US 3343786 A
Description (OCR text may contain errors)
Sept. 26, 1967 T. D. SHARPLES CENTRIFUGE HAVING PLURAL CONVEYING MEANS FOR SOLIDS 4 Sheets-Sheet 1 Filed Feb. 21, 1964 INVENTOR.
HAZPLES ATTORNEY T I- I CQIAS D. S
Sept. 26, 1967 T. D. SHARPLES I Q 3,343,786
CENTRIFUGE HAVING PLURAL CONVEYING MEANS FOR SOLIDS Filed Feb. 21, 1964 4 Sheets-Sheet 2 Bowl V 20 RPM Fos'rer Fi rsf Section Bowl 20 RPM Slower 80 RPM Slower INVENTOR. THOMAS D. SHA PLES ATTORNEY Sept. 26, 1967 T. D. SHARPLES 3,343,786
CENTRIFUGE HAVING PLURAL CONVEYING MEANS FOR SOLIDS Filed Feb. 21, 1964 4 Sheets-Sheet 4 INVENTOR.
T I- l OMAS 0. sHAZPLEs ATTORNEY United States Patent CENTRIFUGE HAVING PLURAL CONVEYING MEANS FOR SOLIDS Thomas D. Sharples, Lansdale, Pa., assignor to Pennsalt Chemicals Corporation, Philadelphia, Pa., a corporation of Pennsylvania Filed Feb. 21, 1964, Ser. No. 346,555 Claims. (Cl. 2337) This invention relates to a solids discharge centrifuge and provides improved means for conveying solids toward the solids discharge port. More specifically this invention relates to a centrifuge of the type comprising a bowl having a helical solids conveyor mounted within it to move the solids toward their discharge port.
Solids discharge centrifuges of the type comprising a bowl having a helical solids conveyor and means to drive the bowl and conveyor at diflerent speeds are old in the art. An example is disclosed in the Patent 2,703,676 which issued March 8, 1955 on an application filed by Fred P. Gooch. In such devices the centrifuge is often driven by a power means engaging the bowl. Mounted on the bowl is a gear box containing one or more stages of planetary gears, the output of which drives the conveyor.
I have found that the torque involved in the rotation of the conveyor may be ascribed almost entirely to the engagement of the conveyor flights by settled solids adjacent the solids discharge port. The solids as they are scrolled up the beach become drier and drier and present a source of increasing resistance to the movement of the conveyor.
Attempts have been made in the past to reduce the torque involved in the conveying of solids. In one such attempt the pitch of the conveyor in the region of the beach has been reduced as compared to the pitch of the conveyor in the clarifying zone of the bowl. In order to achieve discharge of solids at the desired rate the rotation of the conveyor has been speeded up. While to some extent such an attempt has been successful in that the torque has been reduced somewhat, the efficiency of the device as a clarifier has been impaired.
I have concluded that the cause for the impairment of clarification results in prior art attempts is the mixing action due to the increased speed of the conveyor in the clarification zone. The liquid close to the conveyor flight will always tend to be at the rotational speed of the conveyor while the liquid betweenthe flights tends to be at the rotational speed of the bowl. The greater the difference in speed between conveyor and bowl the greater the difference in centrifugal force between the liquid next to the flights and that between the flights. This difference gives rise to secondary flows that in turn cause remixing of already settled solids. Naturally, the greater the differential speed the more violent the remixing.
Under the present invention I provide a conveyor having at least a pair of coaxial helical conveyors or conveyor sections. The first is a section preferably of relatively high pitch which is rotated at low speed and is disposed in the clarification section of the bowl. By rotating at low speed relative to the bowl the first section induces a minimum amount of secondary flow in the liquid and minimizes remixing of solids. The second section located intermediate the first section and the solids discharge port moves the solids up the inclined beach. It is rotated at a relatively high speed relative to the bowl in the first section, but may be of low pitch to avoid the development of high torques.
It is an object, therefore, of the present invention to provide a solids discharge bowl conveyor means having at least a pair of helical conveyor sections, one in the clarification zone and rotating at relatively low speed but preferably of high pitch, and the other preferably of relatively low pitch intermediate the first section and the solids discharge port, and being rotated at relatively high speed with respect to the bowl. The overall effect is reduced torque and better clarification.
Another object of the invention is to provide a structure in such a centrifuge by which the relative speeds of the conveyor sections may be changed easily.
