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#4448179 - 07/03/17 09:57 AM Brake fluid effects on plastic, seeking advice
rurockn Offline


Registered: 07/31/09
Posts: 3
Loc: Dallas, TX
I work for an injection molding company and one of our customers tests requires a small part to be submerged in DOT3 brake fluid for X amount of time, rinsed off, and then destructively tested. We have not changed out process or raw material. Our raw material has been tested multiple times in recent months and is pure and meets all requirements.... yet suddenly we are failing testing after the DOT3 test. Many people and labs have been involved and cannot seem to nail this down. I have used this website many times in the past for my vehicles and thought, well, maybe someone out there can help out with this issue.

The idea I keep coming back around to is maybe some DOT3 additives have changed over the past few years? For many years we used the same DOT3 brake fluid, we had dozens of small bottles that would last about a month each. Suddenly when we are buying new DOT3 fluid, we are failing testing. Any thoughts or ideas if the fluid today could be more aggressive than a few years ago?

Note: the plastic is polycarbonate polyester blend.

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#4448200 - 07/03/17 10:24 AM Re: Brake fluid effects on plastic, seeking advice [Re: rurockn]
bmod305 Offline


Registered: 06/23/08
Posts: 265
Loc: Minnesota
Are you using any slip agents or colorant in the mix? Any changes in the suppliers? Are you using a moisture tester before molding? Cleaning of barrel and screw any different this round? i.e different purging compounds. I'm the Production Manager for a molder in MN. We mold some parts that are used as clutch master fluid reservoirs using dot 3, 4, and 5 brake fluid with no issues.

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#4448362 - 07/03/17 01:35 PM Re: Brake fluid effects on plastic, seeking advice [Re: rurockn]
Boomer Offline


Registered: 09/19/08
Posts: 1934
Loc: Pennsylvania
Just a couple of thoughts from a retired organic chemist.
1. Any chance that the composition of the polyester or polycarbonate has changed or that polymerization catalyst might ne present that was not present in the past? Your description almost sounds like the polymer is losing molecular weight (maybe by transesterification with the polyethylene gylcol).
2. Take some of the DOT 3 fluid and add a few drops to water and check the pH. Do you have any of the old Dot 3 fluid to use as a comparison? Is the new stuff more acidic or basic than the old stuff?
3. Is there any indication that the part is undergoing some type of polymeric crystallization during immersion? Does the polymer test strip whiten during immersion? If so, did it used to do this?
4. While this is simple, have you checked all of the temperature and strain/stress measurement systems? Are you really pushing/pulling/bending with the same force that you used to apply? Have you calibrated the test machine(s) with a known material?
5. Extract the DOT 3 material with pure hexane and take a sample of the hexane after the extraction and run a gas chromatographic analysis on it. Again, if you have an old sample for comparison, this would be even better.
_________________________
2013 VW Passat TDI SE, 56,350 miles Castrol Professional VW507 5W-30
2017 VW Golf All Track 14,5000 miles Castrol Professional VW505 10W-40

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#4449029 - 07/04/17 05:32 AM Re: Brake fluid effects on plastic, seeking advice [Re: rurockn]
Boomer Offline


Registered: 09/19/08
Posts: 1934
Loc: Pennsylvania
Bmod 305 talks about moisture and this is a good point. Brake fluid is VERY hygroscopic. Is the new material tested for moisture? Were the cans left open? Really worth checking.
_________________________
2013 VW Passat TDI SE, 56,350 miles Castrol Professional VW507 5W-30
2017 VW Golf All Track 14,5000 miles Castrol Professional VW505 10W-40

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