Description

The present invention relates to a milling apparatus of the type used for micronization of a flow of raw material in powder, for example sodium bicarbonate, which will be used in systems for treating fumes.

The apparatuses of the above specified type use a mill with a rotor inserted in a casing which is crossed by a flow of air and raw powder product to be micronized. Typically, the mill can be of the hammer type, provided downstream of a granulometric selector, typically of the squirrel-cage type, which allows the passage of powder micronized below a prefixed granulometry.

Said flow is determined by a sucking fan placed downstream of the mill: in the known apparatuses, the air flow mixes with the raw powder product at an intersection between two ducts, one arranged for the air flow and another one in which the raw powder product is provided by gravity through a hopper and a feeding screw. This aspect distinguishes this type of mills from the one thereto the grinding mill described in US patent application No. 2021/0,039,108 A1 belongs, wherein the grinding chamber receives an air flow which is pumped inside the chamber itself from a pumping system arranged upstream of the mill, whereas the products to be ground are introduced by a separate duct.

The suction, downstream of the grinding chamber by a suitable sucking system, is capable of determining a flow of air which is mixed with the raw powder product, within a relatively precise range, which is selected to allow the optimum operation of the grinding rotor.

An apparatus of this type is described in utility model in Italy No. VA2004A000017. However, this type of apparatus involves significant drawbacks. In fact, this type of apparatus results to be very bulky, and even not very effective in terms of noise reduction. Moreover, such apparatuses involve, in their circuit for the passage of air, various and consistent pressure drops which make them not very efficient from the energy point of view.

The technical problem underlying the present invention is to provide a milling apparatus allowing to obviate the drawback mentioned with reference to the known art.

Such problem is solved by a milling apparatus as specified above and as defined in the enclosed claim 1.

In this milling apparatus, the grinding chamber is defined in a casing which comprises a side access wall crossed by the crankshaft of horizontal axis grinding rotor w, and in the side access wall a first opening is formed above the hole therethrough the crankshaft passes.

The milling apparatus further comprises a silencing chamber which is adjacent to the grinding chamber and which is separated therefrom by the above-mentioned side access wall, which then comprises a second opening for the passage of air, positioned below the crankshaft hole.

The main advantage of the milling apparatus according to the present invention lies in the fact of allowing an effective positioning of the silencer in the apparatus frame, as well as an improvement of the mill performances in terms of obtained granulometries.

The present invention will be described hereinafter according to a preferred embodiment example, provided by way of example and not for limitative purpose with reference to the enclosed drawings wherein:

* figure 1 shows a perspective view of a milling apparatus according to the present invention;

* figure 2 shows a perspective view of the lower portion in partial section of the milling apparatus of figure 1;

* figure 3 shows a perspective view of an exposed detail of the milling apparatus of figure 1; and * figure 4 shows a side elevational and cross view of the milling apparatus of figure 1.

By referring to the figures, a milling apparatus is designated as a whole with 1; it is of the type which is used for the micronization of a flow of raw material in powder, which hereinafter will be designated in short as powder product, starting from a variable granulometry, not suitable to the use provided for the micronized product .

By way of example, the powder product could be sodium bicarbonate which, once micronized, is used in systems for the treatment of fumes.

However, it is meant that the present invention is directed generally to the field of micronization of any powder product which requires high flows of product, until 6 tons per hour.

In the milling apparatus 1 the powder product at first is contained in a hopper 2, which internally comprises a feeding screw and which has, at the lower end thereof, a dosing device 35, controlled by a first auxiliary engine 3, known in the art as micro-dosing element, which is useful to feed the powder product inside a grinding mill, designated with 8, where the powder product is micronized.

The dosing device 35 is connected to the mill 8 by means of a first duct 4 for the introduction of the powder product.

The apparatus 1 comprises a frame 5 formed by a plurality of beams supporting said hopper 2 and having feet 6 arranged at the corners of a base quadrilateral 7, rested upon the ground.

The grinding mill 8 of the milling apparatus 1 is of the type with horizontal axis, with a grinding rotor 12, of the hammer type, with horizontal rotation axis. The grinding mill 8 further comprises a casing 13 enclosing the grinding rotor 12; it defines a grinding chamber 14 and comprises a cylindrical shell 10, or the peripheral cylindrical wall with high thickness of the casing 13 (figure 2) surrounding the rotor 12 and which is arranged to cooperate therewith, and in particular with the hammers 9 impacting on the powder product and addressing them on the internal cylindrical wall.

On the top of the casing 13, the milling apparatus 1 comprises a granulometric selector 15 with horizontal axis, of the carousel type, or a squirrel-cage type, which in turn is enclosed in a second casing 16. It is actuated by a second service engine 18 suspended on the second casing 16 at a rear wall thereof 17.

On the contrary, at the front wall, the granulometric selector 15 has a second outlet duct 19, which is intended to transport a flow of air and micronized powder product, exiting the grinding chamber 14 and the selector 15.

The air flow is sucked from a suction system which then is placed downstream both of the grinding chamber 14 and the grinding rotor 12, and of the selector 15; the grinding chamber 14 then is in depression with respect to the outside, causing the inlet of the air therein, as it will be described hereinafter. The suction system is also placed downstream of the second outlet duct 19 which is then connected to a separation device of the micronized product.

