US3904137A

US3904137A - Sewage grinder

Info

Publication number: US3904137A
Application number: US550068A
Authority: US
Inventors: Gilbert E Anderson; George V Morris
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 1974-02-07
Filing date: 1975-02-14
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

A blender having two nested grindstones which meet along a frusto-conical surface and rotate with respect to each other about their common axis. The grindstones are of rough textured ceramic having perforations as large as 1/4 inch at the surface of each grindstone. Abrasion of the sewage material against the stones introduces new perforations and cutting edges. The design of the grindstones inhibits the clogging of the stones by metallic, ceramic, or plastic objects found in sewage and also inhibits jamming of the blender by long fibrous materials.

Description

United States Patent [191 Anderson et al.

[ SEWAGE GRINDER [75] Inventors: Gilbert E. Anderson, Fall River.

Mass; George V. Morris, Riverside, RI.

[731 Assignee: Raytheon Company. Lexington,

Mass.

[22] Filed: Feb. 14, l975 [2|] Appl. No.: 550,068

Related US. Application Data [63] Continuation of Ser. No. 440.439. Feb. 7, I974.

abandoned.

[52] US. Cl. Z4l/259J; 24l/26Ll; 24l/293; 241/299 [5 l] Int. Cl. 1302C 2/00 [58] Field of Search 24l/242. 251.2591, 260. 24l/26l.l, 261.2, 26l.3, 29]. 293. 299

[56] References Cited UNITED STATES PATENTS l.863,l84 6/l932 Brazeay ct al. 241/2591 2.l20.697 6/l938 Finnegan 24l/26l.l 2.306.672 l2/l942 Tuckcr.... 24l/259.l 3.160.355 l2/l964 Chiaverina.. 24l/29l 3.297.262 1/1967 Skardal .i 241/242 X Sept. 9, 1975 3369.763 2/[968 Perry 241/293 3.5l4.079 5/1970 Littlc. Jr. 24l/26l.l X 3.614.826 lO/l97l Pilao 24l/293 OTHER PUBLlCATlONS Hafer, C. H., Toner Brick Grinding; IBM Bulletin, Vol. 12, No. 6, p. 777. Nov. l968.

Primary Examiner-Granville Y. Custer, .lr. Assistant Examiner-Howard N. Goldberg Attorney, Agent, or Firm-David M. Warren; Joseph D. Pannone; Milton D. Bartlett 5 7 ABSTRACT A blender having two nested grindstones which meet along a frusto-conical surface and rotate with respect to each other about their common axis. The grindstones are of rough textured ceramic having perforations as large as A inch at the surface of each grindstone. Abrasion of the sewage material against the stones introduces new perforations and cutting edges. The design of the grindstones inhibits the clogging of the stones by metallic. ceramic, or plastic objects found in sewage and also inhibits jamming of the blender by long fibrous materials.

15 Claims. 3 Drawing Figures SEWAGE GRINDER This is a continuation of application Ser. 440,439, filed Feb. 7, 1974, abandoned.

BACKGROUND OF THE INVENTION Modern sewage treatment plants are frequently provided with apparatus for performing chemical analyses of the component materials of raw sewage. Preparatory to performing such analyses, the sewage material must be broken up into fine particles which will remain in suspension for a sufficiently long period of time to permit such analyses; premature settling of these materials will render the analyses incorrect.

A problem arises in that the pulverizing or grinding of the materials in raw sewage entails the grinding of a wide variety of objects ranging from fecal matter. string, hairs and other fibrous materials to objects of plastic, sand and cellulose. It is recognized that blenders have been used in the food and chemical industries for many years in blending food ingredients such as those in mayonnaise, and the hard pigments utilized in paint making. These blenders range in structure from the bladed structure ofa food mixer to a serrated, hardened steel mill for relatively hard materials. Such blenders are typically of the batch-type which admits a limited quantity of material at any one time. However. none of these blenders is required to process the wide variety of materials found in raw sewage, nor are they required to operate conntinuously for weeks and months at a time without being clogged or jammed by these materials or breaking down from overheating. In addition, it is recognized that a sewage blender may be required to run whether or not the liquid of the sewage is present, and must be impervious to the wide variety of chemicals anticipated in raw sewage.

