Solid material comminution or disintegration – Apparatus – Comminuting elements
Reexamination Certificate
1999-11-18
2001-03-27
Rosenbaum, Mark (Department: 3725)
Solid material comminution or disintegration
Apparatus
Comminuting elements
C241S183000
Reexamination Certificate
active
06206310
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a rotary mill comprising a cylindrical shell lined with an interior lining and intended to contain material to be ground and a charge of grinding implements, in which the lining, which is made up of rings of juxtaposed individual lining plates, has interior longitudinal undulations to encourage the lifting of the charge and of the material to be ground as the mill rotates.
BACKGROUND OF THE INVENTION
The invention is more specifically aimed at mills used in cement making and in the mining industry. These mills consist of a metallic cylindrical shell rotating about its longitudinal axis and containing a grinding charge made up of grinding implements, generally balls, but which may also consist of cylindrical pebbles, ball-shaped pebbles, etc. of varying size. The material to be ground is introduced from one side of the mill and, as it progresses towards the outlet, on the opposite side, it is ground and crushed between the grinding implements.
As the mill rotates, the material to be ground and the grinding charge are lifted up by the lining and, from a given instant, slide downwards again. It therefore follows that the charge of the mill is essentially concentrated in the fourth trigonometric quarter if the mill is rotating in the trigonometric sense, and in the third quarter if the mill is rotating clockwise, and occupies therein, in a radial plane, a “bean”-shaped area as shown in FIG. 4A of Belgian Patent Application 09301481. Grinding is achieved by the shear and frictional forces as the mass moves. To obtain effective grinding and avoid breaking the linings and the grinding implements, it is necessary for the lining to have a profile such that it lifts the charge up as far as a level such that this charge remains compact, because lifting it too much causes balls to be thrown out further than the base of the charge, that is to say that the balls directly strike the lining, without the interposition of material to be ground. From another viewpoint, the charge has to be lifted up high enough for there to be good agitation of the mass. It goes without saying that the fill co-efficient plays a deciding role in the efficiency of the grinding and that the bean-shaped area occupied by the charge has to be of a shape, position and size that are clearly determined in order to achieve effective and optimum grinding.
To encourage the lifting of the material and of the charge, it is known practice for longitudinal undulations which are adapted to the conditions and parameters in which the mill operates to be provided on the plates that form the interior lining of the mill. The problem, however, is that although the undulations or profiles of the grinding plates are adapted to a given mill, this will perhaps no longer be the case if the conditions change. It should in fact be pointed out that the lifting of the charge and of the material depends on a great many factors such as, for example, the size of the mill, its rotational speed, the size of the grinding implements, etc.
Furthermore, the lining plates are subject to intense wear which means that, even if the lifting conditions are optimum at the start, they may rapidly degrade as a result of the change in profile of the plates which is brought about by wear.
Known lining plates also have the handicap of being quite heavy, of the order of 40 to 50 kg, which means that handling them is difficult and dangerous. Reforms in health and safety at work legislation are in any case tending to forbid the handling of objects that weigh more than 25 kg.
Another constraint is that of replacing the worn plates and of attaching them to the shell, especially when they are bolted. In fact it should be pointed out that the shells have, so that the lining plates can be attached, drillings which are arranged generally according to a standard layout, but these standards may vary from one manufacturer to another. Any model of plate which does not suit these standardized drillings would lead to the need to make another drilling in the mill, something which cannot be envisaged because it is an extremely expensive operation which results in holing the shell and an increased risk of leakage of ground material.
Document DE 1126709 describes a mill in which the lining plates form steps in the direction of rotation. Various plates of differing radial depths follow on from one another in a determined order. The face with the greatest radial depth is at the front, when viewed in the direction of rotation. This has the drawback that the grinding implements are thrown, and this reduces the effectiveness of the grinding and increases the risk of the plates becoming broken. Furthermore, the steps of one ring are offset with respect to the steps of an adjacent ring, that is to say that the steps are not axially aligned. This gives rise to shear forces which increase the rate of wear of the plates on the edges.
Document WO 86/04267 also describes a mill in which the lining plates are arranged in steps to form lifting ramps. In this grinder, there is, in fact, just one type of step. Furthermore, the plates are bolted to the shell which means that the layout of the plates is restricted to the configuration of the holes in the shell.
In mills with stepped linings, the inclination of the ramps has to be increased when the diameter of the mill increases. In known mills, this leads to an increase in thickness of all the plates, which increases the total weight of the lining.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a new type of lining which makes it possible to reduce the drawbacks described hereinabove and, more specifically, to provide a mill in which the lining is formed of lining plates which allow the lifting profile to be adapted to the parameters and conditions in which the mill operates, and which alters more gradually under the effect of wear.
In order to achieve this objective, the invention proposes a lining of the type described in the preamble, which is characterized in that each plate has, on the rear face, when viewed in the direction of rotation, a step of a radial height that is taller than the front face, in that each ring of plates comprises several different types of plate which differ, at least, in terms of the radial height of their step and in terms of the nature of their material and which follow on from one another, in the circumferential direction, in a determined order. A certain number of one of the types of plate are attachment plates bolted to the shell, all the other plates not necessarily being attached to the shell by bolts but being held in place by a simple arch bracing effect.
Given that several types of plate of differing shape are available, it is possible, through a judicious choice based on testing, to combine the various types of plate to form a clearly determined lifting profile which allows optimum lifting adapted to the conditions in which the mill operates.
According to another aspect of the invention, the various types of plate also differ in terms of the nature of their material. It is therefore possible to combine the various types of plate as a function of their risk of wear. It thus becomes possible to produce a lifting profile which is less vulnerable to wear, that is to say to conserve the initial lifting profile for longer. It is furthermore possible to combine the plates in an optimum way in order to have both good wear resistance and good impact resistance.
The lining plates, with the exception of the attachment plates, preferably comprise, on their radial faces, at least one longitudinal rib in the case of one and a corresponding longitudinal slot in the case of the other, or vice versa, so that they can nest together and be held in place by the attachment plates.
Given that most of the lining plates are not bolted to the shell but are simply held in place by nesting together, there are fewer constraints due to the arrangement of the drill holes in the shell when installing such a lining.
Each of the plates is preferably sized so
Magotteaux International
Rosenbaum Mark
Schmeiser Olsen & Watts
LandOfFree
Rotary mill does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rotary mill, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rotary mill will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2443991