US 3853305 A
A pugmill mixing apparatus having a mixing box portion which is selectively lowerable from a normal mixing position to a position spaced substantially apart from the mixing members. The lowerable mixing box portion includes a discharge opening and a discharge gate for controlling the discharge of material being mixed during normal operation of the pugmill, and the lowering or dropout capability of the mixing box portion permits the pugmill to be safely and conveniently serviced. Interlock circuits are provided to prevent operation of the pugmill while the mixing box is in the lowered position.
Claims available in
Description (OCR text may contain errors)
United States Patent Mize 1451 Dec. 10, 1974 MIXING APPARATUS WITH DROPOUT LOWER PORTION Inventor. Erbie Gail Mize, Chattanooga,
Assignee: Astec Industries, Inc., Chattanooga, Ind.
Filed: Apr. 16, 1973 Appl. No.: 351,413
U.S. Cl 259/179, 259/41, 259/104 Int. Cl 1301f 7/04 Field of Search 259/178 A, 179, 178 R,
References Cited UNITED STATES PATENTS 8/1956 Madsen 259/179 6/1966 Hunter 259/178 A Primary Examiner-Robert W. Jenkins Attorney, Agent, or Firm-Jones, Thomas & Askew ABSTRACT A pugmill mixing apparatus having a mixing box portion which is selectively lowerable from a normal mixing position to a position spaced substantially apart from the mixing members. The lowerable mixing box portion includes a discharge opening and a discharge gate for controlling the discharge of material being mixed during normal operation of the pugmill, and the lowering or dropout capability of the mixing box portion permits the pugmill to be safely and conveniently serviced. Interlock circuits are provided to prevent'operation of the pugmill while the mixing box is in the lowered position.
9 Claims, 3 Drawing Figures 7/1966 Balazer 259/104 This invention relates in general to mixing apparatus and in particular to improved pugmill mixing appara- 'tus.
Mixing apparatus of the type commonly known as a pugmill is used in a variety of applications where it is desired to mix together two or more ingredients. Although pugmill mixing apparatus may be provided in a number of sizes and configurations, depending upon the physical characteristics and the volume of the material to be mixed, pugmills generally have at least a pair of shafts which are driven for rotary motion and which have a number of mixing paddles extending radially from the shafts. The shafts and mixing paddles are positioned within a receptacle such as a box or hopper for receiving the ingredients to be mixed by the rotary motion of the mixing paddles, and the receptacle is typically provided at a lower location with an opening which is selectively closable by a door for controlled discharge of the mixed ingredients.
Pugmills are frequently used for mixing material having characteristics which tend to damage the mixing paddles and other portions of the pugmill. For example, pugmills are used to mix asphalt and aggregate compositions used for paving purposes and the like. The stones or gravel which are an ingredient of these aggregate compositions tend to wear out the mixing paddles and other components of a pugmill mixing apparatus, and it is understood in the art that such wear-subject components of pugmills must be periodically replaced. To repair or replace the mixing paddles and other internal components of prior-art pugmills used for mixing asphalt aggregate compositions or the like, it has been necessary for a repairman to enter the interior of the pugmill through the material discharge opening or through another opening provided especially for maintenance purposes. This means that the repairman must actually place himself within the relatively uncomfortable and confined mixing region of thepugmill, and must accomplish the necessary repairs under working conditions which are not conducive to efficient operation. More importantly, any repairman who is within a pugmill is in danger of being severely injured or killed if the pugmill should be inadvertently started at that time, and a number of deaths have actually occurred in this manner.
Accordingly, it is an object of the present invention to provide improved pugmill mixing apparatus.
It is another object of the present invention to provide pugmill mixing apparatus having improved maintenance capabilities.
It is still another object of the present invention to provide pugmill mixing apparatus capable of being repaired without requiring physical entry into the region normally comprising the mixing chamber.
