PDA

View Full Version : Anodizing and Ventilation



hwingo
02-23-2011, 10:30 AM
Quite a few years ago I purchased an anodizing system (and I still have it). I received it in the dead of winter (it was 30F below zero) so I acted STUPID and decided to anodize some parts in my kitchen. This was NOT a bright thing to do. Although the process only produces hydrogen gas, H2SO4 is picked up with effervescence and H2SO4 fumes quickly filled the house. We had to open every door and window to vent our home. It must have been bad because I am still cleaning feces out of my underwear.

All being said, I was considering the fabrication of an enclosed hood, 3X4X2 feet, (like the ones used in chemistry labs) with exhaust fan. I would like to keep it simple. Anodizing will not be a frequent event therefore I don’t want to spend a lot of money on a “protected” exhaust fan. My concern is, H2SO4 will attack the fan’s metal components cutting its life expectancy short. I considered cutting a hole in the top of the hood and using a Wet-Dry vac as the ventilating source. The exhaust hose would be vented to the outside.

For those having some experience with anodizing, what are your thoughts on using the Wet-Dry vac to vent gases to the outside?

Harold

squirrel
02-23-2011, 10:34 AM
Can you spell suicide..... H2 is extremely flamable. You need an expolsion proof fan for that application.

rockrat
02-23-2011, 10:39 AM
I dont know if I would trust a shop vac to do the job. Not to say that it couldn't but I would have to think more about it. The bigger issue is the air that is replacing the exhausted air. If you remove air from a room, where does the air that replaces it come from? Generally, it is from the leaks and cracks in the house letting outside air in. Why not force outside air into the area where the work is being done and then out an exhaust? That being said...

A similar subject was kicked around here before concerning paint booths. You might want to take a look at small portable paint booths that use positive ventilation to force the air in the area out. This method keeps fresh clean air moving past the fan and there is little chance of the fan being an ignition source or becoming corroded from the fumes.

Search the past threads around here and see what comes up for paint booths.
Rock~

Black_Moons
02-23-2011, 01:01 PM
How about venturi action?

Shopvac 2" *exhaust* hose run into the center of a 6" exhaust pipe near the exit. Result is high speed air picks up air from around the 2" exhaust point and takes it along for the ride out the 6" exhaust pipe.
(Alternatively, compressor can be used, But could be more of a waste of energy.. Not sure)

Id also consider doing it outside... Iv heard vaporised acids love to attack (rust) everything metal in the room.

garagemark
02-23-2011, 01:18 PM
You might create a venturi in the ductwork and use your shop vac as a blower to exhaust the gases. There would then be no fan in the ductwork, thus no explosion issues. You would probably need to fool with dimensions and flow rates a little.

Just a thought.

Mark

On edit, Black Moons beat me to it.... So it must work if we both think so.

Weston Bye
02-23-2011, 01:23 PM
Running for an continuous hour or so is hard work for most consumer-duty shop vacs.

Black Moon's suggestion for a venturi-type system, but driven by a continuously-duty blower makes sense.

Why not just do your work outdoors? Well, not at 30 below, but cold is better when anodizing, as deeper penetration is possible and cooling the bath is easier. You don't need to hover over the pot during the whole process.

I did some indoor anodizing once, but later found some badly rusted tools in the vicinity of where I did the dirty deed.

Duffy
02-23-2011, 04:27 PM
You might be well advised to cobble together a proper chemical lab style fume hood. A four foot wide hood, with the front sash open 12 inches, needs enough air through it to give an average face velocity of 100-125 ft/min. This translates into about 500 cfm. Not a lot, any small furnace circulating fan will easily give that output.
DO NOT believe that more is better in this application. Any less can cause problems and much more will only cause more problems. This air flow will, by the way, create a safe working environment for virtually ANY gas or fume. There are exceptions, but you wont run into them.
How do I know this? This is what did for a living for about 20 years. I worked mostly in research labs, but the principles are a constant.

gzig5
02-23-2011, 05:36 PM
Here is one option for a fan. There are others and the little computer fans are all plastic and cheap enough to pitch if they die.
http://www.surpluscenter.com/item.asp?item=16-958-A&catname=

Duffy
02-23-2011, 07:00 PM
Because of the entrained sulfuric acid, the exhaust will play hell with any ordinary blower or fan. Ideally, you want a belt driven all-plastic utility set or a vane axial unit. THAT is unlikely to happen. The one listed in the Surplus Center MAY work. The only problem that I forsee is with the motor being in the air stream.
Do not forget, this will not be a full-time operation, so maybe a fan that dies an early death is alright for the purpose.
A decent double-spool range hood fan would work and they turn up in the garbage or garage sales or at Habitat.

