US2322720A

US2322720A - Apparatus for the treatment of liquid solids mixtures

Info

Publication number: US2322720A
Application number: US436450A
Authority: US
Inventors: Charles H Scott; Harry A Linch
Original assignee: Dorr Co
Current assignee: Dorr Co
Priority date: 1942-03-27
Filing date: 1942-03-27
Publication date: 1943-06-22
Anticipated expiration: 1960-06-22

Description

K H 'June 22, 1943. c. H. SCOTT ETAL 2,322,720

APPARATUS FOR THE TREATMENT OF LIQUID soup MIXTURES Filed March 27, 1942 5 Sheets-Sheet l FIIG.I.

.WVENTOKS June 22, 1943. Q sc ET AL 2,322,720

APPARATUS FOR THE TREATMENT OF LIQUID SOLID MIXTURES Filed March 27, 1942 5 Sheets-Sheet 2 June 22, 1943. c, scoT-r 1- AL 2,322,720

APPARATUS FOR THE TREATMENT OF LIQUID SOLID MIXTURES Fil ed March 27, 1942 5 Sheets-Sheet a i u mw "QM o Q I I o ME I 1 F'IG.6.

June 22, 1943. c. H. scoTT EI'AL APPARATUS FOR THE TREATMENT OF LIQUID SOLID MIXTURES Filed March 27, 1942 5 Sheets-Sheet 4 C vs June 22, 1943. c, SCOTT ETAL 2,322,720

APPARATUS FOR THE TREATMENT OF LIQUID SOLID MIXTURES Filed March 27, 1942 5 Sheets-Sheet 5 my I W96 m9 F'IG .9.

INVENTORS Patented June 22, 1943 2,322,720 mourns roa 'rn'a' murmur or anx'rna LIQUID SOLIDS Charles B. Scott and Harry A. Lincli, Westport, Conn asslgnors to The Don Company, New York. N. Y., acorporation of Delaware Application March 27, 1942, Serial No. 436,450

4 Claims.

This invention relates to apparatus for treating liquid solids mixtures or suspensions of solids in liquids, by detaining them in a tank while subjecting them to agitation, or to sedimentation, or to both, which apparatus is provided with agitating or sediment raking members or with both,

that rotate about a vertical axis in the tank.

In the type of apparatus herein more particularly considered, the tank has an inner, and an outer annular treatment chamber in concentric arrangement, that is, an inner circular chamber is surrounded by an annular chamber, both chambers being provided with members to move there-'- in in a circular path about a common vertical axis, although at differential speeds. Therefore, concentric vertical shafts, that is an inner shaft surrounded by a hollow shaft, are provided, each shaft carrying members which extend into one of the aforementioned concentric chambers to operate therein in circular paths about the common vertical axis.

In a more specific sense, the invention relates to improvements in drive mechanism for the concentric vertical shafts.

It is among the objects of this invention to provide a unitary drive mechanism by means of which both concentric shafts can be rotated at the desired speed dilferential from a single source of power,-such as a motor. Other objects are to provide such a mechanism that is compact with shaft will be rotated at a rate determined by the reduction ratio.

The planetary or reduction gear mechanism comprises a plurality of epicycloidally moving or so-called planetary gears, and it is desirable that the torque load be transmitted from the primary shaft to the secondary shaft substantially evenly through all of the planetary gears at the same time. However, because of manufacturing ln-accuracies or unevenness of the gear teeth, such .uniform distribution of equal shares of the torque load for each planetary gear is not ordinarily between the planetary gears, thereby reducing the efficiency of the mechanism, increasing the wear and tear, and increasing power consumption.

' According to the invention, these difllcultles are avoided by floatlngly mounting some component member or members of the reduction gearing proper in such a manner that the torque loads transmitted through the planetary gears will interbalance. As a result substantially equal shares of the torque load will be transmitted through the respective planetarygears substantially at all times, sothat wear and tear are reduced and operating efliciency is increased with attendant decrease in power requirements.

