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Re: Moving table (fixed gantry) with two ballscrew
Hi Ivan -
1) Durigrid is a high modulus ceramic (alumina) that increases the modulus of the mix. Replacement with sand will produce a lower modulus casting than when using durigrid E sand ~ 70GPa E alumina ~ 300GPa
2) Fibers are added to Portland cement to bridge the inevitable drying cracking that occurs with Portland. There are concrete grouts based on calcium sulphoaluminate that potentially do not crack, these are the preferred cements for machine parts
BluCem-CSA-Cem-LR-R2.pdf (bluey.com.au)
3) Large machine parts are very low stressed and the fibers serve no purpose unless you are trying to improve the modulus. My tests have been disappointing in trying to improve the modulus using steel fibres. So I would not use them as they complicate the pour. If your concerned about sagging then the design is totally inadequate.
4) Buildings require failure modes that are safe ie the structure needs to be able to deform and absorb energy yet stay together vs suddenly falling down. Thats why ductility is required. Again not needed in machine designs. They are very low stressed and will not "fail" like a building may fall down.
5) I'm sure there are cement grouts that can be cast to very thick sections in europe. Try Sika products they have suitable grouts and are cheaper then Tegno products. I use one from the local hardware its E=56GPa and can be cast to 500mm by itself. The thickness can usually be increased by adding more aggregate. See attched data sheet.
Keep at it. Peter
Re: Moving table (fixed gantry) with two ballscrew
Hi Peter. Nice to hear from you again after so many years. As always you are ready to help. Thank you so much !
I know about sikagrout 3350. But it is not available in Bulgaria. It is expensive to order Durigrid to Bulgaria. I will be satisfied with the modulus of quartz sand if it is not problematic for this cement. It will still be bigger stiffness than EG.
Tegno price is EUR50 for 25kg and EUR25 shipping. I need 6 peaces x 25 kg = 6x75 = EUR450
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Re: Moving table (fixed gantry) with two ballscrew
All the materials from moertelshop.eu arrived today.
- TEGNO® UHPC special cement
- superplasticizer FLUP®-PCE-375
- ECLIPSE® FLOOR shrinkage reducer
It remains to buy quartz sand locally from here. The prices are around 7-8 EUR for a 25kg bag.I made an excel table to calculate the necessary quantities of quartz sand with which I want to replace the original aggregates.
I hope I have no mistakes. I think I will choose the blue recipe (1-3mm + 3-6mm) because of the larger amount of quartz sand and correspondingly greater stiffness.
Is this correct?
Re: Moving table (fixed gantry) with two ballscrew
I see a technical error in the specific density (gravity) of dry sand. It should be 2650 (not 2560). Small differences are obtained.
Re: Moving table (fixed gantry) with two ballscrew
Hi Ivan - Can you share the technical data sheet and the safety data sheet for the shrinkage reducer? Peter I looked up the "shrinkage reducer" and other companies describe it as a mould release aid. alcohol ethoxylate is a surfactant that helps the water wet the ingredients and stabilises the emulsion. I think it helps to reduce cracking by helping the mixture slip along the mould surface as it shrinks. This means the cast has less tensile stress in it caused by the grip on the mould surface. This helps with very large casts like floors and slabs... Keep it up. Peter
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Re: Moving table (fixed gantry) with two ballscrew
Safety data only in German. PLOPP is a mould release agent.
Peter, What do you think about the aggregates? Should I follow the original recipe for 1-3mm + 3-6mm Durigid (replaced with quartz sand same particle sizes).Or to use the experimental best ratio I reached in this post: test 11 - (33%: 0.10-0.25mm, 33% 1-2mm, 33% 3-5mm ?
https://www.cnczone.com/forums/mecha...ml#post2341738
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Re: Moving table (fixed gantry) with two ballscrew
Hi Ivan - Making UHPC is up to you. Playing with recipes is fun but the end game is getting a material you understand if your trying to "design" the structure via FEA. So unless you can test for modulus then making up recipes is wasted time & $$$ In my opinion. But lots of people make concrete machines with no knowledge of the material and they work, so go for whatever you think is best.
