IgnrntNewb

Compressor Tank Questions

Recommended Posts

I'm in the process of building a propane forge from an old air compressor tank I was given. The current interior dimensions are 13-3/4" diameter x 28" length. After insulation, I plan on having a 6" diameter x 25-26" interior length, giving me a volume of between 705 and 735 cubic inches. I've just finished building the double Frosty T burner set up to heat the cook chamber. None of this really has anything to do with my question(s). I just wanted you to know what I'm working with.

Question for anyone who's used an air compressor tank, or anyone else who knows...: What kind, if any, prep-work should I do to the interior surface of the tank before laying down insulation? Mine has a fair amount of surface rust and I'm wondering if I should paint the interior after taking out the rust. 

Thanks in advance!

20191122_170421.jpg

20191203_161736.jpg

Share this post


Link to post
Share on other sites

First why do you need such a long forge?  Will you be specializing in decoratively twisted stair balusters?

I know it's not for swords as heating more than you can work before it drops below forging temps degrades the steel, (grain growth, decarburization and scale losses). But it must be something long that you can work all at once, otherwise you will be throwing away money in fuel costs.---Like driving a dump truck for your daily driver because once or twice a year you need to move a load of gravel!

Share this post


Link to post
Share on other sites

What Thomas is getting at, is that length versus diameter matters a LOT in this kind of forge. Too much length requires too many burners, eventually creating too much back pressure for natural aspiration to work properly. In short, extra long forges are the equivalent of driving the car with its emergency brake on.

Share this post


Link to post
Share on other sites

My username isn't a joke. I'm as ignorant in these matters as they come. I haven't come here thinking I know anything about what I'm doing. I've come here to make sure I do it as close to correctly the first time as I possibly can by asking those who've already done it correctly.

The reason my tank is as long as it currently is is because that's what I was given. I've done a lot of research looking for answers to questions that I have, but there are many questions that I don't even know I need to ask. What interior diameter/length should I shoot for? Should I avoid building something that requires two burners for the time being? 

While I'm not currently aiming at forging sword-length blades, I am interested in doing some 18-24" blades along with the other smaller blades that I'll do more often. I'm not married to any particular dimension. I'm here for the sole purpose of humbly asking those who know to teach one who doesn't. Tell me what I'm doing wrong and I'll fix it.

 

 

Share this post


Link to post
Share on other sites

Have you tried skimming through the forges 101 thread? I would shoot for an interior of 300-350 cubic inches with a single 3/4 inch Frosty burner. It would be possible by cutting the tank about in half. This thread will be a good primer for you. You already have a head start with the two burners you have built, which look good to me.

https://www.iforgeiron.com/topic/61288-my-consolidated-notes-for-new-forge-builders/

 

Share this post


Link to post
Share on other sites
38 minutes ago, Irondragon Forge & Clay said:

Have you tried skimming through the forges 101 thread? I would shoot for an interior of 300-350 cubic inches with a single 3/4 inch Frosty burner. It would be possible by cutting the tank about in half. This thread will be a good primer for you. You already have a head start with the two burners you have built, which look good to me.

https://www.iforgeiron.com/topic/61288-my-consolidated-notes-for-new-forge-builders/

 

Thank you for your response. I have skimmed more than a few threads over the past few weeks, including the 'Forges 101' thread. There is an inexhaustible amount of info here. So much so that finding answers to specific questions can be quite difficult. 

I'm still hoping that someone will have some insight for me on my original question as to whether or not to paint the inside of the forge after I knock the rust off.

I do appreciate the link very much. I've gone through some of it over the past hour or so, but the drink is currently taking effect in the best possible way, and I am subsequently losing my ability to remain focused. So while I look forward to gleaning as much knowledge as possible from those who know WAY more about this than I do, I'm afraid I'll have to postpone any further gleaning until tomorrow.

Thanks again for all your responses!

Share this post


Link to post
Share on other sites

I'm not Mikey, but my name is Mike so here goes. One T burner will get a well built forge with an inner volume of 300-350ci. Up to welding temperatures. Don't get caught up in thinking you will build a better mousetrap. Find a proven forge and burner design and follow them exactly. Later on you can tinker after you know what a good forge is and what you want to do out of it.  

Pnut

Share this post


Link to post
Share on other sites

For the longer blades you plan to hammer out, you may consider building a small solid fuel forge so that you are not heating more of your steel than you can work in one pass. Otherwise you may have strength issues in your final product due to all the decarb and large grain structure (brittle and poor edge retention). Solid fuel forges are not difficult to whip up, and the big forge you are making is going to heat a lot at once.

Share this post


Link to post
Share on other sites

Thanks again to everyone who has taken the time to respond. Being that I don't even know how to build the hypothetical mousetrap here, I certainly don't assume I can build a better one. Thank you all for the insight and advice. I will be cutting my tank down by half and using a single burner. After that comes lots more study on the proper insulation process. I've read a lot, but there are still a few things I'm not sure I've fully grasped yet, possibly because I'm unfamiliar with most of the terminology. Anyway... I'll start another topic for those questions if I'm unable to figure it out through study.

Thanks again!

Share this post


Link to post
Share on other sites

The propane forge I use the most was made from an Oxygen welding tank---Way heavier wall than is needed. it's 14" long with a door in back to push longer stuff through.  I've been using it close to 20 years so far with two smaller NA burners.  I don't use mine for welding; but I have melted steel in it accidentally and created new and unusual additions to the english language.

