Abstrict A rotor for a vertical shaft impact crusher includes a vertical
wall segment having a first wall portion which is tangential to
the rotor and is located adjacent to the periphery of the rotor,
and a second wall portion, which is angled in relation to the first
wall portion and extends from the first wall portion into the rotor.
The second wall portion includes a first section, which extends
from the interior of the rotor towards its periphery and forms and
obtuse first angle with the first wall portion, and a second section,
which connects the first section and the first wall portion. The
second section and the first wall portion form a second angle, which
is smaller than the first angle, and at least one pocket for retaining
material.
Claims 1. A rotor for a vertical shaft impact crusher, said rotor comprising
a horizontal upper disc and a horizontal lower disc, said discs
being separated by at least two vertical wall segments defining
between them an outflow opening for material leaving the rotor,
said wall segments each having a first wall portion being substantially
tangential in relation to the rotor and being located adjacent to
the periphery of the rotor and a second wall portion being angled
in relation to said first wall portion and extending from the first
wall portion into the rotor, wherein said second wall portion comprises
a straight first section extending from the interior of the rotor
towards the periphery of the rotor, said first section forming an
obtuse first angle with said first wall portion, and a second section
connecting the first section and the first wall portion said second
section and said first wall portion forming a second angle being
smaller than said first angle, said second section and said first
wall portion forming at least one pocket for retaining material.
2. A rotor according to claim 1 wherein said first angle is approximately
110-155.degree..
3. A rotor according to claim 2 wherein said first angle is approximately
120-150.degree..
4. A rotor according to claim 1 wherein said second angle is approximately
75-100.degree..
5. A rotor according to claim 4 wherein said second angle is approximately
86-94.degree..
6. A rotor according to claim 1 wherein a horizontal length of
the second section is less than a tip distance, wherein the tip
distance is defined as the shortest distance between the second
section and a trailing edge of a wear tip located adjacent to a
free vertical edge of the first wall portion.
7. A rotor according to claim 6 wherein said horizontal length
is 20-70% of the tip distance.
8. A rotor according to claim 7 wherein said horizontal length
is 35-60% of the tip distance.
9. A rotor according to claim 1 wherein a second pocket for retaining
material is formed between said first section and said second section.
10. A rotor according to claim 1 wherein the wall segment is adapted
for building a bed of material extending continuously from the first
wall portion to a rear support plate mounted at the first section
of the second wall portion.
Description TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to a rotor for a vertical
shaft impact crusher, said rotor comprising a horizontal upper disc
and a horizontal lower disc, said discs being separated by at least
two vertical wall segments defining between them an outflow opening
for material leaving the rotor, said wall segments each having a
first wall portion being substantially tangential in relation to
the rotor and~being located adjacent to the periphery of the rotor
and a second wall portion being angled in relation to said first
wall portion and extending from the first wall portion into the
rotor.
BACKGROUND ART
[0002] Vertical shaft impact crushers (VSI-crushers) are used in
many applications for crushing hard material like rocks, ore etc.
U.S. Pat. No. 3154259 describes a VSI-crusher comprising a housing
and a horizontal rotor located inside the housing. Material that
is to be crushed is fed into the rotor via an opening in the top
thereof. With the aid of centrifugal force the rotating rotor ejects
the material against the wall of the housing. On impact with the
wall the material is crushed to a desired size. The housing wall
could be provided with anvils or have a bed of retained material
against which the accelerated material is crushed.
[0003] The rotor of a VSI-crusher usually has a horizontal upper
disc and a horizontal lower disc. The upper and lower discs are
connected with a vertical rotor wall. The upper disc has an aperture
for feeding material into the rotor. The material lands on the lower
disc and is then thrown out of the rotor via openings in the rotor
wall. The vertical rotor walls are provided with wear tips of a
hard material, such as a hard metal or a ceramic, to protect them
from wear caused by the material leaving the rotor at a high speed.
The wear tips are usually made from a hard material to resist wear.
The hard material is however sensitive to impact by large objects,
such as stones. Thus rotors are usually provided with means for
building a bed of retained material against the vertical rotor wall.
The bed of material is intended to protect the vertical wall from
wear and to protect the wear tip from impact of large objects.
