Rotary mill

A rotary milling system includes a rotatable cylinder, a discharge grate, a discharge housing surrounding the grate, a valve moveable between an open and closed position being in fluid communication with the discharge housing, and a conveying pipe extending from the valve. The cylinder can include grinding media for abrading a product when the cylinder is rotated. The product is suspended and ground within a liquid medium. Upon conclusion of the milling, the valve is opened to allow the liquid medium and milled product to pass through the discharge housing and the conveying pipe. The liquid medium can flow back and forth through the grate during the milling operation, with the valve preventing discharge before conclusion. A liquid-drawing apparatus can be used to draw the milled product through the conveying pipe into a separator tank after opening the valve.

BACKGROUND

The present invention relates to rotary mills. More particularly, the invention relates to an automated system for reliably discharging rotary mills that include liquid in the milling cylinder.

Rotary mills, also known as ball mills, pebble mills, rod mills, or tumble mills, are well known in the art. A traditional rotary mill includes a horizontal rotating cylinder that rotates about a central axis. The cylinder includes grinding media that is generally spherical, cylindrical, or another uniform shape. In the case of milling with a liquid medium, solid target materials are placed along with a liquid medium into the cylinder for milling. The cylinder is rotated, causing the grinding media to tumble along with the target material, with the grinding media abrading and impacting the solid target materials. Continued rotation of the cylinder produces a milled product in the form of particles suspended in liquid media.

Upon completion of the milling process, the milled product is discharged from the cylinder. The cylinder includes an opening with a solid cover that can be manually removed and replaced with a discharge grate, which will retain the grinding media but allow the milled product to pass through.

In the case of a wet milled product, the cylinder can remain stationary if the liquid suspending the product is a low-viscosity fluid, the liquid can flow past the media due to gravity. If, however, the liquid is a non-Newtonian or a high-viscosity liquid, the cylinder can be rotated to discharge the milled product.

Alternatively, the grinding media and milled product can be dumped from the cylinder without the use of a grate, and subsequently separated by a grate, filter, or vibrating sifter.

The rotary mill also includes a discharge housing that surrounds the rotating cylinder to define an annular space between the cylinder and the housing. The housing also includes a collection hopper at its bottom. When the milled product is discharged, as described above, the milled product will enter the annular space and fall into the hopper.

However, the above discharge process can result in dirty conditions, with milled product adhering to the inner surface of the housing as well as the outside of the cylinder. Retrieval of the milled product from the discharge housing can also result in milled product entering the surrounding area. These conditions can reduce the amount of milled product recovered, as well as lead to cross-contamination issues and cleaning problems. In the case of liquid milling, the operator must make and break a liquid piped connection to the discharge housing, exposing the milled product and potential solvent vapors to the surrounding area during this break in the connection.

Accordingly, there is a need for a discharge system that can reliably deliver the milled product from the cylinder while limiting loss of milled product and exposure of the milled product to adjacent areas and operators.

SUMMARY

To address the above and other problems, a rotary milling system is provided that includes a rotatable cylinder that defines a cavity and a central longitudinal axis. A discharge grate is provided on a sidewall of the cylinder to define an opening to allow milled product to pass therethrough. A discharge housing surrounds the discharge grate and defines a cavity. A valve is connected to an outlet of the discharge housing and the valve is moveable between a closed position and an open position to selectively allow liquid medium and suspended solids therein to pass through the valve when open while preventing passage when closed. A conveying pipe is in fluid communication with an outlet side of the valve and a liquid-drawing apparatus operatively associated with the conveying pipe and disposed downstream of the discharge housing to draw liquid medium in the conveying pipe away from the discharge housing.

The system may include a rotary union connected with the conveying pipe. The system may also include a secondary pipe connected to the rotary union, wherein the rotary union couples the secondary pipe and the conveying pipe.

The system may also include a separator tank operatively coupled to the conveying pipe, wherein the liquid drawing apparatus is in fluid communication with the separator tank.

In one aspect of the system, the valve can be a ball valve, pinch-type valve, or gate-type valve. The valve may be manually or pneumatically operated between the open and closed positions.

