posted August 27, 2007 06:06 AM            

I have a problem where the material is coming out of the vent port. The material builds up slowly in the ven port and soon it will be full such that I have to clear it every 20 minutes.

What can i do to prevent this from happening? Anything I can adjust from the process?

Thanks in advance for your inputs.

posted August 28, 2007 04:32 AM            

More frequent screen changes and/or increasing Die and adaptor temps to reduce backpressure will help as a quick fix.

Experimenting with barrel temp settings to reduce the rate material is being conveyed in the first stage and increase the rate it is being conveyed in the second.

Permanent solutions could be, modify your screw to include a blister ring at the end of the first stage, fitting a melt pump so the second stage of your screw doesn't have to "pump" material through screens and die.

What materials are you processing and what are you extruding?

Steve

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Steve Hodgson

posted August 29, 2007 10:38 PM            

Thanks for your reply.
We are processing HIPS Sheet and actually, we have tried increasing both the first and second stage of the barell temperature and it does help to reduce the amount of material coming out of the port but it is still coming out.

I believed that the main reson will be the viscosity of the material. Currently the HIPS that we are using is having Melt flow of 3.1 g/10min and when we tried another resin of Mfi 3.6 g/10min, it works really fine (without any material coming out of vent port) but we are then facing difficulty in controlling the sheet thickness and the thermoforming product of this higher mfi grade is not as good so we would prefer to use the grade with 3.1 mfi.

Current barrel temperature throughout is at 240 deg C.

Apart from the barrel temp, what else can I regulate in the process to get better material flow in in the barrel?

Thanks for the help.

posted August 31, 2007 08:03 PM            

Also, if your barrel is side vented, then polymer will more readily flow out of the vent if the vent is on the side where the flow is moving up (against gravity.)