How is weld polishing achieved, inside fermentation tanks?

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JohnB

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Greetings to all! I am looking to experiment with building a conical custom made fermentation tank (1BBL). For a limited period I will have hands on an automatic TIG wire feeder and Tig machine, a turntable and a pair of rollers. Since I have access to super mirror polished sheets from my local shop (they will form cone, cylinder etc.), I wanted to ask the community of how to achieve the amazing exterior sanding lines we all see on tanks… My guess is that makers use a stationary belt sander and rotate the tanks but whether right or wrong, how do they equally polish the weld inside the tank? That last one is what puzzles me the most as for sanitation reasons is the most important! Any videos, photos, ideas will be much appreciated.
 
Blue tape works well for striping welds. Look into 80-120 grit flap wheels, 3m gray wheels, yellow wheels and Scotch Brite
 
Really? I wouldn't have thought about the blue tape as I 'd think the flapped disc would easily destroy it. I will test this method on a round piece and will report results. Generally speaking I 'd say I am good with the angle grinder but without some special method/trick I have no way accomplishing the result of the attached image. Another idea was to have the shop round 2 strips (thickness of 2mm) 1" wide and at length of the tank's circumference place them apart the distance of the weld plus an inch or two and use them as protection while polishing . Two problems with that though ... placing one at the cone would require some out-of-the-box-thinking to keep in place, and second I wouldn't be able to perform the task inside the tank for obvious reasons. Also placing blue tape inside the tank, again for obvious reasons :) , is not feasible. So they mush have a special technique for polishing accurately inside the tank...hmmmm thinking ... thinking ...
 

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I'm just an amateur at polishing and I haven't seen how that sort of strip is accomplished but maybe they use the blue tape late in the process. Looking at that strip, I think you could do that with a buffing compound right before getting a mirror finish if there was a tape line. It's parallel to the edge of the tape.

No idea though about the inside of the tank. Potentially something on a pole. Die grinders are kind of small. Tape on the inside could be done with a specialized tape roller.
 
I'm a professional food grade welder and that's what we use, of course you wouldnt use this with a flap wheel. Use the flap wheel to take majority of the material down and then apply blue tape, you then finish the stripe by hand with a scotch Brite pad.
If your using an aggressive consumable, you could clamp a guide of sorts- a rolled piece of flatbar etc and ride the edge for a nice clean line
 
I'm a professional food grade welder and that's what we use, of course you wouldnt use this with a flap wheel. Use the flap wheel to take majority of the material down and then apply blue tape, you then finish the stripe by hand with a scotch Brite pad.
If your using an aggressive consumable, you could clamp a guide of sorts- a rolled piece of flatbar etc and ride the edge for a nice clean line
So you did actually mean a green scrubbie there...could you link to the 3M gray and yellow wheels? I'm not sure I'm finding the right ones.
 
We use the red scotch by hand, yellow bristle wheels with a drill and custom made arbor and gray unitized wheels on a grinder. This is all for finishing. We typically use a 60grit sanding disc or 80grit pearl disc to carefully take down the weld and use the above three items to finish it off
 
Flap wheels and Scotch Brite wheels can also be used on an end grinder depending on the project.

Need to remember this can be achieved with a variety of consumables (not limited to what I've linked) but a good finish will always be performed by stepping up from coarse to fine. The art is a balancing act between taking material down fast vs blending after the fact.

Let me know if there's anything I can help with, I've been polishing metal for 18+ years. Also curious how everyone else is getting the job done
 
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Flap wheels and Scotch Brite wheels can also be used on an end grinder depending on the project.

Need to remember this can be achieved with a variety of consumables (not limited to what I've linked) but a good finish will always be performed by stepping up from coarse to fine. The art is a balancing act between taking material down fast vs blending after the fact.

Let me know if there's anything I can help with, I've been polishing metal for 18+ years. Also curious how everyone else is getting the job done
Cool thanks! I've just done two projects, my keggles and my hood. I had found some instructions that were from BobbyM for the keggles. That used black and blue pads from Lowes which I followed up with black then green polishing compound. About two years after that, I made a hood out of kegs but decided to watch a bunch of videos and I tell you what there are a lot of different ways to polish stainless! I saw a lot of people using various sandpaper grits. I didn't necessarily want to buy any more tools as I wasn't sure I would use them. I also went online shopping and discovered all the different consumables, also enlightening compared to Lowes and Harbor Freight although Harbor Freight did have a lot of stuff. Empire Abrasives has these big honking chunks of polishing compounds I found, I was tearing through the small tubes from Harbor Freight. I got a series of three flapper wheels from Empire Abrasives and some felt pads along with black and green polishing compound. That was how I did the hood. I did see a few people use the white as final step but I felt I got a pretty good finish with the green. The flapper wheels worked a lot better than the stuff I bought at Lowes, worked faster, and the wheels lasted longer. Still good actually. And I only used the angle grinder. I saw people using a die grinder and that seemed a little more maneurverable. I might make a sixtel light next and I've thought about polishing up some corny kegs but haven't decided if I could get the tops right on them.

