EP0764470A1 - Process for impact milling and impact mill - Google Patents

Abstract

The rotary mill has the material fed into the centre of the two contra-rotating cylinders (6,8). It is reduced into smaller particles by hitting the blades (7) on the cylinders, ie. the particles are thrown by the inner cylinder onto the blades of the outer cylinder. A recycling path (23,14,15) feeds the coarse particles back into the centre of the cylinders while the fine particles are separated out by a mesh (5). The mesh surrounds the bottom section of the cylinders, and the upper part of the recycling duct. The milling action is adjusted by the feed direction and by the speed of the cylinders.

Description

The invention relates to a method for impact milling, in particular of granular ground material such as grain or cubes, according to the preamble of claim 1, and an impact mill with coaxial rotating rotors driven rotors according to the preamble of claim 4.

It is particularly used for grinding regrind for animal feed.

In conventional impact mills (see e.g. EP-B-51389 or DE-A-3708914) the fineness of the product is largely determined by the perforation of the sieve (sieve fineness), the ground material remaining in the grinding chamber until it is possible to pass through the sieve . The regrind is exposed to a large number of blows of the rotor (s) until the corresponding fineness is reached. This requires a high amount of energy and a partially excessive grinding of the ground material.

Is the sieve arranged in the impact area, such as. B. according to EP-B-98441, in which the rotor of an impact mill is concentrically surrounded by a sieve, the ground material hits the sieve jacket at high speed, which increases the sieve wear.

To improve the energy balance of such impact mills, centrifugal channels have also been proposed (see DE-PS-699100 and DE-A-3708914) in order to use the energy imparted to the regrind particles to convey them out of the impact area onto a subsequent sieve. Even with such tangential centrifugal channels, the ground material is thrown onto the sieve.

Mostly, impact mills have a fixed housing with a rotor arranged and driven therein. It is also known to design disintegrators for very fine comminution with two coaxial rotors driven in opposite directions (DE-A-3417556). The rotors each carry at least two concentric blade rings, the blade rings of both rotors alternately intermeshing. Both rotors are driven by a common drive. For this purpose, one rotor is fastened to a hollow shaft and the other rotor is arranged on a shaft which penetrates the hollow shaft via a bushing. Both shafts are stored in an external bearing. The high design effort is necessary to achieve a turbo effect in accordance with EP-A-48012 with a safe bearing function.

The invention has for its object to provide a method for impact grinding of granular regrind and an impact mill for carrying out the method, which enables a high uniformity of the grinding of the regrind (low scattering of the particle size) with a minimal content of dust fractions with little technical and economic effort . This is done in a surprisingly simple way by the features of the characterizing part of the claim.

The usual grinding of regrind in a plurality of comminution devices (high friction) leads to excessive comminution of the product and high energy consumption, in connection with comparatively high wear. This results from the fact that the grinding material dissolves primarily in the moving layer between the ends of the beater and the sieve surface / sieve chamber. With the turbo effect, the impact between the particles themselves. Surprisingly, it has now been found that the disadvantages of the known prior art can be avoided by using a "pure" impact. According to the invention, the regrind is first accelerated and then bounces against work organs. Since speeds of over 100 m / s are required for this purpose, maximum shredding is minimized Friction achieved by a counter-impact of the accelerated ground material by a movement known per se in the opposite direction. The regrind is first accelerated in a rotating movement and then bounced by converting the speed vector into a vector opposite to the acceleration. Acceleration and impact alternate cyclically in two intermediate zones, which are connected to one another by streams of particles that have not yet been comminuted sufficiently, with the separation of particles of the desired size between the cycles.

The regrind is passed to a first grinding stage, where it is accelerated in a defined direction and strikes a surface of work organs. Under the action of impact, the regrind grains are comminuted into particles of different sizes by transmitting the speed vector opposite to the acceleration. The shredded particles then go to a separator, where they are separated accordingly. The separator is located outside the crushing zone and the particles approach each other tangentially. The particles of the desired size are discharged as a finished product, and coarse particles are returned to the comminution zone in a second comminution stage, where they are subjected to an acceleration and impact again, however, in contrast to the first stage, finer particles are formed. There is again a separation into coarse and finished product outside the comminution zone, the coarse product again being fed to the first comminution stage.

In order to increase the output and improve the granulation distribution in the finished product, a sieve is additionally arranged outside the grinding chamber in order to ultimately increase the sieve area.

Extensive studies confirm the assumption that additional sieve surfaces are only in the part of the grinding chamber or the Product circulation channels is useful in that the product is thrown more or less against the sieve.

