Mixer for Molding Sand

This invention relates to mixing machines for foundry mold sand and the like with increased efficiency and yet a simple and rugged construction.

The desire to expose all of the sand in a mixing vessel maximally frequently and uniformly to the mixing tools has resulted in two types of structure for container mixers. In one type of structure, the container is stationary and eccentric mixing tools move along paths about the container axis of the mixer during mixing operations. In the other type of structure, the mixing container rotates and the eccentric mixing tools or their respective shafts, if driven, are stationary. Theoretically, in the first type of arrangement, the sand is at a standstill with respect to the container and the eccentric mixing tools are moved by the stationary sand; and in the second type of structure, the shaft of the rotating eccentric tool is stationary and the sand is entrained by the rotating bowl and moved toward the eccentric tools. Therefore, in these mixers, an important feature is that the sand does not execute a relative motion with respect to the bowl. Thus, the sand is supposed to be also at a standstill, with the bowl being stationary, and to participate in the rotation, if the bowl is rotating. In order to enhance this behavior, vertical ribs have in many cases been provided along the periphery of the bowl, in order to brake the sand, or the bowl circumference has been equipped with a high friction by an appropriate selection of the material, for example by lining the bowl with rubber. In conventional mold sand mixers with eccentrically disposed tools, it has furthermore been necessary to provide, in addition to the drive for rotating the eccentrically disposed tools about their own axis, a further drive means, either for the movement of the shafts of the eccentrically disposed tools about the bowl axis or for the rotation of the bowl, whereby these machines become complicated and expensive in manufacture and upkeep. Furthermore, at higher speeds of rotation, difficulties are encountered in the central discharging of rotating mixing containers due to centrifugal effects. Also, when the container is at a standstill and the mixing tools rotate in a planetary motion, the drive is effected from above, whereby the introduction of the sand is impeded.

The present invention contemplates providing a mixer which avoids the above-discussed disadvantages and, with a simple construction and correspondingly low manufacturing costs, shows a high mixing efficiency. More particularly, the present invention contemplates providing a mixer having a stationary mixing bowl having a rotating central tool disposed at the bottom thereof for imparting rotational movement to molding sand or the like being mixed. At least one driven centrifugal tool which is spaced from the axis of the bowl extends downwardly into the bowl from above facing spaced relationship to the central tool for imparting further mixing motion to the material in the bowl. According to the invention, each of the centrifugal tools are disposed at fixed positions around the periphery of the staionary bowl, thereby obviating the need for mechanisms to rotate either the bowl or the centrifugal tools about the bowl axis. In preferred embodiments according to the invention, the rotating central tool imparts maximal rapid rotation to the contents of the container.

According to a further feature of the invention, the bowl is provided with a smooth inner surface made of a material with low friction so as to not retard the rotational motion of the bowl contents. In particularly preferred arrangement of the present invention, the inner surface of the bowl, along the walls and the bottom, is provided with a lining of hard-chromeplated steel sheet.

According to another feature of a preferred embodiment of the present invention, the central tool is provided with a plurality of agitator vanes extending radially from a central hub portion to immediately adjacent the vertical wall of the bowl. A plurality of centrifugal tools are also provided which are arranged spaced from one another and from the bowl axis which coincides with the rotational axis of the central tool. The centrifugal tools and the agitator vane are provided at positions with respect to one another such that only a single centrifugal tool faces any of the vanes at any given time. That is, at any given time during operation of the mixer with the central tool rotating such that the vanes sequentially pass under the centrifugal tools, only a single centrifugal tool is directly vertically above a vane moving thereunder at any given time, with all other centrifugal tools being vertically above a space intermediate the vanes at said given time.

