Verify plastic material through testing 2

[bjpil]

Hello,
I need some advice on how to verify and spec out, through testing, a plastic part that will reside in an oil pan. What are some of the typical testing for something like this? I am currently just looking at testing a material and not the part. If it survives the initial testing then I will move on to a prototyped part and look at durability. I initial just want to find out if the material will hold up in an oil pan environment.
BJP

 

[patprimmer]

Nylon will stand up

There is a long history for use of nylon in direct contact with engine oil in such things as timing chain tensioners, tappet covers (rocker boxes).

To test, place the material, with some stress applied, in the oil at appropriate temperature and time to ensure survival.

Do this for various types and brands, new and used oil, as different brands have different makeup and impurities, and used oil has engine blow by as a contaminant.

Measure change of dimension as well as change of properties.

Do a short test at maximum temperature expected, and a longer test at typical temperatures expected. Better still heat cycle the test.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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[bjpil]

Pat,
Thanks for the tips and your examples of nylon, it gives me more confidence that I am going down the right path. But since I have very little experience in plastics I need a better reference frame to help define the testing.

When measuring for dimensional change I assume that using a micrometer to measure thickness is good enough, I should not see large changes due to the oil bath. Correct?

What is the purpose of applying stress to the part in the test suggested? Is this to capture creep due to temperature or does the oil somehow effect the part more when it is being stressed in an oil bath rather than if it were in air?

Last, again because of my limited knowledge, will I see any major change in material properties due to the bath and how much change could I see? I assume you are suggesting tensile testing to check material property. I am kind of skeptical that there will be a distinct change because I thought plastics have large scatter in material properties due to fiber orientation and the oil bath effects may be hidden within this scatter.

Thanks again for your help, as you can see I really could use it to get a better handle on plastics.

BJP

 

[patprimmer]

BJP
You are wise to be cautious. Many engineers and designers experienced and skilled in traditional materials have problems when first adapting to plastics in that, they fail to take full advantage of some unique characteristics, but also fail to understand some limitations as plastics can be very different to traditional materials.

Two things can happen to the size of plastics in hot oil:-
They can absorb some oil and swell.
They can be annealed or stress relieved and shrink and/or warp.

A micrometre can measure swelling as it will be consistent, but stress relieving might be inconsistent and lead to warpage which is harder to measure.

With glass fibre reinforced plastics, there is a substantial difference in properties depending on glass orientation.

The glass fibres will orient themselves in direction of flow, but the degree of orientation will be dependant on fibre length, section thickness, turbulence in the melt and injection speed.

Some plastics resist some solvents when tested in a relaxed state, but are cracked by the same solvents when stressed.

Once good moulding and test conditions are established, the results of tests should be reproducible, as the glass orientation will be consistent. You should test along and across the flow direction to be sure.

The magnitude of the change will depend a lot on the type of polymer, the makeup of the oil, and the time and temperature of the test.

I would test for tensile, elongation, creep, izod, flex modulus and dropped dart impact, if I wanted a very clear picture, and I had no prior experience to draw on.

There is a pool of knowledge of plastics in contact with automotive oils in the engine, in applications like those already mentioned.

Regards
pat pprimmer@acay.com.au
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[rnd2]

BJP
It would be useful if you were able to describe what the part is required to do in terms of desirable thermal, mechanical, as well as electrical properties. This will have an important bearing on material selection.

 

[bjpil]

rnd2,
Thanks for the interest. It is going to be a oil splash guard to help direct the oil. It will be held in place by four or five bolts. I have not figured out what temperatures it will see but I assume from -50 F at cold weather start up to about 250 F at max engine temperature. It is not going to be a structural part but needs to survive vibration and acceleration forces due to its own weight. As you can see I am still in the conceptual stage of this design and could use some help to better define the requirements. I hope this helps.
BJP

 

[patprimmer]

Problems that I see that need to be addressed are:-

Fatigue from force of oil splashing at very high speed.

Creep relaxing the tension on the bolts.

Nylon inlet manifolds accommodate the creep at the bolt holes by moulding in metal inserts to take the force.

Regards
pat pprimmer@acay.com.au
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[rnd2]

You said: "I initial just want to find out if the material will hold up in an oil pan environment."
According to Schweitzer, candidate materials in terms of being resistant to motor oil are:
>>>Metals>>>
Carbon steel, copper, 304 ss & 316ss.

>>>Plastics>>> (value in brackets denotes tested OK up to temp in degrees F.)
Chlorinated polyether (penton)(250F)
Noryl (190)
Nylon 6 (200)
Nylon 11 (200)
Nylon 66 (200)
Polyester isothalic (160)
Polysulfone (200)
PVDF (Kynar) (250)
Ryton (250)
Vinylester (250)
TFE (Teflon) (470)

In addition to the above there are thermosetting plastics in particular re-enforced phenolics and derivitives thereof that are easily capable of handling motor oil in excess of 380 deg. F. as well as load.

