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After I got some inspiration at midnight last night to redo my venting system, I came upon the unfortunate discovery that from the exit of my kiln to the blower, it has all rusted.

 

so..... anyone have any ideas.... The fan still works, but every fitting has rusted to it...

 

I am trying not to reflect my anger and stay positive because I need to fire this kiln by Wed.

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Just kind-of shooting from the hip here - but are you sure it's "rust" (oxidation of the duct & fittings themselves) ?  

Your first two pic's definitely look like it could be rust working its way through whatever coating was (or wasn't) on the interior of the fittings - but that flex-duct looks like it's aluminum.  If that's the case, and you've got the same red/brown inside the flex duct, you may be looking at material that's actually condensed out of the kiln vapors, rather than rusting of the duct itself.    (Aluminum does oxidize - but it wouldn't be 'rust red'.)

 

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That's all perfectly normal. There's always some moisture given off at the start of a firing (even bone dry pots have some moisture in them), and then chemical moisture burns off around 900-1000F. All that moisture mixes with everything that's burning out of the clay and forms some corrosive stuff. Any galvanized steel parts, like the connections to the fan and kiln, will rust, and the flexible aluminum duct will corrode and become brittle and get holes in it. That's how it goes.

If the connections to the kiln and fan are still solid, then don't bother replacing them yet. A little surface rust won't matter. If they're brittle and easily broken, then replace them. They look like end caps with a hole in the middle. Probably a 4" cap with a 3" hole. Easy enough to drill the hole with a hole saw. You could probably just use a 4" takeoff . You'll have to drill out the rivets that attach the connector to the fan. You can attach the new one with 6x1/2 pan head screws if you don't have a rivet gun. You can replace the flex duct with the same thing, it's cheap and easy, or go with something more durable like  rigid duct or a rubber duct like I mentioned in the other discussion. The rubber duct should only be used once you get some dilution of the kiln air as discussed in the other thread.

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30 minutes ago, Rockhopper said:

Just kind-of shooting from the hip here - but are you sure it's "rust" (oxidation of the duct & fittings themselves) ?  

Your first two pic's definitely look like it could be rust working its way through whatever coating was (or wasn't) on the interior of the fittings - but that flex-duct looks like it's aluminum.  If that's the case, and you've got the same red/brown inside the flex duct, you may be looking at material that's actually condensed out of the kiln vapors, rather than rusting of the duct itself.    (Aluminum does oxidize - but it wouldn't be 'rust red'.)

 

That was my first thought, After closer examination, it is rust. The fan itself is rusting kind of badly but still works.

 

I believe the fan metal is not aluminum.

Edited by Brandon Franks

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28 minutes ago, neilestrick said:

That's all perfectly normal. There's always some moisture given off at the start of a firing (even bone dry pots have some moisture in them), and then chemical moisture burns off around 900-1000F. All that moisture mixes with everything that's burning out of the clay and forms some corrosive stuff. Any galvanized steel parts, like the connections to the fan and kiln, will rust, and the flexible aluminum duct will corrode and become brittle and get holes in it. That's how it goes.

If the connections to the kiln and fan are still solid, then don't bother replacing them yet. A little surface rust won't matter. If they're brittle and easily broken, then replace them. They look like end caps with a hole in the middle. Probably a 4" cap with a 3" hole. Easy enough to drill the hole with a hole saw. You could probably just use a 4" takeoff . You'll have to drill out the rivets that attach the connector to the fan. You can attach the new one with 6x1/2 pan head screws if you don't have a rivet gun. You can replace the flex duct with the same thing, it's cheap and easy, or go with something more durable like  rigid duct or a rubber duct like I mentioned in the other discussion. The rubber duct should only be used once you get some dilution of the kiln air as discussed in the other thread.

Im just going to go with a full aluminum duct setup. Im going to do a better job of getting the air moving. 

 

I think the water was building up so much because of those flexible vents. Just going with the straight hard ones and some 90 degree turns with a tee joint allowing some room air in through a vent.

 

Pardon my vocabulary, I am not a plumber or handyman by any means, I don't fully understand all of the jargon used for this stuff.