SUMMARY OF THE INVENTION The aforementioned problems are overcome and other advantages are provided by a sewage blender which, in accordance with the invention, comprises two ceramic grindstones nested within each other and spaced apart along their nesting surface by relatively small distances typically in the range of 0.5 oncthousandths of an inch. Each grindstone is fabricated fl) m an abrasive material such as alpha-type aluminum oxide or silicon carbide. The grit size of the abrasive material is in the range of 40-60 mesh pursuant to the ASME (American Society of Mechanical Engineers) Standard. This material is capable of grinding metallic objects found within the raw sewage as well as objects of softer materials since, as is well known, the abrasive material utilized in these grindstones is commonly used for shaping metallic implements as in a milling operation. Material such as string, hair and animal byproducts are readily dispersed into fine particles by the abrasive material of these grindstones. The surface of one grindstone is made to move past its mating surface in the other grindstone, and inlet and outlet ports are provided for passing the raw sewage between these mating surfaces.

The particles of the abrasive material utilized in the grindstones are vitrified or fused together to form the individual grindstones. A varying porosity is utilized such that the sizes of the pores between the fused particles of abrasive material varies from I?! to in the ratio of the volume of the pores to a unit volume of the material of the grindstone. At the mating surface be tween the two grindstones, a maximum pore size having a diagonal of approximately A inch is present. This non-uniform porosity including the presence of the maximum size pores prevents a glazing of the mating surfaces by the presence of objects of plastic materials in the raw sewage. The rubbing of the grindstones against pebbles and other hard materials that may be found in the raw sewage breaks away particles of the abrasive material to expose new cutting surfaces to fur ther mitigate against any glazing of the surfaces. The ceramic material utilized in the grindstones provides a lower coefficient of thermal expansion and greater dimensional stability than is found with blenders utilizing steel grinding elements, thereby permitting a spacing as small as a few ten-thousandths of an inch between the grindstones without the excessive buildup of heat associated with metallic grinding elements. Accordingly, no external source of cooling is required with this sewage blender. The inlet port is free of any elongated protuberances such as cutting blades, veins. or struts thereby preventing the entanglement of fibrous materials such as hair and string to ensure that there is no jamming or clogging of the blender due to such entanglement. It is also noted that the abrasive materials utilized in the grindstones are chemically inert with the substances found in raw sewage.

In the preferred embodiment of the invention. an inner and an outer grindstone are utilized with the inner grindstone having an external frusto-conical surface while the outer grindstone has an internal frusto conical surface which mates with the corresponding surface of the inner grindstone. The two grindstones are positioned about a common axis with the inner grindstone being nested into the outer grindstone. The outer grindstone serves as a stator and remains stationary while the inner grindstone acts as a rotor and is rotated about their common axis to provide for a grinding action of particles of sewage material which are passed between the mating surfaces. The height of the rotor as measured along its axis is sufficiently great to provide for an adequate retention time between the mating surfaces of sewage particles passed between these surfaces.

BRIEF DESCRIPTION OF THE DRAWINGS The aforementioned features and other aspects of the invention are explained in the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is an elevation view, partially cut away and sectioned, of the blender in accordance with the invention, the figure further including means for rotating the motor of the blender and for positioning the rotor along its axis relative to the stator;

FIG. 2 is an enlarged view of the rotor and stator grindstones of the blender of FIG. I', and

FIG. 3 is a block diagram of a sewage analysis system incorporating the blender of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is seen a blender system 20 incorporating a blender 22, a motor 24 which drives the blender 20 through a flexible coupling 26, and a bearing assembly 28 which positions a shaft 30 of the blender 22. The blender 22 is mounted on a base 32. The motor 24 and the bearing assembly 28 are affixed to a rack 34 having a rail 36 along its bottom edge which slidably mates with a support 38 which is mounted upon the base 32. The rack 34 is slidably positioned by means of a drive screw 40 which is rotated by a motor 42.

The blender 22 comprises a back plate 44, a front plate 46 and a cylindrical case 48 which are coupled together by means of bolts 50 which pass through holes in the front plate 46 and the case 48 to be threadcdly secured into the back plate 44. A stator grindstone 52 is adhesively secured to the front plate 46 and a rotor grindstone 54 is adhesively secured to a collar 56 which is affixed to the shaft 30. A key 58 placed within a slot in the collar 56 and within a slot in the shaft 30 imparts rotation of the shaft 30 to the collar 56 and the rotor grindstone 54. The key 58 is secured within the collar 56, and the collar 56 is pressed against a shoulder 60 of the shaft 30 by means of a sleeve 62 urged against the end of the shaft 30 by means of a screw 64 passing through the center of the sleeve 62 and threadedly secured in the end of the shaft 30.