A centrifugal channel according to DE-A-37 08 914 without a sieve in the channel cannot provide any justified suggestion for this. It is necessary to relocate the additional screen surface mentioned in the curved area of the channel. This enables the fine product to be screened almost completely when the required granulation is reached, which also significantly reduces the power requirement compared to comparison solutions.

When the additional sieve is installed, the channels abut each other at the outlet of the cylindrical chamber and form the common channel, which merges into two separate crossed channels, which are connected to the work areas, in the direction of product travel.

The sieve is mounted in the curved part of the channel in such a way that a space is formed behind the sieve, which is connected to the space of the cylindrical chamber behind the sieve by a pipeline.

The crushing cycle is closed and the particles are separated outside of that, which allows both a reduction in energy consumption and wear of the separating device. At the same time, differentiated treatment of particles of different sizes is achieved. The use of two comminution stages allows the influence on particles with different processing intensities in each stage.

The process can be carried out in an impact or impact mill with a cylindrical chamber, which has inlet and outlet connections for the regrind as well as rotors which are coaxially installed therein and which rotate in the opposite direction with the working elements attached to them. The chamber is perforated and divided into two chamber regions by means of the rotors, the regions crossing one another Channels are connected, which are arranged outside their limits and which result in a closed flow of the regrind.

The result is a closed grinding process with a predeterminable particle size and the possibility of automatic control of the process.

Fig. 1

eine Prallmühle

Fig. 2

einen Schnitt A-A der Prallmühle

Fig. 3

einen Schnitt B-B der Prallmühle

Fig. 4

eine Seitenansicht einer weiteren Ausgestaltung der Prallmühle mit einem Sieb im gekrümmten Teil des Kanals

Fig. 5

einen Grundriss der Prallmühle gemäss Fig. 4

Fig. 6

eine Prallmühle mit darin ausgebautem Schild

Fig. 7

Schild mit Jalousie

Fig. 8

eine weitere Variante der erfindungsgemässen Prallmühle mit offener Rotoranordnung

Fig. 9

eine weitere Ausgestaltungsform gemäss Fig. 8 in einer 3-Rotoranordnung.

The invention is described below using an exemplary embodiment with reference to a drawing. In the drawing they show

Fig. 1

an impact mill

Fig. 2

a section AA of the impact mill

Fig. 3

a section BB of the impact mill

Fig. 4

a side view of a further embodiment of the impact mill with a sieve in the curved part of the channel

Fig. 5

a plan view of the impact mill according to FIG. 4

Fig. 6

an impact mill with a shield removed inside

Fig. 7

Sign with blinds

Fig. 8

a further variant of the impact mill according to the invention with an open rotor arrangement

Fig. 9

a further embodiment according to FIG. 8 in a 3-rotor arrangement.

An impact mill is fed with the material to be ground. This passes through an inlet 2 in free fall into a first working area 12 of a chamber 4. Here, the regrind is passed onto a first row of blades 7 of the rotor 6 under the action of an air flow generated by a rotary movement of a rotor 6. The individual grains of the ground material are gripped by these blades 7, accelerated and thrown against blades 9 of a rotor 8 at high speed. The blades 9 are located between the first and a second row of blades 7 of the rotor 6.

As a result of the impact of the grains against the blades 9 of the rotor 8, which rotates in the opposite direction to the rotor 6, the grains are partially comminuted, accelerated again by means of the blades 9 and hurled against the second, outer row of the blades 7. As a result of the impact effect on the blades 7, the grains are further comminuted into particles of different fineness. These pass from the blades 7 in the direction of rotation of the rotor 6 in a web shape onto the surface of the sieve 5. While the particles in an air cushion move with little friction in the direction of rotation of the rotor 6 on the surface of the sieve 5, separation takes place under the action of centrifugal force and the air flow in a coarse and a fine fraction. Particles that pass through the openings of the sieve 5 leave the impact mill via an outlet 3, while coarser particles, as a result of further movement, enter a side channel 14 and from there into a second working area 13 of the chamber 4. Under the action of the same forces as in the working area 12, the particles are caught by the blades 9 and thrown against the blades 7. Due to the impact, the particles are additionally comminuted, which, leaving the blades 7, move again on the surface of the sieve 5 in the direction of rotation of the rotor 6. The fine fraction is again discharged through the outlet 3 after passing through the sieve 5. The remaining coarse fraction can be fed to a further grinding via the channel 15.

The number of transfer stages of the coarse fractions from the work area 12 into the work area 13 depends on the type of the ground material, its moisture and the intensity of the impact.

