Material Foaming

[cjcoop]

A customer of mine is complaining of a nylon 6 material that is 40%MG is processing at 460 degrees and when he goes to the normal temp settings between 520 - 560F he gets poor surface and the material is foaming out a white foam. I have not seen this happen (I'm going there in the morning) but my first thought was it was wet. My second thought was it was contaminated. Does anyone have a thought on this or maybe have seen this happen. They do say they ran a competitive material in the press at normal temperatures.

 

[patprimmer]

Without being here to see what the temps really are and the particulars of the mould and part, 460 to 480 deg F are fairly typical melt temperatures for Nylon 6.
If it is wet, it should already out gass at 460 deg F

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Pud]

Sounds like it's very damp. Foaming due to contamination is unlikely unless it's mixed with acetal or PVC, but if so, the workshop would have been evacuated by then! (formaldehyde or HCl gases)

Nylon 6 is thermally stable up to 300C for short periods.

A material rep once recounted a tale where one of his customers was complaining of the same thing - it turns out they didn't even have a drier in the company! They just always used it out the bags, which are usually ok to use for non-critical stuff, unless they've been around a long time.

Imho, nylons should be dried as a matter of course prior to moulding: 80-100C for 4 hours. If it has been dried, check that the drier(s) is working!

If the MG suffix means mineral+glass, then even longer drying will be required as the mineral content (if mica) takes ages to get the moisture out.

Cheers

Harry

 

[Demon3]

Wow, I thought the MG might stand for magnesium hydroxide flame retardant, in which case I can totally understand the foaming. Assuming it means mineral/glass filled then I agree with my two "colleagues".

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[cjcoop]

Thanks. I understand those are typical temps for the nylon but i need to convince the customer there is nothing "wrong" with running at these temperatures even if they are use to running in the 520F- 540F range. I still feel it has to be a moisture issue. I had them send me a sample from there dryer and measured it here with a KF and got .183%. Thats still pretty wet to me. I really like to see that closer to .10 or below when processing. I will try and get "true" temperature readings when I'm there to be sure there machine is giving correct readings.

 

[cjcoop]

Yes, sorry I was not more specific but it is mineral glass.

 

[cjcoop]

Thanks for all the responses so far. Any other thoughts are appreciated.

Harry, you would not believe how many times I have been to customers who do not dry nylons or feel there is not a need to dry them. My job is very busy through the summer months and 70% is moisture related.

 

[cjcoop]

Thanks for all the responses so far. Any other thoughts are appreciated.

Harry, you would not believe how many times I have been to customers who do not dry nylons or feel there is not a need to dry them. My job is very busy through the summer months and 70% of it is moisture related.

 

[patprimmer]

When I did tech support for nylon, probably 80 to 85% of moulding problems were moisture related, being wet granules or dry mouldings. Most of the rest where ring check valve.

The only nylon 6 or 6.6 I ever recommended NOT to dry was Akulon when it came in twin packs. It was guaranteed to be less than 0.015% water from memory. Drying it with conventional equipment often raised the moisture level.

If you are in a tropical climate you need a dehumidifier to dry it. Blowing hot wet air on it increases moisture.

0.1% is not really dry enough for a critical moulding. You need about 0.07 or 0.08% especially when te nylon content is diluted by filler.

As someone else mentioned, minerals can hold quite a bit of water and can release it at different temperatures to the nylon.

If it is water in the nylon only,I would expect it to froth even at the 460 melt temeratures. The mineral might explain the no froth at 460 but froth at 520

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[cjcoop]

Just to let everyone know final outcome on this. I went to customer location with "known" dry material and the first shot was great at there normal processing parameters. They do not have moisture analyzer and did not know true moisture on material.

 

[Demon3]

Thanks for the update and happy ending. Getting the end of the story helps the site and to verify that the advice really was of use.

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[alpha0]

I am looking for moisture analyser. Is there anyone who is selling it as a 2nd hand. VS