The front plate 46, the case 48 and the back plate 44 together form a housing which encloses the stator and rotor grindstones S2 and 54. In addition, the front plate 46 is provided with an inlet port 66 having an interior portion which is flared into an anterior chamber 68 via which raw sewage is applied to the interface 70 between the stator and

rotor grindstones

52 and 54. The axial length of the chamber 68 is approximately equal to its maximum diameter which, in turn, is preferably equal to the diameter of the front end of the rotor grindstone 54. The case 48 is provided with a port 72 which includes a section of pipe 74 secured to the case 48 via a gasket 76 and serves as the exit port for sewage which has been processed by the blender 22. Gaskets 78 are placed between the case 48 and the front and

back plates

46 and 44 to make the housing watertight. In addition, a seal 80 is placed within the back plate 44 around the shaft 30 and compressed by means of a spring 82 which pushes against the collar 56 to inhibit the seepage of liquid through the back plate 44.

The back and

front plates

44 and 46 and the case 48 are fabricated from a metal such as stainless steel which is substantially inert to the materials found in raw sewage. The stator and

rotor grindstones

52 and 54 are fabricated from an inert abrasive material such as alphatype aluminum oxide or silicon carbide utilizing a grit size preferably in the range 4060 mesh. A large variety of pore sizes exist among the abrasive particles, the pore size ranging from l%-35% ratio in the volume of the pores to a unit volume of the grindstone material. A diagonal of the largest pore measures approximately /4 inch in length. The particles of the abrasive are preferably bonded together by a fusing process to provide a vitrified grindstone. The securing of the stator and

rotor grindstones

52 and 54 respectively to the front plate 46 and the collar 56 is accomplished by means of a ceramic to metal adhesive such as an aluminum putty sold under the trade name Devcon which is made by the Deveon Corporation of Danvers, Mass. The securing of the blender 22 to the base 32 is accomplished by bolting the back plate 44 to the base 32 by bolts 84; the support 38 and the motor 42 are similarly secured to the base 32.

In operation. therefore, the rotor grindstone 54 is made to rotate by the motor 24. Rotation of the drive screw 40 by the motor 42 advances the shaft 30 along its axis for adjusting the gap between the stator and rotor grindstones S2 and 54 at the interface 70. It has been found that, during the processing of raw sewage by the blender 22, the gap at the interface is retained during a period of from 1 to 3 weeks after which the wearing of the grindstones S2 and 54 has progressed to the point where the gap is excessively wide. Accordingly, adjustments of the gap by the motor 42 is required only once every few weeks, or alternately, the motor 42 may be operated at a very low rotation rate for gradually repositioning the rotor grindstone 54 to compensate for this wearing of the grindstones. For ex ample, the motor 42 may be a stepping motor which is pulsed periodically or whenever the blender output shows excessively large particles.

As seen in FIG. 2, a large proportion of the surface area of the stator grindstone 52 and of the rotor grindstone 54 is void of abrasive material, these voids or pores 86 being seen on both the rotor grindstone 54 and, in the cut-away view, also seen in the stator grindstone 52. The head of the screw 64 is seen to be rounded and to have a cavity 88 adapted to fit an Allenhead wrench for tightening the screw 64. Thus there are no corners or projections upon which fibrous materials ean tangle. It is interesting to note that, in an earlier experimental model of the blender 22, a pinwheel shaped cutter was placed within the anterior chamber 68 and attached to the end of the rotor grindstone 54 in the belief that such a cutter assembly would facilitate the breaking down of long fibrous materials such as hair and thread into small particles. However, in experimental tests conducted at the sewage treatment plant at Cranston, R.I., an accumulation of fibrous materials built-up on the cutter assembly; accordingly, that cutter assembly was discarded. Furthermore, the rotor grindstone 54 and the stator grindstone 52, by themselves, were seen to adequately perform the grinding and blending of particulate matter in raw sewage into sufficiently small particles, less than approximately 100 micron diameter, which can remain in suspension for approximately /z hour. This /2 hour suspension time is more than adequate to ensure that the particles may be processed by a sewage analyzer without settling out before the analysis is completed.

Referring now to FIG. 3 there is seen a typical analyzer system 90 incorporating the blender system 20 of FIG. 1. The analyzer system 90 is seen to comprise a settling tank or a sewage aeration tank 92, a cutter 94 and a pump 96 submerged within the liquid of the aeration tank 92, and an analyzer 98 coupled to the output of the blender system 20 for providing a chemical analysis of the finely blended sewage material emanating from the blender system 20. The cutter 94 breaks up chunks of sewage matter into sufficiently small portions which can be processed by the blender system 20, the pump 96 pumping these small portions into the blender system 20 and for maintaining a sufficient pressure to urge the sewage material through the blender system 20.