One feature in particular relates to a unit for the treatment of liquids with solids in suspension, in which the said liquid or suspension first enters the inner chamber in order to be subjected therein to flocculation of the suspended solids. The liquid, while being flocculated passes vertically through the inner chamber also called flocculation chamber, and from there it passes outwardly into the surrounding annular chamber where it undergoes sedimentation of the flocculated matter. In this type of unit the two chambers may be said to be defined against each other by a circular wall or partition, the lower end of which terminates a distance above the tank bottom.

In this flocculation-sedimentation unit, theinner or secondary shaft. The secondary shaft is consequently identified with the sediment raking arms. Furthermore, the inner or secondary shaft extends downwardly below the end of the surrounding or primary shaft, and since the circular wall or partition which defines the two chambers against each other, terminates above the bottom of the tank, it is possible for the rake arms -to extend from the inner or secondary shaft outwardly over the bottom of the tank unit.

According to this feature a motor driven primary drive gear is unitary and concentric with the vertical primary shaft. A secondary or driven gear is disposed above the motor driven gear and realized, and consequently the torque load shifts concentric therewith and unitary with the secondary or inner shaft. Above this and substantially also concentric with the other two gears is provided a non-rotatable gear which is the third gear, and which is of smaller diameter than the secondary gear. The primary or lowermost gear in turn carries a pair of identical rotatable planetary gear units mounted opposite each other on the primary gear. gear units the secondary gear is geared up with the non-rotatable gear above, which makes the mechanism operative so far as the transmission of torque load from the primary to the secondary gear is concerned. Means are provided to permit horizontal floating of the non-rotatable gear relative to the planetary gears in a manner whereby one-half of the drive torque load is interbalanced with the other half as the load is transmitted through the planetary gear units to the secondary gear.

According to one embodiment the third gear is mounted to float, while the rotary axes of the planetary gear units are fixed relative to the primary gear; according to another embodiment, the planetary gear units are combined in a bodily floating unit, whereas the third gear which is nonrotatable, is fixed and non-floating.

As illustrative of a form of construction by which the invention hereof may be realized, referonce is made to the accompanying drawings constituting a part of this specification, and in which drawings:

Fig. 1 is a plan view: and I Fig. 2 is a sectional view taken along lines 2-2 in Fig. 1, of an apparatus for the treatment of liquid-solids mixtures, in which the improved drive mechanism is embodied.

Fig. 3 is an enlarged detail view of the improved drive mechanism.

Fig. 4 is a section along the line 3 in Fig. 3.

Fig. 5 is a side view of the drive mechanism taken on the line 5-5 in Fig. 3, with part of the casing broken away.

Fig. 6 is a detail perspective view of a torque equalizing coupling member.

Fig. 7 is a sectional detail view of a torque responsive overload cut-out switch device along the line l'l in Fig. 4.

Fig. 8 is the longitudinal section of a modified form of the mechanism.

Fig. 9 is a section'on line 9-9 in Fig. 8.

The apparatus embodying the drive mechanism of this invention serves the purpose of first flocculating the solids that are suspended in a supply of liquid, as by agitation in a flocculating chamber or compartment, and then settling the flocculated matter as sediment or sludge under quiescent conditions in a sedimenation chamber or compartment. In the apparatus of this embodiment both treatment compartments are concentrically arranged in a tank, and the fiocculating compartment is surrounded by the sedimentation compartment.

The apparatus comprises a tank l0 having a slightly conical bottom H provided with a central sludge outlet l2, a sludge discharge, valve [20, and a cylindrical wall portion l3 provided with an annular overflow eflluent launder l3a. Across the top of the tank are mounted a pair of beams Through these planetary i Furthermore supported upon the beams l4 and i5 is a rotary flocculatingand sediment-collecting mechanism 22 comprising a primary hollow vertical shaft 23 carrying vertical agitating members 24 fixed upon and rising from horizontallyextending arms 25 fastened on the hollow shaft 23 and rotating therewith. A series of stationary vertical deflector members 26 is shown to be fastened upon and to depend from the bottom of a radially-disposed feed launder 21. Another series of stationary vertical deflector member 28 is fastened upon and extend downwardly from a bracket portion 29 also supported by the beams M and i5. Still other vertical deflector members 30 and 3| are supported from

corresponding overhead members

32 and 33 respectively which

overhead members

32 and 33 incidentally also have brackets i6 depending from them to support the wall I1. The

overhead members

32 and 33 extend from the beams I t and I5 respectively and at right angles thereto in opposite directions and to two diametrically opposite points at the top of the tank I50. The agitator arms 25 have depending from their underside sediment-collecting blades 34 for removing through the openings it whatever flocculated matter might have settled upon the annular bottom portion l9.

