Patent Application
20130092608
The present invention relates generally to stationary or vibrating screening devices. In particular, an impact screen cloth useful in stationary and/or vibrating screens for screening oversize objects in a material is provided comprising a plurality of longitudinal wear bars positioned on the impact screen cloth in the direction of travel of the material to be screened.
Vibrating and/or stationary screens are used in coal dressing, metallurgy, mine, power station, and the like. They are primarily used for the classification of bulk materials such as coal, minerals, coke, etc. Vibrating and/or stationary screens are also used in the oil sand industry, in particular, in oil sand slurry preparation plants.
Oil sand, such as is mined in the Fort McMurray region of Alberta, generally comprises water-wet sand grains held together by a matrix of viscous bitumen. It lends itself to liberation of the sand grains from the bitumen by mixing or slurrying the oil sand in water, allowing the bitumen to move to the aqueous phase.
As-mined or pre-crushed oil sand is generally mixed with warm or hot water to yield an oil sand slurry. The slurry is then conditioned in a hydrotransport pipeline and subsequently introduced into a large, open-topped, conical-bottomed, cylindrical vessel commonly termed a primary separation vessel (PSV) where the more buoyant aerated bitumen rises to the surface and forms a bitumen froth layer.
It may be desirable to remove the larger aggregates present in oil sand slurry prior to pipelining in order to avoid blockage or damage of downstream equipment, e.g., pump component wear. Thus, vibrating screens may be used at various points during slurry preparation to reject larger lumps of oil sand, rocks and other aggregates, which are large enough to block or damage downstream equipment, prior to pipeline conditioning. Screens may also be used to further screen oil sand tailings slurry prior to treating/disposing same.
However, oil sand slurry is extremely heavy and abrasive due to the large amount of sand, gravel and crushed rock contained therein. Further, primary vibrating screens are generally vibrating with an acceleration of approximately 4-5 g, so that all oil sand slurried material passes over and through the screen cloths of the vibrating screen. This results in the rapid spalling and eventual wearing through of the screen cloths of the vibrating screen (“hole-throughs”), which can lead to production interruption and an unplanned maintenance event.
Thus, it is desirable to have an improved screen cloth that can withstand the abrasiveness of oil sand slurry.
It was discovered that screen cloths of vibrating and/or stationary screening devices used to screen frozen lumps, rocks and the like from oil sand slurry were wearing through much quicker than desired due to the abrasive nature of the slurry. In particular, it was discovered that the first few rows, referred to herein as the impact rows, of screen cloths of vibrating screening devices were suffering from localized wear phenomena resulting from the slurry flow distribution.
In one aspect of the present invention, an impact screen cloth for use in a screening device for screening out oversize objects in a material flowing in a direction is provided, comprising:
a metal plate having a perimeter and comprising a plurality of openings therethrough and forming a grid having longitudinal ligaments substantially parallel to the direction of the material flow and transverse ligaments substantially perpendicular to the direction of the material flow; and
a number of longitudinal wear bars positioned on an equal number of longitudinal ligaments to cover a substantial portion of each longitudinal ligament without covering the openings.
In one embodiment, the height of the longitudinal wear bar is proportional to size of the openings to elevate the oversize objects that are larger than the size of the openings and thus prevent the oversize objects such as lumps and rocks from contacting the transverse ligaments. In one embodiment, impact screen cloths are used in vibrating screening devices and the height of the longitudinal wear bars are generally about 60% of the width of the openings or greater. In one embodiment, impact screen cloths are used in stationary or fixed screening devices and the height of the longitudinal bars are generally about 40% of the width of the openings or greater.
In one embodiment, the impact screen cloth further comprises a number of transverse wear bars positioned between the number of longitudinal wear bars. In another embodiment, the longitudinal wear bars are fabricated from mild steel with high wear material and are welded to the longitudinal ligaments of the perforated metal plate.
In one embodiment, wear materials for the longitudinal wear bars can be ceramics, chromium carbide, tungsten carbide or sintered tungsten carbide. These materials can be thermally (e.g., vulcanizing, welding, brazing, etc.), chemically (e.g., epoxy) or mechanically (e.g. bolted, dovetailed, etc.) attached to the wear bars.
In yet another embodiment, the perforated metal plate is made from structural steel (e.g., high tensile steel, stainless steel, carbon steel, etc.) and is overlayed with multi-pass layers of chromium carbide, tungsten carbide (PTA or Technoginia products) or cast wear products (e.g., ceramic, Kencast or sintered tungsten carbide tile) to increase its thickness. Thus, the increase in structural competence by the addition of longitudinal wear bars minimizes the spalling of the overlay on the metal plate.
