EP2942105A1 - Roller mill and method for controlling a roller mill - Google Patents

Abstract

The invention relates to a roller mill comprising two parallel, oppositely pressed and counter-rotating rollers (1,1 '), wherein one of the rollers (1') orthogonal to the axial direction of this roller (1 ') is displaceable, two drives, which drives each one of the two rollers (1,1 ') are associated and each having an electric motor (2,2'), anda control unit, wherein the control unit, a Master Elekromotor (2) of the electric motors sets a target value (61) for the rotational speed, the control unit prescribes to a follower electric motor (2 ') of the electric motors the torque actual value (62) or the actual speed value (62) of the master electric motor multiplied by a load part factor (64) as desired value (63).

Description

TECHNICAL AREA

The present invention relates to the field of roll mills. It relates to a roller mill with two counter-rotating rollers which are rotatably mounted in a frame, and method for controlling such a roller mill.

STATE OF THE ART

Roll mills are used for grinding materials, in particular ores and cement. Roll mills typically have a roll diameter of 0.8 to 3 meters and a drive power of 0.2 to 5 megawatts. They are particularly energy efficient compared to other mill types. Such a roller mill is used for example in DE 4028015 A1 described.

As in Fig. 1 schematically illustrated, a roller mill comprises two counter-rotating rollers 1,1 ', which rollers 1,1' are mounted horizontally and parallel to each other in a frame rotatably. One of the two rollers 1 'is orthogonal to the axial direction of this roller 1' displaced. As a rule, the other of the two rollers 1 is not orthogonally displaceable. The displaceable roller 1 'is pressed by a spring system onto the fixed roller 1. Each roller 1,1 'has a grinding surface. The opposite grinding surfaces of the rollers 1,1 'form a wedge. Material is filled from above between the rollers 1,1 'in the wedge, guided by the rotation of the rollers 1,1' down and crushed by the wedge. The rotation of the rollers 1,1 'via a drive. Known drives for roll mills usually have two Electric motors, wherein each one electric motor of the rollers is connected.

Fig. 2 shows a roller mill with two drives. Depending on a drive is assigned to one of the rollers 1,1 'and includes an electric motor 2, a propeller shaft 3 and a planetary gear 4. The connection of the radially displaceable roller 1' with the stationary electric motor 2 via the propeller shaft 3. Optionally, it is also possible in that the articulation shaft is connected directly to the shaft of the displaceable roller and the planetary gear is arranged between the articulated shaft and the electric motor. In such an arrangement, such as in DE 10211000749 A1 described, the electric motor and the planetary gear are stationary. Optionally, it is also possible that the electric motor delivers the desired speed for the rollers without a speed adjustment of a transmission. In this case, the drive does not comprise a gearbox and the electric motor is connected directly to the roller via the cardan shaft. Optionally, it is also possible that a direct drive is arranged on the roller itself. In this case, the drive does not comprise a cardan shaft.

The electric motors of the two drives are usually controlled by two separate frequency converter. The control strategy for the electric motors has an influence on the wear of the rollers. In general, the wear of the rollers is influenced, among other things, by the contact pressure of the rollers, the circumferential speed of the grinding surfaces of the individual rollers and the difference between the peripheral speeds of the grinding surfaces of the rollers. In addition, the wear of the two rolls is usually different strength. It can have both the displaceable roller and the stationary roller 1 a greater wear. For the control of a roll mill, the following control strategies from the article " VFD control methodologies in High Pressure Grinding drive systems ", Brent Jones, Cement Industry Technical Conference, 2012 IEEE-IAS / PCA 53 ,

In the first strategy, an identical speed reference is specified for both motors. Thus, both drives try to set the same speed for the motors they control, but act independently to achieve that goal. The problem is that even with identical frequency converters, the speed controls have a fault so that an identical speed of the two rolls can not be achieved in this way and so result in a difference in the peripheral speeds of the grinding surfaces of the two rolls. In addition, it is problematic that the diameter of the roller is not considered. With different roll diameters, such as increased wear on one of the two rolls, even at an identical rotational speed of the two rolls leads to different peripheral speeds of the grinding surfaces of the rolls. Another consequence of this is that the load between the two rolls is not evenly distributed, resulting in relative rotation of the two rolls, which in turn leads to increased wear.

