An air-swept mill has an annular space with a blade ring between a rotary grinding pan and a casing wall for fluid delivery flow. The annular space and the blade ring form a gas directing or guiding device for rotary flow and circulation flow of the fluid delivery flow. Above the grinding pan, in the vicinity of a classifier, the casing wall is provided with at least one removal device for removing a part of an outer oversize flow, which is formed as a vented concentrated flow substantially directly at the casing wall.

BACKGROUND OF THE INVENTION 
(a) Field of Invention 
The invention relates to a method for crushing material of different grain 
size, in which the material is supplied to a rotating, horizontally 
positioned grinding surface of a grinding-classifying chamber having a 
casing wall and is crushed to grinding material particles, in which the 
grinding material particles are supplied with the aid of a delivery flow 
introduced on the circumference of the grinding surface to a classifying 
process and fine material particles are discharged and in which a part of 
the oversize occurring as coarse material particles is removed, as well as 
to an apparatus for performing the method especially an air-swept mill 
having between a rotating grinding pan and a casing wall an annular space 
with a blade ring for a fluid delivery flow. 
(b) State of Prior Art 
It is known to relieve a grinding-classifying chamber, e.g. an air-swept 
roller mill, of the non-crushed or not adequately crushed grinding 
material, the so-called oversize, in that said oversize is drawn off to 
the outside during the grinding process and is then generally returned to 
said process. 
Through the removal of a specific percentage of oversize material, the flow 
resistance in the grinding-classifying chamber drops, so that it is 
possible to reduce the delivery energy for a fluid flow to be expended on 
a unit. The necessary mechanical energy for a mechanical oversize return 
located outside the grinding-classifying chamber is much smaller. 
DE 41 24 416 A1 discloses such a method. Oversize material, which has been 
rejected by the classifier as tailings, on a dropping path to a grinding 
surface are at least partly removed to the outside via a screw conveyor. 
According to a method known from DE-AS 1 152 297 in an air-swept roller 
mill with integrated classifier a fluid, e.g. air or a gas is introduced 
into a grinding-classifying chamber. The fluid is brought in an annular 
space between the grinding pan and the casing wall to such a high speed 
that substantially all the grinding material particles spun off from the 
grinding pan under the action of centrifugal force, i.e. from the charge 
particle size to the finished particle size, are taken up by the fluid 
flow and conveyed to the classifier as a two-phase mixture. 
By means of a fluid flow at a relatively low speed it is ensured that a 
high percentage of largely non-crushed material drops downwards out of the 
mill. In this way the pneumatic conveying energy of the fluid flow unit 
can be lowered as a result of a reduced flow resistance due to a lower 
grinding material load. 
In the known methods grinding material particles are drawn from the 
grinding, classifying, drying and pneumatic conveying process occurring 
the mill and the classifier, so that there is a change to one of the 
numerous factors influencing a complex dynamic grinding-classifying 
system. 
It is known that the modification of one factor, e.g. the modification to 
the speed of the delivery flow in the annular clearance of the removal of 
grinding material particles from the grinding-classifying process, 
influences further parameters, such as e.g. the wall friction, gas 
friction, friction between the gas and grinding material particles, flow 
formation in the mill and classifier, particle distribution and particle 
sizes, so that there must be a new state of equilibrium. 
Even a partial removal of uncrushed or inadequately crushed grinding 
material particles has a negative influence on the grinding bed formation 
on the grinding pan, because coarse particles in conjunction with fine 
particles lead to a maximum packing density and to an almost ideally 
compacted and optimum crushable grinding bed. However, if coarse 
particles, e.g. up to 250%, based on the finished material flow, is 
removed from the grinding material flow enriched with particles and 
circulating in the grinding-classifying chamber, the coarse particles are 
more particularly missing from the grinding bed formation. This leads to 
the disadvantage of there being no autogenous grinding aid on the part of 
the coarse particles. Since during the external delivery process no 
crushing occurs, neither the coarse nor the particles undergo further 
crushing. 
Although a reduction of the flow energy leads to a saving of pneumatic 
delivery energy at the fan, this procedure leads to a reduced crushing 
capacity, so that all things considered there is no saving with respect to 
the overall, specific power requirement. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a method and an apparatus for 
crushing material, which leads to a reduced energy consumption per ground 
ton of crushing material and permits an increased throughput of the 
crushing apparatus or plant. 
