Food processing machine

A meat grinder includes a bone chip remover in which the bone chips are removed at a radially outer region of the grinding plate through a single tangential opening substantially in the plane of rotation of the knife in response to intermittent operation of a valve. Knife blades which have substantial axial depth perpendicular to the plate are curved rearwardly to the direction of rotation, to apply an outward force component or pumping to chips which do not pass through the grinding plate, have terminal ends which sweep about a region radially outwardly of the perforated region of the plate, at a non-grinding or non-perforated region, behind which the chips are trapped and rotated about with the rotation of the knife blades for intermittent purging. The knife is formed with relieved areas at the radially inner ends of the blades to provide a region of communication, adjacent the grinding plate, between successive blades to prevent the formation of a central stagnation region and provide that bone chips missed by one blade may be acted upon by another to move chips outwardly.

BACKGROUND OF THE INVENTION 
This invention relates generally to food processing machines, such as a 
mixer-grinder, and more particularly to a meat grinder which incorporates 
a bone chip remover. 
Generally, meat grinders employed in the processing of beef, pork, veal or 
lamb are used to form a ground meat product from utility grade meat. 
Utility grade beef, for example, generally includes older animals, such as 
older cows or steers, or parts of the younger steers that cannot be used 
for the better cuts of beef. Generally, the choice cuts of animals raised 
for beef are not processed in the mixer-grinders to which the present 
invention applies. 
The meat cutters in large meat processing or meat packing plants are 
commonly paid in accordance with their production in removing the meat 
from the bones of slaughtered animals. As a result of the preparation of 
the meat, a certain amount of foreign material, most commonly gristle and 
bone particles or chips, finds its way into the meat product applied to a 
grinder. Where workers may be working at a piece rate, they may not be 
quite as careful in cutting the meat from the carcass and from the bones, 
and if they nick the bone with a knife, that piece of bone may ultimately 
finds its way into the grinder. For example, circular hand-held knives are 
used to remove meat from ribs, and if the cutter is not particularly 
careful, some bone may be removed along with the meat from the ribs and 
may find its way into a grinder. It has been estimated that, in larger 
meat processing houses grinding utility grade beef, approximately 1/10th 
of one percent (0.1%) of the meat product applied to grinders may consist 
of bone or bone chips. 
Large mixer-grinder machines capable of handling several hundred pounds a 
minute or more, are generally operated on a substantially continuous 
basis. Quite often, the meat is subject to a double grind with the first 
grind being applied to a plate having 1/2 (12.1 mm) or 3/8 inch (9.53 mm) 
openings therethrough to form a relatively coarse grind. Then this meat 
product is either immediately ground a second time in a second grinder to 
a final cut with holes about 1/8 of an inch (3 mm) diameter, or the meat 
product is applied to a mixer-grinder where it is mixed and blended with 
seasoning, fat, extenders or the like, and then ground at a final grinding 
plate having the smaller diameter holes. Thus, the burden falls upon the 
grinder having the finer or final plate to prevent the unwanted bone 
particles from getting into the final product. 
Not only is it undesirable to permit the bone particles to go through a 
grinder and ultimately into the final ground meat product, the presence of 
such particles, or excessive gristle, or other product which does not 
readily pass through the grinder plate severely degrades the productivity 
and capacity of the grinder. After a relatively short period of operation 
the capacity is reduced to the point where cleaning becomes necessary. 
Also, permitting the same to remain in the region of the grinder plate for 
any substantial period of time increases the likelihood that some of the 
bone chips will be reduced in size and passed through the plate, thus 
lowering the grade or quality of the ground meat. Thus, it is a customary 
practice in high capacity grinders, to stop the grinding operation after 
about twenty to thirty minutes of operation and clean out the collected 
bone chips, gristle and the like from the region behind the plate and 
about the knife. For example, a second grind at a grinder may initially 
produce approximately 280 lbs/min of ground meat product, but this will 
drop in about one-half hour's time to 230 or 240 lbs/min, depending upon 
the sharpness and quality of the cutting knife, the grinding plate, and 
the amount of fat, bone or gristle in the product. It becomes necessary to 
remove the grinding plate and clean out the bone chips and other 
particles. Running the grinder for a longer period of time increases the 
likelihood of cutting and grinding up the bones and passing them through 
the plate into the final product. Skilled laborers can thus clean out a 
grinding head in about five minutes down time, representing a loss of 
about ten minutes per hour or about a 15 percent loss of productivity. 
