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I wish to make a layer damped gantry for a 3D printer. It will have two aluminium box section tubes (25mm and 20mm) placed inside each other and the gap between filled with a damping material.
PU resin comes to mind but I wonder what type has the highest damping factor? Or is something else better?
Thanks
I don't think you will get better than PU resin for dampening without going to heavier materials which will bump up the mass which you don't want for moving gantry. But if it's fixed gantry then filling it with concrete will be your best option as it's about the highest up the Stiffness/density chart without getting silly about it.Quote:
Originally Posted by Tenson
See this Young's Modulus- Density chart it graphs which material gives what performance comparing Stiffness to Density. PU is right about in the Middle.
Attachment 28074
I would say a somewhat flexible, viscoelastic type will be best, a certain amount of mineral filler will also likely help. How thick are the walls of your tubes?
I'm not sure there is a clear relationship between modulus, even shear modulus and shear loss factor. So that's why I'm unsure the best resin or material to use.
Does high shear modulus translate to high shear loss? Probably not or a stiff solid would be best.
I know that butyl rubber is pretty good in this respect, it's what they use in car panel damping with a aluminium skin. I could wrap the inner tube in that, then fill the slight remaining gap with polyester resin (like car fibreglass) to constrain it.
But maybe PU though the whole gap is better? Mayne add hollow glass beads? Or fumed silliaca?
I've played with 'Green Glue' in the past but it always stays soft and would just slowly drop out I think. It needs to be captured between the constraining layer under some pressure.
Yes the gantry is moving, I considered concrete filling with a big dose of SBR but I guess it will weigh much more than a double skin alli tube with PU in the gap... maybe not?
I'm no engineer so not that much help with material selection.
I do work with composite and do alot of polyurethane and etc silicone casting. Most cast polyurethanes will usually need either a very good mechanical key or primer/adhesive to help adhere to aluminium (due to aluminiums oxide layer on the surface).
On the other hand, moisture cure polyurethane and silicone has much better bonding characteristics, reason's unknown to me!? 2 part cast PU or silicone are available in a much wider range of shore hardness though...
Food for thought, maybe.
P.S.
Cast silicone will not bond. We make mould's from it that don't require any release wax/film, most castings just peal out no problems.
P.s. again!
That is supposed to be RTV silicone in previous reply! Damn auto spell check...
There doesn't seem to be any direct relationship between modulus and loss: you can get high modulus (stiff) compounds with low loss, and then you get get softer ones with a low loss too. My guess is the problem with GreenGlue in a confined space such as you describe will be that it'll take years to dry as the water (solvent) can't escape easily - a 2 pack product would be better - as long as it doesn't shrink on curing. Might be worth getting in touch with Alchemie to see if they make a resin aimed at damping - they do a big range of PU products.
Easy composites stock 2 part casting resin, simple room temperature cure. Available in small 1 liter quantities, 30, 60 and 90 shore A hardness.
Many 2 part PU's require oven curing and need quite accurate temperature regulation, just something to be weary of.
Maybe suitable just for testing purposes?
A little trick with moisture cure adhesive/sealant is to mix in a tad of hydroscopic filler (corn flour). Goes off in minutes rather than day's/weeks. This will affect its structural properties, but a possible solution.... If your a cheapskate like me! 😉
Link to easy composites PU casting resin.
https://www.easycomposites.co.uk/#!/...ne-Rubber.html
It's that XenCast stuff I was planning to use. PX90.
I might just wrap a layer of butyl rubber around the inner core (I know that damps well) and then fill the gap with polyester resin like car fiberglass repair stuff to constrain it.