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Best Conrod Materials?

Best Conrod Materials?

(OP)
Hello, I'm new to this site. I hope someone may be able to help me.  

I'm designing conrods for an 320hp, 4 cylinder, 2.0 litre engine.  I'm basically looking for a material to use.  Money is no real object, I just dont really have a direction to go with in the investigation.  I have been told that EN24V steel alloy could be good, but I really want the lightest possible material that can get.  I thought about titanium alloys?  

If anyone has any suggestions for me, they would be much appreciated.  

Thanks

RE: Best Conrod Materials?

I'd buy Carillo rods, and spend my money on cylinder head work, etc

RE: Best Conrod Materials?

Titanium rods will give the best strength to weight if cost is no problem.

I believe that Crower offer titanium rods.

Carillo are excellent rods for normally aspirated and moderate boost engines, but are not recommended for high boost, as "H" beams buckle more easily in compression than do "I" beams.

Regards
pat   pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
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RE: Best Conrod Materials?

3
Two things to keep in mind when designing Ti con rods are stiffness and surface engineering.  Ti only has ~ 1/2 the elastic modulus of steel, so deflection of the crank end has to be considered.  One estimate is that the reduction in mass from a well-optimized steel design to one in Ti is only 12-20%.  The most popular alloy is Ti-6Al-4V.  Go to Matweb or alloy producers like Timet or RMI for more information on properties.  Search this site as well.

Regarding surface engineering, Ti has a tendency for fretting and galling, due to its low inherent wear resistance.  High end con rods that use titanium are coated, some times with flame-sprayed Mo in order to improve its surface characteristics.  Other coatings are possible.

RE: Best Conrod Materials?

I am having Titanium connecting rods machined as well. The above post from TVP has me wondering what coatings would be optimum.

The machinist is top notch so I know the quality will be perfect. The engine in question is a destroked, over square  DOCH V6 with a rod ratio of 2.14  I wan't it to handle a lot of RPM and power. It will be running twin turbo's with boost levels above 35 psi. The car is being built specifically for quarter mile use. I am looking for over 1000HP in this setup.

Any info on the coatings or other considerations for the connecting rods would be appreciated.

RE: Best Conrod Materials?

2
"I am having Titanium connecting rods machined as well."

be sure to have the surface cleaned and bead or shot blasting might not be a very bad idea. Machining tends to cause large amounts of surface defects that can lead to failure.

RE: Best Conrod Materials?

Is polishing ti a benefit at all for a rod?

RE: Best Conrod Materials?

Polishing will always help fatigue life. Although you have to be sure that you are not rolling material over small cracks or notches.

RE: Best Conrod Materials?

Thanks, that is a good thing to watch for I may not have considered. Any thoughts on a coating combined with the polishing, or is that a bad idea. I am still also curious if anyone can say what coating would be optimum.

RE: Best Conrod Materials?

Polishing after shot blasting/peening can be helpful in reducing surface roughness, which minimizes local stress concentration during use, while maintaining the beneficial residual compressive stress.  Regarding coatings for titanium, this is definitely a specialized area, and there are only a few vendors that can properly apply them.  I would start with Bodycote Thermal Processing in Santa Ana, CA or a company that specializes in thermal spray like Sulzer Metco.

RE: Best Conrod Materials?

Thanks TVP, that is very helpful. Probably the last question I have on this is the use of a floating Titanium pin, they are coated as well, I am guessing the correct way to do this would be with a bronze bushing or maybe some better material. I have read on here about using silicon bronze and Trojan as well as Beryllium bronze for valve guides and seats, would one of thos e materials also be better for a pin bushing?

RE: Best Conrod Materials?

as far as coating goes what about having them anodised? It helps a lot with surface wear. I don't know how much friction polished anodised Ti would have but it should wear much beter than plain Ti. (and it's such a nifty looking purple)

RE: Best Conrod Materials?

