Continuous process blast mill for finishing cast metal parts

A workpiece cleaning mill that is useful for cleaning castings includes a hollow housing that is established by arranging plural elongated manganese flights side-by-side to establish a cylinder, and attaching the flights to opposed entrance and exit rings. A feed conveyor feeds workpieces into the entrance end, and an exit conveyor conveys the workpieces away from the exit end. Media throwers are disposed at each end to throw high-speed cleansing media, such as shot, into the housing. The housing is rotated as the workpieces move, under the influence of gravity and/or following workpieces being fed into the housing, from the entrance end to the exit end while being bombarded with shot. Steel mesh curtains at each end block the media from passing outside of the mill. Spent media falls through perforations in the flights, and the spent media is conveyed back to a media hopper and thence to the media throwers for reuse. Magnetic valves regulate the amount of media thrown by the throwers.

FIELD OF THE INVENTION 
The present invention generally relates to cleaning manufactured 
workpieces, and more particularly to methods and apparatus for cleaning 
castings by abrasion. 
BACKGROUND 
Cast metal parts (referred to in the art as "castings" and, more generally, 
"workpieces") are cleaned after they are cast by subjecting the castings 
to abrasion. The abrasive cleaning might be undertaken in more than one 
step, with much of the cleaning being accomplished by directing high speed 
shot against the castings. To ensure that the castings are completely 
cleaned, the castings ordinarily are tumbled in an enclosure referred to 
as a "tumbling mill" while being bombarded by high speed steel shot that 
is directed into the tumbling mill. 
It will readily be appreciated that the tumbling mill must be made of 
material that is harder than the steel shot, so that the tumbling mill can 
withstand the cleaning process. Accordingly, existing tumbling mills are 
constructed by arranging a plurality of elongated hardened slats, referred 
to as "flights", side-by side in a conveyor belt configuration inside of a 
housing. The flights, which are made of manganese or some other hard 
metal, are joined by links, and together the flights and links establish a 
conveyor belt that is driven by means of sprockets and rollers to move in 
an endless chain, thereby tumbling castings which have been disposed in 
the tumbling mill. As the castings are tumbled, they are blasted with shot 
to clean the castings. U.S. Pat. No. 4,476,655 is representative of such 
apparatus. 
Unfortunately, it happens that many existing tumbling mills suffer several 
drawbacks. For example, many tumbling mills, such as the one disclosed in 
the above-referenced patent, are batch apparatus, meaning that the 
castings must be loaded into the tumbling mills, cleaned, and then 
unloaded after cleaning. This is labor intensive, and it wastes processing 
time, because as the castings are being loaded and unloaded, the tumbling 
mill must be shut down. Furthermore, not only must the flights be made of 
relatively expensive manganese, but so must the links and the links 
connectors, because they are exposed to the shot. Moreover, much 
maintenance is required on the tumbling mill's internal parts, such as 
sprockets, traction wheels, links, and pins. Still further, castings in 
many previous tumbling mills can become undesirably attached to or 
otherwise stick to the conveyor that is established by the flights. 
As recognized by the present invention, however, it is possible to provide 
a tumbling mill which cleans castings in a continuous process, which is 
simple in construction, and which does not require any components other 
than the inner surface of the flights to be made of manganese. Moreover, 
with this understanding the present invention provides a superior 
apparatus with improved material wear characteristics and enhanced 
workpiece agitation characteristics vis-a-vis simple rotating flightless 
barrel apparatus such as the one disclosed in U.S. Pat. No. 4,277,918. 
Accordingly, it is an object of the present invention to provide an 
apparatus for cleaning castings that uses a continuous cleaning process. 
Another object of the present invention is to provide an apparatus for 
cleaning castings that has a comparatively simple construction. Still 
another object of the present invention is to provide an apparatus for 
cleaning castings that requires only the inside surfaces of flights to be 
made of relatively hard material. Yet another object of the present 
invention is to provide an apparatus for cleaning castings that is easy to 
use and cost-effective. 
SUMMARY OF THE INVENTION 
A continuous operation apparatus is disclosed for cleaning workpieces, such 
as castings. The apparatus includes a plurality of elongated flights that 
are arranged generally side-by-side to establish a blast housing. The 
blast housing defines opposed entry and exit ends and an inner surface and 
an outer surface. At least one drive roller is rollably engaged with the 
outer surface of the blast housing for causing the blast housing to 
rotate. Also, at least one support roller is rollably engaged with the 
outer surface of the blast housing to support the housing. Moreover, at 
least one entrance media thrower is juxtaposed with the entrance end, and 
the entrance media thrower is oriented to direct cleansing media into the 
blast housing. Likewise, at least one exit media thrower is juxtaposed 
with the exit end and is oriented to direct cleansing media into the blast 
housing. At least one entrance curtain is juxtaposed with the entrance end 
to block media from propagating past the entrance curtain, and at least 
one exit curtain is juxtaposed with the exit end to block media from 
propagating past the exit curtain. 
