rx7n3wb

Can you answer why others with them haven't been reporting a problem such as yours? The only difference between theirs and yours was how you handled the situation.. how can you still justify your actions instead of questioning them..

wpgrexx

why not post the last email you received from Mark? I am not trying to be an ******* here at all. I just completely disagree with your opinion on cermet.

timrxmotors

Not so much my opinion,but an account of what happened.I'm not so interested in what happened between me and JHB,but more interested in why the coating failed.I know I had the housings reground,that job was first class,I know the coating was then much thinner,but the same thickness as the original chrome,so why did 0.19mm of coating wear away?It is wrong to say I screwed them up by finishing the job,just is not the case.
Possibly affected by fuel or oil? Not as hard as the chrome?What is the make up of cermet A?

Curtisleeyoung

maybe I missed the parts list but what parts exactly did you have coated?

rx7n3wb

Assuming you measured correctly, I can see why you'd be upset but now we're all just left wondering what might have happened if you let JHB fix the problem, would it still have failed? What facts do you have that the reground housings came out first class besides that they were now factory spec and smoother to the fingers.. when it comes to a specialty service such as cermet which I haven't seen done mainstream, I would leave it to the ones with experience

timrxmotors

I do agree and I wonder what would have happened if JHB had corrected it.No hard facts on the reground finish,apart from it was smoother,and to factory spec,just left wondering why it failed.How can regrinding it affect it's hardness.The apex seals were almost perfect,so I don,t think it was because they had a friction problem with the coating.
JHB would have removed the coating,reapplied it,then ground it back,all I did was ground it back,can't see the difference whichever way it was done.It did save me having to send the housings back to Canada,they had them 2 months the first time,and if I had sent them,I really did not think I would see them again.

rx7n3wb

JHB has been lacking with the info but I do recall in your other thread them mentioning a certain finish that they leave on the coating which was not the same as your smooth reground housings.. the true effects of the finish may or may not have been the cause.

eViLRotor

iTrader: (2)

I don't see one account of failure enough to convince me not to try these coatings, considering all the upsides they may have.

I have a set of new housings in my engine now, and I do see myself using the Cermet coating on then, should I need to rebuild.

Maxthe7man

I dont think it really matters what thickness it was reground, Timrx is asking why the coating is worn off, the regrinding and out of spec aside, who cares what he had reground to, the point is it started to come off...
Timrx says his housing were new, so they were not oil contaminated, but my point was that the housings mazda did, were neither nitrided nor chromed originally which could affect the ability of the ceramic to adhere on post nitrided and chromed parts.
The other aspect is that since ceramic is an insulator,with steel seals, it will remove one source or heat dissipation through the seal face to the housings, probably not an issue with ceramic seals, but definatly one with steel apex seals..Max

Cheesy

The whole PS serries of coatings are pretty interesting, they tend to take along time to run in though ie the seals wear very quickly for a long time compared to some other plasma sprayed coatings (even silicon nitride).

You used the PS coatings as an example that ceremet coatings are good so to speak and most are but you cant really use that to say all ceremet coatings are good. Due to the way they are applied and the different materials available there are thousands of materials that could be classified as ceremets all having different mechanical properties.

As for the friction of the coating this is usually more dependent on the oil that is used (assuming a constant surface finish).

And finally a line that comes up often in my work: Wear is a system parameter not a material property

Trueblue707

I agree with what you say. PS200 is probably not what JHB uses, but mark has said it is very simillar. My point is, ceramics are being used everywhere in high stress/high performance situations and doing better than what was being used before...
http://www.carbideprocessors.com/saws/intro.htm

I'm realy glad to see so many people willing to discuss this issue, rather than reject it alltogether. Ceramics are working in so many different aplications, many of them involving much more stress/temperature than the rotary engine.


What can I say for tim? From what I can deduce it appears that his housings were not prepared properly to begin with. I think max has a good point about adhesion being affected by contaminants and nitrating. I believe JHB grinds the housings to flaten them if they are worn AND to remove the nitride coating to insure proper adhesion. If they were improperly ground or not ground enough, then there could still be unevenes or nitride left. The coating is too thin to "fill in" unenvenes and it wouldn't realy matter if you could/couldn't get it flat if there was some nitrating left on the housing to begin with. If the nitrating realy does affect adhesion then I would expect something like what happened to tim's housings.

