EP1365863B1 - Pendular grinding apparatus - Google Patents

Abstract

The invention concerns a pendular grinding apparatus comprising an inner vertical wall (1) rotating about a main vertical axis (2) and forming a runway (3) for grinding, a support (4) coaxially arranged above the runway (3) and designed to be driven in rotation about the main axis, at least two grinding rollers (8) comprising each a rotating surface (9) about an axis of rotation (10) suspended to the support (4) and arranged such that the rotating surface (9) of each roller should run against the runway or against the material to be ground between the roller and said runway (3), a pressing action of each roller (8) on said runway or on said material to be ground supplied between them resulting from a centrifugal force (Fc) of each roller driven in rotation by the support, the grinding apparatus comprising means (12) designed to combine with the centrifugal force (Fc) of each roller an adjustable force and said combining means (12) being supported therefor on a common central element (14) which can be either fixed to the support (4) or be integral therewith.

Description

The present invention relates to a pendulum mill comprising (-) an inner vertical wall of revolution about a main vertical axis and forming a raceway for grinding,
(-) a support arranged coaxially above the raceway and arranged to be rotated about the main axis, and (-) at least two grinding rollers. These each comprise a face of revolution about an axis of rotation, are suspended from the support and are arranged so that the face of revolution of each roller can roll against the raceway or against the material to be crushed brought between the roller and said path, the roller being rotatable about its axis of rotation, when the common support rotates about the main axis. A pressing of each roller on the raceway or on the material to be ground fed between them results from a centrifugal force of each roller rotated by the support.

A grinder of this kind is known for example by the US Patent 4,522,343 .

In a pendulum mill, the grinding pressure is given solely by the centrifugal force that the speed of rotation of the support gives the rollers and which presses them against the raceway.

The flow rate of the known pendulum mill is proportional in particular to the number of rollers used and to the pressing obtained which produces the grinding, therefore to the centrifugal force F _c which can be calculated as follows: $${\mathrm{F}}_{\mathrm{vs}}\mathrm{=}\mathrm{m}\mathrm{.}{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^{\mathrm{2}}\mathrm{.}\mathrm{R}\mathrm{.}$$

The mass m of a roller is approximately given by: $$\mathrm{m}\mathrm{\cong }\mathrm{\pi }\mathrm{.}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0001.png"\; state="\{\{state\}\}">d</figure-callout>}}^{\mathrm{2}}\mathrm{.}\mathrm{h}\mathrm{.7}\mathrm{850}\mathrm{/}\mathrm{4.}$$

• D : diamètre du chemin de roulement (exprimé en m).
• d : diamètre du galet (exprimé en m).
• h : hauteur du galet (exprimée en m).
• m : masse du galet, (exprimée en kg ).
• ω : la vitesse angulaire (exprimée en rad/s ).
• R : rayon de giration du centre de gravité du galet (exprimé en m).
• F_c : force centrifuge (exprimée en N ).

The radius of gyration R of a roller is given by: $$\mathrm{R}\mathrm{=}\left(\mathrm{D}\mathrm{-}\mathrm{d}\right)\mathrm{/}\mathrm{2}\mathrm{,}$$

• D: diameter of the raceway (expressed in m).
• d: diameter of the roller (expressed in m).
• h: height of the roller (expressed in m).
• m: mass of the roller, (expressed in kg).
• ω: the angular velocity (expressed in rad / s).
• R: radius of gyration of the center of gravity of the roller (expressed in m).
• F _c: Centrifugal force (expressed in N).

For various reasons, including vibration, the speed of rotation of the rollers must sometimes be limited. It is all the more limited as the product must be ground more finely. As a result, during fine grinding, the centrifugal force reduced by the decrease in the rotational speed inevitably leads to a large reduction in mill flow.

To date, this loss of flow can only be compensated by increasing the number of rollers.

An increase in the number of rollers causes a decrease in their diameter d and therefore their mass. This is, in a small proportion, to the advantage of the radius of gyration (D - d) / 2 of the center of gravity of the roller.

In the known mill, one can not compensate very partially a loss of mass, due to a decrease in the diameter of the roller, by increasing the height h thereof.

The object of the present invention is to provide a pendulum mill which can be increased or, where appropriate, reduce the flow rate by acting on a parameter other than the rotational speed, therefore independently of this rotational speed and also the mass of each pebble. At the same time, the object of the invention is to provide means for adjusting the pressing force of the rollers other than by the speed of rotation.

For this purpose, the mill of the invention comprises means arranged to combine with the centrifugal force of each roller an adjustable force and these combination means are supported for this purpose on a common central element which can be either fixed to the support or in to be a part of.

The document US 3,337,142 discloses a pendulum mill having means for combining with the centrifugal force of each roller an adjustable force, which means are supported on or attached to a common central element attached to the central support and comprise a fluid device whose pressure is controlled.

According to one embodiment of the invention, the combining means comprise, to develop on each roller the adjustable force, a fluid device whose pressure is controlled.

