PRINCIPAL SOURCE OF BLACK SPOTS IN MOLDING PROCESS

Even though, carbon contamination continues to be a widespread problem throughout manufacturing. The majority of my customers who work in production teams tend to misinterpret the primary cause of black specks occurring in production. Why is that the case?

Since we began concentrating on only one reason why there are black specks, things have drastically improved. The Heat is the story's principal antagonist, if we were to identify one.

Paying close attention to two contexts where heat is working against a smooth output, you can solve the majority of black speck problems in production.

1. Prolonged residence during machine stops and starts:

Heat progressively breaks down thermoplastic molecules into carbon residues, resulting in the formation of black specks. This frequently occurs when a machine shuts down or starts up. This is why the majority of our customers would call us on Mondays with black dot problems!

You'll see that subjecting resins to high temperatures for an extended period of time in excess leads to black specks if you think about it.

At first , let's focus on the source of the issue rather than disassembling screws or using last-ditch techniques to remove specks. Certain consumers might even use detergent and carbonated beverages. I promise! I've seen it happen.

Clean up before you leave is the solution:

To get rid of any resins or additives that are vulnerable to high temperatures, thoroughly clean the barrel. There are no tricks involved; a purging substance of your choice is necessary.

However, you must make careful to eliminate any resin contamination, regardless of the purging agent you select.

A possible black speck is any resin fragment that is still present.

So, after performing the preventive cleaning, should I leave the barrel empty? Never, as you already know, oxidation may also contribute to the breakdown of resin.

The simplest remedy, which we consistently observe to be effective, is to clean and replace the production resin prior to machine downtime.

Which resins are used in their place?

Polypropylene and Polyethylene, are the protagonists of this tale. When dealing with lengthy residency times, PP and PE have established themselves in the industry. They are also renowned for being affordable and simple to clean.

Before any shutdown, fill the barrel with one of these two substances to stop carbonization from occurring during startup.

2. Materials that behave differently at various operating temperatures:

The issue arises when switching between resins that operate at different temperature because at some point, at least one of them will be exposed to the improper operating temperature.

Switching from a low to a high temperature:

It is not as easy as raising the temperature of the barrels, to the next resin levels when production demands that you switch to a material that operates at least 30–40 °C higher than the one you are now using.

Resins like PVC, POM, and SAN resins are particularly sensitive to these changes because they aren't really made for these kinds of working conditions.

The aim is transitioning as smoothly as possible from temperature range A to temperature range B.

Again, employing PP or PE is the answer. At least for materials that operate below 300 °C. High temperature ranges can be tolerated by PP and PE. You can gradually raise the heat to the new material's working temperature by employing any of these items.

I would recommend using universal purging compounds since they can used to displace wide range of resins.

Switching from a material with a high to low temperature range:

Take in consideration as you lower the barrel temperature.

Pollutants in the form of "gels" may have been seen. When the last run product is left in the barrel in a solid condition.

Consider for a moment the Polycarbonate (290°C) residue in a barrel at 190°C. You are right to assume that it will return to its solid condition, which could create challenges when the material changes.

Clean up is the solution:

First, be mindful to remove all the leftovers from the previous production material.

You can start lowering the temperature to the new range as soon as the final production resin has dissipated, at some optimum point you can start feeding the machine with fresh material to begin production.

One statement summarizing the entire reading:

By avoiding exposing your production resins to the incorrect temperatures, you can stop black specks from appearing.

preventive maintenance purge program by involving the recommended of purging compounds can significantly minimize the amount of carbon buildup, remove the chance of resin and/or color cross-contamination, and reduce the need of screw pulls.

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