I'd stick with a commercial recipe that has a quoted modulus then you can decide on the value of that material in terms of $$$ and modulus. Durigid should give you the highest modulus material but it will be the most costly, fair enough. The Concrete you have is portland cement with a plasticiser. This will get you to 30-35GPa. If you use blue metal (basalt aggregate) you'll get to 40-45GPa and if you use Durigid (alumina) the germans say 80GPa but my flexural tests with 100% alumina/epoxy got to 20GPa from memory so I'm unclear about how they get E80. I think the compression test is biased somehow. So if you use cement and sand I'd use 35GPa as a design value. If this gets you where you want then use sand as this is the cheapest solution. I'm still looking for acoustic testing equipment to measure modulus.... I see acoustic testing is being used in composites more and more.
I emailed Prof Bernhard Sagmeister and corresponded with him about high modulus concrete. He was helpful but not helpful enough for me to be able to replicate the E80 material here. I also corresponded with a concrete chemist here in Australia about their materials and I'm confident that using basalt aggregate you will get E40-50. Sand E35 so pick a number your happy with a get making :)
My current thoughts on using alumina for the agg is that once cast you cannot drill it or machine it. Its like a grinding wheel. If I was confident on the E80 result this is a trade off I'd take. But since I can't get the E80 I stay with the steel fibres and basalt so then its machinable post cast E45. Peter
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Re: Moving table (fixed gantry) with two ballscrew
Re: Moving table (fixed gantry) with two ballscrew
Thanks Peter.
I want at least 45-50GPa
In the commercial recipe for E45 with pit sand 0-2mm and basalt 2-5mm, they give values: Static Young's Modulus 50GPa.
This is for volume of aggregate 45%.
In the recipe with Durigid, volume of aggregate is 51%. Logically, this means that if I use a higher volume aggregate (51%) in E45 recipe I will get high Young's Modulus.
I would use 0-2mm quartz sand and 2-5mm basalt, if the basalt has a higher Young's modulus than quartz sand. What I find as data: basalt: 60-100GPa, quartz sand 70-78Gpa.
In Bulgaria I find basalt chippings wiht data only for mass density: 2754 kg/m3. No data for Young's modulus.
Peter, Is the basalt stiffness than quartz sand?
P.S. About Durigid.
" ...Durigid RG/DR is a synthetically manufactured mineral. Selected natural minerals are fired at 1.400°C. Thereafter, the product will be crushed and classified.
The mineral product shows excellent properties in strength, hardness, wear resistance and high specific density.
It’s range of application lies in the field of polymer- and cement-bond mineral casting.
The use of DURIGID RG/DR as supplement for natural minerals increases the following technical properties of the concrete:
- compression strength - young´s modulus - wear resistance and abrasion - refractoriness and fire resistance Durigid has a long standing history in cement- and asphalt-bond concrete mixtures...."
Re: Moving table (fixed gantry) with two ballscrew
Hi Ivan :
1) Durigid is processed alumina. I tracked the chinese supplier down through the german safety data sheet. The european chemists (in china and in germany) there where quite helpful but they only dealt in shiploads of material. But Australia is the biggest supplier of alumina outside China so I tracked down a similar product here. Available as a grit blasting medium. E=300GPa. 3mm grit. I made solid chunks of alumina with epoxy via vacuum casting and had them flexural tested. Very disappointing <E20 at 65% volume fraction alumina. The issue is twofold. a) alumina like all ceramics is a crystal and it is not isotropic. It has many moduli in each crystal plane so the average modulus is not the highest one quoted. b) the compression test is geometry and packing factor biased. For instance, I can test for the compressive modulus of water in a container and find out that's it has infinite modulus. But I can't make a structure from water. High modulus concrete is used to make slender columns in very high buildings. They need the modulus to improve the buckling and to make the columns as small as possible (like the Burj). So a compressive modulus test maybe valid in that application as the columns are made thick and safe so they do not buckle. Since CNC machines require high flexural stiffness as most of the elements are bending dominant the compressive modulus may not be valid. If I make a stack of aggregate so it all touches it can be quite stiff in compression even without binder... too many variables to work through unless I did a PHd on it.... so I've settled for SIKA grout at 50GPa out of the bag.