There have been a number of attempts to produce a bone chip remover for a 
meat grinder, or to incorporate bone chip removing apparatus into existing 
grinder constructions. A primary problem in designing such systems is 
caused by the difficulty of separating the bone chips and other 
undesirable components such as gristle, from the meat itself without 
suffering a substantial loss of valuable meat product. Thus, it has proved 
to be difficult to separate the entrained chips, which account for only a 
very small percentage of the total meat product, in an effective manner. 
Collection of bone chips, cartilage, gristle, sinews and fat in meat 
grinders tends to occur in large measure in the central region around the 
hub of the knife, immediately behind the plate. Whether this is the result 
of the much larger area at the outer periphery of the plate being open for 
the flow of meat therethrough or the likely greater force exerted by the 
outer flights of the grinder worm is not known. However, this congregation 
at the center of the plate has caused a number of parties seeking 
solutions to the problem of bone chip removal to capture them centrally 
and cause them to exit centrally through a tube or pipe to a disposal 
location outside of the grinder. Exemplary of such efforts are Seydelmann, 
U.S. Pat. No. 3,847,360 issued Nov. 12, 1974 and Seydelmann, U.S. Pat. No. 
3,934,827 issued Jan. 27, 1976. Several commercial versions of central 
discharge of bone chips presently exist in the U. S. marketplace. Such 
units rely primarily on high meat pressure within the grindr, rather than 
physical action of mechanical parts, to force collected bone chips along 
its disposal path. 
Another effort at removing bone chips in meat from behind the final 
grinding plate and causing their disposal is shown in U.S. Pat. No. 
4,153,208 of Vomhof et al, issued May 8, 1979. In that structure, a unique 
knife arrangement is provided to take advantage of the central pressure 
packing of bone chips, channel the bone chips (and presumably red meat 
also) through grooves provided internally of the knife blades themselves, 
use the internal pressure of meat to drive the chips toward an outer 
peripheral region, and then use combined frictional force and pressure to 
drive the bone chips from the cylinder through a tangential slot after 
they have once been captured in a peripheral region. Like the 
aforementioned Seydelmann patents, Vomhof also accepts the apparent 
natural tendency of waste to congregate around the knife hub. 
Unfortunately, expensive meat can also easily follow the same path as the 
waste product, in both types of units where centralized collection is 
relied upon. 
In yet another form of bone chip removal illustrated in Jensen, U.S. Pat. 
No. 4,204,647 of May 27, 1980, an attempt is made to counter the inward 
packing force of bone chips and gristle with knife blades which are 
intended to physically drive such particles radially outward toward the 
periphery of the cylinder. The cylinder periphery is provided with a 
series of slots in the knife plane, into which bone chips and the like are 
packed. As shown in this patent, a hinged shackle is clamped about the 
cylinder exterior to cover the slots. The machine must be stopped when the 
bone chips are to be removed, the shackle removed, and the machine jogged 
to cause meat pressure to extrude the bone chips or whatever is contained 
in the slots therefrom. The outer surface of the cylinder is then scraped 
clean and the shackle reinstalled. In a commercial version of this latter 
device, a slotted ring is provided in place of the shackle. The ring may 
be actuated by an air cylinder from one position in which the slots in the 
ring are out of alignment with the cylinder slots to close the slots, to a 
second position in which they are aligned. When so operated while the 
machine is running, time lost to shutdown is avoided. This design, in 
effect, provides multiple valve ports enabling the machine periodically to 
extrude bone chips collected in the slots. A potential disadvantage of the 
multiple slots of the '647 patent is that if any slots are packed tightly 
with bone chips, there may be loss of easily flowable red meat through 
some slots while the remaining slots remain tightly packed. Ideally, all 
of the slots should be equally packed, should have equal pressure applied 
thereto during purging, and all extrude their waste material 
simultaneously. The likelihood of this happening can be expected to be 
slim, and any tightly packed slots may never be freed of unwanted 
materials until the machine is shut down and manually cleaned. Obviously, 
if a single one of the slots opens up and extrudes whatever bones have 
collected therein before any other slots can open, the soft, easily 
flowable meat immediately therebehind will continue flowing out until the 
valve is closed. 
