Mould a batch rocket

[pierre159]

hello all,

i'm intrested to mould a batch, do you have the proprotion of the mix to have a good result a no cracks. 
Do you advice do mould in 4 parts or 5 parts?
some of you have experience?

thanks in advance
brgds

[martyn]

In most cases you will be better off buying a commercial ready mix, the more components the better but for a 6” batch box four parts would be good although I have seen it done with only two!
You need good mold making skills and a very good way to vibrate the mix.
Most people use fire bricks because that is an easier and well tested method but, if you are confident a cast core can be made to work.

[pierre159]

hello the mixture that I can find is a mortar for masonry refractory bricks. with a resistance of "900°c". only I think that the temperature rises higher in the heart, right?

[martyn]

I don’t know where you live but try googling ‘refractory casting cement’.

The high temperature cement used to make a casting mix is often called fondue cement, it is rated at 1200 cc and is mixed with crushed fire brick and stainless steel needles plus nylon burnout fibers and fiberglass structural fibers.
However most manufacturers will keep the exact recipe to themselves and that is why it’s difficult to mix your own.

Here is an example rutland.com/products/castable-refractory-cement

[pierre159]

after some research I found not far from my home mortar at 1100°c and 1300°c is this sufficient?
Is it possible to pour certain parts with my less expensive mortars.
for example the box can it be molded with a mortar 1000°c easily found and half cheaper (18 euros).
I have thought about the expansions which could be different but in the case of the molding in 5 parts there are assembly joints which in all cases compensate for the different temperatures of the different parts? What do you think?
i don't know the temperatures in the different parts just by reading peter's site i understood that it could go up to 1200°c in the riser.

[fiedia]

Jan 3, 2023 7:14:04 GMT -8 pierre159 said:

 the box can it be molded with a mortar 1000°c easily found and half cheaper (18 euros).

I measured temperatures in the box as high as in the heat riser. In addition, there is more thermal and mechanical constraints in the box than in the heat riser.