Sand Casting an air cooled head
Sand Casting an air cooled head
(OP)
Background: I'm modifying a vintage 2T race engine (porting, intake, combustion chamber etc..) In stock trim, this motor needs better cooling.
I've found a cylinder head (sunburst style fins) that has more mass and more fin surface area, which I want to modify and duplicate in a casting.
I've also found a foundry that will cast this head for me for a minimal fee
My question is around the alloy that they use: 535 ALMAG. I copied this description from http://www.lbfoundry.com/535-almag-aluminum-sand-c...
Aluminum alloy 535.0 is an aluminum magnesium alloy that does not require heat treatment to reach full properties. It has excellent corrosion resistance and machining characteristics. Milling and turning speeds are 4X faster than alloy 319.0, and 16 to 18 times faster than gray iron or malleable iron.
The anodizing rating is excellent and the color is satin white after anodizing.
The polishing rating is also excellent and the castings can be buffed to a silvery white color.
The weldability rating is poor and it also is not recommended for leak tight or pressure type applications.
Typically it is used for parts where dimensional stability and shock resistance is important, such as instruments. It is also used for marine hardware, ornamental fittings and castings where lighter weight and high strength is a prime consideration. Almag 35 is 10% lighter than average cast aluminum alloys, 64% lighter than gray iron and 69% lighter than bronze.
My major concern is that it's not recommended for leak tight or pressure type applications. Yikes! The wall of the combustion chamber will be at least 14mm thick. Should I go for it? Or is it a waste of time?
Thanks for any help or opinions! Todd
I've found a cylinder head (sunburst style fins) that has more mass and more fin surface area, which I want to modify and duplicate in a casting.
I've also found a foundry that will cast this head for me for a minimal fee
My question is around the alloy that they use: 535 ALMAG. I copied this description from http://www.lbfoundry.com/535-almag-aluminum-sand-c...
Aluminum alloy 535.0 is an aluminum magnesium alloy that does not require heat treatment to reach full properties. It has excellent corrosion resistance and machining characteristics. Milling and turning speeds are 4X faster than alloy 319.0, and 16 to 18 times faster than gray iron or malleable iron.
The anodizing rating is excellent and the color is satin white after anodizing.
The polishing rating is also excellent and the castings can be buffed to a silvery white color.
The weldability rating is poor and it also is not recommended for leak tight or pressure type applications.
Typically it is used for parts where dimensional stability and shock resistance is important, such as instruments. It is also used for marine hardware, ornamental fittings and castings where lighter weight and high strength is a prime consideration. Almag 35 is 10% lighter than average cast aluminum alloys, 64% lighter than gray iron and 69% lighter than bronze.
My major concern is that it's not recommended for leak tight or pressure type applications. Yikes! The wall of the combustion chamber will be at least 14mm thick. Should I go for it? Or is it a waste of time?
Thanks for any help or opinions! Todd





RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Sand Casting an air cooled head
Does anyone here know this material's behavior compared to other's?
Thanks again, Todd
RE: Sand Casting an air cooled head
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
The most common sand cast alloy for engine blocks/heads is probably A356-T6, and A357-T6 has a bit better properties, but both alloys have slightly lower RT properties than A535. However, what matters more are the elevated temperature properties of the materials. The flow/fluidity characteristics of the molten alloy can be a concern when trying to sand cast thin section features like cooling fins. But since your casting has a 14mm wall thickness in the area requiring pressure tightness, I don't see this presenting an issue. You should also take care when designing the mold tool to make sure the cylinder wall surfaces will be free from subsurface defects/porosity that will be exposed after machining.
