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crucible repair

Posted: Sat Jul 03, 2010 1:57 pm
by todd goff
Well,I finally got motivated today to look at the latest furnace I have gotten and the outcome was as I thought; not too good. I was optimistic when I looked into the furnace and thought I saw a crack in the crucible and it was. I fought the swing off lid for about 3 solid hours and finally got it free after soaking it with oil and was able to see what I am up against. It appears that the crucible is cracked where the spout comes off of it (tilt furnace). It is a 100 or 125# crucible not sure which but my question is this. There is no crack in the lower part of the crucible but it is probably cracked about 2 to 3" from the top. I was wanting to know if it would be possible to cut out the bad section of crucible and then cement the crucible in place with a plastic refractory. I have never heard of it being done but does anyone think that it might work? Alternately though I would like to know if anyone knows of a source for the larger crucibles from a 125# up to a 300. I like silicon carbide and can't see myself messing around with clay graphite. Any ideas please let me know as I want to get this one going but everyone knows how it is trying to take chicken poop and make chicken salad; boy I need lots of mayonaisse. :lol:

Re: crucible repair

Posted: Sun Jul 04, 2010 1:12 pm
by steamin10
Ouch! If you have a tilting furnace like that, you have discovered the reason for its abandonment. You will not like the price of a crucible that size as they are some $1500 dollars and up in that size.

As far as a patch, that is a tough call, the same forces of heat, and flex at temperature make an effective repair questionable for any period of time. Putting a lining in, out of ram-up plastic refractory is possible, but again limited by being not homogenous to the original. So repair is doubtful over the long term. Based on the hobby guy, it may be worth the constant fiddling, to use it and get the job done, as long as the basic integrety of the vessel is reasonable. Based on that, you have to make the call on the risk element. If I drop a #30 crucible, it can get interesting. If you loose the side of a 125lber, it can get downright dangerous.

I would try to drill the rim a bit into the crack, and pack it with refractory, and see how it holds. Cutting out a piece to patch in, I think is not going to work, because all refractories shrink or move when cured, so a good bond is doubtfull. There is a possiblity of turning the vessel around and pouring from the round undamged side. This may remove enough stress that the entire vessel may live longer.

These goofy things we do (by sane standards of 'normal' people) are mostly dangerous by their very nature, fire, high heat, heavy equipment. All we ever do is control the risk factor to our acceptable level. The longer we do them, and accept the risk, the more likely SOMETHING WILL HAPPEN. Just what, we never know until the system of chance puts it all together. Play with a lathe, you will get cut by chips, and get splinters. Play with molten metals, and you will get a suntan or worse. You decide, I have not repaired such a crucble, but have watched 100 ton metal ladles be relined and made up.

Re: crucible repair

Posted: Sun Jul 04, 2010 4:13 pm
by todd goff
Looks like I may have to "risk it for a biscuit". I am basically at my wits end right now with everything. If you were to buy a new furnace like this it would set you back about 40 grand and likewise I have some other machines that need repair but they sure aren't going to be cheap to fix. The latest saga is that I am going to have to replace 2 tires on a molders friend that I got not too long ago. I finally found 2 of them (company said that only 10 were being made this year in Italy). That is the good news ; the bad news is that each tire will cost 700 bucks each. Oh well, so the saga goes on and on; I actually need 2 crucibles and the darned things cost so much it isn't funny. Last time I checked I actually found one for 700 bucks but money doesn't grow on trees. :?

Re: crucible repair

Posted: Sun Jul 04, 2010 5:47 pm
by steamin10
Welcome to my world. Neat stuff that can be repaired fairly easy, but Oh so expensive.

I dont quite know what a molders friend is, unless is is a drum with sweeps and wheels to mix foundry sands. Two suggestions for that. Industrial cart wheels of various types with iron or steel disc centers can be had for about a C note each. The other possibility is to buy some rubber compound in strand or strip, and wind the rubber on and bake it. You can make a mold or wind some aluminum sheet on it , and bake at about 550 degrees ot vulcanize it. It will become quite liquidy and may run out, but modelers do this on large models all the time. The result may be lathe trimmed, or even ground with a course wheel to shape. We had rubber rolls resurfaced with a 3/4 inch rope of material, that was wrappepd and rolled on a core and hardened to 60 durometer before a finish grind. Saving the core of the wheel may be some work, but not really all that much with some thought.