Black_Moons
02-23-2011, 08:35 PM
Iv run a few shop vacs for over 24 hours... And indeed it is hard on them.. they only lasted about 15 days on average. Thankfuly that was only 3 days outta every year they had to be used in my case. (Basement floods that occured about once a year)

squirrel
02-23-2011, 09:39 PM
Iv run a few shop vacs for over 24 hours... And indeed it is hard on them.. they only lasted about 15 days on average. Thankfuly that was only 3 days outta every year they had to be used in my case. (Basement floods that occured about once a year)
Those must have been the older good ones, the el cheapo's get very hot after a few minutes.

hwingo
02-24-2011, 10:35 AM
You might be well advised to cobble together a proper chemical lab style fume hood. A four foot wide hood, with the front sash open 12 inches, needs enough air through it to give an average face velocity of 100-125 ft/min. This translates into about 500 cfm. Not a lot, any small furnace circulating fan will easily give that output.
DO NOT believe that more is better in this application. Any less can cause problems and much more will only cause more problems. This air flow will, by the way, create a safe working environment for virtually ANY gas or fume. There are exceptions, but you wont run into them.
How do I know this? This is what did for a living for about 20 years. I worked mostly in research labs, but the principles are a constant.



All being said, I was considering the fabrication of an enclosed hood, 3X4X2 feet, (like the ones used in chemistry labs) with exhaust fan. I would like to keep it simple. Anodizing will not be a frequent event therefore I don’t want to spend a lot of money on a “protected” exhaust fan. My concern is, H2SO4 will attack the fan’s metal components cutting its life expectancy short. I considered cutting a hole in the top of the hood and using a Wet-Dry vac as the ventilating source. The exhaust hose would be vented to the outside.

I think Duffy's comments and reasoning are more in order with my thinking. That's why, in my initial statement, I talked about an *enclosed* hood being 3 feet tall, 4 feet wide, and 2 feet deep.

Yes, I can spell H2 (hydrogen gas). I can also spell Hindenburg and I am aware that hydrogen gas can be explosive if the percentage of hydrogen gas increases to as little as ~18% in air. I do believe that the *percentage* of the mix is what is important rather than the *presence* of H2. I have never done a quantitative analysis to determine just how much H2 is generated when anodizing small parts but I suspect it is small. I also suspect, though I admit it's a leap of faith, that having an adequate "draw" of room air into the hood (and out the other end to the outside) will quickly mix generated H2 and "dilute" the small amount of H2 generated significantly decreasing the percentage of H2 in the mix and lower the risk of explosion. We generated some ugly gases in college and to the best of my knowledge, there were no remarkable events when using the hood.

I like the venturi idea. I also like the explosion proof motor idea but those things are expensive.:eek: Still, with all being said, H2SO4 (in vapor form) is still my greatest concern. One has suggested doing this out side and that is a reasonable suggestion ...... except Alaska winters get quite cold. This would limit latitude and I desire unfettered time if needing to anodize a part.

I appreciate all suggestion and thoughts on this matter and I thank you for making the effort to consider my dilemma.

Harold

Duffy
02-24-2011, 06:50 PM
Harold, venturis sure do work, but they have a very high operating cost. For a 4 to 5 foot wide perchloric acid fume hood, figure a 2 hp induction fan. These used to be plumbed up with type 316 SS all-welded duct work, washdown rings every eight vertical feet and all assembly using 316 SS bolts, nuts and washers. I was paid A LOT of money to prepare the protocols and supervise the dismantling of many systems that had a few "substitutions" in the assembly.
I have just been working on a newer unit,all SS but with a plastic vane-axial fan, ($10,000.00 for the fan, by the way,) and an all plastic fume hood with an integral scrubber system.
Incidentally, Gatineau/ Ottawa weather takes no backseat to yours!
For your purposes, and to leave you some funds to build guns, I would suggest the following: Build your enclosure, with a sloping top to the exhaust stack, from melamine board, with carefully caulked along the seams. hinge a piece of polycarbonate, (1/8") across the front, with a 6 to 12 " gap at the bottom. Scrounge up some 6" plastic sewer pipe off-cuts to use for exhaut duct and mount whatever fan you can find on the terminal end. Accept the fact that its life WILL be short.
You dont have to worry about a rear-mounted exhaust plenum with upper and lower pickups; your only problem will be damp, acidic, warm air with a bit of hydrogen in itand it will rise by itself.

