[ardenum]

Evening all and sundry - I've done a small optimisation on E70 material vs steel. A solid column like I have now weighs about 78kg/m whereas a 12mm thick steel one would be 54kg/m.. I made a model and compared the two and they are about right. Both are over the 20N/um target so thats OK. The steel by the time I add a thick flange comes in at 52kg and the E70 material is 56kg.. So again I think I'm at a balanced point. If steel I'd prefer the front face to be 16mm to allow for machining.... decide after some casting tests to see where I get to with that. If I get to E80 then its a no brainer for the concrete casting.... still looking for a tabular alumina supplier... Peter

I have something similar in my 'maximum' build, I want to bolt it first and foremost and then either weld or braze the edges, probably braze with something exotic, since I have no space for a chamfer(the bolts are in the middle of the plates). I also included minimal machined surfaces(lighter color) where the plates touch. What do you think?

https://i.imgur.com/u7UJ8rO.png

[peteeng]

Hi Ard - So you are going to edge bolt? Is that what you mean by "bolts are in middle of plate"? If you edge bolt you don't need to weld. You can lap the edges, bolt and set with epoxy or loctite. You can use less bolts and solder (solder requires far less heat) If welded then stress relief is needed. Comes down to what you want to do and how you want to do it.... Peter

[peteeng]

Hi Ard - Looking at your design again. If the machine you are using to mill the lands or registers is up to the accuracy required to do this then you may as well machine pockets that trap the rail both ways. Other wise you need to use wedges to push the rail up against the land (A) What's the plan to align the rails?

Similarly at B. If you are edge bolting then there is no purpose in spending the money to have the register machined. You will need wedges or cross bolts to pull the plate up to the land. Better just to have a pocket or a flat plate for the structural parts and pay attention to having edges machined square and true. more thoughts?? Peter

[spumco]

[QUOTE=catahoula;2433652So you would be confident machining a braze welded hot rolled steel structure and expecting it to be stable?[/QUOTE]

Yes. Everything moves a bit when you heat it & cool it, but I've done structural repairs on cast iron that stayed put after machining. Think broken corner of a bridgeport table.

If I were to build a big gantry beam and didn't want to have to stress relieve it I'd TIG braze rail surfaces to the beam (like you welded on yours) and then machine them. There will be some movement and stress after initial machining, but if the rail plates are thick enough you could do the machining in stages and do the final surfaces as unconstrained as possible. The gantry itself won't be super-straight, but the rail surfaces should stay put.

Actually, what I'd probably do would be to just build the whole beam up in a triangle shape from tabbed plate, then add the rail surfaces after the beam is sorted out.

[peteeng]

Hi Ralph - Re: TIG Braze. Do you use silicon bronze rod? DC or AC? I had a go at this once but it was rushed with friends welder in between jobs he was doing. Don't have a TIG now.. Tried DC with no luck. Next time would be with AC for cleaning action... Cleanliness (as usual) is key to get flow... Peter

[spumco]

Peter,

Generally DC-. ACHF if the base material is dirty or has a tenacious oxide layer that keeps the filler from wetting out.

Use 2% thoriated electrode, argon shield, and boric acid flux (cheapo Borax & water paste). You can buy pre-flluxed filler, but making a trough out of angle iron and laying a hot rod in it works fine. Preheat rod with propane torch, dip, and the borax sticks.

Above is valid for silicon bronze, phos bronze, and aluminum bronze TIG brazing.

Harris welding has a pretty good application section for filler selection. They don't cover exotic stuff, but the black magic is usually in the flux chemistry (off-shore/marine/naval applications).

