TRIPLE DECK VIBRATORY SCREEN

Field of the invention: This invention relates to the use of a vibratory screen arrangement to separate a particulate stream into two streams having two particle size ranges.

Description of the related art:

Vibratory screens are used to separate products into different sizes. For example, a single deck screen splits products into 2 sizes and a double-deck screen splits products into 3 different sizes and 3 deck screen splits products into 4 different sizes.

Summary of the Invention

The invention provides a triple deck vibratory screen configured with a top and a bottom screening deck each having screening panels with apertures of the same aperture area, and a middle deck as a conveying deck on the triple deck vibratory screen to increase it’s screening area. The conveying deck may be blanked i.e. apertureless over its extent so that screened material cannot pass therethrough

This Invention further provides a triple deck vibratory screen and a method of operation so that it functions as a large single deck screen. The invention thus provides a method for use of a 3-deck vibratory screen to perform the same duty as a much larger single-deck vibratory screen, said method including splitting feed material into two streams of feed material which

Is fed onto the top and bottom deck respectively of the triple deck screen, and to use the middle deck of said 3-deck screen as a conveying deck by using solid impervious blank panels to cover the deck.

The method may include providing apertures in every second panel in the last row of blank panels of the middle carrier deck in register with apertures in the bottom deck. The apertures may all be identical sized apertures.

The method may include having adjacent identical sized apertures of reduced diameter in the last row of panels of both the middle and the bottom deck which are in register, the apertures being of reduced diameter when compared with an embodiment in which the apertures are every second panel.

Furthermore, pipes of complementary diameter to the apertures in the end of the middle and bottom decks may be fitted to pass through both decks. These pipes may be positioned such that they are flush with the top of the middle deck and protrude through the bottom deck. The diameters of these pipes may be such that they fit snugly into the two rows of deck apertures and may be clamped firmly in position.

In a first embodiment, the middle deck and bottom deck may have alternating apertures in flow communication with the pipes that permit flow of material from the middle deck and through the bottom deck, and blank areas between the apertures. The blank zones and the apertures may be of approximately the same diameter so that the pipes are equally spaced apart. In a second embodiment, the middle deck and bottom deck may have a plurality of reduced diameter adjacent apertures in each panel in flow communication with the pipes that permit flow of material from the middle deck and through the bottom deck. The total area of these reduced diameter apertures, and thus the closely adjacent pipes, may be of approximately equal in area to that of the larger diameter pipes of the first embodiment.

Where the first embodiment is used and there are blank zones between the pipes, the pipe diameter of each pipe has approximately double the cross section area of the pipes in the second embodiment where the reduced diameter pipes are closely adjacent so that the overall flow area between the middle and out of the bottom deck are similar in both embodiments.

The number of apertures and thus pipes between the middle deck and the bottom deck may be selected with respect to the materials being separated, however, for every aperture in the middle deck there is a corresponding pipe through the bottom deck.

Typically, the triple deck vibratory screen is actuated by a drive or plurality of drives to vibrate the decks and attached screening panels, including any cross members and side plates. However, in an embodiment of the invention, a plurality of drives actuates oniy the decks and attached screening paneis to vibrate oniy separateiy from the remainder thereof and not the side piates.

Brief description of the drawings

Figure 1 shows a cut-away side view illustrating the flow of material across the 3 decks;

Figures 2 and 3 show 3D views of the feed box and the method of splitting the feed material into two equal streams;

Figure 4 shows one embodiment with a middle deck and bottom deck having alternating apertures in flow communication with pipes that permit flow of material from the middle deck and through the bottom deck, and blank areas between the apertures;

Figure 5 shows an arrangement whereby oversize material from the top deck discharges over the end of this deck and joins the identical oversize material from the bottom deck and this oversized material flows down deck and discharges through gaps on the end of deck between the pipes (the material as such is not shown so as not to clutter the drawing); and Figure 6 shows another embodiment with a middle deck and bottom deck having a plurality of adjacent apertures in flow communication with the pipes that permit flow of material from the middle deck and through the bottom deck.

Detailed description of the invention:

In Fig 1 , the feed material (2) is first split into two equal streams (4) and (5) by means of apertures (18) in the feed box (32). (See Fig 2 for details) These apertures (18) can be changed in position and aperture diameter until an equal feed split to both decks (6) and (10) is achieved.