hwingo
02-25-2011, 12:50 AM
Harold, venturis sure do work, but they have a very high operating cost. For a 4 to 5 foot wide perchloric acid fume hood, figure a 2 hp induction fan. These used to be plumbed up with type 316 SS all-welded duct work, washdown rings every eight vertical feet and all assembly using 316 SS bolts, nuts and washers. I was paid A LOT of money to prepare the protocols and supervise the dismantling of many systems that had a few "substitutions" in the assembly.
I have just been working on a newer unit,all SS but with a plastic vane-axial fan, ($10,000.00 for the fan, by the way,) and an all plastic fume hood with an integral scrubber system.
Incidentally, Gatineau/ Ottawa weather takes no backseat to yours!
For your purposes, and to leave you some funds to build guns, I would suggest the following: Build your enclosure, with a sloping top to the exhaust stack, from melamine board, with carefully caulked along the seams. hinge a piece of polycarbonate, (1/8") across the front, with a 6 to 12 " gap at the bottom. Scrounge up some 6" plastic sewer pipe off-cuts to use for exhaut duct and mount whatever fan you can find on the terminal end. Accept the fact that its life WILL be short.
You dont have to worry about a rear-mounted exhaust plenum with upper and lower pickups; your only problem will be damp, acidic, warm air with a bit of hydrogen in itand it will rise by itself.

Hi Duffy,

I just got home from work and just read you last comment. Like I stated previously, I’m not too terribly concerned with H2. As a side note, minus a barrel (which will not be parkerized) I parkerized the remainder of a rifle last night. This was done on my gas kitchen range under a conventional stove top hood. The parts “fizzed” H2 angrily for nearly 12 minutes at 185F. Either I was fortunate or there was insufficient H2 generated to create an explosion. Another way of approaching this is, there was ample surrounding air that mixed with hydrogen gas to sufficiently lower gas percentage below the percentage necessary to have an explosion. I can never recall that much activity when anodizing.

As I drove home, I had visions of my future vent pipe becoming a “cooling tower” during the anodizing process. I imagined the fan drawing H2SO4 fumes from the hood and pushing it along the vent pipe, all the while condensing and collecting on the inside walls of the pipe. When sufficient amounts had collected, I envisioned small streams of acid running back from whence it came forming an ever growing pool of concentrated H2SO4. Without cleaning out the exhaust pipe after every session, such is more than plausible.

Although it would be a pain in the rump, I can see no way of escaping the need to disassemble the vent pipe and wash the inside with NaHCO3 after every session. In the summer or even in less extreme winter conditions, an alternate site could be used out-of-doors. As one contributor pointed out, “cooler temperatures are the anodizer’s friend”. Still, it would really be nice to have everything indoors and not have to worry about local moose, wandering brown bear, and the dreaded summer black flies and mosquitoes disrupting me or works in-process.

Harold

hareng
02-25-2011, 09:02 PM
How big is this setup?

Used to do sulphuric anodising in an enclosed environment 19% mix but more worried about the fumes from hydrochloric acid.

hwingo
02-26-2011, 01:37 AM
Hi Jonny,

The setup is very small. In the past I used a small plastic travel-cooler as a tank (just large enough to hold four or possibly five sandwiches, and if lucky two apples). The internal capacity was just large enough for a wide cathode (3" wide by 4" tall) and a *stripped* AR-15 lower receiver. I might would find room for a few VERY SMALL pieces.

Harold

darryl
02-26-2011, 03:51 AM
How many friggin' projects do I need-

I had planned to create a vented hood/paint booth/soldering bench type of thing for my workshop. What I had first thought to do was get about 20 of those 12v mini fans and have them blow into a duct which would vent outside. I had thought to have about half of the fans below a benchtop, and half above, and spaced apart fairly evenly. There would be a hood and sides, and the only place for air to enter the 'booth' would be the front. I wanted this thing to be a completely self contained unit, probably on castors. I did then consider the potential for ignition of the vented gasses, and the potential for metal parts to rust up.

