[SS-Propellant] casting vibrator

[Rich Nakka]

dormans wrote:

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> From: ss-propellant-bounces at exrocketry.net 
> [mailto:ss-propellant-bounces at exrocketry.net] On Behalf Of Rich Nakka
> Sent: Sunday, November 27, 2005 1:08 PM
> To: Mateica Vlad
> Cc: ss-propellant at exrocketry.net
> Subject: Re: [SS-Propellant] casting vibrator
>
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> Mateica Vlad wrote:
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> Rich Nakka <richnakka at rogers.com> <mailto:richnakka at rogers.com> wrote:
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>     Gents,
>     While in the process of organizing a stack of technical notes &
>     correspondences, I came across something of interest. In
>     correspondence with a fellow rocketeer in Denmark some years ago,
>     he told me about a vibrator that he used to aid casting of
>     propellants, which was apparently very effective in helping the
>     slurry to flow and fill all spaces in the mould.
>     3.0 kW motor
>     Eccentric flywheel to produce a 25 Hz vibration
>     Vibration amplitude 2.3 mm.
>
>     Something to consider for our casting of those large 34 kg
>     segments. This may help in maximizing our propellant density?
>
>     Richard
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> Interesting ideea Richard. For some good results we need to calculate 
> the excentric dimensions(diameter, mass) and to make a controlled 
> temperature curing oven. In this way we can cast the propellant 
> segment, put it into the oven(where is the vibrator) and slowly cool 
> the oven so that the density well be maximized. we can't cast the 
> propellant into the vibrating mold. the oven can be made simple with a 
> termostat and a heating coil. the electronic schematic for the 
> termostat cand be provided by Prodan Paul from the safty team(he is 
> making a termostat right now for me to easy my casting procedure)
>
> Vlad
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> Good ideas, Vlad.
> Some things we need to bear in mind.
> We may well be casting the segments "in the middle of nowhere". How 
> much wattage is available, etc. (a decent gasoline generator should be 
> able to provide the power we need?)
> For a single firing, 12 segments need to be produced. So the time a 
> segment can spend in the "curing box" would be limited. Perhaps have 
> several curing boxes?
>
> Richard
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> I suspect that the larger the grains get, the easier it will be to get 
> close to theoretical density.  I've notice that everything else being 
> equal, the larger a grain is the better its density.  The nice thing 
> about Sorbitol is that you can heat it well beyond its melting point, 
> with no carmelization, before pouring it.   This has been necessary 
> while casting at the RRS's test area on cold, windy days.  The amount 
> of heat that the propellant loses in the transfer from the pot to the 
> mould, when it's a thin ribbon, can be significant.    By overheating 
> it you can ensure that when it gets in the mould it is still hot 
> enough to be fluid.   We may be able to do that to an extent if we use 
> a sugar alloy since the addition of sucrose doesn't seem to raise the 
> overall melting point of the alloyed sugar.  I think that with careful 
> pouring and preheating tools and moulds we should get the necessary 
> density on a segment that weights 34 kg.  If we have access to a 
> vibrating table, or similar, that we could place that mould on while 
> casting, that'd be great.  Definitely couldn't hurt.
>
> Randy
>
Good point, Randy, about the cooling effect of the wind during pouring. 
This would definitely have to be taken into account for the large 
segments. Perhaps a simple wind shield? Also heating it to a somewhat 
higher temperature is a good thing, I also tend to do this. In addition, 
it lowers the  viscosity of the slurry a bit.
With regard to achieving acceptable  density, test casting will tell us 
whether or not a vibrating table is needed. Something else to keep in 
mind is curing under pressure, I believe this will have to be explored 
as a means of ensuring positive bond to the casting tube. May also help 
density.

Richard

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