18/FN 7- \ i,' ' -- 3 September/October 1989 \ An iconomkal Answer For 1a;nta;ning Qual;V Coolant, joseph /-Hindi Manager of Engineering FLTERTECH, NC. Manlius. NY ositive barrier, conveyor supported, P flatbed filtration is currently used in several industries requiring filtration through disposable or permanent medias. Flow rates on such systems range from 20 CPM to several thousand GPM. Wire drawing, metal rolling, machining, grinding and heat treating are the major processes which benefit from the advantages of these systems. OPERATON As shown below, the dirty solution is transferred to the bed of the filter unit. The bed is equipped with a conveyor system to handle the internal load from the filter process, and support, disposable or permanent filter media. As ditty solution is transferred to the unit, the head of the liquid above the media drives solution through tile barrier leaving dirt deposits to form a filter cake on the media. When utilizingairvacuum, the head of the liquid as well as the pull of vacuum underneath the media are the driving mechanizers. The combination of the media and filter cake act as a depth filter to trap particulate which contaminates the solution to be filtered. As the cake forms, the differential pressure across the barrier increases. The increase causes the liquid level in the filter to rise. At a predetermined height of liquid or pressure differential, the conveyor is engaged causing a short index of new media into the filter pool. The process then repeats. GRAVTY FLTER AR VACUUM FLTER, m-m mm PU e. SZNG Regardless of whether the filter is gravity or vacuum, the filter size is based on the capability of the unit to pass a certain GPM through a square foot of filter media Forexample, when filteringoilversus water soluble coolant, the hydraulic load on the media is much higher, therefore, a lower GPM per square foot would be used. When filtering water with large sized particles where the filter cake is very porous,
SCptembdOctober 1989 - a high CPM per square foot can be used. When comparing the different style filters (gravity, medium vacuum, high vacuum), the allowable GPM per square foot forthe same type solutionvaries. Utilizing a gravity filter where only the head of the liquid is the driving mechanism, a lower GPM per square foot would be required. Utilizing air vacuum where the driving mechanism is liquid head as well as vacuum a higher CPM per square foot is allowed. Because so many variables effect the sizing of this equipment, it is some times advisable to have a filter flow test performed on the solution in question. FN/l9 d' CltTFK PO01 i DEtP 24" FLTER PO01 GRAVTY FLTERS The GF utilizes ashallower liquid pool as compared to the DBCF and is used for smaller flow rates or light dirt load applications. The unit utilizes approximately 8" of liquid pool to create the required differential across the media. The DBCF utilizes approximately 24" liquid pool which is 3 times the head of the GF, resulting in higher filtering capacity. Both units are used for lighter applications, with the DBGF capable of handling the more demanding of these applications. The main advantage of a gravity type filter in lieu of air vacuum is the initial capital cost savings. When properly sized, the units will filter efficiently, however, in most cases the discharge swarf exiting the unit will retain loose solution, possibly causing problems for collection and disposal of the spent media. Another advantage is that the unit does not have to be elevated to overcome vacuum. Therefore, a low profile allowing direct solution return from machines is possible without additional reservoirs. STANDARD AR VACUUM These uniq use a centrifugal exhauster (vacuum producer) to vacate the air from beneath the filter media. The unit will operate at 1-1/2" to 4" of mercufy. The actual vacuum is determined by the characteristics of the solution being filtered as well as the operating level of the liquid pool in the filter. GRAVTY FLTER ON LGHT LOAD COPPER WRE DRAWNG The air leakage described is shown in the cross section view. Air passes between the flat wire belt and the solid portion of the entrance and exit ramps of the filter. Air also exists as entrained air in the solution. The vacuum producer overcomes this air leakage to draw vacuum. These units incorporate an approximate 12" liquid pool, the head of the liquid (approximately l'), plus the negative pressure or inches of mercury allow for much higher GPM per square foot rates through the media. Because of the internal loads generated, construction from heavier gauge steels with additional reinforcement of the vacuum chambers is required. This heavier duty structuring is required to minimize any deflections or "oil canning" in the unit. Numerous systems are successfully operating on metal working applications. The combination of the solutions used and flow rates required, match well with the capability of this form of flatbed.
