Gray Cast Iron Casting Cooling 1

[mechvhstech]

I am a Lean Manfacturing Engineer hence my knowledge in metallurgy is limited (though my fascination for this field has lead to try and learn);.....a major bottleneck in my process is the cooling time (static air-8 hrs) after the component (gray cast iron) is cast.
At what temperature can I force air / water quench a gray cast iron casting without changing material properties + machinability?

Thanks for all the help.

mechvhstech


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Mech Rulz

 

[swall]

A little more information would help. Are these large castings cooling in the mold for 8 hours or are they shaken out and being slow cooled in a tub? What grade of iron is it? Is there a concern with distortion? Are you worried about hard spots?

 

[NickE]

I dont have production experience w/ grey iron, I did study it quite a bit. I'd think that once it was ~800F throughout you would be safe using forced air and a water spray.

 

[mechvhstech]

Swall :

Some of them are large thin walled castings (48" X 31" X 8") though there are a few variations. The CI grade is 25 and they are shaken out (some sand always exists therefore after cooling there is shot blast operation).
As mentioned they are shaken out and transported to a cooling warehouse. There is a concern with distortion although there is a fair amount of machining tolerance. hard spots will probably affect machining.....but will depend on the no. of hard spots in the matrix.

Thanks.

mechvhstech

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Mech Rulz

 

[arunmrao]

I suppose that the molds are green sand and the cores are no bake ones. You are using a vibratory shakeout for separating the sand and metal.As you have mentioned that the castings are thin walled,extreme hot shakeout can lead to cracking and distortion.

Once the castings have solidified and are well below the freezing range possibility of hard spots due to white iron formation does not exist.
You can start using forced air cooling with a thin mist of water once the castings are below 400C. Ofcourse the whole place will be messy and humid. how will you handle this situation.

You may progressively increase the temperature of hot shakeout for rapid cooling as you gain experience. Motor body castings were given a hot shakeout at 750-800 C and then stir air cooled.Higher temperature shakeout would often lead to an epidemic of fin breakage.

 

[mechvhstech]

Arun:

I had a cooling tunnel with a forced air + mist cooling system.
This is similar to the one I have seen with a conveyor mode.

Are you familiar with such as system?

Thank you for all your answers.

-mechvhs

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Mech Rulz

 

[BillPSU]

The eight hour cooling process is not a bottle neck unless you cannot store all the castings produced but a buffer which in lean thinking is a bad thing. Your true bottle neck is how many castings that can be poured. The process of cooling the castings can obviously be reduced which in effect reduces the buffer. The buffer is reduced from a stack of cooling castings in a warehouse to a moving belt buffer of so many cooling castings.

You will probably have to experiment with your casting and determine the appropriate cooling rate as casting cross section variation and surface to mass conditions will affect the ability to cool a casting. There could be other considerations from the machining perspective the cooling could impact the machinability of the iron and the residual stresses in the casting could cause tolerance problems if the part is machined to a tight tolerance.

I hope you are shot blasting after the cooling process not before as the parts will flash rust with the water spray.