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Патент USA US3021963

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Feb- 20, 1952
w. A. BRASTAD ETAL
3,021,953
SIFTER
Filed May 29. [1958
96
FIG. I
20
92
50
FIN
INVENTORS
mmumn
A. BEQSTQD
EREI- F.
DIEKHOFF
STANLEY c. BUSTED
Bvykzzgmwwé
United States Patent 0
1
3,h2l,953
Patented Feb. 2%, l$d2
1
2
3,021,953
,FIG. 2 is a sectional view taken along line 2~—2 of
FIG. 1; and
§ETTER
FIG. 3 is a partial side elevation view of a further
embodiment of the present invention.
The instant invention is exempli?ed in FIG. 1 in a
reciprocating sifter 10 designed in a particular manner
William A. Brastad, Earl F. Diekhotf, and Stanley C.
Rusted, Minneapolis, Minn, assignors to General Mills,
Inc, a corporation of Delaware
Filed May 29, 1958, Ser. No. 738,873
9 Claims. (Cl. 20§—339)
to prevent or cancel out the undesired effects of dynamic
air pressures generated by the reciprocation of the sifter.
The present invention relates generally to sifting ap
The sifter 10 includes an enclosed body portion formed
paratus and more speci?cally to an improved sifting de 10 of suitable wall means such as a removable top wall 12,
vice for classifying ?nely ground or powdered materials.
a bottom wall 14, side walls 16 and 18 and end walls
Sifting devices are known in which material to be sized
20 and 22. Within these walls are generally horizontal
is conveyed across a sifting screen-or sizing surface with
classifying surface 24 having a main sifting or screen
the result that some of the particles pass through the
screen and others pass over ther screen.
Thus the ma— 15
terial is classi?ed into separate fractions of different par
ticle size.
In such devices a sifter box is generally employed to
area 25 extends longitudinally of the sifter Hi.
This
surface divides the body portion into substantially closed
upper and lower chambers or compartments 26 and 23.
The sifter 10 also includes in the top plate 12 an inlet
opening 30 through which material can be fed onto the
imperforate receiving portion or plate 32 at the head or
enclose the sizing surface or screen and prevent the escape
of ?ne particles of stock. The sifter box is reciprocated 20 receiving end of the classifying surface 215. At the op
posite or discharge ends of compartments Z6 and 23 the
to provide the desired sifting action.
sifter 10 is- provided with an imperforate discharge por
While known sifter constructions are satisfactory for
tion or plate 34 adjacent independent outlets 36 and. 38
many purposes, certain problems require special con
which receive the separate discharge of the overs and
sideration when ?nely ground or powdered materials, 25 throughs from the classifying surface 24.
such as ?our milling stocks, are processed. One major
The sifter 10 is supported for reciprocation along a
problem involves the deleterious effect of dynamic air
desired path by hangers 4t) and 42 which are pivotally
pressures within the sifter box. It is this factor with
mounted to a suitable supporting structure 44». The
which the present invention is primarily concerned and
hangers 40 and 42 1are pivotally connected to the sifter
the effect of which is cancelled out to provide improved 30 10 at their lower ends and provide swinging movement
sifting as will be hereinafter disclosed.
thereto along an arcuate path generally perpendicular to
The effect of air within the sifter box has been found
the hangers, to provide conveying and sifting action in
or vibrated to convey the material across the screen and
to create undesirable pressure differentials on opposite
moving the material across the screen area 25.
sides or faces of the sizing screen. Such dynamic pres
The desired reciprocation is given to the sifter 10 in
sure changes may cause the stock to be held fast to the 35 known manner by the connecting rod 46 which is pivoted
screen when it should be free to slide, and conversely to
at its one end to the sifter 1G and at its other end to the
be blown upward away from the screen when it should
eccentric 48 carried by a rotating drive shaft 50, driven
be in close contact therewith. The pressure changes are
by a motor 52.
particularly encountered at rapid frequencies of recipro
As described up to this point, the sifter is designed to
cation, e.g., of the order of six strokes per second.
It is one object of our invention to provide an improved
receive stock through inlet 30 and to move the stock
across the sifting surface 24 from the imperforate re
sifter having means to increase conveying and sifting
efficiency by cancelling out the effect of dynamic air
ceiving end 32 toward the imperforate discharge end 34.
