MIXER DRIVE APPARATUS

Abstract: Mixer drive apparatus, which provides gear reduction for driving the impeller shaft of the mixer. A drive shaft (22) from an electric motor (18) is parallel to the impeller shaft (34) which extends through a support collar of a housing where the collar has a hole therethrough into which the impeller shaft extends into the housing. A hub (38) is rotatably mounted on the outside of the housing (10) and carries a gear (42) which is coupled to a pinion on the motor drive shaft. A coupling (70) is attached to the hub and bridges the hole in the collar. The end of the impeller shaft is cantilevered and overhung from the coupling. A gap is defined between the impeller shaft and the inside surface of the support collar which is adapted to receive a seal assembly. The seal assembly (30) includes a retainer hub which captures a sleeve containing the seal structure in the gap between the coupling and the retainer. The seal sleeve (40) may readily be removed upon disassembly of the coupling, which has two sections defining a split ring which clamps the upper end of the impeller shaft, and has a thrust plate with a bolt therethrough into the end of the impeller shaft for axially adjusting the location of the shaft so as to bring the seal sleeve into engagement with the coupling for rotation there­ with. A support collar on the impeller shift engages the retaining hub when the coupling releases the shaft for the removal and replacement of the seal sleeve assembly. A seal captured by the collar engages the retainer hub and provides a pressure seal to facilitate replacement of the seal sleeve when the mixer is used with a pressurized vessel.

Description: The present invention relates to the mixer apparatus for mixing liquids, liquid suspensions and other materials, and particularly to mixer apparatus having improved impeller drive mechanism. The invention is especially suitable for use in providing mixer apparatus for industrial and commercial applications where mixing is part of the manufacturing or formulating process. Mixer apparatus provided by the invention may also be used for waste water treatment and elsewhere where significant volumetric flow and agitation of the medium being mixed is desired. The invention provides mixer apparatus suitable for industrial and commercial mixing applications as well as for waste water treatment applications which is reliable in performance and can be manufactured at low cost, and particularly wherein seals can be provided which prevent the escape of the medium being mixed or processed from the tank or vessel in which the medium being mixed is contained. In order to develop the necessary torque and speed for a mixing impeller, a gear reduction drive is used for coupling the drive shaft of the electric motor to the impeller shaft. A high reliability gear reducer drive provided in accordance with the invention utilizes an electric motor drive shaft which is parallel to the impeller shaft. While gear reduction drives between parallel drive and driven shafts have heretofore been proposed, the proposed designs have required expensive bearings and alignments. In mixing applications, there is often the need to provide seals to prevent the escape of the material being mixed through the mixer drive into the environment. Parallel shaft gear reduction drives which have been proposed have no provision for such seals. Seals are subject to wear especially when mounted on shafts subject to significant deflection (run-out). It has heretofore been necessary to use seals specifically designed to operate under conditions of large run-out (for example, approximately 60 mils). Such seals are far more expensive than seals which can operate reliably at low run-out (for example, approximately 5 mils). There are therefore a complex of requirements applicable to mixer applications which have militated against the use of parallel shaft gear reduction drives for such applications. Accordingly, it is the principal object of the present invention to provide an improved mixer drive capable of serving commercial and industrial applications with reliability and which may be implemented at reasonably low cost. It is another object of the present invention to provide an improved mixer drive utilizing a parallel shaft gear reducer capable of accommodating seals. It is a still further object of the present invention to provide an improved gear reducer mixer drive which accommodates seals in a compact manner without increasing the size of the drive unit. It is a still further object of the present invention to provide improved mixer drive apparatus which may be converted in the field to a sealed drive without modification. It is a still further object of the present invention to provide improved sealed mixer drive apparatus wherein the deflection of the impeller shaft which is sealed is controlled so as to avoid the need for seals designed to operate under large run-out conditions. It is a still further object of the present invention to provide improved sealed mixer drive apparatus wherein seals are accessible for ready removal and replacement. It is a still further object of the present invention to provide