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Failures that occur during the installation and dry-out phase can have strong impact on the final performance and in some cases even require to repeat the installation and dry-out job if for example an explosive steam spalling has occurred and destroyed the refractory lining even before it could serve its purpose inside a furnace.
This paper
will discuss new raw material developments for refractory castables in three different raw material segments:
• Binder • Additives and Active Compounds • Aggregates
Increased rheological and setting robustness of castables can save costs at different levels. It allows a more precise planning of the installation, demoulding and commissioning so that these process steps can be done with a minimum of resources. Furthermore it increases the probability that the castable installation will be done with the correct water dosage to achieve the targeted porosity and strength level so that the full performance potential can be exploited.
Newly designed additives and active compounds [4] target to improve
the ease of use and robustness of castables and a few examples will be discussed in this paper:
• Deflocculant with better robustness in Silica Fume containing castables
• Deflocculant for ladle castables that acts at the same time as setting regulator to avoid too long set in winter without making it too reactive in summer
• Permeability enhancing deflocculant that facilitates castable dry-out • Shotcrete gelling agent for ladle castables
Another example for a raw material innovation shows that a specifically designed calcium aluminate binder can improve the setting reliability of castables even after long storage time of the castable dry-mix prior to its installation.
Other new binders target the modification of the castable microstructure with the ultimate objective to improve the final performance so that less material is required per ton of produced steel. The positive side effect is that those performance driven products are in most of the cases also more sustainable solutions with a better environmental footprint. Two examples for performance/cost driven binder developments will be discussed in this paper:
• A calcium magnesium aluminate increased corrosion resistance
binder for ladle castables with
• A calcium aluminate binder that reduces costs of dry-gunning installations by reducing the amount of material loss caused by re- bound and improves final performance due to reduced water demand
Also in the field of refractory aggregates new ideas are discussed and example for potential cost savings through weight reduction of the refractory lining with microporous instead of very dense aggregates are highlighted.
ADDITIVES AND ACTICE COMPOUNDS DEVELOPMENTS
Robust deflocculant for silica fume containing castable
A major concern with silica fume containing castables is the robust January 2018 Issue ENGINEER THE REFRACTORIES 15
Figure 4: Ultrasound profile and heat flow An active compound, REFPAC®
Figure 3: Initial vibration flow and after 30 mins
Technical Paper
deflocculation and reliable setting and early strength development when the purity of fillers and aggregates varies. Since calcium aluminate hydration is a wet chemical reaction process including dissolution, saturation, and precipitation steps, each modification of the pore solution chemistry by soluble compounds in variable raw materials can impact this mechanism but also the surface interaction between the deflocculant and the powder that needs to be deflocculated.
100 (RP100), has been developed to provide
an efficient deflocculant that achieves its performances for a large range of raw material combinations. The term Active Compound refers here to a system that consists of an additive system on a mineral carrier. That allows for example in this case of RP100 a 1%-addition to the dry-mix which makes dosage easy, reliable and facilitates a homogeneous distribution within the dry-mix. The active compound is a powder that can also been added to the castable dry-mix by means of automatic dosing equipment. Figure 3 shows the impact of raw material purity on vibration flow of a LCC deflocculated with different additives compared to the active compound. Sodium tri- polyphosphate (TPP) and a specific polycarboxylate ether (PCE) that has been designed for silica fume containing castables show excellent flow after wet mixing (T0) and after 30 minutes (T30). But this is the case only when the formulation uses a high purity bauxite (BX1) and a high purity silica fume (FS1). When switching to lower quality raw materials (BX2, FS2) the deflocculation efficiency is impacted and a higher water dosage would be required which would negatively impact the final performance during application. Unlike TPP and PCE, RP100 doesn’t show this sensitivity to the raw material purity level and also doesn’t have negative side effects on the calcium aluminate bonding mechanism so that strength development doesn’t get delayed (Figure 4).
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