At this early stage of development of this art, little factual information 
exists as to the actual amount of valuable meat which is extruded with the 
unwanted bone, cartilage and gristle. Because of its high cost, the loss 
of red meat must be kept to an absolute minimum. It is doubted that any of 
the prior art bone chip removal systems has the capability of the system 
about to be described, in terms of efficient waste material removal with 
minimum loss of meat with the waste. 
SUMMARY OF THE INVENTION 
The above described shortcomings and disadvantages of the prior art are to 
a great extent overcome by the meat grinder of the present invention. The 
meat grinder as disclosed and claimed herein is generally of the type 
which includes a barrel or cylinder which receives coarse-ground mixed 
meat from a mixer or container, including a delivery screw for conveying 
the premixed meat product through the cylinder to a grinding plate, and a 
cutting knife mounted on the end of the screw engages the product and cuts 
the same as it is forced through the extrusion openings formed in the 
plate. The bone chip remover apparatus includes a discharge outlet or 
opening which is formed generally in the plane or region of rotation of 
the knife in the wall of the cylinder, and incorporates a valve in a 
conduit leading therefrom for momentarily opening the conduit to outside 
pressure or to a region of lower pressure, whereby any material within the 
conduit and inwardly thereof is discharged by the differential pressure. 
An important provision of the invention resides in the construction of the 
knife and the manner in which it cooperates with the plate and the 
cylinder, to cause bone chips and the like to be collected primarily in 
discrete rotating peripheral regions inside the cylinder. The knife is 
formed with blades which have a sweep or a rearward slope or inclination 
at least with respect to the leading edges, providing what can be 
described as a centrifugal pumping action. This is identified as a 
trailing sweep, or arcuately rearward inclination, so that bone chips or 
other solid foreign matter or particles which engage the grinding plate 
but which are not capable of moving through the extrusion holes are 
contacted by the swept-back leading knife edges and are urged outwardly 
into the outer region defined by the unperforated annular outer portion of 
the grinding plate and the blade ends. The tips or ends of the blades 
which extend into this outer portion and in very near proximity to the 
inside of the cylinder, form a moving series of arcuate segments at the 
outer edges of which the bone chips are trapped and are temporarily stored 
and prevented from being further reduced since this annular region is 
radially outward of the extrusion opening pattern formed in the grinding 
plate. 
In the preferred construction of the knife, there is formed a common inner 
relieved region by means of which the space immediately forward of one 
blade may communicate with the space immediately forward of the next 
following blade. A common space is defined between the inner radial ends 
of the blades and the center or inner unperforated portion of the grinding 
plate. This central interconnecting region permits the migration of bone 
chips which may move inwardly or which may not be positively carried 
outwardly, to pass behind one blade and be engaged by the leading swept 
edge of a successive blade, with the potential that it may be thereby 
urged outwardly by reason of the outward force component caused by the 
blade inclination. When a segment between two blades is purged of bone 
chips, the pressure drop in that segment enables the higher pressure in 
the remaining segments to displace some bone chips from the relieved 
region into the lower pressure area. This in turn permits the leading edge 
of the blade in the purged section to pick up such chips and pump them 
outwardly. By providing a single discharge port, only one segment is 
purged at a time, although the randomness of purging will momentarily 
cause one segment to be opening just as the previous one is being closed. 
Bone chips can thus pack into the central relieved region initially, but 
are partially purged therefrom intermittently. 
A timed valve is incorporated into a passageway leading from a tangential 
opening in the cylinder, which may be opened from time to time for a 
relatively short time interval so that the material trapped in the outer 
segments between the blades may be purged. Preferably the timed valve 
means consists of a pneumatically operated plunger valve which opens for 
only a relatively short period of time, substantially less than a single 
revolution of the knife, thus resulting in the venting or purging of only 
a portion of the moving perimeter. Valve operation is random with respect 
to knife rotation and is accomplished on a regular, but adjustable 
intermittent basis. Thus, eventually all of the arcuate segments between 
the blade tips and the outer cylinder wall will be purged of accumulated 
material. In the event the passageway should become plugged tightly, a 
manual override of the timer is possible to maintain the valve open for a 
sufficient length of time to clear the obstruction. 
A further important feature resides in the arrangement by which the 
grinding plate is supported in the cylinder in such a manner as to provide 
for a full circumferential sweep of the tips of the blades about the outer 
unperforated region of the grinding plate. To this end, the open end of 
the cylinder is preferably formed of uniform inside diameter to receive 
the knife, the grinding plate, and also to receive, forward of the 
grinding plate, an annular collar or sleeve. The cylinder is formed with 
an axially aligned pin-locating or receiving groove in the inside surface 
thereof, which groove is positioned radially opposite a corresponding 
outwardly opening pin-locating or receiving groove in the grinding plate. 