improved sealed mixer drive apparatus which maintains a static seal on the tank with which the apparatus is being used when running seal units are being removed and replaced. US-A-3,202,007 discloses a mixer drive with drive and impeller shafts on radially spaced axes and gearing therebetween and with seals between the stationary and rotating parts of the structure. According to the present invention there is provided mixer drive apparatus comprising a housing, an impeller shaft having a first axis of rotation, a drive shaft having a second axis of rotation, and gearing between said shafts, said impeller shaft being secured to and cantilevered from a coupling, characterized by the fact that the impeller shaft is located by the coupling to define an annular gap between said shaft and a collar, said gap having a width radially of said shaft substantially larger than the running clearance for said shaft and being adapted to receive a seal assembly, the seal face of said seal assembly being close to the coupling, and a rotatable hub coaxial with and disposed outside the collar with bearings between said hub and collar. Briefly described, mixer drive apparatus embodying the invention has a housing. A collar extends from the housing and defines, on the inside thereof, a hole through the collar which provides access for the impeller shaft into the housing. A rotatable hub coaxial with the collar is disposed outside of the collar. A gear is mounted on the hub. A drive shaft, as from an electric motor, may be spaced from and parallel to the impeller shaft. A pinion on the drive shaft is coupled to the gear on the hub. A coupling is mounted on the hub and bridges the collar and the hole therein. The impeller shaft is overhung and particularly cantilevered from the coupling. The impeller shaft extends through the hole and is located by the coupling to define an annular gap between the impeller shaft and the collar. The gap has a width radially of the impeller shaft substantially larger than the running clearance for the impeller shaft. The gap is adapted to receive a seal assembly. The seal assembly may be inserted in the field (factory changes are not needed), and is captured in the cap between the coupling and the housing. The seal assembly includes a retaining hub which is fixedly disposed against the inside of the collar and a sleeve assembly which is disposed around the impeller shaft. The sleeve assembly includes a seal member and may be either a dry running seal or a seal which is pressurized with lubricant. The lubricant enters a cavity in the gap containing the sleeve assembly which is filled with the pressurized lubricant. The coupling is preferably a split ring which clamps the top end of the impeller shaft and may be removed so as to expose the sleeve assembly of the seal assembly for ready removal and replacement. A collar on the impeller shaft is disposed to drop on a support surface of the retaining hub when the shaft is released from the coupling for the removal and replacement of the sealing sleeve assembly. A ring seal may be captured in the collar to provide a static pressure seal when the collar engages the retaining hub. The coupling holds the top end of the shaft rigidly and prevents excessive run-out at the location of the seals, which are close to the coupling and therefore not subject to excessive movement even when the shaft is deflected in response to fluid forces encountered in mixing applications. Thus, low cost seals may be used. The invention therefore enables the use of a parallel shaft gear reduction drive which may be implemented at low cost and which is capable of being sealed readily by the insertion of a seal assembly. The invention also enables use of seal assemblies having low cost seals and provides, nevertheless, acceptable reliability and life. The foregoing and other objects, features and advantages of the invention will become more apparent from a reading of the following description in connection with the accompanying drawings in which: FIG. l is a sectional view, in elevation, of mixer drive apparatus embodying the invention; FIG. 2 is a plan view, taken along the line 2-2 in FIG. l and showing the impeller shaft coupling structure from the top; FIG. 3 is an enlarged sectional view of the seal assembly of the mixer apparatus shown in FIG. l; FIG. 4 is a sectional view in elevation, similar to FIG. 3 showing a sealing assembly containing a double mechanical seal which may be used in lieu of the single mechanical seal assembly shown in FIG. 3. Referring more particularly to the drawings, there is shown a housing l0 having a base plate l2 and side walls l4. The housing l0 has an upper section l6 on which an electric motor l8 is mounted. The housing may be covered with a guard 20. The drive shaft of the apparatus is provided by the shaft 22 of the motor which is connected through a flexible coupling 24 to a drive shaft extension 26. Bearings 28 and 29, secured to the housing l0, guide and rotatably support the shaft extension 26. The shaft extension 26 is the drive shaft portion on which a pinion 30 is mounted. The drive shaft has an axis of rotation which is parallel to the axis of 32 of rotation of