Many of the other objects and advantages of the present invention will become apparent from consideration of the following specification which relates to a disclosed embodiment of the invention, and in which:
FIG. 1 shows an isometric view of pugmill mixing apparatus according to the disclosed embodiment of the invention;
FIG. 2 shows a section view taken along line 2-2 of FIG. 1, with the disclosed pugmill being in the raised or operational position; and
FIG. 3 is a section view taken along line 2--2 of FIG. 1, showing the lower portion of the pugmill in the lowered position.
Stated in general terms, a pugmill according to the present invention includes a mixing box having at least a portion which is selectively movable toeither a first position or a second position. When in the first position, the mixing box of the pugmill assumes a normal mixing relationship with the mixing paddles and the remainder of the pugmill apparatus. A gated aperture in the lower portion of the mixing box permits selective discharge of material mixed by the pugmill. When the movable portion of the mixing boxis moved to the second position, however, the mixing paddles and other interior portions of the pugmill are readily accessible for inspection and repair.
The present invention is more particularly shown with regard to the disclosed embodiment as depicted in the Figures, including a pugmill apparatus indicated generally at 10 and having a mixing box 11 including an upper box portion 12 and a lower box portion 13. The upper box portion 12 of the disclosed embodiment is rigidly affixed to a suitable support structure including the beams 14 and 15. A pair of shafts 16 and 17 is mounted for rotation within the mixing box 11, and each of these shafts typically has a plurality of mixing members 18 which are mounted in radially spaced relation to the shafts. In a typical pugmill, the mixing members 18 take the shape of paddles which may be removably connected to the respective shafts l6 and 17, so that repair or replacement of the paddles is facilitated.
The shafts l6 and 17 extend outwardly of the mixing box 11 and are connected through an appropriate reduction gear or other drive arrangement 22 to a source of motive power such as the motor 23. Various types of pugmill drive arrangements are known to those skilled in the art and are not set forth in further detail herein. 1
The lower boxportion 13 of the pugmill may have bottom regions 24a and 25b which are in the shape of a hemi-cylindrical section, in the disclosed embodiment, positioned in closely spaced-apart relation to a lower portion of the region which is swept by the mixing members 18 when the shafts l6 and 17 are rotated. Alternatively, other bottom region configurations of the lower box portion 13 may be provided. The bottom region of the lower box portion 13 is provided with a discharge opening 25, and a closure member 26 is mounted on the bottom region for selective positioning with respect to the discharge opening 25. The closure member 26 may advantageously be mounted for sliding movement along the underside 27 of the lower box portion, for example. Movement of the closure member 26 is provided by a suitable actuating member such as a fluid-powered actuator 29 having a piston rod 30 terminating in a suitable detachable connector such as the clevis 31 for selectively movable connection to a tongue 32 connected with the closure member. The actuator 29 may be attached to a support structure such as the beam 15 by means of a pivotal mounting 36 or the like, for a purpose to be described below.
The entire lower box portion 13 is suspended from the fixed supporting structure, including the beams 14 and 15, so as to be selectively movable between an upper position, as depicted in FIG. 2 and a lower position, as depicted in FIG. 3. Although this movable support and selective positioning of the lower box portion may be accomplished by various types of elevation apparatus, the desired mounting and movement is accomplished in the disclosed embodiment by way of the screw jacks 37, 38, 39, 40, mounted at the four corners of the mixing box 11. As particularly shown in FIGS. 2 and 3, the screw jacks are mounted for support by one or the other of the beams 14 and 15, and the lower box portion 13 is mounted by means of brackets such as at 41 and 42, to the movable or extensible portion of the corresponding screw jacks. Two of these extensible screw jack portions are shown at 39a and 40a in FIG. 3. Each of the screw jacks is connected through a drive train including drive shafts 43, 44, and 45 and righthand drive units 46 and 47 to a suitable source of driving power such as a reduction gear motor 49 capable of rotation in either direction.
