NVH of cylinder head material 2

[gbelly]

I have a design project for an aircooled engine. There is some impact on the cylinder head which transmits thoughout the engine. Is there a better material than aluminium for damping vibration, or an alloy of aluminium.

Has anyone tried curving the cooling fins to stiffen and reduce radiation?

 

[CoryPad]

Magnesium and its alloys have higher damping than aluminium and its alloys. However, joints/interfaces usually dominate damping properties.

Regards,

Cory

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

 

[gbelly]

HAs anyone successfully used Magnesium on a cylinder head. Does it burn?? Any other issues?

 

[CoryPad]

I am unaware of any current production magnesium alloy cylinder heads. There are large efforts to create new alloys for head/block applications - you can perform a Google search to find more information.

Mg alloys usually burn only if they are in finely-divided form (like chips/powders) while simultaneously near a large heat source. A bulk object like a head would burn if heated to the alloy's melting point, which is much higher than the operating temperature of a head. The other issues to consider are strength, stiffness, thermal conductivity, thermal expansion, and creep.

Regards,

Cory

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

 

[gdodd]

If weight is not a problem then go back to old fathfull-flake graphite cast iron. It has the one of the best damping capacities of all modern automotive materials.

 

[Tmoose]

Montesa free-air cooled dirt bikes of the mid 70s had wiggly fins on their aluminum cylinder heads.

Rubber spacers at strategic locations do wonders at reducing fin ringing, plenty of which will be induced by the events going on inside engines like combustion, piston slap or even clearance in clutch components.

A sheet metal shroud around the head can contain the noise a lot and used to enforce useful air flow.

Cast iron air cooled cylinder heads don't cool very well.

 

[Azmio]

Gbelly,

How about using the oil itself to damp the critical NVH point? You can try to create some sort of 'oil reservoir' or oil passages passing nearby or at the critical NVH points.

Mg.. the damping characteristic is better than Aluminium but the Young's modulus or the stiffness is not as good as Al. This metal doesnt help NVH much for highly loaded applications like the block and head. I remember one R&D block that I saw made of Mg has a lot of complicated ribbings.

It is ok for block because the cylinder bore can be coated and the crank bearing has bearing shell to avoid direct contact with crankshaft. However, it will interesting to see how Mg can overcome the problem of rotating camshaft in direct contact with the Mg.

There must be some solution for the Mg head. Anyone out there has tried it before?