Improvements in Sifting or Bolting Machinery.
Year: 1887

page_text: Date of Application, 1st Sept., 1887
Specification Accepted, 9th Mar., 1888
COMPLETE SPECIFICATION.
Improvements in Sifting or Bolting Machinery.
I, FRIEDRICH GEORG WINKLEB, of Zschopau, in the Empire of Germany, Manu
facturer, do hereby declare the nature of this invention and in what manner the same
is to be performed to be particularly described and ascertained in and by the
following statement :-
My invention relates to an improved construction of sifting or bolting machinery
for sifting or separating pulverulent materials, such as meal, cement &c., in which
rotary fans are employed within a sifting or bolting cylinder so arranged as to produce
alternately a pressure and a suction current of air through the surface of the sifting
or bolting cylinder, whereby the particles that may have been made to adhere to the
said surface by the one current and thus obstruct the sifting action, are removed by
the return current so as to leave the entire sifting surface unobstructed. Arrange-
ments for this purpose were described in the Specification to Haddan's Patent
No. 10576 of 1885 (being a communication to him from me) and in order that my
improvements may be readily understood I will proceed to describe the invention
generally with reference to the accompanying drawings in which Figure 1 is a vertical
section of a horizontally arranged machine. Figure 2 is a similar section but in a
perpendicular direction to the plane of the first section. The Figures 3 to 14 show
several constructions of fans to be used in the improved machine.
The disposition of the apparatus may be a vertical, horizontal or inclined one.
A single sifting machine may be employed or as shown in the Figures 1 and 2 two
machines may be arranged one above the other, the upper of which may be used as a
fore-sifting machine and the lower as a finishing sifter.
In this apparatus the essential and novel feature, consist of the arrangement of a
מ'

page_text: fan apparatus F (see Figures 1 and 2) of a particular construction by which the air
is put in motion so as to pass alternately (see the radial arrows in Figure 2) through
the sifting surface S from inside to outside and from outside to inside.
A sifting effect is hereby produced on the material to be sifted and introduced
between the fan apparatus and the sifting surface, as by the air moving from inside to
outside the fine particles are forced through the sifting surface, while the air current
moving from outside to inside removes the coarser particles lying on the inside of the
sifting surface and again frees the meshes of the gauze.
This process will hereinafter be more fully explained in describing the fan apparatus.
The effect of the above named fan apparatus F as well as of other fau apparatus here-
tofore used in sifting machines, may still be considerably increased by a deflecting
grate G arranged between the fan and sifting surface. The deflecting grate may be
made either of flat or angular bars, arranged as louvre blades or it may consist of
round quadrangular or otherwise shaped bars. The separate bars of the guiding grate,
may be fixed or adjustable so that they may be regulated.
The effect of a such a guiding grate is as follows:-
In rotating fans the tangential throwing movement of the particles acted upon, is
prejudicial to the sifting effect as, owing to the acute angle at which the material to
be treated strikes against the sifting cloth, and which is formed by the tangential line
of projections, and the sifting surface, it is rendered difficult for the particles to pass
through the fine openings of the sifting surface. The above named deflecting grate
has for its object to change this tangential throwing direction into a radial one so that
tho sifting particles strike nearly at a right angle against the sifting surface. The grate
may be stationary, or it may be put in rotation; in the latter case it can be considered
as a second fan which is independent of the inner one.
In Figure 1 two sifting machines embodying my invention are placed one above
the other and in the present case the upper apparatus works as a fore-sifter and the
lower as a finishing sifter. The essential parts of the two machines are
identical.
a is the shaft of the fan F and it receives its impulse from the pulley b. The
guiding grate G is by way of example made of bars g g (see Fig. 2) having an
angular cross section.
The bars g g forming a cylindrical casing are connected with the hollow shaft d by
discs cc, or other suitable contrivances, the shaft d being put in rotation by the
pulley e.
