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Old 07-14-2014, 09:31 PM   #1
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Super Plastic: Risers, Manifolds, Heat Exchangers, etc.

Sooo... Why are there not yet available any long lasting...

"Super Plastic": Risers, Manifolds, Heat Exchanger - etc.???

Too costly to manufacturer still? Not good enough plastics still??

Just wondering. Thought there might be a plastic guru on TF!
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Old 07-14-2014, 10:11 PM   #2
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No plastic guru, but I'm thinking industry would see them long before the recreational boating market. I haven't seen them.
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Old 07-14-2014, 11:23 PM   #3
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I am a plastics guy of 35 years but even still I can only apply my experiences and use them to logically speculate as to the answer.

Short version is " Thermal Conductivity "

Long version is ... While we can rarely confirm why something does not exist the temperatures are the likely cause here. The temperatures we see on the outsides of aluminum and iron manifolds or risers are much different than those on the inside before the water becomes effective at heat transfer and are too high for plastics to endure. I say this well knowing that aluminum risers exist and potentially could melt 100 to 200 degrees below what are high potential EGT's but in aluminum's case it's thermal conductivity properties help to pull those temps down enough to protect it in this situation and keep the casting from heat soaking to the point of melting and allow it to work. Same reason there are no aluminum exhaust manifolds on cars. The thermal conductivity of plastic is just no where close to either iron or aluminum and thus not suitable that close to the combustion temperatures as it would rapidly erode internally from the extreme temperatures.

Another consideration is aluminum being $7.00 ish per pound and iron even less is a relative bargain as compared to some highly engineered plastics at more than $20.00 per. pound these days. If it was to be attempted it would require high end expensive grade resins and may even negate all the advantages other than weight.

I am more curious why we have not seen internal coatings that prevent corrosion and make these components last as if they were made from stainless steel.
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Old 07-14-2014, 11:39 PM   #4
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Originally Posted by Doug Doty View Post
I am a plastics guy of 35 years but even still I can only apply my experiences and use them to logically speculate as to the answer.

Short version is " Thermal Conductivity "

Long version is ... While we can rarely confirm why something does not exist the temperatures are the likely cause here. The temperatures we see on the outsides of aluminum and iron manifolds or risers are much different than those on the inside before the water becomes effective at heat transfer and are too high for plastics to endure. I say this well knowing that aluminum risers exist and potentially could melt 100 to 200 degrees below what are high potential EGT's but in aluminum's case it's thermal conductivity properties help to pull those temps down enough to protect it in this situation and keep the casting from heat soaking to the point of melting and allow it to work. Same reason there are no aluminum exhaust manifolds on cars. The thermal conductivity of plastic is just no where close to either iron or aluminum and thus not suitable that close to the combustion temperatures as it would rapidly erode internally from the extreme temperatures.

Another consideration is aluminum being $7.00 ish per pound and iron even less is a relative bargain as compared to some highly engineered plastics at more than $20.00 per. pound these days. If it was to be attempted it would require high end expensive grade resins and may even negate all the advantages other than weight.

I am more curious why we have not seen internal coatings that prevent corrosion and make these components last as if they were made from stainless steel.
Doug - Thanks for informed "plastic" answers. Pretty much as I figured. Your end thought is a good question! - Art
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Old 07-15-2014, 12:23 AM   #5
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I wonder about ceramic or carbon composites.

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Old 07-15-2014, 12:54 AM   #6
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Quote:
Originally Posted by Doug Doty View Post
I am a plastics guy of 35 years but even still I can only apply my experiences and use them to logically speculate as to the answer.

I am more curious why we have not seen internal coatings that prevent corrosion and make these components last as if they were made from stainless steel.
Doug,

Beginning in the late 90's Mercruiser started using a ceramic coating on certain cast iron manifolds and risers. More recently, they developed a 'dry-joint' between the manifold and riser, which eliminated the most frequent failure point in the system. Recently some aftermarket suppliers started offering 'e-coating' in some of their replacement systems. This is supposed to be almost as good as the factory ceramic coating at a considerable cost savings.

Either way, these later coated systems last longer than the original painted cast iron components.

It would be interesting to find out if the earlier engines can be upgraded with the newer ceramic components and dry-joints when replacing the entire systems.

Before my trawler Boomarang, I owned and restored a classic Donzi 22 and learned more about Mercruiser exhaust than I ever wanted to.

Great subject Art and Doug.

Larry
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Old 07-15-2014, 01:01 AM   #7
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Too bad about the plastic - you could buy a 3d printer and make your own.
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Old 07-15-2014, 01:11 AM   #8
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I wonder about ceramic or carbon composites.

Tom
In conjunction with Sandia Nat Lab developments my company delved into ceramic discussions regarding thin consecutive hoops of ceramic materials to withstand 1800 degree f on a continual basis of 60 second temp changes from 500 degrees f back up to the 1800 degrees. This product needed to operate all sunshine hours and last for many, many months at very least. Ceramics were the only material that came close to satisfying this need. In the end the project was shelved due to funds and other items. That said, it seems clear ceramics offer great capabilities to withstand immense temperatures and fast temp changes.

Reason I began this thread mentioning plastics is due to their ease of configuration for manufacturing designs as needed.
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