EP1541238A1

EP1541238A1 - A cladding for a rotary drum mill

Info

Publication number: EP1541238A1
Application number: EP04076748A
Authority: EP
Inventors: Walter Palladini
Original assignee: Certech Srl
Current assignee: Certech Srl
Priority date: 2003-12-11
Filing date: 2004-06-11
Publication date: 2005-06-15
Also published as: ITMO20030337A1

Abstract

The mill comprises a plurality of panels predisposed to clad an internal cylindrical surface of an internally-hollow cylindrical body rotating about a longitudinal axis thereof, at a predetermined peripheral velocity. Means for connection associate the panels to the internal cylindrical surface, which means comprise a plurality of ribs (5), fixed to the internal cylindrical surface, each of which ribs (5) exhibits a perpendicular section which is perpendicular to the internal cylindrical surface of the cylindrical body (2), which section has at least a portion thereof arranged at an acute angle of inclination with respect to the peripheral velocity; a plurality of channels (6) afforded at surfaces (30) of the panels (3) is shaped complementarily with respect to the ribs (5) in order that the ribs (5) are couplable in the channels (6).

Description

Usual rotary drum mills typically comprise an internally-hollow cylindrical body, or drum, which rotates about a longitudinal axis thereof arranged horizontally or with a slight inclination to the horizontal. The material to be milled and the grinding bodies are introduced into the drum; the bodies used for grinding or milling are usually constituted by balls made of a very hard material. As the drum is rotated, the grinding balls are agitated, and grind the material to be milled internally of the drum.
In order to counter the friction with the grinding balls, the drum is internally clad with a high-resistance material, usually rubber or other elastomers.
The cladding comprises a series of panels which are fixed internally of the drum. The panels exhibit a series of longitudinal reliefs, or raising bars, which draw the materials and the balls inside the drum in rotation up to a certain height, from which they then drop, falling onto the underlying materials.
In known-type claddings the panels are fixed to the drum by bolts, the heads of which are lodged in seatings made in the base of the panels, the stalks of which pass through holes afforded in the drum, to be fastened externally with a nut.
Claddings of this type, however, though perfectly functional, have some drawbacks.
For example, the substitution of the panels requires unscrewing all the fastening nuts, which is laborious and time-consuming.
The mill described in Italian patent no. IT 1291313 attempts to respond to this problem.
The patent describes a rotary drum mill in which the cladding is composed of a series of panels which are connected to the internal surface of the drum by means of a coupling between shaped elements and corresponding channels. The shaped elements are associated to the internal surface of the drum, while the channels are made in the backs of cladding panels in positions corresponding to lifter bars.
Though the cladding described in the cited patent does not require the use of bolts for fastening to the drum, it nonetheless exhibits numerous drawbacks. The conformation of the ribs, which exhibit undercuts for blocking the channels, considerably complicates the panel mounting. To achieve coupling between the ribs and the channels, a certain pressure must be exerted on the panels, which usually means using a mallet to tap them into position along the whole length of the drum. The operatives therefore have to get inside the drum to carry out this task.
The dismounting of the panels is also extremely difficult, if done before the panels are completely worn out. To achieve uncoupling between the ribs and the channels a considerable force has to be exerted in order to detach the panels from the internal surface of the drum. This operation is generally performed using a lever, such as a crowbar. In order to do this operation the operatives have to get inside the drum and detach the panels along the whole length of the drum.
A further disadvantage of the cladding described in patent no. IT 1291313 is that the ribs, in order to be inserted in the channels, have to be pointed. This conformation, though bevelled, causes stresses in the material constituting the panels, in rubber or other elastomer material, which stresses are extremely localised and can lead to cracking in the material. This is true both during the mounting operation and progressively during use of the mill, with the result that the working life of the cladding is drastically shortened.
The main aim of the invention is to provide a cladding for drum mills which obviates the above-described drawbacks in the prior art.
