Sieve bed for a sifting machine

Details Sieve bed for a sifting machine Sieve bed for a sifting machine

2002-02-13

2003-10-21

Walsh, Donald P. (Department: 3653)

Classifying, separating, and assorting solids

Sifting

Elements

C209S399000, C209S408000

Reexamination Certificate

active

06634505

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention pertains to an improved sieve bed for a sifting machine. More particularly, the invention relates to an improved mounting pin that allows for a maximum useful surface area for the sieve bed and which also securely mounts a plurality of sieve elements on a support frame of the sieve bed.
BRIEF DESCRIPTION OF THE RELATED ART
Various structures for screening or sifting particulate materials are known in the art. In general, a screening or sifting machine consists of a plurality of sieve elements (also referred to as screening panels and screen modules, among others) that are attached to a support frame with their edges abutting one another to create a contiguous sifting surface. Existing sifting machines can be loosely divided into those devices having sieve elements that are secured to an underlying support frame by means of projections which extend downwardly from the sieve elements themselves, and those devices which are secured to an underlying support frame by means of projections which extend upwardly from the support frame to mate with complimentary cavities formed in the sieve elements.
It is known that the mounting pins can be designed as integral parts of the sieve elements. In one case, half pins are molded onto the opposing edges of adjacent sieve elements; these half-pins are designed to work together to form a whole pin. The half-pins can be driven or snapped jointly into a mounting hole in the support frame. A sieve element such as this suffers from the disadvantage that the mounting pins must necessarily consist of the same material as the sieve elements; this can detract from the quality of the attachment if the sieve elements consist of a relatively soft material. In addition, it is also more difficult in particular to remove the sieve elements, because, each time the elements are removed, the relatively long half-pins must be pulled out of their mounting holes. Another disadvantage of the sieve bed of this type consists in that, after the sieve elements have become worn out, the mounting pins also must be replaced along with the sieve elements. They cannot therefore simply remain on the support frame.
A specific example of the former type of sieve bed is disclosed in U.S. Pat. No. 5,938,042 to Freissle et al. The Freissle patent discloses a support frame made of up of a plurality of frame components in which a pair of complimentary elongate members, each having a plurality of cavity defining formations, are secured to one another so as to form a unitary frame component having a plurality of cavities for receiving respective socket elements therein. When arranged side by side upon a sub-frame comprising a plurality of support beams, the frame components form a support frame to which a plurality of screening panels may be secured. Protrusions depending from the under surface of the screening panels are inserted into socket elements retained within the cavities of the respective frame components. Some of the disadvantages of this design include the fact that the frame components comprise too many constituent parts, require numerous and expensive manufacturing steps, require a higher degree of maintenance, and exert a hold down force upon the screening elements that is limited by the strength of the elastic material from which the protrusions depending from the undersurface of the screening panels are made.
A sieve bed of the latter type described above is known from, for example, DE-GM 78-11,183. In this known sieve bed, the mounting pins are driven from above into the receptacles formed by two adjacent sieve elements. The pins are thus able to pass into appropriately located mounting holes in the support frame and are then spread and tensioned by an expanding mandrel, which can be driven into the mounting pin.
This design of a sieve bed suffers from several disadvantages. A first significant disadvantage is that the receptacle for the mounting pin must be open at the top; this means that it is exposed to the wearing action of the highly abrasive material being sifted. In addition, there is the danger that fines from the material being sifted can get into the attachment area, where they can interfere with the removal of the sieve bed. Finally, both the installation and removal of the previously known sieve bed are relatively cumbersome because the mounting pins must be completely removed and then reinstalled each time the sieve elements are replaced.
Another example of the latter type of sifting machine is disclosed in U.S. Pat. No. 5,049,262 issued to Galton et al. The Galton device consists of a deck frame made up of a series of rigid elongate members spaced apart in parallel relationship and interconnected at regular intervals by cross members. The elongate frame members each include a series of mounting apertures that are spaced apart along each member and oriented normal to the plane of the elongate member for positioning and removably connecting screening modules to the frame. Lock pins are inserted into the mounting apertures so that a top portion of the lock pin extends upwardly from the elongate frame members. Recesses in the edges of the respective screening modules receive the upper portion of these lock pins therein for the purpose of securing the screen modules to the frame. The recesses in at least one embodiment of the screening modules of the Galton patent are constructed and arranged so that the upper portion of the lock pins are wholly encompassed within and between respective screening modules placed over a lock pin. In this embodiment, no portion of the lock pin extends to or above the upper surface of the screening modules.
Some of the disadvantages that this design suffers from include the fact that given that the lock pins described in the Galton patent must be received within an aperture formed through a substantially horizontal surface of the elongate frame members, the frame members are constrained to be at least as wide the widest portion of the lock pins themselves. The relatively large surface area of the elongate frame members reduces the useful area of the screening modules in the assembled sifting machine and thereby decreases the magnitude of the material throughput of the sifting machine. What is more, because the lock pins of the Galton patent must be made from an elastic material in order to insert the lock pins into the mounting apertures in the elongate frame members, the hold down force that the lock pins may exert upon the screening modules is necessarily limited, thereby increasing the likelihood that the screening modules will become dislodged under heavy loading conditions.
In general, wherein elastic protrusions, projections, or lock pins are utilized to secure a sieve element, screening panel, or screening module to a support frame of a sifting machine, the hold down force that may be asserted in these screening elements is necessarily limited. And, as the screening elements themselves are relatively elastic, impact forces imparted thereto by materials being dropped or otherwise placed on the sifting machine are transmitted directly to the mechanisms which secure the screening panels to the support frame of the sifting machine. These impact forces can readily dislodge screening elements not securely attached to the support frame, thereby requiring a user to suspend operation of the sieve machine while the screen panel is replaced. Where a screen panel becomes dislodged during operation, the particulate matter being sifted may also cause undue wear on the screen panels and on the support frame.
In order to reduce the likelihood of a panel becoming dislodged during operation, relatively thin and elastic screening panels have been used. While these thinner screening panels would be subject to relatively higher deflections, their elastic nature would reduce the magnitude of the forces imparted to the mechanisms used to secure the panels to the sub-frame. The use of relatively thin screening panels has in turn resulted in shorter useful lives for the screening elements themselves be

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