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Brass at elevated temps
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Posted by: cramog

01/19/2004, 18:20:43

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I'm working on a prototype of a scale model Porsche engine. My (senior) colleague suggests we make the valves from brass. Stem diameter is 1mm. Steel works o with a scale V8 (on my page) but with this one we're aiming at more authenticity.

My gut instinct is that these wont stand up to cylinder head temps but need to convince my colleague with facts.

Anyone give me some pointers on the application of materials, brass in particular at elevated temps.


Glenn.






Modified by Administrator at Fri, Jan 23, 2004, 07:11:56

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Re: Melting points
Re: Brass at elevated temps -- cramog Post Reply Top of thread Forum
Posted by: RandyKimball
Barney
01/20/2004, 19:26:03

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Melting Points ...

Brass: 1825 - 1616 depends on the alloy
Nickel: 2651
Molybdenum: 4748
Tungsten: 6098
Titanium: 3272
Tin: 449
Carbon Steel: 2500
Chromium: 2939
Aluminum: 1220
Cast Iron: 1990 - 2300
Bronze: 1841

Realize that an enternal cumbustion engine valve actually gets burning gasses across the seat. Of high importance is the combination of melting point and thermo conductivity, valves in a well designed engine transmit heat well via the valve guides to the air or water heat sinks. (I don't have the heat indexes at present.) This is why we see various stainless steels with cores of substances that pass heat quickly in valves.
Of interest would be 15-5PH stainless steel if I were making a model engine, very tough and of good heat index both melting point and transfer wise.

-randy-




The worst idea of you lifetime may be the catalyst to the grandest idea of the century, never let suggestings go unsaid or fall on "death ears".

Modified by RandyKimball at Tue, Jan 20, 2004, 19:29:42

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Re: Melting points
Re: Re: Melting points -- RandyKimball Post Reply Top of thread Forum
Posted by: cramog

01/20/2004, 21:24:29

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Thanks again Randy, always seems that you jump to my rescue.

Case anyone else is interested, I learnt that the term brass encompasses a number of different grades and alloys based on copper and zinc (knew that). A nominal 85% Cu with 15% Zn alloy (commonly called red brass) has fairly poor elevated temperature strength-- it loses a substantial portion of its tensile strength in the range of 300 to 500 C. The same goes for cartridge brass (70% Cu with 30% Zn). I was advised to use some stainless steel (Type 304, Type 316).

I'm familiar with cored valves, spent many hours as an apprentice making a centre punch from a Pratt & Whitney valve - hard as hell even at red heat. It is still in my tool box (45 years on) and gets sharpened about once a year.

I'll try to get hold of some 15-5PH as you suggest. Think you have my email from encounters. Let me know if you're interested & I'll send you a copy of the plans when I'm finished .

Once again thanks.

Glenn






Modified by Administrator at Fri, Jan 23, 2004, 07:11:04

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