Other objects and features of the invention will be apparent to those skilled in the art upon review of the following specification including drawings wherein:
FIGURE 1 is a fragmentary view, partly in section, showing an apparatus embodying the invention;
FIGURE 2 represents schematically a power diagram of an apparatus embodying the invention;
FIGURE 3 includes views of diagrammatic nature and showing relative speeds of the component of an apparatus embodying the invention;
FIGURE 4 is an enlarged fragmentary sectional view showing a portion of FIGURE 1;
FIGURE 5 is a reduced fragmentary sectional view taken on the line 55 of FIGURE 4; and
FIGURE 6 is similar to FIGURE 4 but showing an alternative arrangement of the gearing.
Referring more specifically to the drawings, an apparatus embodying the invention is shown in FIGURE 1 and generally designated 10. It comprises a bowl 12' having a liquid discharge port 14 and a solids discharge port 16. Mounted for relative rotation within the bowl are solids conveying means comprising a first helical conveyor or first conveyor section 18 and a second helical conveyor or second conveyor section 20. A feed tube 22 extends axially into the bowl and is adapted to deliver feed mixture to the interior of the second conveyor section 20.
The vanes 24 accelerate the feed mixture which passes into the bowl through the opening 26 in the conveyor section 20'.
Secured to the end of the bowl 12 is the gear box 28, the inside wall of [Which is formed with a pair of ring gears 30 and 32. Engaging the ring gears are groups of planet gears 34 and 36 respectively. The planet gears, mounted in their respective carriers 38 and 40 engage central sun gears 42 and 44, respectively.
As is conventional, the sun gear 42 of the first stage planetary system has a shaft 46 extending outward of the machine through the hollow hub 48. Drive power for the centrifuge may be applied to hub 48. The shaft 46 may be either held stationary by a conventional torque control device or may be driven in rotation at varying speeds to control conveyor differential speed.
The sun gear 44 is connected through boss 50 to the planet carrier 38 of the first stage, while the carrier 40 for the second stage is secured to the drive spindle 52.
The leftward end (FIGURE 1) of the drive spindle is connected to the hub 54, in turn secured to the second conveyor section 20 which is mounted on appropriate bearings. The first conveyor section 18 is mounted to rotate about the hub 54.
An inward spindle block 56 is secured to the bowl 12 and provided with internal bearings which rotatably mount the spindle 52.
Splined to the spindle 52 is a sun gear 58. This comprises the third stage of planetary gears with the planet gears 60 secured in FIGURES 1 and 4 to the spider 62. The spider 62, rotatably mounted on spindle 52, extends leftward and mounts a splined hub 64 which is secured to the first conveyor section 18.
The other element of the third stage planetary system is the ring gear unit 66 which is secured for rotation to the block 56 which rotates with the bowl 12.
FIGURE 6 discloses a variation in structure of the third stage planetary system. In this variation the planet gears 3 60' engage the central sun gear 58 as in the FIGURE 4 embodiment, but themselves are secured for rotation with the block 56'. The ring gear 66' as in the FIGURE 6 embodiment secured to the spider 62 which is splined to the hub 64 to drive the second conveyor section 1 8 at the speed of the ring gear.
An element schematic diagram of the gear trains is provided in FIGURE 2. In that figure the reference numerals used in the other figures are used to designate corresponding parts, but to avoid confusion each numeral in FIG- URE 2 is succeeded by the letter a. In FIGURE 2 the solids lines shown going to the components with the third stage planetary system represent the arrangement as shown in FIGURE 4. The dotted lines schematically represent the arrangement shown in FIGURE 6.
FIGURES 3A and 3B in simplified diagrammatic form represent embodiments of the conveyor sections and show exemplary rotations relative to the bowl. These figures demonstrate the flexibility of the assembly to different speed requirements. For instance, in FIGURE 3A a first conveyor section having a right-hand thread may be made to rotate faster by, for instance, 20 r.p.rn. than the bowl speed. The lower pitch second conveyor section having a left-hand thread may rotate 80 r.p.rn. slower that the bowl. In the version of FIGURE 3B the high pitch righthand thread first conveyor section may rotate 2O r.p.rn. slower than the bowl while the second conveyor section may rotate 80 r.p.rn. slower than the bowl.
Referring once again to FIGURE 4, the arrangement shown may be converted into the arrangements similar to FIGURE 6 to significantly affect the speed at which the second conveyor section is driven. As shown in FIGURE 4 the block 56 rigidly mounts the annular ring gear drive plate 80 to which in turn is secured the ring gear unit 66. The individual planet gears 60 are actually mounted to rotate about the hubs 82 which are secured to the spider 62 by a central pin and bolts as shown.