The groove in the cylinder extends axially forwardly from the grinding 
plate throughout the forward uniform inside diameter of the cylinder to 
its open end, and the sleeve supports an axially extending locating pin on 
its perimeter or on its outer surface. The outside diameter of the sleeve 
is proportioned to form a close fit with the inside diameter of the 
cylinder. Further, the inside face of the sleeve abuts against the 
adjacent outside surface of the grinding plate, while the outer end of the 
sleeve is engaged by the adjusting ring so that, in effect, the sleeve is 
held in compression against the plate and in turn holds the plate firmly 
in cutting engagement with the knife. The axial extent or length of the 
pin is such that it extends into the plate groove to an axial depth less 
than the thickness of the plate, thereby locking both the plate and the 
sleeve against rotation, while leaving the inside diameter of the cylinder 
in the plane of the knife to be approched very closely by the tips of the 
knife blades. 
It is accordingly an important object of this invention to provide a meat 
grinder having a bone chip remover, as outlined above wherein the bone 
chips, gristle, or other particles which do not readily pass through the 
grinding plate, are moved in a generally radial direction, with the 
rotation of the knife blades, to a region beyond the perforated or 
effective region of the grinding plate and are trapped therein between the 
extended tips of a rotating cutting knife from which region this material 
may be, from time to time, purged. 
A further important object of the invention is the provision of an improved 
cutting knife having rearwardly swept blades, preferably blades which 
sweep along a rearwardly inclined arc, to effect an outward force 
component to bone chips which impinge against the leading edges of the 
blades. 
Another object of the invention is the provision of an improved device, as 
outlined above, in which the inner or root ends of the blades, around a 
hub portion adjacent the grinding plate, are open or otherwise relieved to 
form a common inner passageway which interconnects the regions between 
adjacent blades and provides, in conjunction with the blade tips which are 
in close proximity to the inside of the cylinder, for periodic purging of 
bone chips from the relieved portion in response to cylinder purging. 
Another object of the invention is to provide a bone chip remover in 
combination with a meat grinder in which a tangential opening is formed in 
the cylinder, in the plane or region of the knife, and in which the knife 
is provided with blades which coact closely with the inside wall of the 
cylinder and at a region radially outwardly of the perforations of the 
grinding plate to form rotating, non-extruding regions in which bone chips 
or other deleterious material may be trapped for purging through the 
tangential opening. 
A still further object of the invention is the provision of a bone chip 
remover, of the general kind outlined above, in which knife blades are 
swept rearwardly of the direction of rotation to provide a force component 
on particles incapable of readily passing through a grinding plate for 
moving such particles to a radially outward zone. 
A still further object of the invention is the provision of a meat grinder 
having bone chip removing capabilities in which an opening formed in the 
cylinder wall in the region of the plane of rotation of the cutting knife 
is intermittently vented to discharge bone chip material from a radially 
outer region of the plate by means of an intermittently operated closure 
valve, to remove rotating pockets of bone chip material which are trapped 
in a region radially outwardly of the perforated region of the plate by 
the knife blades. 
These and other objects and advantages of the invention will be apparent 
from the following description, the accompanying drawings and the appended 
claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
General Description 
A mixer-grinder to which the bone chip remover apparatus of the present 
invention has been applied is illustrated generally at 20 in FIGS. 1 and 2 
as including a hopper 21 into which the meat product to be ground is 
applied. It is understood that generally a coarsely ground or flaked meat 
product is applied to the hopper, which may also be in a frozen or 
partially frozen condition. The hopper 21 is provided with a pair of 
coacting, rotatably mounted blending and mixing arms, not shown, which 
engage the meat product in the hopper and mix and blend the ingredients 
prior to final grinding. 
The mixing within the hopper 21 is accomplished by a pair of 
counter-rotating, interrupted helical mixing arms. The mixing arms may 
rotate at a relative low rate of rotation, such as between 10 and 15 
revolutions per minute, as driven by a motor and transmission 23 through a 
secondary speed reduction mechanism 24. The arms making up the blending 
and mixing apparatus may be essentially as shown in Hartley et al, U.S. 
Pat. No. 3,570,569 issued Mar. 16, 1971, or Hartley, U.S. Pat. No. 
