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Old 01-08-2011, 07:42 PM   #1
thecolin
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Default Welding food equipment

Does anyone out there have any tips or resources on welding stainless for brewing? I've got an industrial welding shop, we work on various metals from about 1mm to 5mm thickness, so equipment is not a problem. Almost all of the stainless we work on is AISI 304, which as far as I understand, is considered food-safe, so materials shouldn't be a problem. But I've never done any welding for something that contained food, anything I should be looking out for? Are there any processes/chemicals I should be using/avoiding? I'm thinking of throwing together a stainless fermenter, but I want to be clear on options and methods I may not be aware of before I get started.

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Old 01-08-2011, 09:15 PM   #2
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I am not a welder but I have heard the term "sanitary weld" thrown around. A google search might reveal some info on the procedure.

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Old 01-08-2011, 09:23 PM   #3
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Well, all you are trying to do is not allow any pores in the weld. If you can lay a fat bead down, and grind it smooth afterwards, that should provide a smooth surface. Contamination in the form of the rod or part touching the tungsten is also going to be bad (I would think so anyways, tungsten is partly radioactive, and I wouldn't want it on the inside of my brew equipment). Personally, I would just lay an oversize bead and grind it smooth, then go over it with some very fine sandpaper.

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Old 01-08-2011, 09:37 PM   #4
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Sanitation is the concern. You don't have to worry too much about welds that come in contact with the wort before the boil because the boil will kill any bacteria that is introduced. However, after the boil you have to be able to sanitize any equipment that comes into contact with the wort.

A lot of folks use heat or chemicals to sanitize their equipment. If you can get the equipment hot enough for a long enough period of time it is pretty effective. I ferment in sanke kegs and boil about a gallon of water out of it to "steam clean" and sanitize the inside.

Chemicals are very effective at sanitizing equipment that you cannot heat sanitize.

The problem with welded equipment is that if the portion of the weld that comes in contact with the wort has ANY cracks, gaps, craters or pores they are very hard to clean/sanitize.

In my opinion, a fermentor is a pretty ambitious place to start learning to weld brewery equipment.

There are several threads here with discussions about welding Stainless Steel, I'd suggest you read through them for input.

Good luck,

Ed

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Old 01-09-2011, 05:22 AM   #5
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Thanks for the info. We do a fair number of oil/water tight welds for machines and oil cooled transformer cases that need to be perfectly sealed. But those are big enough for six people to stand inside, welding and finishing the inside of a 20 liter fermenter is going to be a bit more annoying, logistically speaking. =P

I have in fact searched the forum a bit. It seems there are a lot of threads with people trying to find out what type of process to use to weld stainless or looking to weld things onto existing kegs, which isn't really what I'm looking for. Thanks for the suggestions, I'll keep looking around a bit.

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Old 01-09-2011, 12:39 PM   #6
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Since you are familiar with stainless steel welding the only things I can add are the finish on the welds needs to be as smooth as possible, and after any welding or grinding the stainless will need to be re-passivated. A handy setup for polishing welds is the 3-M hook&loop adapter for a 4" grinder and the blue and gray disks, quick change when pads wear out. Using coarser pads (maroon, green) leaves scratches in the surface which is not a good thing and it takes some effort to buff them out.
If you want the ultimate inside finish send the finished fermenter to some one who does "electro discharge polishing" and the inside will shine and be passivated at same time.

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Old 01-09-2011, 03:31 PM   #7
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Thanks kladue, that's useful. Getting some of the smaller finishing tools for a dremel might be useful as well?

I've been trying to teach myself how to do high gloss finished by hand in my spare time (since it's not something we do for clients). Fermenter with an inside mirror finish anyone? Yeah... maybe not. =P

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Old 01-09-2011, 11:18 PM   #8
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Kladue is right on the money as usual. Walter makes a similar disc system if you can't find the 3M. Its what I roll.

TIG is the process of choice. Done properly there shouldn't be any need to really grind anything- the finished weld should not be porous anyway.

Be sure that your welder back purges the weld. If you don't have argon on the backside it will sugar (think REALLY porous). Hard to deal with inside a small vessel...

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Old 01-09-2011, 11:48 PM   #9
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Welds in food service should be flat and or smooth on the inside. If necessary use a backing gas (argon) to prevent backside from sugaring

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Old 01-10-2011, 12:19 AM   #10
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If you get into a situation where back gassing is not possible there are 2 products I know of for protecting the offside of the weld, "Solar Flux" and "Superior #9". These are powders that are mixed with alcohol or water and painted on the weld area as a thick slurry, the fluorides in the flux keep the stainless from sugaring, and it forms a glassy covering like stainless stick rod does. A stainless wire brush in a 4" will usually knock this off after welding, or a flap wheel will do the same.

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