It appears JHB has been able to solve the problem(whatever it was), as there are no other reports of this happening.

I have to say that if I was to purchase brand new housings I would not have them cermet coated. The whole idea is to take what is used and make it better than new at a cost less than buying new. Just my 2 cents.

timrxmotors

It was only the rotor housings I had coated,not the side housings.The pic earlier was of a side housing scored by the cermet coming off the rotor housings,it has taken on the colour of the cermet.
Has anyone any idea of the make up of cermet 'A'?,or the PS200 coating?

Cheesy

PS304 which is probably very similar to PS200. The PS304 coating is applied using a powder with the following composition 60%wt NiCr, 20%wt Cr2O3, 10%wt BaF2/CaF2 and 10%wt Ag.

On the issue of bonding, if the JHB coating is plasma sprayed or uses a similar process the surfaces would most likely be machined/ground and then grit blasted to remove surface contaminants and give a surface that the coating can mechanically key to, becasue sprayed coatings are relativly thick and soft the nitriding on the side plates would have minimal effect on anything. I would be concened with the thickness of the coatings on the housings (if they are infact only as thin as the original chrome).

Trueblue, thats what i hoped you meant. For examples of ceremets being well and truely accepted in other areas Nikasil would be clasified as a ceremet, most (or maybe just alot) cutting tool inserts are ceremets as well

Trueblue707

Oops. I should have read that thread mentioned earlier. I see now the coating looks as though the coating hasn't come of in the kind of pieces I was thinking of.
Those strange colors in the water jacket don't appear to be mineral deposits.



It looks like it suffered from some extreme heat, especially when compared to what it looked like before.



That housing looks beautiful, but something made it fail. The cermet housings I received from JHB are no where near as shinny as your housing looked. I'm sure they made them that way for a reason.

Here is my theory of what happened to your housings.

When you polish something in certain cases you could in fact be making that part more prone to heat buildup from friction. Think of it this way. A regular tire is designed with a tread in order to keep it from loosing traction in wet or otherwise slippery condition. But what happens to the same tire on the race track?
It actually looses traction at high speeds and or hard cornering.
Now look at a race tire. It has no tread and is nice and smooth. It also has fairly poor traction on anything else other than dry pavement. Now, what happens when this tire is used where it was designed for? It provides far better traction at high speeds and or hard cornering. Now why can't the treaded tire provide more traction than the race tire? I'm sure everyone knows.
IT HAS LESS SURFACE AREA IN CONTACT WITH THE PAVEMENT THAN THE RACE TIRE!


Here is my theory of what happened to your housings.

The only way the apex seals can get lubrication is by having the oil injected or mixed into the fuel. Once the oil enters the chamber it doesn't have much time to get to where it needs to go(especially at high rpms). Much of it goes right out the tail pipe. The happy molecules of oil that do accomplish there mission get into seal groves and onto the rotor housing surface. In order for the oil to lubricate well, it needs a place to hold on to.
That is why the chrome Mazda uses is porous and why JHB has a specific finish for their cermet coatings. The pores in the chrome or cermet act as little capillaries holding the oil in place, thus reducing surface contact as the apex seal slides over.
If the surface were to be polished there wouldn't be enough porosity in the finish to capture and hold the oil and an increase of surface contact and friction would result.

That is probably what happened with your housings.

Trueblue707

The oil getting onto the surface was not clinging as well and being swept away by the apex seal due to the greatly reduced amount or pores for the oil to get in and hold on to.
As the rpm's increased, so did the heat from the friction caused by the two very smooth and sparsely lubricated surfaces of apex seal and housing.
As the temperatures approached the heat limits of the cermet coating it began to self lubricate, but couldn't lubricate enough to lower the temperatures.
Again, because there weren't enough "holes" for the lubricant vapor particles to be trapped in.
The friction and temperatures at that point were probably more than enough to begin a galling action on the seals. The seals began to chip, sending pieces throughout the engine which then caused more damage to the seals and scratched up the housings.

