What gun and media for shot blasting cast iron?

dgfoster · May 20, 2021

Shot blasting provides a nice finish for the cast iron casting I pour and sell

Until I recently built my own heat treat oven, I was getting the castings shot blasted as part of the heat treat process. Now that I am doing my own heat treat, I am considering setting up to shot blast the casting. I have a blast cabinet and large vintage USA-made compressor.

So what media size should I use and what brand/style gun?l

The castings range from 5 pounds to 50 pounds. I would be blasting about ten per month.

Denis

thermite · May 20, 2021

dgfoster said:
Shot blasting provides a nice finish for the cast iron casting I pour and sell

Until I recently built my own heat treat oven, I was getting the castings shot blasted as part of the heat treat process. Now that I am doing my own heat treat, I am considering setting up to shot blast the casting. I have a blast cabinet and large vintage USA-made compressor.

So what media size should I use and what brand/style gun?l

The castings range from 5 pounds to 50 pounds. I would be blasting about ten per month.

Denis

I like the finish, but never gave much thought to it on CI. Media for descale is a different animal. Shot blasting we used on alloy steel to intentionally alter surface stresses. Connecting rods were one example of how that has been applied. Dunno if still in-use or not?

So is shot-blast even the best way to do goods meant for uber-stable metrology?

Too much else on my plate just now to even research it..

OTOH, your goods have - so -far - been remaining stable. Very. Might get the oldest one precision ground later this year. Scraping and flaking is for Giant Afican land snails in need of raw material to build bigger Airstreams to live in.

So far, I remain more curious as to what is possible and what you have accomplished than in actually putting them to work!

OTOH, "curious" IS what I do best.

Bill D · May 20, 2021

What about an air needle scaler. Seems like it may give similar results. How many horsepower is the compressor you have?
Bill D

thermite · May 20, 2021

Bill D said:
What about an air needle scaler. Seems like it may give similar results. How many horsepower is the compressor you have?
Bill D

Got one. Not going to get anywhere near the "uniformity" on Denis' nooks and crannies dovetails. Nor even the simpler SE.

Pickle, then media, if it were me. Pittsburgh thing.

dgfoster · May 20, 2021

Regarding the above posts:

I am interested shot blasting as stated.

With respect to metrology concerns the consideration disappears if shot blast proceeds stress relief and that is the plan. Even if it were in the other order my suspicion (unproven, of course) is that the amount of stress induced by small media surface finish blasting, as opposed to large media with intense blasting, would be minuscule. But if one used large media with high intensity, I think significant stresses would definitely be induced.

Denis

lucky7 · May 20, 2021

I’ve only done a little shot blasting and recall it needed more cfm than regular media blasting. Hope your compressor is up to providing 30-50 cfm? Otherwise I’d send it out. Kinda lucky locally as I have a good shot blaster near me. Assume you’re planning to shot blast before trip thru oven? Then maybe a light media blast if fussy?

Are you having problems getting heat treatment locally now?

I’d second Thermite’s comment- my two straight edges from you have stabilized nicely.

L7

DDoug · May 20, 2021

dgfoster said:
Regarding the above posts:

I am interested shot blasting as stated.

With respect to metrology concerns the consideration disappears if shot blast proceeds stress relief and that is the plan. Even if it were in the other order my suspicion (unproven, of course) is that the amount of stress induced by small media surface finish blasting, as opposed to large media with intense blasting, would be minuscule. But if one used large media with high intensity, I think significant stresses would definitely be induced.

Denis

So which is it that you want ?.... :crazy:

SAG 180 · May 20, 2021

dgfoster said:
Regarding the above posts:

I am interested shot blasting as stated.

With respect to metrology concerns the consideration disappears if shot blast proceeds stress relief and that is the plan. Even if it were in the other order my suspicion (unproven, of course) is that the amount of stress induced by small media surface finish blasting, as opposed to large media with intense blasting, would be minuscule. But if one used large media with high intensity, I think significant stresses would definitely be induced.