3,984,056 issued Oct. 5, 1976, and assigned to the same assignee as this 
invention. 
The mixing apparatus forming a part of the mixer-grinder 20 may thus be 
used to blend the meats with moisture, seasoning, fats or other products 
which are desired in the final grind. In large mixer-grinders, the hopper 
may hold 2,000 pounds or more of meat product which may have previously 
been ground or flaked, for a final mixing or grinding. 
The mixer-grinder 20 further includes a grinding section which is 
illustrated generally at 25 in FIGS. 1 and 2. For this purpose a stainless 
steel feed screw (not shown) is located at the bottom of the hopper, and 
is driven by the mixer motor 23. The forward end of the feed screw extends 
into a feed chamber 26 mounted on the forward end of the hopper 21 as 
shown in FIGS. 1 and 2. The feed chamber 26 is open at one side to deliver 
the meat product from the hopper to the inlet or feed bowl portion 28 of a 
grinding cylinder 30, as is perhaps best shown in FIG. 10. The grinding 
cylinder 30 and its feed bowl portion 28 rotatably receive a grinding 
screw or worm which is illustrated generally at 32 in FIG. 10. The worm 32 
includes a feed section 33 at the inner end thereof received essentially 
within the feed bowl portion 28 of the cylinder 30, which has flighting of 
relatively long pitch, leading to a pressure or delivery section 34 
received within the cylinder 30 proper, which has flighting formed with a 
shorter pitch. 
The worm 32 is driven, through reduction gearing 35 by a grinder motor 36, 
shown in FIG. 2, at a speed which is substantially higher than the speed 
of the mixing arms within the hopper 21, in the order of from 200 to 300 
revolutions per minute, for example. The forward end of the grinding 
cylinder 30 supports a conventional end adjusting nut or ring 38. 
Referring again to FIG. 10, the end of the worm 32 has threaded therein a 
protruding stud 39 which, in turn, supports and drives a cutting knife 40 
against a grinder plate 42. Thus, hub 41 of the knife 40 is conventionally 
mounted on the forward end of the screw 32 at the grinding plate 42 for 
cutting the meat product at the plate and for delivery thereof through the 
open end of the cylinder 30. The forward or discharge end of the cylinder 
30 is formed with an enlarged counterbored end or section 45 of uniform 
inside diameter beginning substantially at the forward end of the screw 
32. This enlarged section includes and defines the grinding station, and 
the grinding plate 42 has an outside diameter which forms a close 
clearance fit with the inside wall or surface 46 of the enlarged section 
45. The bottom or inner end 46' of the counterbored section 45 serves to 
help trapped bone chips from moving rearwardly as will be noted 
hereinafter. 
Conventionally, the grinding plate 42 may be formed with a forwardly 
extending knob portion 47 and is further formed with a central aperture or 
opening which receives the forward end of the knife-supporting stud 39 and 
thus pilots and supports the forward end of the worm 32 within the 
cylinder 30. 
The grinding plate 42 used with the bone chip remover apparatus of this 
invention may best be seen in FIGS. 5 and 11, and is essentially of 
conventional construction. Thus, as viewed in FIG. 5, the grinding plate 
42 is formed with an annular pattern of holes or extrusion openings 50 
therethrough, which may be in the order of one-eighth of an inch (3 mm) in 
diameter for the final grind, for example. The extrusion openings 50 are 
formed generally in an annular pattern, the outer diameter of which 
terminates radially inwardly of the plate periphery so that the plate 42 
is formed with a solid non-extruding annular perimeter 52. Similarly, the 
inside diameter of the pattern of openings 50 terminates at the knob 47 to 
form a non-extruding center section 54. 
The grinding plate 42 is further provided with an outwardly opening axial 
key or pin-receiving slot or groove 55 formed in the outer surface 
thereof, shown in FIG. 5. 
