Abstrict An improved double-roll crusher is provided which is especially
suitable for crushing bones having a relatively low content of soft
matter, the crusher being of the general type comprising two parallel
rolls, each comprising an assembly of alternating toothed cutting
discs and spacers so disposed that cutting discs on one roll extend
radially into the spaces between adjacent cutting discs on the opposing
roll in an alternating manner, wherein the improvement comprises
forming the toothed cutting discs so that the gap between adjacent
teeth is trapezium-shaped, the sides of the teeth make a rake angle
of 1.degree.-20.degree., the upper face of each tooth is beveled
5.degree.-35.degree., and the length of the larger base of the trapezium
is close to the maximum desired particle size.
Claims What is claimed is:
1. In a double-roll crusher comprising two rolls having parallel
axes and rotating in opposite directions, each roll comprising a
plurality of alternating toothed cutting discs and spacers so disposed
that cutting discs on one roll extend radially into the spaces between
adjacent cutting discs on the opposing roll in an alternating manner,
the improvement which comprises:
said toothed cutting discs having a plurality of radially disposed
teeth separated by a plurality of gaps therebetween, said teeth
being capable of seizing and crushing bones having a low content
of soft matter; wherein each tooth has four flat lateral sides,
two of which are parallel to each other and perpendicular to the
axis of the roll, the other two of which being inclined, each said
tooth having a flat upper face having a front edge and a back edge,
said upper face being beveled downwardly and rearwardly with respect
to the direction of rotation of the roll at an angle of drive of
from 5.degree. to 35.degree. with respect to the tangent to the
roll, whereby round-shaped parts of bones are hooked by said teeth;
and wherein the uniform cross-section of each said gap has the shape
substantially of a trapezium having a base, two opposite lateral
sides and a top larger than the base, the base being defined by
the bottom of the gap on the inner part of the toothed portion of
the disc, the lateral sides being defined by the inclined adjacent
sides of adjacent teeth, said lateral sides making a rake angle
of from 1.degree. to 20.degree., and the top being defined by a
straight line joining the tops of said lateral sides and corresponding
to the distance between the back edge of each tooth and the front
edge of the nearest adjacent tooth, said distance being substantially
equal to a desired maximum dimension of crushed bone particles.
2. The crusher of claim 1 wherein the angle of drive .beta. is
about 20.degree..
3. The crusher of claim 2 wherein the top of the trapezium-shaped
gap is from about 15 mm to about 20 mm in length; and the height
of the teeth and the width of the spacers between adjacent toothed
cutting discs on each roll are each substantially equal to the length
of the top of the trapezium-shaped gap.
4. The crusher of claim 1 wherein the top base of the trapezium-shaped
gap is from about 15 mm to about 20 mm in length.
5. The crusher of claim 1 wherein the height of the teeth is substantially
equal to the length of the top of the trapezium-shaped gap.
6. The crusher of claim 1 wherein the width of the spacers between
adjacent toothed cutting discs on each roll is substantially equal
to the length of the top of the trapezium-shaped gap.
7. In a method of crushing bones having a low content of soft matter,
which method comprises crushing the bones in a double-roll crusher
comprising two rolls having parallel axes and rotating in opposite
directions, each roll comprising an assembly of alternating toothed
cutting discs and spacers so disposed that cutting discs on one
roll extend radially into the spaces between adjacent cutting discs
on the opposing roll in an alternating manner, the improvement which
comprises:
said toothed cutting discs having a plurality of radially disposed
teeth separated by a plurality of gaps therebetween, said teeth
being capable of seizing and crushing bones having a low content
of soft matter; wherein each tooth has four flat lateral sides,
two of which are parallel to each other and perpendicular to the
axis of the roll, the other two of which being inclined, each said
tooth having a flat upper face having a front edge and a back edge,
said upper face being beveled downwardly and rearwardly with respect
to the direction of rotation of the roll at an angle of drive of
from 5.degree. to 35.degree. with respect to the tangent to the
roll, whereby round-shaped parts of bones are hooked by said teeth;
and wherein the uniform cross-section of each said gap has the shape
substantially of a trapezium having a base, two opposite lateral
sides and a top larger than the base, the base being defined by
the bottom of the gap on the inner part of the toothed portion of
the disc, the lateral sides being defined by the inclined adjacent
sides of adjacent teeth, said lateral sides making a rake angle
of from 1.degree. to 20.degree., and the top being defined by a
straight line joining the tops of said lateral sides and corresponding
to the distance between the back edge of each tooth and the front
edge of the nearest adjacent tooth, said distance being substantially
equal to of the resultant crushed bone particles; whereby the bones
are crushed without shredding any skin associated therewith.