[0004] U.S. Pat. No. 3970257 to MacDonald describes a vertical
shaft impact crusher having a rotor. The rotor is provided with
outflow openings. Each outflow opening is provided with a tip which
is held by a replaceable tip plate. The tip plate is mounted on
a first segment of a vertical plate, said first segment being substantially
tangential to the rotor and located at its periphery. A second segment
of the vertical plate is welded to the first segment and extends,
with an angle of about 120.degree. to the first segment, from the
periphery of the rotor towards a point located at a distance from
the centre of the rotor. A build up of material along the vertical
plate will protect the vertical plate from wear during operation.
It has been found, however, that the build up of material at the
vertical plate is not always stable and that the build up in many
applications may be eliminated during crusher operation. The result
is that the vertical plate, the tip plate and the tip is exposed
to wear and impact by the feed material.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide a rotor
which eliminates or reduces the above mentioned drawbacks of the
prior art and provides an increased rotor life and a reduced maintenance
requirement.
[0006] This object is achieved with a rotor according to the preamble
and characterised in that said second wall portion comprises a straight
first section extending from the interior of the rotor towards the
periphery of the rotor, said first section forming an obtuse first
angle with said first wall portion, and a second section connecting
the first section and the first wall portion, said second section
and said first wall portion forming a second angle being smaller
than said first angle, said second section and said first wall portion
forming at least one pocket for retaining material.
[0007] The rotor of the present invention thus provides for retaining
a stable bed of material inside the rotor. The bed is also sufficiently
thick to protect the wall segment and in particular a tip holder
holding a wear tip adjacent to the outflow opening from impact damages
and to avoid wear on the wall segment and the tip holder. The invention
has particular advantages when crushing very dry material or very
wet material. With prior art rotors it has been very difficult to
obtain a stable bed with such materials due to the inability of
the prior art rotors to hold a sufficient depth of "locked"
stones at the wall segment. The rotor according the invention makes
it possible to obtain a very stable bed of material with any feed
material, also with very dry and very wet materials. The stable
bed reduces the wear on the wall segment. The thick and stable bed
also reduces the risk that large objects fed to the rotor would
impact and destroy the wear tip that is used to protect a free edge
of the first wall portion. The pocket makes it possible to retain
also larger objects which further improve the stability of the bed
of material. Due to the decreased risk of wear the first wall portion
and a holding plate of the tip holder can be made thinner. Thus
the wear tip may be located closer to the periphery of the rotor
resulting in an ejection of material via the outflow opening at
a higher speed, which improves the crushing performance due to increased
impact energy. The higher speed of the ejected material and the
fact that the wear tip is located closer to the periphery of the
rotor decreases the risk that ejected material may slide along the
periphery of the rotor and cause wear to the exterior of the rotor.
[0008] Preferably said first angle is 110-155.degree.. With a first
angle of 110-155.degree. the first section of the second wall portion
will provide for building a stable and suitably thick bed of material
providing a suitable path of the material ejected from the rotor.
At a first angle larger than 155.degree. (still keeping the first
wall portion tangential in relation to the rotor) the bed would
become unnecessarily heavy, which would make the rotor heavier and
increase the risk of imbalance problems during operation. Also the
first section would be located rather near the periphery of the
rotor thereby increasing the risk that dust loaded air circulating
inside the crusher may wear the outer part of the second wall portion.
At a first angle smaller than 110.degree. (still keeping the first
wall portion tangential in relation to the rotor) the bed of material
would not obtain a sufficient thickness to protect the wall segment
from wear.
[0009] Preferably said second angle is 75-100.degree.. A second
angle of 75-100.degree. has proven to provide a pocket suitable
for retaining material and thus for providing a thick and stable
bed of material built up against the wall segment. At a second angle
smaller than 75.degree. larger pieces of material are not well retained
in the pocket, thus the stability of the bed is decreased. At a
second angle larger than 100.degree. the material in the pocket
is not well secured. Thus there is a risk that the material in the
pocket may slide out of the pocket and out of the rotor followed
by a break down of the entire bed of material. It has proven particularly
suitable with a second angle of 86-94.degree.. An angle in said
interval has proven to both allow large objects to be retained in
the pocket and to secure them firmly in the pocket with little risk
of a break down of the bed. Preferably the second angle is 90.degree..
