Refractory materials to help keep position during welding - Page 1
Forum section: electronics / general

author: jpanhalt
author_rank: Super Contributor
timestamp: May 17, 2025, 06:54:33 pm
content: Everything is roughly symmetrical about the green centerline. "A" is a machined bushing. It is symmetrical on the axis. "B" is the arm of a thumb for a small excavator. Its hole is symmetrical on the axis My design will allow reasonably good alignment about the center axis, but I am worried about tilt relative to the rough surface of the "arm." Its roughness is exaggerated for illustration. I need a few thousands tilt alignment at worst. A bucket pin must fit in the hole easily.My working solution is to use dye marker, trial fit, grind, trial fit, grind...etc. until I get a solid fit. Welding will be difficult, I know. I do not have access to a line borer. A tight fitting, over-size pin will be in place during welding. Pin is 35mm diameter.Is there any hard setting, non-friable, refractory material I can add to help prevent tilt during the first few interrupted welds? I suspect most ceramics are too easily crushed.

author: coppercone2
author_rank: Super Contributor
timestamp: May 18, 2025, 01:18:05 am
content: All the ones I know of require like a bake for setting before you try to use them for intended purpose, to get rid of hydrates that form (or something along those lines with chemistry). Are you going to be capable of doing that? The stove ones I think expect the stove to heat up slowly.I think most of them will mal function if you just let it air dry then suddenly heat it, because something is suddenly going to be releasing alot of water as steam in a hurry when its super heated as the hydrates break down. And they will shrink (though I think refractory cement shrinks less). I don't know if they have "no cure" refractory cementsWhat I would imagine anyway is to make it stronger... you can add ceramic media of some sort that crushes harder. It might help. Kind of like adding rocks to cement. I think they have little bars, balls, chunks, etc available. Like the media you put in a fractioning column, it can even be little honey comb cereals, macaronis, etc.. or even large ceramic objectsThe same idea as using perlite in a DIY stove, but instead of insulator you add something hardActually using a cement that is meant for metal to ceramic bonding might get rid of some of those problems (for a fireplace) instead of the repair kind. I think they sell it as a 'glue' on mcmaster but I thought it was super weak/crumbly. Maybe if you add something to it though

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 18, 2025, 10:10:44 am
content: The normal approach is line boring. You first make the hole too small, weld everything together and then bore it to size. There are plenty of youtube video's to show the process. You can also use a (pretty big) milling machine and can even do line boring on a lathe (Blondihacks once made a video of doing this on a small DIY lathe).If you don't have the proper tools, but do have a small (wood?) lathe, then you can make some wooden plugs, use sandpaper or grinding grid on the outside (Steel tube, plugs with outside taper fixed on it, and over that round plugs with a taper on the inside). I think this should work, but it will cost you quite a lot of time. (May be a whole day, and lots of sandpaper) Sanding down steel is not ideal, but because the method is self correcting (especially if you reverse the sand paper every now and then, to improve the roundness and straigtness of the mandrel)

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 18, 2025, 10:20:18 am
content: Another method is to first make partsBconical and then make partsAto size so they center on the cones. But it's nearly impossible to fight welding distortion. It helps if the material is thick and the welds are relatively light. This will require that most of the load is supported by the conical sections.Once I also saw special after market bearing sleeves for this. They were adjustable with conical sections, but this does still require that your holes are round and concentric.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 18, 2025, 03:27:27 pm
content: First, let me add that I searched within a reasonable drive (100 miles) and found no shop with a line borer in 2024. In 1998, there was such a shop within about 5 miles of where I lived. It did major engine rebuilding. Cleveland also had major manufacturing, including a main Ford casting plant (engines and other stuff), GM/Chevy major machine plant, and little feeded shops in the same area. That area is now being considered for a new Cleveland Browns stadium and attractions. I also asked the boss at a nearby machine shop whether he knew of any places in the area that could do it and came up blank.Second, I didn't realize there was a bearing pressed into the thumb ears. There were grease fittings, as there are on buckets. My buckets don't have bushings. That was an error on my part, and if I were to redesign, i would do it differently. However, I was gifted some 1045 ground and polished 3" round by the above mentioned boss, and I am reluctant to impose on him again.I have attached some images to give a better idea of the project. I am never sure in what order attachments here end up here.So, here's an explanation:Dipper & Bucket = Current excavatorThumb = Thing attached over the bucket attachments and acts like a thumbGalled ear = Bushing was in really tight and came our with metal shards in the grease grooveThumb assembly =Imagine a centerline axis with everything pressed or weldedBushing2 = Bushing that will be welded to the earBushing = The little extension on one end fits tightly into to galled ear of the thumbI decided overnight to get the surfaces matched reasonably well, press together, then force steel shims into any obvious spaces. If that fails, I'll remove it and go with my alternative design.