20/FN ' HGH AR VACUUM Operation of these filters require vacuums in the range of 4" to 8" of mercury. The design characteristics vary from the standard vacuum unit to allow operation underthe highervacuum. The concept of operation is similar to standard vacuum, however, due to the higher vacuum, there is a greater load on the filter conveyor. Standard vacuum units utilize a flat wire belt conveyor which has load limitations. The load limitations are based on a per foot width of conveyor. Once the length of conveyor causes the total per foot width load to exceed the allowable load for the flat wire belt, the design must be altered to prevent flat wire belt stretching. This is accomplished with three basic designs. The first, maintains a shorterfilter bed so that the overatl load on the conveyor is minimized. To handle the higher flow rates, greater filter area is required, therefore, the filter is made wider. The conveyor is supported in the vacuum chamber by heavy duty support rollers. The filter body is made of heavier gauge steel and stiffened properly to guard against oil canning. 1 FLTER MDER FOR HGHER CAPACTY - --- September/October 1989 FLTERTECH MODEL SCF AR VACUUM FLTER ON MODERATE LOAD COPPER WRE DRAWNG MAX ALLOWABLE LENGTH BEFORE STRETCHNG OF BELT 1 When increasingthe width of the filter is not permissible or the overall filter area is not sufficient for higher flow rates, a bridge bar type filter can be used. One version of this design utilizes a complete bridge bar conveyorto support the excessive loads generated by high vacuum as shown below. Specially fabricated conveyor flights are manufactured and driven by heavy duty roller chain on each side of the filter. The conveyor flights (bars) are tracked on each side of the filter allowing the flights to act as a bridge to handle the load generated by the high vacuum. This is shown in the figures below. A second version of the bridge bar filter is to utilize two conveyors, standard type heavy duty flat wire belt with an auxiliary bridge type conveyor underneath. The auxiliary conveyor supports the flat wire belt handlingthe high loads. By using the flat wire belt on the entrance and exit ramps, air loss is kept to a minimum. This results in high efficiency operation under high vacuum loads. HEAVY CUTY - - FLAT WRE BFl 1 TON K YOH High vacuum filters have found great success on applications such as aluminum and steel rolling mills where the filter demand is quite high due to large flow rates. Other applications are aluminum wire drawing and alloy fine grindingwhereviscous oils are the solutions to be filtered. SPECAL CHARACTERSTCS As described earlier, regardless of the type of filter, the concept of this style system is the same. Different areas to look at which greatly improved efficiency of operation are the control over index, the air flow on vacuum filters, how the liquid pool is sealed (side seals) and in some applications extraction chambers for de-
September/October 1989 FLTERTECH MODEL LA HGH VACUUM BRDGE BAR CONVEYOR SYSTEM watering discharge swarf and precoat chambers to help in high clarity conditions. ndex Control n most instances, a liquid pool is desired for operation in the filter. These units utilizethedirt ofthesystem to form afilter cake for removal of extremely fine particles, a deep quiet liquid pool is desired. The most efficient operation of the unit is when the unit indexes at its highest level of liquid and stops indexing just 1" to 2" below that level. ndexing can be accomplished basically three ways. The most desired method and mostly used is to index based on the actual level of the liquid pool. A latching circuit is incor- porated with afloat ball to sense the level in the filter. Once the filter reaches its level the index starts, a second switch shuts and conveyor off after the level has dropped. The switches are designed so that the level at these points are adjustable, allowingforan extremelytight index or a more open index depending on the application. n some instances, a vacuum switch can be installed sensing the differential pressure (vacuum) in the vacuum chamber. Once the vacuum has reached a predetermined level, the index is turned on; once the vacuum decreases, the index is turned off. This form of indexing does not always coincide with the level in the liquid FN/21 pool. Due to the fact that controlled liquid level helps the efficiency of the filter a great deal, the pressure method is not as desirable as indexing on direct level. The third means of indexing is on time. A timer utilizes an interval setting and a duration setting. This is often used when the filter is sized not only to handle the filter flow rate but also to remove large quantities of swarf. The timer allows the filter to index, to assure that the swatf is removed from the filter before overloading the conveyor. ndexing on time is also used when the hydraulic load is excessive, to minimize media consumption. Air Flow Modulation An automatic airflow modulation system on the suction of the vacuum producer automatically adjusts the amount of air flow being vacated from the filter in relation to the level of the liquid pool. This modulation allows for higher vacuum before