Denis

Haven't some forum members used old iron brake rotors spun with a motor for an airless shot blasting rig. It would take some experimentation to time the exit and a dedicated cabinet. My only experience with induced stress is small tubular aluminium castings that closed up on the milling machine slotting wheel after being glass bead blasted. The blasted skin had enough stress to try and close up the milled slot.

thermite · May 20, 2021

dgfoster said:
Regarding the above posts:

I am interested shot blasting as stated.

With respect to metrology concerns the consideration disappears if shot blast proceeds stress relief and that is the plan. Even if it were in the other order my suspicion (unproven, of course) is that the amount of stress induced by small media surface finish blasting, as opposed to large media with intense blasting, would be minuscule. But if one used large media with high intensity, I think significant stresses would definitely be induced.

Denis

Not sure what it does. Limited exposure. I would have to read-up on that.

Besides "cosmetic" enhancement, I mean. I might have even been tempted to use Garnet and the "air pencil" micro-blaster I have. Alway got a warm feeling over the frosty chrome body finish on fine film cameras. Have researched having your goods here Miccrolloy Bronzed, TiN coated, electroless Nickel, electroless Cobalt, Copper strike, then livers of sulfur, or flash frost chromed. Would happily settle for Parkerizing, but there is still that precision surface not wanting any signicant change.

Paint just doesn't go there. My "Fosters" are not meant to rub smear off a surface plate.

They are meant to be good enough I can shed that big Herman Grade A plate altogether and still have seriously decent "reference" goods that take up but small storage space. Along with the also compact Davidson goods. Rust is not on that dance-card, and paint goeth not on the precision surfaces, either, even if it were to cover the non-working body, adjacent.

john.k · May 20, 2021

What size shot? cast iron or steel?....it goes from 2mm down to grit size.....I worked in the industry ,and wheel blasters are about 1000% more efficient and cost effective than air blast.....any kind of steel abrasive can be difficult to handle due to condensation /rust that freezes the lot into a solid mass......Consequently can be somewhat labor intensive for ocassional use......On the other hand,one ton of shot /grit lasts just about forever ,so waste disposal isnt a cost item.......and presently ,steel grit doesnt cost any more than garnet,but of course is much heavier on a volume basis.

ferrretcatcher · May 20, 2021

The ones I was around were rosler metal finishters and wheelabrator tunnel blast and tumblast tumble blasters. I think the tumblast used 3mm shot and the tunnel blast used 2mm shot. The shot was used before any machining and normalizing through any oven. Shotblast revealed any slag inclusions before it even went through the oven or machining. The machines used "throwers" what i would consider a high manganese steel impeller that threw the shot at various angles with 20 hp electric motors. Maybe you could do some sort of rotisserie with the casting almost like a engine washer except with a thrower for shot blast. That way you wouldn't have to use so much air and would be minimal air blast shot cleanup in certain areas the thrower couldn't get to.

dgfoster · May 20, 2021

john.k said:
What size shot? cast iron or steel?....it goes from 2mm down to grit size.....I worked in the industry ,and wheel blasters are about 1000% more efficient and cost effective than air blast.....any kind of steel abrasive can be difficult to handle due to condensation /rust that freezes the lot into a solid mass......Consequently can be somewhat labor intensive for ocassional use......On the other hand,one ton of shot /grit lasts just about forever ,so waste disposal isnt a cost item.......and presently ,steel grit doesnt cost any more than garnet,but of course is much heavier on a volume basis.

I guess you are asking somewhat the same question as I am asking. My goal is simply to provide an aesthetically pleasing surface. The finish I am getting out of the sand is satifactory as is. But I do like the slight sheen provided by shot blasting. And that is all I want.

I am guessing that steel shot is the way to go. But, unlike you, I have zero basic knowledge of the process let alone experience.

I am not totally helpless in the shop and could fabricate a wheel unit if the end result is likely a reliable, efficient, and safe device and the time cost is not too great. So, suggestions and links to successful implementations in that regard would be appreciated. But, I am guessing that is not a practical approach.

And my assumption about using air sounds like it may be way off. And costs to set up may be prohibitive for a wheel blaster. I am just exploring the question.

