[0001] This invention relates, in general, to disk screens, and is more particularly concerned
with solving a problem encountered in certain uses of such screens wherein there is
a liability of particles jamming when not large enough to be scalped from the material
being screened and not quite small enough to pass through the screen.
[0002] The problem which the present invention is intended to solve has been encountered
in scalping disk screens which are adapted to handle so-called hog fuel and waste
products remaining as byproducts from supplying of pulp wood to the paper making industry.
Those parts of the pulp wood source material, that is of the trees, which cannot be
used for paper making wood pulp, such as unduly knot-infested tree parts, branches
and bark may be used for fueling boilers. For such use, it is desirable to screen
out incombustible or otherwise undesirable fractions of a hogged fuel or otherwise
broken up supply of the wood fuel material. Scalping disk screens have been employed
for this purpose, such as variously disclosed in U.S. Patents 4 037 723, 4 239 119
and 4 301 930, and which are characterized by having a screening bed provided with
a series of corotating spaced parallel shafts each of which has a longitudinal series
of concentric screen disks which interdigitate with the screen disks of the adjacent
shafts. The spaces between the disks permit material of smaller size to pass downwardly
through the rotating disk bed. Since the disks are all driven to corotate in a common
direction from the infeed end of the screen bed to the outfeed or discharge end of
the bed, the particles of material which are larger than the spaces between adjacent
disks will be advanced on the bed to the outfeed end of the bed. In screening chips
for paper pulp purposes it is desirable to remove any material over a certain dimension
from the properly dimensioned chips which fall through the screen. For hog fuel purposes,
also, the objective is generally to remove oversize and add material such as slivers,
trim ends, rocks, etc. The through flow, or as sometimes referred to underflow, of
the disk bed of the screen, free from slivers, sticks, trim ends, rocks, and the like,
is in most cases the desired hog fuel product. On the other hand, the through flow
may represent the rejects and the overflow, or oversize material may be transferred
to process or rechipping, hogging or fractionating, depending on the type of material
and its end use.
[0003] Among the screenings which should be removed from the hog fuel mass, bits of rock
and tramp metal may be present, and where these are of a size approximating the screening
disk gaps but not quite small enough to pass through readily, there is often the tendency
for such particles, which may be referred to as migrant particles, to become wedged
between adjacent interdigitated disks of the screen bed and jam the same, causing
stoppage of the screen, and often serious damage. The proclivity toward such jamming
and damage in prior disk screens as represented for example, by the beforementioned
U.S. patents will be apparent because the screen disks are rigidly held in axially
spaced relation along their shafts. In addition, the disks themselves for the intended
hog fuel screening uses are generally of a rugged, rigid, steel structure. Each disk
may be about 9 mm thick and about 432 mm in overall diameter. There may be eleven
disks spaced apart bout 102-6 mm on each alternate shaft and twelve disks similarly
spaced on the other shafts, with the disks of adjacent shafts interdigitated and the
spacing between the interdigitated disks being about 25-5 mm . Any particles smaller
than such interdigitated disk spacing will fall through as the material is advanced
across the screening bed, and larger particles will be moved on. Some particles may
be of such an intermediate size or irregular shape that there is a tendency to jam
between interdigitated disks. For example, uneven particles such as rocks or tramp
metal, or even some wood particles which may be partially smaller than the between
the disk spaces and in other respects slightly larger may tend to migrate wedgingly
between and jam the disks.
[0004] It is to the alleviation of the problem just described that the present invention
is directed.
[0005] To this end the present invention provides a disk screen apparatus comprising a screening
bed having a series of corotating spacedparallel elongate shafts each of which has
thereon a longitudinal series of concentric screen disks which interdigitate in axially
spaced relation with companion screen disks on the adjacent shafts. The screening
bed is adapted to screen from particulate material particles which are oversize relative
to the axial screening spaces between interdigitated disks, and resiliently yieldable
means are provided for normally maintaining the disks in generally parallel screening
relation to one another on the shafts, such means permitting adjacent interdigitated
disks to deflect relatively when a migrant particle tends to engage wedgingly between
the interdigitated disks, so that the migrant particle will be prevented from jamming
the engaged disks but will be cleared therefrom automatically in the continuing rotation
of the disks.