The bars of the guiding grate, may also be connected with the frame, carrying the
sifting surface S. The bars of the guiding grate may finally be secured to the frame
of the machine, when a stationary guiding grate is intended to be employed.
The sifting surface S may also be stationary or it may rotate slowly. In the latter
case it is put in rotation by the shaft f by means of chain gear, or by any other means
ordinarily used for that purpose. The number of revolutions of the apparatus shewn
in Figures 1 and 2 may differ according to the nature of the material to be bolted ;
for sifting meal for instance the fan may make from 500 to 800 revolutions, the
guiding grate from 100 to 20 revolutions and the sifting surface from 20 to 30
revolutions.
To render the construction of the fan fully understood, I will give the following
explanations.
In all the sifting machines, heretofore known, the sifting process consists of
throwing the material to be treated against the sifting surface, by means of fans of
different shapes.
The higher the mechanical force whereby the material is thrown against the sifting
surface, the less the fan must be distant from the latter; this has however the incon-
veniences that the line of projection strikes the openings of the sifting machine at too
acute an angle. When the machines heretofore used the fans are arranged at a
greater distance from the sifting surface, it is rather difficult to force the light particles
to be sifted through the sifting surface, because it is difficult to throw these particles.

page_text: Owing to the rotation of the fan blades an air pressure is produced along the whole
sifting surface, which in combination with the throwing movement forces the material
to be treated through the sifting surface.
This sifting effect has however in all the machines heretofore used the great dis-
advantage that, by the uniform air pressure on the inside of the sifting surface
combined with the said throwing effect of the blades, the openings of the sifting
surface will be obstructed from inside to outside. The work done by sifting machines
heretofore employed is dependent on this main disadvantage and many means have
been used to remedy it.
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By observing the fan itself I have found means to free the whole sifting surface
from any obstructed meshes by a cleansing operation moving together with the
rotation of the fan. This means consists in the use of the particular form of the fan
arrangement which has already been employed in blowing machines such as Roots
Blowers" and by which an alternate suction and forcing air current is produced.
Such fans are made to operate for sifting purposes, in the following manner. A
comparatively small number of blades are made to extend from the central axis to
close to, or within a short distance of the sifting surface or of the before mentioned
ring of guide vanes if such are used. In revolving at a high speed, these blades produce
an air pressure in front of them, so that the air is forced from within the sifting
cylinder, outwards through the sifting surface, while immediately behind the blades
a partial vacuum is produced, causing the air that had just been driven out of the
cylinder to be drawn into it again, the fan blades being made to fit closely against the
closed ends of the cylinder so that there is no other passage for the air except through
the screening surface, so that the apparatus is thus made to act practically continuously
with one and the same body of air, which is caused to pulsate backwards and forwards
through the screening surface.
By this peculiar motion imparted to the air the screening surface is effectually
prevented from clogging, as any coarse particles that may be made to adhere to the
inner side of the sifting surface, by the centrifugal force with which the material is
thrown against it, will be effectually removed by the immediately following inward
motion of the air.
In the above described mode of operating the number and intensity of the outward
and inward currents or pulsations will depend upon the speed of rotation and the form
of the fan blades, and I will proceed to describe various modifications in the form of
the blades which I employ for this purpose and the effects produced thereby.
The large peripherical arrows in the Figures 3 to 14 indicate the revolving direction
of the fan blades, and the other arrows the direction of the suction and pressure air
currents. The thickness of the arrows is proportional to the intensity of the pressure
and suction air currents. The thickest arrows show the places where the pressure and
suction air currents are of the highest intensity.
The Figures, 3, 4, 5 and 6, of the accompanying sheets of drawings, illustrate
shapes of fans which are suitable for obtaining the above described purpose.
The suction and pressure air currents are approximately separated, as shown in the
drawings; the cross hatched parts of the figures represents the suction air current,
and the non-hatched part the pressure air current. The limits of the suction and
pressure air currents such as they are indicated in the drawings, correspond to the
actual fact inasmuch as they are produced on the end plates of the fan the parts of
these which are touched by the pressure air, being clean while the parts touched by
the suction air are covered with a fine dust of the material operated upon.