Another thought is that industrial lift truck companies use a lot of press on solid sleeves. You may impress them with your plight and see if anything is close that can be cut to size for mounting, in a press. Having no money can just make you creative.

I do not have thousands of dollars for toy stuff, so getting creative and making do is the rule of the day for me. The machines I build make money for me, however small, or I dont own them. I cant.

Re: crucible repair

Posted: Sun Jul 04, 2010 7:03 pm
by todd goff
Hey Dave, the molders friend is just as you thought. It is a machine with a drum on it that runs along the shop floor and mixes the foundry sand. My wife finally took some pics of some machines out in the shop and hopefully I will have them posted by the end of the night.

Re: crucible repair

Posted: Sun Jul 04, 2010 8:29 pm
by todd goff
Here are the pictures as promised.

Re: crucible repair

Posted: Sun Jul 04, 2010 9:44 pm
by steamin10
Ok, now I have a clear idea of what you have. I was describing a mull with the paddles and wheels. Thats the big upright drum. Your equipment is from a medium sized commercial foundry, and the big wheeled thingy is nothing more than a rototiller on steroids. A fluffer. It does not do a good job on some mixes that require squeezing the sand and rubbing it together to distribute chemicals among the snad grains, that is what a mull does. I manual foundries, the sand pile is flipped and piled by scoop shovel and walked on by the floorman, tested by hand squeeze and any additions are made then.

You can use that stuff, but WOW does it take up the space! Ok, the floor mixer with the tractor tread tires, can be redone at a retread shop, if they want too. belted tread material can be made in a loop, the casing repaired to hold air, and it is heated to set the 'glue' rubber, somewhat like a recap, cold capping. Hot capping requires the correct size mold for the rubber to flow into. Those are big tires, so they will be a bit costy.

It can be done. A freind got ahold of an old style baggage cart, and salvaged only the iron and the wheels. After building a close replica of the cart, the tires had aged and come off of the steel wheels. Even at that age, the tire shop cut 2"out of the circle, and reglued it to the wheel centers. He was warned that the old rubber would probably break apart, if they tried to use it under load, or any speed. But that was done some years ago, and it never failed. Those are the full size carts, that loaded the baggage cars, the floors being approximately even.

I suppose, you have already checked the obvious tractor sized tires, and considered moving axles, and all that. If they are air tires, consider making them foam filled, so they cannot leak, as an alternative. Just thinking outloud, I dont know what resources you have or checked.

Re: crucible repair

Posted: Sun Jul 04, 2010 10:40 pm
by Harold_V
steamin10 wrote:Ok, now I have a clear idea of what you have. I was describing a mull with the paddles and wheels. Thats the big upright drum. Your equipment is from a medium sized commercial foundry, and the big wheeled thingy is nothing more than a rototiller on steroids. A fluffer. It does not do a good job on some mixes that require squeezing the sand and rubbing it together to distribute chemicals among the snad grains, that is what a mull does. I manual foundries, the sand pile is flipped and piled by scoop shovel and walked on by the floorman, tested by hand squeeze and any additions are made then.
Blink! Blink!

Man, you've lost me. Care to discuss that "garden tractor" a little more, Big Dave? It's not clear to me how it works, or its purpose.

Can't help in the least with any of this stuff. The foundry work I've witnessed was obviously at a very low level---all hand tools aside from a power riddle. Sole exception is the friend that runs (ran?) a commercial iron foundry, melting by induction. Uses the furan process.


Re: crucible repair

Posted: Mon Jul 05, 2010 1:12 pm
by steamin10
Ok, I'll try, as I have NEVER seen this particular machine, only like varients.