author: coppercone2
author_rank: Super Contributor
timestamp: May 19, 2025, 08:52:52 am
content: Actually there is one kind of maybeSodium silicate with sand, the one you use for molds, you expose it to CO2 to harden it. It's very hard and can take a OK temperature and it cures from CO2 very quickly. It might work well with other media too like washed gravel pebbles or something added to it. I think you can cast aluminum in it, not sure what happens at higher temperatures, but I do recall at least a few pieces of it were pretty tough when I broke the mold. I think a piece hit me in the eye when i was smashing it with a hammerHmm it soaks too, I wonder what would happen if you added fiberglass 'strands' to it. It reminded me of concrete. I did not like it because the sand I had was not casting sand (very rough) but it made it tough.it says it can do 1100cthese people seem to make bronze castings with it. I only did leadhttps://fab.cba.mit.edu/classes/863.15/section.Architecture/people/Saulnier/pages/casting.htm

author: Kleinstein
author_rank: Super Contributor
timestamp: May 19, 2025, 09:17:24 am
content: I would consider putting in a metal pin for spot welds. With some care it should not effect the pin. For the final weld one would than remove the pin.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 19, 2025, 12:18:59 pm
content: Thank you both. I haven't done much welding in the past few years, except a few fixes here and there with TIG. I have a little practice to do with MIG and will, of course, do an interrupted weld. Steel shims or pins will be used if needed. I'll probably just weld over rather than try to pull them out. I won't know how bad the alignment is until I press the bushing into the part I machined and dry assemble with the 35mm pin.If it works, I will post a picture. If not, I'll start over. I need a thumb that works without bending the pin. The problem is not the cost of new pins, it's removing the bent pin that is hard.John

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 19, 2025, 05:43:02 pm
content: One thing you can try is to let the pin in during welding, and do the welding in short bursts so the inside does not get too hot.The goal is to verify multiple times whether the pin starts binding in the hole, and then weld on the appropriate side to counteract the binding. The more welding is done, the less additional movement there will be with the following welds. This is untested, and a bid dodgy, but it may work.

author: Andy Watson
author_rank: Super Contributor
timestamp: May 19, 2025, 05:59:42 pm
content: Quote from: jpanhalt on May 18, 2025, 03:27:27 pmIf correction after welding is an option, I would consider an expandable hand reamer. You might need an extention to achieve adequate alignment.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 19, 2025, 06:53:09 pm
content: @ Doctorandus_PThat's exactly what I plan to do with a straight pin. The fit to the pin is sloppy (it's an excavator afterall). I plan to wrap the pin with shim (probably 0.002 to 0.003" on the welding side and just force strips on the non-welded end. I discovered yesterday that the used bushing is about 0.0005 to 0.001 out of round and apparently burnished a little end to end. Can't find easily a replacement online, and the thumb manufacturer is Werk-Brau. It has been completely not helpful for details. That used bushing OD is about 1,9975" +/- 0.0005". I've got some 3-point Fowler Holemikes. My hole 1.9955 at several points, which gives an allowable 0.001 to 0.0015" /inch of diameter interference. I will preheat the machined bushing to about 450°F and freeze the commercial bushing. A press fit will hopefully work. The bearing may get loose but can't actually move out of its hole by the way it is designed.@AndyIt's quite hard steel..

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 19, 2025, 11:22:50 pm
content: Quote from: jpanhalt on May 19, 2025, 06:53:09 pmA tight fitting pin is probably better.If you hole gets oblong during welding, you will change the surface "shine" when you force the pin in, and can carefully grind the locations that cause the binding. And when the pin is inserted enough that it (nearly) aligns with the other hole, you can also see in which direction it's slanted.You can also use spotting fluid in the same manner as with hand scraping.With a sloppy pin it's much harder to determine where deviations are.I have also done a few experiments with hand scraping, but I did not have the patience to do it "perfect", and this was also not needed for my application. I noticed that working with sand paper works quite well. You can experiment both with the sand paper (or grinding paste) to create scratches in a certain direction, not to remove (much) material, but just to mark the surface, Then you can use another method to scrape or grind the tight spots quicker.And indeed, as Andy Watson mentioned, an (expandable or not) reamer can also work.

author: Poroit
author_rank: Frequent Contributor
timestamp: May 20, 2025, 08:31:42 am
content: Could you use Vacuum Brazing for this application?https://www.paulo.com/capabilities/processes/brazing/vacuum-furnace-brazing/https://www.bodycote.com/heat-treatment-plants/bodycote-highland-heights-cleveland/

author: jpanhalt
author_rank: Super Contributor
timestamp: May 20, 2025, 11:19:40 am
content: I didn't know about Bodycote, but I did know about precision brazing. There's a company -- probably 30 miles south of Bodycote -- that used that technique for precision attachment of hubs to pressed steel pulleys. I visited that company 25 years ago and was quite impressed. It's a possibility with a proper design, and I will consider it, if the current approach fails.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 20, 2025, 05:15:47 pm
content: Putting that whole dipper arm into a vacuum oven may be a possibility, but it does not seem practical.But regular (brass) brazing sure does look like a viable option.Another idea:What about making a long bearing from a thick walled tube, and then weld that tube into place.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 20, 2025, 06:43:14 pm
content: The longer weldment is plan B. I need to find a 3" pipe with a wall of slightly more than 1/2". Speedy Metals has 3"x1-3/4" DOM steel.Everything pressed together nicely (at 450°F and -15°F). Next step is dry fit and welding.