Impreg

[PierreR]

I gotta ask if anyone has tried impreg to extend the life of engine manifolds and goose necks? Impreg is a system of submerging a casting that has leaks into a hot 400 deg F vat of low voc plastic and pulling a vacuum on it. The air comes out and the plastic runs in when the pressure is released. The plastic then sets up. I have seen it used to comply with military specs calling for a guarantee of no leaking castings.
I plan on changing hoses on both of my engines and might just blast and impreg the castings as a good measure.

 

[twistedtree]

I gotta ask if anyone has tried impreg to extend the life of engine manifolds and goose necks? Impreg is a system of submerging a casting that has leaks into a hot 400 deg F vat of low voc plastic and pulling a vacuum on it. The air comes out and the plastic runs in when the pressure is released. The plastic then sets up. I have seen it used to comply with military specs calling for a guarantee of no leaking castings.

I plan on changing hoses on both of my engines and might just blast and impreg the castings as a good measure.

What sort of temps can it handle?

 

[PierreR]

The foundry that I am still associated with makes castings for Volvo, Mack and JD. Will handle normal engine temps for sure as it is used on engine cooling system parts. Not sure what temps exhaust manifolds get to in marine applications. I am unsure of the failure temps, but they are well above 300 deg F.

 

[twistedtree]

The foundry that I am still associated with makes castings for Volvo, Mack and JD. Will handle normal engine temps for sure as it is used on engine cooling system parts. Not sure what temps exhaust manifolds get to in marine applications. I am unsure of the failure temps, but they are well above 300 deg F.

Sounds fine for intake parts, but I doubt exhaust. 700F+ is common.

 

[RT Firefly]

Greetings,
Interesting question. I looked up phenolic materials used for bonding brake shoes/pads (first thing that came to my mind) and best I could quickly find was max temps around 600F. So there ARE materials (liquids, initially) that will handle elevated temps. Whether 600F is enough is ??? and whether this sort of material would actually work for the intent is also ???.


Edit: Ah Mr. tt. Beat me to it....

 

[PierreR]

I have to really ask on the actual temperatures. The Impreg process might work at close to 600 deg F. My brother works with it all the time.

 

[C lectric]

If you take a look at vessels equipped with EGT guages you will commonly see temps of 500o F plus.

My own run easily shows just 500oF. If I push it very much the temp will climb quite quickly to 700oF plus.

I used to run my engine at 750oF as a max.

However I know some hard charging fishing guys will push to about 900oF as the max.

YOur idea may be good for an intake mfld, or other low temp. applications but even easily run engine exhausts will climb into the 400oF + range.

If you have a turbo equipped engine you may foul the turbo if the sealer burns.

Now to be clear my engine has a coolant cooled exhaust mfld. THe exhaust system is Dry Stack but the exhaust is coolant cooled. My EGT sensor is right at the end of the mfld. literally so I think it is representative of the gas temps to be expected. The coolant of course carries the heat away to the whole cooling system yet I still see temps of 500oF +

Do any of the vehicles you do this for use EGT guages for monitoring?

I am not saying to not do it as I simply don't know but caution you to realize that boat mflds. and exhaust systems water cooled or not, often run much higher temps than many realize.

 

[TowLou]

600 degrees I think is still to low for anything exhaust. Just the other day a 300kw diesel cummins genny with a egt guage was showing that with no load at 1800 rpms. Egt can get much hotter to 1300 degrees on a normal run.

 

[PierreR]

I am fully aware that the exhaust temps can be high but the sealant is meant for water sealing not exposed to exhaust and does not see those temps unless there is a coolant circulation problem.
the applications I am familiar with are for castings carrying coolant such as thermostat housings and water goose necks. I have no experience with this in water cooled manifolds or water injection elbows and that is why I posed the question of " Is it being used somewhere I don't know about".
I know it will work for general cooling castings that have sprung a leak in which no part of them is exposed to exhaust temps.

 

[PierreR]

On my last boat I use to set the controllable pitch propeller for maximum efficiency by EGT near the exhaust valve. Right around 1,300 deg. The manifold was water cooled and the coolant was below the boiling point of the coolant mixture. The Impreg would fail somewhere in between the coolant interface and the hot exhaust but would the layer of remaining Impreg be enough to have a functional casting? I don't know, and that is my question.

 

[Gdavid]

In addition to the potentially damage due to temps exceeding what the plastic can handle, I would be concerned that thermal conductivity would be much lower for the plastic compared to the cast iron.

 

[twistedtree]

600 degrees I think is still to low for anything exhaust. Just the other day a 300kw diesel cummins genny with a egt guage was showing that with no load at 1800 rpms. Egt can get much hotter to 1300 degrees on a normal run.

Ditto on the temp range. Depends on the engine, but some are normal in the 1100F and up range.

