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Josephine ( Joie) Komarmi, Dyna-Purge International Business Manager “Please contact us with your purging challenges.” Contact Us

FREQUENTLY ASKED QUESTIONS:

1. How do you get rid of black specks/carbon buildup?
2. How do you get rid of streaking?
3. How long will it take to purge with a commercial product?
4. How much commercial purge compound is needed to clean?
5. What is the cost of purging? What is the cost of not purging?
6. Are there different types of commercial purging compounds?
7. Are commercial purging compounds safe for use with hot runners?
8. Are any commercial purging compounds FDA approved?
9. Are commercial purging compounds mixed with other resins?
10. Are commercial purging compounds safe to be left in the barrel?
11. What should I know about going from a higher to lower temperature resin?
12. What can I do when Dyna–Purge is too stiff to be displaced with the next resin?
13. What should I know about using heat sensitive resins?

1. How do you get rid of black specks/carbon buildup?

Black specks/carbon buildup are caused by one or more of the following:

1. "Dead spots" or negative flow areas in the barrel, nozzle or die.
2. Hot temperature spots in the machine.
3. Separation of additives, fillers and color concentrates from the carrier system that are left behind when the resin is processed.
4. Degradation of polymers by excess heat, shear action, residence time in the barrel.
5. Start-up and shutdown.
6. Lack of a regular preventive maintenance.

The carbon buildup (like shale rock) will eventually break into pieces and be moved forward by the screw and display itself as black specks in the finished product. The black specks can be reduced but not eliminated by using the next resin — wasting several hundred lbs. of resin and valuable production time — or the black specks can be eliminated by using a commercial purging compound.

Dyna–Purge purging compounds work by a mechanical "non–abrasive" scrubbing action. The unique scrubbing granules in Dyna–Purge safely get into the dead spots and hot spots in the machine and break away the layers of carbon buildup — the layers of separated additives and degraded polymers. This mechanical action will not damage the surface of the screw, barrel or any metal components or tolerances of the plastic processing equipment.

We recommend regular purging with Dyna–Purge after every color change (to remove separated pigment and additives that adhere to the metal of the screw and barrel), resin change (to remove old resin residue that may have different viscosity from the next resin and therefore, clings to the screw and degrades), and whenever there is a start-up or shutdown.

Implementing a regular purging procedure with Dyna–Purge will eliminate the black speck problem, reduce the length of time from color to color and resin to resin transition, adding valuable production time, and reducing wasted raw material.

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2. How do you get rid of streaking?

Often, old color will be trapped in a negative flow area. There is not enough physical turbulence in the area to move the color; therefore, the next material processed picks up trace amounts of color and causes a streak in the part. This streaking will continue until the color that is trapped is "flushed" away by the next resin.

It is noted that if color streaking occurs in the same location on the part, then the entrapment is likely close to the nozzle or die. If the streaking is a moving streak, then the entrapment is likely to be in the barrel and/or feed zone of the machine. Streaked parts are considered scrap, represent non-productive time and lost opportunity.

Purging with Dyna–Purge purging compounds will help the processor remove the entrapped color and flush it away. Dyna–Purge scrubs the color out, reducing the amount of resin wasted (and therefore less scrap), reducing the length of non–productive time, and gives back to the processor valuable opportunity to produce saleable product.

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3. How long will it take to purge with a commercial product?

Factors to consider when determining the length of time it will take to purge:

1. The color — some colors are more difficult than others
2. The type of resin
3. The viscosity of the resident resin and the viscosity of the following resin
4. Age and condition of the processing equipment
5. Size of the machine
6. Skill of the operator
7. Uniformity of purging procedures among the operators
8. The better the preventive maintenance on the plastic processing equipment, the less time. Is there a Standard Operating Policy (S.O.P.) for purging? Is there regular machine maintenance or is purging just an emergency issue?

When there is a regular purging policy (S.O.P.) in place, purging is quick and easy! In our experience, an S.O.P. greatly improves the efficiency of the purge process. Please contact us to develop an S.O.P. for your operators.

There are many different types of purging compounds — some require a mixing with your material and some require a soak time in the barrel to become activated — downtime is expensive. Some products may require repeated applications, others work quicker.

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4. How much commercial purge compound is needed to clean?

Because there are different types of commercial purging compounds: chemical-liquid/solids, concentrates, pre–blends, mechanical — concentrates and ready–to–run, and abrasive type — each has its own formula. Please read the processing instructions that accompany the product. Only by using the compounds as recommended, will you get acceptable results.