According to the invention this object is achieved by a method for crushing 
material of different grain size, in which the material is supplied to a 
rotating, horizontally positioned grinding surface of a 
grinding-classifying chamber having a casing wall and is crushed to 
grinding material particles, in which the grinding material particles are 
supplied with the aid of a delivery flow introduced on the circumference 
of the grinding surface to a classifying process and fine material 
particles are discharged and in which a part of the oversize occurring as 
coarse material particles is removed, wherein grinding material particles 
spun over the edge of the grinding surface are exposed to a rotary 
delivery flow, the spun off grinding material particles are moved upwards 
in a helical flow, close to the casing wall a particle flow is formed as 
an almost vented concentrated flow and the vented concentrated flow is at 
least partly removed from the grinding-classifying chamber and an 
apparatus for crushing material for performing the method, especially an 
air-swept mill, which between a rotary grinding pan and a casing wall has 
an annular space with a blade ring for a fluid delivery flow, the annular 
space and the blade ring forming a gas directing or guiding device for a 
rotary and circulation flow of the fluid delivery flow and above the 
grinding pan in the vicinity of the casing wall is provided at least one 
removal device for removing of a part of the oversize from an outer 
oversize flow. 
According to the invention, the grinding material particles spun by 
centrifugal force from a rotary, horizontally positioned, e.g. almost 
planar, inclined or also through-shaped grinding surface in a 
grinding-classifying chamber are exposed to a rotary flow of a fluid 
delivery flow introduced on the circumference of the grinding surface. The 
grinding material particles, which are conveyed in a helical upward 
movement, form, as a result of a clearly defined delivery flow speed and 
the rotary or twisting flow of a gas directing device for guiding the gas 
an almost vented concentrated or compacted flow, which is at least partly 
removed from the grinding-classifying chamber and is preferably returned 
by means of an external delivery device to the grinding chamber. 
The basic idea of the invention is to form an almost fines-free, external 
oversize flow substantially directly at the casing wall in the form of a 
vented concentrated flow and to at least partly remove its dead material 
or mass. 
Thus, the method according to the invention also provides for the saving of 
pneumatic delivery energy by oversize removal from the 
grinding-classifying chamber in order to reduce the flow resistance. 
Unlike in the case of the known methods, removal only takes place of the 
oversize, which as dead material or mass burden the grinding-classifying 
chamber, because they do not continuously participate in the grinding and 
classifying process. 
It is in particular provided to produce the almost fines-free, vented 
concentrated flow called the external oversize flow, by a clearly oriented 
delivery flow with a speed of &gt;30 m/s, particularly with an twist 
producing gas directing device, e.g. through an angular setting of a blade 
ring in the tangential direction. The rotary flow or flow twist leads to a 
helical upward movement of the fluid flow with the grinding material 
particles spun from the grinding pan. A twisting flow produces centrifugal 
forces due to the internal expansion tendency and they also act on the 
grinding material particles. As a function of their size, said particles 
are also subject to a dragging force of the fluid flow produced in the 
direction of the classifier, i.e. towards the centre of the 
grinding-classifying chamber. The equilibrium conditions which occur are 
dependent on the mass of the grinding material particles. Independently of 
the action of a classifier, which is arranged in integrated manner in or 
mounted on top of an air-swept mill, due to a blade ring classifying of 
the outwardly spun grinding material particles, a grain separation is 
brought about solely by the use of a specifically constructed and arranged 
gas directing device for guiding the gas and a vented concentrated flow is 
formed. 
It is advantageous that in the case of an adequate enrichment or 
accumulation of grinding material particles in the vented concentrated 
flow as a result of gravity action on said particles to bring about a 
downward movement directly at the casing wall, so that a so-called 
particle torus of limited radial extension is formed. The outer oversize 
flow or the particle torus rotates about its vertical axis which is 
parallel or coaxial to the grinding-classifying chamber axis. It is 
important that the outer oversize flow or particle torus is inwardly 
thickened to a specific, radial extension and without participating in the 
grinding and classifying process is kept suspended by an outer downward 
flow and an inner upward flow in the grinding-classifying chamber. 
