Abrading – Abrading process – Utilizing fluent abradant
Reexamination Certificate
1998-09-11
2001-02-20
Scherbel, David A. (Department: 3723)
Abrading
Abrading process
Utilizing fluent abradant
C451S060000, C451S087000, C209S138000
Reexamination Certificate
active
06190235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved method and apparatus for reclaiming and thus recycling used abrasives that have been employed, for example, in surface preparation of steel objects prior to the application of paints or other protective coatings. More particularly, the novel method and apparatus provide for a fluidized bed treatment of the used abrasives with the assistance of suction, to remove contaminants and fines therefrom, thereby producing a high quality re-usable abrasive material well suited for subsequent blast cleaning operations.
2. Description of the Prior Art
Generally, the abrasive media falls into two categories, recyclable and expendable. Silica sand and slags are expendable, low cost abrasives and are, therefore, not considered recyclable. On the other hand, there are abrasives that do not easily break down at impact and are generally more expensive and worth recycling. Steelgrit, garnet, aluminum oxide, staurolite and hematite all belong to this group. Applicant's own U.S. Pat. No. 5,456,628 of Oct. 10, 1995 describes one such recyclable impact material.
The effect of the blast cleaning process on all abrasives resulting from high velocity impacting on steel surfaces being cleaned, causes them to abrade and generate contaminants such as dirt, paint, mill scale, and rust from the treated surface. At the same time a certain amount of fractured, fine abrasive particles are also produced. Generally, the used abrasive is considered reusable if the percentage of fines is not excessive and the contaminants can be extracted to a satisfactory level to meet health and environmental standards.
Various methods and equipment are employed in the abrasive blasting industry to allow spent abrasives to be reclaimed. Practically all presently employed abrasive recycling devices are operated on the principle that uses various air washing methods. In these methods, the relative densities of abrasives and contaminants are taken advantage of, because the abrasive is generally more dense than the contaminants. The contaminated abrasive is caused to fall along a vertical line, preferably in a continuous fashion, so that a uniform curtain of falling abrasive is obtained. An air stream is applied across the falling curtain with an objective to entrain the contaminants and the undesirable fractions of abrasive fines. Usually a cross-directional flow of the air stream is maintained so as to remove the undesirable part of the used abrasive in addition to the contaminants, and the decontaminated abrasive is then collected at the bottom of the cascading curtain for reuse. One such apparatus is described in U.S. Pat. No. 4,394,256 of Jul. 19, 1983.
In such a system, the uniformity of the falling curtain density is important because any opening or discontinuity in the curtain allows the air to accelerate. The resulting increased velocity at the fringe of such curtain openings or discontinuities also removes usable sizes of abrasive particles. On the other hand, reduced air velocity in the areas of denser curtain formation often results in incomplete washing. Such a system, therefore, has significant disadvantages.
Magnetic separation is also used to separate magnetically attractable abrasives from non-magnetically attractable contaminants. Such magnetic separation apparatus is disclosed, for example, in U.S. Pat. No. 5,657,876 of Aug. 19, 1997. This system can, however, be used only with magnetic materials, such as steel grit and shot, which excludes some 98% of the abrasives utilized by the industry.
There are also methods and apparatus using a combination of steps, including a physical separator, a rotary screen separator, a magnetic separator, and air wash separation and sub-atmospheric pressure, for example, as disclosed in U.S. Pat. No. 5,622,265 issued Apr. 22, 1997. Such systems are rather complex and expensive and thus have not achieved widespread acceptance in the industry.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to obviate the above mentioned disadvantages and to provide an improved method and apparatus for reclaiming used abrasives based on a fluidized bed treatment thereof, with the assistance of suction.
Another object is to make such method and apparatus simple and efficient as well as applicable to all types of abrasives.
Other objects and advantages of the present invention will become apparent from the following description of the invention.
In essence, the method of the present invention for reclaiming used abrasives comprises forming a turbulent levitating fluidized bed of such used abrasives in a substantially horizontal elongated enclosure in which the fluidized abrasives are made to move from one end of the enclosure (charging end) to the other and thereof (discharging end), and removing contaminants and fines from the fluidized used abrasives by means of a plurality of suction outlets positioned in a predetermined sequence and at predetermined levels along the elongated enclosure.
The expression “turbulent levitating fluidized bed” means that the bed of used abrasives must be fluidized so as to rise within the elongated enclosure to a certain level, namely to levitate in the enclosure rather than to fill the enclosure completely as shown, for example, in U.S. Pat. No. 4,946,044 of Aug. 7, 1990 disclosing an aeration separator. Moreover, the levitating bed must be fluidized in such a manner as to make it turbulent or teetering. Such fluidized bed provides vigorous agitation or scrubbing action of the levitated used abrasives, which liberates the adhering contaminants, such as paint and coating residue, from the abrasive particles.
Such turbulent, levitating fluidized bed may be formed by blowing fluidizing air through a porous bottom of the elongated enclosure. To further assist in achieving satisfactory levitating fluidization, the elongated enclosure may be vibrated during the reclaiming process. Also, the fluidizing air may be heated to remove any moisture that may be present in the used abrasives.
To facilitate movement of the fluidized particles within the enclosure, the enclosure or its bottom surface is preferably tapered downward from its charging end to its discharging end.
The apparatus of the present invention comprises an elongated enclosure with a charging end and a discharging end and a porous bottom; means for continuously or intermittently charging used abrasives at the charging end; means for blowing air through the porous bottom of the elongated enclosure so as to form a turbulent levitating fluidized bed of the used abrasives having contaminants and fines therein; means for moving the fluidized bed of such abrasives along the elongated enclosure from the charging end to the discharging end; a plurality of suction outlets positioned in a predetermined sequence and at predetermined levels along the elongated enclosure such as to sequentially remove the contaminants and the fines from the used abrasives as they travel in the form of the turbulent levitating fluidized bed from the charging end to the discharging end of said elongated enclosure, thereby producing reclaimed abrasives at said discharging end; and means for collecting said reclaimed abrasives as they exit the discharging end of the elongated enclosure.
The elongated enclosure preferably has a generally U-shaped cross-section with a flat bottom which normally contains a multitude of micro-perforations producing micro-jets of blowing air that generate a turbulent levitating fluidized bed above the bottom surface. The elongated enclosure, or at least its bottom, is preferably tapering downward from its charging end to its discharge end so as to facilitate movement of the fluidized abrasives along the enclosure. Moreover, means are preferably provided to vibrate the elongated enclosure or at least its bottom, during the operation of the apparatus. Furthermore, means may be provided for heating the fluidizing air to remove moisture from the used abrasives in case they are wet or moist. Thus, the
Csabai Julius J.
Csabai Julius S.
Berry Jr. Willie
Primak George J.
Scherbel David A.
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