I want to build a couple of Conicle fermenters about 13 gallon (UK) these
fermenters are usually made using SS Hoppers made by Toledo Metal Spinning .
The problem is getting them to Australia is prohibitive , so I want to
fabricate myself , I have worked out how to plot the conical from the Snips
website , what I need now is to find out how to protect the under side of
the weld , shield it with gas obviously ......how do the Pro's do this ?
You make back-purging widgets to flow argon behind the weld.
Few people buy them
Most build their own.
I have made scads of them.
A simple one is a line of gas lens collet bodies soldered together.
Have a partner follow the weld on the other side with the jet, or just
position it, weld a few inches, reposition and repeat.
Don't get in a hurry.
SS loves to distort from heat.
You could try capping off the whole thing and filling the interior with
argon, but it would take a while to purge all the air out.
Very important to spread the heat out and use the lowest amperage
Do some tests to see exactly how much amperage it takes to get a clean
weld on the backside with your purge jets in place.
You will have to pickle the welds after welding to remove stray iron
particles from the surface.
This is called Passivation.
Commercial pickling pastes are available, but be very careful, they are
I do a lot of welding for Breweries around Seattle.
In addition to Ernie's recommendations, aluminum stock can easily be
machined to do the job. A router can be used with a carbide flute
to machine a trench in some bar stock. This trench will channel the
argon behind the weld, and maintain an inert atmosphere behind the
weld. Since you are welding a conical surface, the area in contact
with the curved surface of the cone can be profiled to match, a grinder
will do the job. This will allow you to match the changing
radius of the conical section. You can make a template to help
you profile the aluminum for a real good match. It isn't that
hard from what I've experienced, and depends on how critical
the part is, and how much argon you can waste. In your case,
you can probably live with the little bit of argon waste for
a couple of parts.
In a sectional view of the alu stock, here is what the trench
should look like:
| |__| |
A top view of the trench:
| ________________________________________________ |
| (________________________________________________) |
You can easily make a piece to match the length of the weld,
and the pointed end of the cone as well. The reality is that
you don't need a milling machine to make this type of tooling,
a high-powered router will do the job.
Next, you add a barbed fitting to feed the inert gas to the
trench, on the back side:
| |__| |
Since the aluminum stock is easy to work with, you can also
drill the part to feed from any point. Sometimes, feeding
from the ends is useful. Instead of going to the trouble of
putting a barbed fitting, I now drill a 1/4" hole, stick a
piece of 1/4" ss tube, and strike the aluminum with a hammer
to lock the ss tube in place. Some tygon tubing easily seals
onto the 1/4"ss tube. This technique will allow you to make
very small, or very thin jigs.
Your sheet stock is bent into the conical shape, and you are left
with a straight line butt weld. The aluminum stock can provide several
functional features, including back-purging of the weld, mechanical
support for the butt weld, and it can act as a heat sink to help
minimize the distortion from welding. One of the ends of the aluminum
stock can be longer to allow holding in a vise. This may facilitate
making a better cone.
One method to avoid distortion in ss welding is to weld short
stitches. You start by tack welding. The tacks should be very
close together for thinner stock. I think the rule of thumb is
that the spacing between tacks should be about 4x to 8x the thickness
for ss. You then make very small stitches linking the tacks together,
and you join pairs in different parts of the weld. Avoid joining
juxtaposed pairs of tacks. The parameter of import is to NEVER weld
continuously for long periods. This is what causes distortion in
thin sheet stock. If you run some test pieces, you will be able
to gauge how much time the torch can stay on continuously before
things start to deform. You then try to stay well below half this
time. Usually, the 4x rule spacing, and joining non-juxtaposed
pairs works fine.
The aluminum is easy to machine to match complex surfaces and
joints, it doesn't distort, and doesn't get welded to the ss.
You can even run some cooling water through the aluminum, but
machining the extra conduits is a bigger job. If you were making
these all day, some water cooling would be a real benefit. These
jigs can get hot.