In the preferred embodiment of the invention, the width of the gap between the rotor grindstone 54 and the stator grindstone 52 is approximately one/fourthousandths (0.00025) inch; the rotor grindstone 54 rotates at 3600 revolutions per minute, and the pump 96 is a centrifugal pump delivering liquid sewage at a flow rate of 6 gallons per minute at a line pressure of 40 pounds per square inch to the blender 22. The outer diameter ofthe rotor grindstone 54 varies from approximately 1 inches to 2 inches, and the axial length of the rotor grindstone 54 is approximately 1 inch.

With respect to the pores 86 of FIG. 2, it is noted that the larger pores serve the function of clearing the sur faces of the

grindstoncs

52 and 54, particularly from the glazing effect of plastic type materials which become embedded in the smaller pores producing a smooth, nongrinding surface. In addition, it is noted that the

grindstones

52 and 54 are of a solid abrasive material rather than merely a deposition of such abrasive material upon a metallic substrate. The use of the solid abrasive material permits the wearing away of such material to introduce new cutting edges so that the blender 22 continuously rcfurbishes its grinding surfaces. That portion of the abrasive material having the small sized pores serves the function of grinding and shearing metallic, ceramic, plastic, vegetable and mineral material. In the preferred embodiment of the invention. the small pores and the large pores are arranged in a random fashion. however, it is believed that differing arrangements of these pores will produce good results if the variously sized pores are arranged fairly uniformly within the abrasive materials of the rotor and

stator grindstones

54 and 52.

It is understood that the abovedescribed embodiment of the invention is illustrative only and that modi fications thereof will occur to those skilled in the art. Accordingly, it is desired that this invention is not to be limited to the embodiment disclosed herein but is to be limited only as defined by the appended claims.

We claim:

1. A blender for grinding a mixture of substances drawn from the class of substances found in raw sewage, said class of substances including pebbles, metal, hair-like fibrous material and plastic material, said blender comprising:

first and second grinding members having respectively first and second abrasive surfaces thereof, said surfaces being of similar geometric form to permit the nesting of said first member within said second member;

means for moving one of said abrasive surfaces relative to the other of said abrasive surfaces;

means for guiding particulate matter between said first and said second abrasive surfaces, said first and said second members being spaced apart a distance sufficient to admit entry of the substances in said class of substances between said first and said second abrasive surfaces; and

said first abrasive surface being composed of an abrasive ceramic material having pores therein, said pores being of varying dimensions, smaller ones of said pores being interleaved among larger ones of said pores, said abrasive ceramic material being harder than said metal of said raw sewage to permit a grinding thereof, said abrasive ceramic material being structured to permit a breaking off of particles thereof in response to pressure exerted between said first and said second members by a pebble of said raw sewage entrapped between said first and said second members, said larger pores being sufficiently large to prevent glazing by said plastic material, there being a suffieient number of said smaller pores between said larger pores having cutting edges for grinding said hair-like fibrous material.

2. A blender according to claim 1 wherein the largest of said pores is greater than the smallest of said pores by a factor of at least 10:1.

3. A blender according to claim 2 wherein said sec ond abrasive surfaces comprises an abrasive material having a varying porosity.

4. A blender according to claim 3 wherein one of said abrasive surfaces is a frusto-conical surface and the second of said abrasive surfaces mates with said frustoconical surface.

5. A blender according to claim 4 wherein said moving of said one of said abrasive surfaces is a rotation about the axis of said frusto-conical surface.

6. A blender according to claim 5 wherein said guiding means includes a chamber anterior to said rotating surface and means for providing a hydrostatic pressure within said chamber.

7. A blender for grinding a mixture of substances drawn from the class of substances found in raw sewage, said class of substances including pebbles, metal, hairlike fibrous material and plastic material, said blender comprising:

first and second grinding members having respectively first and second abrasive surfaces thereof. said surfaces being of similar geometric form to permit the nesting of said first member in said sec ond member;

means for positioning one of said mcmbc rs relative to the other of said members;

means for rotating one of said members relative to the other of said members;

means for guiding particulate matter between said first and said second abrasive surfaces, said first and said second members being spaced apart a distance sufficient to admit entry of a substance in said class of substances between said first and said second abrasive surfaces; and

said first abrasive surfaces being composed of an abrasive ceramic material having pores therein, said pores being of varying dimensions, smaller ones of said pores being interleaved among larger ones of said pores, said abrasive ceramic material being harder than said metal of said raw sewage to permit a grinding thereof, said abrasive ceramic material being structured to permit a breaking off of particles thereof in response to pressure exerted between said first and said second members by a pebble of said raw sewage entrapped between said first and said second members, said larger pores being sufficiently large to prevent glazing by said plastic material, there being a sufficient number of said smaller pores between said larger pores to permit grinding of said hair-like fibrous material of said raw sewage.

