Vacuum pug mill

A pug mill having a housing and a cantilevered shaft extending through the housing includes, in seriatim, a vacuum chamber, a wall, a mixing chamber and a reduction cone. A communication port about the shaft is positioned in the wall between the vacuum chamber and the mixing chamber. Vacuum can be maintained within the mixing chamber by air passing through the port. An auger associated with the shaft forces clay toward the reduction cone. This creates a seal for maintaining vacuum within the mixing chamber and extrudes cylindrical blocks of conditioned clay without significant air bubbles. A deflection plate rotating with the shaft and a spiral element about the shaft keep the communication port clear. The shaft is eccentrically mounted. The dividing wall is removable.

BACKGROUND OF THE INVENTION

The field of the present invention is pug mills for mixing and conditioning clay for ceramics.

Pug mills are designed for producing clay conditioned for the manufacture of ceramics. The mills typically are used to mix clay powder and water or rehydrate, remix and/or recondition existing clay. Powders and water may also be mixed with existing clay to form a homogeneous product. The clay, once mixed, is most conveniently extruded through a reduction cone to form cylindrical or rectangular blocks also known as pugs.

Pug mills upon which the present design is based are disclosed in U.S. Pat. No. 4,322,169 entitled CLAY MIXING APPARATUS and U.S. Pat. No. 5,716,130 entitled VACUUM PUG MILL, the disclosures of which are incorporated herein by reference in their entirety. These pug mills include a mixing chamber expending to an extruder in communication therewith. A shaft is rotatably mounted relative to the mixing chamber and the extruder. Mixing blades associated with the mixing chamber are fixed to the shaft as is an auger associated with the extruder. The shaft is rotatably mounted by bearings such that an extension of the shaft through the mixing chamber and the extruder is cantilevered from the bearings. The bearings are positioned in a housing including a drive motor and drive train for forcibly rotating the shaft. The shaft is rotatable in either direction about its axis. When rotated in a first direction, mixing takes place. When rotated in a second direction, the clay is advanced by the mixing blades and by the auger for extrusion through the reduction cone.

In addition to the conditioning of clay to achieve an appropriate moisture content and homogeneity, it is advantageous to remove as much air as possible. Air entrapped in the clay when fired can expand to ruin the article manufactured. Also, entrapped air can adversely affect throwing operations as it makes the clay “short” and hard to work with. The pug mill disclosed in U.S. Pat. No. 5,716,130 provides a vacuum chamber in communication with the mixing chamber for drawing a vacuum on the clay to remove air from being mixed into the clay. A cover on the end of the reduction cone or a solid body of clay being extruded therefrom provides a sealed mixing chamber to permit the drawing of the vacuum.

U.S. Pat. No. 5,716,130 provides a mechanism for maintaining a clear communication port between the mixing chamber and the vacuum chamber of that mill. It remains that material being pugged can still overwhelm the communication port and interrupt the application of vacuum in the mixing chamber.

SUMMARY OF THE INVENTION

The present invention is directed to a pug mill which provides for vacuum associated with the mixing process with enhanced communication of vacuum from the mixing chamber to the vacuum chamber.

In a first aspect of the present invention, the pug mill includes a mixing chamber and a vacuum chamber with a wall therebetween. The wall includes a communication port. A pug mill shaft extends through the communication port. A deflection plate is fixed on the rotatably mounted shaft in the mixing chamber immediately adjacent the wall and extending radially outwardly from the shaft beyond the communication port. The deflection plate has two deflection surfaces which each extend at a shallow incline away from adjacent the wall to meet at a common apex.

In a second aspect of the present invention, the pug mill of the first aspect further includes a spiral element fixed about the shaft and extending from the deflection plate through the communication port. The spiral element includes clearance through the communication port to allow air to pass from the mixing chamber to the vacuum chamber.

In a third aspect of the present invention, the pug mill includes a mixing chamber and a vacuum chamber with a wall therebetween. The wall includes a communication port. A pug mill shaft extends through the communication port. The shaft of the pug mill is eccentrically mounted at least as to the mixing chamber to allow enhanced access of the vacuum to the body of the material being mixed.

In a fourth aspect of the present invention, the pug mill includes a mixing chamber and a vacuum chamber with a wall therebetween. The wall includes a communication port between the mixing chamber and the vacuum chamber. The chambers each include a housing. The housings mate together with the wall being removable for critical accommodation of various mixing materials.

In a fifth aspect of the present invention, any of the foregoing aspects may be combined to greater advantage.

