corliss valve material

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corliss valve material

Post by reubenT » Sun Feb 15, 2015 10:54 pm

Working on a full size engine for practical use. Brass rod in cast iron is what I'm thinking of doing. Probably better than steel valve rods. It'll be 2" thick bolt on heads with valves in head. A 4"x10" cylinder made of a dozer engine sleeve. I've decided on corliss valves for their steam efficiency (lack of long steam ports) and it's capability of fully independent valve action, allowing infinite cutoff control of inlet while exhaust remains constant, and using the governor to control the cutoff. In time this engine may get thousands of hours put on it, will be used to run sawmill, sorghum press, grain mill, pulling a steam hood for grow bed sterilization, as well as general tractor work. (water tube boiler)
What I want to know is about brass. Is 1/2 hard brass machinable? or should I use soft brass. Or which has better wear properties against cast iron?

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Re: corliss valve material

Post by Harold_V » Mon Feb 16, 2015 12:51 am

reubenT wrote: What I want to know is about brass. Is 1/2 hard brass machinable? or should I use soft brass. Or which has better wear properties against cast iron?
Hardness in the sense described isn't really hard. It's just work hardened from being manufactured, and will most likely machine better than it would if it is annealed. For ease of machining, the half hard is a great choice.

Remember, almost all copper alloys can't be heat treated, although some can be. You're not dealing with hardness the same way you'd expect with heat treated steel.

Some bronze alloys (often referenced as brass) can be difficult to machine. They aren't necessarily hard, just tough or abrasive. Amongst them you can count aluminum and manganese bronze.

You might investigate the use of phosphor bronze for your project. It's somewhat tough to machine, but very resilient. If you like its properties but prefer something easy to machine, you can turn to leaded phosphor bronze. For machining, I have long held that it is the most friendly copper alloy known.

I suggest you avoid common brass (360 alloy, for example), which has a high zinc content and may not have great wear qualities.

Hope something I've said here helps.

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Re: corliss valve material

Post by reubenT » Wed Feb 18, 2015 2:11 pm

Thanks, I was looking at 360 assuming it would make good bearing metal. Is 360 too soft? I already got a rod of it to make bushings for a dozer track idler wheel. Now I'm wondering how well that will wear. It runs in gear oil bath. While the engine valves have just a little lube from the inline oiler. (I got some high pressure babbitt metal for the main load bearing on the staam engine shaft)

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Re: corliss valve material

Post by Fender » Wed Feb 18, 2015 3:26 pm

I agree with Harold. 360 brass will work, but it's going to wear out pretty fast. I've seen full-size steam pumps with bronze valve or piston rods, but these have a higher tin and copper content than common brass. Hardness isn't really the issue, it's wear resistance. I've heard it said (tongue in cheek) that brass has the same wear qualities as balsa wood!
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Re: corliss valve material

Post by gwrdriver » Thu Feb 19, 2015 3:26 pm

Seems to me SAE660 bearing bronze would make a very good material for the job.
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Re: corliss valve material

Post by steamin10 » Thu Feb 19, 2015 10:10 pm

Once again, definition. Bronze alloys are copper based. Bronze is majority copper/tin, Brass is copper/zinc. Sheet Copper and alloys are softened by heating and rapid quench cooling from red heats. They then work harden, as any sheet knocker knows.

Dont try to work brass hot, it is hot short meaning it will crumble when force is applied.

The act of silver soldering will effect the hardness of some small parts in brass, making them soft. With really good silver solder, Brass may melt, as it is close enough in temp to make for a bad surprise without good heat control. Beware.

Bronze is a superior material for engine parts, imho, and boiler fittings that are mounted on copper as they will not lose zinc to the boiler waters and weaken.
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