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Control of Raw Material Bulk Density Variations in a Plastic Forming Process

IP.com Disclosure Number: IPCOM000081748D
Original Publication Date: 1974-Aug-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 40K

Publishing Venue

IBM

Related People

Flynn, DC: AUTHOR

Abstract

Variations in raw material bulk density being fed to a plastic forming apparatus such as an extruder, are accommodated by monitoring pressure and temperature states at different points in the path of the melted plastic. A constant melt output rate is maintained by control of the feeding apparatus, such as by maintaining control of the feed-screw torque at a constant predetermined value.

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Control of Raw Material Bulk Density Variations in a Plastic Forming Process

Variations in raw material bulk density being fed to a plastic forming apparatus such as an extruder, are accommodated by monitoring pressure and temperature states at different points in the path of the melted plastic. A constant melt output rate is maintained by control of the feeding apparatus, such as by maintaining control of the feed-screw torque at a constant predetermined value.

For plastic extruder 10, a good melt and thus a quality resulting product is determined by maintaining a minimum of pressure and temperature variations within extruder die 11. Melt condition is determined by output 12 from a thermocouple in die 11 and output 13 from a pressure transducer in 11, which are monitored as analog inputs to computer 15. A predetermined variation from an established target alerts computer 15 to the potential production of an inferior product. Computer 15 monitors the temperature/pressure condition as reflected at lines 16 and 17 from additional thermocouples and pressure transducers which are downstream of feed screw 18.

A screen pack 20, consisting of several woven mesh screens, is usually installed to remove contaminants from the melt and improve melt mixing. There will be some pressure-temperature drop across the screen pack 20, the amount being a function of the number of screens and their degree of coarseness or fineness. The permissible range of pressure-temperature variations is determined from the screen pack manufacturer's recommendations and experience with a particular extruder. The condition of screen pack 20 is determined as a possible cause of die temperature/ pressure off-target variations. This is easily established by the following relationship: P1 - P2 = K1, T1 - T2 = K2 where the acceptable values of K1 and K2 are known.

Assuming K1 and K2 are within limits but P2 and T2 are of values which indicate an unacceptable final product, computer 15 is alerted that an unacceptable bulk density variation condit...