Denis

dgfoster · May 20, 2021

ferrretcatcher said:
The ones I was around were rosler metal finishters and wheelabrator tunnel blast and tumblast tumble blasters. I think the tumblast used 3mm shot and the tunnel blast used 2mm shot. The shot was used before any machining and normalizing through any oven. Shotblast revealed any slag inclusions before it even went through the oven or machining. The machines used "throwers" what i would consider a high manganese steel impeller that threw the shot at various angles with 20 hp electric motors. Maybe you could do some sort of rotisserie with the casting almost like a engine washer except with a thrower for shot blast. That way you wouldn't have to use so much air and would be minimal air blast shot cleanup in certain areas the thrower couldn't get to.

So, the impellers I see on eBay. They must be caged with a cap that encorporates a "chute" to collect the shot and direct it through a hose or some sort of nozzle. A 20HP motor would really make quite a stream of shot I would think. My needs would not be very great. If it took me ten minutes to da a casting 2 feet long, I would be OK.

Denis

Shaybuilder · May 20, 2021

The nicest finish is with a wheelabrator and steel shot, very fast and not time consuming as a sandblast cabinet. It would be worthwhile to try and find someone with a wheelabrator and pay them to do it since the wheelabrators are fairly expensive. I looked at a small used one and it was 10K.

john.k · May 20, 2021

In fact ,the impeller only needs mechanical strength and balance....abrasion resistance is provided by rubber ...pure natural rubber sheet cut and glued onto the wearing surfaces.......needs replaced from time to time ,and is expensive....stuff like managanese steel is used for mud and gravel pumps ,that take much larger particles ......Steel grit and shot is quite low on the abrasion list,nothing like garnet ,or even silica......The other good point of shot is that it doesnt destroy bearings like the steel grit....one single grain of steel grit will destroy the whole hydrostatic steering system on a mobile crane....In fact "Old Tommy " the mechanic destroyed half the fleet until his workshop was moved away from beside the blastroom ,where steelgrit used to fall like rain.....An efficiency expert dreamed up that one ...utilize the wasted space in the blast shed....Looked good on paper.

john.k · May 20, 2021

There is also some thought that using steel blast media causes testicular cancer,but I dont think its been proved.......but two of the blasters did have it .Its easily cured if caught early.

Turbowerks · May 20, 2021

Look a peterson or kanas instuments ab502 shot blaster. They are used in automotive machine shops. Could squeeze a 3 foot casting at an angle could find one used for probably 1000 and up less if you could find a worn one that needs some tlc look them up they dont use up much space.

Sent from my iPhone using Tapatalk

dgfoster · May 20, 2021

Shaybuilder said:
The nicest finish is with a wheelabrator and steel shot, very fast and not time consuming as a sandblast cabinet. It would be worthwhile to try and find someone with a wheelabrator and pay them to do it since the wheelabrators are fairly expensive. I looked at a small used one and it was 10K.

Got a feeling after the various posts that you may be right.

Denis

thermite · May 20, 2021

dgfoster said:
Got a feeling after the various posts that you may be right.

Denis

I'd say it is down to whether your "aesthetics" goal is industrial uniformity to a higher grade of finish than the average foundry-bear... (just Wheelabrate it) or ... personalizing each one with a bit of air-brush grit artistry, or even electro-chemical etching from a mask ("engraved" firearms come to mind) even individualized whimsey

"Captive in a foundry. As planned."

"Busy Ironing. Leave a massage."

"Let's get something straight."

"Assembly 6 of 4 parts."

That last one is akin to intentionally walling-up a faster than light starship drive master control panel in an ancient cavern. With the Mercury displacement contactors mounted upside-down.

Assurance that scholars of a far-distant future must craft dissenting scholarly papers as to what it meant as to the decline of technical competence in our once-alleged civilization.

Sometimes you just have to take the long view of a practical joke to get any serious mileage out of it.

PackardV8 · May 21, 2021

Yes, what you want is an automotive/light industrial shot blast cabinet. The most even finish comes from the drum type which have a rubber belt with turns slowly and tumbles the workpiece to expose all sides to the blast medium.

jack vines.

What gun and media for shot blasting cast iron?

Diamond

Diamond

Diamond

Diamond

Diamond

Titanium

Diamond

Titanium

Diamond

Diamond

Aluminum

Diamond

Diamond

Cast Iron

Diamond

Diamond

Cast Iron

Diamond

Diamond

Hot Rolled

Similar threads