8. A combination according to claim 7 wherein said positioning means includes means for adjusting the position of one of said members relative to the other of said members.

9. A combination according to claim 8 further comprising means for urging fluid between said abrasive members.

10. A combination according to claim 9 wherein one of said abrasive members has an exterior frusto-conical surface and a second of said abrasive members has an internal frusto-eonical shape which is matcable with said first frusto-conical shape.

14. A combination according to claim 10 wherein said positioning means further comprises a chamber anterior to said rotating member, the length of said anterior chamber approximating its width.

15. A combination according to claim 14 wherein said rotating means includes means for attaching said rotating member to a rotatable shaft of said rotating means, said attaching means having an external surface free of protuberances which induce entanglement of fibrous materials.

Claims

1. A blender for grinding a mixture of substances drawn from the class of substances found in raw sewage, said class of substances including pebbles, metal, hair-like fibrous material and plastic material, said blender comprising: first and second grinding members having respectively first and second abrasive surfaces thereof, said surfaces being of similar geometric form to permit the nesting of said first member within said second member; means for moving one of said abrasive surfaces relative to the other of said abrasive surfaces; means for guiding particulate matter between said first and said second abrasive surfaces, said first and said second members being spaced apart a distance sufficient to admit entry of the substances in said class of substances between said first and said second abrasive surfaces; and said first abrasive surface being composed of an abrasive ceramic material having pores therein, said pores being of varying dimensions, smaller ones of said pores being interleaved among larger ones of said pores, said abrasive ceramic material being harder than said metal of said raw sewage to permit a grinding thereof, said abrasive ceramic material being structured to permit a breaking off of particles thereof in response to pressure exerted between said first and said second members by a pebble of said raw sewage entrapped between said first and said second members, said larger pores being sufficiently large to prevent glazing by said plastic material, there being a sufficient number of said smaller pores between said larger pores having cutting edges for grinding said hair-like fibrous material.

3. A blender according to claim 2 wherein said second abrasive surfaces comprises an abrasive material having a varying porosity.

4. A blender according to claim 3 wherein one of said abrasive surfaces is a frusto-conical surface and the second of said abrasive surfaces mates with said frusto-conical surface.

7. A blender for grinding a mixture of substances drawn from the class of substances found in raw sewage, said class of substances including pebbles, metal, hair-like fibrous material and plastic material, said blender comprising: first and second grinding members having respectively first and second abrasive surfaces thereof, said surfaces being of similar geometric form to permit the nesting of said first member in said second member; means for positioning one of said members relative to thE other of said members; means for rotating one of said members relative to the other of said members; means for guiding particulate matter between said first and said second abrasive surfaces, said first and said second members being spaced apart a distance sufficient to admit entry of a substance in said class of substances between said first and said second abrasive surfaces; and said first abrasive surfaces being composed of an abrasive ceramic material having pores therein, said pores being of varying dimensions, smaller ones of said pores being interleaved among larger ones of said pores, said abrasive ceramic material being harder than said metal of said raw sewage to permit a grinding thereof, said abrasive ceramic material being structured to permit a breaking off of particles thereof in response to pressure exerted between said first and said second members by a pebble of said raw sewage entrapped between said first and said second members, said larger pores being sufficiently large to prevent glazing by said plastic material, there being a sufficient number of said smaller pores between said larger pores to permit grinding of said hair-like fibrous material of said raw sewage.

10. A combination according to claim 9 wherein one of said abrasive members has an exterior frusto-conical surface and a second of said abrasive members has an internal frusto-conical shape which is mateable with said first frusto-conical shape.

11. A combination according to claim 10 wherein said rotating is accomplished about a common axis of said internal and external frusto-conical surfaces.

12. A combination according to claim 11 wherein a larger one of said pores of varying size is greater than a smaller one of said pores of varying size by a factor on the order of 35:1.

13. A combination according to claim 12 wherein said abrasive members are fabricated from the class of abrasive material consisting of aluminum oxide and silicon carbide.