2
The forged ones are 4340 chrome moly, Titanium can be good, a tip if you are having your machined could be to use a titanium top with a steel bottom, then make the bottom .25mm wider on each side.

As for Carillo, they make I-beams. Cunningham also makes some of the best rods around, and also do titanium, you should give them a try. The russian company I bought my valves from might offer some Ti rods in a month or two, ill keep you guys updated if you are interrested, so far they are talking of around $200-$250 per rod, but they use their own titanium, which have improved properties over the commonly used 6Al-4V, also do excellent coatings.

RE: Best Conrod Materials?

http://www.cunninghamrods.com

Had a quick look, the Russian Ti has a elastic modulus of around 139-142 vs +-114 for all other grades available, this could mean a considerably lighter rod than previously possible.

RE: Best Conrod Materials?

ZoRG,

You stated that you bought valves (titanium) from a Russian supplier. Did you take delivery before the Bush administration imposed the tariff on Russian titanium products? I believe this tariff went into effect in early November 2004.

If you could elaborate on this I would be thankful. We are looking for a new supplier of titanium parts. The US companies are overpricing the material without justification as compared to the world wide abundance of titanium currently.

Will

RE: Best Conrod Materials?

Does anyone have "facts" on titanium's ability to cycle?  I think everyone knows that aluminum connecting rods are used for short term applications and then the aluminum con rod is discarded. How many different titanium alloys are available? How many different heat treatment processes must be done to the titanium to bring the material to its highest strength? I believe the best titanium alloy only has a tensile strength of 170,000 psi, while 4340 300-M alloy steel has a tensile strength is excess of 240,000 psi. That means to me, that if I use titanium, to get the strength of steel,dimensionally my rod has to be bigger and possibly heavy.
 Also, even tightening the connecting rod bolts can be difficult because they will want to gall to the titanium. I have seen the plasma moly spray come off and I have seen microwelding on titanium rods. I believe the F1 engines use DLC coatings to prevent galling.
 Carrillo has a Gen IV steel that is light as titanium, yet has the charateristics of steel, according to "Race Engine Technology" magazine editor Ian Bamsey, issue 008 dated June 2005.
 Porsche used thrust type bearings on their titanium connecting rods, this way there was never a chance of microwelding or galling. I believe Pankl made the connecting rods for Porsche.
 Then there is another issue of grain structure. Are the titanium rods going to be forged, or cut from billet? Obviously, forging titanium is going to be even more expensive, but that is how to get the maximum strength.
 I think too many people think titanium is just one alloy, and they are not familiar with the many different alloys and heat treatment processes involved to obtain the strength. Having a rod made of titanium is no guarantee you have a strong and reliable connecting rod.
 How do you test titanium for cracks and fatigue, you can not use MagnaFlux testing.
 Aerospace landing gear is all made of 300M steel, and they could use titanium if they wanted. Why is titanium not used in this most demanding application?
 I know Porsche has had suspension springs made of titanium and even drive axles made of titanium, but I know of no one making a crankshaft of titanium. I suspect titanium has some unique but limited qualitiies.
 How about some knowledgable engineers commenting on this very important subject?

RE: Best Conrod Materials?

So many questions!  

Aircraft are built with a very keen eye on cost/weight ratios.  It's cheaper to use 300M than a Ti alloy for such large parts as landing gear.  But a good Ti alloy gear would be lighter for the same strength, but somewhat larger.

You need to keep in mind that the strong Ti alloys are ~75% of the strength as high strength steel, but only half the weight.

RE: Best Conrod Materials?

Hi Metalguy; thanks for your response.
 I would love to have answers, that is why I am in this forum.
 I believe that 300M is used because it is much less notch sensitive. I think titanium is very sensitive to scratches, which would result in cracks and then failure. Also, 300M can be  easily inspected for cracks using MagnaFlux process.
 If titanium is 75% the strength and 50% the weight, then for equal strength the titanium part is only 33% lighter. Are all other properties of titanium equal to high strength steel?

RE: Best Conrod Materials?

