continuous_filtration_rotary_backflush_Patt_filtration
Continuous Filtration is not necessarily constant flow or constant
pressure filtration.
Of course, if planned shutdowns exist for other reasons such as color
changes or housekeeping, and filtration media renewal is done during
this time, then the production predictability goal becomes academic.
For those processors who need to maintain predictable production,
several solutions are offered. Each solution involves the concept of Continuous Filtration. In the industry, Continuous Filtration is achieved by changing screens without slowing or stopping the extrusion line to effect the change.
One solution used to provide continuous filtration is a modified slide
plate screen changer. The slide plates are hydraulically driven and are
set up in a one way track. Three slide plates, or blocks, are in the
track as the screen change begins: one active block, one heated standby
block and one recently cleaned block.
While this solution offers a method of continuously replacing clogged
screen packs and qualifies as a continuous filtration device, it depletes
the volume of material flowing to the die at each prefill and may cause
the line to tear. Entrapped air is removed under operator's control.
In general terms, the continuous filtration process consists of passing the molten polymer and contamination through a porous screen pack that entraps the solids in its matrix or retains them on its surface. Anything larger than the opening size cannot pass through, and will clog the screen
and increase the pressure drop across the screen if no clean filter
media is introduced.
Discontinuous filtration occurs when "Throughput" is the time based volume of polymer that can be filtered before the screens need to be changed, causing production interruptions. Fine screens with high retention efficiencies tend to plug faster and need to be changed more frequently.
Continuous filtration: "Throughput", with a ROTARY IIITM means the
volume of material that can be filtered without any interruption to
production. The microprocessor control will always keep the same amount
of open screen area in the flow path while maintaining a constant
differential pressure, essentially offering an unlimited screen area.
Only by timely adaptation to economic and technological changes could
we start to become the leader in the field of polymer filtration. Our
integration of engineering skills and advanced technology puts us on
the leading edge continuous filtration development.
There are many techniques that can be used in polymer continuous
filtration. Unfortunately some techniques would have serious
deleterious effects on the polymer. It is simply not worth a lengthy
discussion about how to filter contaminants and cause material
degradation.
Degradation could generate carbon specks whose diameter is less than
the screen pack's final continuous filtration layer and the result
could be a more highly contaminated product, albeit with smaller
particulate.
The basic idea of continuous polymer filtration is to force polymer to
flow through some media whose porosity is such that particulate larger
than the pore size will be retained while the polymer and contaminants
smaller then pore size will pass through freely.
However, increasing continuous filtration area means changing polymer
flow characteristics within the flow channel and, in some heat
sensitive polymers, causing degradation.
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