Note: Descriptions are shown in the official language in which they were submitted.
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B~ckground of the Invention
Modern sewage treatment plants are fre~uently 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
suf~iciently 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
of a food mlxer 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 continuously for week-s 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
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be impervious to;the wide variety of chemicals anticipated
30 ~ in ~aw sewage.
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The aforementioned problems are overcome and other advantages are
; provided by a sewage blender which, in accordance with the invention there
is provided, 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 abra-
sive surfaces thereof, said surfaces being of similar geometric form to per-
~; mit 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 abra-
I sive surfaces~ said first and second members being spaced apar~ a distance
j sufficient to admit entry of the substances in said class of substances be-
1i tween said first and said second abrasive surfaces; and
~I said first abrasive surface being composed of an abrasive ceramic material
having pores therein, said pores being of varying dimensions, smaller ones
1 of said pores being interleaved among larger ones of said pores, said abras-
ive ceramic material being harder than said metal of said raw sewage to per-
~ 20 mit a grinding thereof, said abrasive ceramic material being structured to ~ .
I permit a breaking off of particles thereof in response to pressure exerted
.I between said first and said second members by a pebble of raw sewage entrap-
ped between said first and said second members, said larger pores being suf- .
. ficiently large to prevent glazing by said plastic material, there being a
! sufficient number o-f said smaller pores between said larger pores having
cutting edges for grinding said hair-like fibrous material.
¦ There is further provided a blender for grinding a mixture of sub-
stances drawn from the class of substances found in raw sewage, said ~l~ss -~
~ of substances including pebbles, metal, hair-like fibrous material and plas~
! 30 tic material~ said blender comprising:
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first and second grinding members having respectively first and second abra-
sive surfaces thereof, said surfaces being of similar geometric form to per-
mit 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 matterbetween said first and said second abra-
sive surfacesg said first and said second mémbers being spaced apart a dis-
tance 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 suffic- ~ `
iently large to prevent glazing by said plastic material, there being a suf-
ficient number of said smaller pores between said larger pores to permit
grinding of said hair-like fibrous material of said raw sewage. ``
The invention, more specifically, provides for two ceramic grind-
stones nested within each other and spaced apart along their nesting surface -
by relatively small distances typically in the range of 0.5-5 one-thousandths
of an inch. Each grindstone is fabricated from 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 materia~ is capable of grinding metal-
lic objects found within the raw sewage as well as objects of softer materi-
als since, as is well known, the abrasive material utilized in these grind-
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stones is commonly used for shaping metallic implements as in a milling oper-
ation. Material such as string, hair and animal by-products 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 grindstonesO A vary-
ing porosity is utilized such that the sizes of the pores between the fused
particles of abrasive material varies from 1% to 35% in the ratio(~of the vol-
ume of the material of the grindstone. At the mating surface between the
two grindstones, a maximum pore size having a diagonal of approximately
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one-quarter 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
further mitigate against any glazing of the surfaces. The
ceramic material utilized in the grindstones provides a
lower coefficient of thermal expansion and greater dimen-
sional stability than lS 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 build-up of heat asso-
ciated with metallic grinding elements. Accordingly~ no ;
external source of cooling is required with this sewage
blender. The inlet port is free of any elongated pro- ~
tuberances such as cutting blades~ veins, or struts -
thereby preventing the entanglement of fibrous materials
j 20 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.
`1 In the preferred embodiment of the invention, an inner
`~ and an outer grindstone are utilized with the inner grind-
,:
stone having an external frusto-conical surface while the
~ outer grindstone has an internal frusto-conical surface
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which mates with the corresponding surface of the inner
! 30 grindstone. The two grindstones are positioned about a
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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 partlcles of sewage material which are
passed betl~een the mating surfaces. The height of the rotor
as measured along its axis is suf-ficiently 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:
Figure 1 is an elevation view, partially cut away and
sectionedJ of the blender in accordance with the invention~
the figure further including means for rotating the rotor
of the blender and for positioning the rotor along its axis
relative to the stator;
Figure 2 is an enlarged view of the rotor and stator
grindstones oE the blender of Figure 1~ and
, Figure 3 is a block diagram of a sewage analysis system
incorporating the blender of Figure 1.
Description of the Preferred ~mbodimeDt ~ -
Re-ferring now to Figure 1, there is seen a blender
system 20 incorporating a blender 22, a motor 24 which
drives the blender 20 through a flexibl~e 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.
