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How to Reduce Colour Change Costs with a Purging Compound

by | Injection, Pet Preform

Believe it or not, we have spent the last 10 years working with one main goal in mind: Helping injection molders reduce scrap in the most simple way possible. 

We have been approaching production managers stating: 

“ We can help you to reduce scrap during material changes with our purging compound”. 

The answer is almost always the same one: “Prove it”. 

Therefore, we have been put in front of hundreds of machines around the globe. As you could imagine, we are always asked to do the most difficult and stubborn material change they have!

In this article, we want to share all the learnings from our own and our customers’ experience when looking to reduce scrap during material changes. 

The role of thumbs: Use a purging compound. 

I know you have heard this many times, but seriously, almost every time using the right purging compound reduces scrap rates. Purging compound manufacturers spend years developing formulas that clean better than resins.  Try them, use them, adapt them to your material changes.

If it’s a matter of whether or not using a purging is the cost effective solution for you, you can review  our updated price guide of purging compounds.

Black specks produce an increase on scrap rates: Use the right shutdown and start-up procedure to avoid them. 

Discarding pieces after a long shutdown due to the presence of blacks is something very common but not hard to achieve as soon you tackle down the cause of them. 

Check out how to avoid them by focusing on the two main causes of blacks specks during production. 

Another “oldie” cleaning hack: Using a lower MFI resin to push contamination out the machine. 

Commonly used before injection molders discover a suitable purging compound. 

Try using a higher density material when purging. You will get a slightly higher dragging force caused by the lower MFI resin, that could help you to save a couple of shots. 

  1. Grandpa’s Colour change tip: Increase the temperature could help to remove contamination faster.

Our “technical guy” said, he learnt this from his grand grand father, but we are not sure whether it is true or not. The fact is, that this has been a common practice in the industry for ages. For difficult colour changes, we recommend increasing the temperature of the nozzle, tips and hot runners to the maximum allowed by the resin. Think about it, by doing this, you will decrease the viscosity of those residues stuck in low flow areas, making them easier to be pushed out of the system. Give a try!

  1. To do colour changes efficiently. Clean the hot runners properly.

Yes, we have been there. Sometimes you clean the barrel in two minutes and feel confident that you will resume production soon but then: Colour streaks coming from the mould won’t go away for ages. 

We have customers that were producing even more scrap when cleaning the hot runners compared to the discarded material when cleaning the barrel.  Purging compounds suitable for the hot runners have been available for you for a good while now. Using the right purging compound will help you to save unnecessary scrap during material/colour changes. 

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