GB1586851A

GB1586851A - Centrifugal mill

Info

Publication number: GB1586851A
Application number: GB43171/77A
Authority: GB
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1976-10-21
Filing date: 1977-10-17
Publication date: 1981-03-25
Also published as: FR2368300A1; AT357850B; NO144285C; NO772528L; BE859952A; IT1086907B; SE425551B; NO144285B; DE2647578A1; DE2647578C2; JPS6057376B2; SE7711792L; JPS5351567A; CA1089428A; FR2368300B1; ATA467277A; ZA775871B

Description

(54) CENTRIFUGAL MILL (71) We, METALLGESELLSCHAFT AK TIENGESELLSCHAFT, a body corporate organized under the laws of the German Federal Republic, of 14 Reuterweg, 6000 Frankfurt (Main) 1, German Federal Republic, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement::- This invention relates to a centrifugal mill of the kind comprising a cylindrical grinding drum, which is arranged to rotate about its own longitudinal axis and simultaneously to revolve on a circular orbit around a stationary axis of revolution, which is parallel to the longitudinal axis of the drum, at a constant angular velocity ratio, the distance between the axis of the drum and the stationary axis of revolution being smaller than the radius of the grinding drum, and a drive mechanism for rotating the grinding drum about its longitudinal axis and for revolving the grinding drum on the circular orbit about the stationary axis. Such a centrifugal mill will be hereinafter referred to as- "a centrifugal mill of the kind set forth".

Centrifugal mills for intermittent pilot operation have been described in "Rock Product", February 1951, pages 93-97-.

A centrifugal mill of the kind set forth for batch operation has been proposed in which the distance between the longitudinal axis of the drum and the stationary axis of revolution is less than the radius of the grinding drum so that there is allegedly no critical or limiting speed of revolution of the mill. The critical velocity is the velocity above which the material being ground and the grinding elements form- under the action of centrifugal force a covering on the wall of the grinding drum so that there is no longer a grinding action. However, the spacing of the drum axis and the axis of revolution by a distance which is smaller than the radius of the grinding drum - does not in itself ensure subcritical conditions and a high grinding rate.

tIt is an object qf the invention to provide a centrifugal mill which can be operated continuously in the sub-critical range at a high grinding rate per unit of volume of the grinding drum, in which the grinding drum is readily accessible and can be replaced quickly and simply and in which a simple mounting for the drum is provided and the transmission of uncontrolled stresses and vibration is minimised or avoided while the structural expenditure is small.

According to the present invention there is provided a centrifugal mill of the kind set forth, wherein the ratio of the diameter of said circular orbit to the inside diameter of the grinding is from 0'3 and 10, and the arrangement is such that when the mill is in operation the angular velocity of the grinding drum on said circular orbit about the stationary axis of revolution and the angular velocity of the grinding drum about its own longitudinal axis are equal and of opposite hand, wherein a charging device is provided at one end of the grinding drum and a discharge device is provided at the other end, the grinding drum being mounted in an approximately horizontal position in at least one U-shaped rocker the lower portion of which or each of which carries a bearing designed to be rigid in the vertical direction and movable in all other directions, and wherein the grinding drum is fixed between two abutments associated with respective limbs of the or each rocker, each limb of the or each rocker being mounted in an eccentric bearing which is secured to an eccentric-driving shaft provided with counterweights and mounted in bearings.

The limbs of the or each U-shaped rocker may extend at right angles or at any other angle to the lower portion of the rocker or may extend along arcs of circles to the lower portion of the rocker. Altematively, the entire rocker may have the configuration of an arc of a circle. The bearing in the lower portion of the rocker may consist of a balltype pivot bearing or of a pin having a suitable play on that side of the bearing which faces the grinding drum and on which the bearing is connected to the grinding drum.

That side of the bearing which faces the lower portion of the rocker is suitably connected to the rocker by a screw-threaded joint. The abutments provided on the limbs of the or each rocker preferably extend horizontally but may alternatively be somewhat inclined.

There is either a small play between the abutments and the grinding drum or the abutments contact the grinding drum. The eccentric bearings are preferably of roller-type pivot bearings. The drive shafts are suitably connected to one or more transmissions by highly elastic couplings, which are torsionally rigid, and these transmissions can be driven by one motor or a plurality of motors. Where two transmissions are provided, they must be coupled to each other so that a synchronous operation of both eccentric shafts is ensured.