[0010] Preferably the horizontal length of the second section is
less than a tip distance being the shortest distance between the
second section and a trailing edge of a wear tip located adjacent
to a free vertical edge of the first wall portion. An advantage
with this embodiment is that there is no or little risk that the
bed of material is divided into two sub-beds with a part of the
second wall portion being exposed to wear. With a too long second
section the bend formed between the first section and the second
section may extend out of the bed of material and into the flow
of material ejected by the rotor. Such exposure would lead to rapid
wear of the second wall portion, particularly at said bend. More
preferably said horizontal length is 20-70% of the tip distance.
A horizontal length of the second section smaller than 20% of the
tip distance makes it difficult for the pocket to retain larger
objects. Thus the bed of material becomes less stable. A horizontal
length of the second section larger than 70% of the tip distance
increases the risk that the bed is divided into two sub-beds making
it less stable. Also the bend between the first section and the
second section may extend out of the bed and may thus be subjected
to wear.
[0011] According to another preferred embodiment a second pocket
for retaining material is formed between said first section and
said second section. The second pocket increases the stability of
the bed and decreases the risk that the bed may break down.
[0012] Preferably the wall segment is adapted for building a bed
of material extending continuously from the first wall portion to
a rear support plate mounted at the first section of the second
wall portion. A continuous bed of material provides the best protection
against wear and the lowest risk of imbalance in the rotor during
operation. A continuous bed is robust to different material types,
material sizes and material amounts fed to the rotor since the material
profile of the entire bed changes according to the prevailing operating
conditions.
[0013] These and other aspects of the invention will be apparent
from and elucidated with reference to the embodiments described
hereafter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention will hereafter be described in more detail
and with reference to the appended drawings.
[0015] FIG. 1 is three-dimensional section view and shows a rotor
for a VSI-crusher
[0016] FIG. 2 is a three-dimensional view and shows the rotor of
FIG. 1 with the upper disc removed.
[0017] FIG. 3 shows the view of FIG. 2 as seen from above in a
two dimensional perspective.
[0018] FIG. 4 is a three-dimensional view of a wear tip and tip
holder.
[0019] FIG. 5 shows a part of a wall segment as seen from the inside,
i.e. in the direction of arrow V in FIG. 3 of the rotor.
[0020] FIG. 6 shows a part of a wall segment as seen from the outside
of the rotor, i.e. in the direction of arrow VI in FIG. 3.
[0021] FIG. 7 shows a another embodiment of a tip holder.
[0022] FIG. 8 is a three-dimensional view of still another embodiment
of a tip holder.
[0023] FIG. 9 is an enlarged top view and shows a wall segment
of FIG. 3.
[0024] FIG. 10 is a top view and shows a bed of material built
up against the wall segment shown in FIG. 9.
[0025] FIG. 11 is a top view and shows a second embodiment of the
invention.
[0026] FIG. 12 is a top view and shows a third embodiment of the
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0027] FIG. 1 shows a rotor 1 for use in a VSI-crusher. The rotor
1 has a roof in the form of an upper disc 2 having a top wear plate
3 and a floor in the form of a lower disc 4. The lower disc 4 has
a hub 6 which is welded to the disc 4. The hub 6 is to be connected
to a shaft (not shown) for rotating the rotor 1 inside the housing
of a VSI-crusher.
[0028] The upper disc 2 has a central opening 8 through which material
to be crushed can be fed into the rotor 1. The upper disc 2 is protected
from wear by upper wear plates 10 and 12. The upper disc 2 is protected
from rocks impacting the rotor 1 from above by the top wear plate
3. As is better shown in FIG. 2 the lower disc 4 is protected from
wear by three lower wear plates 14 16 and 18.
[0029] The upper and lower discs 2 4 are separated by and held
together by a vertical rotor wall which is separated into three
wall segments 20 22 and 24. The gaps between the wall segments
20 22 24 define outflow openings 26 28 30 through which material
may be ejected against a housing wall.
