throw blast media introduced into the wheel assembly against a work piece. An impeller has a media inlet adapted to receive blast media and a plurality of impeller media outlets that allow egress of blast media upon rotation of the impeller. A motor coupled to the impeller drives the rotation of the impeller and the wheel assembly. A control cage surrounds the impeller and is secured to the wheel assembly. The control cage includes a cylindrical body defining an interior chamber. The cylindrical body has an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber. The opening has a trailing edge, with the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

Description

CONTROL CAGE FOR CENTRIFUGAL BLAST WHEEL MACHINE

BACKGROUND OF THE DISCLOSURE

1. Field of the Disclosure

The present disclosure relates generally to abrasive blast wheels and methods for cleaning or treating surfaces of work pieces, and more particularly to a control cage for a centrifugal blast wheel machine.

2. Discussion of Related Art

Centrifugal blast wheel machines generally include a rotatable wheel having a plate or a pair of spaced plates that carry radially extending blades. Particulate matter is discharged from a center of the blast wheel onto rotating surfaces of the blades, which propel the particulate matter against surfaces of a work piece to be cleaned or treated. Specifically, blast media is fed from a feed spout into a rotating impeller situated within a control cage at the center of the blast wheel. The media is fed from the impeller, though an opening in the control cage, and onto the heels or the inner ends of the rotating blades. The media travels along the faces of the blades and is thrown from the tips of the blades at the work piece surfaces to be treated.

From observing the internal operation of a blast wheel, it is shown that abrasive blast media that flows out of the opening of the control cage is not well controlled. The abrasive blast media is picked up by the blades near the outside diameter of the control cage, while some of the media is picked up much further down the blade, resulting in more of a "batting" effect than throwing the abrasive media in a controlled manner. Additionally, some abrasive blast media passes under the blade and is eventually picked up by following blades, but in an uncontrolled manner. Abrasive blast media particles that miss the control cage opening continue to spin around between the impeller outside diameter and the control cage inside diameter. It is inefficient for abrasive blast media to be propelled around this space more than once. SUMMARY OF THE DISCLOSURE

One aspect of the present disclosure is directed to a centrifugal blast wheel machine comprising a wheel assembly having a plurality of blades configured to throw blast media introduced into the wheel assembly against a work piece and an impeller positioned about an axis of the wheel assembly. The impeller has a media inlet at one end adapted to receive blast media and a plurality of impeller media outlets constructed and arranged to allow egress of blast media upon rotation of the impeller. The centrifugal blast wheel machine further comprises a motor coupled to the impeller to drive the rotation of the impeller and the wheel assembly and a control cage surrounding the impeller and secured to the wheel assembly. The control cage includes a cylindrical body defining an interior chamber. The cylindrical body has an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber. The opening has a trailing edge, with the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

Embodiments of the centrifugal blast wheel machine further may include configuring the outer surface of the cylindrical body of the control cage with a raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The beveled edge may taper away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The control cage further may have a first flange extending outwardly from an end of the cylindrical body and a second flange extending inwardly from an opposite end of the cylindrical body.

Another aspect of the present disclosure is directed to a control cage for a centrifugal blast wheel machine. In one embodiment, the control cage comprises a cylindrical body defining an interior chamber. The cylindrical body has an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber. The opening has a trailing edge, the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

Embodiments of the control cage further may include configuring the outer surface of the cylindrical body of the control cage with a raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The beveled edge may taper away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The control cage further may have a first flange extending outwardly from an end of the cylindrical body and a second flange extending inwardly from an opposite end of the cylindrical body.

