Can I use these instead of stainless needles?

[Mahone]

I am having a very difficult time finding stainless steel needles but I have found Dramix 3D steel reinforcing fibres. They are not stainless. Can I use them to reinforce a home brew cast oven? Thanks.

[david s]

No, I wouldn’t. There is a reason stainless are the recommended reinforcing and that is because they are in an environment where moisture and heat are big contributors to corrosion. Better to leave them out.

[Mahone]

Thanks david, looks like I’m back to the drawing board. Do you know of any other product that would be ok to use? Nothing but dead ends trying to track down these needles here.

[UtahBeehiver]

Check with David S, i believe he says AR (alkali resistance) glass fibers may be substitute for melt extract fibers (aka SS needles)

[BenKeith]

Have you seen these?

Refractory Reinforcing 1" 430 Stainless Steel Needles

I had a link but found out I couldn't do that so here's what they are called
You can also do a search under this discription.
refractory reinforcing stainless steel fiber

[david s]

Check with David S, i believe he says AR (alkali resistance) glass fibers may be substitute for melt extract fibers (aka SS needles)

I use both melt extract fibres (stainless steel needles) as well as AR (alkaline resistant fibreglass fibres and carbon nanotube fibres in conjunction with castable refractory. But if you are using a home-brew castable (3:1:1:1 sand hydrated lime, powdered clay), the most important fibre addition is the very fine polypropylene fibres, which burn out and give the castable a degree of protection from steam spalling. You can skip the reinforcing fibres, it will still work ok.

[robi]

Any thoughts on Basalt Fiber to reinforce the dome instead of stainless steel needles...

Basalt fiber is a relative newcomer to fiber reinforced polymers (FRPs) and structural composites. It has a similar chemical composition as glass fiber but has better strength characteristics, and unlike most glass fibers is highly resistant to alkaline, acidic and salt attack making it a good candidate for concrete, bridge and shoreline structures.

2021 update: No longer a newcomer, basalt FRPs are competing with E-glass FRPs in the marketplace. Similar in mechanical properties, basalt FRPs have gained the equivalent mechanical properties of E-glass FRPs with the Florida Department of Transportation (FDOT) and other agencies.

Compared to carbon and aramid fiber, it has the features of wider application temperature range -452° F to 1,200° F (-269° C to +650° C), higher oxidation resistance, higher radiation resistance, higher compression strength, and higher shear strength. (Note that application temperatures of FRPs are limited by the glass transition temperature of the matrix, which is lower than the application temperature of the fibers.)

[david s]

Sounds like they’ll be ok, but only just, as 650C is the top of their range, which is only a bit more than the temps it will see in an oven. Presumably they begin to melt at anything north of 650C. I’ve been experimenting with carbon nanotube reinforcement which is working well so far.

[robi]

Sounds like they’ll be ok, but only just, as 650C is the top of their range, which is only a bit more than the temps it will see in an oven. Presumably they begin to melt at anything north of 650C. I’ve been experimenting with carbon nanotube reinforcement which is working well so far.

I just wanted to say thank you Dave for your reply here ... after being sick and then caring for sick family I am finally back to full strength and working on my new oven... I will look into carbon nanotube for my dome cast reinforcement, can you share any more info about how to use it, currently all I am finding appears to be in a powdered form.

While I have you, if I may please ask a question regarding castable, I bought 5 sacks of "industrial use only" refractory castable, I am pretty sure it won't be enough for my dome (scope creep, but happy wife = happy life), what do you think about mixing one part 3:1:1:1 homebrew with 1 part refractory cement. I am not sure if the refractory cement has any strength or burnout fibers, I assume I should add both if after sieving I don't find any.



Thank you so much Dave for your thoughts,
Robi

[david s]

There are many types of castable refractory, but they generally belong to one of two groups, either insulating castable or dense castable. You want the dense castable rather than insulating because you are after conductivity, thermal mass and strength. A hard, dense, durable inner dome then insulated well on the outside, will give you the required strength and thermal mass. The density should be around 1800-2000 kg/m3 or (1.8kg-2.0 kg/litre) The carbon nano tube reinforcing I use is called Edencrete, a liquid admix. I believe it is the only product of this type available. I know of another manufacturer developing a graphene admix for concrete, but they have yet to develop it via a liquid admix and obtain the required approvals for its commercial use.

Sieve a sample of the castable to check if it contains burnout fibres, most dense castables do.

Regarding mixing the castable refractory with home-brew to extend it, DON'T. Because the chemically active ingredient is calcium aluminate cement, it reacts with both normal portland cement and lime as an accelerant. As the castable already has a very short pot life, it needs to be placed quickly in small quantities because it goes off fast. Anything that accelerates the process just reduces working time. During summer I always have to use chilled water with the stuff to extend the short working time. Perhaps you could lay up a thinner layer of the castable refractory and then cover it with another layer of homebrew over the top to achieve the required thickness. Most cast ovens have an inner dense dome around 2' thick, although the monster 1.6m internal diameter oven I'm currently working on is 3.5" thick.

[robi]

Regarding mixing the castable refractory with home-brew to extend it, DON'T.

Copy that, thank you, the idea felt good in my untrained head, I am so glad I asked. I will definitely do the two-layer... thanks for the great suggestion, I can do that.

Back to the subject of reinforcement, after looking at their website, that Edencrete stuff looks game-changer amazing. Looks like it can be added to homebrew or dense castable. In my first build, I was not satisfied with the perceived strength/hardness of homebrew, that said, the oven is holding up very well to near-daily use (baking, roasting, pizza-ing ;~) followed by a week off.

In your experimentation, did you only use the Edencrete and burnout fibers or did you include reinforcing fibers? How much of the product did/will you use in the 1.6m x 3.5" thick dome you are working on? I need to now find a distributor.

Thanks for sharing your awesome knowledge

[microbe]

Have you seen this product? I have bought some, if it ever stops raining I will render my oven. They recommend 10kg per cubic metre.

Chopped Basalt Fibre

Features:

• High tensile strength
• Resistant to alkali in concrete and require no special coatings
• Resist cold down to -260°F and heat up to 1,500°F
• Do not conduct electricity or induce electrical fields
• Will not harbor bacteria or microbial growth
• Good fatigue resistance

Applications:

• Reinforcement of cement and asphalt
• Reinforcement of laminates

Chopped basalt fibres can be mixed directly into polymers and concrete to increase tensile strength and reduce cracking and chipping.

I expected it to be brittle, but it it is flexible, but bounces back to shape. I was also wondering about splinters, but I doubt that will happen.

[david s]

They look interesting, i’ve not tried them. How long are they? Sometimes long and stiff fibres will stick out from the rendered surface. You can either pull them out before the surface has set or sand them off after.

[microbe]

They look interesting, i’ve not tried them. How long are they? Sometimes long and stiff fibres will stick out from the rendered surface. You can either pull them out before the surface has set or sand them off after.

I bought 12mm but they also have 30mm. They don't stick out at all.