In the second strategy, an identical torque reference is specified for both motors. The problem is that in case that the drive torque is greater than the load torque, accelerate the roll mill or delayed in the opposite case. This results in a changing rotational speed of the roller mill proportional to variations of the ground material, which is also disadvantageous for the operation of the roller mill. In the third strategy, one of the electric motors is defined as master and the other electric motor as follower. Fig. 3a shows a schematic representation of the signal flow of a roll mill with this control strategy in an initial phase. Both frequency converters 5 are given an identical speed reference 61 as in the first one Steuerungsstratgie. Fig. 3b shows a schematic representation of the signal flow of a roll mill with this control strategy in a production phase. After reaching a defined load threshold, the frequency converter 5 of the follower is no longer given the identical speed reference 61 but actual torque value 62 of the masters. This allows a better uniform distribution of the loads on the two rolls and a reduction in the peripheral speed difference of the grinding surfaces of the rolls and thus leads to a reduction of the individual wear of the rolls. Optionally, the master follower strategy can use the actual speed (speed follower) value of the master as the reference for the followers in the production phase, rather than the actual torque value (torque follower). In this case, both frequency inverters 94 are given an identical speed reference and after switching to the production phase, the follower is given the actual value of the speed of the masters. The problem with the master follower strategy is that wear can only be optimized individually for each roller in terms of service life. It is not possible to optimize the wear of both rolls in the overall system of the roll mill so as to maximize the life of the roll mill.

PRESENTATION OF THE INVENTION

Object of the present invention is to provide a roller mill, which has an increased life.

This object is achieved by a roller mill with the features of claim 1. Preferred embodiments are subject of the dependent claims.

BRIEF DESCRIPTION OF THE FIGURES

Figur 1

eine schematische Darstellung eines radialen Schnitt einer Walzenmühle aus dem Stand der Technik;

Figur 2

eine Walzenmühle mit zwei Antrieben aus dem Stand der Technik;

Figur 3a

eine schematische Darstellung des Signalflusses bei einer Walzenmühle mit Master-Follower Steuerung aus dem Stand der Technik in einer Anfangsphase;

Figur 3b

eine schematische Darstellung des Signalflusses bei einer Walzenmühle mit Master-Follower Steuerung aus dem Stand der Technik in einer Produktionsphase; und

Figur 4

eine schematische Darstellung des Signalflusses bei einer erfindungsgemässen Walzenmühle;

Figur 5

einen beispielhafter Zusammenhang zwischen der Abnutzung der Walzen und der Wahl des Lastverteilfaktors;

The invention will be explained in more detail by means of exemplary embodiments in conjunction with the figures. The figures show:

FIG. 1

a schematic representation of a radial section of a roll mill of the prior art;

FIG. 2

a roller mill with two drives from the prior art;

FIG. 3a

a schematic representation of the signal flow in a roll mill with master-follower control of the prior art in an initial phase;

FIG. 3b

a schematic representation of the signal flow in a roll mill with master-follower control of the prior art in a production phase; and

FIG. 4

a schematic representation of the signal flow in a roll mill according to the invention;

FIG. 5

an exemplary relationship between the wear of the rollers and the choice of the load distribution factor;

The reference numerals used in the drawings are summarized in the list of reference numerals. Basically, the same parts are provided with the same reference numerals.

WAYS FOR CARRYING OUT THE INVENTION

Fig. 4 shows a schematic representation of the signal flow in a roll mill according to the invention. The controller provides a speed controller of the frequency converter 5 of the master electric motor 2 before a target value 61 for the speed. The resulting by the regulation of the speed for the master electric motor 2 actual value 62 of the rotational speed is in one Multiplier 65 multiplied by a load distribution factor 64. The resulting value is given as a setpoint for the speed controller frequency converter 5 for the follower electric motor 2 '. Additionally is in Fig. 4 an optional feedback of the torque actual values of the master electric motor 2 and the follower electric motor 2 'to a controller 66 is shown, which controller may be a PID controller, for example, to ensure a closed regulator circuit. The output of the PID controller is added or subtracted from the original speed reference 61, and then passed to the frequency converter of the follower electric motor 2 'as the setpoint. By the load distribution factor, the wear of the individual rollers can be influenced relative to each other.

