Bakelite degradation in oil

[kclim]

Was after some information on the above topic. I have a plastic component which I suspect is bakelite, which has been operating in a mineral oil environment for 20+ years (temp ~70°C).

The component has failed with minimal deformation. I'm trying to determine whether degradation in service has lead to a reduction in properties.

My understanding is that bakelite may be attacked by organics (oil), which may dissolve the bakelite and leave it more susceptible to rupture.

What tests can be performed on the failed piece to determine whether (and how far) degradation had occurred?

Thanks in advance

 

[rodneybennet]

I am sure whether bakelite is chemically corroded by mineral oil (i.e. by some sort of corrosion front). However, the lighter species of the mineral oil mixture will solve in the bakelite resin. This will soften the polymer, which will reduce the mechanical properties. The rate of softening will depend on the diffusion rates of the lighter species in the mixture. Moreover, the temperature is an important factor here - substantially above ambient.

Although I do not know the exact processing conditions, mechanical loading, possible reinforcements, fillers etc., the 20+ years sounds reasonable (if we do not consider weathering conditions, such as moisture and UV exposure).

The bakelite resin can be tested according to ASTM D570, using fit-for-purpose sample dimensions and temperature condititions.

Note that current physical-chemical simulations are so able to deal with the above problem - in a much more efficient manner.

Also find more information on:

http://www.composite-agency.com/materials-forum.htm

Regards,

 

[kclim]

Thanks for your reply.

It turns out that the material isn't bakelite, but probably a glass fibre reinforced ABS. My understanding is that these composites have some inherent brittleness.

The query was regarding a failure analysis, in light of the above we're taking a different approach and looking at other components.

 

[rodneybennet]

Hi kclim,

Indeed, ABS with glass reinforcements is a sligthly different story. ABS it resistant to aliphatic hydrocarbons, but not to aromatic (such as benzene, toluene, ethylbenzene, xylene) and chlorinated hydrocarbons. ABS shows stress cracking in the presence of certain organic compounds.

The above may be an important factor.

Regarding intrinsic mechanical properties: impact and toughness of ABS are outstanding. Impact resistance does not fall off rapidly at lower temperatures. Stability under limited load is excellent. However when impact failure takes places, the failure is ductile rather than brittle. Water has little effect on the mechanical properties of ABS.

 

[rodneybennet]

By the way, my first reply contains several errors, due to a serious system hick up. Here is the correct version:

I am NOT sure whether bakelite is chemically corroded by mineral oil (i.e. by some sort of corrosion front). However, the lighter species of the mineral oil mixture will solve in the bakelite resin. This will soften the polymer, which will reduce the mechanical properties.

The rate of softening will depend on the diffusion rates of the lighter species in the mixture. Since diffusion rates are raised exponentially by temperature, here the system temperature - being substantially above ambient - is an important ageing factor).

Although I do not know the exact processing conditions, mechanical loading, possible reinforcements, fillers etc., the 20+ years sounds reasonable (if we do not consider weathering conditions, such as moisture and UV exposure).

The bakelite resin can be tested according to ASTM D570, using fit-for-purpose sample dimensions and temperature condititions.

Note that current physical-chemical simulations are so able to deal with the above problem - in a much more efficient manner.

 

[patprimmer]

Glass filled ABS will have very different properties to unfilled ABS. The glass greatly reduces the elongation at break and also leads to brittle type failure.

ABS is attacked by many solvents as mentioned above and is subject to oxidation at elevated temperatures.

There are many grades available and the properties vary considerably because of significant variations in the properties of the base resins and because of significant variations in reinforcement packages from grade to grade.

Diffusion rate is a mute point after 20 years as it will be approaching equilibrium at any reasonable temperature in a much shorter time frame than 20 years.

ABS would not be my choice for a part that was to spend a lot of time immersed in oil.

Cotton fabric, wood flower filled phenol formaldehyde (one trade name Bakerlite) is commonly used in machine parts subject to contact with oil. It has very good long term thermal and bearing properties and has exceptional rigidity and dimensional stability. It has low elongation at break even when new.

For a part to endure very long life at 70 deg C immersed in oil, I would seriously consider a very well stabilised glass filled nylon or Polyester, but the choice will depend on many factorsalmost none of which are declared in the OP.



Regards

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[Demon3]

Yes, ABS would be a terrible choice for all the reasons Pat mentioned. It's unlikely your part is ABS, if it was it would have failed much earlier. It should be easy to see if it's ABS by FTIR as the cyano group has a distinctive absorption peak.

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

 

[rodneybennet]

Regarding the previous quote: "Diffusion rate is a mute point after 20 years as it will be approaching equilibrium at any reasonable temperature in a much shorter time frame than 20 years":

This one may be to bluntly. It all depends on the frequency/period/cycling of the actual chemical exposure. If there was a recent change in e.g. pipeline operation, the chemical exposure and resulting penetration depths (especially of the lighter species), can be one of the root causes for material failure.

Regards,

 

[patprimmer]

It would need very infrequent exposure for short times with cleaning between exposure to not approach equilibrium after 20 + years at about 70 deg C.



Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[rodneybennet]

Patprimmer,

Now, I definitely agree with you!

Thanks.

Rodney