Preferably the bearings of one eccentricdriving shaft are pivotally connected to a base frame at one point. This ensures that manufacturing tolerances of the rockers and levers cannot result in additional loads on these parts.

One abutment of each rocker preferably consists of a resilient bearing and the resiliency of the bearings may be due to the provision of springs or of pneumatic or hydraulic means. This ensures that the grinding drum is held by a defined force and that the transmission of forces due to thermal expansion to the rockers is avoided.

One abutment of each rocker is conveniently provided with a sensor for measuring the reaction force of the grinding drum, the sensor preferably being a load cell. Such an arrangement enables a simple and accurate monitoring and automatic control of the operating conditions of the operating conditions of the grinding drum to be achieved.

The grinding drum is preferably mounted in two interconnected rockers, two rockers constituting a structurally simple and satisfactory holder. The connection between the rockers prevents parallel displacement thereof.

In order to enable the invention to be more readily understood, reference will now be made to the accompanying drawings, which illustrate diagrammatically and by way of example an embodiment thereof, and in which Fig. 1 is a top plan view of a centrifugal mill, Fig. 2 is a side elevation of the mill shown in Fig. 1 viewed from its discharge side, Fig. 3 is a side elevation similar to Fig. 2 but partly in section, and Fig. 4 is a side elevation showing the mechanical movement of a rocker and of a grinding drum of the mill.

Referring now to the drawings, there is shown a centrifugal mill having a grinding drum 1 which has a smooth lining. In practice, however, lifting bars are provided on the inside or a lining is provided which has an irregular surface so that the movement of the material to be gound in the drum is improved.

These lifting bars and lining are not shown for the sake of clarity. The grinding drum 1 is mounted in two U-shaped rockers 2 and 2a, which have limbs extending at right-angles to the lower portion of the rocker. A bearing 3, provided in the lower portion of each df the rockers 2 and 2a, is designed to be rigid in the vertical direction and to be movable in all other directions. On the side facing the grinding drum 1, the bearing 3 consists of a ball-type pivot bearing while, on its side facing the lower portion of each rocker 2 and 2a, the bearing 3 is screw-connected to the lower portion by means of a screw-threaded pin, which extends through the bearing, and lock nuts. As a result, the bearing 3 is vertically rigid and is movable in all other directions owing to the provision of the ball-type pivot bearing.

Two abutments 4, 5 are secured to the inside of the limbs of each of the rockers 2 and 2a. The abutments 4 on one side are in the form of resilient bearings comprising built-in springs, while the abutments 5 on the other side are provided with load cells 18. The bearings, 3, 4 and 5 retain the grinding drum 1 and its end walls 22 and 23 between a charging device 20 at one end of the drum and a discharging device 21 at the other.

When it is desired to remove the drum 1, it is only necessary to remove the screw connections of the bearings 3. The limbs of the rockers 2 and 2a are mounted in respective eccentric bearings 6 and 7, which consist of self-aligning roller bearings. The eccentric bearings 6 and 7, are secured to respective eccentric-driving shafts 8 and 9, which are provided with counterweights 10 and 11 and mounted in bearings 12 and 13 and 14 and 15 respectively. Lead plates 240 are mounted in the counterweights 10 and 11 and may be used to control the mass of the counterweights. The bearings 12 and 13 are firmly screw-connected to a base frame 16, and the bearings 14 and 15 are pivoted to the base frame 16 by pins having centres 17. The lower portions of the two rockers 2 and 2a are interconnected by a flanged tube 19 (Fig.

3) and the eccentric-driving shafts 8 and 9 are connected to a transmission and drive unit by couplings 24 and 25.

Fig. 4 shows only the rocker 2, the grinding drum 1, the eccentric-driving shafts 8 and 9, and the eccentric bearings 6 and 7. The distances between the centres 26 of the eccentric-driving shafts 8 and 9 and the centres 27 of the eccentric bearings 6 and 7 define the radii of the circular orbits of revolution G along which the grinding drum revolves about a fixed axis. As shown in the drawings, the ratio of the diameter of the circular orbits of revolution G to the inside diameter D of the grinding drum is about 0 4. The distance between the longitudinal axis 28 of the grinding drum 1 and the imaginary axis of revolution 29 of the grinding drum 1 is smaller than the radius of the grinding drum 1.

