GB2026343A - Improvements in or relating to grinding machinery - Google Patents

Abstract

A grinding machine of the kind comprising a generally cylindrical grinding chamber (10) part of whose peripheral wall is formed by a perforated screen (11), a rotor (12) disposed within a grinding chamber which pivotally mounts a plurality of radially extending grinding hammers (15), a duct (16, 17) for introducing material to be ground into the interior of the chamber there to be acted upon by the hammers, which may be reversible means for drawing air from the interior of the chamber through the screen to convey ground material from the chamber, and a baffle (18) disposed in the duct and movable selectively between two positions therein such that the material to be ground may be directed into the chamber, generally tangentially, either with or against the direction of rotation of the rotor, the grinding hammers, in a preferred form of the invention, having surface portions which prevent impacting materials from re-entering the feed chute, thus avoiding choking of the latter. <IMAGE>

Description

SPECIFICATION Improvements in or relating to grinding machinery This invention concerns a grinding machine of the kind comprising a generally cylindrical grinding chamber, part of whose peripheral wall is formed by a screen and a rotor disposed within the grinding chamber which pivotally mounts a plurality of grinding hammers, means for introducing material to be ground into the interior of the chamber there to be acted upon by the hammers and means for drawing air from the interior of the chamber through the screen to convey ground material from the chamber.

It is well-known that different impact speeds are better suited for the comminution of different kinds of material.

The present invention is based upon an appreciation of the possibility of providing a grinding machine of the kind referred to wherein the material to be ground can be introduced generally tangentially into the grinding chamber with or against the direction of rotation of the rotor as desired, thereby achieving a selected of two possible impact velocities between the hammers and the material to be ground for a given rotor speed.

According to the present invention, there is provided a grinding machine of the kind comprising a generally cylindrical grinding chamber, part of whose peripheral wall is formed by a perforated screen, a rotor disposed within the grinding chamber, a plurality of radially extending grinding hammers mounted on said rotor for rotation therewith, a feed duct communicating with the grinding chamber for introducing material to be ground in the grinding chamber there to be acted upon by the hammers, and means for drawing air from the interior of the chamber through the screen to convey ground material from the chamber, characterised by a baffle disposed within said feed duct and movable selectively between two positions in the duct such that the material to be ground may be directed by the baffle into the chamber, generally tangentially, either with or against the direction of rotation of the rotor.

The invention will be further apparent from the following description with reference to the figures of the accompanying drawings which show, by way of example only, one kind of grinding machine of the kind referred to and embodying the invention.

Of the drawings: Figure 1 shows a diagrammatic vertical cross-section through the machine; Figure 2 shows a side elevation of the machine of Fig. 1; Figures 3a to 3 c illustrate three possible configurations for the hammers forming part of the grinding machine; and Figure 4 is a view similar to Fig. 1 showing part of a modified form of grinding machine.

Referring now to the drawings it will be seen that the grinding machine essentially includes a generally cylindrical grinding chamber 10 disposed with its axis in a horizontal direction and the lower half of whose peripheral wall is formed by a perforated screen 11.

Within the chamber 10 there is a rotor generally indicated at 1 2 and comprised by a plurality of axially spaced discs 1 3 mounted on a shaft 14 which is coincident with the axis of the chamber 10 and which is connected to a reversible drive motor M (Fig. 2).

Each of the discs 1 3 pivotally mounts a plurality of grinding hammers 1 5 in known manner.

A feed duct 1 6 extends vertically downwardly to communicate with the interior of the grinding chamber 10 at its upper side centrally over the axis thereof. The feed duct 1 6 incorporates a portion 1 7 at its junction with the chamber 10, which portion has a crosssectional area which increases downwardly so as to generally have the shape of a prism of trapezium-like section.

Disposed within the portion 1 7 is a baffle 1 8 generally in the form of a solid triangular prism and mounted for lateral sliding movement between a first position against one wall of the duct (indicated in full lines) and a second position against the opposite wall (indicated in broken lines) to direct material entering the chamber 10 from the duct 1 6 tangentially into the chamber either with or against the direction of rotation of the rotor (indicated by the arrow X) respectively.

To either side of the portion 1 7 are kibbling plates 1 9 forming part of the peripheral wall of the grinding chamber 10 against which material to be ground is thrown by the hammers 1 5 to assist in the grinding thereof. It will be noted that the underneath surface of the baffle 1 8 is similar to, and thus forms an extension of, the associated one of the kibbling plates 1 9 adjacent which the baffle is located.

The screen 11 is surrounded by a chamber 20 from which air is exhausted through a duct 21. This air is drawn from the interior of the chamber 10 to pass through the apertures in the screen 11, thus entraining ground material to remove it from the grinding chamber 10 and keeping the screen 11 clear. The air enters the grinding chamber 10 along with the material to be ground through the duct 16. This air enters the duct 16 through an aperture 22 thus deflecting material to be ground over a baffle 23 to enter the portion 1 7 whilst dense matter such as stones in the feed strike the baffle 23 and are ejected from the duct 1 6. At least part of the air exhausted at 21 may be re-cycled, with or without filtration, to the aperture 22.