I collected the fans, but now I'm thinking that the 'filter wall' idea would be better. One place I worked at had such a thing- the entire rear wall had a built-out section with a single large fan evacuating the space between the filter wall and the rear wall of the room. The filters collected whatever overspray there was that didn't hit the floor first. In the case of fumes only, the filters wouldn't have anything to collect, but maybe they could at least partially neutralize some gasses with an appropriate type of filter.

My needs are far less severe- occasional soldering or paint bomb, sometimes smelly gluing, almost always small parts, so it really only needs to be a desk sized thing. A vent fan from a microwave oven is a plastic squirrel cage, and the motor could easily be located outside of the filter wall. Any metal shafting still used could be protected with an epoxy coating, or another shaft material could be used extending from the motor. These fans are often multi-speed and will blow a surprising amount of air so I think they would be able to do the job. In any event, plastic squirrel cages are available, and can also be made- it's not rocket science.

The mention of incoming air to replace exhausted air is important. Not only do you need a free-flowing source, you may need to heat that source since you could be blowing a lot of heated air outside the building. The amount you blow out might be restricted by how quickly you can heat incoming replacement air. With doors on the front of the cabinet, you could minimize the amount of flow required, depending on the project at hand. You could tend to the project, then close the doors, leaving only a small opening somewhere to allow for some minimum flow rate to continue.

Still a good project, still on my list to do.

hareng
02-26-2011, 09:38 PM
Wouldnt worry about it Harold, sounded like a big monster industrial setup you have.

boslab
02-26-2011, 11:55 PM
we have big fume cubboards at work but i dont think you need to go that far, they are nice to work in however, the fans are bifurcated so the motor is not in the pipework, its outside, HCl fumes will quickly destroy 316 stainless, you should be able to see through the pipe in a couple of months but we boil hydrochloric to dissolve metalic samples like iron to titrate it to get a %Fe, boiling concentrated HCl dosent take prisoners, neither does boiling Hydrafluric HF, that even eats the glass so its boiled in PTFE beakers.
Go with an old cooker hood and some 4" pvc pipe to the great outdoors
works for me, plastic curtain can be added at the side.
regards
mark

Rosco-P
02-27-2011, 09:57 AM
Shopvacs have universal motors. You might not want a motor with potentially sparking brushes near or in the path of explosive gasses. You could look for a used/scrap Torit dust collector (62 series?) and use the motor and blower assembly from it. It will have an explosion proof motor and electrics.

ed_h
02-27-2011, 10:15 PM
There is no doubt that hydrogen can be a dangerous gas, but a little rational thought may indicate that for a small home operation, there isn't much likelihood of serious problems.

If my highschool chemistry doesn't betray me, a current of one amp for a second gives us a coulomb of charge, and it takes 96500 coulombs to convert a "mole" of an ion to a mole of an element (at least in the case of hydrogen, which takes a single electron to convert from H+ to H), and it takes 2 hydrogen atoms to make a molecule of hydrogen.

So I believe it would take 193000 coulombs to get a mole of H2. At standard temp and pressure, a mole of a gas occupies 22.4 liters, so one amp for a second would only generate about 0.1 ml of hydrogen. Ten amps for an hour would give us a little over four liters of gas.

A small (8 x 8 x 8 foot) room has almost 15000 liters of air, yielding a hydrogen concentration of about 0.03% (in addition to the trace already there). This is if none of the hydrogen escaped the room, which it is really good at. This also assumes 100% efficiency in the production of gas.

My memory or my calculations could be faulty, but based on them, I suspect that the sense of danger may be exaggerated.

vincemulhollon
02-28-2011, 06:58 PM
This is if none of the hydrogen escaped the room, which it is really good at. This also assumes 100% efficiency in the production of gas.

And assumes theoretically perfect mixing.

The biggest problem is the cascade effect.

So inside the tub there's only a ml of h2, enough to splash you with a pop.
Then you jump back still holding the wires and tip the tub over.
The you try to run out the door because you're freaked out, and slip and break your leg.
Its just all downhill from there.

But your chemistry numbers are correct, the acid vapors will damage your lungs long before the H2 explodes.

hwingo
03-01-2011, 01:34 AM
And assumes theoretically perfect mixing.

The biggest problem is the cascade effect.

So inside the tub there's only a ml of h2, enough to splash you with a pop.
Then you jump back still holding the wires and tip the tub over.
The you try to run out the door because you're freaked out, and slip and break your leg.
Its just all downhill from there.

But your chemistry numbers are correct, the acid vapors will damage your lungs long before the H2 explodes.

