posted July 28, 2005 11:55 AM               

What would maximum extruder barrel pressure normally be?

posted July 28, 2005 12:15 PM               

A 24:1 6" screw would be about 144 inches long and a 30:1 about 180 inches. More length has the potential for higher output rates because of the increased barrel contact area used for melting.

What would maximum extruder barrel pressure normally be?

Typically barrels are made to withstand 10,000 psi. It is possible for the pressure along the screw to exceed 10,000 psi while the head pressure is less than 10,000 psi. In order to prevent equipment damage it is important to correctly match material, screw and process conditions. That said, it is somewhat rare that the mechanical stength of extruders is exceeded, but it does happen.

Does melt temperature changes affect viscosity as much as screw speed. For instance if you go from a 360 F to a 385 F on zone 1 or feed zone.

It depends on the combination of polymer characteristics, frictional properties, screw design, barrel-throat design and processing conditions. That is why I employ a number of tools, tests, theories and software to try and sort these things out. Some of these items can be seen on my web site.

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Best Regards,

Tom Cunningham

Extrusion Technical Services

posted July 28, 2005 01:45 PM               

(30) screw flight turns at the (1) screw diameter. Typically screws are "Square Pitch" meaning that the screw flight advances the same length of the diameter of the screw every rotation around the screw. So a 30:1 6" screw will have a nominal length of 30 * 6" = 180".

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Best Regards,

Tom Cunningham

Extrusion Technical Services
www.ExtrusionTechnicalServices.com