Within the hollow shaft 23 and concentric therewith operates another vertical shaft 3% herein called the secondary shaft because it rotates at a slower rate than the primary hollow shaft 23, because of the reduction gear ratio between the two shafts and which is part of the drive mechanism to be described.

The secondary shaft 35 carries radially-extending rake arms 36 provided with sedimentcollecting plowing blades 37, which shaft 35, when it rotates, will gradually convey scdimented material over the bottom i l of the tank from the outlying zones thereof to the centrally-disposed sludge outlet 6 2 for discharge.

Both the primary hollow shaft 23 and the secondary shaft 35 are supported by and depend from the reduction gear drive mechanism proper which mechanism will now be described by reference to Figs. 2, 3, 4 and 5.

The primary hollow shaft 23 is fastened as by flange and bolt connection 39 to the hub portion 658 of a primary gear or worm gear 3! reinforced by ribs Mia and driven by a worm d2 fixed on a worm shaft 211 journalled in the box portion @3 of an annular casing portion or frame M in which the Worm gear H is rotatably supported by means of an annular bearing 35. The annular casing portion M is mounted by means of gusset plates Ma upon and supported by the beams l4 and i5 and also by a pair of shorter transverse beams 46 and d1 interconnecting the beams It and i5 and constituting therewith a supporting frame. The gear casing 34 has lugs 44b and bolts Me whereby it is mounted.

Upon the underside of the worm gear M there are provided a pair of lugs 48 and 49 diametrically opposed to each other and having fixedly mounted therein gear

axles

50 and 5! respectively. Each of these axles carries rotatably thereon a planetary gear assembly in the form of apalr of pinions of differential diameters and keyed together and constituting together with the axle what is herein termed a planetary gear unit in which the upper pinion is somewhat larger than the lower pinion, the ratio being determined by the reduction ratio of the gear as will be more specifically described below. The axle 50 has a reduced portion 59a by means of which it is fitted and seated shown in Fi '7).

. an opening 55 and is held-inthe cover 14 by locknut=55c. The planetary gear assembly 'or unit :rotatably mounted on axle 55 comprises a smaller pi-nion52 having an upwardly-extending hub portion 55 upon which is fitted andto which iskeyed as at 54a somewhat larger pinion 55. Similarly the opposite or companion'axle' 5| has a rotatable planetary gear assembly or unit comprising a lower smaller pinion 55 to which is keyed an upper somewhat largerpinion 51, which planetary gear assembly is identical with that comprising the pinions 52 and", and rotatableu what is herein called the secondary gear 55 be"- causeit is fixed to the secondary vertical shaft 35 as by meansof

key connections

59 and 55, and

by a split ring 5| engaging in a groove 52 at the b o o 2,322,720 in the "lag", and is held by a nut "band a' the cover portion 14 of the casing and co 9 mm "therein. a

, The operating relationship between the annu l'ar member 15 which may herein be called the torque reaction member, with the "out switch device 15 is, as follows: I

The annular member I has an arm 54 provided with a seat ior one end of the spring 15 the other end of which is confined by a seat member '55 adjustable by means of an adjusting or et screw 51 that is screwed into the end wall" of a boxfportion "which is part or the casing cover 14 and which houses the overload cut -out upper end of the shaft 35, the halves of the split ring being fastened to the hub portion 58a of the secondary.gear-55, to hold the shaft in place in the hub portion 55a. The secondary gear 55 has an annular bearing upon-the primary gear or worm gear 4l'.; Both the larger pinions 55 and 51 of the respective planetary gear assemblies mesh with a stationary or master gear 54 that is held against rotation relative to the stationary gear casing although having limited horizontal play allowing it a floating movement in a horizontal direction at right angles to the center-tocenter line of the pinions 55 and '51.

toand betweenthe pinions 55 and 51 so that a substantially equal share of the driving torque load is transmitted from the primary gear 4i .through each planetary gear assembly, that is the assembly of

pin ons

52 and 53 on the one hand, and-pinion assembly 55 and5'l on the other hand; to thesecondary gear 55.