index and lower vacuum after index when the liquid pool is at minimum state. After index, the new media introduced can allow extremely fine particles to pass through under higher vacuum. The modulation automatically takes care of this and also conserves energy. Side Seals The side seals of the filter are extremely important in minimizing migration of contaminant into the clean portion ofthe sys- tem. Shown below is the cross section of a labyrinth style moving side seal. The labyrinth design is such that dirty liquid must pass through the top sea!s and theii down underneath the moving seal before entering the clean section of the filter. This style seal allows for the clean bottom surface of the movingseal to be in contact with the clean surface of the stationary seal angle. The head of the liquid in the filter along with the vacuum underneath help maintain a positive contact between the moving seal and the seal angle. STPTONARY SEPL ANGLE Extraction r MoV"G SEAL PONTS T-
fz/fn September/October 1989 Vacuum filters have the capability of dewatering discharge swarf. A separate zone on the discharge ramp of the filter has openings and is undervacuum allowing the air flow to be pulled through the swatf once it has left the liquid pool. This air flow helps remove any loose liquid entrained in the swarf. The length of the extraction zones vary depending on the dryness requirement of the swarf. The liquid extracted is routed back into the system so that expensive coolants are not lost Precoat Precoat sectiions on the entrance ramp are incorporated when high clarity is desired. During index the first few inches of media pass through the precoat zone. This zone allows the liquid with extremely fine particles to be routed back to the dirty'portion of the system. During the system cycle, the precoat section builds filter cake so that during the next index this new precoated section of media passes in the clean section of the filter. At this point all of the liquid has passed through a prebuilt filter cake before entering the dean chamber. COMPLETE SYSTEMS The following page shows some typical setups using flat bed filters. Filter with sloped bottom dirty tank. Figure "C" shows a filter over top of a rectangular tank with a sloped bottom dirty compartment. The process is the same where excess solution is filtered allowing clean to overflow into the dirty. The slope bottom of the dirty compartment minimizes any settling of solids which can build up and cause galvanic corrosion in the tank. Filter with existing reservoir. System "D" is used widely when a existing reservoir is already in place. The use of a suction box allows for the dirty coolant from theworkto betransferred to the box. The filter feed pump pulls from the box up to the bed of the filter allowing excess to be pulled in from the bottom of the box at the same time. The clean solution is then directed back down into the reservoir near the clean supply pump inlet Diagram "E" shows the same type operation without the suction box. Filter with pump away. System "F shows a filter in conjunction with an integral reservoir where solution is directed to the filter, clean solution is pumped direct to the work This is done quite often with gravity filters where the water leg between the resewoir and the filter is not critical. Filter with conveyorized tank. The first diagram shows the filter in conjunction with a self-cleaning conveyorized tank The diw liquid is pumped from the dirty portion of this tank up to the filter allowing filtered solution to flow into the clean compartment n most cases, it is desirable to filter more coolant than is required at the machines, allowing the excess solution to overflow back to dirty. This action assures having sufficient clean for the process, also any floating tramp oils or contaminants are skimmed back to the dirty. Filter with conical bottom tanks. This system shows the filter above two conical bottom tanks. The solution is transferred from theworktothedirtytank and introduced into the tankon a tangential motion basis. The solution circulates in this tank keeping the particulates in suspension. A filter feed pump transfers the dirty solution up to the filter, clean solution drains by gravity to the clean tank. The clean supply pump transfers liquid back to the work. The conical designed tank is completely self-cleaning with no wearing components.
... 2lFN DAYKN LQUD LEVEL DETECTOR FOR VENTED TANKS The daykin Liquid Level Detector will detect various levels of extremely contaminated liquids, or slurry solutions with efficiency and reliability in applications. Since liquid in any tank exerts a pressure proportional to the depth and density, levels can be detected by sensingthe resistance to air flow from the end of a pipe placed inside near the bottom of the tank. Pressure switches contained in the enclosure can detect up to twelve different levels. Settings are made with a standard screwdriver adjustment. The actual liquid depth is indicated in linear inches on a four inch gauge mounted in the face of theunik- For more information contact Daykin Electric Corporation, 34425 Schoolcraft, Livonia, M 481 50 or use reply card. Circle Reader Reply Card #25