2) Basalt (here we call if blue metal) is stiffer than sand so results in a stiffer mix. The bigger the aggregate the better the chance of a higher E. This is because of mechanical stacking as I mention above. Unfortunately, the basalt and sand people can't tell you or me what the E is of their materials. Granite, basalt and marble can have low 50GPa or high 110Gpa E, without testing who knows. You take your chance when you make the mix. my concern for you is that you have bought Portland cement and even with additives it still shrinks big time....
So do the best you can with what you have and if you do FEA use a low value say E40 or E45 so your conservative. I have an enquiry in with a USA company that supplies ultrasonic test equipment for material testing... will be interesting to hear from them...
All this research has pushed me back to aluminium or steel. Aluminium I can make parts on my router or contract them and get E70 absolutely. If I go steel I get E200 which is super attractive. Comes down to size as well, parts bigger than can be put on a mill means casting in UHPC or metal. I also have an enquiry in at a Malaysian caster for a big aluminium cast machine base, no news on that yet... My intent is to make production machines so I need a reliable material and process. If I was making a one off machine for myself I think I'd go with a fancy steel brazed lattice structure designed using generative algorithms just for fun ... I keep coming back to high quality plywood. Its the cheapest stiffest material around, easy to work with. 17mm F17 ply is same stiffness as 10mm aluminium and its 1/3 the price... Peter
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Re: Moving table (fixed gantry) with two ballscrew
In this pdf I see very low values of basalt (Etna) : 25GPa
For me, it is a big risk to use basalt with unclear characteristics, in the presence of quartz sand, for which the real modulus is known, even if it is a little lower.
Re: Moving table (fixed gantry) with two ballscrew
Quote:
Originally Posted by
peteeng
...<e20 at="" 65%="" volume="" fraction="" alumina.="" the="" issue="" is="" twofold.="" a)="" alumina="" like="" all="" ceramics="" a="" crystal="" and="" it="" not="" isotropic.="" has="" many="" moduli="" in="" each="" plane="" so="" average="" modulus="" highest="" one="" quoted.="" b)="" compression="" test="" geometry="" packing="" factor="" biased.="" for="" instance,="" i="" can="" compressive="" of="" water="" container="" find="" out="" that's="" infinite="" modulus.="" but="" can't="" make="" structure="" from="" water.="" high="" concrete="" used="" to="" slender="" columns="" very="" buildings.="" they="" need="" improve="" buckling="" as="" small="" possible="" (like="" burj).="" maybe="" valid="" that="" application="" are="" made="" thick="" safe="" do="" buckle.="" since="" cnc="" machines="" require="" flexural="" stiffness="" most="" elements="" bending="" dominant="" may="" be="" valid.="" if="" stack="" aggregate="" touches="" quite="" stiff="" even="" without="" binder...="" too="" variables="" work="" through="" unless="" did="" phd="" on="" it....="" i've="" settled="" sika="" grout="" 50gpa="" bag.
my concern for you is that you have bought Portland cement and even with additives it still shrinks big time....
...
Yes. 0.5mm for 1 meter. For this reason I have no metal inside the castings. All metal parts are attached with bolts passing through holes through the entire thickness of the castings. And I will wait a 2 month for final shrinkage and them I will start montage of metal items. The main shrinkage is at the beginning of the drying process. </e20>
Re: Moving table (fixed gantry) with two ballscrew
I would not worry about the Etna basalt figures - just don't use Etna Basalt! Its young and porous. Use old black basalt that's the stiffest... at least 20-30 million years is a good vintage.... Peter