The feed box (32) (See Fig 2 for more detail) consists of but not limited to three rows of panels. There is typically one row of bottom blank panels (38) and two rows of mixed blank panels (38) and blank panels with apertures (18). The remaining panels on the top and bottom decks have screening apertures typically of 0.5 mm to 12 mm.

The usual function of a feed box (32) is to cushion the impact of the falling material (2) onto the screen before traveling down the top screening deck. In this invention the feed box is used for an additional purpose, that is to split the feed (2) into two equal streams by means apertures (18) in some of the panels as shown in Fig 3. The middle deck (8), which is a solid conveying deck in which the panels are blank and not apertured like those of the top and bottom deck, conveys fine materials i.e. fines to the end of the deck and down the pipes.

These apertures are sized and positioned such that the feed (2) is split into equal streams of feed (4) and (5) of Fig 1.

The screening decks (6) and (10) are both fitted with the same aperture screening panels in order to separate the feed material into the same fractions of oversize and undersize products.

The one split stream (4) flows normally along the top deck (6) and discharges off the end of the top deck (6).

The fine screened undersize material (22) from under the top deck (6) is screened through the top deck and onto the conveying middle deck (8).

The oversize material (4) from the top deck (6) discharges over the end of this deck (6) and joins the identical oversize material (5) from the bottom deck (10) This oversized material flows down deck (10) and discharges through gaps (40) on the end of deck (10) between the pipes (26) (See Fig 4 and 6). In Fig 4 the pipes 26 are of around 300 mm diameter while in Figure 6 the pipes are of a reduced diameter of around 180 mm and the gaps between the pipes are larger than that in Fig 4 so that the screened oversize material can pas between them.

This combined oversize material (14) flows into the oversize chute (16) Thus, the combination of the two streams of oversize (4) and (5) is combined as one product (14).

The undersized material (22) from under the top deck (6) flows down the solid conveying deck (8) and wells up against the blank off plate (24). It then flows down pipes (26) into the hopper (28) below and joins up with the undersize material (30) from under the bottom deck (10).

Thus products (22) and (30) are exactly the same undersize material joined up as one product in the hopper (28) below.

Figure 5 shows an end blanked off section (24) of the middle deck and the pipe arrangement. These pipes carry the screened material from the top deck through the middle and bottom decks and into the hopper below. In Fig 6 there are more apertures and pipes but these are of a smaller diameter than those shown in Fig 4. Furthermore, in Fig 6, the apertures and pipes 26 are adjacent while in Fig 4, the pipes 26 are of a larger diameter and spaced alternatively on every second panel. Without limiting the scope of the invention, the embodiments below describe potential working options of the invention.

Embodiment 1): Method of splitting the feed of material (2) onto a vibratory screen into two nearly equal streams using openings in the feed box wear panels (18) and (38). Embodiment 2): Method using the middle deck (8) of a 3-deck screen as a carrier deck to convey the screened material from the top deck (6) to the end of this carrier deck using solid blank panels instead of the usual screening panels with apertures

Embodiment 3): Method of closing off the discharge end (24) of this carrier middle deck. This allows the screened material (22) to flow down the large open pipes (26) evenly distributed at the end of this deck, or as in embodiment 2, to flow down the greater number of smaller pipes in every panel at end of this deck.

Embodiment 4): Method of using these pipes (26) to pass through both the middle deck (8) and bottom deck (10) so as to discharge the undersize material (22) from below the top deck (6) into the hopper (28) below the screen..

Embodiment S): Method of using gaps (40) between the pipes (26) on the discharge end of the bottom deck (10).

These gaps (40) allow the oversize material (5) traveling down this deck to pass between the pipes (26) and join the oversize material (4) from the top deck to form one common stream of material (14) using the same apertures on both top (6) and bottom deck (10) Vibratory screens are 3 dimensional machines and size and mass increase exponentially with increase in screen area size.

Thus a 2,7m x 7,5m triple deck screen with the same combined screen area using 2 of the decks is approximately two thirds of the mass and cost of a 4.3m x 9.15m single deck screen.

The inventor believes that the invention as illustrated has a financial advantage in the costs of the screen and the structure to support it. Moreover, there are additional savings in crane and transport costs.