How to specify allowable porosity for iron castings? 4

[GaryU]

I am looking for a way to specify the allowable porosity in the iron castings we buy (most are ductile, but some are gray iron). I know there are several ASTM standards such as E 446 which discuss using radiographs for various defects. While I have read some of these standards, I do not have the referenced radiograph "binders". These documents are quite expensive (around $3000 for set of 3) and I am not sure this is what I need.

All I want to do is define in general terms the maximum amount/size of any porosity which may be present. I do not want to specify what type and power of equipment is used.

Any ideas on the best way to accomplish this?

 

[swall]

I've been down this path with automotive ductile iron castings. First of all, you have to ask yourself if you really need/really can afford purchasing castings produced under radiographic control. What industry are you in?

 

[GaryU]

We supply to just about every industry you can think of. I have current projects for construction, heavy truck, and also general industry.

I am not looking for parts to be 100% inspected (x-ray). Parts are x-rayed at the start of production and then periodically checked using x-ray, destructive sectioning, etc.

What I am looking to do is simply establish a standard definition regarding what size and quantity of porosity will be acceptable. Our manufacturing and procurement people can work with the various vendors (both domestic and abroad) to establish what method and frequency works best for a given situation.

 

[Goahead]

Are you ready to perform destructive testing on a certain production percentage?
If you do not want to resort to radiography, the alternative could be to develop suitable criteria for ultrasonic testing.
This would require a standard part where the backside echo attenuation has been measured and correlated with the general amount of porosity present.
The worst part (with minimum backside echo) out of a production run could be found and its level of porosity determined by alternative means, and then accepted as a standard.
Because if you do not specify a method to check size and quantity of porosity, why would you want to establish a standard definition?

http://www.welding-advisers.com/

 

[dbooker630]

I'm in the heavy axle business and I specify E446 at the beginning of any new part (PPAP) for internal soundness. Normally use level 2 for high soundness, 4 for normal and 5 for low.
For as-cast surfaces I use the Manufacturers Standardization Society's MSS-SP-55 specification which shows visual standards. I recommend purchasing this book. You can set your own standards based on the reference photographs, for overall condition or for just an isolated area.
As far as size is concerned, I generally go with .060" diameter and .030" deep for porosity, shrink and sand holes if they are in a critical area. Double the size for a lower soundness area.

You'll also have to establish allowable number of holes in a particular area and also what is negligible. Also you'll have to establish whether repairs are allowed. I wouldn't in a high soundess area. Of course only you can determine what is high and low soundness areas for your application.

 

[arunmrao]

Normally Level 2 defects is safe to specify for shrinkage,hot tears,gas porosity etc. This level of acceptance will meet most of the requirements. Aerospace,nuclear and higher application castings demand nil defect or Level 1 acceptance. The more rigid your acceptance,higher will be the cost for you.

Define 100% ultrasonic testing and 5-10% radiography inspection. Perhaps you can also incorporate destructive testing,wherein you section the castings for inspection.

 

[GaryU]

Thanks to all for the comments.

I would like to get a better understanding of the ASTM E 446 levels. How do I correlate the levels to size and quantity? Is this defined in the radiograph binders referenced in the standard (the ones that are $3000)?

 

[swall]

dbooker630--couldn't have said it better myself.

 

[ijzer]

The E 446 is valid for wall thickness up to 2 inch. There are no allowable porosity sizes or densities specified. Only rference foto's showing an example of each acceptance level (from 1 to 5) for each type of defect.