8. The method of claim 7 wherein the angle of drive is about 20.degree.;
the top of the trapezium-shaped gap is from about 15 mm to about
20 mm in length; and the height of the teeth and the width of the
spacers between adjacent toothed cutting discs on each roll are
each substantially equal to the length of the top of the trapezium-shaped
gap.
9. The method of claim 8 wherein the rolls rotate at unequal speeds,
the ratio of speeds being from 1.2 to 2 and the speed of the slower
roll being from 100 to 150 rpm.
10. The method of claim 9 wherein the bones are first broken in
a prebreaker and then crushed.
11. The method of claim 10 wherein said content of soft matter
is less than 20%, and the resultant crushed bone contains substantially
no particles having a size greater than 16 mm, and less than 10%
of particles having a size less than 3 mm.
12. The method of claim 7 wherein the rolls rotate at unequal
speeds, the ratio of speeds being from 1.2 to 2.
13. The method of claim 12 wherein the speed of the slower roll
is in the range of 100 to 150 rpm.
Description BACKGROUND OF THE INVENTION
The present invention relates to an improved double-roll crusher
for crushing fatty bones used to obtain rendered bones of low fat
content suitable for the production therefrom of gelatin and also
glue or animal meal.
Fatty bones are obtained from slaughter houses or as waste from
butcher shops. Bones from such sources are often associated with
meat and fat. They cannot be used as such for the production of
gelatin. Usually they are treated in order to take off the major
part of the fat and to obtain the desired granulometry. Most often
fatty bones are first sorted to eliminate foreign substances such
as pieces of iron or plastic material and they are afterwards sent
to a prebreaker and a crusher. The crushed bones are then heated
by steam to a temperature of about 90.degree. to 95.degree. C. and
charged in a press in order to recover a solid cake consisting largely
of bone and a liquid consisting of molten fats, water soluble substances
and in some cases bone powder and other proteinous substances. The
rendered bones are then dried and introduced into a unit for the
preparation of gelatin.
The crushing is intended to reduce bones to a particle size or
granulometry suitable for producing gelatin and for obtaining a
good separation of noncollagenous proteinous material during the
rendering in a press. This granulometry usually ranges between 3
and 18 mm. Furthermore the crushed product must not contain more
than a small proportion of powder. This bone powder has a tendency
to clog the rendering press and cannot be used for the production
of gelatin. Therefore it is necessary to separate the bone powder
before the gelatin production step, thereby producing a byproduct
which can be used as meat meal, but has a low price because it has
a low albumin content. Furthermore, the granulometry must not exceed
the highest granulometry acceptable for the acid treatment of the
bones in gelatin production. Moreover, since the size of the press
outlet is close to the maximum particle size of bones acceptable
for the acid treatment in gelatin production, excessively large
bone particles are liable to block up the press.
OBJECTS OF THE INVENTION
Accordingly, one object of the present invention is to provide
an improved double-roll crusher suitable for crushing bones to produce
particles of a precise, homogeneous granulometry.
Another object of the invention is to provide an improved double-roll
crusher suitable for crushing bones with a minimum of powder production.
A further object of the invention is to provide an improved double-roll
crusher suitable for crushing bones having a low content of soft
matter.
Upon further study of the specification and appended claims, further
objects and advantages of this invention will become apparent to
those skilled in the art.
SUMMARY OF THE INVENTION
Briefly, these objects of the invention may be attained by providing,
in a double-roll crusher comprising two rolls having parallel axes
and rotating in opposite directions, each roll comprising an assembly
of alternating toothed cutting discs and spacers or spacer portions
so disposed that cutting discs on one roll extend radially into
the spaces between adjacent cutting discs on the opposing roll in
an alternating manner, the improvement comprising said toothed cutting
discs being so shaped that the gap between adjacent teeth on a disc
has the shape substantially of a trapezium, the smaller base of
which is defined by the bottom of the gap on the inner part of the
toothed portion of the disc, the larger base of which is at the
periphery of the disc, and the lateral sides of which, defined by
the adjacent sides of adjacent teeth, make a rake angle .alpha.
of from 1.degree. to 20.degree.; wherein the upper face of each
tooth is flat and is beveled downwardly and rearwardly with respect
to the direction of rotation of the roll at an angle of drive .beta.
of from 5.degree. to 35.degree. with respect to the tangent to the
roll; and wherein the length of the larger base is substantially
equal to the maximum desired dimension of the resultant crushed
bone particles.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation of a crusher according to the invention;
FIG. 2 is a partial cross sectional view of one of the cutting
discs showing the shape of the teeth and the gaps therebetween;
FIGS. 3 and 5 are diametric cross-sectional views of the rolls
showing engagement of the teeth; and
FIGS. 4 and 6 are partial side elevations also showing the engagement
of the teeth.