* The means for thus balancing or equalizing the transmission of the driving forces to obtain a balanced driving torque, comprise a floating coupling member'55 (see also detail Fig. 6) in the form of an annularbody portion 55a having at its underside a pair of diametrically opposed lugs or teeth 55 and5l, and at its topside a pair of lugs or

teeth

55 and 59 also diametrically opposed to each other, but staggereclat right angles to the lugs The lugs or teeth 55 ,and 51 have\sliding lit in corresponding grooves 55 and 51 at the underside.

l5 and 'il formed by respective pairs of lugs-10a and lflb, and Ha and Nb, provided on the topside of thestationary gear 54, whereas the lugs or teeth 58 and59 enga e in a s milar fashion in corresponding

grooves

12 and 13 formed by re spective pairs of lugs 12a and 12b, and 13a and 19b, provided upon theunderside of the top portion of a gear casing cover 14 that is fastened upon thestationary 'a'nnular casing portion 44 as bymeans of bolts I5; More precisely, the upper grooves 1-2 and 13 are provided upon the unders de ofjan annular member 15 that is rotatably mounted as at I1 1n the casing cover 14, but nor- In this way the stationary gear 54 can balance itself relative switch device 19' and is'provided with a cover 550.

overload cut- The spring 15 being adiustably confined between rotatable annular member I5 while the torque load upon the mechanism does not exceed amaximum that i pro-determined by the adjusted tension of the compression spring I8. However,

a should an overload make itself felt upon the rake mally held against rotation by a force equalling the driving torque reaction, by a compression spring 15 which is part of an overload cut-out switch device 19 (adetail section of which is The annular member 15 has means-of a retaining ring 15a fastened to the anarms 35 due to resistance of sedimented matter encountered by the sediment-collecting plowing blades 51, then the resulting torque reactionwill e transmitted from the stationary or master gear 54 through the-floating coupling member 55 to theannular torque reaction member 15, and cause a corresponding compression of the spring 15. Simultaneously with the compression $1 spring 15 in proportion to the torque load reaction, a finger 92 extending upwardly from the seat portion 55 of the, annular member 15, will actuate an alarm or cut-out switch 93. Thus an alarm cam be'sounded or a motor 94 driving the worm 42 will be stopped. Drive means between the motor (and the worm 42 are shown to include reduction gearing 95 and a chain drivebetween the reduction gearing 95 and the worm shaft 42a, comprising sprockets 95 and 91, and a drive chain transmitting driving power from the .sprocket 95 to the sprocket 91. The chain drive ,is enclosed by a housing 99 mounted upon a baseplate I55 by means of brackets I ill, the baseplate I59 in turn being-mounted upon the supporting beams s. 3 to s applied to the treatment apparatus shown in Figs. 1 and 2, is as follows;

A continuous supply of solids in suspension passes through the feedlaunder 21 and from there enters the flocculation chamber 20 at the top thereof. A liquid thus fed spreads over the area of the flocculationcompartment, and while slowly descending through successive horizontal strata, itissubjected to gentle agitation by the vertical agitating member 24 co-operating with and passing by the stationary deflector members '25 and 25, and "and 51. The moving members 24 as well as the