Stiffness (elastic modulus) is less with Ti.

Best regards,

Matthew Ian Loew


Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Best Conrod Materials?

Hi mloew; would you mind explaining more on the subject? I get the impression you know more about titanium. If the tensile strength is less then high strength steel and the stiffness is less then high strength steel, then a connecting rod in titanium would have to be dimensionally more robust to be equal with high strength steel. If the titanium connecting rod was dimensionally the same as the steel counter part it would not have the tensile strength or the compressive strength, is that correct? Thanks.

RE: Best Conrod Materials?

Gary

All materials have some unique but limiting qualities, otherwise we would use one material for everything from drinking water to rocket fuel.

Have you tried a google search on titanium, titanium alloys, titanium properties, titanium connecting rods etc.

Magazine editors are not always qualified nor experienced engineers. They often have arts degrees. They may have business degrees. If they are unscrupulous their opinions may be swayed by their advising customers.

If F1 use titanium in rods, but not cranks, I guess they do it for a reason, that reason being overall balance of properties vs overall balance of properties required, like bearing qualities of the journal.

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.

RE: Best Conrod Materials?

Gary,
Ti can be examined very well via dye penetrant, esp. fluorescent (Zyglo).  While they are not as sensitive as mag., a good examiner will find cracks if they are present.

I'd have to look it up, but I'm not sure that Ti alloys such as the popular 6/4 alloy are more sensitive to notches than 300M.  Another factor in fatigue cracking is corrosion, which is a factor in nearly all fatigue.  Ti alloys are FAR more resistant to CF than steels, depending on the actual envirnment, of course.

RE: Best Conrod Materials?

Dear PatPrimmer; Yes I have done many Google searches on titanium and have researched the subject for years. The Acura NSX uses titanium connecting rods, the new Corvette street car is using titanium connecting rods, the new Porsche GT3 street car is using titanium connecting rods; but that does not tell me anything. Reducing the recipricating mass will reduce the loads on the rod bearings, this is good. Reduced recripricating mass can provide better endurance and possibling an increase in the engines rpm.
 I believe this thread started by JB83 asking about what material would be best used for connecting rods. I think we could discuss H, I, and A beam designs too. We could discuss the advantages and disadvantages of many different materials aluminum, titanium, and steels. So far I have only read about opinions and not facts. I believe alot more goes into manufacturing a connecting rod then just the choice of material. I believe the heat treat processes and the shot peening have a very important role.
 If anyone knows more about the titanium alloys and the different manufacturing processes for titanium I think it would be a valuable contribution to this forum.
 I would like to thank everyone in advance for contributing, I find this to very a very interesting subject. Thank you.

RE: Best Conrod Materials?

One "fact" is that the strong Ti alloys have a fatigue curve similar to steel and unlike Al alloys, in that they have an infinite life if the stresses, etc. are below some value.

RE: Best Conrod Materials?

Gary

What exactly are you trying to do.

On the one hand you seem to have a considerable but incomplete collection of data, both anecdotal and real, on the other you seem confused as to what to do with it.

Are you trying to decide whether or not to use titanium rods in a particular engine, or on a range of engines, or are you contemplating making them.

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.

RE: Best Conrod Materials?

"I believe alot more goes into manufacturing a connecting rod then just the choice of material. I believe the heat treat processes and the shot peening have a very important role."-Gary

Gary-

Here's how I would go about a material/process selection in view of your statements.

0)Determine goals. IE A connecting rod that will NEVER fail is possible but wont reach the goal of high RPM operation. One that can handle 25,000rpm is also possible, this one could be cost porhibitive though.

(The above is a complex way of saying: Cheaper, Stronger, Longer lasting, lighter. Pick 2)

1)Decide on the material. (the reason I put this first is that almost all the other details hinge on this.)

2)Design the part. This would take into account specific stiffness, specific strength, geometry, stress concentration, etc...

3)Determine manufacturing method. This must take into account the goals in 0 the material in 1 and the part design in 2.