Prototype qty sand castings are always expensive, even now that there is equipment that can 3D print sand molds directly from a CAD model. So for one or two custom A/C motorcycle cylinders, you might be better off making them using a combination of CNC machining and welding. You mentioned that you require increased cooling from your cylinder design. With A/C two-stroke cylinders/heads, the heat transfer efficiency around critical areas like the combustion chamber is helped by optimizing the conductive heat path from the chamber wall to the cooling fins. So what you want is the minimum practical chamber wall thickness and the highest density of cooling fins on the adjacent outer surface. Increasing the heat transfer area of the cooling fins by simply making them longer is not an efficient way to improve cooling. It is better to keep the fin length shorter, and increase their density by making the fins thinner and reducing the air gap between them. You can get at least two times the fin density using CNC machining that you can with sand casting. Here's an example of what can be achieved with a machined A/C cylinder head (well before CNC machines were available).
Hope that helps.
Terry
RE: Sand Casting an air cooled head
The closest I have come to actually doing anything like that is cutting fine slots in an aluminum sheet heatsink blank using a table saw. Woodworking tools work pretty well on aluminum; you just have to beware of the chips, which come off hot and stick to your skin.
Mike Halloran
Pembroke Pines, FL, USA
RE: Sand Casting an air cooled head
That A/C aircraft cylinder head I linked was machined from a die forging. The cooling fins, intake/exhaust ports, combustion chamber, etc were all 100% machined using 1940s technology.
RE: Sand Casting an air cooled head
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Sand Casting an air cooled head
This application is a "free air" design in which the air passing by the engine is not forced by a fan or directed by any shrouding. Average Speed is somewhere around 20mph.
I have a great PDF file that I'd like to share, but don't know how. Here's the Synopsis in JPG format:
My thoughts, so far:
In this case, The wide fins make sense and having a good draft will aid in transferring the heat to the outer edges of the fins, as well as ease of casting. More mass in the cylinder head will buffer the peaks of the heat cycle in high throttle / low velocity applications such as a long hill climb.
There are some fins which have been truncated at the factory for clearance of other components. These are what I wish to build back to original height. I think epoxy may do the trick for the pattern model. But there are also large voids that need to be filled in (combustion chamber, and on the outside of the chamber). Can I use modeling clay or will that stick to the sand?
Thanks again for all the help!
RE: Sand Casting an air cooled head
Modeling clay may be too sticky for patterns and would tend to deform when the pattern is rammed. The softest material I can remember being used in patterns is a hard wax. Pattern makers would take a tool with a ball on the end and use it to form filet radii. This is called 'waxing filets'. You might stop by a pattern shops and ask.
Remember that a casting made from your existing head will have a few percent shrink.
RE: Sand Casting an air cooled head
I seem to recall free air fin spacing needed to be > 1/4" started to prevent viscosity slowing down convection, which is the primary mechanism heat is removed from fins. All typewritten and xeroxed It was an important discovery to me at the time because thermal glass manufacturers were bragging on how their windows with a 5/8" airgap were so superior to those with 3/16" gaps, and even the Shelter institute was advocating a BIG air gap when home building thermal windows.
My fine collection of free air cooled motorcycles seems to support 1/4 inch as a minimum spacing
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
Dan - Owner
http://www.Hi-TecDesigns.com
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
You asked " did that paper give any info on forced air currents over those fins? "
I don't recall, but I should have been more specific that I believe the scope of the document was vertical fin spacing for free air cooling of stationary objects relying solely on self generating convection.
I suspect the OP is working with bike velocity induced cooling, perhaps with airflow mucked up with fairings and certainly obstructed by frames and wheels and stuff.
Here is the fin spacing that won a few world MX championships back in the 60s. Ground speed on the order of 45 mph or so max and often quite a bit less.
http://cdn.supercross.com/images/stories/features/...
The sunburst style was adopted by the conservative factory and then incorporated on production bikes.
http://tenwheel.com/imgs/a/b/m/t/f/1973_cz_400__cz...
This one came close.
http://www.wischt.com/machine/MJC-VR-right.jpg
Here is the fin spacing used on the legendary yamaha TZ race bikes in the few days before water cooled heads.
Ground speed a bit higher than the CZ.
http://www.motosvit.com/Yamaha%20TZ750/1972%20Yama...