An advantage of the invention is that the cladding is extremely easy and fast to mount.
A further advantage of the invention is that the connection between the cladding and the drum is extremely stable and secure.
A further advantage of the invention is that the cladding is especially resistant to the formation of cracks and to wear.
Further characteristics and advantages of the present invention will better emerge from the detailed description that follows, of a preferred but not exclusive embodiment of a cladding for rotary drum mills, illustrated purely by way of example in the accompanying figures of the drawings, in which:
figure 1 is a schematic perspective view and a detail of the invention;
figure 2 is a detailed perspective view of a first element of the cladding;
figure 3 is a detailed perspective view of a second element of the cladding;
figure 4 shows the elements of figures 2 and 3 in front view and during assembly;
figure 5 shows the elements of figures 4 when assembled.
The figures of the drawings represent an illustration of a cladding for a rotary drum mill according to the present invention.
The cladding comprises a plurality of panels 3 predisposed to cover an internal cylindrical surface 20 of an internally hollow cylindrical body 2 rotating about a longitudinal axis x thereof at a predetermined peripheral velocity. The panels 3 are associated to the internal cylindrical surface 20 using means for connection.
The means for connection comprise a plurality of ribs 5 fixed by welding onto the internal cylindrical surface 20 of the cylindrical body 2, each of which exhibits a section which is perpendicular to the longitudinal axis of the cylindrical body 2 which section has at least one portion thereof arranged with an acute angle of inclination α with respect to the vector representing the peripheral velocity of the cylindrical body 2.
The means for connection further comprise a plurality of hollow seatings or channels 6, afforded at the lower surfaces 30 of the panels 3. The lower surfaces 30 are predisposed to be contactingly coupled with the internal cylindrical surface 20 of the cylindrical body 2. The channels 6 are counter-shaped with respect to the ribs 5 so that the ribs 5 can be coupled in the channels 6.
The ribs 5 and the channels 6 exhibit coupling surfaces 5b, 6b, which are inclined according to the acute angle of inclination α. The coupling surfaces 6b define wedge-shaped portions 3c in the panels 3. The coupling surfaces 5b, 6b are predisposed to enter into contact in the coupling between the ribs 5 and the channels 6.
The connection of the panels 3 to the internal cylindrical surface 20 of the cylindrical body 2 is extremely simple and rapid. The panels 3 are arranged in succession on the internal cylindrical surface 20 so that the channels 6 are inserted, at least with one leader section, on the ribs 5. At this point it is sufficient to slide the panels 3 on the internal cylindrical surface 20 up until the ribs 5 are inserted in the respective channels 6. The sliding and the following blocking of the panels 3 which lead to the correct insertion of the ribs 5 in the channels 6 can be obtained, for example, by rotating the cylindrical body 2. Since the angle α is an acute angle with respect to the peripheral velocity of the cylindrical body 2, in the "rising" tract of the circular pathway, each panel 3, by effect of the rotation of the cylindrical body 2, inserts into one of the ribs 5 by dint of its own weight. The insertion effect is accentuated during the operation of the mill. The material to be ground inside the cylindrical body 2 is partially drawn in rotation due to the friction between the panel 3 and the material itself. During the "rising" part of the rotation, the resultant of the friction forces between the material and each panel 3, thanks to the arrangement of the coupling surfaces 5b, 6b which are inclined according to the acute angle of inclination α, increases the insertion force of each rib 5 in the respective channel 6. The wedge-shaped portions 3c are forced into corresponding complementary spaces defined between the ribs 5 and the internal cylindrical surface 20, solidly fixing the panels 3 to the internal cylindrical surface 20.
The panels 3 exhibit at least one longitudinal relief, known as a lifter bar 7, arranged at the opposite surface to the surface 30, so as to be projecting internalwards of the cylindrical body 2, and at least one channel 6 which is staggered downstream of the rotation direction with respect to the longitudinal relief. Further, the panels 3 at least partially exhibit a progressively-diminishing thickness in the direction of rotation.