an impeller shaft 34. The impeller shaft is coupled at the top thereof to the mixer drive and extends downwardly out of the mixer drive housing l0 into a tank or other vessel in which materials to be mixed are contained. This tank may be a closed tank, in which event the base plate l2 is connected to the nozzle assembly of the closed tank either directly or through adapter rings or flanges (not shown) so as to seal the nozzle. The closed tank is sealed by a seal assembly 36 which includes a retaining hub 38 and a sealing sleeve assembly 40 which will be described in detail hereinafter. The mixer apparatus may be used on an open tank, in which event the seal assembly need not be used. It will be apparent as the description proceeds that the seal assembly may readily be inserted in the field and without any modification of the mixer unit when required. The impeller shaft torque and speed reduction is obtained through the use of a ring gear 42 which is coupled to the pinion 30. The gears may provide a reduction of ten to eighteen to one in speed, and of course a corresponding increase in torque. Helical gears are shown for the ring gear 42 and the pinion 30 and are preferred. If additional reduction and speed and increase in torque is required an extra pinion and spur gear may be used. A collar 44 extends upwardly and inwardly from the base plate l2 of the housing l0. The collar has a hole 46 therethrough, through which the impeller shaft 34 extends out of the housing l0. The housing l0, its collar 44 and other parts of the housing may be a casting which is suitable machined, especially along the inner periphery (which defines the hole 46) and outer periphery of the collar 44. The collar 44 rotatably supports a hub 48 on bearings 50 and 52. These bearings are secured by a ring or bearing retainer 54 which is held down by screws 56, only one of which is shown in FIG. l, but which are evenly spaced around the ring 54. The ring gear 42 is attached to a flange on the hub 48 by bolts 58. An oil seal ring 60 is disposed between the hub 48 and the retaining ring 54. The housing l0 is also closed by a cover 62 which is sealed at the hub 48 by an outer oil seal 64. A chamber is defined under the cover within the housing l0 which contains a bath of lubricating oil. A dipstick 66 may be used to check the level of the oil. All of the gear drive bearings 28, 29, 50 and 52 are oil splash lubricated. The impeller shaft 34 is cantilevered at its top end by a coupling 70 which is secured to the top end of the hub 48 by bolts 72. The top end of the hub 48 is rabbitted as shown at 74 so as to locate the coupling. The coupling has two sections 76 and 78 which define a split ring. The ring may have bearing surfaces on the inside thereof which engage the top end of the shaft. Four bolts, or cap screws 80 and their associated nuts 82 extend through the sections 76 and 78 and clamp the shaft 34 at its top end thereby supporting and cantilevering the shaft 34 only at its top end. No special guide bearings for the shaft are used or required. A key 84 connects the coupling to the shaft which has a key way for receiving the key 84. Portions of inner periphery of the split ring may be recessed so as to assure contact along four diametrically opposed surfaces of the top end of the shaft 34. A thrust plate 86 is attached by screws 88 to the top of the coupling 70. A bolt or cap screw 90 extends through a hole which is along the axis 32 of the shaft into a threaded hole through the top surface of the top end of the shaft 34. The axial position of the shaft 34 may be adjusted by turning the screw. Preferably the shaft end is indexed and registered against the undersurface of the thrust plate when the shaft is located and secured to the coupling 70. The hole 46 in the collar 44 and the shaft 34 define an annular gap therebetween. This gap is substantially wider than required to accommodate the run-out of the shaft due to deflecting forces which may be applied thereto. Such forces are generated by fluid forces on the impeller as the impeller rotates in the medium being mixed. The gap is provided to receive the seal assembly 36. The retaining hub 38 of the assembly has a flange 94 which is connected to the housing base plate by bolts 98. The retaining hub 38 captures the sealing sleeve assembly 40 inside the gap and between the retaining hub 38 and the coupling 70. A collar l00 is attached to the impeller shaft as by a set screw l02 so as to normally dispose the under surface of the collar l00 above the surface of a radially inward extending step l04 of the retaining hub 38. Preferably a sealing ring l06, which may be an "O" ring, is captured in a notch in the under surface of the collar l00 adjacent to the surface of the shaft 34. This sealing ring l06 is better shown in FIG. 3. The sealing ring fits into a chamfer l08 which extends around the inner edge of the step l04. When the split ring coupling 70 is loosened, the shaft 34 drops until the collar l00 engages the step l04. A static seal is then provided by the sealing ring l06. Then the closed tank with which the mixer apparatus is associated and on which the housing l0 is secured remains sealed. The coupling can