US 4,832,882 A · Method of removing impurities from a material

Abstract

A waste recovery method for producing essentially pure thermoplastic material from waste thermoplastic material containing impurities is disclosed to be comprised of an extruder, primary and secondary filtes, and a pelletizer. In addition, a plurality of pressure sensors are provided at several points within the system for measuring the pressure of a flow of molten thermoplastic material therethrough. A microcomputer is coupled to the pressure sensors for determining the pressure sensed by each, the microcomputer further being coupled to a plotter for plotting the pressures. An operator, by observing a rise in the plotted pressures, is enabled to activate a filter changing system in order to replace a clogged filter with a clean filter when the pressure equals a predetermined critical pressure point indicative of a filter being substantially clogged with impurities. Thus, the impurities held by a filter are not dislodged and forced to pass through the filter due to the pressure exceeding the critical pressure point.

Claims13

Dependent claims

A method of removing impurities from a material comprising the steps of:

pressurizing the material;
filtering the pressurized material with a filter such that the impurities are retained in the filter;
measuring a rate of pressure rise of the pressurized material in order to determine the time that the pressure reaches a predetermined critical pressure point indicative of the filter being substantially clogged;
and
providing a clean filter at a time related to the time that the pressure reaches said predetermined critical pressure point whereby the impurities retained in the substantially clogged filter are not forced to pass through the filter due to a further pressure rise causing the pressure to exceed the predetermined critical pressure point.

2 more elements

A method of removing impurities from polypropylene to produce essentially pure polypropylene comprising the steps of:

heating the polypropylene to a temperature such that the polypropylene is melted but the impurities are not melted;
extruding the polypropylene to provide a flow of polypropylene under pressure;
filtering the flow of polypropylene with a filter to produce a filtered flow of substantially pure polypropylene and a gradually increasing quantity of a filtrate of impurities at the filter;
measuring the rate of rise of a pressure of the flow during the step of filtering;
observing the measured rate of rise of the pressure of the flow to determine the time at which the pressure of the flow increases to a predetermined critical pressure point indicative of the filter being substantially clogged with impurities;
and
providing a clean filter at a time related to the time that the pressure of the flow reaches said predetermined critical pressure point whereby the filtrate is not forced to pass through the substantially clogged filter and into the filtered flow due to a further rise in pressure causing the pressure to exceed the predetermined critical pressure point.

4 more elements

Dependencies are inferred from the claim text.

Method of removing impurities from a material

Life of this patent

Method of removing impurities from a material

Life of this patent

Abstract

Claims13