stationary members

25 and 25 .have li -shaped cross-section which promotes a kind of agitation that produces numerous and gentle'contacts of the fine suspended and normally unsettleable solids with each other, until theyjbecome coagmented into agglomeratlons or I flocs capable of subsequent sedimentation under quiescent condition The agitating members 24 move in circular repetitive paths at a speed that is conducive to the formation the, fines, which speed determines the R. P. M. required or the primary shaft 23that carries the members 24. The liquid carryingthe solids now in. the form of flocs continues downwardly and passes through the opening I8 in the bottom or the flocculating compartment 2!! into the quiescent space below andv around the flocculating. compartment, which quiescent space represents the. sedimentation compartment 2|. Whatever flocs may become lodged upon theannular bottom I9 of the flocculating compartment will be removed by the blades 34 and'be caused to Join the drifting flow of the other flocs downward through the opening I8. In the sedimentation compartment the flocs are allowed to settle to the bottom I I of the tank I while clarified liquid that'is substantially freed of .the ilocculated solids, is allowed to rise and to overflow into the annular launder I312. The settled solids on the bottom I I are engaged by the blades 31 of the rake arms 36 which rotate with the secondary shaft 35. The rotationof the rake arms will gradually convey the settled matter over the bottom II towards and into the 4| through each planetary gear assemblyto the gear 58 and thereby to the secondary shaft 35.

Whilethe faster moving agitator members 24 will not encounter any undue torque resistance,

.it is possible that an undue accumulation of sediment upon the tank bottom I I will impose an excessive load upon the rake arms 36 and thereby upon the secondary shaft 35, andthe excessive resistance thus encountered will react through the gear 58 and the planetary assemblies into the stationarygearfi l which in turn will cause a corresponding excess torque reaction to be transmitted to the torque reaction member 16. This excess torque in turn causes a slight degree of instance, over a range from. 5:1 to :1, but for use with the fiocculator clarifier drive herein illustrated in Figs. 1 and 2, a practical range of the ratio may be expected to be approximately from 10:1 to 20:1. V

The prime mover for this mechanism is the

motor reducer unit

94 and 95 which transmits the driving power from the sprocket through a chain to the sprocket 91 that is herein assumed to rotate the worm 42 in a clockwise direction, thereby rotating the worm gear 4| clockwise when looked upon from the top. This moves the

planetary gear assemblies

52, 55, and 5 6, 51, respectively, bodily in a cyclic path. Since the larger planetary gears and 51, respectively, mesh with the stationary gear 64, and since the planetary gears 55 and 51 respectively are unitary with the respective smaller planetary gears 52 and 56, this bodily movement oi the planetary gear assemblies ,will cause a rotation counterclockwise of the secondary gear 58 that meshes with the smaller planetary gears 52 and 56. The

R. P. M. of the gear 58, of course, is identical with that of the'secondary shaft or raking shaft 35. The torque equalizing floating coupling mem ber ,65 is movable in one horizontal direction AA with respect to the stationary gear 64 by reason of sliding engagement of the lugs 66 and 61 with the grooves 10 and 1I, respectively, and it is movable also ina horizontal-direction B--B at right angles to the direction A-A but only with respect to the stationary gear housing because of the sliding engagement of the

lugs

68 and 69 with the

grooves

12 and 13 respectively. In view of this arrangement it is the function of the coupling member to allow and to cause the stationary gear 64 to adjust itself during'the operation of the mechanism fioatingly in such a manner that an equal portion of the total driving torque will be transmitted from the worm gear rotation of torque reaction member 16 against the pressure of the spring 18. A sufllcient compression of the spring I8, depending upon the amount of excess torque being absorbed'by the spring, will allow the finger 92 of the torque reaction member 16 to actuate the switch 93 whereby the drive motor 94 may be stopped, and/or an alarm be sounded.

According to a modification shown in Figs. 8 and 9, the drive mechanism according to this invention is constructed as follows:

The mechanism as a whole is supported upon a beam construction I4, I5, 46 and 41, similar to that previously described in conjunction with the embodiment of Figs. 3 to 6. The primary hollow shaft 23 and the secondary shaft 35 rotating within the hollow shaft, are substantially the same and operate substantially the same with respect to each other, as previously described.

The primary hollowshaft 23 is fastened as by flange connection to the hub I02 of a worm gear I03 that is rotatable upon an annular bearing I04 provided in an annular trough-like portion I05 of a gear casing that is similar to the one shown in the embodiment of the mechanism in Figs. 3 to 6, and this casing is also mounted upon the supporting beam construction in the same manner as shown in the preceding embodiment.

The worm gear I03 having stiffener ribs I03a is herein termed the high speed or primary gear in the sense defined in the preceding embodiment,

'and it is driven by aworm I06 on worm shaft in Fig. 7.