Sweitzer has this to say about corrosion of nonmetallics:
"Plastic materials are attacked by solvation or a chemical reaction. Solvation is the penetration of the plastic by a corrosive element that causes softening,swelling and ultimate failure. Plastics,in contrast to metals, do not exhibit a corrosion rate; usually they either completely resist attack or deterioate rapidly. Because of this difference in corrosion mechanism the two types of notation were established.
Since corrosion is a function of temperature,the tables reflect this by indicating the suitability of each material at varying temperatures. When a material is indicated to be unsatisfactory at a specific temperature, it is also unsatisfactory at all temperatures above the one shown. A blank in the chart indicates that no data is available.
There are many plastic formulations,which may vary from manufacturer to manufacturer. An indication in the chart that a specific material is suitable for use with a specific corrodent does not mean that the formulation used by all manufacturers will be suitable. This must be verified with the specific manufacturer.
A word of caution should also be given regarding temperatures. The table only shows the resistivity to corrosive attack at various temperatures. Before the material is specified for use, the physical properties at the operating temperature must be examined to ensure that the material has the proper mechanical strength for the application."

Hope this helps.

 

[bjpil]

Pat and RND2,

Thanks for the help, you have both given me more to think about.

The table RND2 provided kind of makes me question the Nylon that I was thinking of using. The injection molder quoted a "Wide spec 30 glass nylon 6/6", whatever that means. The injection molder also proposed injecting a gas into the part to reduce the material needed. With what you have provided makes me even more cautious because now there are small pockets in the material that may absorb the oil and maybe cause more problems.

Thanks,
BJP

 

[patprimmer]

30% Glass Filled Nylon 6.6 with a good heat stabiliser system will work fine at well over 200°F

Data from Bayers literature suggests:-
Long term service temperature without load
Heat stabilised 30% GF type 6 >200°C
Heat stabilised 30% GF type 6.6 >250°C
High load heat deflection temperature
Heat stabilised 30% GF type 6 200°C
Heat stabilised 30% GF type 6.6 250°C

There is extensive precedent on heat stabilised 30%GF 6.6 being used in inlet manifolds, by Totota, Honda, Nissan, VW, BMW, MB, GM, Ford, Porsche, Subaru, etc etc etc.

Same for radiator header tanks.

Same for carburetor parts and fuel filters and fuel pumps.

I have even seen an engine run with a 45% GF heat stabilised Nylon 4.6 valve spring retainer. This is a heavily loaded part in contact with engine oil, and at a considerably higher temperature than the oil on the exhaust valve.

I have personally used non reinforced, but graphite and molybdenum di sulfide filled nylon 6.6 as gudgeon pin retainers on race car engines that sustained outputs of 500 hp for 12 hour races.

Molybdenum di sulfide filled nylon 6.6 is used extensively as a timing chain tensioner bearing surface.

Noryl will solvent stress crack in the real world where some fuel always dilutes the oil as the engine runs.

I would not use wide spec for this application.

I would use a brand name, copper iodide heat stabilised, 30% Glass Filled, Nylon 6.6 for this.

Brand names might be Zytel by DuPont, Durathan by Bayer, Ultramid by BASF, Vydene by whatever Monsanto calls themselves these days, Akulon by DSM, Grilon by Emserwerk, or Duralon by Duromer.

Companies like Atofina, Asahai, Mitsubishi, Hulls, Celenese, Snia, also have or did produce these materials.

I should declare that I have a vested interest, as I currently sell some materials for Duromer.

There are many more, but you can do a google search or get OEM spec from auto companies as easily as I can.

Gas injection can be suitable if the design calls for it, and the moulder is so equipped, and really knows his stuff.

I would be a bit suspicious of a moulder who recommends wide spec, when you already have concerns.

My advice would be to use prime, and concurrently test a few different batches of the wide spec material.

I would not consider a wide spec material where the heat stabiliser package spec was in question.

Regards
pat pprimmer@acay.com.au
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.

 

[bjpil]

wow, thanks

BJP

 

[dwightdixon]

The big resin producers such as Dupont and Bayer should be able to give you certification which automotive spec. testing their material have passed. I sure GM, Ford, and Chrysler have an engine oil pan specs. No sense reinventing the wheel.

 

[bjpil]

dwightdixon ,

Thanks for your input but as I have found over the years, many specifications are 1) over written, 2) may not include new material, 3) may lump too many applications into one large specification or 4) they may be poorly written which all may results in unnecessary cost increase to the part. Also, it is an engineer’s responsibility to ask questions to get a better understanding of a problem and to learn from it. If you are not learning something new then you are just regurgitating back someone else’s answer that may no longer apply.

BJP