In another aspect of the present invention, a screen for use in a vibrating or stationary screening device, the screen having a feed end and a discharge end, for screening oversize objects in a material is provided, comprising:
a number of screening rows positioned end to end between the feed end and the discharge end, each row having at least one screen cloth and each screen cloth comprising a metal plate having a perimeter and having a plurality of openings therethrough to form a grid having longitudinal ligaments substantially parallel to the direction of the material flow and transverse ligaments substantially perpendicular to the direction of the material flow;
whereby the at least one screen cloth of at least one screening row further comprises a number of longitudinal wear bars positioned on an equal number of longitudinal ligaments to cover a substantial portion of each longitudinal ligament without substantially interfering with the openings.
In one embodiment, the at least one screening row is the screening row closest to the feed end. Thus, the primary impact zone is reinforced by providing additional sacrificial material in the form of longitudinal wear bars.
In one embodiment, the screen for use in the vibrating or stationary screening device comprises at least two screening rows, each screening row having at least one screen cloth, wherein the at least one screen cloth of the screening row closest to the feed end has a greater number of longitudinal wear bars than the at least one screen cloth of the next screening row.
Other features will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific embodiments, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the following figures. It is understood that the drawings provided herein are for illustration purposes only and are not necessarily drawn to scale.
a is a top view of a screen cloth of the prior art.
b is a cross-section of a screen cloth of the prior art.
c is an enlargement of a portion of the cross-sectional view of
d is a perspective view of another screen cloth of the prior art.
e is the longitudinal section of the screen cloth of the prior art shown in
a is a top view of an embodiment of an impact screen cloth of the present invention.
b is a cross-section of the impact screen cloth embodiment shown in
c is an enlargement of a portion of the cross-sectional view of
d is a perspective view of the impact screen cloth shown in
e is the longitudinal section of the impact screen cloth shown in
The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
Turning first to
b is a cross-section of screen cloth 10 and
d is a perspective view of another prior art screen cloth where additional supporting structures have been added to increase the strength of the screen cloth. In this embodiment screen cloth 110 is fabricated from a large steel plate 114 having a perimeter comprising sides 118a and 118b, top edge 120 and bottom edge 126. The direction of flow is from the top edge 120 to the bottom edge 126. A plurality of substantially square openings 112 are cut or punched (flame, plasma) on the plate 114 to form a mesh comprising longitudinal ligaments 144 and transverse ligaments 146.
It is understood that multiple of these screen cloths will be installed in a vibrating or stationary screening device's main cross members to form the screening deck (also referred to herein simply as the screen) of the vibrating or stationary screening device. Screen cloths can be attached to the main cross members by means of bolts inserted through bolt holes 150.
In the embodiment shown in
a to 2e illustrate one embodiment of an impact screen cloth of the present invention. Impact screen cloth 210 comprises perforated plate 214 having a first side edge 218a, a second side edge 218b, a top edge 220 (material or feed end) and a bottom edge 226 (oversize exit end). Openings 212 in perforated plate 214 are rectangular in shape and the size of the openings is dependent on the size of the oversize that one desires to screen out. Generally, the openings are of a consistent size as well. As was the case with perforated plate 114 of
In the embodiment shown in
b is a cross-section of screen cloth 210 and
As was the case in the embodiment shown in
It is understood that longitudinal wear bars can be fixed to the perforated plate 214 by any means known in the art, for example, welding the bars thereon. In one embodiment, impact screen cloth 210 of the present invention comprises a frame having first side edge 218a, second side edge 218b, top edge 220 and bottom edge 226) which supports a plurality of longitudinal ligaments 244 and a plurality of transverse ligaments 246 which ligaments intersect to form a mesh or grid. The openings 222 formed between the longitudinal ligaments 244 and transverse ligaments are generally uniform in size. The longitudinal ligaments extend essentially from the feed end to the oversize exit end and the transverse ligaments extend essentially from the first side edge to the second side edge. The longitudinal ligaments are raised relative to the transverse ligaments as a result of the attached longitudinal wear bars 222.
e show bolting plates 248 which provides further support when bolting the screen cloth 210 to the screening device. Optionally, the screen cloth 210 may further comprise transverse stiffeners 249.
The use of longitudinal wear bars on the first two rows of screen cloths increased the life of the screens from about 500 hours to about 2000 hours. Even more importantly, however, is that such an arrangement of more reinforcement in Row 1, less in Row 2, and none in subsequent rows, results in uniform wear across all screen cloths of the screen 402. This optimizes the run time of the vibrating screen device so that the operator does not have to shut the device down multiple times to change screen cloths.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are known or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims.