Analogous to Fig. 3 An application of the torque follower principle instead of the illustrated speed follower principle is also possible in FIG.

Fig. 5 shows an exemplary relationship between the wear of the rollers and the choice of the load distribution factor. In the diagram, the wear 112 of the respective roll is shown in the form of reduction of the roll diameter over the rotational work already performed by the respective roll. Under the turning is to understand the necessary for the grinding of the previously painted material, cumulative torque over the time required for grinding. The curves 113, 114 adjust the wear of two rolls of a pair of rolls as a function of the turning work there. The curve 114 shows a greater wear of the corresponding roller than the wear of the roller which is shown in the curve 113. In the case shown, the load factor is now chosen so that the roller with the accumulated greater previous wear carries a smaller part of the load required for the meal. The higher the differential accumulated wear between the two rollers, the smaller the corresponding one Lastverteilfaktor. With the same accumulated wear of both rollers, the load is distributed as a factor of one. In this choice of the load factor, the goal is to achieve as equal as possible wear of the rolls of a pair of rolls, for example, to replace both rolls in a maintenance.

But there are also other objectives in the choice of the load factor possible, such as the strong wear of the already more worn roller and the conservation of less worn roller. In general, the load distribution factor may be a positive real number including zero.

LIST OF REFERENCE NUMBERS

1, 1 '

roller

2, 2 '

electric motor

3

propeller shaft

4

planetary gear

5

frequency converter

61

Speed setpoint

62

Actual value master

63

Setpoint Follower

64

Lastverteilfaktor

65

multiplier

66

regulator

111

Rotational power of the roller

112

Wear of the roller

113

Wear of the sliding roller

114

Wear of the non-displaceable roller

115

Load distribution factor in dependence on the rotational power of the rollers

Claims (6)

Comprising roller mill
two parallel, counter-pressed and counter-rotating rollers (1, 1 '), one of the rollers (1') being displaceable orthogonal to the axial direction of this roller (1 '),
two drives, which drives each one of the two rollers (1,1 ') are assigned and each having an electric motor (2,2'), and
a control unit, where
the control unit prescribes a setpoint value (61) for the rotational speed to a master electric motor (2) of the electric motors,
characterized in that
the control unit prescribes to a follower electric motor (2 ') of the electric motors the torque actual value (62) or the actual speed value (62) of the master electric motor multiplied by a load part factor (64) as desired value (63). Roll mill according to claim 1, wherein the load distribution factor (64) in consideration of the contact pressure of the rollers (1,1 ') and / or the wear of the individual rollers (1,1') is determined. Roll mill according to claim 2, wherein the wear of the individual rolls (1,1 ') is described by the quotient of the diameter reduction of a roll and the amount of material which has been ground from this roll so far. Roll mill according to one of the preceding claims, wherein the diameter of the rollers (1,1 ') is determined and the load distribution factor (64) is determined in consideration of these values. A roll mill according to claim 1, wherein the load distribution factor (64) is determined by the operator of the roll mill. Method for controlling a roller mill, wherein the roller mill
two parallel arranged, pressed against each other and counter-rotating rollers (1,1 '), wherein one of the rollers (1') orthogonal to the axial direction of said roller (1 ') is displaceable, and
comprises two drives, which drives each one of the two rollers (1,1 ') are assigned and each having an electric motor (2,2'),
characterized in that the method comprises the steps of: a) specification of a target value (61) for the rotational speed or the torque for a master Elekromotor (2) of the electric motors; b) determining the actual torque value (62) or the actual speed value (62) of the master electric motor (2); c) multiplying the actual value (62) of the master electric motor (2) by a load part factor (64); and d) specification of the result from step (c) as a setpoint for a follower Elekromotor (2 ') of the electric motors.

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