-Ralph

[peteeng]

Thanks Ralph - I didn't have flux last time I tried. I figured flux would be required or AC. I don't like fluxed rods prefer to preflux the job and hot dip the rod... only plan on oxy stuff at the moment but would like to try TiG brazing again some time seems easier then the gas torch... Off to do first cast of CSA... I looked at TiG electrodes a little while ago and there seems to be several more then the 3 last time I as in that line of work (some 20 years ago) Pure, thoriated and zirconiated, now theres other "ated" stuff in there.. Peter

[peteeng]

Afternoon All - Just poured the first CSA brick. Very fluid. There was a small screw hole and I thought, its concrete won't come out of that!! Poured it in and out it seeped. So I folded up the plastic around the box and grabbed some packing tape to bandage it. Cheap tape every turn it split! Bugger...

After that all went well. The start of mix is like dough then when you add the last amount of water its done.... The good fluidity means there's room to add stuff, that's the next pour... release it tomorrow and have a look. Its raining so easy wash up. Not like epoxy, have to throw all the buckets, etc and mixers out...

I added minimum spec water to this batch, next may add max spec to see the diff.... plus may help the planned fibre mix...Peter

[peteeng]

Extra evening all - Turned on the laser today!! Bonus day first pour and a laser!! Now I have to get Argus to move! Usually letting the smoke out is bad news Peter

[pippin88]

CSA: am I right in thinking minimum water content is strongest?

[peteeng]

Hi Pippin - Looking at the data sheet yes I expect that's right, The water addition rate is 20-25% by weight and the mechanical properties are spec'ed at the 20% figures. I would expect the fibre addition will counter the strength delta. At 20% water the density is 2140 and at 25% its 2040kg/m3... Ah here it is, take compressive strength at 28 days

20% 90MPa 25% 70MPa... So minimal water is best... Next is to see how much fibre I can get in there and still have it flow... Peter

[ardenum]

What's the plan to align the rails?

Taper gibs or push screws(as referenced in your NSK picture). Haven't modeled it yet though.

You will need wedges or cross bolts to pull the plate up to the land.

I don't quite get this, can you elaborate more? Do you mean I'd have a space between the side plate and the register otherwise? I thought it's fine since the braze material will flow into it afterwards?

[mactec54]

Hi Cat and others - re fillet building - To create equal "strength" joints to welding, a large fillet is required. But for a machine part the strength is not the issue its stiffness which can be achieved using a small fillet or even if there is no fillet (soft solder - silver solder) but the gap is filled with braze then you have nearly 100% local stiffness equality which is what you want. Bronzes have similiar stiffness to cast iron 100-120GPa so they have excellent strain transfer in a joint. cheers Peter

There's also MIG brazing which maybe easier for many people--- would help those that can't get to thermal stress relief...As this process does not melt the parent the resulting internal strain is considerably less then welding... and TIG brazing as well...

https://www.millerwelds.com/resource...brazing-basics

The large fillet is required as the yield strength is about 1/2 the strength of the parent but as stated this is not a strength application. In Milli the max part stress is about 2MPa (290psi) so its tiny tiny compared to the yield of the materials used that's why CSA concrete can be used as its tensile strength is about 10Mpa...

This does not help as the stress is already in the steel so even if you brazed the joints the stress is still in the steel so when you machine it it will move for sure, the steel you put in your CSA needs to be stress relived blasted and then you are ready to cast them in your CSA if you don't then they will move when you machine them which would also affect the bonding in the CSA or Epoxy Granite

For Tig Brazing using silicon bronze you don't use flux, the argon is the flux you start with a clean metal base here is a good site with lots of good real information

https://www.weldingtipsandtricks.com...and%201990%20f

[mactec54]

Thanks Ralph - I didn't have flux last time I tried. I figured flux would be required or AC. I don't like fluxed rods prefer to preflux the job and hot dip the rod... only plan on oxy stuff at the moment but would like to try TiG brazing again some time seems easier then the gas torch... Off to do first cast of CSA... I looked at TiG electrodes a little while ago and there seems to be several more then the 3 last time I as in that line of work (some 20 years ago) Pure, thoriated and zirconiated, now theres other "ated" stuff in there.. Peter

You can use both Ac or Dc for Tig Brazing no flux is required for silicon bronze or aluminum bronze filler rods

[mactec54]

Afternoon All - Just poured the first CSA brick. Very fluid. There was a small screw hole and I thought, its concrete won't come out of that!! Poured it in and out it seeped. So I folded up the plastic around the box and grabbed some packing tape to bandage it. Cheap tape every turn it split! Bugger...