[0006] Other objects, features and advantages of the invention will be readily apparent
from the following description of a representative embodiment thereof, taken in conjunction
with the accompanying drawings although variations and modifications may be effected
without departing from thespirit and scope of the novel concepts embodied in the disclosure
and in which:
Fig. 1 is a fragmental side elevational schematic illustration of a disk screen apparatus
embodying the present invention;
Fig. 2 is an enlarged fragmentary top plan view of the screening bed of the apparatus
;
Fig. 3 is an enlarged fragmentary sectional detail view taken substantially along
the line III-III in Fig.2; and
Fig. 4 is a fragmental sectional elevational detail view taken substantially along
the line IV-IV in Fig. 3.
[0007] As schematically shown in Fig. 1, a disk screen apparatus 5 of the kind with which
the present invention is concerned comprises a frame 7 supporting a screening bed
8 having a series of corotating equally spaced parallel shafts 9 of generally similar
coextensive length and each of which has thereon a longitudinal series of equally
spaced concentric screen disks 10 which interdigitate, as best seen in Fig. 2, with
the screen disks of the adjacent shafts. To attain the proper disk interdigitation,
there is a differential number of the disks 10 on the alternate shafts 9, such as
eleven disks alternating with twelve disks. In a typical arrangement of the disk screen
apparatus 5, wherein the disks are of dimensions such as described hereinbefore ,
the screen bed 8 may comprise twelve of the shafts 9 carrying, in the aggregate, 138
of the disks 10. The shafts 9 are preferably hollow tubular and of noncircular cross
section (Figs. 3 and 4 ) and provided with respective stub shafts 11 at their opposite
ends which are suitably journaled on the frame 7.
[0008] Means are provided, as is customary, for driving the shafts 9 and thereby the disks
10 in unison in the same direction, clockwise as seen in Fig. 1, part of the drive
means being identified at 13.
[0009] Material such as hog fuel to be screened is delivered to the infeed end of the screening
bed 8 by means of a chute 14. The arrangement may be such that desirable size particles
of the material drop down through the screen bed 8 and are received in a hopper 15
for disposition while oversize and odd shaped particles are carried on the screening
bed 8 toward the discharge end of the bed. Those particles which are advanced by the
screen bed 8 to its discharge end are discharged to an outfeed chute 17, as indicated
by directional arrow.
[0010] For hog fuel screening the disks 10 are preferably of round lobed, undulating perimeter
having a uniform series of lobes 18(Fig. 3) and mounting of the disks on the respective
shafts 9 is desirably with the disks alternately torsionally offset along each shaft
to have the lobes alternate substantially as seen in Fig. 3. Such alternation is provided
for in the assembling of each set of disks on its shaft by having the shafts of substantially
square cross-section and the disks provided with respective central apertures 19 which
are of the generally complementary cross-section to the shafts and with clearance
notches 20 aligned with the corners of the shaft perimeters. Thus, by properly formation
of the shaft-receiving apertures 19 for the alternate disks of each set, when the
set of disks is mounted on its shaft, the lobes will be in proper alternate relation
to one another throughout the set.
[0011] Resiliently yieldable means are provided for normally maintaining the disks 10 in
generally parallel screening relation to one another on their shafts 9, and such means
permitting adjacent interdigitated disks in the screen bed 8 to deflect relatively
when a migrant particle MP tends to engage wedgingly between interdigitated disks
10, so that the migrant particle MP will be prevented from jamming the engaged disks
but will be cleared therefrom automatically in the continuing rotation of the disks
in the screen bed. In a preferred arrangement, resiliently yieldable, generally annular
spacers 21 are mounted on the shaft 9, in each intance, between each pair of adjacent
disks 10 therealong for maintaining a substantially accurate longitudinally spaced
relation between the disks. In a preferred construction, the spacers 21 comprise molded
elastomeric members of a 70° Shore hardness, solid polyurethane being suitable for
the purpose. The elastomer may, if preferred, be fabric reinforced similarly as conveyor
belting to attain adequate stiffness and durability while still allowing sufficient
resilient deformation for the present purpose.