In a housing 1 of the impact mill, rotors 6 and 8 with blades 7 and 9 attached to them are arranged horizontally and coaxially. The rotors 6, 8 are surrounded on their outer circumference by a sieve 5, as a result of which a cylindrical chamber 4, which is divided into two working areas 12 and 13 by the rotors 6, 8.

The rotors 6, 8 are driven by electric motors 10 and 11.

The rotor 6 has two rows and the rotor 8 has a row of blades 7, 9, which is divided into two halves with the rotor disk. One half of the blades 9 of the rotor 8 is arranged between the rows of blades of the rotor 6.

An inlet 2, which is arranged on the side of the working area 12 on the housing 1, serves to feed the impact mill with regrind. An outlet 3 for the ground material (finished product) is arranged below the chamber 4.

In continuation of the sieve 5, channels 14 and 15 are arranged on the housing 1 for returning the insufficiently comminuted (coarse) particle fractions. The channels 14, 15 are arranged outside the chamber 4. The width of the channel 14 corresponds to the width of the row of blades 7 of the rotor 6, which is arranged closer to the axis 16. The channel 14 has a curved, curved shape, starting from the chamber 4 and opening laterally and centrally into the working area 13. Channel 15 is designed analogously. It also starts from chamber 4 and opens laterally and centrally into work area 12.

The size of the gap between the ends of the blades 7 and the sieve 5 is to be dimensioned such that the movement of the comminuted product on the sieve 5 takes place under the action of the centrifugal force without the direct action of the outer blades 7.

The angle of attack of the blades 7, 9 should be chosen to be correspondingly small in order to achieve the described wear-reducing movement path of the particles.

The electric motors 10, 11 are loaded approximately the same.

The perforated part of the chamber 4 can be dismantled in order to allow a screen change.

The perforated part of the chamber 4 should also take up as large a part of its cylindrical surface as possible in order to achieve an efficient separation process.

By increasing the number of rows of blades 7, 9 on the rotors 6, 8, the number of grinding stages can be increased, e.g. B. on seven stages, the rotor 6 then having three and the rotor 8 two rows of blades 7, 9.

To increase the output and to improve the granulation distribution in the finished product, it is expedient to use a further sieve 17, which is attached outside the cylindrical chamber 4. The channels lie against one another at the outlet of the cylindrical chamber and form the common channel, which merges into two separate crossed channels 14 and 15 in the direction of product travel, which channels are connected to the working areas 13 and 12.

The sieve 17 is mounted in the curved part of the channel 23 in such a way that a space 18 is formed behind the sieve, which is connected to the space 19 of the cylindrical chamber 4 behind the sieve by a pipeline 20.

The device with the sieve 17 works as follows:

The grain enters the chamber 12 via the pipe 2, is crushed with the blades 7 and 9, which are fastened to the corresponding rotors 6 and 8, and comes to the sieve 5, where the ground product is separated into two fractions. The fraction of desired fineness is withdrawn from the device as a finished product through the outlet 3, the coarse fraction which does not pass through the opening of the sieve 5 has passed through channel 23 to sieve 17. The crushed material is subjected to a further separation according to fractions on the sieve 17. The passage through the sieve 17 reaches the space 18 located behind the sieve, from where it is directed into the space 19 of the cylindrical 4 located behind the sieve. The product from the space behind the sieve is discharged as a finished product through outlet 3.

The fraction which has not passed through the openings of the sieve 17 passes through the channel 14 for further grinding. The finished product passes through the sieve 5, the insufficiently comminuted product portion is directed as a repulsion via the duct 15 from the sieve 17 into the work area 12 for further grinding.

It must be emphasized that the separation on the screen 17, as well as on the screen 5, takes place under the action of the centrifugal force of the air flow generated by the rotors. The fineness of the grinding is regulated by exchanging the sieves for perforations required.

The performance of the device can also be increased by using a shield 21 which is attached to the outlet of the cylindrical chamber 4, between the large rotor and the screen 5. The shield 21 can consist of one piece or can be equipped with a blind 22.

The shield 21 can be used to direct the product fraction, which has had insufficient contact with the surface of the sieve, onto the sieve 5 for further separation. In addition, the shield 21 helps to generate the necessary pressure of the air flow on the sieve 5, thereby increasing the intensity of the passage of the particles through the openings in the sieve.

The blind 22 in turn helps to increase the blowing intensity of the sieve 17. In addition, the inventive Principle in a further embodiment also open arrangements of the opposing rotors. The rotors are arranged side by side in one plane (FIGS. 8, 9).

Without direct limitation to these variants, it makes sense to arrange two or three rotors next to one another and connected by channels, this being possible in a horizontal or vertical plane and resulting in lower production costs.