Stock which can pass through the perforated screen 25
is carried along the lower chamber and discharged at 38, _
ressures within the sifting chamber.
Another object of our invention is to provide an im
while the overs of screen 25 are discharged at 36.
provide sifting device having rigid partitions disposed at 45 In actual operation, however, such a sifter often‘ ex
particular locations within the sifting chamber to gen
hibits uneven and erratic movements of the stock, which
crate equal dynamic pressures above and below the sur- ‘
we have termed “surging.” For example, the convey
faces of the sizing screen.
ing movement of stock at the head or receiving end has
A further object of our invention is to provide an im 50 been observed to slow up and even back up toward the
proved reciprocating or vibratory sifter having a screen
inlet, while stock at the tail end moves even faster off the
surface which is enclosed to prevent dusting-out of the
screen and leaves a gap or bare areas on the screen 25.
material conveyed and having means for cancelling out
A thick pile of stock then accumulates at the head end
the effect of dynamic air pressures which affect the sift
and gradually expands along the screen, but without ap
ing operation.
A still further object of our invention is to provide an
improved sifting apparatus wherein rigid means is pro
55 parent conveying action. As the stock ?nally expands
toward the discharge end ‘and covers the screen, the con
veying movement of the layer may begin again. Stock
vided perpendicular to the direction of ?ow of the ma
terial to be sized for controlling ?uctuations in pressure
on opposite sides of its sizing surface.
~
Another object is to provide a sifter construction hav~
near the tail end moves off more rapidly, until the layer
again seems to break in the center screen area, with the
60 portion nearest the inlet backing up toward the inlet and
ing increased symmetry in construction above and below
the ends of the sifting surfaces to equalize the generation
of dynamic pressures.
Other objects and ‘advantages will become apparent 65
from the following speci?cation in which certain pre
the other portion moving more rapidly to the outlet.
Such surging is believed to impair the sifting action, since
some stock is held and sifted too long at the head end,
while other stock is discharged too soon with inadequate
sifting.
It is our belief that the inertia of the ?uctuating air
columns within the upper and lower chambers of the
sifter tends to affect the sifting and conveying operation
by creating pressure differentials on opposite sides 11
and 13 of the sizing screen 14. These pressure differen
proved sifter embodying features of the present inven 70 tials
appear to work in opposition to the desired sifting
ferred embodiments of the invention are described.
In the drawings which form a part of this application:
PEG‘ RE 1 is a schematic side elevation of-an im
tion;
.
.'
.
'_
.‘
1..
and conveying'action.
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3,021,953
For example the construction of the sifter is such that
the ends of the upper and lower chambers are not sym
mertical or balanced in their effects on the enclosed air
columns. Thus the area 54 at the head end of the lower
A
Lion are added at speci?ed locations. One such parti
tion 68 is located in the head end of the upper chamber
between inlet 30 and the head end of screen area 25.
Another partition 76 is preferably located at the tail end
of the upper chamber 26 above the frame member 66.
most chamber or compartment 28 is essentially closed by
These partitions are constructed with sufficient rigidity
the lower portion of head end wall 26. On the other
to prevent them from ?exing substantially in response to
hand, the inlet 36 through which the material enters the
reciprocation of the sifter. Thus the partitions serve as
Sifter body provides a sizeable opening for the corre
walls which can close the major cross section of the
sponding head end 56 of upper chamber or compartment
26 above the screen 25 and receiving surface 32. Dur 10 chamber in which they are located and can generate
dynamic pressure which neutralize or overcome the un
ing sifting as noted above, the di?erences in relative free
desirable effects of dynamic pressures generated in the
dom of movement of the air in these compartments (ex
other chamber.
cluding for the moment the partitions to be described
The rigid partitions 68 and 70 which are suspended
below) will cause pressure differentials which can give
15 beneath the top wall *12 within the upper chamber 26
rise to the undesirable results noted previously.
may be identically constructed. Because they do not
Thus air or ?uid columns in the compartments 26 and
completely close the ends of the chamber but provide a
28 above and below the screen 25 have aninertiawhich.
limited pas-agew-ay for stock just above the surfaces 32
tends to hold the ?uid column stationary as the sifter 10
and 34, they may he referred to as semi-partitions.