[0030] At each outflow opening 26 28 30 the respective wall segment
20 22 24 is protected from wear by three wear tips 32 34 36
located at the trailing edge of the respective wall segment 20
22 24.
[0031] A distributor plate 38 is fastened to the centre of the
lower disc 4. The distributor plate 38 distributes the material
that is fed via the opening 8 in the upper disc 2 and protects the
lower disc 4 from wear and impact damages caused by the material
fed via the opening 8.
[0032] During operation of the rotor 1 a bed 40 of material is
built up inside the rotor 1 against each of the three wall segments
20 22 24. In FIG. 3 only the bed 40 located adjacent to the wall
segment 20 is shown. The bed 40 which consists of material that
has been fed to the rotor 1 and then has been trapped inside it,
extends from a rear support plate 42 to the wear tips 32 34 36.
The bed 40 protects the wall segment 20 and the wear tips 32 34
36 from wear and provides a proper direction to the ejected material.
The dashed arrow A describes a typical passage of a piece of rock
fed to the rotor 1 via the central opening 8 and ejected via the
outflow opening 26. The arrow R indicates the rotational direction
of the rotor 1 during operation of the VSI-crusher.
[0033] Each wall segment 20 22 24 is provided with a cavity wear
plate 44 46 48 each consisting of three cavity wear plate portions.
The cavity wear plates 44 46 48 protects the rotor 1 and in particular
the wear tips 32 34 36 from material rebounding from the housing
wall and from ejected material and airborne fine dust spinning around
the rotor 1.
[0034] In FIG. 4 a first embodiment of a tip holder 50 is shown.
The tip holder 50 has a holding part 52 shaped as a rectangular
parallelepiped. The holding part 52 has a longitudinal recess 54
in which the wear tip 36 is located. The wear tip 36 may be welded
or glued to the holding part 52. The holding part 52 has two hooks
56 58. The two hooks 56 58 are located at the opposite face of
the holding part 52 in relation to the recess 54. A holding plate
60 is attached to the holding part 52. The holding plate 60 which
is a flat rectangular plate, is attached to the holding part 52
at a position between the hooks 56 58 and the recess 54. At an
end of the plate 60 said end being remote from the holding part
52 a round, threaded bar 62 is attached. The bar 62 is located
in generally the same plane as the holding plate 60 and is perpendicular
to the wear tip 36.
[0035] As can be seen in FIG. 4 the holding plate 60 has a smaller
vertical extension than the holding part 52. Thereby an upper shoulder
64 and a lower shoulder 66 are formed at the respective transitions
between the plate 60 and the part 52.
[0036] In FIG. 5 a part of the wall segment 20 as seen from the
inside, i.e. in the direction of the arrow V in FIG. 3 is shown.
The wall segment 20 comprises a first wall portion 20a which is
substantially tangential to the disc 4 and thus the rotor 1. A second
wall portion 20b is fixed to the first wall portion 20a. The three
wear tips, 32 34 36 each held by a tip holder 50 are attached
to the wall 20 in such a way that the wear tips 32 34 36 form
a continuous, vertical row of wear tips. The second wall portion
20b is provided with holes 68 70 72 through which the round bar
62 of the respective tip holder 50 extends.
[0037] As can be seen in FIG. 5 the lower wear plate 14 is inserted
under the lower shoulder 66 of the tip holder 50 holding the lower
tip 32. This shoulder 66 thus assists in holding the wear plate
14 in place under the shoulder 66. The upper shoulder 64 (not shown
in FIG. 5) of the tip holder 50 holding the upper wear tip 36 in
place holds an upper wear plate in place in a similar manner. A
retractable pin 74 extending through the wall 20 further assists
in holding the wear plate 14 in its proper position. Since the three
tip holders 50 shown in FIG. 5 are identical they can replace each
other. After some time of operation, usually causing most wear at
the centre wear tip 34 the tip holders 50 may be taken out and
then put back again at new positions to enable more hours of operation
before the tips 32 34 36 are worn out.
