Carbon‐Bonded Alumina Spaghetti Filters by Alginate‐Based Robo Gel Casting

Abstract

Metal melt filtration has become very popular over the past decades as it provides the possibility of removing nonmetallic inclusions from metal melts and reduces the amount of flow turbulence during mold filling. However, especially, the filtration of steel melts is associated with particularly harsh conditions which might require special filter solutions regarding increased strength and specified flow path. Herein, a novel approach for the manufacturing of cellular ceramic materials is investigated. Thereby, a slurry containing alginate is pumped into an aqueous solution containing Ca2+ or Ba2+ ions. The natural capability of the alginate for gelation leads to the in situ stiffening of the slurry in contact with the cross‐linking solution. Periodic strut patterns can be realized by moving the nozzle with the aid of a computer‐assisted robotic system. The influence of sodium alginate and solid content on the slurry rheology and the process parameters is analyzed based on a fixed carbon‐bonded alumina composition. Furthermore, alternative combinations of alginate types and alkaline earth sources are tested on their suitability for gel casting and their influence on the residual carbon content after pyrolysis. A suitable filter is successfully applied in steel melt immersion tests.

Compression Behavior of Carbon‐Bonded Alumina Spaghetti Filters at Room and High Temperatures

“…The filter preparation process was reported previously. [27] The raw materials used for the filter preparation in this study are shown in Table 1.…”

“…[14,23,25,26] Recently, a new approach has been introduced by Wetzig et al for the manufacturing of Al 2 O 3 -C filters which could overcome the aforementioned drawbacks of the replica route. [27] The socalled alginate-based robo gel casting shapes a cellular structure according to the following process: the alginate-containing slurry is added through a nozzle into a calcium or barium salt solution with the help of a robot system which allows a controllable movement of the nozzle to form the desired structural pattern. A gelation process occurs in the solution through chelation between the alkaline earth metal ions and the alginate chains, making the cast structure (including the strut core) stiff.…”

“…Properties such as slurry rheology, sample shrinkage, and residual carbon content as well as behavior under contact with steel melt have been investigated. [27] Mechanical tests at room temperature have been carried out by means of compression on green and fired bead samples with a radius of 3.7 AE 0.3 mm. [27] No compression test on real spaghetti filters has been carried out yet.…”

“…[27] Mechanical tests at room temperature have been carried out by means of compression on green and fired bead samples with a radius of 3.7 AE 0.3 mm. [27] No compression test on real spaghetti filters has been carried out yet. DOI: 10.1002/adem.202100613…”

Metal-Ceramic Beads Based on Niobium and Alumina Produced by Alginate Gelation

“…This approach is especially useful in the food or pharmaceutical industry, for example, to encapsulate materials in alginate beads. However, technical applications, such as the gel casting of “spaghetti filters” for steel melt filtration, are possible, as well [ 17 , 18 ]. Alternatively, it can be beneficial to delay the gelation process by adding a chelating agent, which forms a complex with the calcium ions.…”