vibrates. ‘If the sitter it} is moving to the right, however,
Each semi-partition consists of an inverted L shaped
as indicated by the arrow 58 in FIG. 1, the tendency of
plate 72 and a substantially flat plate 74 which extends
the air to remain in its original position, and the move
across the width of the chamber 26 generally normal
ment of end wall 2% to the right, will produce a region
to the direction of ?ow of the stock 76. Plates 72 and
of higher density or higher pressure at 54 during such
74 are secured together by a plurality of screws or bolts
movement. Conversely, when the sitter moves to the
left as indicated by the arrow 69, the end wall 20 tends to 25 78 positioned in vertically slotted openings 80 in plates
74 and bolt holes 82 in plates “72-. The bolts 78 are pro
move away from the enclosed column of air in compart
vided with wing nuts 84 which hold or retain the plates
ment 23 to produce an area of lesser density or lower
72 and ‘74 together so that the lower edges 86 of the
presure at 54. These pressure variations within the sifter
plates 74 can be held in a desired adjusted spaced rela
10 are for practical purposes termed “air slugging” or
30 tion above the top surface of the receiving and discharge
dynamic air pressures.
plates 32 and 34. Accordingly one can readily loosen
The effect of “air-slugging” is somewhat dilferent above
the wing nuts v34- and slide plate 74 vertically to adjust
the screen 25, however, since the inlet 30 will permit ‘the
the spacing between the lower edges 86 of the plates 74
escape of part of the air column from the head end 56 of
and the top surface of the receiving and discharge plates
upper compartment 26 during movement of the upper
portion of end wall 20 and Sifter 10 to the right. Like 35 32 and 34.
By means of these semi-partitions 68 and 70, the dele
wise the inlet 3% will admit further air as the end wall 20
terious effects of dynamic air pressures within the charm
and sifter 16 move to the left. Thus the inertia of the
hers 26 and 28 are overcome or cancelled out, and inter
body of air above the screen 25 will not cause “air-slug
ference with conveying and sifting is prevented. This,
ging” or dynamic pressure of the same magnitude as that
below the screen. Hence the higher pressure at 54 tends 40 apparently results from the increased effective symmetry
of the upper and lower chambers. ‘
to lift the material being conveyed away from the screen
_ For example, by adjustment of the wing nuts 84, the
lower edges 86 of the plates 74 are raised or lowered as.
required so that a minimum opening is provided which
will ‘allow the stock 76 to pass, but will allow little or no
25 just when it should be in contact with the shifting
surface in order to obtain the ‘desired conveying and
sifting movement to the right. Likewisethe lower pres
sure at 54 during the movement of the sifter 10 to‘ the 45
air to flow in or out. Thus in effect the semi-partitions
left tends to draw the material conveyed down against
68 and 70 retain the air above the screen 25 captive during
the screen 25 and ‘move the material to thepleft, just
reciprocation of the sifter 10 and exert forces on the air
when it should remain free of the screen in order to ob
mass or column in upper chamber 26. These forces gen
tain relative movement toward the tail end of the sitter.
At the tall or discharge ends 62 and 64 of the respec 50 erate dynamic pressures in phase with reciprocation of the
sifter, which overcome the undesired effects previously
tive upper and lower chambers 26 and 28, the effects’ of
described. Thus the conveying effect at the head end is
dynamic pressures appear to increase the conveying ac
not slowed down or reversed, and the unduly rapid contion. Here, when the upper portion of'tail end wall 22
veying at the tail end is avoided.
moves to the right (arrow 53), it tends to create an area
of low pressure above the tail end of screen 25.
55
While the lower portion of end wall 2 may have 'a
similar effect in the region 64, an even more important
factor in this area is the presence of the usual frame
member 66 which supports the end of screen 25. This
member acts as a wall portion immediately below the 60
screen.
As it moves to the right it further decreases
the dynamic pressure at 64 beneath screen 25. The net
result is a pressure dilferential in which the lower pressure
below the tail end of the ‘screen holds stock on the screen
as the screen moves to the right. _
H
g
, Conversely, the increased dynamic pressures due’t'o
movement of wall 22 and frame 66 to the left (arrow
60) result in a pressure differential which ‘pushes the stock
The undesired pressure differences generated by recipro-
cation of a conventional sitter are accordingly neutralized
or overcome, and an equalization of pressures above and:
below the screen 25 within the chambers 26 and 28 pro
vides improved sifting and conveying to the stock at both
the head and tail of the sifting surface.