In the illustrated embodiment, the panels 3 exhibit a plurality of lifter bars 7 and a plurality of channels 6 staggering downstream of the rotation direction with respect to the corresponding lifter bars 7. The lifter bars 7 are separated by portions 3 a of the panels 3 which each exhibit a progressively-diminishing thickness in the direction of rotation.
The staggered arrangement of the lifter bars 7 with respect to the channels 6 and the decreasing thickness of the panels 3 in the rotation direction of the cylindrical body 2 reduce the incidence of wear on the working life of the cladding. During mill operation the material to be ground in the cylindrical body 2 is drawn in rotation by the cylindrical body 2. During the "rising" part of the rotation, the material to be ground and the grinding balls are raised by effect of friction with the panels 3 and by the presence of the lifter bars 7 up to a certain height, at which, by effect of the rotation angle, they detach from the panels 3 and fall downwards. During the descent the material to be ground and the grinding balls impact, at least partially, on the panels 3, and more precisely impact on the front side 7a, i.e. the side facing towards the rotation direction of the underlying lifter bars 7 and the zones close to the front side 7a of the portions 3 a of the panels 3. The downstream-stagger of the channels 6 with respect to the lifter bars 7 and the greater thickness the portions 3a exhibit in proximity of the front side 7a of each lifter bar 7 guarantee a greater quantity of material in the critical wear points, especially at the front sides 7a. At these critical wear points the distance between the front side 7a and the end of the channel 6 is very considerable.
Each rib 5 is constituted by at least one section, connected to the internal cylindrical surface 20 of the cylindrical body 2, which is defined by a shaped sheet of steel. In particular, the two free edges of the fashioned sheet of steel are parallel and connected to the internal cylindrical surface 20, for example by welding. As can be seen in the figures of the drawings, the steel is shaped so that the coupling surface 5b is inclined by angle α.
At least the edge 12 of the fashioned steel sheet which is folded to form the element constituting the single rib 5 which, with reference to the rotation direction of the cylindrical body 2, is located posteriorly with respect to the other free end of the same steel sheet, and exhibits slots 11 which enable the rib to be welded to the internal cylindrical surface 20 of the cylindrical body 2. In particular the slots 11 afford access for the welding to the other free edge, otherwise difficult to access from the other side i.e. where the portion 3c inserts.
The element constituting the single rib 5 exhibits an external surface with is free of live edges. This greatly limits the chance of lacerations in the rubber due to the load exerted by the grinding balls and the grinding material.
In the illustrated example the ribs 5 are arranged on the internal cylindrical surface 20 of the cylindrical body 2 and are parallel to the longitudinal axis x of the cylindrical body 2 itself. Alternatively the ribs 5 can be parallel to one another but inclined with respect to the longitudinal axis x; this can be required, for example, if the lifter bars 7, typically parallel to the channels 6, exhibit a certain inclination with respect to the longitudinal axis x.
The ribs 5 are preferably arranged at a constant angular distance and extend over the whole length of the cylindrical body 2. For special constructional requirements the ribs 5 can also be arranged at a non-constant angular distance and/or can extend over only a part of the length of the cylindrical body 2.
To improve the stability of the cladding the panels 3 each exhibit four edge surfaces 3b at which the panels 3 are joined to assemble the cladding. Some of the edge surfaces 3b are arranged to form a projecting end 9 of a panel 3 and others are arranged to form a recessed seating 10 which fits into the projecting end 9 of another, adjacently-arranged panel 3.
The invention offers important advantages. Firstly the cladding is extremely rapidly and easily mounted. It is sufficient to place the panels 3 on the internal cylindrical surface of the rotating cylindrical body and slide them slightly over the cylindrical surface. Thanks to the conformation of the ribs and the channels the connection between the cladding and the drum is extremely stable and secure and is further improved during mill operation. The position of the channels with respect to the lifter bars in each panel and the variable thickness of the panels themselves make the cladding especially resistant to the formation of cracks and to wear.

