|1.||A vibratory screen apparatus comprising a screen, a system of spray nozzles disposed underneath the screen, and means for feeding a fluid, such as water or oil, through the nozzles at the underside of the screen.|
|2.||Apparatus according to claim 1 in which the system of spray nozzles comprises an undulating conduit formed with a plurality of upwardly directed nozzles.|
|3.||Apparatus according to claim 1 or 2 and further comprising an automated timer mechanism for intermittently directing the fluid at the screen.|
|4.||A method of cleaning a vibratory screen comprising feeding a fluid, such as water or oil, at the underside of the screen though a system of spray nozzles disposed underneath the screen.|
|5.||A method according to claim 4 in which the spray nozzles are mounted below that area of the screen on which the solids accumulate, and a fine spray is used at a relatively low volume and at a pressure of between 5 and 500 psi (35 to 3500 kPa) to provide an ■'intermittent spray of fluid to the screen.|
|6.||A method according to claim 4 in which the spray nozzles are mounted under all areas of the screen, and a spray of a coarser nature is used at a relatively high volume and at a pressure of between 20 and 2000 psi (150 to 15,000 kPa) .|
|7.||A vibratory screen apparatus substantially as herein described with reference to, and as shown in, the accompanying drawings.|
Field of invention
This invention relates to a screen spray system, in particular for a vibratory sifting screen.
Background to the invention
Under certain circumstances vibratory screens suffer poor performance due to the following conditions:
(1) An accumulation of sticky solids on the screen: this is due to the reticence of solids to transport along the screen face. This is further aggravated where the screen is designed with the screen mounted at an incline away from the direction of horizontal transport. Where a linear motion is employed as the pattern of vibration, the accumulation of sticky solids is often more severe than where an eliptical motion is employed.
(2) The occurrence of screen blinding: this is due to sand or other near-sized particles locking into the screen mesh.
To counteract the above conditions the following known techniques are presently used to remove solids from the screen:
1. Manual labour to pull solids off the screen with scraper type arrangements.
2. Use of pressure washer from the top of the screen.
3. Use of high pressure high volume hoses.
In the case of blinding of the screen with near-sized solids the following techniques are presently used:
1. Remove screen from machine and manually scrub mesh.
2. Remove screen from machine and pressure wash the mesh from the rear.
It is an object of this invention to reduce the necessity for performing the above known techniques.
Summary of the invention
According to the present invention there is provided a vibratory screen apparatus comprising a screen, a system of spray nozzles disposed underneath the screen, and means for feeding a fluid, such as water or oil, through the nozzles at the underside of the screen.
The invention also extends to a method of so cleaning a vibratory screen.
The spray may be used at low and/or high pressure, and either on a continuous or intermittent basis.
To counteract the accumulation of sticky solids, the spray nozzles are mounted typically below that area of the screen on which the solids accumulate, and a fine spray used at low volume and at a low pressure of between say 5 to 500 psi to provide intermittent jets of fluid to the
screen. The fluid is preferably compatible with that fluid to be screened, ie water in the case of water-based fluids or oil in the case of oil-based fluids. The spray acts to lubricate the interface between the solids and the conveying action of the screen and has the effect of greatly increasing transport of the solid.
Alternatively, to counteract screen blinding due to near- sized material, a higher pressure spray at increased volume and a spray of a coarser nature may be used under all areas of the screen. Pressure could typically be between 20 and 2000 psi. The spray may be intermittent or continuous.
The action of the spray assists solids to be removed from the mesh or reduces their tendecy to lock into the screen.
In either of the above cases nozzle jets of different types may be employed and the pressure and duration of the spray varied. An automated timer mechanism may also be employed.
The system of spray nozzles preferably comprises an undulating conduit provided with a plurality of upwardly directed nozzles.
Brief description of the drawings
The invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Figure 1 is a side view of a vibratory screen apparatus in
accordance with the invention, and
Figure 2 is a perspective view of a spray nozzle assembly forming part of the apparatus of Figure 1
The vibratory screen apparatus shown in Figure 1 includes a supported primary screen 10 having a horizontal portion 12 with an inclined portion 14 to the right, as viewed in the drawing.
Under the screen 10 are disposed cross members 16 of rectangular section, which form part of the framework structure of the apparatus. Mounted between the members 16 are four assemblies 18 of spray bar nozzles, which direct a spray of water, or alternatively oil, at the underside of the screen 10.
As shown in greater detail in Figure 2, each assembly 18 comprises a conduit formed into an undulating or serpentine shape and provided with an array of thirty upwardly directed nozzles 20.
In use, water or oil is fed to each assembly of spray bar nozzles, so that a liquid spray is directed at the underside of the screen 10. This maintains the screen relatively clear of sticky solid accumulations, and also assists the transport of the material to be sifted, as it travels from left to right along the screen.