In establishing the desired e?ective symmetry of the
upper and lower chambers, one should consider the ef
fects of the stock outlets'as well as inlet 30.
During operation of the sitter 10 stock admitted through
65 inlet 30 'may‘arrive at a rate which effectively closes o??
all-or part of the inlet. One may recognize the degree of
pressure‘ relief -'a?‘orded by the'dischar'ge outlets 36 and
38 which receive the overs 88 and the throughs 90 of
the stock 76, and‘lo‘cat'e the ‘semi-partitions 68 and 70
upwardly away from the screen on this return stroke.
The net elfectis to increase the conveying e?ect and hurry 70 accordingly. The partitions are adjusted to provide a
minimum opening adjacent the lower edges 86 of the
the material off the discharge end of the screen.
According to the present invention means are intro
duced to increase the effective symmetry of dynamic pres
plates 74 which will allow the stock 76 to be conveyed
across the surface of the screen 125.
'As willbeenoted in FIG. 1 the sitter 1t!‘ issubstantially
sure. generation in the upper and lower chambers 26 and
‘2a. For this purpose partitions of apprc riate construo .75 closed to outside atmosphere with the inlet 30 connected
3,021,953
to stocking 94 and a hopper 96. Likewise the discharge
outlets 36 and 38 may be connected to stockings 98 and
100 and to a hopper 102 and further sifter 104, respective
ly. Thus the present device provides not only an improved
sifter having increased sifting and conveying e?iciency,
but also one in which the “dusting-out” of particles is sub
stantially prevented.
By adjustment of a speed changer 92 attached to the
6
means in said chamber for feeding stock to be classi?ed
thereto, outlet means for discharging classi?ed stocks, a
sifting surface intermediate said inlet and outlet means for
classifying said stock during said reciprocation, a substan
tial'y imperforate receiving plate at one end of said sifting
surface below said inlet means, a relatively air-tight dis
charge plate at the opposite end of said sifting surface
adjacent said discharge means, means for reciprocating
said devices including said chamber, wall members and
motor 52 the rate of reciprocation of the sifter 10 may
be controlled so that the stock 76 is conveyed at a given 10 sifting surface as a unit along a given path, and rigid anti
rate.
In FIG. 3 a further embodiment of the invention is
shown. Under certain operating conditions the air within
the chamber 26 may tend to blow underneath the lower
surging partition means disposed above each of said
plates and having an area transversely of said direction of
reciprocation, which partition reciprocates with said wall
members and thereby moves a volume of air within said
edge 36 of the plate 74 and escape through the outlet 30 15 chamber above the sifting surface in desired phase and
during reciprocation. To prevent such action, the pre
correlation with the reciprocation of said chamber to
ferred form of FIG. 3 replaces plate 74 by an L shaped
provide improved sifting and conveying.
member 106 having'an arm 108 extending generally paral
6. The device of claim 5 wherein each of said rigid
lel to the direction of ?ow of the stock 76. This arm
partition means comprises a pair of plate members ex
provides a relatively long restricted passage between the 20 tending across the width of said chamber and wherein at
partition and screen as indicated by the numeral 110.
least one of said plate members on each partition is ad
The stock effectively closes most or all of this passage and
justably mounted with respect to the sifting surface of
further retards any movement of the air past the incom
said chamber.
ing stock.
7. An improved sifting device comprising a sifting
The above description presents a disclosure of the in 25 chamber enclosed by a plurality of wall members, means
stant invention. The speci?c construction details of the
for reciprocating said chamber along a given path, an inlet
sifting device 10 are used for illustration only and should
and outlet means in said chamber, a sizing surface divid
accordingly not be considered as limiting the invention
ing the sifting chamber into an upper and a lower com
to the exact form disclosed. For example, depending on
partment and movable as a unit with said enclosed cham
the shape and location of such frame members as 66 (FIG. 30 ber, and rigid partition means secured for reciprocating
1) it may be desirable to increase the effective symmetry
movement with said chamber and disposed within said
at the discharge ends of the upper and lower chambers
upper chamber adjacent said outlet means and having a
by adding a further semi-partition 112 at the end of the
substantial area transversely of said path and thereby
lower chamber directly beneath upper partition 70, as
moving the volume of air within the outlet end of said
35 chamber in correlation with said reciprocation.
shown in the dotted outline in FIG. 1.