DETAILED DISCUSSION
It has been found that the crusher of the invention makes it possible
to crush bones containing less than 20% of soft matter, i.e., meat,
fats and the like, to such a granulometry that there are substantially
no particles of bone having a size greater than 16 mm, and less
than 10% of particles having a size less than 3 mm.
The crusher of the invention has a large capacity. A crusher having
outer dimensions of 90 cm.times.130 cm fed with particles having
a granulometry not exceeding 40 mm issuing from a prebreaker can
treat 7 tons per hour of fatty bones. The crusher of the invention
also has the advantage of being self-cleaning, thus avoiding stoppage
for cleaning. Moreover, the crusher is very selective for bones
and does not shred skins present in the bones. Their separation
is therefore easier.
A better understanding of the invention may be obtained from a
further description of certain embodiments, and with reference to
the drawings. These embodiments are merely illustrative and not
limitative of the scope of the invention.
As illustrated in FIG. 1 the crusher comprises two cylindrical
rolls (1 and 2) having parallel axes disposed in the same horizontal
plane. The two rolls are set in a housing. According to the embodiment
illustrated in FIG. 1 the housing comprises two side plates (8
and 9) and front and rear plates (10 and 11). The spaces (12 and
13) between the rolls (1 and 2) and the side plates (8 and 9) are
sufficient to allow substances adhering to the rolls to be recirculated.
In a crusher having a 90.times.130 cm housing, these spaces are
about 8 cm wide. Each roll is coupled with a drive motor (14 and
15) fitted with a speed-reducing gear in order to control the speed
of rotation. The speeds of rotation of opposing crusher rolls (1
and 2) are normally different, and preferably in a ratio of from
1.2 to 2. The speed of rotation of the slower roll is preferably
in the range of about 100 to 150 rpm.
Each roll is made from a plurality of discs stacked one on top
of another. According to the embodiment shown in FIGS. 4 and 6
each disc comprises a protruding part bearing teeth (3) and a recessed
part of smaller diameter and slightly thicker than the toothed part
forming the spacer (4). In an alternative embodiment (not shown),
the rolls are made by alternately stacking discs bearing peripheral
teeth and spacer discs having a smaller diameter and a slightly
greater thickness than the toothed discs.
The teeth each have four lateral faces. Two of these faces are
parallel to each other and perpendicular to the axis of the roll.
The two other faces are symmetrically inclined so that the gap between
adjacent teeth on the same disc has the shape substantially of a
trapezium, the smaller base of which is defined by the bottom of
the gap on the inner part of the toothed portion of the disc and
the larger base of which is at the periphery of the disc and defined
by the back edge of the top of each tooth and the front edge of
the top of the nearest adjacent tooth. The size of the large base
is substantially equal to the maximum desired dimension of the resultant
crushed bone particles, and is preferably between 15 and 20 mm.
The two lateral sides of the trapezium which are defined by the
adjacent sides of adjacent teeth make a rake angle .alpha. ranging
between 1.degree. and 20.degree.. Smaller angles are used for crushing
bones containing a higher proportion of soft matter, e.g., meat,
skins. Angles lower than 1.degree. impair the mechanical stability
of the device.
Referring to FIG. 2 the trapezium-shaped gap between adjacent
teeth, abdc, is defined by the lateral sides of adjacent teeth,
ab and cd, the bottom of the gap, bd (the corners optionally being
rounded off), forming the shorter base of the trapezium, and the
line joining the tops of adjacent lateral sides, ac, forming the
larger base or top of the trapezium. The top of each tooth is flat
and is beveled downwardly and rearwardly with respect to the direction
of rotation of the roll. The angle of drive .beta. between the inclined
plane of the bevel and the tangent to the roll ranges between 5.degree.
and 35.degree., the value of .beta. being preferably about 20.degree..
The presence of this bevel is especially important in avoiding
rejection of round-shaped parts of bones such as the ball end of
a ball and socket joint. For angles greater than 35.degree., the
bones are not hooked by the teeth. The height of the teeth is preferably
close to, or substantially equal to, the length of the larger base
of the trapezium. The thickness of the spacer discs or spacer portion
of combined cutter-spacer discs is also close to, or substantially
equal to, this length.
The toothed cutting discs of each roll are so disposed that they
extend radially into the spaces formed by the spacer discs or portions
and adjacent toothed cutting discs of the opposing roll, in an alternating
manner.
The depth of engagement or interpenetration of the toothed cutting
discs of opposing rolls may vary between interpenetration only to
the extent of about the height of the teeth, as shown schematically
in FIGS. 3 and 4 and interpenetration to about double the height
of the teeth, so that the bottoms of the gaps between teeth on opposing
rolls are substantially parallel at the point of closest approach,
as shown in FIGS. 5 and 6.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and without
departing from the spirit and scope thereof, can make various changes
and modifications of the invention to adapt it to various usages
and conditions. |