written by: Bob Agnew, editor
A large manufacturer of industrial and consumer coatings recently introduced a newly formulated, fast drying, water based latex paint to their production engineering group without an appreciation of its effects on current manufacturing techniques, specifically, filtering and filling. The excitement about its acceptance in the water based latex paint market was shadowed by the increased cost in getting a quality finished product into its container's for shipment.
It seemed the formulator's overlooked fast drying paint results in rapid accumulation of "skins" when the free surface of the paint is addressed to atmosphere for brief periods of time. While most of the differences in preparation of the paint were addressed with minor changes in tank linings, operating and cleaning procedure's, filtration and filling of the new product was becoming extremely expensive, and the delays encountered by the filling supervisor awaiting product resulted in shutting down and starting of the fill line as a routine.
DCF
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Prior to the reformulation,
the paint would be pumped from the base of blend vessel
using an air-operated double diaphragm pump onto the
surface of a large, open, vibrating screen. The solids
would be vibrated to the outer circumference and removed
while the filtered paint would exit and be directed into
an accumulating vessel where a second diaphragm pump
would supply the paint through a finishing filter to a
reservoir within a rotary drum filling machine where it
would be dispensed into the appropriate containers. A
level control within the rotary filler would signal the
pump located at the base vessel to come on and off as the
level in the rotary would rise and fall. Conventional
products were produced this way for years and even the
most experienced engineer's, operator's and maintenance
supervisor's expected the newly formulated product to be
produced in the same manner with little change in the
process conditions or components. Unfortunately the skins, which are inherent in nearly all latex paint products, were not only physically larger they were heavier than the conventional paints. Pumping presented no problems, however, once the paint addressed the vibrating screen filter the heavier skins would not be as easily removed. The skins which would not vibrate off the screen took valuable screen open area which would result in a loss of flow to the accumulating vessel which in turn would be empty when the rotary called for paint. Under these conditions an operator would shut the fill line and manually scrap the skins from the vibrating screen. This procedure would result in occasional damage to the screen and maintenance would be called to replace the screen, all the while flow to the filling line would be interrupted. In their quest to find solutions to their filtration and filling problems process engineering contacted Ronningen-Petter Engineered Filter Systems, Portage, MI., where they were introduced to the DCF-800 Series self-cleaning filter. After a thorough review of the filtration technology and its application a DCF-800 filter with field adjustable automatic controls with manual overrides to initiate cleaning and purging was installed. The DCF self-cleaning filter closed the loop, it was not open to atmosphere during the filling process. As the newly formulated paint was pumped from the supply vessel it entered the top of the DCF and was directed downwardly through the inside diameter of a slotted, machined smooth, wedge wire element where the paint passed through leaving the skins and other unwanted solids deposited on the screen surface permitting the "finished" paint to exit the lower side of the filter and into the rotary reservoir. The solids are removed by initiating a vertically mounted pneumatic actuator with a circular cleaning disc attached at the fluid end. When called upon the cleaning disc travels downwardly then upwardly removing the solids from the screen while the natural fluid flow path directs the removed solids to the bottom of the filter. The solids accumulate in the bottom of the filter until a pneumatically actuated valve opens for a brief period allowing the pressure within the filter to purge the solids from the filter. The DCF permitted removal of the vibrating screen filter and the second diaphragm pump which was located downstream of the accumulating vessel. By closing the process loop airborne dirt and other particulate which would enter the accumulating vessel requiring the use of the "finish" filter was no longer a concern, and the process was further simplified by removal of the "finish" filter and accumulating vessel. With its ability to clean-in-place and purge solids without an interruption in flow, reduce cleaning and maintenance time as fewer process components are required, and provide high quality water based latex paint products to the filling line proven, the manufacturer has plans to incorporate the DCF self-cleaning filter technology on new filling installations scheduled for other locations. |
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