Yet another aspect of the disclosure is directed to a method of operating a centrifugal blast wheel machine. In one embodiment, the method comprises: feeding blast media from a feed spout into an impeller of the centrifugal blast wheel machine; accelerating the blast media by rotating the impeller giving rise to a centrifugal force that moves the blast media in radial direction, away from an axis of the impeller; moving the blast media in a generally circular direction into a space between the impeller and a control cage; metering an amount of blast media through an opening of the control cage onto blades of a blast wheel; and moving the blast media along lengths of the blades to accelerate and throw the blast media toward a work piece. The control cage includes a cylindrical body defining an interior chamber. The cylindrical body has an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber. The opening has a trailing edge, the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

Embodiments of the method further may include configuring the outer surface of the cylindrical body of the control cage with a raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The beveled edge may taper away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening. The trailing edge of the opening may have a beveled edge. The control cage further may have a first flange extending outwardly from an end of the cylindrical body and a second flange extending inwardly from an opposite end of the cylindrical body. BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:

FIG. 1 is a perspective view of a portion of a centrifugal blast wheel machine;

FIG. 2 is another perspective view of the centrifugal blast wheel machine;

FIG. 3 is an exploded perspective view of the centrifugal blast wheel machine;

FIG. 4 is a perspective view of a feed spout of the centrifugal blast wheel machine;

FIG. 5 is a perspective view of a control cage of the centrifugal blast wheel machine;

FIG. 6 is another perspective view of the control cage;

FIG. 7 is another perspective view of the control cage;

FIG. 8 is a cross-sectional view of the control cage; and

FIG. 9 is a perspective view of the control cage and blades of the centrifugal blast wheel machine.

DETAILED DESCRIPTION

The blast wheel of embodiments of the present disclosure is designed to throw metallic shot, grit, cut wire, etc., which together may be referred to as "abrasive," "abrasive blast media," "abrasive media," "blast media," "media" or any suitable description of particulate matter. The blast wheel machine typically consists of four primary components that act in conjunction to throw the media at a target object to be cleaned, peened or otherwise have its surface prepared. An impeller acts to accelerate the abrasive media once the media is fed into a wheel assembly. The impeller rotates within the interior of a control cage, which may also be referred to as an "impeller case." The control cage acts to meter the abrasive blast media flow through an opening formed in the control cage to direct the flow of media onto rotating blades by adjusting the position of the opening. The control cage is stationary within the blast wheel under operating conditions. The blades (generally from two to twelve in number) rotate outside of the control cage and propel the abrasive blast media along their radial length toward the target. A bare wheel, which may also be referred to as a "runner head" or simply as a "wheel," holds the impeller and blades, and typically rotates the impeller and blades between 1500-3600 revolutions per minute (rpm) by way of a power source, which in one embodiment is an electric motor.

A control cage of embodiments of the present disclosure is designed to provide a smoother transition of abrasive blast media from an impeller onto a throwing blade of a centrifugal blast wheel machine. The control cage further prevents the media from spinning around inside the control cage inner diameter after passing an opening of the control cage, and lessens the amount of media that passes underneath the throwing blade when transitioning through the control cage. The leading edge of the control cage opening is optimized to facilitate a smoother flow of abrasive onto the throwing blade. A trailing edge of the opening is modified to prevent media from spinning around the interior of the control cage and to prevent the media from passing underneath the blades. These improvements result in more efficient flow of media onto the blades, and to less consumption of media due to impacts and grinding from the impeller, control cage and blades. The overall increase in efficiency of the control cage is offered in conjunction with the more efficient and gentler pick up of the semi curved blade to improve a transition of the abrasive flow from the impeller onto the blade.

Referring to the drawings, and more particularly to FIGS. 1-3, a centrifugal blast wheel machine is generally indicated at 10. In one embodiment, the centrifugal blast wheel machine 10 includes a housing, generally indicated at 12, which is designed to house the components of the centrifugal blast wheel machine. The centrifugal blast wheel machine 10 further includes a rotating impeller 14 supported by a drive shaft, a control cage assembly, generally indicated at 16, which surrounds the impeller, and a wheel assembly, generally indicated at 18, which receives the control cage assembly. A motor 20 is provided to drive the rotation of the impeller 14 and the wheel assembly 18. The arrangement is such that blast media is fed from a feed spout 22 into the rotating impeller 14, which is driven by the motor 20. By contact with vanes of the rotating impeller 14 (as well as with other particles of media already in the impeller), blast media particles are accelerated, giving rise to a centrifugal force that moves the particles in radial direction, away from the axis of the impeller. The blast media particles, now moving in a generally circular direction as well as outwards, move through openings formed in the impeller 14 into a space between the impeller and a control cage of the control cage assembly 16, still being carried by the movement of the impeller vanes (also known as impellor dams) and the other particles.

