Casting Surface Quality

[Mark1957]

I'm looking for suggestions / ideas on how to improve overall surface quality of a: 65-45-12 ductile cast iron, sand casting, weight 103 lbs, dimensions 38.50" long X 24" wide with some cross sections 2"-3" thick.
Currently the as cast surface requires hours of grinding and polishing per piece before powder coating to remove porosity, surface irregularities, grind marks, etc.
I'm open to casting process changes, material type changes, coating changes, post processing that could be done, anything. We are designing a new part so we're trying to consider all options to improve the current condition as long as the total cost remains close to the same.

 

[swall]

Are the issues with the powdercoat mainly cosmetic, or are you experiencing corrosion problems?

 

[NickE]

"We are designing a new part so we're trying to consider all options to improve the current condition as long as the total cost remains close to the same."

Nope not a chance....

No quality improvements are free, even if its only a capital investment in a new shake out process, there will always be some increase in piece price.

Maybe finer sand? but then you might have troubles with mold filling cause the greensand mold will be less porous.

 

[Mark1957]

swall,
The powdwer coating issues with this part are typical...some out gassing, etc; but not the main problem. If the parts were painted without grinding and polishing the painted surface would not be acceptable. Corrosion has'nt been a problem.

Mark1957

 

[Mark1957]

NickE,
I agree with your comment. An increase in piece price would be ok, depending on results of course.
When I say total cost I mean that if we could find a casting process or improvement in the current one that maybe more costly the grinding and finishing cost could go down. Thanks for your other suggestions.
Mark1957

 

[arunmrao]

Mark

What is the molding process used. Green sand molding or no bake molds. Most of the problems you mention are related to green sand molding. Please consult local Foseco representative for assistance.

Is it posible to add machining allowance,so that a skin cut will remove most of the surface defects.

What is the mold coating used and how is it applied? Perhaps a changeover to Zircon based coatings might help.

Control the pouring temperature as the casting is a chunky one,high pouring temperature is not beneficial.

Ductile iron castings properly shot blast give an excellent finish and are free from most of the defects you mentioned.

Lastly consider alternate vendor!!

 

[BillPSU]

What is causing the most problems of appearance? The parting line, gates and riser attachments or the cast surface?
If the molding material is green sand and the problem is the casting surface then move to a no-bake sand process. If the problem is parting line or gates and risers you will have to go to the foundry and ask for help. Redesign the gates and risers to improve appearance. If the problem is parting line shift or some other parting line problem again you will have to talk to your foundry.

 

[mog69]

If it's a cosmetic surface finish you're looking for, and the surface isn't functional in the sense that nothing bears / rolls / impacts it, how about going to an epoxy coat finish that would fill typical gas porosity, laps, cold shuts, type defects ?