The advantages afforded by the invention reside in that owing to the fact that the angular veolocity of the grinding drum on the circular orbit G and the angular velocity of the drum about the axis 28 are equal and opposite a particularly high grinding rate is ensured. The centrifugal forces are substantially equal at all points of the crosssection of the grinding drum, and the vectors of acceleration at all points are parallel and have the same direction. The mill will thus always operate in the sub-critical range even at a high grinding rate, and the design ensures an exactly circular motion in a simple manner. The grinding drum can be mounted and replaced quickly and simply without the need for a high expenditure of work so that shutdown times are short.Satisfactory mounting and holding of the grinding drum is ensured with a small structural expenditure, while transmission of uncontrolled vibration to the rockers and other parts is avoided. The grinding drum and charging and emptying devices are easily accessible, and additional drive means for rotating the grinding drum on its own axis are not required.

WHAT WE CLAIM IS: 1. A centrifugal mill of the kind set forth, wherein the ratio of the diameter of said circular orbit to the inside diameter of the grinding drum is from 0-3 and 1-0, and the arrangement is such that when the mill is in operation the angular velocity of the grinding drum on said circular orbit about the stationary axis of revolution and the angular velocity of the grinding drum about its own longitudinal axis are equal and of opposite hand, wherein a charging device is provided at one end of the grinding drum and a discharge device is provided at the other end, the grinding drum being mounted in an approximately horizontal position in at least one U-shaped rocker the lower portion of which or each of which carries a bearing designed to be rigid in the vertical direction and movable in all other directions, and wherein the grinding drum is fixed between two abutments associated with respective limbs of the or each rocker, each limb of the or each rocker being mounted in an eccentric bearing which is secured to an eccentric-driving shaft provided with counterweights and mounted in bearings.

2. A centrifugal mill as claimed in claim 1, wherein the bearings of one eccentricdriving shaft are pivoted to a base frame.

3. A centrifugal mill as claimed in claim 1 or 2, wherein one abutment of the or each rocker consists of a resilient bearing.

4. A centrifugal mill as claimed in any one of claims 1 to 3, wherein one abutment of the or each rocker is provided with a sensor for measuring the reaction force of the grinding drum.

5. A centrifugal mill as claimed in any one of claims 1 to 4, wherein the grinding drum is mounted in two interconnected rockers.

6. A centrifugal mill of the kind set forth substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. between the longitudinal axis 28 of the grinding drum 1 and the imaginary axis of revolution 29 of the grinding drum 1 is smaller than the radius of the grinding drum 1. The advantages afforded by the invention reside in that owing to the fact that the angular veolocity of the grinding drum on the circular orbit G and the angular velocity of the drum about the axis 28 are equal and opposite a particularly high grinding rate is ensured. The centrifugal forces are substantially equal at all points of the crosssection of the grinding drum, and the vectors of acceleration at all points are parallel and have the same direction. The mill will thus always operate in the sub-critical range even at a high grinding rate, and the design ensures an exactly circular motion in a simple manner. The grinding drum can be mounted and replaced quickly and simply without the need for a high expenditure of work so that shutdown times are short.Satisfactory mounting and holding of the grinding drum is ensured with a small structural expenditure, while transmission of uncontrolled vibration to the rockers and other parts is avoided. The grinding drum and charging and emptying devices are easily accessible, and additional drive means for rotating the grinding drum on its own axis are not required. WHAT WE CLAIM IS:

1. A centrifugal mill of the kind set forth, wherein the ratio of the diameter of said circular orbit to the inside diameter of the grinding drum is from 0-3 and 1-0, and the arrangement is such that when the mill is in operation the angular velocity of the grinding drum on said circular orbit about the stationary axis of revolution and the angular velocity of the grinding drum about its own longitudinal axis are equal and of opposite hand, wherein a charging device is provided at one end of the grinding drum and a discharge device is provided at the other end, the grinding drum being mounted in an approximately horizontal position in at least one U-shaped rocker the lower portion of which or each of which carries a bearing designed to be rigid in the vertical direction and movable in all other directions, and wherein the grinding drum is fixed between two abutments associated with respective limbs of the or each rocker, each limb of the or each rocker being mounted in an eccentric bearing which is secured to an eccentric-driving shaft provided with counterweights and mounted in bearings.