When the blast media particles that have passed though the impeller openings into the space between the impeller 14 and the control cage assembly 16 reach an opening provided in the control cage assembly, rotational and centrifugal forces move the particles through the opening and onto ends of the vanes. The control cage assembly 16 functions to meter a consistent and appropriate amount of blast media onto the blades of the wheel assembly 18. As the vanes of the impeller 14 rotate, the blast media particles are moved along their lengths and accelerate until they reach the ends of the vanes and thrown from the ends of the vanes. Although the impeller 14 is shown to be cylindrical in shape, the size and thickness of the impeller may vary depending on the size of a blast wheel assembly and the desired performance characteristics. For example, the impeller 14 may have interior or exterior walls that taper in either direction along its axis.

Typically, the impeller will be made of a ferrous material, such as cast or machined iron or steel, although other materials may also be appropriate. In one particular embodiment, the impeller is formed of cast white iron.

The wheel assembly 18 of the centrifugal blast wheel machine 10 includes a hub or wheel 24 and a plurality of blades, each indicated at 26, to throw blast media introduced into the wheel assembly to treat the work piece contained within the housing 12. The arrangement is such that the impeller 14 is positioned about an axis of the wheel 24 of the wheel assembly 18, with the impeller having a media inlet at one end adapted to receive blast media and a plurality of impeller media outlets constructed and arranged to allow egress of blast media upon rotation of the impeller. The control cage of the control cage assembly 16 surrounds the impeller 14 in a position in which the media outlet of the control cage assembly is adapted for passage of blast media to the heel ends of the blades of the blast wheel assembly 18. As mentioned above, the motor 20 is coupled to the impeller 14 and to the wheel assembly 18 to drive the rotation of the impeller and the wheel assembly. Referring additionally to FIGS. 5-7, the present disclosure is directed to the control cage assembly 16 for the abrasive blast wheel assembly 18 that is configured to lock a control cage of the control cage assembly in place. In one embodiment, the control cage assembly 16 of the present disclosure includes a control cage 28 having a cylindrical wall 30 forming a housing defining an interior chamber and a media outlet or opening 32 formed in the cylindrical wall for allowing the egress of blast media from the interior chamber. A typical centrifugal blast wheel machine 10 having the control cage 28 is used to treat a surface (not shown) of a work piece by projecting blast media (not shown) at the surface. The treatment may be in the nature of cleaning, peening, abrading, eroding, de-burring, de-flashing, and the like, and the blast media typically consists of solid particles such as shot, grit, segments of wire, sodium bicarbonate, or other abrasives, depending on the surface being treated and/or the material being removed from the surface.

The control cage 28 of the control cage assembly 16, typically formed of cast iron (or similar material), is positioned concentrically around impeller 14 and, is

approximately cylindrical in shape. Like the impeller 14, however, the control cage 28 may have other shapes, and may, for example, taper internally and/or externally in either direction along its axis. The control cage 28 also includes an outer flange or locking ring 34, which mates with an adaptor plate 36, which in turn is mounted on the wheel 24 of the wheel assembly 18, fixing the control cage with respect to the wheel and preventing the control cage from rotating with respect to the wheel upon operation of the blast wheel assembly 10. A retaining ring 38 is further provided to firmly secure the locking ring 34 and to prevent the rotational movement of the control cage 28 with respect to the adaptor plate 36 after securing the adaptor plate to the blast wheel 24 of the blast wheel assembly 18. The control cage 28 is then locked in place by placing the feed spout 22 onto the control cage and by firmly securing a feed spout bracket 40, which is shown in FIG. 4.

In other embodiments, the control cage 28 may be restrained from movement by attachment to other stationary elements of the blast wheel assembly 18 or its environment (as indicated above), or, in some cases, may be allowed to or made to rotate in one or both directions. As shown, one of two retaining rings 38 may be provided, with one of the retaining rings having markings or other indicia that allow a user to position the control cage 28 in a certain desired rotational orientation, so as to control the direction of the media being thrown by the blast wheel assembly 18.