In another aspect, the opening of the discharge grate is always open and provides fluid communication between the discharge housing and the cavity of the rotatable cylinder, allowing fluid to pass between the discharge housing and cylinder during rotation of the cylinder while blocking solid grinding media from passing through the discharge grate.

The system may include a transmission coupled to the cylinder for rotating the cylinder.

The liquid-drawing apparatus can include a vacuum coupled to the separator tank or it could include a pump connected in line with the secondary pipe. Where the liquid-drawing apparatus includes a pump, the pump can be any suitable type of pump such as a centrifugal pump, positive displacement pump, lobe pump, eccentric screw pump, rotary pump, or diaphragm pump. The conveying pipe can extend into and through the first trunion member.

In another aspect, the system can include a valve disposed in line with the secondary pipe and a delivery pipe extending from the valve and in fluid communication with a tank for housing liquid medium to be delivered to the cylinder. The delivery pipe is configured to deliver liquid medium to the cylinder through the secondary pipe and conveying pipe. The valve has a first position where the liquid delivery pipe is blocked from the secondary pipe and a second position where the liquid delivery pipe is in fluid communication with the secondary pipe. A pump can be disposed in line with the delivery pipe for pumping liquid medium from the tank toward the cylinder.

In another approach, a method for discharging milled product from a rotary mill is provided. The method includes rotating a cylinder in which a plurality of grinding media, liquid medium, and product to be milled are disposed; grinding the product to be milled to produce a milled product and suspending the milled product in the liquid medium while grinding; discharging the liquid medium and milled product through a discharge grate disposed on the cylinder from the cylinder into a discharge housing that surrounds the discharge grate; opening a valve that is connected to a conveying pipe, wherein the valve is in fluid communication with the discharge housing and the conveying pipe to permit fluid to flow from the discharge housing to the conveying pipe; discharging the liquid medium and milled product from the discharge grate into the conveying pipe; and actuating a liquid-drawing apparatus to draw the liquid medium and milled product out of and away from the housing and through the conveying pipe.

The method can include rotating the cylinder while the valve is open and the liquid-drawing apparatus is actuated.

The method also may include transferring liquid medium back and forth between the discharge housing and the cylinder through the grate while rotating the cylinder. During this operation, the valve may be open or closed while transferring liquid medium back and forth through the grate.

In one aspect of the method, the cylinder, discharge housing, discharge grate, conveying pipe, and valve rotate together about a central axis. The rotation of the cylinder, discharge housing, discharge grate, conveying pipe, and valve may be relative to a stationary secondary pipe and separator tank. The secondary pipe may be coupled to the conveying pipe via a rotary union.

In another aspect of the method, the liquid-drawing apparatus is a pump connected in line with the secondary pipe.

DETAILED DESCRIPTION

Referring now to the drawings,FIGS. 1-7Billustrate a rotary mill system10for milling a desired product. The system10includes a rotatable cylinder12, a discharge grate14in the side of the rotatable cylinder12, a liquid-tight housing18mounted to the cylinder12and surrounding the grate14, and a conveying pipe20for discharging milled product from the cylinder12.

With further reference toFIG. 1, the cylinder12includes a generally cylindrical sidewall22extending between a first end wall24and a second end wall25. The sidewall22and end walls24and25define a cavity26having a longitudinal central axis A. The cylinder generally includes grinding media28disposed within the cavity26for performing a traditional rotary milling operation. The amount of grinding media28depends on the needs of the user. For example, the cavity26could be approximately 50% full of grinding media28by volume. Of course, other amounts, such as 30-60%, could also be used.

The grinding media28may be any suitably hard material, such as carbon steel, stainless steel, tungsten carbide, alumina, zirconia, porcelain, or the like. The grinding media can have different sizing as necessary. For example, in one form, the grinding media can be between ¼ inches in diameter to 1 inch in diameter. Of course, it could also be as small ⅛ inch or as large as 3 inches in diameter. The grinding media28is preferably a uniform size; however, the media size used in a particular operation could be different, where some of the media could be, for example, 1 inch in diameter with others being 2 inches in diameter. These sizes are merely exemplary and it will be appreciated that various other sizes of the grinding media could also be used.