I 06a mounted in a box-like portion I01 of the gear casing. Inside the hollow or primary shaft 23 rotates the secondary shaft 35 which is keyed as at I08a to a gear I09 which is herein defined as the low speed or secondary gear of thereduction gear train of this mechanism. A split ring I09a engages in a groove I09b at the top end of the secondary shaft 35, and is fastened to the secondary gear I09 as by screw bolts I090, for holding the gear I09 against longitudinal displacement; upon the secondary shaft 35. Above and coaxial with the secondary gear I09 is provided a stationary master gea'r H0 mounted in a cover portion III of the gearcasing, which cover portion is bolted down upon the annuIar trough-like portion I05 of the casing. The mas ter gear H0 is normally stationary, although it is mounted in the cover portion III so as to be rotatable under overload. Normally, however, the master gear I I0 is held against rotat on, that is, held against the driving torque of the mechanism;. by the correspondingly adjusted compression spring of an overload responsive device provided in the box-like portion IIZ of the cover portion III, which device is similar to one shown A pair of m which comprises an upper annular portion planetary gear assemblies H3 and are mounted in an annular cage structure III and a lower annular portion I", both annular portions being rigidly inter-connected as byspacer portions Ill. Each of the planetary gear assemblies H3 and Ill comprises a lower smaller and an upper larger gear, boththe smaller and the larger gear of each assembly being rigidly inter-connected so as to revolve as a unit within the annular cage structural I5, which cage structure in turn rotates together with the primary or worm gear I03 by reason of coupling means to be described. Both planetary gear assemblies H3 and Ill mesh with the secondary gear I09 and with the stationary or master gear I I at diametrically opposed points thereof, that is to say, a lower gear II9 of the gear assembly I I3 meshes with the secondary gear I09, while an upper gear I20, which is somewhat larger in diameter than the gear II9, meshes with the master gear 0. Similarly, at the opposite side, a lower gear I2I that is identical to the gear II9 meshes with the secondary gear I09, while a somewhat larger gear I22 that is identical to the gear I20, meshes with the master gear H0.

The secondary gear I09 has an annular bearing I23 upon the primary or worm gear I03. Coupling means are provided between the annular cage construction H and the primary or worm gear I03, that is to "say, upon the underside of the cage construction H5 there are provided a pair of guide lugs I24 and I25, each of which has a sliding fit in corresponding grooves I23- and I2'I, each groove in turn being formed'by a pair of lugs provided on the top side of'the primary gear I03. The guide lu s I24 and I25 engaging in the grooves I28 and I21 respectively, permit the annular cage structure II5 to adjust itself during the operation of the mechanism, in a horizontal direction along a line perpendicular to a line that extends from center to center of the two gear assemblies I I3 and I I4.

The operation of the mechanism according to the embodiment in Figs. 8 and 9 is, as follows:

The worm shaft I060. rotating in clockwise direction. turns the primary or worm gear I03 and thereby also the primary shaft 23 in a clockwise direction when looked upon from above. Together with the worm gear I03 rotates the cage structure II5. Since the larger gears I20 and I22 of the two respective planetary gear assemblies H3 and H4 mesh with th master gear IIO, it is clear that the somewhat smaller gears H9 and I2I of the respective gear assemblies will drive the secondary gear I09 relative to the primary gear I03 at a reduced speed, that is determined by the differential between the diameters of the secondary gear I09 and the master gear IIO, the latter being the smaller one of the two. Consequently, the secondary shaft 35 will rotate countercurrently to the primary shaft 23, namely, in counter-clockwise direction.

During the operation of the mechanism the total driving torque imparted to the primary or worm gear I03 will be transmitted in equal shares by the planetary gear assemblies H3 and H4 to opposite points of the secondary gear I09.