In a preferred embodiment, an entrance conveyor is positioned for conveying 
workpieces into the entrance end of the housing. Similarly, an exit 
conveyor is positioned for conveying workpieces away from the exit end, 
and workpieces are pushed from the entrance end to the exit end by other 
workpieces. To further promote passage of workpieces through the housing, 
a tilt mechanism is disposed beneath the blast housing for tilting the 
blast housing, whereby workpieces are urged from the entrance end of the 
housing to the exit end by gravity. 
Preferably, the apparatus still further includes an entrance ring, an exit 
ring, and a plurality of fasteners, and the flights extend between the 
rings with the outer surface of each flight being held against the rings 
by the fasteners. As disclosed further below, each fastener extends from 
the outward surface of a flight into which it has been welded into a 
respective ring, such that the fasteners and rings are shielded from the 
cleansing media by the flights. 
Desirably, an entrance vestibule is juxtaposed with the entrance end and an 
exit vestibule is juxtaposed with the exit end. The entrance and exit 
curtains are respectively suspended in the entrance and exit vestibules. 
At least one of the vestibules can be distanced from the blast housing to 
permit a person to enter the blast housing. 
To permit reclaiming cleansing media, at least some of the flights are 
perforated along respective exit segments to permit cleansing media to 
pass therethrough to a spent media chamber. The flights, however, are not 
perforated along respective entrance segments, to thereby promote mixing 
of the media and the workpieces. A media conveyor conveys media from the 
spent media chamber to a media hopper. Then, a feed conveyor feeds media 
from the hopper to the thrower. A respective magnetic control valve is in 
communication with each thrower for regulating media input thereto. 
In another aspect, a tumbling mill for cleaning workpieces includes a 
rotatable housing including plural elongated manganese flights that define 
respective entrance ends and exit ends. The entrance ends are attached to 
an inner surface of an entrance ring, whereas the exit ends are attached 
to an inner surface of an exit ring. Steel curtains are arranged to block 
high speed cleansing media in the housing from propagating out of the 
mill. 
In still another aspect, a method is disclosed for cleaning workpieces 
which includes providing a housing having open entrance and exit ends. The 
method also includes conveying workpieces to the entrance end, rotating 
the housing, and directing high speed cleansing media into the housing 
from both ends. Media that propagates past the open ends is blocked.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, a blast mill is shown, generally designated 
10, for cleaning workpieces 12. In the preferred embodiment, the 
workpieces 12 are castings; accordingly, the blast mill 10 cleans the 
workpieces 12 by bombarding the workpieces 12 with cleansing media 13 
composed of high speed steel shot. It is to be understood, however, that 
the principles of the present invention can be applied to workpieces other 
than castings, and that the composition of the cleansing media is 
established as appropriate for the particular workpieces that are to be 
cleaned. 
As shown in FIG. 1, the mill 10 includes a hollow cylindrical housing 14 
defining an open entrance end 16 and an open exit end 18. In the preferred 
embodiment, the housing 14 is established by a plurality of elongated, 
parallelepiped-shaped flights 20 that are arranged generally side-by-side 
as shown to establish the housing 14. Preferably, each flight 20 is 
fourteen feet (14') long and is made of an alloy of which 11%-14% is 
manganese. 
FIG. 1 shows that the flights 20 are held in the cylindrical arrangement 
shown by opposed steel entrance and exit rings 22, 24, with the rings 22, 
24 defining the ends 16, 18 of the housing 14. As more fully disclosed 
below, the flights 20 are attached at their ends to the respective inner 
surfaces of the rings 22, 24 by means of steel fasteners. With this 
combination of structure, the flights 20 extend between the rings 22, 24 
with the outer surface of each flight 20 being held against the inner 
surface of the rings 22, 24 by the fasteners. Consequently, the fasteners 
and rings are shielded from the cleansing media by the flights 20. 
