How to reduce scrap during colour changes

by | Injection, Pet Preform

Reduce scrap colour change

Every morning, after I grab my morning tea, I open my laptop and I start answering calls and emails from all over the world with the same query:

How can I improve the results of my colour changes?

Below, I point out the proven tips I have shared for many years, where my customers have answered back saying; “Thanks! It worked!”

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!

2. The most used technique: Planning your production from Light to Dark Colours. 

You have probably learnt this one in your first job at the factory and used it a lot.

Dark resins will cover up lighter pigments faster, making them less visible in the final product generating less scrap. This technique certainly works, but it’s not always easy planning production using this approach. If you need to adjust colour on the go, try the other colour tips below. 

Reduce scrap colour changes
The most used technique: Planning your production from Light to Dark Colours. 

3. Using a purging compound decreases scrap rates. All the time, everytime.  

No matter how optimized I have seen colour changes procedures using virgin resin, purging compounds will always take less time and less scrap to remove the last colour resin. 

I believe that the problem of deciding to use a purging compound is to determine whether or not it is a cost-effective solution. 

If this is your concern, check out this updated cleaning cost guide of purging compounds. 

FREE Download: Purging Compound Price Guide

purging compound guide

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

Yes, we have been there. Sometimes you clean the barrel very quickly and start feeling confident that you will resume production soon, But then: Colour streaks start coming from the mould and 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. 

Which techniques do you use for colour changes? reach out for sharing your tips or to seek support. 

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