After that all went well. The start of mix is like dough then when you add the last amount of water its done.... The good fluidity means there's room to add stuff, that's the next pour... release it tomorrow and have a look. Its raining so easy wash up. Not like epoxy, have to throw all the buckets, etc and mixers out...

I added minimum spec water to this batch, next may add max spec to see the diff.... plus may help the planned fibre mix...Peter

Looks good If you plan it right the pieces you make you can use around the house or garden if you are not destroying them in testing

Add some pieces of steel with anchors to check for bonding, I have some pieces out side in the cold ( 0 to -10 ) to check for shrinkage and pull away from the steel

[peteeng]

Morning All - Released the CSA block this morning. I checked it last night and it got to 45C exotherm. Released easy as expected with the mylar tape and plastic. Sanded the edges and here it is. A bit small for a stepping stone Mactec but maybe next one I should do bigger, plus I'll add some colour I think maybe safety orange. Its current density is 2173kg/m3 (by weights should have been 2140 so close) so now wait 28 days for full strength & stiffness or bake it in my kitchen oven at 60C for a few hrs... Re steel inserts - the CSA supplier has primer suitable for steel so that's a help in that area. I plan to use aluminium (I know about the CTE delta but I don't like steel...) so it can be finished in a router. Not there yet... Biz is quite, so today may cast the fibre version... Peter

[peteeng]

Hi Ard - Re land. The plates you use are unlikely to be straight so when you place them up against the land they will not touch in spots. If you have a TiG/MiG welder you can tack them while holding it against the land. The tack will pull it into the land. For the structure the land is not needed so you can sidestep that (and reduce cost) by not using the land as it has no function ? Peter

[spumco]

How does argon improve surface wetting or clean oxides?

Flux has two purposes - shield the materials from atmospere, and clean the surfaces to promote wetting. ACHF alone is not sufficient unless matherials are perfectly clean.

Flux is not required for GTAB SiB or AlB, but it helps. And it's required for fuel torch braze welding.

"Welding Tips N Tricks" while helpful, is not a persuasive technical source. If you want to read about braze welding fluxes go to AWS' web site any buy some standards.

[mactec54]

How does argon improve surface wetting or clean oxides?

Flux has two purposes - shield the materials from atmospere, and clean the surfaces to promote wetting. ACHF alone is not sufficient unless matherials are perfectly clean.

Flux is not required for GTAB SiB or AlB, but it helps. And it's required for fuel torch braze welding.

"Welding Tips N Tricks" while helpful, is not a persuasive technical source. If you want to read about braze welding fluxes go to AWS' web site any buy some standards.

You obvious have not done Tig welding yourself or you would know, yes flux is needed for most Torch welding but not Tig

Ac actually cleans better than using Dc so depends what you are doing, any materials that need to have a quality weld need to have a clean weld area

[peteeng]

Evening All - Up to cast No2. I have 2mm long steel fibres that I have been playing around with for a while. I have infused these with epoxy and now have chucked some into CSA grout. Both times have not come up to expectations... They clump and don't pack well. Especially they change the rheology of the CSA quite a bit... I wanted to add 1kg of fibres to the mix but didn't get past 0.5kg... Gave my Bosch drill quite a work out. When I poured it out into the mould it looked like the durcrete stuff in the video. It sort of climbed out of the bucket in large drips. But when it hit the mould it smoothed out... My target has been a E70 mix but that won't happen here. I expect if the maths are right to get 40-45GPa out of this mix so must be similar to Durcrete E45 material I think....... Now to make a mould to do some modulus testing... I wonder if I can infuse with water? Peter