Again, just my two cents.

timrxmotors

Thanks for the input.The apex seals weren't chipped at all,they looked fine.Lubrication was 100:1 premix.
Engine ran fine for 700 miles,until it went on the rolling road.Coolant temp stayed at 86C.I put in 106 octane race fuel,first run I had 349rwhp,then went downhill after that.Something was happening to the coating.I found this on Aus Rotary about the R26B:-
''Chrome-carbide based cermet,applied by detonation gun spray.Providing stable cermet coating is important to secure engine reliability,and of utmost importance in preventing exfoliation of the coating during driving.Regarding exfoliation,various processes were investigated to solve variation factors.''
So is it possible that the race fuel reacted with something beneath the coating,exfoliation occurred,made more possible because the coating was thinner,turning it into carbide grinding paste?Everything inside the engine was coloured.
I thought I had exactly the same coating as the R26B engine,but cermet A certainly doesn't look like a chrome based material,it has a stainless steel appearance.What is it?

BLUE TII

iTrader: (9)

I believe how the coating material is ground to spec may affect its adhesion as well.

I seem to recall Scallywag mentioning if during the grinding process there is too much heat built up it will affect the coatings adhesion to the liner.

IAN

iTrader: (3)

Keep up the good info I called JHB and talked with them for about half and hour.

I'm extremely interested in this since I have 6 housings that could use this treatment. (and the fact that mazda no longer makes housings). If this works I guess I really only need one set since they can refinish them at a discount if you happen to scour the cermet during an apex seal failure.

The only answer I got concerning rotor clearance was that these housings are returned back within mazda specs.

I only know of one person running these coatings and his motor is still fine. Another person will be running it as well.

I only heard of two people with concerns regarding this process.

Apparently jhb has a race car that has been using cermet A process for 6 years without issues.

This all sounds promising. I've been told that they are raising the prices in october.


Now to figure out what type of apex seals I should go with.

Ian

Trueblue707

Cheesy allready said what he thinks is close to what JHB uses. I believe he knows far more about cermet composition than I do. I will say that maybe instead of NiCr for the greatest ingredient Cr3C2 is used because JHB says there coating has carbide in it, just like (maybe exactly?) the cermet Mazda used.

I just found this cool site with magnifide samples of different thermal coatings.
(It has a lot of info on the process and methods of aplication as well!)

http://www.gordonengland.co.uk/pmg21.htm



I would be very interested in seeing some more pics, especially of the exhaust port side of the housings. Did you put the factory 2mm bevel back around the opening? (or at the very least on the closing edge of the port)

I don't want to be sounding like a lawyer, but you did say on now's thread...
When I said chipping I wasn't thinking of anything larger than 1mm. Are your seals reusable or aren't they. Being "scored" and being "fine" are two very different things to me.

Please don't take all this offensively. I'm just one of those (sometimes annoying) people who are always too particullar or meticulus about most things.
I get reprimanded alot for taking to long do do stuff or making it more complicated than it really is. (like my posts for example)

timrxmotors

when I first looked the apex seals did appear scored,but once stripped,they were very smooth.Suggests that it wasn't the apex seals alone affecting the coating.
I have seen housings scored badly with different apex seals,but this wasn't like that,it had worn off and it appears it wasn't hard enough to damage the apex seals,but hard enough to score everything else.

Kenku

Kinda sorta offtopic, but anyone know if it'd be feasible to get these cermets to bond to, say, aluminum?

Cheesy

They can be made to bond to aluminum very well, especially if a bond coat is applied to the surface before the functional coating. the bond coat i have used is a twin wire Ni-Cr coating with a bit of Al this gives an exothermic reaction (gives off heat) on the surface. Alot of production piston engines have a coating sprayed directly onto the aluminium bore, these sort of processes are relativly common

Kenku

Eeeeexcellent. That solves so many problems I was having with some of my wackier ideas...

mattmaclennan

Hey Cheesy, hows your coating? Tim is looking at a few poduction processes and materials next week. Looking forward to seeing some results! Anyone else have any results from coated housings

Cheesy

I havent got or tried any of the JHB coatings, im testing coatings (and seals) for the pivotal engine for my masters in mechanical engineering. From the sound of it the PS304 coating may be similar to the JHB stuff but it may also be completely different. In the conditions encountered in the two stroke engine the PS304 wears out the compression seals pretty qucikly until it has run-in and it will wear out a couple of sets doing this, although the higher temps in a rotary may mean it will work better, the coating that has given the least wear on the seals is an iron, iron carbide, iron oxide molybdenum plasma sprayed coating