We have set forth in this application the principles
8. A sifting device comprising an enclosed sifting
believed to be involved and some of the ways in which
chamber having an inlet and outlet means for receiving
the invention may be practiced.
and discharging material to be classi?ed, classifying means
We claim:
within said chamber between said inlet and outlet means,
~10
1. In a reciprocating sifter comprising a conveying and
means for moving said chamber and said classifying
sifting surface having an imperforate receiving end, a
means as a unit relative to said material whereby it is
discharge end, and a perforated sifting area between said
classi?ed, and dynamic air pressure generating means ad
ends, a body portion having walls enclosing said con
jacent one of said inlet an outlet means in close proximity
veying and sifting surface and providing separate substan
with said material and located and arranged to generate
tially closed upper and lower chambers extending longi 45 dynamic air pressures in response to relative movement
tudinally above and below said surface, means for re
of said chamber, thereby preventing air slugging and
ciprocating said body chambers and sifting surface longi~
surging of the stock within said chamber during said rela
tudinally as a unit and thereby conveying stock across
tive movement.
said sifting area from the receiving end to the discharge
9. An improved sifting device comprising a reciprocat
end, an inlet for stock at the receiving end of the upper 50 ing sifting box, means for reciprocating said box along a
chamber and an outlet for stock at the other end of each
given path, a sizing screen dividing said box into an upper
chamber, the improvement comprising an anti-surging
and a lower chamber and movable therewith, an inlet
partition located in said upper chamber between said
located at a ?rst end of said upper chamber, outlets lo
inlet and said sifting area at a point adapted to equalize
cated at the second end of each chamber, rigid anti
dynamic air pressures in said upper and lower chambers, 55 surging partitions between said inlet and said screen and
said partition being secured for reciprocating movement
between said screen and at least one of said outlets, said
with said body and sifting surface and having an upper
partitions extending transversely of said path and having
edge adjacent said top wall, side edges adjacent said side
a shape and area substantially closing the passage through
walls, and a bottom edge spaced closely above said surface
"the upper chamber except for a minimum opening re
and thereby providing a restricted passage adapted to be 60 quired by the stock to be passed through the device for
substantially closed by stock passing from the inlet to the
sifting area.
7
a‘
' I
2. A sifter according to claim 1 in which said partition
has a ?ange at its lower edge, said ?ange extending paral
lel to the sifting surface and thereby providing a relatively 65
long restricted passage adapted to be closed by said stock.
3. A sifter according to claim 1 having a similar parti
tion at the discharge end of the upper chamber.
4. A sifter according to claim 3 having a similar parti
tion in the lower chamber extending downwardly from 70
said surface at the discharge end of said perforated sift
ing area.
sifting, and said partitions being secured for reciprocating
movement with said box.
'
References Cited in the ?le of this patent
UNITED STATES PATENTS
398,692
794,936
1,214,506
1,686,107
1,793,018
2,047,713
5. An improved sifting device comprising a sifting
2,589,957
chamber enclosed by a plurality of wall members, inlet 75 2,903,135
Bittinger _____________ -_ Feb. 26,
Harris ______________ __ July 18,
Brasack ______________ __ Feb. 6,
Sewell _______________ .._ Oct. 2,
Runge _______________ __ Feb. 17,
1889
1905
1917
1928
1931
Simpson ____________ __ July 14, 1936
Pearman ____________ __ Mar. 18, 1952
Dryg ________________ __ Sept. 8, 1959
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No. 3,02l‘953
February 209 1962
William A. Brastad et al.
It is hereby certified that error appears in the above numbered pat
ent requiring correction and that the said Letters Patent should read as
corrected below.
Column 2v line 52' for "areas" read -- area -—; column 3.
line 42, for "shifting" read —— sifting ——; line 56, for "2"
read -- 22 --; column 4, line 11, for "pressure" read pres
sures —--3 line 18, for "pasageway" read —— passageway ——;
column 6,, line éllY after "material" insert —— along a desired
—_o
Signed and sealed this 12th day of June 1962‘.
(SEAL)
Attest:
ERNEST W. SWIDER
Attesting Officer
DAVID L. LADD
Commissioner of Patents
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