With the above disclosure in mind, the workpieces 12 are conveyed into the 
entrance end 16 of the housing 14 by an entrance conveyor 26. Also, an 
exit conveyor 28 is positioned for conveying workpieces 12 away from the 
exit end 18 of the housing 14. In accordance with the present invention, 
workpieces 12 are pushed from the entrance end 16 to the exit end 18 by 
other workpieces 12, as the other workpieces 12 are conveyed into the 
housing 14. As the workpieces 12 travel through the housing 14, the 
workpieces 12 are bombarded by the cleansing media 13, and the housing 14 
is rotated to tumble the workpieces 12 to thereby promote complete 
cleaning of the workpieces 12 by the media 13. 
Turning first to the cleansing media 13 bombardment, two entrance media 
throwers 30 (only one entrance thrower 30 shown schematically in FIG. 1 
for clarity) are juxtaposed with the entrance end 16 of the housing 14. As 
shown, the entrance media throwers 30 are oriented to direct cleansing 
media 13 into the housing 14. Preferably, a hollow entrance vestibule 32 
is engaged with the housing 14, and the entrance media throwers 30 are 
mounted on the entrance vestibule 32. 
Similarly, two exit media throwers 34 (only one exit thrower 34 shown 
schematically in FIG. 1 for clarity) are juxtaposed with the exit end 18 
of the housing 14. As shown, the exit media throwers 34 are oriented to 
direct cleansing media 13 into the housing 14. As recognized by the 
present invention, by directing cleansing media 13 into the housing 14 
from both ends 16, 18 thereof, uniform disposition of the media 13 within 
the housing 14 is promoted. In the presently preferred embodiment, the 
media throwers 30, 34 are Bronco sixty horsepower sixteen inch media 
wheels made by RCK Industries, Inc. of Dousman, Wis. 
Preferably, a hollow exit vestibule 36 is engaged with the housing 14, and 
the exit media throwers 34 are mounted on the exit vestibule 36 (FIG. 1 
shows the exit vestibule 36 in an exploded relationship with the exit 
media thrower 34 and the housing 14). If desired, as indicated in FIG. 1 
the exit vestibule can be pivoted away from or translationally moved away 
from the housing 14 to permit a person to enter the housing 14. 
Advantageously, a plurality of, preferably four (4), steel mesh entrance 
curtains 38 are suspended within the entrance vestibule 32 and accordingly 
are juxtaposed with the entrance end 16 of the housing 14 to block media 
13 from propagating past the entrance curtains 38. Likewise, a plurality 
of, preferably four (4), steel mesh exit curtains 40 hang within the exit 
vestibule 36 and accordingly are juxtaposed with the exit end 18 of the 
housing 14 to block media 13 from propagating past the exit curtains 40. 
The workpieces 12, however, can pass through the curtains 38, 40. 
Now addressing the means by which the housing 14 is rotated, a plurality 
of, preferably three (3), polyurethane drive rollers 42 (only one drive 
roller 42 shown in FIG. 1 for clarity) are rollably engaged with the outer 
surface of the housing 14 as shown. The drive rollers 42 are rotatably 
mounted in respective channels 43 (best shown in FIG. 2) that are formed 
on a hollow base 44, and when the drive rollers turn, the housing 14 
rotates in response. 
To turn the drive rollers 42, respective drive motors are coupled to the 
drive rollers 42. Specifically, as shown in FIG. 1 an axle of each drive 
roller 42 is coupled via a chain drive 46 with an associated sprocket 48. 
In turn, the sprocket 48 is coupled to a gear assembly 50. If desired, the 
sprocket 48 can be coupled to the gear assembly 50 via a second sprocket 
(not shown). Power from a motor 52 is transferred through the train 
discussed above to the drive roller 42 to turn the drive roller 42 and 
thereby cause the housing 14 to rotate. In the presently preferred 
embodiment, the motor 52 is a ten horsepower (10 HP) twelve hundred 
revolutions per minute (1200 RPM) "C" faced variable speed electric motor, 
and the gear assembly 50 is a CONE double reduction right angle gear 
assembly with a one hundred fifty to one (150:1) reduction ratio and a 
double enveloping tooth design. It is to be understood that the speed of 
the motor 52 is established as appropriate for the desired speed of 
rotation of the housing 14, the speed being dependent on the particular 
characteristics and requirements of the workpieces 12. 
In addition to the drive rollers 42, a plurality of support rollers 54 are 
rollably engaged with the housing 14. Accordingly, the housing 14 is 
rotated by the drive rollers 42 and supported by the support rollers 54. 
