Screen Changer Polymer Melt Filtration FAQs

 

Does it matter if the screen changer is installed vertically or horizontally?

No, it does not matter because the operational principle of the unit (cooling water for the polymer seals and heaters to soften the polymer seals) is not affected by the relative orientation of the unit to the floor or ceiling. 

Do you have to stop the operation to change a roll of screen?

Yes, the extrusion process has to be stopped during this procedure to allow the polymer seals of the machine to be melted out, which, in turn, allow for the insertion of a new roll of filter ribbon.

How long does it take to change a roll of screen?

Replacing and installing a new roll of screen requires a maximum of an hour of downtime. The screen changer is supplied with the appropriate instructions, tooling and features to minimize the downtime required for this operation. Because the yield of a 120' roll of screen is equivalent to several hundred screen packs, a roll of screen typically lasts between four - six months. For this reason, changing a roll of screen is generally done during a regularly scheduled shut-down.

What kind of water quality is needed to operate the screen changer?

The cooling water used in the screen changer heat exchanger goes through cycles of heating above boiling point and cooling to the low temperature required to freeze the polymer seals.  For this reason the flow rate and the temperature should be according to the recommended specification per screen changer size / process.  In addition, the coolant should have a non-corrosive tendency and low mineral deposits.  There are a variety of sources - city water, well water, river water, tower, chiller with or without glycol, and so on.  Any of these sources being considered for use with the screen changer should supply the above referenced qualities.  A simple laboratory test showing - PH, alkalinity, total dissolved solids, calcium hardness, residual chlorine, calcium, Langelier saturation index, Langelier stability index, etc., could be used to evaluate the major qualities of the cooling water.

 How many zones does the screen changer require?

The screen changer has two different types of heating zones: PROCESS HEATING ZONES and SCREEN MOVEMENT HEATING ZONES. The process heating zones are the screen changer BODY with its associated upstream and downstream adapters.
     
These zones are regularly controlled by the extrusion main heating controls.  Most applications require three heating zones: (1)  for the upstream adapter, (2)  screen changer body and (3)  the downstream adapter.    
   
Screen movement heating zones are regulated by the HITECH controls. These zones refer to the sections of the screen changer ( Inlet Flange, Cooling Chamber, Exit Flange). These zones vary in number according to the type of process and the size of the screen changer.  HITECH™ controls provide the required instrumentation for these heating zones.

 


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