GRINDING PLATE SUPPORT 
Means forward of the grinding plate 42 for supporting the grinding plate 
within the section 45 of the cylinder 30 providing for limited axial 
movement of the plate and for preventing rotation of the plate within the 
cylinder includes an annular sleeve 60, FIG. 12. The sleeve 60 is formed 
with an outside diameter which, like the plate 42, forms a relatively 
close fit with the inside diameter or wall 46 of the cylinder. The sleeve 
60 is proportioned to extend slightly forward of the terminal or forward 
end of the cylinder 30 to be engaged by an inwardly extending conventional 
annular flange 62 of the adjusting ring 38, as shown in FIG. 10. The 
sleeve 60 includes an axially inwardly extending locating key or pin 65 
preferably integral therewith which is partially received in an axially 
elongated cylindrical groove 66 formed in the section wall 46, and axially 
alignable with the slot or groove 55 formed in the plate 42. The location 
pin 65 is supported on the sleeve so that approximately one-half the 
diameter of the pin 65 is received in the sleeve 50 and extends axially 
rearwardly from the sleeve 60, so that it may be partially received within 
the notch or groove 55 of the plate 42 and partially in the cylinder 
groove 66. When so received, the rear wall 67 of the sleeve 60 is in flat 
abutment with the adjacent annular peripheral or forward face of the plate 
42, essentially outwardly of the pattern of holes 50 and at the 
non-extrusion perimeter portion 52. 
The axial length of the pin 65 rearwardly of the sleeve 60 is substantially 
less than the total axial depth of the plate 42 so that, allowing for 
normal wear and resurfacing of the grinding plate 42, no portion of the 
pin 65 will extend to the inside cutting or grinding surface 68 of the 
plate. Accordingly, the grinding surface 68 of the plate 42, including the 
outer non-extruding perimeter portion 52, is free of any obstruction, thus 
providing for an unobstructed sweep of this periphery throughout a full 
360.degree. extent by the blades of the knife 40. 
The sleeve 60 transmits force from the end adjusting ring 38 to the plate 
42 and from the plate 42 to the knife 40 to assure a proper cutting 
contact with the blades of the knife 40 against the cutting surface 68 of 
the plate 42. The pin 65 locks the plate 42 against rotation relative to 
the cylinder. The sleeve 60 may conveniently be provided with side finger 
openings 69, as shown in FIGS. 10-13, to assist in its insertion and 
removal from the cylinder 30. 
BONE CHIP REMOVER 
As previously noted, the bone chip remover of this invention is applied to 
the cylinder at the region of the knife 40, and a substantial portion of 
the apparatus is illustrated in FIG. 3. 
FIG. 3 shows a fragment of the grinding plate, but primarily shows the 
cutting region or grinding chamber formed immediately behind the grinder 
plate with the knife in place, while the unit is under operation. The 
individual bone chips or particles which do not move through the grinding 
plate are illustrated generally at 70. The bone chips 70 and a certain 
inevitable amount of accompanying meat product are removed through a 
tangential outlet opening 72 formed in the cylinder wall 46, radially 
opposite the knife 40. The outlet opening 72 leads immediately to a 
generally tangential aligned conduit or passageway 73 formed in a wall 
extension 74 of the cylinder 30. The outlet opening 72 is thus positioned 
at the high pressure grinding region outwardly of the knife blades and, as 
shown in FIG. 11, immediately axially inwardly of the grinding plate 42. 
This region is bounded forwardly by the portion 52 of the plate 42 and 
rearwardly by the counterbore surface 46'. Together they aid trapping of 
bone chips to assist in packing them into the passageway 73. The 
passageway 73 leads directly into an aligned opening formed in an adapter 
76 bolted onto the wall extension 74 by means of bolts 78. The adapter 76 
is connected to the inlet 79 of valve means indicated generally at 80. The 
valve means 80 has the function of momentarily opening the passageway 73 
into a region of relatively lower pressure, for purging of accumulated 
bone chips 70. 
Valve means 80 is formed with a cylindrical conduit or body 82 which 
reciprocally houses a closure plunger 85. The plunger 85 is movable 
between a position in which the inlet 79 is closed off, as shown in FIG. 
3, to a retracted position in the direction of the arrow 86 in which the 
inlet 79 is uncovered, permitting momentary flow as illustrated by the 
arrow 87. 
Means for operating the plunger 85 in a reciprocating manner includes a 
double-acting air cylinder 90 having air inlets 91 and 92 by means of 
which a piston within the cylinder 90 is controlled, to control the 
movement of the valve plunger 85. In the event any food or meat particles 
are carried by the plunger to a region above the plunger, a purge line 93 
is provided by means of which such meat particles may be bled off to a 
remote region, so as not to impede the proper operation of the plunger 85. 
