Technical Paper
www.ireng.org
NEW ACTIVE COMPOUND RANGE FOR REFRACTORY CASTABLES WITH SUPERIOR ROBUSTNESS
Christoph Wöhrmeyer*, Phil Edwards, Carl Zetterström Kerneos S.A., Paris-La Defense, France,
www.kerneos.com
Abstract
Despite modern castable technology the quality consistency of the castable dry-mix, the robustness during the castable installation, and the safety during the dry-out process are areas that require special attention to further save cost and time. A new Active Compound range has been developed with the objective to make refractory castables more robust. As examples, three new products of this Active Compound range are discussed more in detail in this paper. It has been investigated how a new deflocculation system stabilizes the flow and setting time when impurities in the raw materials of silica fume rich low cement castables are variable. Another example is a new deflocculation system for high purity Alumina- Spinel and Alumina-Magnesia castables. This new Active Compound targets not only an excellent flow at lowest possible water demand, but aims at a lower impact of ambient temperature variations on working and setting time. The third example is discussing how the permeability of castables can be optimized in order to improve the robustness and safety during the critical step of castable dry-out. All these three Active Compounds have in common that they can easily be dosed into the drymix with automatic dosing systems or as one bag per ton of dry-mix. This eliminates dosing errors and increases the castable dry-mix consistency.
Introduction
Low cement (LCC) or deflocculated castable technology has been widely adopted in the past decades due to the improved thermomechanical properties and corrosion resistance that these castables display in service. These improvements in performance have been made possible by the increased sophistication of refractory formulations and improvements in installation methods. However, along with these overall improvements also some draw-backs have been experienced. The robustness of these sophisticated materials to small changes in the system is amongst the topics that need special attention and was the motivation to develop a new range of active compounds (REFPAC®
) that cope with these sensitivities.
They aim at improving dry-and wet-mix quality consistency to achieve more predictable rheological and setting characteristics at job sites, and to make the dry-out process more robust and safe.
This paper is specifically focusing on three aspects:
• Improvement of the robustness to variabilities in the content of soluble elements in raw materials for silica fume containing LCC’s
• Improvement of the robustness to ambient temperature variations of steel ladle castables
• Improvement of the dry-out process of dense deflocculated castables.
In the first part of this paper a new silica fume deflocculating active compound, REFPAC®
100 (RP100), is investigated with respect to its
robustness to impurities in silica fume and bauxite fines and compared with sodium tri-polyphosphate (TPP) and a PCE-based deflocculant. The second part of this paper studies the new deflocculating active compound REFPAC® 500 (RP500) and how it improves the setting robustness in environments with variable ambient temperatures. The lithium-free RP500 targets an accelerated set of alumina-spinel and alumina-magnesia castables at low temperature without impacting too much workability at high temperature. A new concept of creating gas permeability for cement bonded castables will be discussed in the third part of this paper. REFPAC®
MIPORE 20 (MP20), a
permeability enhancing active compound (PEAC) targets a release of water during the dry-out process at lower temperatures than with PP-fibers to make the water removal process safer.
All three examples have in common that the active compounds can be precisely dosed into the dry-mix with automated powder feeding systems or added as one bag per 1t of dry-mix.
Test materials and experimental setups
The typical compositions and application areas for the three new active compounds are summarized in Table 1. Their effects have been tested in different model formulations. The formulation concepts will be explained in the following chapters. The vibration flow of the castables has been tested using an ASTM cone with a height of 50 mm, a lower inner diameter of 100mm and an upper inner diameter of 70 mm. The flow values have been determined directly after wet mixing and after different time intervals. The ultrasound velocity profiles have been used to analyze the structuration of the castables. ICP has been used to measure the amount of soluble elements in different silica fumes and bauxite fines. To measure castable permeability a VacuPerm equipment has been used that uses a vacuum decay technique. XRD, DSC and SEM techniques have been applied to analyse hydrate phase formation. With
macro-thermogravimetric
measurements the dry-out process has been simulated. Castable cubes of different sizes have been cured and then heated with heating schedules to study the de-watering process. Tests at different ambient temperatures have been conducted in big climate chambers that allow all equipment, raw materials, and water to be at the test temperatures.
Test results and discussion
Robustness of rheology and setting of silica fume containing LCC’s with variable raw materials
A model formula as shown in Table 2 was used to investigate the performance and robustness of the newly developed deflocculating active compound REFPAC®
100 (RP100) and to compare it with the traditional 14 ENGINEER THE REFRACTORIES September 2017 Issue
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