[0012] In the preferred construction, the spacers 21 are molded with respective central
passthrough openings 22 which are complementary to closely fit the perimeter of the
associated shaft 9 in corotatively keyed relation. All of the spacers 21 are of equal
length. On their outer perimeters, the spacers 21 may be cylindrical and of a diameter,
at least at their endsequal to the inside diameter of annular mounting shoulders provided
by concentric annular rings 23 attached as by means of welding to the respective opposite
faces of each of the disks 10 adjacent to and about the central clearance holes 19
in the disks. By having the central openings 19 in the disks slightly oversize relative
to the perimeter of the associated shaft 9, the shoulder rings 23 are adapted to support
the disks 10 in uniformly loosely spaced relation to the associated shaft. By their
resilient stiffness, the spacers 21 will normally maintain the disks 10 in substantially
accurate spaced parallel relation. However, when a migrant particle MP such as a rock
or other tramp material such as metal tends to wedge between adjacent interdigitated
disks 10, the resilient spacers 21 are adapted to yield as the disks are deflected
and permit the particle MP to be automatically cleared to move onward or pass through
the screen in the continuing rotation of the disks in the screen bed.
[0013] At the opposite ends of the shafts 9, the series of spacers is placed under endwise
axial inward snug-up compression by means of retainer plates 24 received slidably
about the outwardly projecting portions of the respective stub shafts 11 and drawn
up by means of bolts 25 against the outer ends of respective adaptor spacers 27 of
similar construction as the spacers 21. Conveniently the bolts 25 are threaded into
an associated outer filler or spacer plate 28 which may be welded to and project a
short distance outwardly from the adjacent end of the shaft 9 to serve as a stop to
avoid overcompressing the series of spacers 21,27 which are placed under endwise thrusting
compression by the retainer plate 24 in each instance.
[0014] A stabilizer filler plate 29 may be secured as by welding to the inside of the associated
hollow shaft 9 and the inner end portion of the associated stub shaft 11 in each instance.
[0015] In a desirable relationship, the disks 10 may be permitted by virtue of their resiliently
yieldable mounting and the clearance relation to the shafts in which the inner perimeters
of the disks are maintained by the spacers 21, to have about 3 mm relative movement
when an article such as the particle MP tends to wedge between any pair of interdigitated
disks. It will be apparent that in Fig. 2 the relative deflection has been somewhat
exaggerated for illustrative purposes. Any objects or particles large enough to resist
dropping down between disks will be carried on the screen bed 8 to discharge, while
any objects or particles which are smaller than would tend to wedge between the disks
will automatically pass through the screen bed.
[0016] It will be understood that variations and modifications may be effected without departing
from the spirit and scope of the novel concepts of the present invention.
1. In a disk screen apparatus comprising a screening bed having a series of corotating
spaced parallel elongate shafts each of which has thereon a longitudinal series of
concentric screen disks which interdigitate in axially spaced relation with companion
screen disks on the adjacent shafts, said screening bed being adapted to screen from
particulate material particles which are oversize relative to the axial screening
space between interdigitated disks:
resiliently yieldable means for normally maintaining said disks in generally parallel
screening relation to one another on said shafts;
said means permitting adjacent interdigitated disks to deflect relatively when a migrant
particle tends to engage wedgingly between the interdigitated disks, so that themigrant
particle will be prevented from jamming the engaged disks but will be cleared therefrom
automatically in the continuing rotation of the disks.