The cylinder12also includes a first trunion30and a second trunion32extending outwardly from the end walls24and25, respectively, along the central axis A. The trunions30and32support the cylinder12for rotating. More specifically, the system10includes a pair of vertical support members34a,34beach having a base36a,36bfor contacting a support surface such as a floor and a bearing38a,38bfor engaging and supporting the trunions30and32for rotation therein.

The cylinder12further includes a loading opening40extending through the sidewall22for delivering grinding media28or the product to be milled. An access hatch or loading cover42can be mounted over the opening40for sealing the opening40in a manner known in the art. The loading opening40can be diametrically opposed from the discharge grate14on the opposite side of the cylinder12. However, other locations of the loading opening40in the sidewall22could be used.

Turning toFIGS. 2A and 2B, the system10includes a transmission portion44, including a motor46, gear reducer48, and belt50. The gear reducer48is operatively coupled to the first trunion30. The transmission portion44can generally operate and be controlled in a manner known in the art to rotationally drive the cylinder12through the connection between the gear reducer48and the first trunion30.

Referring backFIG. 1, the discharge grate14is provided on the sidewall22of the cylinder12. The discharge grate14is configured with openings52that are sized to retain the grinding media28within the cavity26, while allowing the milled product to pass through the openings52. In one form, the openings52can be in the form of slots approximately 0.25 inches wide. However, it will be appreciated that other opening sizes could be used to retain the grinding media28while allowing the product to pass.

With reference toFIGS. 3 and 4, the housing18surrounds the discharge grate14to create a liquid-tight seal between the housing18and the cylinder12. Accordingly, the housing18may be attached to the sidewall22of the cylinder12. The liquid-tight seal between the housing18and the cylinder12helps to limit milled product that is suspended in the liquid medium from escaping to the adjacent area or onto the outer surface of the cylinder12outside the housing18. Thus, the cylinder12and the surrounding environment may be kept cleaner relative to a housing surrounding the entire cylinder12. A cavity54is defined by the space between the housing18and the cylinder12into which milled product and liquid can be temporarily stored after passing through the openings52in the grate14.

The housing18further includes an outlet pipe56extending outward therefrom and generally perpendicular to the grate14. The outlet pipe56is liquid-tight with the housing cavity54and open to the housing cavity54. Liquid medium and milled product within the cavity54will therefore flow into outlet pipe56without leaking into surrounding areas.

The outlet pipe56includes a bend58of approximately 90 degrees such that the outlet pipe56extends generally parallel to the axis A.

The grate14remains open to the cavity54of the housing18during milling, such that the product and liquid medium within the cylinder12will be able to flow through the grate14in both directions during milling. However, the liquid medium and product will be prevented from flowing beyond the housing18and pipe56during the milling process as further described below.

With reference toFIGS. 1, 3, and 4, the system10further includes a liquid-tight valve60attached to the outlet pipe56after the bend58. The valve60could be a ball valve, a pinch-type valve, or a gate-type valve. The valve60is moveable between an open and closed position. In the closed position, the liquid medium and product will be retained within the housing cavity54, pipe56, and cylinder12. The valve60remains closed during the milling process, such that the medium and product can flow back into the cylinder12as it is rotated for additional milling. Accordingly, the milled product and liquid medium that flows into the housing18isn't trapped in the housing and prevented from additional milling, even though it may flow past the grate14multiple times during milling. The valve60ensures that milled product and liquid medium will not progress further into the system until such time as discharge is desired. The valve60is positioned between the outlet pipe56and the conveying pipe20, such that when the valve is opened, liquid medium and milled product will flow through the outlet pipe56and into the conveying pipe20for further processing.

When discharge is desired, the valve60is opened, allowing the milled product and liquid medium to travel out of the housing18and cylinder12through the outlet pipe56and past the valve60. The valve60can be manually actuated to move it between the open and closed positions. Alternatively, the valve60can be automatically actuated.

In the case of manual operation, an operator can be positioned adjacent the housing18with limited interaction with the liquid medium and milled product. In the case of automated operation, the operator can be positioned remotely to open and the close the valve60likewise limiting interaction with the liquid medium and milled product.

An automated valve60can be pneumatically activated in a manner known in the art. The pneumatic pressure can be provided by a supply line66(shown inFIG. 1) extending radially from the first trunion30, as well as longitudinally through the first trunion30to an air supply source (not shown).