then be removed to expose the sleeve assembly 40 for ready removal and replacement from the top of the apparatus. The flange 94 of the retaining hub 38 may be welded thereto as shown at ll0. The retaining hub may be made of stainless steel or any other suitable alloy or material in order to withstand corrosive environments, and a facing ll2 may be adhered to the underside of the retaining hub 38 and its flange 94. FIG. 3 shows additional threaded holes ll4 which may be used to attach the flange which assembles the mixer drive to the nozzle of a closed tank. FIG. l and FIG. 3 illustrate a single mechanical sleeve assembly 40 as the seal. This assembly may be provided as a cartridge and secured in the retaining hub 38 by a retaining ring l20, which may be a "C" washer. The sleeve assembly 40 has a sleeve ll6 which is attached to a ring l22 by a set screw ll8 in a ring l20 around the sleeve ll6. The sleeve ll6 is sealed by a seal ring (an "O" ring) l24. A plurality of springs l26 which bear against the ring l22 compress carbon washer l28 against a ceramic seat ring l30. Drive pins l27 extend from the ring l22 into the washer l28 so that the ring l22 and washer l28 and sleeve ll6 are coupled to rotate together. "O" ring seals l32 and l34 are located between the washer l28 and the sleeve ll6 and between the inner periphery of the retaining member 38 and the seat l30. The seat l30 defines a seal face l40 with the washer l28. Pins l42 (see also FIG. l) extend into a slot l44 in the underside of the coupling 70. These pins l42 engage the coupling 70 in the slot l44 so that the sleeve assembly consisting of the inner sleeve ll6, the ring l22 and the washer stack l28 rotates with the shaft 34. The seal face l40 is extremely close to the coupling member. The coupling member rigidly clamps and supports the shaft 34. Accordingly there is very little deflection and run-out at the location of the seal face l40. Such run-out can be controlled to about 5 mils or less. Accordingly, the sleeve assembly 40 of the seal may be a low run-out dry running seal as shown in FIGS. l and 3. When escape of any gas or other medium from the vessel is detrimental, a pressurized double mechanical seal, such as shown in FIG. 4 may be used as the seal sleeve assembly 40. This assembly is also removable and replaceable by removing a retaining ring l50, similar to the ring l20 (FIG. 3). This sleeve assembly 40 has two seat rings l52 and l54 at the bottom and top thereof. The upper seat ring l54 is assembled with a flanged ring l56 which is retained by the retaining ring l50. The rotating parts of the assembly 40 have two carbon washers l58 and l60 which, with the seats l52 and l54 define sealing faces l62 and l64. The washers l58 and l60 are biased against the faces by collars l68 and l70 which are engaged by a helical spring l72. These rotating parts of the sleeve assembly 40 rotate with a sleeve l74 which is indexed against the top surface of the collar l00. Tangs l76 extend upwardly into the slot l44 (FIG. l) and engage the coupling 70 so that the sleeve l74 and the rest of the rotating parts of the assembly 40 are driven and rotate with the shaft 37. A ring l80 which is disposed in a slot in the sleeve l74 retains the sealing assembly 40 on the sleeve l74 between the ring l80 and a step l82 so that the sleeve l74 and all of the other parts of the sealing assembly 40 may be removed as a unit for replacement when the seal faces l62 and l64 wear out. Holes l84 for pulling tools may be provided in the flanged ring l56 to assist in the removal of the sealing assembly 40. The sealing faces are kept under pressure of a hydraulic liquid, such as a conventional seal lubricant, which is supplied through lubricant inlet and outlet passages l86 and l88. The cavity into which the pressurized lubricant is supplied is defined by the inside surface of the retaining hub 38, the sleeve l74 and the upper and lower seats l52 and l54, l56. Seal rings, such as "O" rings are provided between the sleeve l74 and the shaft 37 and between the seats l54 and l56 and the seat 52 and the retaining hub so as to preclude any leakage through the seal assembly 36. The rotary parts of the sealing sleeve assembly 40 of the double mechanical seal assembly 36 shown in FIG. 4, similarly with the rotary seal assembly 40 of the single mechanical seal assembly shown in FIG. 3 are located adjacent to the rigidly supported top end of the shaft 34 where deflection is minimal and run out at the seal faces l62 and l64 is not excessive (for example, approximately 5 mils). Accordingly the sealing sleeve assembly 40 provides reliable sealing performance over a long lifetime. Since the cavity containing the rotating seal parts of the double mechanical seal assembly shown in FIG. 4 are pressurized to a pressure greater than the tank with which the mixer drive is used, the pressure in the tank is not capable of driving material or gases contained therein through the seal assembly 36 into the environment. It will be apparent that removal of the coupling 70 will enable the replacement of the rotary sealing sleeve 40 parts from the top of the unit as was the case with the single mechanical seal shown in FIGS. l and 3.