It is appropriate to at least partly remove from the marginal zone area 
oversize fractions of the outer oversize flow, said removal taking place 
continuously and under air exclusion. 
It is particularly appropriate to return the removed oversize fractions 
following external mechanical conveying in bypass round the air-swept mill 
and classifier, the supply taking place together with a fresh material 
charge or separately therefrom. 
According to the method of the invention oversize fractions of the outer 
oversize flow of 200.+-.50%, based on the finished product rate of the 
mill, or any percentage below this can be removed, without impairing the 
effectiveness of the crushing process and the classification. A continuous 
removal of the outer oversize material not participating in the grinding 
and classifying process leads to a continuous relief of the 
grinding-classifying chamber and to a reduction of approximately 30% of 
the flow energy to be expended. The disadvantage occurring in the hitherto 
known methods, that an adequately crushed grinding material particle 
fraction is also removed from the grinding process does not occur here. 
An apparatus for crushing material with especially an airswept mill, 
particularly for performing the method, provides a gas directing device 
formed by a per se known blade ring in an annular space around a rotary 
grinding pan for forming a rotary and circulation flow of the fluid 
delivery flow and at least one removal device in the vicinity of the 
casing wall of the air-swept mill for an oversize fraction of an outer 
oversize flow or the vented concentrated flow. 
A preferred removal device is a pocket connected tangentially in the mill 
and/or classifier casing, in which collect the oversize rotating on the 
wall under centrifugal force and gravity action and which can be 
automatically vented by dynamic pressure action. Appropriately the pocket 
is provided with an outlet connection issuing an air lock. 
In order to be able to remove oversize fractions from the outer oversize 
flow with a given thickness and virtually peel off the same, it is 
appropriate to have an almost slot-like removal area with an adjustable 
opening. For example, it is possible to remove an oversize fraction with 
the aid of a guide plate pivotably located on the casing wall. It is also 
possible to have a vertically or horizontally displaceable plate, which 
permits an increase or decrease in the size of the removal area. 
From the pocket the removed oversize faction can be supplied in the vented, 
compressed state, particularly by gravity, to a mechanical conveying 
device, e.g. a bucket elevator. This mechanical conveying device can be 
connected to a further crushing device. Preferably the mechanical 
conveying device is connected for the purpose of returning the removed 
oversize fractions to a charging device for the charge or directly to the 
grinding-classifying chamber or the grinding pan for an almost central 
supply. 
In an development of the apparatus according to the invention the 
mechanical conveying device is supplied at least partly with the inner 
oversize separated from the classifier and/or the grinding material 
particles dropping downwards over the grinding pan and to return the same 
to a further crushing process, particularly the air-swept roller mill 
grinding pan. 
The gas directing device for guiding the gas is constructed in such a way 
that a fluid flow entering the air-swept mill below the grinding pan is 
forced into a rotary or twisting flow, so that the grinding material 
particles spun off said pan are conveyed upwards in a helical path and 
directly to the casing wall. 
Appropriately the blades of a blade ring positioned at an angle and in the 
tangential direction form flow channels through which a fluid flow at a 
speed of &gt;30 m/s exerts an ejector action, so that the outer oversize flow 
or concentrated flow rotating close the casing wall is produced.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an air-swept mill 4 with a grinding pan 6, on whose grinding 
surface 5 are separately driven or roll by frictional resistance grinding 
rolls 7. Above the grinding rolls 7 and in an integrated arrangement 
within a grinding-classifying chamber 8 bounded by a casing wall 15 is 
provided a classifier 29 with a classifier rotor 24. 
The material of different grain size to be crushed is supplied almost 
centrally to the grinding surface 5 as a charge 10 by means of a not shown 
supply mechanism. Between the casing wall 15 and the grinding pan 6 is 
formed an annular space 14, in which a blade ring 16 of blades arranged 
and constructed in a clearly defined manner forms an annular gas directing 
device 19, whose flow channels 20 give a delivery flow 9 of a fluid, 
particularly a gas, an ejector action. As a result of an angular setting 
of the blade ring 16 in the tangential direction a rotary and circulation 
flow 21, 22 is produced in the immediate vicinity of the casing wall 15, 
in which the grinding material particles 13 are taken up in a virtually 
vented concentrated flow 17. 