With reference toFIGS. 1 and 3, the liquid medium and milled product can be delivered for further processing from the housing18through the outlet pipe56and past the valve60via the conveying pipe20. The conveying pipe20is therefore in fluid communication with the housing18when the valve60is open. For example, the conveying pipe20is mounted or connected to the valve60at a location away from the discharge grate14and the cylinder12. The conveying pipe20has a generally circular cross-section and includes a longitudinal portion70extending generally parallel to the central axis A of the cylinder12. The conveying pipe20further includes a curved elbow portion72extending from the longitudinal portion70and transitioning into a radial portion74, which extends toward the central axis of the cylinder12. The radial portion74is coupled with the second trunion32at a point generally along the central axis A of the cylinder12. The radial portion74of the pipe20transitions into an axial portion76that extends along the central axis A of the cylinder12and into a rotary union80. As a whole, the pipe20defines a passageway82having a central axis and extending through the pipe20. The passageway82is in fluid communication with the housing cavity54when the valve60is open, so that liquid medium and milled product can be conveyed from the housing18through the pipe20.

Because the housing18remains open to the cylinder12during milling and discharge, the pressure within the housing18and cylinder12is generally the same. The housing18does not therefore require individual pressure control and does not require the use of an additional check valve or bleed valve to maintain a desired pressure within the cavity54or to operate as a vacuum breaker. Vacuum prevention in the cylinder12and housing18can be accomplished by way of a vent line84extending through the trunion30and into the cylinder12.

With reference toFIGS. 1 and 5, the system10further includes a secondary pipe86extending axially from the rotary union80and into a separator tank88. The separator tank88is in the form of a liquid-air separator tank. The secondary pipe86is fluidly coupled to the axial portion76of the conveying pipe20via the rotary union80in a manner known in the art. The separator tank88defines a cavity90for receiving liquid medium and milled product that has been conveyed form the conveying pipe20and through the secondary pipe86. The separator tank88can be connected to a blower or vacuum91.FIG. 1illustrates that the blower or vacuum91is connected at the top of the tank88. The blower or vacuum91can provide a negative pressure to the tank88as well as the secondary pipe86and conveying pipe20for drawing the milled product toward the tank88.

For the liquid discharge of liquid medium and milled product, the tank88includes a valve96mounted to the bottom of the tank88. The separator tank88can be a cyclone separator, which can separate the milled product from the liquid. The milled product can be vacuumed out of the tank88through the blower or vacuum91mounted at the top of the tank88, and the valve96will release the liquid from the tank88.

In an alternative approach, and with reference toFIG. 5, the system10can include a pump98mounted in line with the stationary secondary pipe86between the separator tank88and the rotary union80. The pump98can be in the form of a positive displacement or centrifugal pump, or any pump with an eccentric screw, rotary, diaphragm, lobe, or the like. This type of pump98is beneficial for liquid discharge in that it can provide an alternative method for discharging the milled product by pumping the liquid medium in which the milled product is suspended. This is generally not available for discharging dry milled product.

Accordingly, the use of the pump98makes the vacuum91attached to the top of the separator tank88redundant. Thus, when the pump98is used, it can be used without the vacuum91. However, if desired, the vacuum91and pump98could be used together. If no vacuum is mounted to the top of the tank88, the top of tank88will vent.

With reference again toFIG. 1, the cylinder12, trunions30and32, bearings38, secondary pipe86, rotary union80, and the radial portion76of the conveying pipe20are coaxially aligned along the central axis A of the cylinder12. As the cylinder12rotates about its central axis A via the trunions30and32and bearings38a,38b, the coaxially aligned components, not including the secondary pipe86and rotary union80, will rotate as well. The housing18, mounted to the cylinder12, will rotate along with the cylinder12. The outlet pipe56and valve60will likewise rotate along with the cylinder12. The remaining portions of the conveying pipe20will rotate with the cylinder12and remain connected via the valve60and outlet pipe56to the housing18. The housing18and separator tank88can remain fluidly connected when the valve60is open through the pipes20and86while rotating. Thus, the milled product can be delivered to the tank88if the cylinder12is either rotating or stationary.

Having described the general structure of the system10, the function of the rotary milling system10described above will now be described in further detail.