Dyna–Purge is a mechanical type, non–abrasive purging compound. It is pre–blended so there is no need to mix with your own resin. Because the processor does not need to mix with his resin, the cost per lb. is the cost per lb. — there are no hidden costs!! Dyna–Purge is pre–blended and ready to use.

As a rule of thumb, the recommended amount is:

• injection molders: 2 lbs per diameter inch or the screw
• extruders: 5-10 lbs. per diameter inch of the screw.

Cases may vary depending on the following:

1. The color — some colors are more difficult than others
2. The type of resin
3. The viscosity of the resident resin and the viscosity of the following resin
4. The better the preventive maintenance on the plastic processing equipment, the less time. Is there a Standard Operating Policy (S.O.P.) for purging? Is there regular machine maintenance or is purging just an emergency issue?
5. Age and condition of the processing equipment
6. Size of the machine
7. Skill of the operator
8. Uniformity of purging procedures among the operators.

Dyna-Purge is proven most effective in a "cost to purge" independent study. See for yourself on our "IMM Article" or download the PDF.

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5. What is the cost of purging? What is the cost of not purging?

There is a considerable difference in price among the various commercial types of purging compounds — all are a higher price per lb. than resins.

The factors that need to be included in the cost issue to determine the "cost to purge" (an analysis developed by the Dyna-Purge Division of Shuman Plastics, Inc. — see "Cost To Purge") are to calculate the:

1. cost of purge compound
2. cost of machine downtime (includes machine adjustment, soak and manual mixing)
3. cost of carrier resin
4. post purge cost of resin
5. cost of post purge downtime

More importantly to consider is the cost of not purging. The processor will generate an inordinate amount of scrap, have reduced productivity, and will incur substantial opportunity cost.

We encourage all plastic processors to use an effective commercial purging compound that is formulated for the process/resin /temperature needed to purge. Dyna-Purge offers 10 different grades to fill injection molding and extrusion applications.

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6. Are there different types of commercial purging compounds?

There are three main types of commercial purging compounds, and also hybrids** of these types.

1. Chemical types: Liquid & solids — these are often concentrates that need to be let down into your own next resin or are supplied as pre–blended in a carrier. This type of purging compound requires that the purge compound be added to the machine and the purging compound be allowed to soak in the barrel for a specific length of time and with adjusted heats without the screw turning to allow the chemical reaction to occur. Heat will activate the chemical reaction — this chemical reaction modifies the molecular chain of the polymers that need to be purged, making it easier for the next material to flush it out. Chemical purges can be effective but costly from a cost per lb. and also a "cost to purge" basis, as purging takes longer because of the soak time. Some of the chemical type purging compounds also release ammonia or others fumes which may be harmful to machine operators. Also the need to elevate heats and extended soak time causes polymers to be exposed to potentially unsafe process conditions further exposing operators to risk. Some polymer breakdown may expose equipment to caustic acids cause pitting and wear.
2. Mechanical/Abrasive: This group of purging compounds are often concentrates, but can be supplied as pre-blends. The carrier system is loaded with a high % of glass fibers or beads, and inert fillers, including clays, calcium, talc, TIO2. These purging compounds clean by aggressively scouring the barrel and screw. Their aggressive and high filler content cause excessive wear on the critical tight tolerances of the screw and barrel, and may result in a screw replacement long before the normal replacement time.
3. Included in this group of purging compounds are the non–melting type purging compounds. These can cause mini explosions when they are processed at high temperatures or through tight nozzles or die clearances. They can be hazardous to equipment— because of high–pressure buildup — and to operators exposing them to potential heat burns.
   
   **HYBRIDS — Share the same risks and drawbacks of 1 and 2 in some proportion.
4. Thermoplastic Mechanical/Non–abrasive: This group of purging compounds are the easiest to use, the safest for the equipment and machine operators, as well.

Dyna–Purge falls into this group. Dyna–Purge is a thermoplastic (non-chemical) blended purging compound. The Dyna-Purge formula includes polymer carrier systems with unique "soft scrub" scrubbing granules. The scrubbing \granules soften on the outside, but remain solid on the inside so that the metal surfaces of the screw and barrel are scrubbed softly and thoroughly without wear. The specially formulated carrier system flushes the old color, degraded material and contamination out of the machine.

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7. Are commercial purging compounds safe for use with hot runners?

Among the three main types of commercial purging compounds, there are several that can be used with hot runner systems. The question that the processor should ask is: "Which is best for my equipment and machine operators, and which will deliver the best results?"