To increase the sifting effect the sifting surface must be tightly stretched so as not
to participate in the air pulsations. The fan constructions shown in the Figures 3, 4
and 5, are not quite perfect; the transition from the pressure space in front of the
blades, to the suction space behind them taking place too suddenly, that is to say
the sifting effect is limited nearly to a line rotating inside the cylinder with
the fan.
This has the inconvenience, that a large quantity of the pressure air seeks to take

page_text: +
the course more favourable to compensation, that is to say, towards the suction space
past the outer edge of the blade, instead of passing through the sifting surface; in
this arrangement a great speed is necessary for obtaining a certain effect.
It has been endeavoured to change the pressure line which formerly moved along
the sifting surface, into a pressure surface, whereby a sufficiently long time is given to
the pressure air to pass through the sifting surface, (to expand) before the suction
wave begins to act, so that during this time a sifting effect of longer duration is
attained. This is produced for instance, already by the form of blades shown in Fig. 6.
where these are made of a certain width at the periphery.
In Fig. 7 an extended group of fan blades is arranged, at a in the pressure space,
to cause the pressing effect to begin earlier; in the suction compartment a group of
blades b is also provided for the purpose of maintaining the pressure air forced out of
the pressure space still under pressure for some time.
In. Figure 8 the blade groups a are arranged for the same purpose in the
pressure space, as in Fig. 7.
Instead of the blade group 6 of the suction compartment represented in Fig. 7,
Fig. 8 shows between the pressure compartments and the suction compartment a
number of blades e extending from the periphery to the centre and forming closed
air chambers, whereby the pressure air escaping from the pressure space is maintained
under continued pressure at a higher degree than in the arrangements shown in Fig. 7.
In Figure 9 the fan blades d characterised in Fig. 5 and extending to the centre form
already by themselves a blade group, the effect of which is still further increased by
a blade group arranged at the periphery.
Besides the blade group arranged between the pressure and suction groups for the
purpose of continuing the effect of the pressure air, there is in the suction compartment
itself a number of blades e characterized by Figure 5 and arranged in groups, which
have for their purpose to divide the suction compartments into several separate
suction compartments in such a manner, that the powerful sucking current, which
is at the back of the expansively working pressure wave, is protected against any
pressure air.
In Figure 10 the suction space is likewise divided into several suction compart-
ments for the same purpose as in Figure 9. The pressure space does not require
any blade group as the pressure air which has act in a plane is already produced
by an extended arch-like fan blade. Owing to the effect of the pressure air spread
over planes as well as to the division of the single suction space into several suction
spaces, it is possible to obtain the rarefaction of air at a lower number of revolutions
than that which the fan shown in the Figures 3, 4, 5, and 6 require.
In the fan constructions illustrated in the Figures 9 and 10 there is still pressure
air in the suction space of the fan, namely at the ends of the blades, therein arranged
as may be seen in the diagram. This circumstance is of course prejudicial to the
good effect of the fan. By numerous experiments carefully and accurately carried
out, I have invented new fan constructions which produce an excellent effect and
which may therefore be considered as the best of the fans constructed according to
the new principle. In these fans the blades in groups are replaced by closed blades
arranged in the suction and pressure space. In this way a peculiarly shaped blade
drum is formed, the surfaces of which are not conaxial surfaces of a cylinder.
The Figures 11, 12 and 18, show some forms of these peculiarly shaped fans.
If it be desired to provide in these fans blades arranged in groups such as shewn
in the Figures 7 to 9, the back-flow of air from the pressure space into the preceding
suction space would be prevented in an efficacious manner. These blades are not
shewn in the drawings as they may easily be applied according to the above given
explanation.
Figure 11 shews a suction compartment of great intensity, sucking up so large a
quantity of air at that there is not sufficient room for the same in the pressure
compartment, so that a back-flow of part of the pressure air at f' in the shortest road
towards the suction space will be produced below the suction curve as shown by the

page_text: arrows, and also in Figures 12 and 13 so that only the portion f¹ of the air drawn in,
acts as pressure wave.
