US 5,961,734 A · Methods for purging process lines of additives for thermoplastic materials

Abstract

Methods are provided whereby additive for thermoplastic materials may be recovered in a primary additive supply system simultaneously with the supply of an additive from a secondary additive supply system to a molten thermoplastic stream. Each of the primary and secondary additive supply systems is provided with respective recirculation lines so as to prevent sedimentation of the additive. According to the present invention, therefore, a protocol is employed whereby substantially all of the additive in the additive supply system, including that quantity of additive in the recirculation lines, may be recovered so that a fresh supply of additive (which oftentimes is different from the previous additive) may be connected for injection into the molten thermoplastic stream at the appropriate time.

Claims22

Dependent claims

A method for purging and cleaning process lines of an additive supplied to a thermoplastic melt comprising the steps of:

(a) supplying an additive from a discharge port of an additive supply tank to an input side of a recirculation pump;
(b) operating the recirculation pump so as to force the additive from an output side of the recirculation pump through a main supply line to a thermoplastic melt, while continuously recirculating a portion of the additive through a recirculation line fluid-connecting the main supply line at the output side of the recirculation pump to an input port of the additive supply tank;
and thereafter
(c) recovering additive in the main supply and recirculation lines by stopping the operation of the recirculation pump and concurrently forcing the additive out of the main supply line and the recirculation line with a purge fluid.

1 more element

A method of purging one additive from process lines of a first additive supply system while simultaneously feeding another additive from a second additive supply system to an extruder common to both said first and second additive supply systems comprising the steps of:

(a) fluid-connecting main additive supply lines of both said first and second additive supply systems between a respective additive supply tank and a common control valve such that said one and another additives may respectively be received as an input to said control valve and such that said control valve has one output to the extruder and another output to a waste site;
(b) supplying additive from the additive supply tank of the second additive supply system through the main additive supply line of the second additive supply system and to the common control valve and positioning the common control valve so that the supplied additive is directed to the extruder;
while simultaneously
(c) back-flushing the main additive supply line of the first additive supply system with a fluid so as to clean the same.

1 more element

Dependencies are inferred from the claim text.

Methods for purging process lines of additives for thermoplastic materials

Life of this patent

Methods for purging process lines of additives for thermoplastic materials

Life of this patent

Abstract

Claims22