With the cylinder12in a stationary position and the valve60in the closed position, the loading cover42can be opened to allow access into the cavity26of the cylinder12. The desired product to be milled can be deposited into the cavity26along with the desired liquid medium for subsequent milling by the system10. Additionally, grinding media28can be deposited into the cavity26or removed from the cavity26depending on the needs of the user.

The liquid medium can be any suitable and known medium used for wet milling. For example, without intending to limit the liquid medium, the liquid medium can include water, solvents, emulsifiers, surfactants, alcohols, ethers, and other organic liquids as well as mixtures. The liquid medium can have varying viscosity depending on the needs and desires of the user for the milling procedure. In one approach, the liquid medium can be a low viscosity Newtonian liquid. In another approach, the liquid medium can be a high-viscosity thixotropic or shear-thinning liquid. The type of liquid medium used will affect the manner of discharging the liquid medium and milled product at the conclusion of the milling process, which will be further described below.

Once the desired amount of product and grinding media28are present in the cavity26of the cylinder12, the loading cover42can be replaced on the cylinder12to create a seal and limit milled product from exiting the cavity26during the milling process. Similarly, the valve60is in the closed position, thereby preventing liquid medium and milled product from exiting the housing cavity54and cylinder12during the milling process. The discharge grate14remains open, allowing liquid medium to flow between the housing18and cylinder12.

With reference toFIGS. 6, 7A, and 7B, with the product ready for milling, the cylinder12can be controllably rotated by the transmission portion44of the system10in a manner known in the art.FIG. 6illustrates the liquid medium99present in the cylinder12.FIGS. 7A and 7Bshows the rotation of the cylinder without the liquid medium99illustrated. The cylinder12will rotate about its central axis A via the interface between the trunions30and32and the bearings38. As the cylinder12rotates, the grinding media28is lifted and then tumbles back down to the bottom of the cylinder12. This tumbling causes the grinding media28to abrade and impact the solid product. There are two types of action for the grinding media depending on the speed of rotation of the cylinder12. “Tumbling” occurs at lower rotational speeds, with the grinding media28rolling or tumbling across the build-up of media28in the lower portion of the cylinder12and is illustrated inFIG. 7A. “Cataracting” occurs at higher rotational speeds, where the media28free-falls from the top of the cylinder12to the mass of media28at the bottom of the cylinder and is illustrated inFIG. 7B.

To assist in lifting the grinding media during operation, the cylinder12can include a plurality of longitudinally running ribs12awithin the cavity26of the cylinder12. These ribs12acan be seen inFIGS. 7A and 7B.

As stated above, and with reference toFIG. 6, the solid product to be milled is processed in a wet milling operation using the liquid medium99in addition to the solid product to be milled. In the wet milling operations, the solids are milled in the liquid medium99and the milled product is discharged as a liquid suspension or dispersion. The rotational speed of the cylinder12will ultimately result in either the tumbling or cataracting described above, causing the grinding media28to be lifted and then fall or tumble to abrade the product.

During the rotation of the cylinder12, the housing18and conveying pipe20will rotate about the central axis of the cylinder12. Because the conveying pipe20extends to couple with the trunion32and into the rotary union80, the pipe20remains in fluid communication with the outlet side of the valve60mounted to the outlet pipe56and the secondary pipe86leading to the separator tank88.

At the conclusion of the rotation of the cylinder12during the milling process, the cylinder12will contain the milled product as a wet solid in a liquid medium. Depending on the type of liquid medium used, the milled product may require additional rotation of the cylinder12.

When the cylinder12is rotated, as shown inFIG. 6, the liquid medium and milled product will flow through the grate14and into the housing18when the grate14and housing18are positioned below the central axis A. As the cylinder12is rotated, the housing18will rotate upward and then ultimately downward. When the housing18is above the central axis A, the liquid medium and product will flow through the grate from the housing18back into the cylinder12. During rotation, rotational and inertia forces will result in some liquid medium and product remaining in the housing18, even when the housing18is above the central axis A, as shown inFIG. 6.FIG. 6shows various rotational positions of the housing18and valve60and illustrates the presence, or lack thereof, of the liquid medium99in the housing18at these various rotational positions.