As mentioned above, the media opening 32 of the control cage 28 allows egress of blast media upon operation of the blast wheel assembly 18. In the illustrated embodiment, the media opening 32 is approximately rectangular in shape when viewed from the side (i.e., in a direction perpendicular to its axis) and is approximately 3/5 the height of the cylindrical wall 30 of the control cage 28. The size, shape, and location of the media opening 32 may vary depending on the application, however. The length of the media opening 32 is measured in degrees, from the innermost portion of the opening furthest ahead in the direction of rotation to the outermost edge of the trailing portion. While the media opening 32 of the shown embodiment is approximately seventy degrees for a wheel rotating in either direction, in other embodiments, the length of the opening (in either direction) may vary, depending numerous factors such as the overall size of the blast wheel assembly 18, the nature of the media being thrown, and the desired rate of flow, as would be understood by one of skill in the art.

Referring back to FIGS. 1-3, the wheel assembly 18, which is arranged concentrically around control cage 28, includes the plurality of blades 26 sandwiched between a rear wheel and a front wheel of the wheel 24 of the wheel assembly. The various parts of wheel assembly 18 are typically formed of cast iron, although they may also be made of any other appropriate material and/or method. The wheel assembly 18 is connected to the motor 20, in this embodiment by means of key inserted to lock a shaft of motor to the rear wheel of the wheel assembly, so that wheel assembly may be rotated by motor during operation of the blast wheel assembly. Blades 26, each of which have a heel end and a tip, are constructed and arranged to direct the blast media at the surface being treated. The blades 26 may be of any suitable size and any suitable shape, including one or more of straight, curved, flared, flat, concave, or convex shapes.

Referring to FIGS. 5-7, and additionally to FIG. 8, the control cage 28 of embodiments of the present disclosure includes the opening 32 formed in the cylindrical wall 30 of the control cage. The cylindrical wall 30 may also be referred to as a cylindrical body. The cylindrical wall 30 has an outer surface 42 and an inner surface 44. On the outer surface 42 of the cylindrical wall 30, adjacent a trailing edge 46 of the opening 32 of the control cage 28, there is a first raised surface portion 48. Similarly, on the inner surface 44 of the cylindrical wall 30, adjacent the trailing edge 46 of the opening 32 of the control cage, there is a second raised surface portion 50. As shown, both raised surface portions 48, 50 extend from the trailing edge of the opening 32 in a short arc length in the direction of rotation of the blades and impeller. Both raised portions 48, 50 are continuous along a width of the opening 32. Although not shown, a raised surface portion formed on an outside diameter of the control cage 16 prevents abrasive from passing underneath the pickup edge of the blade 26 of the wheel assembly 18. A leading edge 52 of the opening 32 is also beveled.

FIG. 9 illustrates the operation of the impellor 14, the control cage assembly 16 and the wheel assembly 18. As shown, the abrasive material enters the control cage 28 of the control cage assembly 16 through the impeller 14. Once inside the control cage 28, the abrasive material is metered onto the blades 26 of the wheel assembly 18 through the opening 32 formed in the cylindrical wall 30 of the control cage 28. As shown, the first raised surface portion 48 prevents abrasive from going under the blade. The second raised surface portion 50 prevents abrasive from traveling within the control cage additional cycles. The beveled leading edge 52 enables a better transition of abrasive material on the blades 26.

The short arc length of each raised surface portion 48, 50 prevents significant grinding of abrasive media between the blade 26 and the control cage 28. Additionally, a benefit of the raised portions 48, 50 is realized within the first few degrees of rotation of the blade 26 past a trailing edge of the control cage 16 that negates the requirement to fully machine an outside diameter of the control cage 28 to a close tolerance. Similarly, the second raised surface portion 50 on the inner surface 44 of the cylindrical wall 30 of the control cage 38 acts to prevent abrasive from remaining in the gap between the control cage 28 and impeller 14 thereby preventing the trapping of abrasive media for an additional rotation before possibly exiting the control cage opening 32.