The motor 49 is connected to an elevation control 53, which may be provided by a conventional bidirectional motor control apparatus, through circuitry including a limit switch 54 having a control member 55 positioned with respect to the actuator 29 to place the limit switch 54 in an open-circuit condition when the actuator is displaced by rotation about the pivotal mounting 36 from the normal position as shown in FIGS. 2 and 3. This angular displacement of the actuator 29 is diagrammatically represented by the broken arc arrow 59 on FIG. 2.
The mixer motor 23 is connected to a suitable control apparatus 56 through a second limit switch 57 having an actuating member 58 selectively engagable by a member 58a mounted on the bracket 41 or by some other member which is mounted on or connected for movement with the lower box portion 13. Alternatively, the limit switch 57 could be connected for actuation by the extensible member 40a, for example, of the screw jack 40. The limit switch 57 is connected in circuit with the mixer motor 23 to permit operation of the mixer motor when the lower box portion 13 is in the fully raised position, as shown in FIG. 2, and to break the motor operating circuit whenever the lower box portion is lowered from this fully raised position.
Considering now the operation of the disclosed embodiment of the present invention, it will be understood by those skilled in the art that aggregate material and asphalt, or any other materials to be mixed, are introduced into the mixing box 11 and are mixed by rotation of the shafts l6 and 17 and the mixing action of the mixing members 18. Furthermore, it will be understood that discharge of the mixed material is accomplished by applying power to the actuator 29 to move the closure member 26 to a position allowing discharge of the material through the discharge opening 25.
When it is necessary or desirable to inspect or to repair the mixing members 18 or any other structure within the interior of the mixing box 11, the interconnection between the clevis 31 and the tongue 32 is disengaged and theactuator 29 is then operated to withdraw the rod 30 to the'position shown in FIG. 3. It will be seen at this time that the closure member 26 remains in closed position. The elevation control 53 is then operated to rotate the motor 49 in the direction driving the screw jacks 37-40 to move the lower box portion 13 from the upper or mixing position, as shown in FIG. 2, to the lower position as shown in FIG. 3. The maximum downward movement of the lower box portion 13 may be limited, if desired, by an appropriately placed limit switch (not shown). When the lower box portion 13 is fully lowered, it will be seen that the interior of the pugmill 10, especially including the mixing members 18, is fully exposed for inspection and repair, without requiring a workman to enter the confined mixing box either through a discharge opening 25 or an access aperture as previously required in prior art pugmill apparatus. The mixer motor limit switch 57 has broken the circuit to the mixer motor, upon lowering of the lower box portion 11, thereby preventing inadvertent powered operation of the shafts 15 and 16. Even if powered operation of these shafts should accidentally occur, such as through the coincidental malfunction of the limit switch 57 and operation of the mixer control 56, while the pugmill is in the lowered position as shown in F IG. 3, 1 the substantial spacing between the mixing members 18 and the bottom of the lower box portion 13 give the workman an opportunity to escape from the path of the rotating mixing members.
When inspection or repair of the pugmill is completed, the motor 49 is operated to cause the lower box portion 13 to return to the configuration shown in FIG. 2. The actuator 29 is then operated to place the clevis 31 in position adjacent the tongue 32, the clevis and tongue are reconnected, and the pugmill is once again ready for mixing operation.
Assuming that an inadvertent attempt is made to move the lower box portion 13 to the lowered position as shown in FIG. 3, without first disconnecting and retracting the clevis 31 and the rod 30 of the actuator 29, the initial downward movement of the lower box portion 13 causes the actuator 29 to pivot about the pivotal mounting 36 in the manner denoted at 59. This pivotal movement of the actuator 29 brings the actuator into contact with the control member 55 of the limit switch 54 to break the control circuit of the motor 49. Thus, the lowering operation is prematurely terminated before structural damage occurs to the pugmill, and the lowering operation cannot be recommenced until the actuator is disconnected and returned to position out of engagement with the limit switch 54.