Though I didn't go through the "mental gymnastics" as Ed-H has done for us, my previous experiences affords me the luxury of "leap of faith", thus, as I have stated several times throughout this topic, my concern regarding H2 explosion is slight and is dwarfed by a past experience with H2SO4 when anodizing. The Grand Architect of our universe has blessed me with remarkable olfactory receptors and tear glands. Not only are olfactory receptors used for pleasure, they often serve a more noble purpose that being to sound the call of danger and to elicit the "fight or flight" response. Also, tearing serves many function, one being to dilute harmful airborne agents in an attempt to preventing damage to the eyes and yet another is to sound an additional alarm when one chooses to ignore previous alarms of danger. Burning of the lungs is another clear indicator that "something stinks in Denmark".

As previously stated, the presence of H2SO4 vapors is my greatest concern because I have been on the receiving end of this corrosive product when anodizing using a very small container. Such experience is one not quickly forgotten and one that I do not wish to revisit. When exposed to H2SO4 vapors, I fear for my health and if these vapors were wandering about freely in my shop, my next concern would be for anything metal that I might hold in high regard.

My thread has taken some interesting twists & turns. One such "twist" is various proposals regarding an appropriate evacuation system. Of particular interest is the "type" of exhaust fan that could/should be employed. We've talked about explosion proof fans, dust proof fans, corrosion resistant fans, and venturi systems. I'm willing to display my ignorance at the expense of being brought from darkness to light. We've discussed the possibilities of using a wet/dry vac as a meager exhaust system but I think it was generally agreed that a wet/dry vac would likely over-heat if left running for 15 minutes or longer. But one point regarding the wet/dry vac that was not so convincing is that the wet/dry vac did not have a "sealed motor" which could possibly lead to a fire/explosion. Why would a company willingly sell a product that is used to suck up fine particulate or liquids without first considering potential risks to person or property and the liability that the company may incur for placing person or property at risk? Sears, Dewalt, et. al are no small companies. Surely they've researched the worthiness of their product and the liability this product may pose. People do crazy things and I am no exception. I've used my Sears wet/dry vac to suck up a pound of corn flour (not corn meal) that fell from the kitchen counter and broke on the floor. Flour is a fine dust and flour is explosive. I used my wet/dry vac to suck up spilled kerosene and I've vacuumed a sundry of saw dust and other particulate without incident? If the motors of wet/dry vacs are not sealed, why would one not realize fires and explosions in our shops and homes? Surely various manufacturers would have taken fires and explosions into account when offering these products for sale.

Harold

Weston Bye
03-01-2011, 06:54 AM
While not addressing the shop vac issue, I daresay that the vast majority of our members (or their wives) have encountered - indeed manufactured - sulfuric acid:

The act of chopping onions releases sulfur rich vapors into the air. When these vapors reach the moisture on the surface of the eye, the sufur combines with the water in the tears, forming sulfuric acid, inducing more tears, providing more water to combine with additional sulfur vapors, etc... The root end of the onion is richer in sulfur than the rest, so should be cut last.

That being said, I am surprised that the vapors I encountered while anodizing have not produced similar effects. Rather, any vapors inhaled didn't cause pain but gave me the definite impression that they were bad and caused an immediate cough and a desire to get away.

hareng
03-01-2011, 12:53 PM
And heres me diving in to the 19% sulphuric up to my elbow to retrieve a part that fell off, just wash off with water works every time.

DeereGuy
03-01-2011, 01:57 PM
I have been anodizing inside of my shop now since September. The room I have the ano tank in is separate from most of my machinery. The tank is also set right below a window. I have a window fan that gets put in and turned on whenever I am anodizing.

In addition to this I am using a product called Fumetrol (spelling my be incorrect). My wife is very sensitive to smells and she cannot detect when I have something in the ano tank. Note that I am not using the LCD method and my current PS is always maxed out at 6 amps.

I have just ordered a new 50V 30A PS and it will be run at 7 to 8 amps most of time.

ed_h
03-03-2011, 10:39 AM
The biggest problem is the cascade effect.


Vince--

It's hard to deny the cascade effect, since I'm sure we've all experienced it.

In my setup, the acid coming from the tank seems to be more of a fine mist created by the bubbling action, and not so much a true vapor or gas like HCl. I usually run my anodizing tank with a loose fitting lid that seems to limit the acid escape, while preventing H2 buildup.