2. Apparatus according to claim 1, wherein said means comprise spacers maintaining
said disks in predetermined spaced relation along the respective shafts.
3. Apparatus according to claim 2, wherein said shafts are of non-circular cross section,
and said spacers comprise molded units having openings therethrough complementary
to the cross section of the shafts.
4. Apparatus according to claim 3, wherein the spacers have cylinrical annular perimeters
at least at their opposite ends, and said disks have annular shoulders engaging said
perimeters whereby the disks are maintained concentric relative to said spacers.
5. Apparatus according to claim 4, wherein the disks have central apertures loosely
related to their shafts.
6. Apparatus according to claim 1, wherein said resiliently yieldable means comprise
elastomeric spacers.
7. Apparatus according to claim 6, wherein said elastomeric spacers comprise solid
polyurethane having 70° Shore hardness.
8. Apparatus according to claim 1, wherein said disks are loosely mounted on their
shafts, said means comprise resilient spacers maintaining predetermined spaced relation
between said disks, and means for applying longitudinal snug-up pressure to the spacers
along each shaft.
9. Shaft means for use in a disk screen apparatus wherein a screening bed has a series
of corotative spaced parallel elongate shafts each of which has thereon a longitudinal
series of concentric screen disks which interdigitate in axially spaced relation with
companion screen disks on the adjacent shafts, said screening bed being adapted to
screen from particulate material particles which are oversize relative to the axial
screening spaces between interdigitated disks, said shaft means comprising:
resiliently yieldable means for normally maintaining said disks in generally parallel
screening relation to one another along a shaft perimeter;
said resiliently yieldable means permitting said disks to deflect relative to disks
with which interdigitated in the screening bed when a migrant particle tends to engage
wedgingly between interdigitated disks, so that the migrant particle will be prevented
from jamming the engaged disks but will be cleared therefrom automatically in the
continuing rotation of the disks.
10. Shaft means according to claim 9, wherein said resiliently yieldable means comprise
spacers maintaining said disks in predetermined spaced relation along the respective
shaft perimeter.
11. Shaft means according to claim 10, wherein said shaft perimeter is of non-circular
cross section, and said spacers comprising molded units having openings therethrough
complementary to said cross section.
12. Shaft means according to claim 11, wherein the spacers have cylindrical annular
perimeters at least at their opposite ends, and said disks have annular shoulders
engaging said spacer perimeters whereby the disks are maintained concentric relative
to said spacers.
13. Shaft means according to claim 12, wherein the disks have central apertures loosely
related to the shaft perimeter.
14. Shaft means according to claim 9, wherein said resiliently yieldable means comprise
elastomeric spacers.
15. Shaft means according to claim 14, wherein said elastomeric spacers comprise solid
polyurethane having 70° Shore hardness.
16. Shaft means according to claim 9, wherein said disks are loosely mounted on their
shaft perimeter, said resiliently yieldable means comprising spacers maintaining predetermined
spaced relation between said disks, and means applying longitudinal snug-up pressure
to the spacers.
17. An elongate shaft assembly adapted for use in a disk screen apparatus wherein
a screening bed has a series of such shaft assemblies corotatable to advance material
along the bed from one end to the other end, said shaft assembly having :
a shaft with a longitudinal series of concentric screen disks loosely mounted thereon
and which disks are adapted for cooperating in interdigitated screening relation with
the similar disks on adjacent shafts in the screening bed;
resiliently yieldable combination spacer and mounting means for engaging said disks
and maintaining them in predetermined spaced relation to one another and to said shaft;
and shoulder means on said disks engaging said combination spacer and mounting means.
18. A shaft assembly according to claim 17, wherein said combination spacer and mounting
means comprise molded elastomeric members, and said members and said shaft having
means keying the members corotatively with the shaft.
19. A shaft assembly according to claim 17, including means keying said disks corotatively
with respect to the shaft.
20. A shaft assembly according to claim l7,including means maintaining said spacer
means under longitudinal snug-up pressure along said shaft.