If the liquid has a low viscosity, the liquid medium and the solid milled product contained in the liquid can generally flow through the grinding media28toward the bottom of the cylinder12without requiring additional rotation. Gravity will cause the liquid medium and solid milled product suspended therein to flow into the housing18and continue to flow into the housing as the housing18is evacuated during discharge. If the liquid is non-Newtonian or has a high viscosity, the cylinder12may require additional rotation to allow the liquid medium and suspended milled product to travel toward and past the grate14and into the housing for discharge therefrom.

If the chosen liquid medium does not generally require additional rotation of the cylinder12to discharge the product, the cylinder12is rotatably positioned such that the discharge grate14is at the bottom of the cylinder12. The liquid medium and suspended milled solids will flow into the housing18due to gravity. The valve60can be opened automatically or manually. In either case, the liquid medium and suspended milled product will pass through the grate14without exposing the operator or the surrounding environment to the milled product or solvent vapors. Rather, the product remains substantially contained within the housing18as it travels through the housing18, outlet pipe56, valve60, and conveying pipe20to be discharged.

If the cylinder12is required to rotate to discharge the milled product, for reasons described above, the valve60can remain in the open position allowing the liquid medium and suspended milled product to pass through the grate14and the housing and into the conveying pipe20. During rotational discharging procedures, the liquid medium and product will discharge through the grate14and the housing18when liquid medium and milled product are present in the housing. When the housing18is positioned above the central axis A, there may not be any liquid medium or milled product remaining in the housing18after it had fallen back into the cylinder12. In these instances, the liquid medium and milled product will resume being discharged when the housing18returns to a position where gravity allows the liquid medium and milled product flow back into the housing18.

The milled product will remain contained within the system10during this rotation. As described above, the valve60can be automatically opened via a pneumatic connection. The air delivery line66to produce the pneumatic connection will rotate along with the cylinder12during the rotation.

While the liquid medium and milled product are being discharged through the grate14and into the cavity54of the housing18and beyond the opened valve60, the conveying pipe20can convey the milled product to the separator tank88. More specifically, a vacuum or negative pressure can be applied to the conveying pipe88from the blower or vacuum91mounted to the tank88when the vacuum91is present in the system. The vacuum will be applied through the secondary pipe86, the rotary union80, and the conveying pipe20to pull the milled product from the housing cavity54. This vacuuming of the milled product from the housing18allows for the housing18to be substantially smaller than the total volume of product that is discharged. In the case of the liquid discharge described herein, a slight vacuum is drawn to motivate fluid flow.

The vacuum applied through the conveying pipe20can occur with the cylinder12and housing18either stationary or rotating. Because the conveying pipe20and housing18rotate along with the cylinder12, and the conveying pipe20is coupled to the rotary union80, the negative pressure to retrieve the discharging product is not dependent on the cylinder12rotating or remaining stationary.

Similarly, in addition to or alternative to the described vacuum produced by the vacuum91, the pump98can be actuated to move the liquid medium and product through the system during discharge. The pump98can be actuated either while the cylinder12is stationary or while the cylinder12rotating.

Accordingly, the vacuum91and pump98can generally be referred to as a liquid-drawing apparatus.

The use of a vacuum or negative pressure on the system10, in addition to retrieving the product during the discharging process, can also be used to clean the system. The conveying pipe20and secondary pipe86can have a generally circular cross-section to limit the amount of build-up of product between the cylinder12and the tank88.

Moreover, the use of negative pressure or a vacuum through the system10also limits instances of milled product escaping past a seal and into the surrounding area or into contact with an operator. Rather, the negative pressure will continue to pull milled product back into the system10in the event of a leak in one of the seals, in contrast to a system that forces air through a passageway that would push milled product out of a leaking seal or joint and into the surrounding area.

Additionally, to prevent build-up of product within the conveying pipe20, rotary union80, and secondary pipe86, these components can be made from tri-clamp sanitary connections that retain little milled product, and can be broken down and easily cleaned.

At the conclusion of the retrieval process, the valve60can be closed, manually or automatically, to allow for another milling operation. The milled product can be retrieved from the separator tank88in a manner known in the art.

In the above description, the system10has been described as having liquid medium within the cylinder12. The liquid medium can be added to the cylinder12via the loading opening40, along with the grinding media and product to be milled.