The plunger valve 85 is operated on an intermittent basis, such as in a 
cycle of operation, in which the plunger valve 85 is retracted to a 
flow-permitting position in the direction of the arrow 86 for a relatively 
short period of time, and thereafter immediately returns to its flow 
blocking position, as shown, during which time a slug of bone chip laden 
meat material is discharged in the direction of the arrow 87 into a 
discharge pipe and into a catch basin, a bucket or the like. 
As noted above, the knife 40 and the grinder plate 42 cooperate in a unique 
manner to cause the bone chips and other particles which do not readily 
pass through the extrusion openings or perforations 50 in the grinder 
plate to be carried and moved outwardly of the grinder plate and trapped 
at a peripheral region of the plate within the enlarged grinding portion 
45 of the cylinder 30. To this end, reference may be had to the 
perspective view of the knife FIG. 4 and the detailed views as set forth 
in FIGS. 6-9. 
It will be seen that the knife 40 is provided with four symmetrical knife 
blades 100 integrally leading from the hub 41. Each of the blades 100 is 
formed with a substantial axial depth, corresponding substantially to the 
axial dimension of the opening 72 formed in the wall of the cylinder 
portion 45. Thus, each blade 100 is formed with a leading or forward face 
surface 102 which is essentially normal to the grinding face 68 of the 
grinding plate 42. The tips 103 of the blades extend radially beyond the 
perforated region of the plate, and sweep or overlie the non-extrusion 
outer or non-perforated section 52, as shown in FIGS. 3 and 5. The outer 
ends or terminal surfaces 104 of the tips 103 of the blades 100 form a 
close running fit with the adjacent cylinder wall 46 thereby defining 
between the blades arcuate segments of the outer section 52 of the 
grinding plate. The tips of the knife blades 100 are slightly relieved as 
indicated at 105 in FIGS. 6 and 9 for the purpose of equalizing the wear 
of the knife, by confining rubbing contact of the knife to the perforated 
region of the plate. 
The knife blades 100 are arranged essentially in staggered relation around 
the square stud-receiving central knife opening 106 in the hub 41, and the 
knife blades 100 are only slightly tapered in thickness. The forward or 
face surface 102 of each of the knife blades 100 is generated by or forms 
an arc about center C-1 of FIG. 6, while the back or trailing surface 108 
is formed as an arc about center C-2. The axial forward edge adjacent the 
plate consists of a ground cutting edge 111 flush with the cutting face 68 
of the grinding plate 42 and a trailing surface 110 beveled inwardly as 
illustrated in FIG. 8. 
In order to assist in the movement of bone chip particles radially 
outwardly into the arcuate regions between the blades at the cylinder 
wall, the knife blades 100 are formed with a forward surface 102 which is 
inclined to the direction of rotation, as illustrated by the arrows 112 in 
FIGS. 3 and 6, to provide an outward force component or pumping action to 
those of the particles or chips 70 which do not readily pass through the 
grinding plate. 
The forward surface 102 of each of the blades 100 of the knife 40 presents 
to the bone chips a surface which is inclined and recedes from the 
direction of rotation in such a manner that an outward force component is 
applied to the chips to assist in movement thereof to the outer regions of 
the grinding plate. The curved surface 102 is preferred since the partial 
wrap or a rearward inclination further maintains the angle between a 
tangent line and a radius at any point on the surface such as to provide a 
useful outward force component. Stated another way, the forward blade 
surfaces 102 may be considered as being formed with a curvature in the 
radial direction which recedes from the direction of rotation 112 so that 
bone chips and other fragments 70 encountering such forward surfaces of 
the blades are propelled or are urged toward the blade tips, where they 
are then trapped outwardly of the perforated region of the plate between 
the non-extrusion section 52 and the counterbore 46' and where these chips 
then are rotated about the inside perimeter of the cylinder portion 45 by 
the blades 100. The region between any two blades is therefore carried 
around by the knife from its throat area to the tips until the meat 
opposite the perforations is extruded through the plate and the material 
trapped behind section 52 is purged through opening 72. 