[0038] FIG. 6 shows a part of the rotor as seen from the outside,
i.e. in the direction of the arrow VI in FIG. 3. As can be seen
the hooks 56 58 of each tip holder 50 grips around the free vertical
edge 76 of the first wall portion 20a. The threaded bar 62 of each
tip holder 50 extends out of a hole 68 70 72 (of which only the
hole 72 is indicated in FIG. 6) and is fixed towards the second
wall portion 20b by a nut 78.
[0039] When mounting a tip holder 50 of the type described above
the tip holder 50 is first allowed to slide along the first wall
portion 20a. Thus the plate 60 and the threaded bar 62 are guided
in a direction parallel to the first wall portion 20a until the
hooks 56 58 engage the free edge 76 and in such a way that the
bar 62 passes through the hole 72. The nut 78 is screwed onto the
part of the bar 62 extending on the outside of the second wall portion
20b. The nut 78 is a domed nut and thus protects the end portion
of the threaded bar 62 from wear and from being hit by rocks. The
risk that the end portion of the threaded bar 62 would be damaged
such that dismounting the nut 78 becomes difficult is thus minimized.
The nut 78 is tightened such that a certain, desired tension is
obtained in the parts of the tip holder 50 that are located between
the nut 78 and the hooks 56 58. The nut 78 being located on the
second wall portion 20b is protected by the first wall portion 20a
from abrasive particles that often swirl around the rotor 1. Thus
there is a limited risk that the nut 78 is worn down during operation
of the crusher.
[0040] When a worn tip holder 50 is to be replaced a bed of material
40 has built up against the inside of the wall segment 20. The worn
tip holder 50 may be released according to the following method.
Firstly the nut 78 is unscrewed a few turns such that it is not
tightly fixed to the bar 62. A hammer or similar tool is used to
imply a force or a strike on the nut 78 and thus to the end part
of the threaded bar 62 in the direction shown with an arrow H in
FIG. 6. The nut 78 thus serve as a surface for implying the force
or strike. The force or strike makes the tip holder 50 and in particular
the threaded bar 62 and the plate 60 release from the often well
compacted material bed 40. The nut 78 is then removed from the bar
62 such that the tip holder 50 may be taken away by guiding it away
from the second wall portion 20b in a direction, which is indicted
by an arrow D in FIG. 6 being substantially parallel to the first
wall portion 20a. Thus a time consuming process of removing the
bed 40 before dismounting the tip holder 50 may be avoided.
[0041] In FIG. 7 another tip holder 100 is shown as seen from the
inside of a rotor 1. The main differences compared to the tip holder
50 shown in FIG. 4 is that the tip holder 100 has a wide holding
plate 160 and two threaded bars 161 and 162. The threaded bars 161
162 extend through holes 168 170 respectively, in the second wall
portion 20b. The tip holder 100 has an upper shoulder 164 and a
lower shoulder 166 for abutting against an upper wear plate (not
shown) and a lower wear plate 14 respectively. A wear tip 136 located
in a recess 154 of a holding part 152 extends over the whole vertical
distance of the outflow opening. The tip holder 100 is mainly used
for rotors 1 of smaller vertical extension and for rotors 1 were
the mutual exchangeability of the tip holders 50 described above
is not desired.
[0042] In FIG. 8 yet another tip holder 200 is shown. The main
differences between the tip holder 200 and the tip holder 50 shown
in FIG. 4 is that the tip holder 200 has no holding plate and that
threaded bars 261 262 are attached directly to a holding part 252.
The open space formed between the bars 261 262 forms a material
space. When such a tip holder 200 is attached to a rotor 1 the amount
of material and the size of material that may be trapped in the
bed 40 just behind the holding part 252 is increased. A wear tip
236 is fixed in a recess 254 of the holding part 252. The holding
part 252 has two hooks 256 258 for securing it to the vertical
free edge 76 of the first wall portion 20a. The bars 261 262 may
have the additional function of acting as shoulders for holding
horizontal wear plates in the correct position.
