Made of 406 'Alfa' Stainless Steel (Superior to 304 or 310 SS).
Each "needle" is 1 mm x 25 mm.
Sold in 1 lb bags.
1) Add 1 lb of Stainless needles per 55 lb bag of Castable for added Strength. They minimize cracks and limit breakage if cracks occur, increasing lifespan (like rebar).
2) Heat new castables gradually &/or intermittently to slowly evaporate water vapour avoiding steam pressure's risk of forming cracks.
3) Use only recommended water. Typical 5 to 6.5% water by weight. Just 2% extra water (ie 8.5%) can decrease strength by 40% in some castables.
4) Vibration can help avoid Voids (20 seconds with a vibrating sander) BUT avoid excess vibration to avoid weakening by stratification.
Excerpt from 107-page Research Thesis by Peterson in 2014: "After prolonged heat and thermal shock exposure, needles help maintain integrity and mechanical properties of samples. The study also found that corrosion due to oxidation was a major contributing factor to the way needles performed; and concluded that a concentration of 3% 406 “Alfa 1” stainless steel reinforcing needles added to the working lining of a taconite furnace is recommended."