Claims: Mixer drive apparatus comprising a housing (10), an impeller shaft (34) having a first axis of rotation, a drive shaft (26) having a second axis of rotation, and gearing (30, 42) between said shafts, said impeller shaft (34) being secured to and cantilevered from a coupling (70), characterized by the fact that the impeller shaft (34) is located by the coupling (70) to define an annular gap (46) between said shaft and a collar (44), said gap having a width radially of said shaft substantially larger than the running clearance for said shaft and being adapted to receive a seal assembly (36), the seal face (140) of said seal assembly being close to the coupling (70), and a rotatable hub (48) coaxial with and disposed outside the collar (44) with bearings (50, 52) between said hub and collar. Apparatus according to claim 1, characterized in that the seal assembly (36) is captured in the gap (46) between the coupling (70) and the housing (10). Apparatus according to claim 2, characterized in that the seal assembly (36) includes a retaining hub (38) in said gap fixedly disposed against the inside of said collar, and a sealing sleeve assembly (40) around the impeller shaft (34), said sleeve assembly including seal members, the coupling being removably mounted on the rotatable hub (48) and being removably mounted to the impeller shaft for exposing the sleeve assembly for removal and replacement. Apparatus according to claim 3, characterized in that the retaining hub (38) has a wall which is disposed against the collar (44) and a step-defining surface (104) extending radially inward toward the axis of the gap (46), the impeller shaft (34) having a support collar (100) attached thereto, said support collar being spaced from said surface when the impeller shaft is secured to the coupling (70) and being engageable with said surface when the impeller shaft is released from the coupling whereby to support the shaft while said sleeve assembly (40) is being removed and replaced. Apparatus according to claim 1, characterized in that the seal assembly (40) comprises a sealing sleeve assembly (40) and a retaining hub (38) disposed within the collar (44) in the gap (46) for capturing said sealing sleeve assembly therein. Apparatus according to claim 5, characterized in that said sealing sleeve assembly (40) comprises a seal member (116) on the impeller shaft (34) and a seat member (130), the seal assembly (36) having a retaining hub (38) disposed inside and against the inner periphery of the collar (44), said seat member bearing and held stationary against the retaining hub. Apparatus according to claim 6, characterized in that the seal member comprises a sleeve (174, Fig. 4) on the impeller shaft (34), a pair of seats (152, 154) axially spaced from each other to define a cavity in the gap between said seat members, the impeller shaft, and the retaining hub (38), and means for supplying pressurized hydraulic fluid to said cavity. Apparatus according to claim 1, characterized by the fact that the coupling (70) has a pair of sections (76, 78) defining a separable split ring, said coupling being secured to the rotatable hub (48) and bridging the gap (46) in the collar (44), and means (80, 82) for removably securing the impeller shaft (34) in clamped relationship with said sections within said split ring. Apparatus according to claim 8, characterized in that the impeller shaft (34) has an end surface perpendicular to the axis thereof, and thrust plate (86) secured to the coupling (70) at the end of the slit ring (76, 78) facing away from the rotatable hub (48), said end surface of the impeller shaft being secured to said thrust plate. Apparatus according to claim 9, characterized in that a bolt (90) extends through the thrust plate (86) and the end surface of the impeller shaft (34) in threaded engagement with said impeller shaft for moving the impeller shaft axially to locate it in the split ring (76, 78), and in that a key (84) is provided in at least one of the split ring sections and in engagement with a key way in the impeller shaft, said key being captured by said thrust plate.

Inventors: HUTCHINGS, WILLIAM F., MCINTOSH, GEORGE C.
Applicants: GENERAL SIGNAL CORPORATION
Application year: 1987
Main classification: B01F15
IPC codes: B01F7, B01F15