TROMMEL SCREEN Technical Field

[0001] This invention relates to trommel screens.

Background Art

[0002] Trommels are used for classifying objects for sorting, grading and separating different sizes of mixed solids in many applications and include rotary screens which are provided with openings, for example rectangular or square openings, to allow objects less than a dimension of the opening to pass through, while retaining larger objects within the screen. In general, a number of screens, for example having different opening sizes, are secured end-to-end in order to allow the length and/or properties of the trommel to be modified. If the individual screens are separable from each other and from other components of the trommel, such an arrangement also allows individual screens to be replaced without the need to replace the entire trommel.

[0003] Nevertheless, the cost and time involved in replacing an entire screen is significant and, where only part of a screen is in need of replacement, it would be desirable to be able to replace part only of the screen rather than the entire screen.

[0004] Moreover, each screen is a welded assembly and does not permit of any adjustment, for example in the size of the openings, and if an alternative opening size is required a screen must be removed and replaced with an alternative screen at considerable cost.

[0005] It is therefore an object of the present invention to provide a trommel screen which in part only of the screen can be altered, such as removed, replaced or adjusted without requiring the entire screen to be replaced.

Disclosure of Invention

[0006] According to the present invention there is provided a trommel screen comprising: at least two annular flanges, one flange being provided at each end of the screen; a plurality of tie bars extending axially of the trommel screen between the flanges and secured to the flanges in the regions of opposite ends of each bar; and a plurality of screen bars extending axially of the trommel screen between adjacent flanges and removably mounted to the flanges in the regions of opposite ends of each bar, the screen bars defining therebetween in the circumferential direction of the trommel screen a dimension of an opening for the passage of objects through the screen.

[0007] The opposite end regions of the screen bars may be secured to axial faces of the annular flanges. To this end, the screen bars may each be formed with a flange at each end, the flange having a planar face for abutting against the axial face of the adjacent annular flange. The screen bars may be secured to the annular flanges by suitable means, such as threaded fasteners, extending through apertures in the flanges of the screen bars and engaging in the annular flanges. The flanges of the screen bars may each be provided with an axially extending arcuate lip which covers the radially inner face of the adjacent annular flange.

[0008] Blanks may be provided, removably mounted to the annular flanges intermediate adjacent screen bars. The blanks may have a planar face for abutting against the axial face of the adjacent annular flange. The blanks may be secured to the annular flanges by suitable means, such as threaded fasteners, extending through apertures in the blanks and engaging in the annular flanges. The blanks may each be provided with an axially extending arcuate lip which covers the radially inner face of the adjacent annular flange.

[0009] At least one set of arcuate spacer bars may be provided, each bar extending between adjacent tie bars and removably secured at end regions of the spacer bar to the respective tie bar, the set of spacer bars substantially forming a circle, the spacer bars defining therebetween, or between a spacer bar and an adjacent annular flange, in the axial direction of the trommel screen a further dimension of an opening for the passage of objects through the screen.

[0010] Apertures may be provided in the tie bars for positioning spacer bars at a plurality of locations therealong.

[0011] At least one further annular flange may be provided coaxial with and intermediate the end annular flanges. [0012] Radially inner faces of the tie bars may be provided with an axially-extending liner plate.

Brief Description of Drawings

[0013] For a better understanding of the present invention and to show more clearly how it may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which:

[0014] Figure 1 is a side elevational view of part of a trommel incorporating embodiments of trommel screens which can be adjusted in accordance with the present invention;

[0015] Figure 2 is a sectional view along the line M-Il in Figure 1 ;

[0016] Figure 3 is a perspective view of a cylindrical skeleton forming part of one of the trommel screens shown in Figure 1 ;

[0017] Figure 4 is a perspective view of a spacer bar forming part of the trommel screens shown in Figure 1 ;

[0018] Figure 5 is a perspective view of a screen bar for use in the trommel screen shown in Figure 1 ;

[0019] Figures 6 and 7 are perspective views of blanks for use with the trommel screen of Figure 1 ; and

[0020] Figure 8 is a perspective view of a liner plate for use with the trommel screen of Figure 1.

Best Mode for Carrying Out the Invention

[0021] Figure 1 shows a trommel barrel assembly which includes an inlet component 1 , an outlet component 3 and two screens 5, 7. Figure 2 shows a cross-sectional view of one of the screens 7. Figure 3 shows one of the screens 5, 7 during an intermediate stage of assembly.

[0022] Referring first to Figure 3, each screen comprises two end annular flanges 9 and an intermediate annular flange 11 which is positioned mid-way between the two end flanges. The three annular flanges are interconnected by means of a plurality (four as shown) of longitudinal tie bars 13 which are secured in radial recesses provided in the flanges. Thus, the annular flanges and longitudinal tie bars form a type of cage on which further components of the trommel screen can be mounted.