In another approach, and with reference toFIG. 8, the liquid medium can be provided through the secondary pipe86and conveying pipe20.

In this approach, the system10includes a second tank100. The second tank100can be referred to as a pre-mix tank, where the liquid medium is present in the tank100and the product to be milled can be added to the tank100, as well. A mixer102is operable to mix the liquid medium with the product to be milled. This is possible when the product to be milled is initially fine enough to be pre-mixed and pumped along with the liquid medium through the secondary pipe86and conveying pipe20. In some instances, however, the product to be milled may be too large to stay in suspension within the liquid medium. In this case, the product to be milled can still be added to the cylinder12through the loading opening40with the liquid medium supplied from the tank100.

The system10includes a medium delivery pipe106that extends generally from the bottom of the tank100and intersects with the secondary pipe86at a location between the rotary union and the separator tank90. The system includes a three-way valve108disposed on the secondary pipe86at the intersection of the secondary pipe86and the delivery pipe106. The three-way valve108is operable to allow for liquid to flow from the conveying pipe20through the secondary pipe86, through the valve108, and toward the separator tank90during discharge. In this position, the valve108prevents liquid from flowing into the delivery pipe106. The valve108is also operable to allow liquid to flow from the tank100, through the delivery pipe106, through the valve108, and further through the secondary pipe86toward the conveying pipe20and ultimately to the cylinder. In this position of the valve108, liquid will not flow through the valve108toward the separator tank90.

The system10also includes a second pump110disposed in line with the delivery pipe106. The pump110can be of a type similar to those discussed above with reference to the pump98, or other known pump types capable of pumping liquid. The pump110can be actuated manually or pneumatically.

Thus, the above described optional structure for delivering liquid medium provides an alternative to adding the liquid medium through the loading opening40or another location on the cylinder12. The above described structure remains generally fixed in place, and does not rotate along with the cylinder12.

In practice, to supply the liquid medium from the tank100, the cylinder12is preferably in a stationary position. Further, the cylinder12is preferably rotated to a position such that the discharge housing18is located above the axis A. This location of the discharge housing18is beneficial because it results in the grinding media being disposed generally below the discharge housing18, from which the liquid medium will be entering the cylinder12. In this approach, the liquid medium will not have to flow against backpressure caused by gravity or by its flow through a tortuous path defined by the grinding media. However, the discharge housing18could also be located below the axis A when delivering the liquid medium into the cylinder12if desired or if necessary.

While the above description relates to the cylinder12being stationary during delivery of the liquid medium, the delivery of liquid medium from the tank100could also be performed while the cylinder12is rotating, if desired or necessary.

To deliver the liquid medium, the valve108is set such that the delivery pipe106is in fluid communication with the secondary pipe86, and the path toward the separator tank90is blocked. The valve60is similarly set to the open position to allow liquid medium to flow therethrough. The pump110is actuated, drawing liquid medium from the tank100and pumping it through the delivery pipe106toward the secondary pipe86. Liquid will enter secondary pipe86and flow toward the rotary union80, where it will then flow into the conveying pipe20. The liquid medium will continue through the conveying pipe20and through the valve60, where it will then enter the discharge housing18. The liquid medium will then flow through the discharge grate14, which is open to the cavity26of the cylinder12, and into the cylinder12.

When delivery of the liquid medium to the cylinder12is complete, the pump110can be de-activated and valve60can be closed. Valve108can then be moved to the position where the delivery pipe106is blocked and flow through the secondary pipe86toward the separator tank90is re-established.

In one approach, the valve108is disposed between the pump98and the rotary union80. In another approach, the valve108can be disposed between the pump98and the separator tank90. In this approach, the pump98could be used to draw liquid from the tank100and through the delivery pipe106toward the conveying pipe20if the pump is capable of reversing the direction of the flow. The pump98can also be used to pump out liquid medium that was not ultimately delivered to the cylinder12by pumping the liquid medium as if it were the liquid medium being discharged.

In the case where the pump98is between the valve110and separator tank90, and not part of the path through which the liquid medium is delivered from the tank100to the cylinder, the pump110could be used to pump liquid medium back into the tank100if the pump110is capable of two-direction pumping.