Benefits of screen Changer extrusion applications
Benefits of screen Changer extrusion applications
are so outstanding that screen changers are widely used in various extrusion lines. Screen changer
used for extrusion lines can improve the quality of products.
Benefits of screen Changer extrusion applications:
Steady incremental rate of screen travel eliminates head pressure and melt pressure fluctuations due to screen clogging. As a result, the gauge is maintained within very close tolerances.
Formation of die lines is eliminated
There are no mechanical, metal-to-metal seals that can wear and begin to leak over time. Instead, cold circulating water form perfectly leak-proof seals. Screen changers will not leak polymer or any of the blowing agent gas, even over many years of continuous operation.
There are no hot breaker plates to handle or dirty screen packs to change. The screen moves imperceptibly slowly and continuously so as not to disturb the polymer flow, and the continuous motion of the screen automatically adjusts to correspond to the rate at which the screen is clogging.
With the elimination of pressure fluctuations due to screen clogging, uniform gauge control is maintained indefinitely. The “bubble” will never collapse, and the frost line will not waiver, even over months of non-stop operation.
Biax - no web breaks associated with screen movement:
The elimination of pressure fluctuations due to screen clogging results in uniform melt temperatures and flow rates, thereby significantly improving gauge control.
The continuous movement of the filter ribbon prevents contaminants from building up and degrading. By contrast, the operating mode of slide-plate screen changers can dislodge decomposed polymer particles and other contaminants, resulting in scrap film being produced for some time after each screen change.
Sheet & film - no process disruptions:
The only moving element in a screen changer is the 120’ roll of filter screen. The yield of such a roll is equivalent to several hundred “screen packs” in a conventional, slide-plate type screen changer, and a roll of screen lasts many months in non-stop operation.
The 120’ roll of filter screen advances at a slow, incremental rate so as not to disturb the polymer flow. Process disruptions associated with screen movement are eliminated.
The incremental rate of screen travel automatically adjusts to correspond to the rate at which the screen is clogging. Melt pressure and temperature fluctuations caused by screen clogging are eliminated, and, as a result, uniform gauge control is maintained indefinitely.
Pipe & profile: consistent wall thickness:
With of the elimination of melt temperature and melt pressure variations caused by clogged screens, process parameters are kept within extremely tight tolerances. As a result, consistent wall thickness is maintained throughout months of non-stop operation.
There are no hot breaker plates to handle or dirty screen packs to change and clean. Process disruptions associated with screen changes are eliminated. Accordingly, there is no day-to-day operator involvement in the operation or maintenance of the screen changer.
The operating mode of screen changers blends seamlessly into the co-extrusion process. The 120’ roll of filter screen moves at a steady, incremental rate so that fluctuations in melt pressure and melt temperature resulting from clogged screens are eliminated.
The physical dimensions of screen changers are another significant advantage in co-ex lines. Filters are significantly smaller than other types of screen changers, thereby resulting in shorter distances the melt has to travel to the feed block.
Filters do not require any auxiliary power sources, such as cylinders or hydraulics to clutter up the densely packed space between the extruder barrels. As a result, screen changers can be fitted into the smallest available spaces.
Using 120’ rolls of filter screen, the screen changers do not need to be accessed to change hot breaker plates and dirty screen packs or cylinders.
Blow molding - uniform parison wall thickness & length:
Because of the steady, incremental rate of screen advancement, head pressure and flow rates remain uniform even over the longest production runs.
With the elimination of melt temperature and melt pressure variations caused by clogged screens, the parison wall thickness and length will not vary. In programming the wall thickness of the bottles, no extra allowances need to be made.
Installed immediately after the extruder, the screen changer will function as a central filter, thereby ensuring significantly longer stand times of the down stream spinnerets, in some cases as much as a factor of 8 - 10.
When processing low denier fibers/filaments, or very narrow diameter monofilaments, maintaining gauge accuracy is critical. In a screen changer, this is achieved via the precisely controlled, incremental rate of screen advancement. The extruder head pressure and melt flow rates remain uniform during long, uninterrupted production runs.
Filters allow for quick and efficient change-over at times of material recipe changes, with minimal down time.