Plastics / Nylons in new gasoline

[quadracer12]

Hello all,

I have a question about plastics and nylons in modern gasoline. I am dealing with some carb floats that are made from Acrylonitrile styrene resin. The material is breaking down and chipping off in fuels with ethanol. Is anyone else fighting this fuel battle? Does anyone know the correct plastic or nylon that can be used in fuel systems? Thanks for the help!

 

[TStaples]

There are many plastics that are currently being used in fuel systems. I can speak from the perspective of fuel injectors, rails, regulators, and such. Various grades of Polyamides (Nylon) are utilized successfully in most situations. I have used 30%-40% glass filled PA6 PA66, and PA12 resins in multiple projects on gasoline and gas/alcohol blends. I have utilized mineral filled Acetels (Delrin) in several gas/alcohol applications. I have also used mineral and glass filled Polyphenylene Sulfides (Ryton PPS) with success when greater thermal resistance or strength is needed. I have also used Liquid Crystal Polymer (LCP) on 2 different projects, that included alcohol fuels (Brazilian market products), but it's very expensive. You would only use it where nothing else works. I have also used a smattering of other resins.

The general order is Nylon or Acetel, then only move up the cost path to PPS, LCP, or some other resin if the application has unusual requirements. The normal starting point for a structural bit would be 35% Glass Filled PA66. I have ended up using that probably 50% of the time, or more.

-Tony Staples

http://www.tscombustion.com

 

[TStaples]

quadracer12,

I forgot to mention that I've never used ASA in a fuel system component. I'm not even familiar with it. A quick search on Matweb indicates that it has some resistance to alcohols, as it is sometimes used for electric razor housings, which could see alcohol residues from facial contact. However, ASA isn't listed as being recommended for gasolines or motor oils, as it can be attacked under certain conditions.

I think you are on the right track; Find another material.

-Tony Staples

http://www.tscombustion.com

 

[quadracer12]

I was looking into PA66 but was unsure about its alcohol resistance and chemical resistance compared to PA12(which I believe has less chemical resistance). Thanks for your help, your expertise is much appreciated!

 

[patprimmer]

Unfilled nylon 6.6 swells slightly in 100% aliphatic alcohols at 25 deg C

It is very resistant to other normal pump fuels, which is one of the reasons it is the base resin used almost exclusively for manifolds.

It would certainly be OK at 10% ethanol and probably OK for E85 if the nylon was glass filled.

I don't have my data for polyesters or acetal, but I expect both will be about the same as nylon.

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.

 

[WGJ]

If you go the acetal route, make sure the grade is a copolymer and not homopolymer.
If your alcohol loaded fuel absorbs any water and then the fuel gets hot, the homopolymer breaks down / becomes brittle.
I'm not a chemist, this is experience on the same component made from the two grades.


Bill

 

[patprimmer]

Co-polymer is somewhat more stable to hydrolysis than is homo-polymer.

Alcohols absorb water.

From memory, Acetal is hydrolysed slowly at 60 deg C and fairly rapidly at 80 deg C, for this reason it can be used for hot water plumbing in regularly replaced items like jumper valves.

It cannot be used for steam irons or kettles as the water gets hot enough to severely limit life.

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.

 

[WGJ]

Pat, I'm beginning to think that you are an Obi-Wan Kenobi and have control of 'the Force' in engineering knowledge.
I kneel before you.

Bill

 

[patprimmer]

Bill

I am both a chemist and an engineer of sorts, actually being a Charted Textiles Technologist which is half engineering, half polymer chemistry.

I spent most of the last 30 years in technical marketing rolls in the field of Engineering Plastics. In a totally isolated country with about 20 million people and a very large geographic spread, that means you need a large product pallet to be viable. Not an an Obi-Wan Kenobi, just a naughty little boy. Seriously, the question hit directly on my exact field of experience.



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.

 

[WGJ]

Yo Pat, respect, as the contemporary language of youth has it.

I certainly respect all-rounders, it's a dying art.
I sit among software types, electronic types and mech boys and, sadly, many of them do not transcend their self-imposed boundaries.
Engineering, for me, has been a life of curiosity. I'm not especially skilled at anything but know bits about all sorts (I think). Have a good Sunday.

Bill