 

[PierreR]

Keep in mind here that in Impreg, the inside of the manifold is not coated in plastic. The only plastic is trapped in the porosity causing the leak so there is a very minor amount of plastic remaining. This plastic is very expensive but actual deposit of plastic is very small. To your visual eye you would see no difference between a casting that leaks and one that has been through the Impreg process. The conductivity is unaffected. Keep in mind that new engines that you currently buy may very well have castings that went through the Impreg process. It is often OEM specified to guarantee that the castings are watertight.
In short, some of you are already running under this process without knowing it. I am only exploring the idea for fixing castings that have sprung a leak rather than scrap them.
This process is totally acceptable and not new. My only question still remains. If this process is out there in the repair business instead of only in new parts, I would like to know rather than recreate the wheel so to speak.
This process would not work for large leaks.

 

[Lepke]

600°F is the very low end of exhaust temps. If the engine has a turbo, you can at least double that.

 

[twistedtree]

Keep in mind here that in Impreg, the inside of the manifold is not coated in plastic. The only plastic is trapped in the porosity causing the leak so there is a very minor amount of plastic remaining. This plastic is very expensive but actual deposit of plastic is very small. To your visual eye you would see no difference between a casting that leaks and one that has been through the Impreg process. The conductivity is unaffected. Keep in mind that new engines that you currently buy may very well have castings that went through the Impreg process. It is often OEM specified to guarantee that the castings are watertight.
In short, some of you are already running under this process without knowing it. I am only exploring the idea for fixing castings that have sprung a leak rather than scrap them.
This process is totally acceptable and not new. My only question still remains. If this process is out there in the repair business instead of only in new parts, I would like to know rather than recreate the wheel so to speak.
This process would not work for large leaks.

It's a really interesting process, and I can imagine a lot of places where it would be a good fit. In fact, I had a new cast brass pipe elbow (3/8") that was leaking through the casting, and this seems like a perfect process for repairing something like that.


The down side is that in all my years working on cars, boats, etc., that's the only casting leak that I have encountered. Maybe that's because everything has already been impregnated and I didn't know it? I definitely have encountered cracked exhaust manifolds, but it's unclear to me whether this process is suitable for repairing a crack? For example, will it prevent the crack from getting larger? I think this is why people are focusing on exhaust temps - because that's pretty much the only place where casting leaks develop - and it's cracks, not porosity. So in terms of an aftermarket opportunity to apply this process, the key question is whether it can be used to repair exhaust manifold cracks, both structurally and temperature tolerance.

 

[GoneFarrell]

My only concern is the plastic thermoplastic or thermoset? I suspect the former. If so, will it remelt at the bath temperature of 400 F, and if it does, will it remain in place?

Years ago I did similar on porous aluminum robot castings. Put the casting on the deck of a helium leak detector. Sniffed out the leaks, brushed epoxy cut with acetone on the spots, viola! A hard vacuum capable robot casting.
Brief searching I cannot find a vendor for the service you seek.

Also, my experience is exhaust rot is largely on the hot inside and contaminated with salts.

 

[sunchaser]

Impreg epoxies have been used in all sorts of casting applications for well over half a century, back to casting failures found in in WWII factories in fact. If you've got a high volume metal casting chances are it has seen the impreg process. Foundry specs, and impreg epoxy use, are set by both the foundry and the customer to not only avoid casting failure in the field but to avoid rejection during the QA/QC protocols.

There are college courses and specialty classes (Metallurgical Engineering) in this science. That is when and where I learned about this application. BTW, not all "offshore" casting suppliers routinely use this process. If a foundry does not offer impreg on a standard basis it is usually off the bidders list.

 

[PierreR]

Sunchaser, I don't remember covering it in college. Metallurgical Engineering/Chemical Engineering MTU 78. I retired at 44, then consulted part time for several years.

 

[sunchaser]

PR
Where I went to college it was mentioned as part of the extractive metallurgy curriculum and brought in in foundry classes. Very brief mentions though as best I recall. Once I got into large high pressure autoclave operations metal porosity issues were sometimes dealt with via resin “treatment.”

About 15 years ago when touring large casting operations in China impreg resins were mentioned too in combatting mold and casting porosity.

Thanks for bringing the subject up. If one is really curious on the subject I’d guess a very large number of light metal die casting manufacturers such as your relative mentioned would indeed be a wealth of information.

 

[Northern Spy]

My only interaction with impreg, was to radiograph random cast pieces we purchased to ensure impreg was NOT used. Mind you these were high temp use specialty castings in which we had poor quality offshore substitutions made without our knowledge, and porosity was a contributing factor to shortened lifespan.

If this is a mass produced part, how do you know they haven't already been impregged?

It sounds as if you are solving a non-problem. But I get the desire, if it is available and relatively inexpensive.

 

[Capt8888]

Ceramic coating?