According to a particular embodiment of the invention, the combination means comprise an annular casing of elastic material, an internal space of which is supplied with pressure-controlled fluid and an external surface of which is arranged to control the pressing of the rollers on the path rolling stock or on grinding material.

Other details and particularities of the invention will emerge from the secondary claims and from the description of the drawings which are appended to the present memorandum and which illustrate schematically, by way of non-limiting example, particular embodiments of the mill according to the invention.

The figure shows in elevation and section two different embodiments of the pendulum mill of the invention.

In the illustrated embodiments of a pendulum mill, the latter has a vertical inner wall 1 of revolution about a main vertical axis 2 and forming a raceway 3 for grinding. A support 4 is arranged coaxially above the raceway 3 and is arranged to be rotated about the main axis 2 by the shaft 5 of a gearbox 6.

At support 4, in particular in the form of a star, are suspended, each time an arm 7, at least two grinding rollers 8 each having a surface of revolution 9 about an axis of rotation 10 and arranged so that their face of revolution 9 can roll against the rolling path 3, or against the material to be milled brought between the roller 8 and said path 3, when the support 4 rotates about the main axis 2. The roller 8 can then turn around its rotation axis 10.

Each arm 7 is carried by the support 4 so as to be pivotable thereon about a horizontal pivot axis 11. In general, the axes of rotation 10 and pivoting 11 corresponding to an arm 7 do not intersect.

According to the invention, the mill comprises means 12 arranged to combine with the centrifugal force of each roller 8 an adjustable force for pressing on the rolling path 3 or on the material to be ground fed between them. These combination means 12 may, if necessary, form an assembly supported only by the arms 7 to which they are attached. Indeed, the pressing forces are balanced in principle in a regular manner between the rollers 8.

The combination means 12 comprise for said pressing a fluid device 15 acting on the rollers 8 and whose pressure is controlled according to the desired pressing.

The combining means 12 may comprise an annular casing 18 of elastic material, an internal space of which is supplied with pressure-controlled fluid and an outer surface 19 of which is arranged for controlling the pressing of the rollers 8 on the rolling track 3 or on the material to grind.

The annular hose 18 may be a standard vehicle tire, mounted on a standard wheel acting as a central element 14.

In an assembly proposed in full lines in the figure, the outer surface 19 of the annular casing acts on each roller 8 via the arm 7 carrying the roller 8. In this case, said casing 18 can be fixed to the support 4 and turn with him.

By cons, in a variant shown in dashed lines in the figure, the outer surface 19 of the annular casing 18 acts on the surface of revolution 9 of the rollers. The annular hose 18 must be rotatable relative to the support 4.

It should be understood that the invention is in no way limited to the described embodiments and that many modifications can be made thereto without departing from the scope of the claims.

Thus, it is to be considered as technical equivalent of the vacuum system which has just been described, a not shown assembly in which each roller 8 is pushed towards the raceway 3 by the annular hose 18, supplied with adjustable pressure and is drawn in opposite direction by a spring not shown. It is easy to understand that, in this case also, the centrifugal force F _c opposes the force of said spring which can be considered as substantially constant for the stroke that it travels following the movement of the arm 7. The Hose 18 then adds its adjustable force to the centrifugal force F _c to obtain a control of the resulting force of grinding press.

In the pendulum mill of the invention, an abutment system (not shown) may be provided to act on each arm, for example, in order to keep the rollers 8 at a desired distance from the raceway 3, in order to determine in this way a fineness grinding.

It is found that an object of the invention furthermore consists in that the resultant of the forces applied on the central element 14 and / or on the support 4 is zero, among other things an equilibrium being obtained automatically in the fluid systems described. above.

Claims (1)

1. Centrifugal mill comprising:

   - an internal vertical wall (1) of revolution about a principal vertical axis (2) and forming a rolling track (3) for grinding,

   - a support bracket (4) disposed coaxially above the rolling track (3) and arranged to be set in rotation about the principal axis (2),

   - at least two grinding rollers (8), each comprising a face of revolution (9) about the rotation axis (10), suspended from the support (4) and arranged so that the face of revolution (9) of each roller (8) can roll against the rolling track (3) or against the material to be ground brought between the roller (8) and the said track (3), the roller (8) being able to turn about its rotation axis (10) when the support (4) turns about the principal axis (2),

   - pressing of each roller (8) on the rolling track (3) or on the material to be ground brought between them resulting from a centrifugal force (F_c) of each roller (8) driven in rotation by the support (4),

   - means (12) arranged to combine an adjustable force with the centrifugal force (F_c) of each roller (8), bearing for this purpose on a common central element (14) that can be either fixed to the support (4) or form part thereof and comprising, in order to develop the adjustable force of each roller (8), a fluid device (15), the pressure of which is controlled,

   characterised in that the combining means (12) comprise an annular tube (18) made from elastic material, an internal space of which is supplied with fluid at controlled pressure and an external surface (19) of which acts on the surface of revolution (9) of the rollers (8) in order to control the pressing of the rollers (8) on the rolling track (3) or on material to be ground.

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