Here the full text of my lecture at the Sassuolo Meeting 11.21.2013
REFRACTORY ALTERNATIVES TO FUSED-CAST FOR SUPERSTRUCTURE IN GLASS FURNACES: NEW MATERIALS
In a rapidly changing environment, technical but also macro- and micro-economical factors push the volume and value of the global fused cast refractory market toward reduction. At the same time, new refractories, alternative to electrofused for traditional applications, such as the superstructure of the glass furnace, are emerging with clear technical and economic advantages.
When, back in 1971, I began to deal with fused cast refractories, they were booming in all application niches.
This class of materials, including the AZS coming as an evolution from electrofused mullite by addition of Baddeleyite, represented a step forward in the application so intense to enable an epochal improvement in the quality of the glass produced.
The fused cast aluminas (alpha-beta and beta) were also introduced massively in glassmaking since the '40s, representing the ideal complement to the technological platform of float process in the production of flat glass, making it possible a quality incomparably higher than in the recent past.
The gradual conversion of virtually all glass melting furnaces towards the use of fused cast refractories, allowed to duplicate it in a few years and then triple the life of the furnace and to increase the specific pull, exploiting the possibility of increasing the process temperature and the level of thermal insulation.
The electrofused refractory, initially introduced at the glass contact, were applied progressively in the superstructure to balance the campaign life and to take advantage of the exceptionally low cession of defects.
The alpha-beta alumina was used in glass contact of downstream furnaces sections at lower temperature (WE , channels) when the quality of the glass itself is the critical factor: float glass, high quality container and specialty glass products have found great benefit from the elimination of zirconium in the distal sections of the furnace.
Other fused cast special chemistries, such as for example HZFC were introduced to further increase , in specific cases, the durations of the campaign, but primarily to reduce the generation of defects resulting from the exudate production and release of primary and secondary crystals of baddeleyite, characteristic of electrofused AZS . Fused cast aluminas are, on a purely technical stance, the ideal complement to the oxy-fuel platform for superstructure and crown applications, and only economic considerations have limited, up to now, their use.
THE ECONOMIC FACTOR AND THE EXPANSION OF NICHE
In addition to the extensive technological motivations, however, a more powerful engine, at least until the '80s and '90s, has led to a progressive enlargement of the application niche of fused cast materials.
This engine has been represented, for several decades, by the limited diffusion of manufacturing know-how, the resulting soft global competition and, as a natural consequence, the high financial profitability of these products under such an oligopolistic scenario.
The understandable consequence was, therefore, the determination to enlarge the application market, even more than the technically supported frame.
As an example of a somehow forced introduction, in my opinion, you should ascribe a relatively popular application in the regenerative package, the so-called cruciforms, whose value contribution for the glass industry has always been a subject of debate, as opposed to the classical applications of basic and other advanced compositions and sizes (chimney blocks), but without an unambiguous conclusion.
In the latter case, however, the possibility of establishing a comprehensive package including the materials for regenerators along with glass contact and superstructure fused casts, provided a definite marketing and commercial advantage.
The consequently huge volume stretching justified, in the past, considerable investments, both in R&D and dedicated manufacturing of these products.
The specific contribution of profitability for products such as cruciforms, however, has never been comparable to that of the materials in contact and superstructure, having to compete with poorer materials toward which, however, was not easily demonstrable a great performance advantage.
ECONOMIC FACTORS DESTABILIZED THE SCENARIO
With this scenario we reached the mid '80s, when new elements have gradually changed the market situation of refractory materials for glassware.
The gradual introduction of "low-cost" (and generally "low- quality") fused cast, the progressive dominance of the financial aspects in the management of western glass industries, the trend in the price of raw materials indispensable for fused-cast such as zircon sand and, more recently, the advent of an unprecedented economic and financial global crisis, converged to transform a high-margin product in a low-profit commodity.
The first type of fused-cast to be commoditized were the AZS, which constitute the absolute majority of the mix; second in the line was the fused-cast aluminas, and soon will be the turn of specialties like HZFC. The sequence was overlying the introduction of low-cost materials in the specific segments, even though it would be too simplistic to attribute to this factor the entire responsibility of the observed phenomenon, and the process is still ongoing.
Whatever the causality, it is a fact that the electrofused refractories are no longer today, and for both western and eastern players (including "low-cost" players), an high profitability margin. The large increase of global manufacturing capacity, mainly concentrated in the Far East, has further contributed to making this market progressively less and less palatable.