A good example is a part I helped do significant development work on. Many materials are compatible with the design and production method. We had to decide on an optimum though. After much effort 17-7CH900 was chosen. Yes its more expensive than 301, lower strength than top quality carbon steel, less conductive than Alloy360, lower fatigue performance than 7C27Mo2; however the compromises made in the material selection have given us a part that works in ninety odd percent of the applications I've seen. Yes there is always one thing better and we could say that Elgiloy would make a phenomenal connecting rod. It costs >$160/lb though. Let alone forging it, processing it, heattreating it.

nick

RE: Best Conrod Materials?

Great input Nick.

I hope that is what he is looking for.

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.

RE: Best Conrod Materials?

Hi Everyone;  The original forum post from JP83 asked a very general question about which material could he have connecting rods made and what did people in this forum know about the titanium alloys. Personally I think it was an excellent question. There are many materials, many processes, and many heat and surface treatments used to produce connecting rods. There are now some new steel alloys that have exceptional strength to weight values, it would be invaluable if a few material engineers could tell us about these alloys.
 My point about titanium is that there is more to titanium then most people know. Some connecting rod manufactures forge their titanium, which is the very best way to manufacture a titanium connecting rod. Some manufacturers are making titanium connecting rods from extruded or billet plate. Titanium in its best alloy and best forging, still only has 70% of the tensile strength of a high strength steel. Titanium in its best alloy and best forging has half the modulus of eleasity of high strength steel. Just from the tensile strength and modulus it should be obvious that titanium in it absolute best alloy and forging is NOT equivalent to high strength steel.
 In a race engine, where the titanium connecting rod can be replaced often, titanium could reduce the weight of the connecting rod by 25%. If the titanium was the same dimensions of the steel rod, the weight savings could be as much as 40%.
 Are you going to accept a machined, billet titanium connecting rod, or will you want one of the better forged alloys? How many companies have forging dies, and how many can forge titanium? The real question becomes, do you want to pay $10,000.00 for a forging die, plus the cost of machining, heat treating, and surface finishing?
 You can purchase a high strength steel rod for $300.00 each, the cost of a titanium specialty rod could easily cost over $1000.00 each. In the end, the ti rod may be lighter, but you will have to replace it more often.
 One of the better titanium alloys is called Ti-6246 (Ti-6Al-2Sn-4Zr-6Mo) originally developed by Pratt & Whitney over 35 years ago, and is available from Timet. There is a newer Ti alloy called Ti-200, maybe someone can obtain some info on this alloy?

RE: Best Conrod Materials?

Why do you think Ti rods would have to be replaced?  I already told you that there is a stress level below which Ti doesn't develop fatigue cracks.  A good Ti rod can be both lighter and stronger than a good steel rod, the only exception *might* be if the steel were something like the 350 alloy used for *centrifuges*.  The Ti rod would be larger in cross section than the steel, so you can stop being concerned with E.

RE: Best Conrod Materials?

Metalguy, thank you for your responses, I am beginning to understand the subject much better. I think we would both agree that the weight savings would not be 40%, titanium vs steel? In order to keep the big bore round and within tolerance, the mass would have to be larger. I think you would agree that having a titanium connecting rod made by an "aftermarket" supplier is no guarantee the rod was designed or manufactured "below stress levels"?
 Based on my research, I think a titanium connecting rod, manufactured and forged from the better alloys could have a weight savings of 25%, but it would not have the tensile strength of a similiar 4340 steel rod.
 My only point is that purchasing titanium rods that are lighter, is no guarantee that you are receiving a connecting rod that is equal in strength to steel. If the weight of the ti rod is 40% less then the steel, then the steel rod was over engineered, or the ti rod was under engineered.

RE: Best Conrod Materials?

Here are several good papers on the design and mechanics of conrod design.
If you register you can get all the data you will vere need for a lot of conrod materials in Fatigue Database, just below these articles.

http://www.steel.org/autosteel/bar_rod/index.htm

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