It will be understood, of course, that the foregoing relates only to a preferred embodiment of the present invention and that numerous alterations andv modifications may be made therein without departing from the spirit and the scope of the present invention as defined in the claims.
What is claimed is:
1. Pugmill mixing apparatus comprising:
a mixing box for receiving a quantity of material to be mixed, said mixing box including an upper box portion and a lower box portion;
support means mounting said upper and lower box portions for selective relative positioning in an operational position, whereat said upper and lower box portions are proximal to each other, and to a nonoperational position, whereat said upper and lower portions are separated from said proximal relative position;
atleast one rotatable shaft extending through and in fixed position relative to said upper box portion;
motive means operatively connected to rotate said shaft;
a plurality of mixing elements connected to said shaft for mixing movement within said mixing box when said shaft is rotated by said motive means;
said lower box portion having a bottom portion with a material discharge opening disposed therein; and
gate means on said lower box portion and selectively positionable to block or to unblock said discharge opening.
2. Pugmill mixing apparatus as in claim 1, wherein:
said support means includes a fixed portion on which said upper box portion is mounted in fixed relation;
elevator means carried by said fixed portion and supporting said lower box portion in place below said upper box portion; and
said elevator means being selectively operative to raise said lower box portion to said operational position or to lower said lower box portion to said nonoperational position. 3. Pugmill mixing apparatus as in claim 2, wherein said motive means is a first motive means, and further comprising:
second motive means normally supported in predetermined position by said fixed portion of said support means and having an operating member extending to selectively detachable connection with said gate means while in said operational proximal relative position; said operating member of said second motive means being operable to position said gate means to either of said blocking and unblocking position; and
means responsive to displacement of said second motive means from said predetermined position to provide a signal condition.
4. Pugmill apparatus as in claim 3, further comprismg:
third motive means operatively associated with said support means for movement of said box portions to either of said relative positions; and
said third motive means being rendered inoperative in response to said signal condition.
5. Pugmill mixing apparatus as in claim 1, wherein:
said mixing box is of generally rectangular overall configuration;
said support means comprises a separate vertical movement means disposed to each corner of said mixing box and interconnecting said lower and upper box portions for said selective relative positioning; and
operating means operatively connected to each of said vertical movement means to accomplish concurrent relative positioning by said vertical movement means so that said upper and lower box portions are uniformly positioned.
6. Pugmill mixing apparatus as in claim 1, wherein:
said mixing elements extend radially from said shaft;
said bottom portion of said lower box portion has a surface partially defining the interior of said mixing box and conforming in contour to a portion of the path defined by said mixing elements when said shaft is rotated; and
said surface of said lower box portion being disposed in closely spaced apart relation to the radial extremities of said mixing elements when said upper and lower box portion are supported by said support means in said operational position.
7. Pugmill mixing apparatus as in claim 1, further comprising:
means responsive to relative positioning of said upper and lower box portions away from said operative relative position to render said motive means inoperative to rotate said shaft.
8. Mixing apparatus comprising:
a mixing receptacle for receiving material to be mixed;
mixing means disposed at a mixing location in said mixing receptacle and movable to mix material received within said mixing receptacle;
motive means selectively operative to impart said mixing movement to said mixing means;
said mixing receptacle having at least a lower portion which is mounted in selectively movable relation to said mixing means for selective movement to either a proximal position or a distal position relative to said mixing means;
a selectively closable material discharge opening in said lower portion of said mixing receptacle; and
means responsive to movement of said lower portion away from said proximal position to render said motive means inoperative.
9. Mixing apparatus as in claim 8, wherein:
said selectively closable material discharge opening includes gate means movable to close or to open said material discharge opening;
second motive means mounted in fixed relation to said mixing location and having an actuating member detachably connected to said gate means; and
means responsive to displacement of said second motive means resulting from movement of said lower portion away from said proximal location while said actuating member is attached to said gate means to provide a signal condition.