On the trailing edge 46 of the opening 32 of the cylindrical wall 30 of the control cage 28, the opening has a pronounced bevel that acts to widen the distance between the inside of the control cage 28 and the outside of the impeller 14. During operation, a considerable amount of abrasive is conveyed between the outside diameter of the impeller 14 and the inside diameter of the control cage 28. By increasing the distance between the two surfaces just prior to passing through the control cage opening 32, radial velocity of abrasive media is better controlled, thereby resulting in a smoother transition onto the pickup point of the blade 26. Similarly, the shape of the bevel on the trailing edge 46 acts to guide the exiting abrasive media toward the blade pickup.

Additionally, the first raised surface portion 48 on the outer surface 42 of the cylindrical wall 30 of the control cage 28 acts to move the release point of the abrasive media closer to a pickup point of the blades 26. The result is a more efficient transition of abrasive media from the control cage 28 to the blades 26. Similar to the beveled trailing edge 46, the relatively short arc length of the first raised surface portion 48 negates the requirement to fully machine the outer surface 42 of the control cage 28 to a close tolerance.

The control cage of 28 embodiments of the disclosure is envisioned for use on any number of impeller designs used within the industry, with varying shapes and sizes of control cage openings 32. Also, the lengths of the first and second raised surface portions 48, 50 on the trailing edge 46 can vary, depending on wear characteristics during operation. The magnitude of the first and second raised surface portions 48, 50 can be varied to accommodate various blade and impeller configurations.

As described above, the features on the trailing edge 46 of the control cage opening 32 act to mitigate these effects by directing the abrasive more efficiently onto the blades 26 and to stop the abrasive from flowing around the control cage interior more than one revolution. As referenced above, the length of the opening 32 (in either direction) may vary, depending numerous factors such as the overall size of the blast wheel assembly 18, the nature of the abrasive media being thrown, and the desired rate of flow, as would be understood by one of skill in the art. In general, the length of the control cage opening 32 will determine the length of the blast pattern; the longer the opening, the longer the blast pattern, and vice versa.

The control cage 28 enables a more efficient operation of the internal components of the centrifugal blast wheel machine 10, which includes reducing abrasive blast media consumption. The energy supplied to the blast wheel machine 10 (most frequently by the electric motor 20) is used more efficiently when the abrasive media that is thrown by the wheel 24 is deposited more directly onto the blades 26, rather than spinning around in the space between the impeller 14 and control cage 28 or passing underneath the blades.

Embodiments of the blast wheel machine 10 include the motor 20 capable of generating horsepower typically in ranges between 20-100 horsepower, although not limited to this range. Moreover, the blast wheel machine 10 of embodiments of the present disclosure may be configured to have multiple blast wheels. Therefore, it is desirable to have the abrasive blast media move through the control cage 28 to transition onto the blades 26 as soon and as efficiently as possible.

Also, by moving onto the blades 26 more efficiently, the abrasive media is less prone to breakdown by any grinding effect within the control cage 28 interior.

The operation of the centrifugal blast wheel machine 10 is as follows. The blast media is fed from the feed spout 22 into the rotating impeller 14. By contact with the rotating impeller vanes (as well as with other particles of media already in the impeller 14), the blast media particles are accelerated, giving rise to a centrifugal force that moves the particles in radial direction, away from the axis of the impeller. The blast media particles, now moving in a generally circular direction as well as outwards, move through the impeller 14 openings into the space between the impeller and the control cage 28, still being carried by the movement of the impeller vanes and the other particles.

When the blast media particles that have passed though the impeller openings into the space between the impeller 14 and the control cage 28 to the media opening 32, the rotational and centrifugal forces move the particles through the media opening and onto the heel ends of the blades 26. The control cage 28 functions to meter a consistent and appropriate amount of blast media onto the blades 26. As the blades 26 of the blast wheel 24 rotate, the blast media particles are moved along their lengths and accelerate until they reach the tips, at which point they are thrown from the ends of the blades toward the work piece.