In the FIGURE 6 embodiment the block 56 rigidly mounts the annular planet gear drive plate 90 which in turn secures the housing 92. Each of the planet gears 60" as with the other shown embodiment is actually annular and mounted to rotate about respective hubs 94 which may be secured to the plate 90 by central pins and bolts as shown. The ring gear 66' is secured to the spider 62 to transmit the ring gear rotation to the first conveyor section.
Under the construction shown the speed of the first conveyor section can be easily changed by replacing the plate mounted on the block 56, turning the planet gears end-for-end and modifying the spider 62 as necessary to secure the planets or the ring gear.
Examples of difference in rotation of the first conveyor system using the alternative arrangement in FIGURE 4 and FIGURE 6 will give a further grasp of the significance of the arrangement. Assuming that the spindle 52 is rotating 24.5 r.p.rn. relative to the bowl when the latter running at 4000 r.p.rn., the conveyor section 20 will have an absolute rotation of 3975.5 r.p.rn.
When the third planetary stage which drives the conveyor section 18 has its output from the planet gears as shown in FIGURE 4, the planet gear ratio will give the first conveyor section a speed of about 6.1 r.p.rn. relative to the bowl with an absolute r.p.rn. of 3993.9.
When the output of the third stage comes from the ring gear as disclosed in FIGURE 6, the spindle speed will be reduced by a ratio of 3 to 1 so that the speed of the conveyor section 18' will be 8.2 r.p.rn. or 4008.2 r.p.m. absolute.
As another example, if the speed of the spindle 52 were 77 r.p.rn. less than the bowl speed, the conveyor section 18 would have an r.p.rn. of 19.2 less than the bowl, or 25.6 more than the bowl depending on whether the FIG- URE 4 or FIGURE 6 arrangement is employed.
An essential element of the invention resides in structure which permits a conveyor arrangement in a solid bowl centrifuge with conveyor means comprising at least two sections which may be driven at different speeds, the differential between bowl and the conveyor sections in the clarifying zone of the bowl being less than the differential between the bowl and the conveyor section of the beach section of the bowl. By this means solids may be moved at the desired rate up the beach by a relatively high conveyor differential with corresponding reduced torque. At the same time the relatively slow differential of the conveyor section in the clarifier zone permits effective settling of the solids in that zone with a minimum of turbulence and remixing.
While in its preferred embodiments the invention employs conveyor sections of different pitch as related above, with the first conveyor section being of greater pitch than the second conveyor section, many benefits of the invention can be enjoyed by having the conveyors of the same pitch.
It should also be understood that while the means for driving the components of the apparatus disclosed are in the form of planetary gear systems, other means of driving are envisioned. For instance, hydraulic torque motors, hybrids of gears and torque motors and planetary chain sprocket drives as well as other means are contemplated.
Thus while this invention has been shown in but limited forms, it will be obvious to those skilled in the art that it is not so limited but is susceptible to various changes and modifications without departing from the spirit and scope of the claimed invention.
1. A solids discharge centrifuge comprising a bowl having a feed mixture inlet, a solids dicharge port and a liquid discharge port adjacent opposite ends of the bowl respectively, solids conveying means within the bowl, the solids conveying means including at least a pair of helical conveyors having different pitch disposed substantially on the axis of the bowl and both adapted to move solids generally in the same longitudinal direction of the bowl toward the solids discharge port, the second helical conveyor be- I ing disposed intermediate the first helical conveyor and the solids discharge port, said second helical conveyor having a lower pitch than said first helical conveyor, and means for driving the first helical conveyor and the second helical conveyor at different speeds of rotation with respect to the bowl, with said second helical conveyor being driven at an appreciably higher speed than said first helical conveyor.
2. A solids discharge centrifuge as described in claim 1 wherein the first and second helical conveyors are of different hand thread, said driving means driving said first and second helical conveyors in opposite directions of rotation.
3. A solids discharge centrifuge as described in claim 1 wherein the first helical conveyor and the second helical conveyor are connected respectively to elements of a planetary system comprising a sun gear element, a ring gear element and a planet gear element, the other element being connected to the centrifuge bowl.
4. A solids discharge centrifuge as described in claim 3 wherein the first helical conveyor is connected to the ring gear element.
5. A solids discharge centrifuge as described in claim 3 wherein the first helical conveyor is connected to the planet gear element.
References Cited UNITED STATES PATENTS 2,703,676 3/ 1955 Gooch 233- 7 3,282,497 11/1966 Schmiedel 233-7 FOREIGN PATENTS 876,531 8/1942 France.
95,753 l/1898 Germany.
M. CARY NELSON, Primary Examiner. HENRY T. KLINKSIEK, Examiner.