The grinding rotor 12 is dragged in rotation by a crankshaft 11 which is suspended on supports 23, connected to the frame 5, and it is connected to a drivetrain 33 imparting its rotation, the drivetrain 33 in turn being connected to a not represented main engine.

The first casing 13 of the grinding mill 8 has a side access wall 20 which contributes to delimit, together with the above-mentioned shell 10 of the casing 13, the grinding chamber 14; this access wall 20 then is vertically arranged and it has an external face facing towards said drivetrain 33; the side access wall 20 has a central hole 34 which is crossed by the crankshaft 11 of said grinding rotor 12.

The side access wall 20 has a first opening 24, having a circular shape, which is placed above the hole 34 of said crankshaft 11.

The first opening 24 is connected to said first duct 4 for the introduction into the grinding mill 8 of the raw powder product coming from the hopper 2.

In particular, such first opening 24 has a centre which is positioned on the vertical line passing through the centre of the hole 34, that is at the centreline of the cylindrical casing 13, and then the whole passage section for i the powder product is placed above the crankshaft 11.

Inside the first duct 4 the powder product moves by gravity and due the push induced by the dosing device 35; on this regard, the first duct 4 has a curved connection involving a deviation of 90° in proximity of said first opening 24, so that the raw powder product enters the grinding chamber 14 with a flow transversal to the rotor 12, sucked by the depression caused by the suction system which is downstream of the grinding mill 8.

The milling apparatus 1 comprises a silencing chamber 26 to decrease the operating noise, mostly due to the air flow which is sucked inside the grinding chamber 14 through a second opening 25 which will be described hereinafter .

The silencing chamber 26 is formed by a third casing 27 which is of the box-like type, that is formed by walls substantially arranged like a parallelepiped. The silencing chamber 26 is arranged within the base quadrilateral 7, contained between beams 6 thereto the walls of the chamber 26 are connected.

The silencing chamber 26 is positioned adjacent to the grinding chamber 14, and the side access wall 20 separates the grinding chamber 14 from the silencing chamber 26 which, in this embodiment example, is positioned wholly below the crankshaft 11, which then does not cross it.

In order to allow the passage of the air through the silencing chamber 26, the side access wall 20 has a second opening 25 which, contrary to the first opening 24, is then positioned below the hole 34 for the passage of the crankshaft 11. The second opening 25 is arranged for inletting air and it has a shape with circular segment, with the segment convexity facing downward and with a radius of curvature of the convexity which is substantially equal to its distance from the axis of the crankshaft 11.

In this way, the air and the flow of powder product are separately fed in the grinding chamber 14, as highlighted by the arrows A and B in figure 3, and they mix inside thereof .

The silencing chamber positioned below the crankshaft 11 allows to reduce considerably the overall dimensions. Moreover, the grinding chamber 14, through the second opening 25, faces directly in the silencing chamber 26, by reducing considerably the charge losses of the sucked air flow.

The silencing chamber 26 in case can include sound- absorbing material, for example as internal coating.

The silencing chamber 26 comprises a bottom wall 28 in which a plurality of open holes 29 for inletting air are formed, positioned in proximity of the ground, therethrough the air is sucked, as highlighted by the arrow C in figure 4.

Moreover, the silencing chamber 26 internally comprises a plurality of tubular ducts 30 having each one a different length from that of the other tubular ducts.

Each one of the tubular ducts 30 is connected to a respective open hole 29. In the present example, the tubular ducts 30 extend vertically and are wholly included inside the silencing chamber 26.

On this regard, each tubular duct 30 has an access end corresponding to the respective open hole 29 and which is positioned substantially below the apparatus 1, between the frame 5 and the feet 6.

Moreover, each tubular duct 30 has an outlet end which is at a certain height from the bottom wall 28 of the casing 27.

In this way, the tubular ducts 30 work like organ pipes and have the capability of dampening different frequencies of the noise induced by the passage of the air flow, without involving an excessive pressure drop.

Each outlet end has a top wall 31 and a side discharge hole 32, involving a deviation of the corresponding air flow of about 90°, but with an extension of 360° around the tubular duct 30, as highlighted by arrows D in figure

2.

By adjusting the number and the height of the tubular ducts 30 then it is possible to optimize the performances of the silencing chamber 26: optimum performances can be obtained already with five ducts arranged on a single row, but it is meant that they could increase by number and be arranged with a different pattern, for example on several rows, however by occupying the space corresponding to the base quadrilateral 7 of the frame 5 of the milling apparatus 1.

The arrangement of the silencer in a chamber shaped like a parallelepiped and the use of tubular ducts 30 arranged like organ pipes allow a clear space and conduit saving, considering that in the known milling apparatuses the silencer generally is arranged outside the frame, far from the grinding chamber, since the air flow had the function of transporting the raw powder product, by mixing therewith, upstream of the grinding mill.

On the contrary, in the herein described apparatus the silencer is directly connected to the grinding chamber and the air flow is introduced directly inside thereof, with low pressure drops, thanks to the downstream suction .

To the above-described milling apparatus a person skilled in the art, with the purpose of satisfying additional and contingent needs, could introduce several additional modifications and variants, all however comprised within the protective scope of the present invention, as defined by the enclosed claims.