Therefore, it is a principal object of the present invention to provide an improved vacuum pug mill. Other and further objects and advantages will appear hereinafter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning in detail to the drawings, a pug mill is illustrated inFIGS. 1 and 2. The assembly includes a sealable chamber housing assembly10, a gear casing12and a power box14. The housing assembly10encloses a sealable chamber defined by a mixing chamber housing16and a vacuum chamber housing18. The mixing chamber housing16includes a reduction cone20at the end of the housing16, an access port22and a hatch cover24for access to the interior of the sealable chamber. A cover26covers an extrusion port28at the end of the reduction cone20for selectively sealing the sealable chamber. The gear casing12and power box14provide controls, a drive motor and gearing for driving a shaft extending through the vacuum chamber housing18and mixing chamber housing16. A source of vacuum (not illustrated) is provided in communication with the vacuum chamber housing18through the power box14as well. The vacuum chamber housing18also includes an access port and cover to allow cleaning out of any clay material which may accumulate in the chamber.

Turning toFIGS. 3 and 4, a mixing chamber32is revealed within the mixing chamber housing16. This chamber32includes a mixing zone34and an auger zone36. The mixing zone34is generally cylindrical while the auger zone36includes the reduction cone20leading to the extrusion port28. The vacuum chamber housing18is revealed inFIGS. 3 and 4to include a vacuum chamber38.

A wall40is located between the mating housings16and18. In the embodiment illustrated, the wall40is positioned in a channel cut into the mating face of the vacuum chamber housing18and held in place by the abutting mixing chamber housing16. A seal42is located outwardly of the wall40between the mating flanges of the mixing chamber housing16and the vacuum chamber housing18. The wall40may also be retained in this position through attachment to one or the other of the housings16,18. The wall40divides the sealable chamber between the mixing chamber32and the vacuum chamber38and includes a communication port44therethrough to provide vacuum throughout the sealable chamber. A circular flange46extends the communication port into the interior of the vacuum chamber38.

A shaft48is rotatably mounted to the closed end of the vacuum chamber housing18as well as in the gear casing12to extend through the vacuum chamber38and the mixing chamber32to the reduction cone20. The shaft48includes a key50to couple with a hollow shaft gear within the gear casing12. The shaft48is powered by a motor (not illustrated) through the gear casing12and can be controlled to be driven in either direction. Mixing paddles52are attached to the shaft48so as to be located in the mixing chamber32. A wide range of such paddle configurations and placements may be employed. The flight of an auger54is located at the end of the cantilevered shaft48to reside within the auger zone36. A deflection disc56extends radially about the shaft48within the vacuum chamber38to define a barrier to prevent clay material from moving along the shaft to the seal bearings58. The deflector disc56is shown displaced from both the wall40and the seal bearings58.

A deflection plate60is also fixed to the shaft48. The location of the deflection plate60on the shaft48places the deflection plate immediately adjacent the wall40on the mixing chamber side. It is preferable that the deflection plate60be as close as practical to the wall40and yet not touch the wall as the shaft48rotates. The deflection plate60extends radially outwardly from the shaft48beyond the extent of the communication port44. The deflection plate60includes two deflection surfaces62,64facing the mixing chamber32. These surfaces62,64each extend at a shallow incline away from the adjacent wall40to meet at a central radial apex, the two surfaces being symmetrical about the apex as seen inFIGS. 4 and 5. A spiral element66affixed to the shaft48extends from the deflection plate60through the communication port44. Sufficient clearance for air to pass through the communication port44about the shaft48and spiral element66is also provided.

The pug mill operates by controlling the rotational direction of the shaft48. With the shaft rotating in one direction, the mixing paddles52and the auger54urge the clay material within the mixing chamber32toward the wall40so as to remain in the mixing chamber32. When the rotation of the shaft48is reversed, the mixing paddles52and the auger54advance the clay material away from the wall40through the reduction cone20and the extrusion port28.

With the rotation of the deflection plate60, the leading deflection surface62resists the movement of the advancing clay material toward the communication port14with the mill in the mixing mode. The other deflection surface64also urges the clay material away from the communication port44with the shaft rotating in the other direction in the extrusion mode. The spiral element66spirals in the opposite direction from the flight of the auger54and the inclination of the mixing paddles52. The spiral element66thus advances clay material entering the communication port44back toward the mixing chamber32when the mixing paddles52and the flight of the auger54are moving the clay material toward the communication port14. With the shaft48rotating in the opposite direction, the mixed material moves toward the extrusion port28away from the wall40, providing relief to the spiral element66which is then rotating in a way which would urge clay material to move into the vacuum chamber38. During operation with the vacuum source actuated, it has been found that a cycling of the shaft48through rotation in both directions can assist in keeping the mixed material away from the communication port44.

In the preferred embodiment, the shaft48is also eccentric to the rotational axis at least in the area of the mixing chamber32. The shaft48is shown to be displaced laterally from that axis at position68by a small amount. Clearance is provided for the spiral element66, the mixing paddles52and the auger54within the sealable chamber to accommodate the eccentricity. By eccentric rotation of the shaft48, a pathway may be generated along the shaft48for the extraction of air from the body of clay material being mixed.

Thus, a pug mill with improved air extraction is disclosed. While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art that many more modifications are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.