[0023] As is best shown in Figure 4, the longitudinal tie bars 13 are interconnected intermediate the flanges 9, 11 by circumferentially extending spacer bars 15. The spacer bars may be cast or fabricated and have a fixing flange at each end for securing the spacer bars to the tie bars by means of threaded fasteners (not shown). Each spacer bar extends over 90 degrees and is secured at its ends to adjacent tie bars 13 such that a set of four spacer bars forms a circular support having essentially the same diameter as the flanges 9, 11. The circumferentially extending spacer bars 15 can be positioned at any one of a plurality of axial positions, for example being secured to holes positioned along the tie bars 13, and more than one set of spacer bars can be provided if desired. In this way the spacing between the spacer bars and between a spacer bars and an adjacent flange 9 or 11 effectively defines one of the dimensions of the screen openings which may vary, for example, from 50 mm to 1000 mm.

[0024] Extending between adjacent flanges are a plurality of axial screen bars 21. The axial bars may be cast or fabricated. One of the bars 21 is shown in Figure 5 and comprises a bar provided with a flange at each end. The flanges are formed with a substantially planar face which abuts against the adjacent annular flange 9, 11 and is secured thereto by means, for example, of threaded fasteners which pass through apertures formed in the flange of the screen bar 21 and engage with the annular flange 9, 11. To this end, an annular array of regularly spaced threaded recesses or apertures is formed in the annular flange 9, 11. The radially inner edge of each flange of the screen bars 21 is formed with an axially-extending arcuate lip which engages within the radially inner face of the adjacent annular flange 9, 11 to resist radially outward movement of the screen bar and also to protect the radially inner face of the annular flange.

[0025] The circumferential spacing between the axial screen bars 21 can be adjusted by selecting the required number and type of axial screen bars and effectively defines the other dimension of the screen openings. For example, the circumferential spacing may be from 50 to 1000 mm. Thus, the screen openings may be square or rectangular depending on the arrangement of spacer bars 15 and axial bars 21. [0026] Where the circumferential spacing between the axial bars 21 is at a minimum, all the threaded recesses or apertures in the annular flanges 9, 11 will be occupied by the threaded fasteners for the end flanges of the axial screen bars. However, where the circumferential spacing is greater than the minimum, certain of the threaded recesses or apertures will be unoccupied by the threaded fasteners and the radially inner face of the annular flange will be exposed to objects within the screen. In this case, the region of the threaded recesses or apertures is covered with a blank 25, 27 as shown in Figures 6 and 7 and secured in place with threaded fasteners. The blanks each have a planar face for abutting against the annular flange and an axially-extending arcuate flange which covers and protects the radially inner face of the annular flange 9, 11. A larger blank 25 is used where there is a relatively large gap between the axial spacer bars, while a smaller blank is used where there is a relatively small gap between the spacer bars.

[0027] The radially inner face of each tie bar 13 is covered with an axially-extending liner plate 29. The liner plate 29 may be cast or may be fabricated and is essentially a narrow flat plate which is secured to the tie bar at suitable intervals, for example in the region of each end flange 9 and in the region of the intermediate flange 11. The liner plates provide protection against wear from the objects within the screen during use thereof.

[0028] Because the trommel screen is made of a number of separable parts, in particular the spacer bars 15 and axial bars 21 , a damaged bar can be removed and replaced simply by removing the appropriate threaded fasteners, removing the bar and replacing it with a new bar and finally replacing the threaded fasteners.

[0029] Similarly, the dimensions of the screen openings can be modified without the need for replacing the entire trommel screen. This may be a more involved operation that replacing one or a small number of spacer bars or axial bars, but it is still relatively straightforward. If the longitudinal (axial) dimension of the openings is to be changed, then the threaded fasteners securing the spacer bars 15 to the tie bars 13 are removed and the spacer bars are re-arranged along the axial length of the tie bars (using more or fewer spacer bars as required) to the desired dimension for the openings and are secured in position with the threaded fasteners. If the circumferential dimension of the openings is to be changed, the threaded fasteners securing the screen bars 21 (together with any blanks 25, 27) are removed and the screen bars are re-arranged (using fewer or more screen bars as required) to the desired dimension for the openings together with the blanks and both the screen bars and the blanks are secured in position with the threaded fasteners. Of course, both the longitudinal (axial) and circumferential dimensions of the openings can be changed if desired. Clearly the number of trommel screens forming the trommel itself can be varied. Moreover, the number of flanges forming part of each trommel screen can also be varied depending, for example, on the axial length of the screen.