The product reaches the rotor 24 via an inlet 2 ', is accelerated and comminuted and reaches the working space of the counter-rotating rotor 26 via the channel 25, with a renewed acceleration and second comminution taking place. The comminuted product is then discharged from the grinding chamber via the channel 27 and separated (not shown). In a modification of this, after the first comminution in the grinding chamber of the rotor 24, the product reaches the grinding chamber of the rotors 26, 28 running in the same direction via the channel 25, 25 'and is comminuted again. The comminuted product via the channels 27, 27 'into a common, not explicitly shown channel again for separation.

The significantly lower energy requirement compared to conventional impact mills and the low friction influence lead to a negligible heating of the impact mill according to the invention during operation and thus to a low moisture loss of the ground material.

As a result of the operation of the impact mill according to the invention without aspiration, it is also possible to grind barley economically.

When grinding grain into flour, the impact mill can be used as a B1 and B2 passage.

The impact mill according to the invention is not limited to these embodiments.

Reference numerals

1

casing

2nd

inlet

3rd

Outlet

4th

chamber

5

Sieve

6

rotor

7

shovel

8th

rotor

9

shovel

10th

Electric motor

11

Electric motor

12th

Workspace

13

Workspace

14

channel

15

channel

16

axis

17th

Sieve

18th

room

19th

room

20th

Pipeline

21

sign

22

louvre

23

channel

24th

rotor

25, 25 '

channel

26

rotor

27, 27 '

channel

28

rotor

Claims (14)

Process for impact milling of particularly granular regrind using a mill with horizontally mounted rotors that run in opposite directions to one another and by arranging a known centrifugal channel for returning crushed regrind after a first grinding stage to a further grinding stage, the regrind initially in a chamber (4) with the rotors of an impact mill, characterized in that a, the regrind is accelerated by blades (7) of a first rotor (6) and impinges against blades (9) of an oppositely rotating rotor (8) and is crushed, b that the ground material in the direction of the movement path of the rotor (6) hits a sieve (5) at a small angle and is separated into fractions, c that the remaining coarse fraction is continued in the direction of movement and subjected to renewed acceleration, impact and sieving, the grinding stages according to a and c being carried out in separate working areas (12, 13) of the chamber (4). A method according to claim 1, characterized in that the coarse fraction continues according to c, in a channel (14, 15). A method according to claim 1, characterized in that acceleration and impact alternate cyclically in two intermediate zones, which are connected to one another by streams of grinding material insufficiently comminuted, with a separation of a fine fraction between the grinding stages, the impact occurring in the intermediate stages with different intensities. Impact mill for carrying out the method according to claim 1,
characterized in that
the impact mill consists of a housing (1) with therein horizontally and coaxially arranged rotors (6, 8) to which blades (7, 9) are attached, one rotor (6) having at least two rows of blades (7) and the other rotor (8) have at least one row of blades (9), which is arranged between the rows of blades (7), and of a screen (5) surrounding the rotors (6, 8) on their outer circumference and one on the side of the chamber (4) arranged inlet (2) and an outlet (3) arranged below the chamber (4) and further consisting of a continuation of the sieve (5) forming channels (14, 15). Impact mill according to claim 4, characterized in that the rows of blades (7, 9) are divided in half with the rotor disk and thus form separate working areas (12, 13). Impact mill according to claim 4, characterized in that the channels (14, 15) are arranged outside the chamber (4) and open in a curved shape from the chamber (4) laterally into the working areas (13, 12), the width of the channel (14) corresponds to the width of the inner row of the blades (7). Impact mill according to claim 4, characterized in that the sieve (5) is replaceable. Impact mill according to claim 4, characterized in that the rotors (6, 8) are driven rotating in opposite directions, preferably by separate drives. Impact mill according to claim 4, characterized in that the blades (7, 9) have an angle of attack of preferably not more than 15 °. Impact mill according to claim 4,
characterized in that
the two channels (14, 15) for increasing the performance and for improving the granulation in the finished product are designed to form a common channel (23) which merges into two separate crossed channels, a sieve (17) in its curved part is attached, whereby a space behind the sieve (17) is formed, which merges into the space behind the sieve (17) of the cylindrical chamber (4). Impact mill according to claims 4 and 10, characterized in that [to increase the output] at the exit from the cylindrical chamber (4), between the large rotor and the sieve (5), a curved shield (21) is installed. Impact mill according to claim 11, characterized in that the shield (21) is equipped with a blind (22). Impact mill according to the preceding claims 4 to 12, characterized in that the rotors (24, 26, 28) are arranged next to one another in one plane and are connected to one another by channels (25, 25 ', 27). Impact mill according to claim 13, characterized in that the plane is arranged horizontally or vertically.

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