Roll-up Primer

General Characteristics

Air is used to support the plastic as it exits the die until the vacuum can take hold and form it into the correct shape. However, there are limits to how much air can be used without creating issues. Think of the plastic as a shallow tray of pudding. If you blow slightly on the surface nothing will happen, but if you blow harder you will create a wave of moving pudding. Roll-up is the corrugations trapping the ‘wave.’

If roll-up is occurring, it is likely caused by: (sometimes it can be a combination of these)

1. Air pressure, the higher the air pressure, the more the plastic will be moved. There is a balance between not enough to support and too much to produce faults.
2. The temperature of the plastic, the cooler this is, the less the plastic can roll (to a point).
3. The plastics thickness, the thicker the plastic, the more air is required to support it, and the higher the air, the more chance of creating a roll.
4. Speed of the plastic exiting the tooling, this die gap, and the bigger the die gap, the slower the flow and requires more air to stretch the plastic.
5. Melt strength, the materials melt strength is a large factor and the higher this is, the more air can be used during the process making production easier (but too high and it will affect the formation the pipe and cuff).
6. Airhole blockages, if the air holes are blocked on the tooling, the air pressure will not be balanced and will give different support to certain sections of the pipe.

Note: Sometimes roll-up is not consistent all the way around and can show up in certain areas. When this happens, it can be the result of

1. Corrugator is not centered to the die tooling and cool plug.
   1. You can verify this by checking the compressed wall thickness around the pipe.
2. Airhole blockages, if the air holes are blocked on the tooling, the air pressure will not be balanced and will give different support to certain sections of the pipe.