As mentioned above, workpieces 12 are pushed through the housing 14 by 
following workpieces 12. Additionally, to promote passage of the 
workpieces 12 through the housing 14, the entrance end 16 of the housing 
14 can be tilted above the exit end 18. To undertake such tilting, at 
least one and preferably two screw jacks 56 are positioned beneath the 
base 44 near the entrance end 16 to raise the entrance end 16 above the 
exit end 18 and thereby promote passage of the workpieces 12 through the 
housing 14. To prevent slippage of the housing 14 on the base 44, a cam 
follower 58 that is welded on the base 44 abuts the exit ring 24. 
The present invention also envisions control of the rate of cleansing media 
13 introduction into the housing 14. More particularly, the media throwers 
30, 34 are fed media 13 from a media hopper 60 via type "AR" helicoid 
conveyors 62, and respective control valves 64 are disposed in the inlets 
to the media throwers 30, 34 to regulate the amount of media 13 that is 
input to the throwers 30, 34. Preferably, the control valves 64 are 
magnetic valves that have no moving parts and, hence, that are low 
maintenance. In the preferred embodiment, the control valves 64 are 
magnetic control valves made by Jack Champlain of Mishiwak, Ind. The 
valves 64 can be adjusted as desired to establish a predetermined media 13 
throughput to the throwers 30, 34. 
In addition to controlling the rate of media 13 introduction to the housing 
14, the present invention contemplates recycling spent media 13. In 
understanding the recycling process, reference is made to FIGS. 1 and 2. 
As shown in FIG. 2, each flight 20 is formed with perforations 65 along a 
respective exit segment 20A, and the housing 14 includes a perforated 
grate 67 (FIG. 1) under the exit segments 20A, to permit cleansing media 
13 to pass therethrough to a spent media chamber 66 (FIG. 1). In contrast, 
the flights 20 are not perforated along respective entrance segments 20B, 
thereby promoting mixing of the media 13 and the workpieces 12. 
Accordingly, media 13 falls through the perforations 65 into the spent 
media chamber 66. The media 13 is then conveyed via a sixteen inch (16") 
type "AR" helicoid and screw trough conveyor 68 to an air wash device 70 
(FIG. 1). Per principles of the present invention, the air wash device 70 
is any device known in the art that is appropriate for separating sand 
from the media 13. From the air wash device 70, the media passes through a 
magnetic rotating drum 71 to further separate the media 13 from debris, 
and then the media 13 is conveyed to the hopper 60. If desired, a magnetic 
sensor 72 senses the level of media 13 in the hopper 60 and generates a 
signal to stop the conveyor 68 when the level of media 13 in the hopper 60 
reaches a predetermined level. 
Additional details of the preferred flight 20 cooperation of structure can 
be appreciated in cross-reference to FIGS. 2 and 3. Post-like metal 
fasteners 74 are disposed into holes that are formed into the radially 
outer surfaces 20C of the flights 20, and the fasteners 74 are then welded 
into their respective flights 20. The fasteners 74 do not extend past the 
radially inside surfaces 20D of the flights 20. I have found that 
disposing the fasteners into holes in the flights and then welding them in 
place reduces the risk that the fasteners might break off from their 
respective flight. 
As shown, each fastener 74 protrudes outwardly toward one of the entrance 
and exit rings 22, 24, with which the fastener is engaged. In other words, 
the outer surfaces 20C of the flights 20 are juxtaposed with the radially 
inward surfaces 22A, 24A of the rings 22, 24. Consequently, the fasteners 
74 advantageously are not exposed to the media 13, nor are the rings 22, 
24 exposed to the media 13. 
Further, as shown in FIG. 3, the flights 20 are generally positioned 
side-to-side, but are not flushly positioned side-to-side. Instead, to 
promote agitation of the workpieces 12, the flights 20 overlap each other 
as shown. If desired, as shown in FIG. 4 the outer surface 20C (relative 
to the orientation of the flights 20 when combined into the housing 14) of 
each flight 20 can be welded to a steel strength member 76 which is 
oriented perpendicularly to the flight 20. Accordingly, the flight 20 with 
strength member 76 establishes a "T"-shaped transverse cross-section. 
While the particular CONTINUOUS PROCESS BLAST MILL FOR FINISHING CAST METAL 
TS as herein shown and described in detail is fully capable of 
attaining the above-described objects of the invention, it is to be 
understood that it is the presently preferred embodiment of the present 
invention and is thus representative of the subject matter which is 
broadly contemplated by the present invention, that the scope of the 
present invention fully encompasses other embodiments which may become 
obvious to those skilled in the art, and that the scope of the present 
invention is accordingly to be limited by nothing other than the appended 
claims.