Since it is so heavy I welded some small sq tubing to the sides and slid in L shaped sq stock to have a stock holder for both the front and rear doors.  The neat thing is that the tubing I use is an easy slip fit when aligned and then locks in place when set for use and so it doesn't shift when working stock over it.

If you have read into the postings you have probably run across the "There is no one gas forge that will be optimum for *everything*!" Build the one that will get you started well and build others as you gain experience and need them. (I have 3 propane forges and several coal/charcoal forges and have still dug a trench forge in the yard at times when I needed to heat long pieces.)

Lets see for an 18" blade you can do fine with a forge with a 9-10" hot spot.  Viking swords were done in forges with about a 6" hot spot.  (As real wrought iron needs to be quite hot to work we can get an idea of how big the hot spot they used by looking at twists done for things like the Oseberg Tripod.)

Share this post


Link to post
Share on other sites
On 12/3/2019 at 7:29 PM, IgnrntNewb said:

So Mikey... Is it your opinion as well that I should cut my tank down to 300-350 cubic inches and go with a single burner? 

That's really two questions in my view. Yes, cut the tank in two. As to the burner part; You can get along fine with a single 3/4" burner; but superbly with two 1/2" burners.

Share this post


Link to post
Share on other sites
10 hours ago, Mikey98118 said:

You can get along fine with a single 3/4" burner; but superbly with two 1/2" burners.

Well crap... Now you went and woke up every little OCD monster I've got running around in my head. They were fast asleep until I read that comment...

Are these 1/2" burners you suggest still Frosty's 'T' design? If so, can I just reduce 1"x1"x3/4" 'T' down to 1/2" black pipe Or would I need to go 3/4" T reduced to 1/2"?

Share this post


Link to post
Share on other sites

When you scale down the burner you scale down most parts. 1/2" inch T would have a 3/4" to 1/2" redducing T fitting, a 1/2" nipple and a 0.023" mig tip. (Anyone correct me if I have my imperial wrong). In these cases it is the ratios that matter. On my phone now so cannot easily find all the threads discussing the 1/2" T burner, there are a couple. 

Share this post


Link to post
Share on other sites
6 hours ago, IgnrntNewb said:

Are these 1/2" burners you suggest still Frosty's 'T' design? If so, can I just reduce 1"x1"x3/4" 'T' down to 1/2" black pipe Or would I need to go 3/4" T reduced to 1/2"?

To be utterly clear; that should work wonderfully well, but Frosty would have to answer the question about 1"x1"x3/4" 'T' down to 1/2" black pipe Or versus  3/4" T reduced to 1/2"? I'm inclined to always "always go with the sure bet," but it may not matter in this case.

Share this post


Link to post
Share on other sites

Thanks again, Mikey, and to Monkey Forge as well, for the responses. I'm sure Frosty is a very busy man, but I am VERY interested to read what he has to say about this one. In the mean time, I could always try to reduce it and see how the flame looks, post a video, get some input, etc...

Share this post


Link to post
Share on other sites

Tried to just reduce the 3/4 T down to 1/2" pipe... (1st video) That certainly didn't work... 

So I went and got the 3/4 - 1/2" T and, trimmed the tips back quite a bit, and it looks like I'm back to a similar flame as where I was with the 3/4" burners. I'm gonna leave it a lone until I get them mounted in the forge, at which point I'll finish tuning them. 

Anybody see anything right off the bat that I missed or could do different/better?

1/2" burners, take 2...

Share this post


Link to post
Share on other sites

My burner spacing look ok? I haven't cut the tank in half yet, but I put a black mark where it'll be cut to show where these burners will be centered. 

Should the holes in the tank for the burners be cut to fit as tightly to the half inch pipe as possible while still allowing it to slide up and down for adjustment? 

20191206_145241.jpg

Share this post


Link to post
Share on other sites

Yes, the burner spacing, and planned tank length, look good. The last video shows both burners running in the ball part, but not running the same. The furthest flame from view might be a little bit reducing; or it might not. Neutral is burner range--not an exact point on that range. The two burners seem to have landed at each end of that range. What to do? "If it ain't broke, don't fix it." Finish building the forge, and then look for "dragons breath"; if there is no exhaust flame, without simply turning the gas pressure way up high, then "no harm, no foul."

Let the kid wave hi in the next video. We're all curious :D

Share this post


Link to post
Share on other sites
12 minutes ago, Mikey98118 said:

Let the kid wave hi in the next video. We're all curious :D

Lol... Will do!

I'm pretty sure the tip in the burner furthest from view still need to be trimmed a bit. It's a little longer than the other. I just figured I'd wait until they were in the forge to do the final tune.

Should the holes in the tank for the burners be cut to fit as tightly to the half inch pipe as possible while still allowing it to slide up and down (when not tightened, obviously...) for adjustment?

 

Share this post


Link to post
Share on other sites

That is generally not the best idea, because most burners need a LITTLE secondary air, to burn their fuel completely. There are various ways to limit an over abundance of secondary air, but no convenient way to make up a dearth of it. 

Share this post


Link to post
Share on other sites

IgnrntNewb, I too consider myself an extreme novice. I see a lot of similarities between what you have shaping up and the one I built. Mine is 19" long, 7" dia and after the fact, I learned the sq.in. suggestion of 350. It takes both my 3/4 burners to get it hot. If I had it to do over I would build it shorter. As for securing your burners, have a look at the  pictures on my thread and see what you think. They stay put and it doesnt affect the flame that I can tell.

 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.