steel choice 1

[kenre]

I an designing a small high performance 2 stroke engine.

For reliability and longevity reasons i will be using a steel bearing housing in place of the cast alloy housing normally used, less thermal expansion and higher stiffness to ensure greater life of the bearings.

Full hard O1 steel can be used, but i would like to avoid the heat treatment and internal grinding needed.
So looking for something with a bit of strength and exellent machinability.

A couple of alloys i have looked at are P 20 (M200), M315 and
4140 Ultimate, Bohler uddeholm steel.

Any other suggestions? or real world machining experience?
First few manual machined, and then to CNC once design is completed.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[CoryPad]

Do you require high hardness for wear resistance? Otherwise, why are you considering tools steels?



Regards,

Cory

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

 

[kenre]

Cory, there is no wear at all on these parts, the are a bolt on housing, with a bearing pressed into each end. total length about 50mm. I was looking at tools steels purely for the strength factor, to help the bearings keep there shape, as the Aluminium housings distort under engine firings, leading to uneven wear and early failure of said bearings. Al housing also need large press fits to hold the outer races, to eliminate outer ring movement due to thermal expansion differences. This upsets the C3 bearing clearances.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[BobM3]

Unless you are worried about yielding the material, strength doesn't help much with distortion. Modulus is the key factor and that is constant for all steels.

 

[TVP]

kenre,

How many of these things do you anticipate manufacturing in a day/month/year? What would be the final dimensions of the housing?

 

[dbooker630]

What about prehardened 4140 - trade names like Sheffield #10 (Maintenal). Our toolmakers and millwrights use a lot of this without additional heat treating. If you can machine a Brinell of 269-321 HB without difficulty this may be your choice.

 

[EdStainless]

I would expect that and medium carbon steel in the Q&T condition would work the same. Can you find 1035 heat treated? This shouldn't be too difficult to machine.
The stiffness and thermal expansion will not be any different for various alloys or strengths.
As long as the temper temperature is above the max operating temperature all should be fine.

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[kenre]

Very helpful! to everyone!

At this stage required quantities is an unknown, minimum of 12, max......?
I can source 1030, 1040 and 1045 bright steels.

Any one of these must be much harder than Cast and heat treated 601 Al im sure.

I will be doing more reading on the modulus, very interesting!

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[Tmoose]

As a first cut, if the aluminum housing thckness was 5 or 6 times thicker than the race it should be "stiff enough" to maintain the bearing geometry.

Sometimes bearing housings that hold the bearing cantilevered let the bearing tip under heavy loads, and most bearings don;t like that. Similarly, Typical 2-stroke Built-up (pressed together) cranks are not very stiff, and may respond to firing and inertia loads by flapping like a butterfly, putting the main journals 'way out of alignment. Any signs of fretting on the crankpin where it is pressed into the crank halves?

Any signs of detonation on the spark plug or piston? Ball and roller bearings can't take impact loads very well. I'm not sure if the wrist pin, con rod, or main bearings would be likely to object first.

 

[kenre]

Tmoose, These engines are single cyl 15cc glow ignition for model race boats. Sort of similar to the common Radio control Aircraft engine, but much more powerful. Disc or drum induction, Steel conrods, tuned pipes, 50% nitromethane, 20% oil, the rest methanol. around 7 horsepower at over 20,000 rpm. Wide open throttle racing for over a minute, bouncing in and out or water.

I have one engine with a steel bearing housing where the bearing is over 3 years old, and still like new. Normally bearing are toast after 12 months.

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!

 

[kenre]

Also, these engines run on the verge of detonation, sometimes light detonation is unavoidable for max performance.

I gather there is no steel that woulod be better or worse than any other?

http://www.retallickeng.com.au

Was told it couldnt be done, so
i went and did it!