The back surfaces 108 of the individual blades 100 are thus also curved and 
are substantially parallel to the axis of the cylinder or, in other words, 
normal to the grinding face. The inner ends of the blades, at a generally 
common region of the hub 41 adjacent the grinding face but essentially 
inwardly of the extrusion region 50, at the non-extrusion center region 
54, are axially relieved as illustrated by the relieved portion 120 in 
FIGS. 6 and 9. The relieved portion 120 provides for communication, or 
provides a space, between the knife and the adjacent surface of the 
grinding plate. The chips, which may be forced dynamically by reason of 
the overall flow toward the center of the knife blade, if not carried 
radially outwardly, may migrate through the common opening defined by the 
relieved area 120 to be engaged by the leading edge 102 of a succeeding 
blade 100. Thus, the relieved portion 120 effectively prevents the 
formation of stagnant pockets at the inner or root ends of the blades 
which might otherwise tend to accumulate gristle or chips. As any one 
region between two blades is purged through the opening 72, the much 
greater pressure in the other three regions between blades will force bone 
chips collected in relieved area 120 to move toward the opening 72 and 
thus within the range of the curved face of a blade. This is made possible 
to some degree by the tips of the blades being able to essentially seal 
off the purged region, although the backside of the region is open to meat 
under high pressure except at counterbore 46'. This has been observed by 
noting that bone chips are frequently in one of the four knife throats 
more than the others right after a purging. 
The chips will thus be concentrated generally in the manner illustrated in 
FIG. 3 and will be rotated by the blade tips about the grinding plate at 
the non-perforated outer region. Since the region immediately behind the 
grinding plate is at relatively high pressure, when the valve plunger 85 
is momentarily opened, at least one of the arcuate segments or regions, 
and perhaps a portion of another will be purged of accumulated material 
through the tangential outlet 72. Since the timing of the valve 80 is not 
related to the same time base as the rate of rotation of the knives, 
eventually each of the rotating region will be purged while other regions 
tend to continue accumulating a concentration of bone chips. As the bone 
chips concentrate, good meat product is thereby displaced for proper 
cutting and movement through the grinding plate in the normal manner. 
Operation 
The operation of the apparatus of this invention is largely self-evident 
from the foregoing description. Preground or coarsely ground or flaked and 
perhaps partially frozen meat, fat, extenders, spices or other materials 
desired in the final grind are entered into the hopper 21 of the 
mixer-grinder 20 and mixed by the internal mixing arms. At the conclusion 
of the desired mixing, the mixer motor 23 is reversed in direction, thus 
delivering the mixed product in the conventional manner to the inlet 
section 28 of the grinding cylinder 30 where the product is picked up by 
the screw 32 and carried forwardly to the enlarged cylinder grinding 
region 45 where the same is acted upon by the rotating blades of the 
cutting knife, acting against the grinding plate 42. 
In the manner previously noted, the bone chip particles 70 will be 
accumulated and temporarily stored in the outer periphery adjacent the 
tips of the blades. The purge valve means 80 will be operated by the air 
cylinder 90 on an intermittent timed basis of relatively short duration, 
so that the plunger 85 is momentarily opened, venting the passageway 73 to 
a region of relatively low pressure, such as atmospheric pressure, thereby 
suddenly causing an expelling of the accumulated bone chips from whatever 
arcuate segment is exposed to the tangential opening 72. 
The duration of the opening of the valve means 80, and the frequency which 
the same is opened, is not particularly critical to the operation of the 
invention. For example, the plunger 85 may be opened for as short a time 
as a 0.050 second or less, or it may be opened for a substantially longer 
period of time, such as 1/2 second, depending upon the operating pressure 
within the cylinder, the grinding rate or speed of rotation of the worm 
32, the nature of the food or meat product being ground, and the extent of 
contamination by bone chips. Likewise, the frequency of operation of the 
plunger may be controlled or varied by suitable timing means, not shown, 
applying control air pressure to the operating cylinder 90. Thus, for 
example, the plunger may be operated as frequent as once every two or 
three seconds, or the plunger may be operated only a few times a minute, 
as necessary to effect a purging and removal of the accumulated bone 
chips, without undue removal and waste of uncontaminated meat product. The 
mixer-grinder 20 may thus be operated on a more or less continuous basis, 
at least over a period of time which substantially exceeds that which it 
could otherwise be operated, where it is necessary manually to clean out 
accumulated bone chips, thus eliminating the periodic necessity of 
stopping and disassembling the grinder for this purpose. A manual override 
(not shown) is also provided for purging independently of the automatic 
control system in the event the passageway becomes plugged. A button may 
simply be used to actuate air cylinder 90. This can be done anytime it is 
noticed that material is not being discharged. 
While the form of apparatus constitutes a preferred embodiment of this 
invention, it will be understood that the invention is not limited to this 
precise form of apparatus, and that changes may be made in either without 
departing from the scope of the invention.