Edited by Brandon Franks

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 My thoughts were mostly concerning your pic of the flex-duct, with the note that says 'A lot of rust' - thinking that if you have 'rust' inside an aluminum duct, it's traveling there from somewhere else, because aluminum doesn't produce the red/brown rust that we see in your pics of the (presumably) steel fan housing and end connector.

 

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Smooth ducts move air much better than ribbed ducts but they are harder to assemble. That said the galvanized ducts you can use Ospho deruster to neutralize (takes 24 hours before paint) any rust and paint with high heat aluminum spray paint sold at any hardware store -you can paint and get more life out of them.If you are buying new metal (not aluminum or stainless) you can paint with said paint and get more life from the start . Use self tapping sheet metal screws as Neil said above.

I would do this with those two rusty metal pieces in last photos as they are not yet to bad and can clean up well with deruster and paint .
as to the Ospho Youtube it to see how its done-best viewed at midnight as well

Edited by Mark C.

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4 hours ago, Brandon Franks said:

After I got some inspiration at midnight last night to redo my venting system, I came upon the unfortunate discovery that from the exit of my kiln to the blower, it has all rusted.

 

so..... anyone have any ideas.... The fan still works, but every fitting has rusted to it...

 

I am trying not to reflect my anger and stay positive because I need to fire this kiln by Wed.

IMG_3146.jpeg

IMG_3145.jpeg

IMG_3131.jpeg

The more dilution (room air) you mix in the less corrosive the atmosphere will become. Vent fans that have no dilution air draw such a small quantity of air that the velocity in the suction side piping begins to corrode first and since the velocity is low the water in the pipe does not evaporate readily which ends up as a corroded mess. Find or fabricate a proper mixing manifold and your issues will decrease 100 fold. On kilns like yours, I have simply drilled three holes Equally spaced around that sheet metal collar in the picture and simply started with 1/2” diameter and slowly enlarged them as need be all using a step drill. The hole into your kiln looks rather large as well. It’s hard to tell from the picture though. Look at some of the stuff on the market, they all operate very similarly.

Edited by Bill Kielb

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2 hours ago, Bill Kielb said:

The more dilution (room air) you mix in the less corrosive the atmosphere will become. Vent fans that have no dilution air draw such a small quantity of air that the velocity in the suction side piping begins to corrode first and since the velocity is low the water in the pipe does not evaporate readily which ends up as a corroded mess. Find or fabricate a proper mixing manifold and your issues will decrease 100 fold. On kilns like yours, I have simply drilled three holes Equally spaced around that sheet metal collar in the picture and simply started with 1/2” diameter and slowly enlarged them as need be all using a step drill. The hole into your kiln looks rather large as well. It’s hard to tell from the picture though. Look at some of the stuff on the market, they all operate very similarly.

Don't know the hole size, came pre-drilled.

 

I am going to test a few methods to get the room temp air in. I will attach the start of the method I am going to try first. Very similar to the one in the video you shared in the other topic. I have tested it using a simple paper method I thought of and measuring the curve the paper makes when the fan is on with and without the vent intake in place and it seems to be = so I think the amount of air being taken from the kiln should be = even with the new intake.

IMG_3155.jpeg

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4 hours ago, Bill Kielb said:

The more dilution (room air) you mix in the less corrosive the atmosphere will become

Also, I think I found the source of the rust in the aluminum. Where I had the connection to the kiln, I had 4 screws. They were magnetic so I assume they are iron alloy or something. They were *SUPER* corroded. I have the original screws, ~1/8th of an inch had been eaten away from the exposed areas of the screws.

 

ALSO, do you know what the fittings to attach the venting pipe to the wall are called. I cannot seem to find them.

Edited by Brandon Franks

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2 hours ago, Brandon Franks said:

Also, I think I found the source of the rust in the aluminum. Where I had the connection to the kiln, I had 4 screws. They were magnetic so I assume they are iron alloy or something. They were *SUPER* corroded. I have the original screws, ~1/8th of an inch had been eaten away from the exposed areas of the screws.

