The art of Purging – case studies

Every production technology has its specific purging problem,

Flat die extrusion with dies or vents, Blow Film with its spiral mandrels,

Blow Molding with heads & parting lines & Injection molding with

Hot runners & color changes.

Add to all this a conglomeration of materials, colors & additives which

Can complicate matters for the technician to know what the best purge is for

his specific problem.

Eko-Plastic has a wide range of on the shelf purging products that give

Good results in the different production technologies & with most of the

Plastic resins.

Some times we are challenged by a customer to solve a specific

Cleaning problem that he has & is unable to solve with our regular

Purging compounds & technology.

Eko-Plastic in these cases has tailor made purging compounds to solve some of these challenges.

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Composition of the purges:

The composition of both the basic purges EKO GGX NEW & EKO COLD in the two cases that are described here are based on a PE carrier with a MFI which is suitable for the resin in use & a sufficient viscosity to remove the material while not mixing with the material.

The composition of the purge compounds both contain two different abrasive additives with a range of Mohs from 2-6 at different ratios of loads & at a maximum size of 1.5 microns. The abrasive additives act as a scrubber & loading filler of the system & the difference in size of the additive is of most importance to obtain optimum loading of the system.

The compound is also comprised of an endothermic blowing agent added at different loading ratios according to the need of the technology & resin in use.

The abrasive components of the purge composition are released along with the blowing agent as the binder melts into the stream of the resin. Additional scrubbing action is added by the abrasive to the resin mixture & the abrasive additionally functions as sites of nucleation for the newly forming gas bubbles produced by the degradation of the blowing agent. The small size of the abrasive particles less than 1.5 microns increase the number of potential nucleating sites which contributes to the even distribution of the gas bubbles within the melt flow. This even distribution within the melt flow helps to improve the scrubbing action of the purge concentrate.

The EKO GGX NEW was given an additional additive of EKO FILM P at a ratio of 90/10 loading. The EKO FILM P adds a further dimension to the scrubbing action of the EKO GGX NEW this chemical compound which is acidic is a proton donor attaching itself to the resin during the 10 minute period that the purge is stopped for during the cleaning process. This addition effectively changes the purge to a two tier action of mechanically abrasive scrubbing & chemical attachment to the resin creating a pushing & pulling reaction.

One of the leading producers of polyurethane belts in the world.

It producers conveyor belts, profiles & other components  of the highest quality.

1. Problem definition.

Long periods of change over lasting for 3 hours from various colors & Polyurethane with shore hardness’s ranging from A60- A96 & more. A Flat die extruder of a of width 1600 mm & diameter of screw 135 mm.

2. Objectives:

     The objective was to produce a purge that would flow with ease to the full width

     of the flat die. Clean obstinate colors quickly & be versatile enough to cope with

     Polyurethane resin with a wide range of shore hardness’s, to be heat stable to      

    shut down the machinery on & to reduce considerably the time for change over     

     with a relatively small amount of purge compound.

1. Chosen solution.

A physical cleaning compound with non aggressive cleaning components with a low Mohs factor, also comprising of a blowing compound to produce pressure & the ability to reach all the dead areas in the extruder.

A carrier resin for the compound with a suitable MFI & Viscosity which can

handle the large variety of Shore hardness’s & be expelled from the extruder

with ease.    

1. Tests.

The Purge was tested over a 12 month period on Volta Belts flat die extrusion,

with various modifications over this period of time. Initially we tested with EKO GGX NEW which purged the Polyurethane out but its viscosity was not suitable to flow easily to the full width of the die & also proved difficult for the polyurethane with lower Shore factors to flush it out from the extruder.

We then produced the tailor made EKO COLD with its modified MFI which flowed quickly to the width of the die, purged the varying shores of the resin & flushed out easily.

Even so we met with problems during the testing & development one of them was a problem of the purge causing bridging in the feeding zone of the extruder, this problem was cleverly solved by Volta Belts extruder technician Yossi who elevated the temperature in the feeding zone by 10c.     

1. Conclusions:

The purge shortened the cleaning process to one hour on average from its previous 3hours. The amount of purge used is an economical 25 Kg for a large 135mm flat die extruder. The purge also proves successful in shutting down the line during weekends stopping the black spots created by the degrading of polyurethane.

Polysack Neot Mordchai.

Polysac produces high quality netting for a wide varity of uses on two new PE fiber extruders.

The fiber is then taken to the weaving department & woven to PE netting of various

widths & density’s.

1. Problem definition;

During production gels & degraded material builds up in the extruder gear pump & head  from time to time flush’s out of the head causing a discontinuity in the flow of the PE from the die  cutting the fibers, causing the fiber to be lost on the floor of the factory & not onto the take off spindle it was intended for.

To shorten the time of color change over & to solve the problem of color contamination.

The purge also has to be stable for closing down on for week-ends.

2. Objectives:

A purge which is robust enough to clean the extruder, but has fine cleaning additives of a small diameter which can pass easily through a die head with very small die orifice gaps for the fiber. Also stable enough to withstand cooling & reheating & flushes out quickly without leaving any traces of purge behind.

3. Chosen solution:

A combination of EKO – GGX New which is a physical purging compound &

EKO-FILM P which is a chemical purge.

The purging compounds were mixed at a ratio of 90% EKO-GGX NEW & 10% EKO-FILM P.

The EKO GGX NEW gives the cleaning ability for cleaning degraded resin & master

Batches without damaging the small orifices & is extremely effective while closing down the machines.

The EKO FILM P has a chemical reaction, connecting itself to the resin & pulling it out of the machine.

4.Tests.

The material has been tested & used on both lines for 9 months. At the out set only Eko-GGX New was used, after receiving good results from this we decided to upgrade the purge with the addition of 10% Eko-Film P.

The trails were conducted to clean contamination from the extruders & to close down

The extruders on week ends.

1. Conclusions.

The Eko-GGX New with the addition of 10% Eko Film P purged the extruders clean from all contamination resulting in fast cleaning & trouble free production.

The closing down process proved fast & effective cutting out completely the build up of contaminated material resulting in quick clean start ups.