Each gear assembly takes substantially one-half the torque load since the planetary gear cage Hi can adjust itself currently in the manner above described, so that inaccuracies or inequalities in the gear teeth will cancel out during the operation. Due to the even distribution of the torque transmitting force evenly to and through both planetary gear assemblies 3 and lit, a true and powerful torque is imparted. to the secondary gear I09, relatively low gear pressures are obtained.\thc wear and tear consequently reduced. and he mechanism can be made relatively lighter d more compact. .Low gear pressures also fact itate the problem of lubricating the teeth. g

In case of an undue overload, that is a load in excess of a pre-determined normal operating load or torque imposed upon the secondary shaft 35, the excess torque reaction will cause the master gear IIO to rotate Just suillciently against the spring pressure of the overload responsive device contained in the box-like portion II2 of the casing, to sound an alarm and/or stop the drive motor substantially in a manner described in conjunction with the disclosure of the overload responsiv device in Fig. '7.

While an example of the mechanism according to this invention is herein shown toimpart differential speeds to the agitator paddles 28, 30,

3|, on the one hand, and to the rake arms 35. on the other hand; it should be understood that the invention is not to be limited to this specific embodiment. For instance, the flocculating compartment 20 along with the paddle mechanism therein might be omitted, and the reduction gear drive might serve to impart balanced torque rotation to the shaft 35 alone, for overcoming the sludge raking load.

We claim: A drive gear mechanism comprising a primary gear, stationary means for supporting said primary gear for rotation about a vertical axis, means for driving said primary gear, a vertical shaft, a secondary gear above and rotatably supported by said primary gear and substantially concentric therewith and rotatable relative thereto and connected with said shaft to rotate therewith, a non-rotatable gear above the secondary gear and having substantially concentric rela tionship therewith and bein of different diameter than said secondary gear, stationary structure to provide for non-rotatable mounting of said non-rotatable ear, a pair of opposedly arranged planetary gear units rotatably mounted upon said primary gear, by which units said sec,- ondary gear is geared up to said non-rotatable gear thereabove, and means for mounting the non-rotatable gear and the planetary gear units in a manner to permit them to float horizontally relative to one another so as to interbalance the torque loads being transmitted simultaneously through each of said planetary gear. units 2. Mechanism according to claim 1, in which the non-rotatable gear is fioatingly mounted, while the position of the rotary axes of the planetary gear units upon and relative to the primary gear is fixed, and in which the means for floatingly mounting the non-rotatable gear comprise a floating coupling member concentric with said non-rotatable gear'and interposed between said non-rotatable gear and said stationary structure, means providing coupling engagement of said floating member with said non-rotatablev gear to permit horizontally guided floating movement of said gear in one direction with respect to said member, and means providing coupling engagement of said member with said stationary structure to permit horizontally guided floating movement of said floating member with respect to said stationary structure in a direction at right angles to said first mentioned horizontally guided fioat-/ ing movement.

3. Apparatus according to claim 1, in which said stationary structure comprises a housing for the gear mechanism, and in which the non-rotatable gear is flcatingly mounted, while the position oi the rotary axes oi the planetary gear units upon the primary gear is fixed, and in which the means for floatingly mounting said non-rotatable gear comprise a floating coupling member substantially concentric with said non-rotatable gear, and interposed between said non-rotatable ear and the top portion of said housing, means providing coupling engagement of said floating coupling member with the non-rotatable gear to permit horizontally guided floating movement of said gear in one direction with respect to said floating coupling member, and means providing coupling engagement of said floating coupling member with the top portion of said housing to permit horizontally guided floating movement of said member with respect to said top portion oi the housing in a direction at right angles to said first mentioned horizontally guided floating movement, with the addition of a member rotatably mounted in the top portion or the housing and substantially concentric with the primary ear and embodying said last mentioned means for provid ng coupling engagement, and overload responsive means associated with said housing,

comprising means for resiliently absorbing the member, for stopping the driving power of the mechanism. v

4. Apparatus according to claim 1 in which the non-rotatable gear i non-floatingly mounted,

V and in which the planetary gear units are mounted in an annular body. surrounding said primary and said secondary gear, and constituting a bodily floating unit, and in which means are provided for coupling engagement of said floating unit with the primary gear to allow for horizontal self-adjusting movement oi said floating unit in a direction at right angles to the center-to-center line 01' said planetary gear units.

CHARLES H. SCOTT. HARRY A. LINCH.