Even fan cooled snowmobile fin spacing was fairly coarse. Mostly The fins just got shorter.
http://www.snowmobileforum.com/attachments/vintage...
At what point die and sand cast manufacturing, optimum fins size and spacing for cooling, or some other thing set the dimensions is comPLETEly unknown to me.
My first and perhaps final thought would be, it worked fairly well for them.
RE: Sand Casting an air cooled head
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Sand Casting an air cooled head
Time to start gathering up all my doorstops. :)
RE: Sand Casting an air cooled head
In reality, the raw material cost will not be a huge factor in the price of your casting. If the trimmed casting weighs say 10lbs, then the amount of metal that will be poured would be something like 20-25lbs. The cost of aluminum casting ingot is probably not much more than $5/lb, so the material cost for a casting should be less than $150. And the raw material cost will be modest in comparison to the cost of constructing and preparing the mold tool.
Good luck to you.
Terry
RE: Sand Casting an air cooled head
14mm chamber wall thickness seems on the thin side. Thick, solid aluminum is strong and a good heat spreader. The larger the area of fin base the more fins can be accommodated. The base is larger with a greater wall thickness. The only way to increase cooling over the existing design is with more fin area, so this suggests more fins on a larger fin base and longer fins.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
http://asnowsquall.smugmug.com/photos/449037160_7Y...
The tight fin spacing on the HOT intercooler line is in contrast to the cast cylinder fins. My hunch that may be due as much to the differences in manufacturing methods for each component as the cooling requirements.
RE: Sand Casting an air cooled head
regards,
Dan T
RE: Sand Casting an air cooled head
Mechanical "noise" is at least a small design factor on these bikes: Nobody wants to hear the "jingling" of the wrist pin bearing amplified. My bikes need to pass a sound test at tech inspection. There are a few different ways to combat engine noise and "fin rattle" that I've seen, but they all seem to be Band-Aid approaches. Yamaha frequently uses rubber dampers between the fins of their cylinders and on the heads, they bridge the fins with the casting, as seen at the top of this thread. I'm not sure what to do here: I'm also wondering if my design (more taper in the fin, larger root width) will aid in keeping the fins from becoming sounding boards for the bearings and combustion.
Thanks everyone for your thoughts and comments. I really appreciate all the help with this project! I'll post pics of my pattern as soon as I get something nice to look at.
RE: Sand Casting an air cooled head
First steps. Clean and cut the webs out. Parting line will be centered behind the middle remaining webs and over the spark plug area. These webs may be continued across the entire head.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
I also want to widen the root width of the fins. I plan in using a popsicle stick to create the radius at the bottom of the fins. Hopefully I can extend the fins a bit to regain the surface area that will be lost.
I'll also rebuild the fins that got truncated at the factory to clear the pipe. And connect the fins that were cleared in the middle for the studs. So, all the fins will be continuous and I will be able to machine the sparkplug hole and stud locations wherever I need them to be.
RE: Sand Casting an air cooled head
http://image.motorcyclistonline.com/f/features/267...
Aftermarket "solution"
http://bringatrailer.com/wp-content/uploads/TY/via...
490 with adequate cooling.
http://databikes.com/imgs/a/c/x/h/o/maico__mc_490_...
The cylinder-to-head joint is not in the obvious location
http://www.maicoonly.co.uk/images/schematics/1983/...
RE: Sand Casting an air cooled head
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
Solution treat 540 degC for 6.5 hours quench in boiling water and the age for 16 hrs at 215 degC
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
Why go thru all of this trouble when you can design and optimize your head using 3D CAD and FEA? And then have it made using DLMS in almost any aluminum alloy you want? If you limit yourself to using sand casting for this head then you are restricted to using aluminum alloys that have lower mechanical properties.
When it's all said and done, the cost of using DLMS won't likely be much different than the total cost of having the head sand cast.
RE: Sand Casting an air cooled head
Google was of no help.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head
I did have the Alloy designation but am struggling to find it now.
RE: Sand Casting an air cooled head
RE: Sand Casting an air cooled head