Plate Grates

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kcameron
Posts: 266
Joined: Wed Aug 17, 2011 4:23 pm
Location: Syracuse New York

Plate Grates

Post by kcameron »

I've heard a few good things about the idea of plate with hole pattern for coal grates instead of the sandwich of bar stock as the grates. What I don't know is the suggested hole size and spacing. One key point I've heard is that the top hole is smaller than the hole in the bottom. The shape of the hole through the plate should be either stepped or chamfered so the top small size is very shallow before it gets wider. This was so anything falling through the hole had very little area to grab on the way through before the hole became bigger and it would just fall though clean. I recall some even doing this with slots mixed with holes too.

The grates I'm replacing are the flat bar type. Yes they are stainless steel, but the nuts and bars holding them together were not and most have melted considerably over time. Also for this engine I've got to make them into three parts to fit through the firebox door. Each about 2 inch wide. The old were fixed in the firebox and only allowed tilting them to clean out.

As for construction methods, the flat bar is simple enough if you have a tig welder at hand. But if you have a CNC then the plate isn't that hard either.

I'm looking for hints on what to consider about using plates for this. Thickness, materials, hole design, sizing and spacing are clues I'm looking for. I know enough about the normal flat bar grates.
-ken cameron
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Glenn Brooks
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Re: Plate Grates

Post by Glenn Brooks »

I tried drilling some SS plate to use as a grate years ago. It was an utter failure. The holes Didn’t offer near enuf airflow to feed the coal bed or draft properly. Probably the only way to know what size holes you need is do the math to determine total air flow over through the grate in relation to cylinder size or heating surface of the flues. Generally speaking, you’ll likely end up with some percentage around 50% or greater for open space in the overall grate area for airflow. You might be better off milling slots in the plate, rather than drilling holes... and consider using stainless plate, to resist the temps better.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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Builder01
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Re: Plate Grates

Post by Builder01 »

Ken, I know you have seen my grate. The bars are tapered in cross section and are stainless steel. It is a welded assembly. This material is available from Blackgates Engineering. You can cut it up however you want. Might be just what you need if you want a bar grate.
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Asteamhead
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Re: Plate Grates

Post by Asteamhead »

Hello kcameron,
There are some grates made of stainless steel 1.4571 (316 Ti) with tapered :!: holes in use wich showed good and sustaining results.
A photo of such grate of medium size of about 8 by 5 " and 1/2 " thickness with holes of about 12 mm (1/2 ") may help?
A free area for the air well below 50 % :idea: has proven to achive best combustion of anthrazite coal :)

Good luck!
Asteamhead
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Grate of 44 1263, scale 1 in 10, well proven during many years
Grate of 44 1263, scale 1 in 10, well proven during many years
jscarmozza
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Re: Plate Grates

Post by jscarmozza »

Ken, search 'rosebud' grates. I have two identical 1" Atlantics, one fitted with conventional grates and the other fitted with a rosebud grate. I run the rosebud on Anthacite or a 50-50 mix of Anthracite and Bituminous coal, it performs well. If I recall correctly, the open area on a rosebud grate (the small side of the hole) is only about 12% of the grate surface area. I drilled the holes in my grate with a LARGE center drill so I got the conical hole in one operation. The theory of the rosebud grate is the conical hole acts as a Venturi and accelerates the combustion air into the coal bed causing it to float on a jet of air. That's why a rosebud grate is recommended for Anthracite that needs a lot of combustion air to burn. Check it out, like everything else in this hobby, it may or may not be right for you.
John
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kcameron
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Re: Plate Grates

Post by kcameron »

This is some interesting ideas about the grates. It may lead to some experiments to see what works best. Biggest issue I'm foreseeing is that the height of normal grates vs the plate being thinner. Where I set the brackets have to take that into account. We'll who else has further ideas, comments, pictures, etc...
-ken cameron
Syracuse Model Railroad Club http://www.SyracuseModelRr.org/
CNY Modelers http://www.cnymod.com/
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mailto: kcameron@twcny.rr.com
In the Upstate New York US area of the world
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NP317
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Re: Plate Grates

Post by NP317 »

I suspect those questions about gate and firebox designs have been researched in detail by railroads during steam operation years.
Many books contain research results. You just need to identify those sources ad pay attention.

My Friend Keith Sternberg is good at locating those resources, and altered his Allen Ten Wheeler design using that old information.
Results: He blocked off the forward 1/3 of the firebox grate for coal burning.
His engine fires amazingly hot, uses little coal, with the blanked off grate section as a combustion chamber.

Keith calculated grate surface area based on cylinder swept volume, steam pressure, RPM, and fire tube cross sectional area.
He really does The Numbers, and his results demonstrate the value of his approach.

He also designed balanced slide valves (based on old technical information) that clearly decrease the stresses on the Stephenson valve gear.
This is a change I also wish to make on my own Allen Ten Wheeler.
Old info. Still applicable today. We should be paying attention.
RussN
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