According to another feature of the invention, the centrifugal tools are rotated oppositely to the direction of rotation of the agitator vanes of the central tool. Another feature of a preferred embodiment of the invention is that the axes of the centrifugal tools deviate from the vertical so that their spacing from the central axis of the bowl (also rotational axis of the central tool) is larger at the top than at the bottom. The centrifugal tools are configured and spaced with respect to the bowl so as to engage the top layer of sand during mixing operations. Another feature of a preferred embodiment of the invention is in the inclusion of a plurality of obliquely oriented, exchangeable vane plates on each of the agitator vanes, which vane plates are spaced from one another along the length of the vanes from the shell or wall of the mixing bowl to the central drive hub.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.

FIG. 1 is a schematic lateral sectional view of a mixer constructed in accordance with the present invention; and

FIG. 2 is a top schematic view of the mixer of FIG. 1.

FIGS. 1 and 2 show the mixing container 1 with a drive system 2 and a drive engine 3 for the central agitator vanes 4 being arranged underneath the container. The centrifugal tools 5 are driven individually by motors 6. The directions of rotation 9 (see FIG. 2) of the centrifugal tools 5 are in opposition to the direction of rotation 8 of the agitator vanes.

The level or height position of the centrifugal tools 5 in the container 1 is selected so that they contact the upper layer of sand 10, as formed during operation of the mixer.

A sealable flap 7 is provided on the outer periphery of the container for accommodating discharge of the contents thereof, while an opening 11 is provided for filling the container.

A lining 12 formed substantially with hard-chromeplated smooth surfaces is provided at the bowl shell or vertical walls, and the bottom plates 13 are constructed of similar hard-chromeplated material.

The disposition of the centrifugal tools at positions spaced from the central hub and fixed along the periphery of the bowl facilitates the provision of the large free feed opening 11. The disposition of the discharge opening 7 at the lateral side of the bowl or container makes it possible to advantageously utilize the centrifugal force imparted by the central tool vanes 4 for discharging the contents of the bowl. The elimination of the drives for the rotation of the bowl or for a planetary movement of the centrifugal tools renders the manufacture and upkeep very economical. Also, the possibility of simultaneously employing a high speed for the tools and a large amount of material filled into the mixer permits processing of large amounts of sand with the apparatus of the present invention.

The details of the driving connections for the mixers have not been included, since known driving mechanisms, mainly electric motors and the like for rotating drive shafts, can be readily used.

The following dimensional example is given to facilitate an understanding of the present invention and the practice thereof by others, and is not intended to limit the scope of the claims. The centrifugal tools are preferably positioned with their axis of rotation extending in the range of 7.degree. to 10.degree. with respect to the vertical. The agitator vanes 4 are inclined approximately 30.degree. with respect to the horizontal. While the central tool preferably rotates in the range of 45 to 55 rpm, with a consequent tip speed of between 6.8 and 8.2 meters per second (assuming a diameter of 2.85 meters for the bowl and slightly less for the central tool), the centrifugal tools are preferably rotated in the range of between 1000 and 1200 rpm wth a tip speed of between 23 to 29 meters per second (assuming the diameter of the centrifugal tool can be in the range between 450 and 470 mm). The top of the outer portion of the central tool is spaced approximately 290 mm from the horizontal floor, while the tips of the individual vanes 4 are spaced approximately 170 mm from the floor. The bottom portion of the centrifugal tools is spaced approximately 420 mm from the horizontal floor of the bowl such that, during operation, the centrifugal tool is immersed in the material being mixed over most of the travel path of the rotating centrifugal tool. For example, the material in the mixing container will extend approximately a total of 800 mm from the horizontal floor of the bowl at the outer edge to a minimum practically zero height at the central portion of the container. Although the above-noted specific dimensional ranges form part of a preferred embodiment of the invention, such dimensions are not intended to limit the scope of the claims. For example, with changes in the diameter of the basic mixing container, corresponding changes in the dimensions of the remaining structure will also take place.

While we have shown and described one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art and we therefore do not wish to be limited to the details shown and described herein but intended to cover all such changes and modifications as are encompassed by the scope of the appended claims.