Hand molding is the most expensive way to do founding, and many machines were built over the years to ease the great physical labor intensity of this work. That is what the shakers and presses and other equipment is in the other shots. The mull cuts the FLoormans time conditioning the sand, and is used for mixing new sand and reconditioning returns when necessary. Originally natural sands, but now artificial oil sands. Resin bonded sands ( Furan and two part bonding agents) and coremolds are a diferent animal. I worked in a large foundry (HUGE is the word, 100ton castings, and sand put in reclaimers with Case W45-C loaders) and these things are diferent for the work done.

The equipment here is what you would see through the 50's and 60's in a mid sized commercial foundry. The tractor tired thing is operated to run over a sand pile, and as I said it first bull dozes the shakeout chunks to an approximate height and slowly runs over the clumps, and a drum of paddles whack down and throw the sand rearward, like a garden tiller. It crawls along and eats all the clumps and leaves a finely chewed bed of soft sand, that is mostly used for facing a mold, and simply screened sand is used for backup to fill the mold box. The flask is made up on the Mold table usually cope first, and then rolled and the drag is madeup. Either a filler is added and scraped to the top or a press board is used to push down the sands inthe flask, The two huge clamp like things are shakers (or jumpers ) that rotate somwhat while thumping up and down some inches. The little one with all the arms on a platten is a sqeezer, and used for vibrating/sqeezing the sand into a flask mostly one sided, to get the impressions for ganged small parts. That is then stripped and put on a flat drag.

One of the problems with these things is floor clearance, it must get very close to the floor, or it leaves a layer of course lumps, that can effect surface finish, instead of soft sand that will hug the face of the mold. So if the tires are eggy or lumpy in any way, it works against the objective of no hassle and speedy process. This is far from the only answer, as foudnries have used hanging shakers that take a couple of shovels of sand that when shaken through are used for facing. Sometimes on a simple trolly this cable hug affair can serve several stations at various times, to generate the material for that step of the process.

Furan and resin bonded sands are a fast knuckle headed way to make medium sized castings. It is expensive in terms of materials and maintenance, becasue the machines get gummed up with the resins, and mixers must be constantly cleaned of the cement hard residues. It requires little skill, usually just run through a belted or screw type delivery arm, that is swung over the delivery point, and a monkey (nickname for a new floorman) uses a pole rammer, nothing more than a few 2x2's nailed together to make a heavy T, some 7 inches wide, to push the sand into voids under the mold parts. The mold can be separted at any point , by simply screeding it off smooth, not needed to be level, and putting a sprinkle of untreated sugar sand over the bonded sand, using newspaper to divide the layers and running more resin bond over that, till the mold box is full. Furan, starts out a light yellow, and turns a dark red-orange as it sets (our colorant). In about an hour or so the completed mold can be lifted out of the pattern box and setup in the pouring area.

Before they closed they had a new vacuum system, that LOOSE sugar sand was run into molds covered with common plastic sheet, given a cover sheet, and a vacuum pulled, and the cope and drag were set up without any further process and poured while under vacuum. I want to experiment with this process in home shop scale, and I dont see why it would not work the same way. Think of the savings in chemicals and labor!

We did some 45-60 tank hulls, turrets, gunshields, and side plates every month by this expensive method, and I observed Murphy's law influence things all the time. Anyway, that was the begining of the process for the Armor Line, that had about 100 units in process at any given time. I was in every department at the time, running the heavy overhead cranes. Mostly around the machine shops, where skill was required so as not to bump any of the calibrated mills, flame cutters, and tempermental stuff that had to be right on, or a turret would not match its precision bearing. We shipped the finshed castings to Chrysler Tank division in Michigan, where they did the build and testing.

I will close here, but you get the drift. I had associations with a couple of iron foundries, but have not had work done in some time now.

There are as many ways to use this equipment, as there are products to be made, but understand that one sqeeze, is equal to many minutes of a floorman ramming and shifting sand to build the mold, a lightyear jump in labor cost. It is why most small foundries closed, along with pollution standards, and had to find special nitches for products to survive. People get lazy and effect the bottom line, or you invest in equipmnet that takes human time out, making a variable much more steady.

Also you need to understand there are small to medium shops that have pouring carosels that are nearly hands off from start to finish, and more less pour a mold every minute. I have seen the adds, and some pictures of operations, but never laid eyes on them.