A screw conveyor 24 is provided for conveying ground material from the enclosure 20.

In a preferred arrangement the drive motor M is a two-speed motor, thus permitting the possibility of four different impact speeds between the material to be ground and the hammers 15.

If the drive motor is capable of operating at either 1,500 rpm or 1 ,000 rpm and the dimensions of the machine are such that the resulting tip velocity of the hammers 1 5 is 17,000 or 11,333 feet per minute respectively, and the material to be ground can be introduced into the grinding chamber 10 tangentially at a linear speed of 3,000 feet per minute either with or against the direction of rotation of the hammers, initial impact velocities of 20,000 feet per minute 14,000 feet per minute and 8,333 feet per minute are attainable and such are best suited for barley, wheat and maize respectively.

It will be appreciated that when the baffle 1 8 is located in the left hand side of the duct portion 1 7 when viewed in Fig. 1, and material fed to the grinding chamber is thus directed against the direction of rotation of the rotor, there is a tendency for the material to be thrown by the hammers 1 5 back into the duct portion 1 7 thus restricting the flow of material into the grinding chamber. This effect can be at least partially overcome by modifying the shape of the hammers 1 5. To this end, the hammers may have a configuration as shown in Fig. 3a, where the inclined surface 25 changes the direction of rebound of impacting material to a sufficient extent to direct the rebounded material onwards into the chamber rather than upwardly into the duct.

It is common practice to provide an aperture at each end of each hammer so that the hammers can be reversed when worn. Fig. 3b illustrates a hammer configuration which has inclined surfaces 26, but in this case, the hammer is reversible. Fig. 3c shows another arrangement providing, at each end of the hammer, a plurality of inclined surfaces 27.

With this arrangement, the extreme reduction in the width of the hammer provided by the configuration illustrated in Fig. 3b, which might significantly reduce the strength of the hammer, is avoided. In the arrangements illustrated in Figs. 3a to 3c, the angle of the inclined surfaces is approximately 30 with respect to a central radial axis of the hammer when installed. This angle is considered to be sufficient to reduce the likelihood of material being thrown upwardly into the duct whilst maintaining a sufficient impact velocity of the hammer surface against the incoming feed.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations such as might readily occur to one skilled in the art, being possible without departing from the scope thereof.

For example, as illustrated in Fig. 4, the baffle 1 8 may be replaced by a plurality of baffle members 30, 31 disposed in a louvre arrangement which is rotatable to direct the feed to one side or the other of the feed duct portion 1 7.

Furthermore, whilst the foregoing description refers to adjustment of the baffle 1 8 or the baffles 30, 31 to direct a flow of material either wholly with or wholly against the direction of the rotor, it is envisaged that with certain materials it may be an advantage to place the baffle part way between its extremes of adjustment thus to direct some of the material with the direction of rotation of the rotor, and the remainder against the latter. For this purpose, the position of the baffle or baffles may be gradually variable so as to enable an operator to select the most suitable position for the prevailing operating conditions.

Claims (9)

1. A grinding machine of the kind comprising a generally cylindrical grinding chamber, part of whose peripheral wall is formed by a perforated screen, a rotor disposed within the grinding chamber, a plurality of radially extending grinding hammers mounted on said rotor for rotation therewith, a feed duct communicating with the grinding chamber for introducing material to be ground in the grinding chamber there to be acted upon by the hammers, and means for drawing air from the interior of the chamber through the screen to convey ground material from the chamber, characterised by a baffle disposed within said feed duct, and movable selectively between two positions in the duct such that the material to be ground may be directed by the baffle into the chamber, generally tangentially, either with or against the direction of rotation of the rotor.

2. A grinding machine according to claim 1, wherein said baffle is disposed within a portion of said duct which increases in cross sectional area as it extends towards the grinding chamber.

3. A grinding machine according to claim 1, or claim 2, wherein said baffle is generally in the form of a solid triangular prism mounted for lateral sliding movement between positions adjacent opposite walls of the duct.

4. A grinding machine according to any one of claims 1 to 3, wherein one or more wall portions of the grinding chamber are formed as kibbling plates, characterised in that the surface of the baffle which faces the grinding chamber is similar to, and thus forms an extension of, one of said kibbling plates when the baffle is in one or the other of said positions.

5. A grinding machine according to claim 1 or claim 2, wherein the baffle is formed as a plurality of. baffle members arranged in the form of a louvre wherein each baffle member is pivotable about an axis generally parallel to the axis of the rotor.

6. A grinding machine according to any one.of the preceding claims, wherein the rotor has selectively reversible direction of rotation.

7. A grinding machine according to an one of the preceding claims, further characterised in that the rotor is capable of being driven selectively at a plurality of speeds.

8. A grinding machine according to any one of the preceding claims, further characterised in that at least a portion of the impact surface of each of said grinding hammers is inclined with respect to a central radial axis of the hammer and at such an angle as substantially to prevent material which rebounds from same from re-entering the feed chute.

9. A grinding machine according to claim 8, wherein said angle of inclination with respect to the central radial axis of the hammer, is in the region of 30 .

1 0. A grinding machine, substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.