Liquid purification or separation – Processes – Including controlling process in response to a sensed condition
Reexamination Certificate
2002-09-16
2004-12-28
Cecil, Terry K. (Department: 1723)
Liquid purification or separation
Processes
Including controlling process in response to a sensed condition
C210S767000
Reexamination Certificate
active
06835315
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
The present invention relates to filters for use in removing solids from a solid/liquid mixture or metal working fluids and more specifically relates to a highly efficient filter assembly for use in swarf removal systems that can operate in large or small areas.
Many industries employ machining and grinding devices such as drills, mills, cutting devices, grinding wheels, etc., to remove metal pieces, chips, “strings” and other fines from work items thereby forming the work items into final products. Hereinafter removed metal material will be referred to as swarf. To remove swarf often a liquid stream is employed that is directed at the machining point and that “washes” the swarf from the machining area.
To collect the liquid for reuse a tank and conveyor are provided below the machining point. Swarf is washed into the tank and settles to the conveyor that is arranged near the bottom of the tank. Relatively heavy swarf settles quickly to the conveyor is transferred to a swarf collection bin. Smaller fines stay in suspension and eventually form a liquid/swarf mixture that is extremely “dirty”. Dirty liquid cannot be used for machining or grinding purposes primarily because such liquid can clog spraying hardware, load wheels, scratch parts and cause metal working fluid degradation.
To render dirty liquid reusable most swarf handling systems include some type of filter to separate swarf from the liquid. Filtering effectiveness is extremely important as clean liquid reduces maintenance downtime, extends coolant life, improves machining precision and often extends tool life.
Many different filter configurations have been implemented. One filter configuration includes a metallic drum having small holes in the drum side wall. The drum is disposed on its side and the underside of the drum is disposed below a liquid-solid mixture level so that there is a pressure differential between the inside and outside of the drum. Liquid pours through the drum holes into the drum interior while swarf fines are stopped by the drum wall. Eventually accumulated fines form a swarf cake on the undersurface of the drum (i.e., on the submersed wall section). Liquid inside the drum is removed to maintain the differential pressure within the drum. When the holes in the underside of the drum become clogged, the drum is rotated such that an adjacent drum side faces downward and filtering continues. Pressure sensors for determining when to rotate a drum filter due to clogging are known in the art. One configuration of the above described type is described in U.S. Pat. No. 3,000,507 (“the '507 patent) entitled “Rotary Filter” that issued on Sep. 19, 1961.
Drum filters of the above described type have several shortcomings. First, after clogging, the holes must be cleared prior to reuse. Second, often the drum holes cannot be made small enough to remove very small fines. Third, such filters often require extended periods to filter the amount of liquid required. Fourth, such filters often must be substantially submersed (see the '507 patent) in order to cause a required pressure differential between the inside and outside of the drum. In addition to increasing the differential pressure, many drum filter references teach that a large portion of the drum should be submersed to increase filtering area.
The industry has developed several systems for unclogging holes or removing accumulated solids from drum filters. The '507 patent teaches a blower that blows air through drum holes from the inside of the drum thereby dislodging accumulated cake chunks and clearing the holes. A discharge chute is positioned under the discharge area so that dislodged chunks do not fall back into the tank. Unfortunately air blowers work best where drum holes are relatively large and therefore systems of this type often produce liquid that remains relatively dirty after filtering.
Another filter cleaning solution has been to provide a mechanical “cake knife” along a filter path and adjacent a filter surface that effectively scrapes cake chunks from the surface of the filter. While removing accumulated cakes from the surface of a filter drum, unfortunately this solution does little to clear swarf from filter holes or apertures.
One other filter cleaning or clearing solution that has been adopted by many in the industry is to provide a liquid sprayer that sprays the back surface of a filter with a clean liquid to knock accumulated cake chunks off the filter. Where liquid clearance systems are used, the tank typically is extended under the clearance area so that clearance liquid and cake chunks are redeposited in the tank after a clearing process. The cake chunks, being relatively heavy, settle to the bottom of the liquid tank. To remove the cake chunks from the tank, a conveyor or drag chain is placed along the bottom of the tank that drags the chunks therefrom to a point above a swarf bin where the chunks are deposited.
One other technique for loosening accumulated swarf cakes is to cause distortions in the shape of the filter media. To this end, after a cake has been formed, the cake naturally tends to maintain its compacted shape, even when the underlying filter shape is altered. Thus, when filter shape is altered, the cake often breaks into chunks and the chunks fall from the filter. U.S. Pat. No. 3,667,614 titled “Filtering Apparatus” which issued Jun. 6, 1972, teaches one configuration that relies in part on filter deformation for cake removal.
To increase filter effectiveness some configurations provide a mesh or material filter media around the drum wherein the media includes much smaller holes and tortuous paths therethrough so that even extremely small swarf bits are removed from the liquid during filtering. In these cases the filter media is typically sealed to the drum via bands adjacent the top and bottom drum ends so that swarf cannot pass into the drum without passing through the filter media. Such sealing is extremely important to ensure that only clean liquid passes through the filter.
To increase filtering speed some drum type filters increase the pressure differential between the inside and outside of the drum by removing air from within the drum to provide a vacuum therein. One patent that describes a system of this type is U.S. Pat. No. 5,954,960 (“the '960 patent”) titled “Rotary Drum Type Dehydrator” which issued Sep. 21, 1999. While creation of a vacuum speeds up the filtering process, often, because air is pulled through the drum wall section that is not submersed while liquid passes through the submersed wall section, the vacuum is relatively ineffective unless a massive and, in some cases, prohibitively expensive pump is employed. The '960 patent relies in part on the presence of a built up cake on the un-submersed section of the drum to increase the vacuum effect. Nevertheless, in order to facilitate efficient filtering typically the filter media should be rotated prior to complete clogging of the media (i.e., filtering efficiency is substantially reduced prior to complete clogging). Thus, the cake that accumulates prior to drum rotation typically is insufficient to block air from entering the inside of the drum.
In addition to drum type filters other filter configurations have been developed that use a vacuum inside a filter chamber to increase filtering speed. U.S. Pat. No. 4,242,205 (“the '205 patent”) teaches a filter box submersed inside a liquid-solid mixture tank wherein an upper wall of the box forms an opening and a flexible filter belt is arranged so that a portion of the belt covers the opening. The belt is periodically slid across the opening so that different filter sections cover the opening at different times and a liquid sprayer is used to clean the soiled filter sections. A vacuum is formed inside the box. In this case, because the filter box has only a single open wall a relatively small pump can be used to generate a vacuum in the box thereby increasing filte
Fox Robert J.
Nelson Keith K.
Cecil Terry K.
Jorgensen Conveyors, Inc.
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