[0043] FIG. 9 shows the wall segment 20 in greater detail. As mentioned
earlier the first wall portion 20a is located adjacent to the periphery
of the rotor 1 and thus adjacent to the periphery of the lower disc
4 (and at the periphery of the upper disc 2 which is not shown
in FIG. 9) and is substantially tangential to its periphery. The
second wall portion 20b has two sections. A first section 80 being
a substantially straight plate starts at the rear support plate
42 and extends substantially perpendicularly therefrom towards the
periphery of the rotor 1. The angle S between this first section
80 of the second wall portion 20b and the first wall portion 20a
is 130.degree.. At a perpendicular distance D from the first wall
portion 20a the second wall portion 20b has a bend 82. The bend
82 divides the second wall portion 20b into the first section 80
and a straight second section 84 which, at an angle T of 90.degree.,
is welded to the first wall portion 20a at one end thereof. The
length of the second section 84 thus equals the distance D from
the bend 82 to the first wall portion 20a. A tip distance E is defined
as the shortest distance from the second section 84 to a trailing
edge 37 of the wear tip 36. The trailing edge 37 is the rear portion
of the wear tip 36 as seen in the direction of the passage of a
piece of rock (see the dashed arrow A in FIG. 10). The length D
of the second section 84 is about 37% of the tip distance E. The
second section 84 and that part 86 of the first wall portion 20a
which is located adjacent to said second section 84 together form
a pocket 88.
[0044] FIG. 10 shows the function of the pocket 88 during operation.
As noted earlier a bed 40 of material will build up against the
wall segment 20 during operation of the rotor 1. The pocket 88 will
capture material during start of crusher operation and build up
a stable bed 40 extending continuously from the first wall portion
20a to the rear support plate 42. The direction of rotation R of
the rotor 1 will cause a centrifugal force that pushes captured
pieces of material, schematically represented by a piece M in FIG.
10 into the pocket 88 and secures them there. The profile of the
bed 40 of material will fluctuate due to slight differences in size
and composition of feed material, slight variations in feed amount
etc. The pieces M secured in the pocket 88 will, however, stabilise
a stationary material profile L1 and ensure a good protection of
the wall segment 20 against wear and of the tip holder 50 and the
wear tip 36 against wear and impact of large objects. The varying
material profile of the bed 40 during operation, indicated by the
line L1 indicating the stationary (or minimum) material bed, line
L2 indicating an average material profile, and line L3 indicating
a maximum sized material bed, does not influence the protective
function of the bed 40. The thick minimum material profile L1 assist
in building a thick average material profile L2 which further improves
the wear resistance characteristics of the bed 40 of material. The
exact appearance of the passage of a rock piece, indicated by the
dashed arrow A, will vary somewhat depending on the actual profile
of the bed 40. During operation a force, indicated with an arrow
K in FIG. 10 will tend to push the bed 40 outwardly from the rotor
1 due to a component of the centrifugal force generated by the rotor
1. The pieces of material M secured in the pocket 88 will however
prevent the bed 40 from leaving the rotor 1 thus ensuring a stable
bed 40 and little wear.
[0045] FIG. 11 shows a second embodiment in the form of a rotor
201. The rotor 201 has a wall segment 220 and a lower disc 204 (and
a not shown upper disc). The wall segment 220 differs from that
described in FIG. 9 and 10 in that a first wall portion 220a, and
thus the tip holder and the wear tip (not shown in FIG. 11), is
located closer to the periphery of the rotor 201. Thus the right-angled
distance D1 from the first wall portion 220a to a bend 282 which
divides a second wall portion 220b into a first section 280 and
a second section 284 is larger compared to the distance D shown
in FIG. 9. With a tip holder of the type described above mounted
on the first wall portion 220a D1 would be about 50% of the actual
tip distance. Thus a pocket 288 having the possibility of retaining
very large pieces of material is created.
[0046] FIG. 12 shows a third embodiment in the form of a rotor
301. The rotor 301 comprises a wall segment 320 and a lower disc
304 (and a not shown upper disc). A second wall portion 320b of
the wall segment 320 has a first section 380 being a substantially
straight plate that starts at a rear support plate 342 and extends
substantially perpendicularly therefrom towards the periphery of
the rotor 301. The angle between this first section 380 of the second
wall portion 320b and a first wall portion 320a is 130.degree..