The vented concentrated flow 17 is formed by a blade ring classification of 
the crushed grinding material particles 13 spun from the grinding surface 
5 to the annular gas directing device 19. As a result of the helical 
upward movement of the flow twist produced in the gas directing device 19, 
the vented concentrated flow 17 is not deflected towards the classifier 
29. Following an enrichment with grinding material particles 13 gravity 
comes into action and together with an ejector action on each flow channel 
20 a circulation flow 21, 22 is formed about a virtually vertical axis, 
which is characterized by an internal upward flow 21 and an external 
downward flow 22. This overall flow extending in the wall area of the 
air-swept mill 4 is of limited radial extension and constitutes a particle 
torus. 
The particle torus can be looked upon as a dead mass 23, which thickens to 
a specific radial extension and is then kept suspended only in a flow area 
without participating in the grinding and classifying. 
The particle torus, an outer oversize flow 18 circulating about a vertical 
axis, starting from the ejector action of the flow channels 20, sucks in 
both fluid and grinding material particles in accordance with the arrow 
35. These fractions come from a circulation (arrows 40) within the 
grinding-classification chamber 8. As a result of the lower partial 
pressure a higher proportion flows from above through the centre of the 
air-swept mill and with the crushed Grinding material flow over the 
Grinding surface 5 to the edge of the Grinding pan 6. A relatively small 
proportion is sucked in between the upward flow 40 and the casing wall 15. 
The outer oversize flow 18 or the particle torus, which as a result of the 
construction of the Gas directing respectively Guiding device 19 rotates 
helically about the axis 12 of the air-swept mill 4, is subject to a 
relatively stable twist flow which attempts to expand. The centrifugal 
force of the vertical or twist flow is utilized for removing oversize 
fractions from the outer oversize flow 18. 
FIGS. 2 and 3 are a highly diagrammatic representation of an arrangement 
and construction of a removal device 25 in the upper area of the casing 
wall 15. The removal device 25 is constructed as a pocket 27, positioned 
tangentially on the casing wall 15 on a level with the classifier 29. The 
pocket 27 has a slot-like removal area 26 and a bottom discharge opening 
28 located at right angles to the removal area. In said pocket 27 collects 
the oversize material of the outer oversize flow 18 rotating under 
centrifugal force and Gravity action on the casing wall 15 and are 
automatically vented by dynamic pressure action. The almost slot-like 
removal area 26 of the removal device 25, in order to permit a regulated 
removal of the oversize fractions, is provided with an adjustable Guide 
plate 31, which is articulated by means of a vertical pivot pin 32 to the 
casing wall 15. As a function of the opening angle of the Guide plate 31 a 
larger or smaller, shell-like fraction of the outer oversize flow 18 can 
be removed. The discharge opening 28 can be constructed as an adjustable 
opening in the same way as the removal area 26. 
FIG. 4 is an equipment diagram with the essential units for performing the 
method according to the invention. The material of different grain size to 
be crushed, e.g. in the form of a three-component mixture, is supplied to 
a charging device 38 and by means of an inlet connection 39 to the 
air-swept mill 4. Together with the charge 10 are supplied oversize 
fractions of the outer oversize flow 18 from a pocket 27 in the form of 
the removal device 25 and with the aid of a mechanical conveying device 
36, e.g. a bucket elevator. Together with the oversize fraction of the 
outer oversize flow 18, grinding material particles 33 and in particular 
oversize material which has dropped downwards over the annular gas 
directing device 19 (FIG. 1), are passed to the mechanical conveying 
device 36 and charged in bypass manner to the air-swept mill 4. Most of 
the crushed grinding material particles undergo classification with the 
aid of the integrated classifier 29. The fine material particles pass in 
the fluid flow via a fines outlet 11 into a filter 42, where the fluid and 
in particular a process gas is separated from the fines and by means of a 
fan 43 and optionally by a furnace 44 is preheated to a clearly defined 
temperature returned to the air-swept mill 4. 
The tangentially positioned removal device 25 is provided with an outlet 
connection 34, optionally a dosing-discharge conveyor 41 and an air lock 
37.