Shot Blasting - Blackish SUrface finish 2

[ajxxx]

Guys,

Anyone face this issue before? the parts do tend to be on the blackish side after shot blasting - shots used s110, material shot blasted = hot rolled/ cold rolled steel cages....this especially is an issue when new shots are added...

need to run "dummy lots" with scrap parts to lighten the shade...after a couple of hrs run the shots do indeed give lighter shade shot blasted parts...

very weird? anyone think media work-balance issue? anyway to resolve this...we do regular sieve analysis and they do pass...

any help appreciated

 

[arunmrao]

I presume that your dust collector is working well and the bags,cyclones etc are properly maintained. With the addition of new media,the blackening occurs,perhaps need to check the media, and sieve analysis,also if some of the new media is getting pulverized and resulting in dust .

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[Compositepro]

Your new steel shot has a black oxide layer left from the manufacturing process. This will create black dust until it is worn off.

 

[ajxxx]

i assume the black oxide layer is left back...any solutions for that....i mean to use my machines and run scrap to wear it out doesnt seem to good for us right now...yes the dust collection system has just been renovated and is working fine..but this issue has been there for a long time and need to figure out a way to eliminate it..using low carbon shots/ steel wire cuts is 1 option but if i just wanted to use the same media than i get stumped....dont want to get customer approvals for new media trials so wanted a good option for the current conditions...thanks

 

[Zinov]

Hi ajxxx,
We proved similar pb with SS.
The root cause was the oxide layer left after Heat treatment.

Solution was:
1-Perform heat treat under vacuu, to avoid decraburization.
2-Descale parts after heat treat and before blasting.
for our grade we found the supllier suggestion
to descale the material after Heat treat.
It looks complicated as treatment but most of surface treatment shops are very familiar with.
Regards,
Zinov

 

[ajxxx]

Thanks Zinov,

U mean descale my parts? i would have to go all the way to my material supplier to get it done isnt it? we get material in the form of hot rolled and cold rolled steels...arggg..guess would have to look into that option

 

[swall]

I'm having a hard time getting my arms around this one. ajxxx-what do the parts look like before blasting? Do they have black scale on them? What kind of blast machines are you using--wheels or nozzles? Your new shot should look nice and shiny--I have never seen shot with a "black oxide" film on it, per Compositepro. ajxxx--you say the parts are blackish looking after blasting--it is hard to tell if you mean that not all of the original oxide is being removed from the parts or if your process is pounding some contamination into the surface. Have you tried running clean metal through the blaster to see what it looks like after blasting?

 

[ajxxx]

parts are more darker after blasting . They do not have any scale as they go through a degreasing operation before blasting. We use wheel tumblasts. Shots of steel are made from casting with .8-1% carbon and are indeed black. They are not made from SS so they wont be shiny. There is no oxide on parts .It is steel so is much shinier pre blasting. That is my issue!

 

[swall]

ajxxx--yes, I understand your issue. I can see only two explanations. 1--your dust separator is not working. 2--you have some other contaminant in the system, possibly oil.

 

[arunmrao]

The steel shots are high carbon material. The oil,must be from improper washing after oil quench and temper . Also during packaging of these materials a rust preventive oil might have been used.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year