Claims

A cladding for a rotary drum mill, of a type comprising a plurality of panels arranged to clad an internal cylindrical surface of an internally-hollow cylindrical body rotating about a longitudinal axis thereof at a predetermined peripheral velocity; means for connection being included for associating the panels to the internal cylindrical surface; characterised in that the means for connection comprise:

a plurality of ribs (5) fixed to the internal cylindrical surface (20) of the cylindrical body (2), each of which plurality of ribs (5) exhibits a section which is perpendicular to the longitudinal axis of the cylindrical body (2), which section is provided with at least a portion thereof which is arranged at an acute angle of inclination (α) with respect to a vector representing the peripheral velocity;

a plurality of channels (6), afforded at first surfaces (30) of the panels (3), which first surfaces (30) are predisposed to be coupled contactingly with an internal cylindrical surface (20) of the cylindrical body (2); the plurality of channels (6) being shaped complementarily with respect to the ribs (5) in order for the ribs (5) to be couplable in the channels (6).
The cladding of claim 1, characterised in that the ribs (5) exhibit first coupling surfaces (5b) which are inclined at an acute angle of inclination (α) and the channels (6) exhibit second coupling surfaces (6b) which are inclined according to the acute angle of inclination (α) and which define, in the panels (3), wedge-shaped portions, the first coupling surfaces (5b) being predisposed to contact with the second coupling surfaces (6b) in a coupling between the ribs (5) and the channels (6).
The cladding of claim 1, characterised in that the panels (3) exhibit at least one lifter bar (7), arranged at a second surface opposite the first surface (30), which lifter bar (7) projects internally of the cylindrical body (2), and at least one channel (6) which is staggered downstream of a rotation direction of the cylindrical body (2) with respect to the lifter bar (7).
The cladding of claim 1, characterised in that the panels (3) exhibit at least partially a thickness which progressively diminishes in a direction which is the rotation direction of the cylindrical body (2).
The cladding of claim 1, characterised in that the panels (3) exhibit a plurality of lifter bars (7), arranged at the second surface opposite the first surface (30) so as to project internally of the cylindrical body (2), and a plurality of channels (6) which are staggered downstream of the rotation direction with respect to the lifter bars (7), the lifter bars (7) being separated by portions (3a) of the panels (3) which each exhibit a thickness which progressively diminishes according to the rotation direction.
The cladding of claim 1, characterised in that each rib (5) comprises at least one element which is connected to the internal cylindrical surface (20) of the cylindrical body (2), which element is a shaped steel sheet.
The cladding of claim 1, characterised in that the ribs (5) are arranged on the internal cylindrical surface (20) of the cylindrical body (2) and are parallel to one another.
The cladding of claim 1, characterised in that the ribs (5) are arranged on the internal cylindrical surface (20) of the cylindrical body (2) and are preferably parallel to the longitudinal axis (x) of the cylindrical body (2).
The cladding of claim 1, characterised in that the ribs (5) extend for at least a part of a length of the cylindrical body (2).
The cladding of claim 1, characterised in that the ribs (5) extend over an entire length of the cylindrical body (2).
The cladding of claim 1, characterised in that the ribs (5) are arranged at constant angular distances.
The cladding of claim 1, characterised in that the panels (3) exhibit edge surfaces (3b) at which the panels enter into contact to realise the cladding; some of which edge surfaces (3b) exhibit appendix projections (9), some of which edge surfaces (3b) exhibit seatings (10), which seatings (10) are complementarily shaped so that the projections (9) of each panel (3) can fit into the seatings (10) of an adjacent panel of the panels (3).
The cladding of claim 6, characterised in that at least an edge (12) of the shaped steel sheet constituting the element which is a rib (5), which edge is a rear edge with respect to the rotation direction, exhibits slots for enabling a welding of the rib (5) to the internal cylindrical surface (20) of the cylindrical body (2).
The cladding of claim 1 or 13, characterised in that the element constituting the single rib (5) exhibits an external surface which is free of live edges.