It should be observed that the control cage 28 of embodiments of the present disclosure provides a smoother transition of abrasive media onto the throwing blade 26 from the impeller 14, prevents media from spinning around inside the control cage inner diameter after passing the opening 32, and lessens an amount of media that passes underneath the throwing blade when transitioning through the control cage. Having thus described several aspects of at least one embodiment of this disclosure, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the disclosure. Accordingly, the foregoing description and drawings are by way of example only.

What is claimed is:

Claims

1. A centrifugal blast wheel machine comprising:

a wheel assembly having a plurality of blades configured to throw blast media introduced into the wheel assembly against a work piece;

an impeller positioned about an axis of the wheel assembly, the impeller having a media inlet at one end adapted to receive blast media and a plurality of impeller media outlets constructed and arranged to allow egress of blast media upon rotation of the impeller;

a motor coupled to the impeller to drive the rotation of the impeller and the wheel assembly; and

a control cage surrounding the impeller and secured to the wheel assembly, the control cage including a cylindrical body defining an interior chamber, the cylindrical body having an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber, the opening having a trailing edge, the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

2. The centrifugal blast wheel machine of claim 1, wherein the outer surface of the cylindrical body of the control cage has a raised surface portion adjacent the trailing edge of the opening.

3. The centrifugal blast wheel machine of claim 2, wherein the trailing edge of the opening has a beveled edge.

4. The centrifugal blast wheel machine of claim 3, wherein the beveled edge tapers away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening.

5. The centrifugal blast wheel machine of claim 1, wherein the trailing edge of the opening has a beveled edge.

6. The centrifugal blast wheel machine of claim 1, wherein the control cage further has a first flange extending outwardly from an end of the cylindrical body and a second flange extending inwardly from an opposite end of the cylindrical body.

7. A control cage for a centrifugal blast wheel machine, the control cage comprising:

a cylindrical body defining an interior chamber, the cylindrical body having an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber, the opening having a trailing edge, the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

8. The control cage of claim 7, wherein the outer surface of the cylindrical body of the control cage has a raised surface portion adjacent the trailing edge of the opening.

9. The control cage of claim 8, wherein the trailing edge of the opening has a beveled edge.

10. The control cage of claim 9, wherein the beveled edge tapers away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening.

11. The control cage of claim 7, wherein the trailing edge of the opening has a beveled edge.

12. The control cage of claim 7, further comprising a first flange extending outwardly from an end of the cylindrical body and a second flange extending inwardly from an opposite end of the cylindrical body.

13. A method of operating a centrifugal blast wheel machine, the method comprising:

feeding blast media from a feed spout into an impeller of the centrifugal blast wheel machine;

accelerating the blast media by rotating the impeller giving rise to a centrifugal force that moves the blast media in radial direction, away from an axis of the impeller; moving the blast media in a generally circular direction into a space between the impeller and a control cage;

metering an amount of blast media through an opening of the control cage onto blades of a blast wheel; and

moving the blast media along lengths of the blades to accelerate and throw the blast media toward a work piece,

wherein the control cage includes a cylindrical body defining an interior chamber, the cylindrical body having an outer surface, an inner surface, and an opening formed therein to allow the egress of blast media from the interior chamber, the opening having a trailing edge, the inner surface of the cylindrical body having a raised surface portion adjacent the trailing edge of the opening.

14. The method of claim 13, wherein the outer surface of the cylindrical body of the control cage has a raised surface portion adjacent the trailing edge of the opening.

15. The method of claim 14, wherein the trailing edge of the opening has a beveled edge.

16. The method of claim 15, wherein the beveled edge tapers away from the inner surface to the outer surface of the cylindrical body so that a far edge of the beveled surface forms part of the raised surface portion adjacent the trailing edge of the opening.

17. The method of claim 13, wherein the trailing edge of the opening has a beveled edge.

18. The control cage of claim 13, wherein the control cage further has flange extending outwardly from an end of the cylindrical body and a second flan extending inwardly from an opposite end of the cylindrical body.