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The motor 24 and the bearing assembly 28 are affixed to a
rack 34 having a rail 36 along its bottom edge which
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slidably mates l.~ith a support 38 which is mounted upon the
base 32. ~he 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 threadedly 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 Imarts rotation of the shaft 30 to the
collar 56 and the rotor grindstone 54. The key 58 is secured ~:
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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 52 and 54. In additîon, 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 eq~al to its maximum diameter - ~ .
: which, in turnJ is preferably equal to the diameter of the .~
.
~; front end of the rotor grindstone 54. The case 48 is
. provided with a port 72 7.:~hich includes a section of pipe :-.; :
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30 74 secured to the case 48 via a gasket 76 and serves as
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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
~atertight. 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 substantia:lly inert to the materials found in raw
sewage. The stator and rotor grindstones 52 ancl 54 are
fabricated from an inert abrasive material such as alpha-
type aluminum oxide or silicon carbide utilizing a grit
size preferab]y in the range 40-60 mesh. A large variety
of pore sizes exist among the abrasive particles 9 the
pore size ranging from 1%-35% ratio in the volume of the
pores to a unit volume of the grindstone material. A
diagonal of t]ie largest pore measures approximately
one-quarter inch in length. The particles of the abrasive
are preferably bonded together by a fusing process to pro-
vide 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 Devcon
Corporation of Danvers, Massachusetts. 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
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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
52 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 70 is retained during a period of from
one to three weeks after which the wearing o~ the grindstones
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52 and 54 has progressed to the point where the gap is
excessively wide. Accordingly, adjustments of the gap by
10 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 grind-
stone 54 to compensate for this wearing of the grindstones.
For example, the motor 42 may be a stepping motor which is
pulsed periodically or whenever the blender output shows
excessively large particles.
As sèen in Figure 2, a large proportion of the surface ~:
area of the stator grindstone 52 snd of the rotor grindstone
54 is void of abrasive material, these voids or pores 86
20 being seen on both the rotor grindstone 54 and, in the
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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 Allen-head wrench for tightening
the screw 64. Thus there are no corners or projections upon ~ ;
which fibrous materials can tangle. It is interesting to
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note that, in sn 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 ~ ;
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54 in the belief that such a cutter assembly would ~ -
facilitate the breaking down of long fibrous materials ~
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such as hair and thread into small particles. ~lowever, in
experimental tests conducted at the sewage treatment plant
at Cranston, Rhode Island, 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 su-fficiently small
particlesg less than approximately 100 micron diameter,
which can remain in suspension for approximately one-half
hour. This one-half 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 Figure 3 there is seen a typical ;
analyzer system 90 incorporating the blender system 20 of
Figure 1. 'I`he 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
, 20 tank 92, and an analyzer 9g 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
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maintaining a sufficlent pressure to urge the sewage
` material through the blender system 20.
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In the preferred embodiment of the invention, the
width of the gap between the rotor grindstone 54 and the
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stator grindstone 52 is.approximately one/four-thousandths
(.00025) inch) the rotor ~rinds-tone 54 rotates at 3600 ''' '
revolutions per rninute, and the pump 96 is a centrifugal
pump delivering liquid sewage at a ~low rate of six gallons
per minute at a line pressure of 40 pounds per square inch
to the blender 22. The outer diameter Or the rotor grindstone
54 varies from approximately one and one-half inches to two
inches, and the axial length of the rotor grindstone 54 is
approximately one inch.
With respect to the pores 86 of Figure 2, it is noted -
that the larger pores serve the function of clearing the
surfaces of the grindstones 52 and 5~ particularly from
the glazing effect of plastic type materials which become ': '
embedded in the smaller pores producing a sm'ooth, non-
grinding 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 metalllc 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 continu- ~
ously refurbishes its grinding surfaces. That portion of ~'
the abrasive material having the small sized pores serves ;
the function of grinding and slIearing metallic~ ceramic9
plastic, vegetable and mineral mat'erial. In the preferred
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embodiment of the invention, the small pores and the large
pores are arranged in a random fashion5 however, it is ''
believed tha~ differing arrangements of these pores will
` produce good results if the variously sized pores are
arranged fairly uniformly wlthin the abrasive materials
of the rotor and stator grindstones 54 and 52.
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It ;s understood that the above-described embodiment
of the invention is illustrative only and that modifications
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.
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