A second section 384 of the second wall portion 320b is welded to
the first wall portion 320a and forms a right angle with the first
wall portion 320a. The second section 384 and that part 386 of the
first wall portion 320a which is located adjacent to said second
section 384 together form a first pocket 388 for retaining pieces
of material. The length D2 of the second section 384 is about 37%
of the tip distance E as defined in FIG. 9. At the end of the second
section 384 and thus at a perpendicular distance D2 from the first
wall portion 320a the second wall portion 320b has a first right-angled
bend 382. The bend 382 provides a shoulder section 387 being parallel
to the first wall portion 320a and located a distance D2 therefrom.
The length El of the shoulder section 387 is about 27% of the above
mentioned tip distance. In general E1 should be 20-70% of the tip
distance E. At the end of the shoulder section 387 a second right
angled bend 383 is formed thereby providing a third section 390.
The third section 390 forms a right angle to the first wall portion
320a and has a length D3 which is about 37% of the tip distance.
In general D3 should be 20-70% of the tip distance E. The third
section 390 and the shoulder section 387 together form a second
pocket 389 for retaining pieces of material. A third bend 385 of
the second wall portion 320b forms the transition from the third
section 390 to the first section 380. The two pockets 388 and 389
provides for an improved capacity for retaining material and also
decreases the tendency of material to flow outwardly of the rotor
(compare the arrow K of FIG. 10). Thus the arrangement of FIG. 12
provides for building a very stable bed of material against the
wall segment 320. Arrangements with three or more pockets are also
possible. In such a case the dimensions of each subsequent pocket
are preferably set in accordance with the ranges given above for
D3 and E1. It should be noted that the tip distance E is always
based on the distance to the second section and not the distance
to any third or fourth section.
EXAMPLE
[0047] A test was made with a rotor having wall segments 20 22
24 according to the embodiment described in FIG. 9. The rotor had
a diameter of 850 mm and was installed in a vertical shaft impact
crusher. The rotor was rotated at 1500 rpm. During the first minute
of operation a first material having a characteristic size of about
10 mm was fed to the rotor. Then a second material having a characteristic
size of about 40 mm was fed to the rotor for about 40 hours until
9500 tons of material had been crushed. The crusher was then stopped
and the bed 40 of material built up against the wall segment 20
was investigated. It was found that the bed 40 had an outer layer
comprising material originating from the second material (the 40
mm material). Under the outer layer a stable bed of material (compare
line L1 in FIG. 10) originating from the first material (the 10
mm material) was found. The fact that the stable bed of material
originated from the first material (the 10 mm material) shows that
the rotor according to the invention was able to very quickly (in
less than one minute) build up a protective bed 40 of material against
the wall segment and also to keep that bed 40 of material stable
and secured during continuous operation of the crusher.
[0048] It will be appreciated that numerous modifications of the
embodiments described above are possible within the scope of the
appended claims.
[0049] Thus the pockets for retaining material may have other depths
and other angles T between the second section and the first wall
portion. However, as described above, an angle T of about 90.degree.
has proven to give a very stable bed and the ability to retain also
large objects.
[0050] The angle S between the first section 80 of the second wall
portion 20b and the first wall portion 20a is preferably 110-155.degree..
It has however been found that an angle S of 120.degree. and larger
provide a more even bed profile and a more stable bed. The extra
bed weight resulting from an angle of over 150.degree. is seldom
motivated by a further increase in bed stability. The angle S is
thus more preferably in the range of 120-150.degree..
[0051] The length D, D1 D2 of the second section 84 284 and 384
respectively is preferably 20-70% of the tip distance E. A length
D, D1 D2 of the second section 84 284 384 respectively, of 35-60%
of the tip distance E has been found to provide a particularly good
balance between the desire to capture large objects in the pocket
and the desire to obtain a thick and continuous bed 40 of material,
said bed 40 having a sufficient thickness also adjacent to the bend
82 282 382. Preferably the stationary bed 40 of material (compare
line L1 in FIG. 10) has a substantially even thickness along the
first section 80.
[0052] The second wall portion 20b comprising at least two sections
80 84 could be made from one bent metal sheet or could be made
from separate pieces welded together. It is preferable to make the
second wall portion 20b from one sheet of metal since this reduces
the risk of breakdown and decreases the manufacturing costs. |