1675318981723.jpeg
 
I'm just an amateur at polishing and I haven't seen how that sort of strip is accomplished but maybe they use the blue tape late in the process. Looking at that strip, I think you could do that with a buffing compound right before getting a mirror finish if there was a tape line. It's parallel to the edge of the tape.

No idea though about the inside of the tank. Potentially something on a pole. Die grinders are kind of small. Tape on the inside could be done with a specialized tape roller.
The more I think of what aeviaanah wrote and posted, the more I get the blue tape ! Regarding the inside I was also thinking of custom made device to hold a grinder accurately in place and then turn it 360 while touching the weld. Tricky stuff :) ! How would you see though inside the tank is another story...maybe by attaching a cheep wifi camera.
 
Flap wheels and Scotch Brite wheels can also be used on an end grinder depending on the project.

Need to remember this can be achieved with a variety of consumables (not limited to what I've linked) but a good finish will always be performed by stepping up from coarse to fine. The art is a balancing act between taking material down fast vs blending after the fact.

Let me know if there's anything I can help with, I've been polishing metal for 18+ years. Also curious how everyone else is getting the job done
Wow ! Thank you so much for the info ! This will help a lot ! Would you say a 400G is needed or should I stop at a lower one ? I wasn't aware of the bellow disc(s) . Please correct me if I am wrong but the arbor (also available on the website) is to be used with a drill and not with an M14 angle grinder. My local machinist can custom made for me an attachment for my Dewalt grinder which also has a speed dial and it has proven a big plus.

Scotch-Brite Radial Bristle Brush, T-C, 6Diax7/16W, 400G 61500187762 | Zoro

I think I read somewhere you use a manual backstand with one of the wheels (and the drill?) but I can't locate where, how do you use that?

Still scratching my head regarding the inside :) ... Oh by the way after finishing all work, does the surface need passivation and/or pickling or not (for the inside as well) ?
 
Wow ! Thank you so much for the info ! This will help a lot ! Would you say a 400G is needed or should I stop at a lower one ? I wasn't aware of the bellow disc(s) . Please correct me if I am wrong but the arbor (also available on the website) is to be used with a drill and not with an M14 angle grinder. My local machinist can custom made for me an attachment for my Dewalt grinder which also has a speed dial and it has proven a big plus.

Scotch-Brite Radial Bristle Brush, T-C, 6Diax7/16W, 400G 61500187762 | Zoro

I think I read somewhere you use a manual backstand with one of the wheels (and the drill?) but I can't locate where, how do you use that?

Still scratching my head regarding the inside :) ... Oh by the way after finishing all work, does the surface need passivation and/or pickling or not (for the inside as well) ?
IMO 400g is good. The art is in not starting too rough and then having to buff it out. There's a sliding scale between using something aggressive to save time then to only use something less aggressive to hide the grind marks you just made. I always start with 80grit when sanding.

I use the yellow bristle brush on a drill, might be cool to try on a grinder one day. They come with a stack of cylindrical spacers to utilize various size arbors. We use a 1/2" stainless allthread with a flat washer and hexnut on both sides of the wheel.

I work in a shop that processes mild steel, stainless and aluminum, I recommend passivating any food contact surfaces due to any potential contamination of iron. Look into a product called Citrasurf, they make a gel based passivation fluid and it's relatively safe (citric acid). I've never pickled anything.

When you buy your stainless, make sure you get PVC coated preferably on both sides. This keeps the material nice through fabrication and welding. When it's in the flat (before rolling/forming) you can use a ruler and a piece of sharpened copper to cut away areas near the welds. You then peel off these strips prior to tacking and it'll serve the same purpose as the blue tape. Leave as much PVC on wherever possible until the job is complete
 
Interesting thread, and as I have zero experience with regards to welding/polishing any kind of metal just curious as to what "Blue Tape" does and it's use for striping welds?
It gives you a fine line between polished area near the weld and the finish from the mill whether that may be #2 std, #4 brushed or #8 mirror. Similar to how it works when painting!
 
IMO 400g is good. The art is in not starting too rough and then having to buff it out. There's a sliding scale between using something aggressive to save time then to only use something less aggressive to hide the grind marks you just made. I always start with 80grit when sanding.

I use the yellow bristle brush on a drill, might be cool to try on a grinder one day. They come with a stack of cylindrical spacers to utilize various size arbors. We use a 1/2" stainless allthread with a flat washer and hexnut on both sides of the wheel.

I work in a shop that processes mild steel, stainless and aluminum, I recommend passivating any food contact surfaces due to any potential contamination of iron. Look into a product called Citrasurf, they make a gel based passivation fluid and it's relatively safe (citric acid). I've never pickled anything.

When you buy your stainless, make sure you get PVC coated preferably on both sides. This keeps the material nice through fabrication and welding. When it's in the flat (before rolling/forming) you can use a ruler and a piece of sharpened copper to cut away areas near the welds. You then peel off these strips prior to tacking and it'll serve the same purpose as the blue tape. Leave as much PVC on wherever possible until the job is complete
Certainly a lot of ideas :) which I will try and report back :)
 
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