 

ALSO, do you know what the fittings to attach the venting pipe to the wall are called. I cannot seem to find them.

This hard to do without instrumentation, but in the design in the video the original pickups or mixing manifolds were left In place with the factory holes in them. An addition exhaust air grill was added above but each leg then received a balancing damper so that after adjustment, the original draw from the factory design kiln pickups was guaranteed.
 

Actually if the upper vent became completely blocked, it still would run and still had the factory dilution air to keep it cool.  The factory design works so I would make sure you include the holes nearest the kiln else this leg will always corrode excessively.

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In factory systems the dilution air is greater than the kiln air, in order to cool the kiln air sufficiently. The goal is to cool the air enough that it's no hotter than a clothes dryer, under 150F. Just drill some holes at the kiln connection and you'll be good to go.

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2 hours ago, neilestrick said:

In factory systems the dilution air is greater than the kiln air, in order to cool the kiln air sufficiently. The goal is to cool the air enough that it's no hotter than a clothes dryer, under 150F. Just drill some holes at the kiln connection and you'll be good to go.

The mount to my kiln is two inches long. I have very limited space to drill the holes there. Those screws have gotten really tight into the kiln, and I am not sure I will be able to get them off without completely disassembling my kiln. I think my best option is to drill smaller holes and make the cool air intake connection closer to the kiln.

 

I drilled two 2/8th holes into the connection to the kiln, but that is the largest I could go while keeping the piping taking air out of the kiln tight.

 

 I think it will just be easier to move that tee joint 2 feet from the kiln and have it suck in air about 4 feet down from the fan. That way there is more sufficient time to mix the air than in my original idea.

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4 minutes ago, Brandon Franks said:

The mount to my kiln is two inches long. I have very limited space to drill the holes there. Those screws have gotten really tight into the kiln, and I am not sure I will be able to get them off without completely disassembling my kiln. I think my best option is to drill smaller holes and make the cool air intake connection closer to the kiln.

 

I drilled two 2/8th holes into the connection to the kiln, but that is the largest I could go while keeping the piping taking air out of the kiln tight.

 

 I think it will just be easier to move that tee joint 2 feet from the kiln and have it suck in air about 4 feet down from the fan. That way there is more sufficient time to mix the air than in my original idea.

Yeah, not a fan of the tee idea really without some way to damper the airflow. I have done this on kilns piped like yours but simply slipped the fittings together and drilled three hole as close as possible. Reasons for the location, minimize corrosion, it provides the maximum available power to still withdraw air from the kiln, and it was virtually goof proof once completed.

For all of those that were piped like yours, most of the ductwork was excessively corroded and one of them, the fan finally died from corrosion and overheat.

As far as the hole into the kiln, you could always patch and re-drill if oversized.

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1 minute ago, Bill Kielb said:

Yeah, not a fan of the tee idea really without some way to damper the airflow. I have done this on kilns piped like yours but simply slipped the fittings together and drilled three hole as close as possible. Reasons for the location, minimize corrosion, it provides the maximum available power to still withdraw air from the kiln, and it was virtually goof proof once completed.

For all of those that were piped like yours, most of the ductwork was excessively corroded and one of them, the fan finally died from corrosion and overheat.

As far as the hole into the kiln, you could always patch and re-drill if oversized.

I will put a damper in there and test it. Just based on what I have tested so far, it seems to work fine (without a damper).

 

My whole venting system is 12 feet of piping, I am not concerned about the fan not being able to blow air far enough (one of my original concerns.)

Back-flow is what I am concerned with, but with a damper (or two maybe, it won't be an issue.

 

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37 minutes ago, Brandon Franks said:

I will put a damper in there and test it. Just based on what I have tested so far, it seems to work fine (without a damper).

 

My whole venting system is 12 feet of piping, I am not concerned about the fan not being able to blow air far enough (one of my original concerns.)

Back-flow is what I am concerned with, but with a damper (or two maybe, it won't be an issue.

 

Those vents can handle up to 60 feet of duct with a couple of elbows. You'll be fine.

Just add a short extension to the kiln connector where you can drill the dilution air holes.

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