In order to prevent this action supplemental blades were arranged above the surface
of the main blade, between the currents indicated by the arrows f' and f' so as to
leave a small suction space behind such blades so that the air at f on its way from the
principal suction space to the pressure space at f1 does not encounter too high a
pressure on the conaxial pressure surface of the main blade, and is consequently not
obliged to flow back on this surface towards the suction space.
Moreover it has been found that such supplemental blades arranged in the suction
space, act the more favourably the larger they are, but in increasing their size it was
found necessary to impart an inwardly bulged form to the conaxial pressure surface of
the main blade, in order to give room between them for the above mentioned small
suction space.
Finally it has been found that the group of supplemental blades formed in such a
manner in the pressure space, may very advantageously be replaced by a single
peculiarly shaped closed blade, having three surfaces as shown at g Figure 14. The
return of the pressure air towards the principal suction space, has been essentially
reduced by the rarefaction of the air, which is produced at the back of that peculiarly
shaped blade. The entire backward flow of the pressure air towards the suction space,
is, however, impossible with suction blades, having curve like commencements as at j
Figures 11 and 13, because the suction, which is absolutely protected by the curved
surface, draws in too rapidly and violently its quantity of pressing air. For this
reason the suction space has been partially opened again by an inward curvature, as
shown at Figure 14 in such a manner that about a quarter of the distance from one
pressure wave to the next pressure wave has been opened, and that the curve-like
conaxially shaped part of the suction blade commenced only after this opening, at a
correspondingly lower point i. By this is obtained that the whole pressure air drawn
in by the principal suction space at f, passes without back flow to the pressure space
partly at and partly at and is even sucked up by the latter, on account of the
rarefaction of the air which is produced at the back of the peculiarly shaped blade g.
By this means is obtained that the suction wave operates during a longer time than in
the arrangement at Fig. 11, as will be seen by the arrows, and that the quantity of
pressure air and consequently the sifting effect is essentially increased.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is :-
1. In sifting machines, which work with fans of the kind herein referred to the
closure of the suction compartment from the pressure compartment, inside the fan by
angularly shaped, straight or curved blades the apices of which are at the centre of
the axis, or outside the same, and the connexion of the ends of the limbs by one or
more plane or curved surfaces, which fit to a certain extent close against the cylindrical
sifting surface, substantially as herein described, with reference to Fig. 6.
2. In sifting machines which work with fans, the addition to the main blades of the
fans other blades, arranged in groups in the suction or pressure space for the purpose
of removing the most violent pressing effect from the most violent sucking effect at
a sufficient distance for giving the pressing air the necessary time to pass through the
sifting surface, whereby the pressing and sucking effect is distributed not on single
points but on larger surfaces, substantially as herein described with reference to
Figures 7 to 10.
3. In sifting machines which work with fans, the arrangement of closed fan
blades the surface of which are composed of convex, concave or straight parts or of
a combination of these parts with each other, substantially as herein described with
reference to Figures 11, 12, 13, and 14.
4. In sifting machines which work with fans, the arrangement of closed fan blades
in combination with fan blades, arranged in groups for the purpose of removing the

page_text: most violent pressing effect from the most violent sucking effect to a sufficient distance
for giving the pressure air the necessary time to pass through the sifting surface,
whereby the pressing and sucking effect is distributed not on single points but over
larger surfaces.
5. In sifting machines, which work with fans, the arrangement of closed fan blades
in combination with fan blades arranged in groups which are either entirely or
partially formed as closed blades, substantially as herein described with reference to
Figure 14.
6. In sifting machines which work with fan works, the combination of a fan with a
stationary or revolving deflecting grate, and with the stationary or revolving sifting
surface as herein described and shown in the accompanying drawings.
Dated this 1st day of September 1887.
ABEL & IMRAY,
Agents for the Applicant.