In this scenario, as an obvious consequence, the amount of resources invested in R&D to compete on quality and develop new products and services has dramatically dropped, while most of the scarce resources employed have been devolved to make it technically accessible lower quality raw materials, once considered unacceptable in the production of fused-cast refractories.
NEW CONDITIONS ALLOW THE INTRODUCTION OF NEW MATERIALS TECHNICALLY MOTIVATED
Despite the incompressibility of many cost factors in the production of electrofused, these materials, though no longer sponsored by a high level of profitability, will stay predominant for a long-term in the applications with the highest performance demands, the glass contact, where to date do not exist, except for limited niches, technologically comparable alternatives.
The same, however, can no longer be said for the superstructure.
Here, in fact, the fused-cast refractories have some weak points such as the production of pollutant exudate, a poor resistance to thermal shock, the high and inhomogeneous thermal conductivity and, last but not least, the severe constraints for size and shapes of individual blocks (peculiar of the very production technology) that increase the number of components, making in turn complex the assembly technique; anyone with experience of installing multiple arches and extensions with complex geometries, have had to deal with the use of aids (e.g. disposable centrings) and specially trained personnel to handle these complications.
Those who wish to hold forth on the ideal refractory superstructure, will probably describe a material which is highly resistant to chemical attack of the combustion environment and batch carry-over, dimensionally stable at operating temperatures, with little or no yield of defects, thermal shock resistant and with adequate and homogeneous thermal conductivity. Also, a not very high density and the ability to be formed into large pieces would be considered among the fundamental characteristics.
As you can see , this description does not fit, if not partially, to the fused cast refractory. If these materials have enjoyed, at least until yesterday, a nearly ubiquitous use in the superstructure, the reason must be traced from one side to the objective difficulty balancing the duration of the glass contact (equipped with electrofused) with conventional sintered materials, and on the other hand to the lack of interest that refractorists have shown to develop materials and alternative solutions, as long as the fused-cast were a highly profitable product, controlled by a few companies with a leading position in the oligopolistic refractory market for glass application.
These conditions, however, are today largely modified.
It is not surprising, therefore, that new technological solutions, outside the range of electrofused, are rapidly gaining large market shares in the superstructure application, starting from the glass container segment.
Why, then, what it was not possible for recent decades (the use of alternative materials to fused cast in the superstructure), it is becoming possible now?
As said, the major technical obstacle, beside considerations of profitability margin, was represented by the fact that the "traditional" sintered materials manifested an insufficient resistance to alkali (acid materials such as silica), or an excessive sensitivity to nephelitic conversion that caused spalling under the influence of batch carryover (traditional sinter AZS) or, again, poorly resistant to creep at operating temperatures.
NEW MATERIALS FOR SUPERSTRUCTURE
In the last decade, a U.S. company specialized in the manufacture of monolithic refractories in large shapes (Special Shapes Refractory Co. of Alabama), has developed AZS sintered materials of new generation for which, working on the formulation and type of raw materials, have been effectively overcome the problem of nephelitic conversion, without compromising the undeniable advantage of being able to produce shapes (pre-formed and sintered) highly homogeneous and incomparably larger than fused-cast in size (typically, arches in a single piece).
These superstructures are mounted with savings of 50% on the timing and costs of erection, with greater dimensional stability in preheating and intrinsically free from exudation.
These materials (for which there is now a history of use long enough to assume a campaign life at least comparable to that of electrofused refractories), could certainly ensure a reduced incidence of defects by exudate and undeniable advantages associated with a reduced and homogeneous thermal conductivity.
The shortened assembly time and the ease of configuration are also non-negligible advantages associated with the use of these new advanced materials.
The knowledge platform developed for the formulation of these materials, already extended to high alumina refractories for use in glass contact in WE and channels, can be applied to develop other sintered refractory alternative to the traditional applications of fused cast.
The resulting reduction of the fused cast market in superstructure, in the recent decade progressively oriented towards low-cost, represents a contrast to the expansion of the whole low-cost segment and helps pushing the western producers of fused cast towards layers with better profitability (contact glass and high performance) and, perhaps, re-development of new products and services that can compete in terms of the value/cost, and not only on the strictly commercial aspects.
New market conditions, global economic factors, have led to a technical evolution that has brought into play western manufacturers capable to escape the clutches of a purely commercial low-cost in sectors that are geared to commodities.
Once again, the concept of action and reaction allows players particularly able to ride the wave of innovation , and to all of us a glimmer of optimism for the future.
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