Dyna–Purge P is a thermoplastic blended purging compound that is safe to use throughout hot runner systems and is safe for the machine operator.

With any product, it is important that the right grade is used for the right process and application. See our "Grade Selection Guide" to learn about the 10 different grades of Dyna–Purge.

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8. Are any commercial purging compounds FDA approved?

Purging compounds are an intermediary product — a maintenance product that is never intended for manufacture into finished plastic product. Purging compounds are not FDA regulated. They can be formulated with ingredients (resins, additives) that can be FDA compliant. Dyna-Purge is formulated with FDA compliant ingredients.

Dyna-Purge is successfully used in hundreds of medical, food, pharmaceutical and other critical applications where FDA and other stringent third party approval are required. Please contact us to learn more about Dyna-Purge and using it in your plastic processing facility.

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9. Are commercial purging compounds mixed with other resins?

Among the three main types of purging compounds, there are several grades that are offered as concentrates. They are to be mixed with a carrier — either a commodity resin or the next material to be processed. The main problems with concentrates are: adding the right amount, hand mixing so that blend is uniform, stocking carrier and flushing resins.

Please note that when using a concentrate and letting it down into the processor's own carrier resin, the cost of the resin that is used should be included in the cost of purging. We refer to this as a hidden cost and often discounted by the user — the same can be said for the mixing time required.

Dyna–Purge is a pre–blended, ready–to–run thermoplastic purging compound — uniform and consistent from lot to lot, drum to drum, box to box. It is easy to use, plus there are no hidden costs. Simply scoop or pour Dyna–Purge from the package right into the machine.

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10. Are commercial purging compounds safe to be left in the barrel?

This is a good question because purging before shutting down makes for an easier start–up. Among the three types of purging compound, only thermoplastic mechanical non–abrasive are safe to be left in the barrel for shutdown.

The chemical types are only active for the period of time during the purging process. It is important that all chemical residual be removed before shutdown for the protection of the equipment.

The mechanical abrasive will freeze in the barrel, and left in the barrel, may result in damage to the screw on start-up.

Dyna–Purge is a thermoplastic mechanical non–abrasive purging compound that can be used for shutdown and start–up. We recommend that the machine be purged with Dyna-Purge at shutdown to clean, and that the barrel be filled with Dyna–Purge during shutdown. Dyna–Purge is very stable — it will not degrade upon start–up. Dyna–Purge ensures that start–ups will be easier and faster than with other types of purging compounds.

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11. What should I know about going from a higher to lower temperature resin?

Ideally, a grade such as Dyna–Purge M, with a wide temperature range(350 to 600°F), can be used to transition from a higher temperature resin to a lower temperature resin. However, in some instances, purging with Dyna–Purge until clean and then shutting off the machine will allow for additional contamination to be removed. Leave in the machine a half to full barrel of Dyna-Purge. Turn the machine off and let it cool down. Once it has cooled down reheat to the last process temperature and purge out the remaining Dyna-Purge. Once completed, lower the temperature for the next resin, introduce the resin and push out the remaining Dyna-Purge. This purging procedure allows for the Dyna-Purge in the barrel to cool down and become integrated with any built-up residual stuck to the barrel or screw.

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12. What can I do when Dyna–Purge is too stiff to be displaced with the next resin?

While Dyna–Purge is often stiffer than the resident resin, it is also formulated to be "post purged" with ease. However, if the next production resin has a very high melt flow (i.e. 30 G) the material might not be able to adequately displace Dyna–Purge, since the higher melt resin will flow over Dyna–Purge rather than displace it. We suggest "bridging" the melt flow difference by blending the Dyna–Purge, at a 50/50 ratio, with a higher melt resin. The higher melt resin becomes the carrier system for Dyna–Purge and makes it easier to displace the Dyna–Purge and transition to the next production resin. Another solution might be using a different grade of Dyna–Purge, with a carrier system that flows easier.

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13. What should I know about using heat sensitive resins?

Because resins, such as PVC, are very sensitive to heat and can be a major cause of carbonization due to oxidation, and then leading to degradation within just a few minutes, we suggest that you not starve the screw, as we normally recommend. For instance, if you're processing PVC at the usual temperature range of 320 to 340°F(160 - 171°C), the Dyna–Purge V, having a range of 320 to 400°F(160 - 204°C), would be the right choice. Dyna-Purge should be introduced at the end of the heat sensitive resin run, which can be accomplished by introducing the Dyna–Purge on top of the resident resin in the hopper. Continue to purge until the purge is "clean and free of contamination."

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